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Matamba E, Richards LR, Cherry MI, Rambau RV. Phylogeography of the mesic-adapted striped mouse, Rhabdomys dilectus chakae (Rodentia: Muridae) in forest margins of the Eastern Cape and southern KwaZulu-Natal provinces of South Africa. Biol J Linn Soc Lond 2022. [DOI: 10.1093/biolinnean/blac087] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Abstract
Rhabdomys is a genus that occupies a variety of habitats, including forest margins. Among the Rhabdomys taxa, Rhabdomys dilectus chakae has a distribution that covers the eastern seaboard of South Africa, with a poorly defined divergence date from its sister taxon Rhabdomys dilectus dilectus. Here, we study three mitochondrial markers (cytochrome b, cytochrome c oxidase I and partial control region) of R. d. chakae across the Eastern Cape and KwaZulu-Natal forests of South Africa, aiming to determine the cladogenesis (molecular dating) and effective population size of this subspecies through time, in addition to its cladogenesis in relationship to other species within the genus. A phylogenetic analysis revealed six clades within Rhabdomys, confirming that our study area is occupied solely by R. d. chakae, to the exclusion of other recognized sibling species. A fossil-calibrated Bayesian relaxed molecular clock estimated a recent split between R. d. chakae and R. d. dilectus ~1.4 ± 0.35 Mya and between two Rhabdomys pumilio groups, coastal A and B, at 1.16 ± 0.44 Mya. Coalescent Bayesian skyline plots revealed a stable population of R. d. chakae in the study area that was in slow decline until 2500 years ago, when there was an expansion in the late Holocene. Radiation within Rhabdomys dates as far back as 4.27 Mya, and subsequent demographic fluctuations primarily reflect palaeoclimatic changes.
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Affiliation(s)
- Emmanuel Matamba
- Department of Botany and Zoology, Stellenbosch University , Matieland , South Africa
| | | | - Michael I Cherry
- Department of Botany and Zoology, Stellenbosch University , Matieland , South Africa
| | - Ramugondo V Rambau
- Department of Botany and Zoology, Stellenbosch University , Matieland , South Africa
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Welman S, Jastroch M, Mzilikazi N. Obligatory homeothermy of mesic adapted African striped mice, Rhabdomys pumilio, is governed by seasonal basal metabolism and year-round "thermogenic readiness" of brown adipose tissue. J Exp Biol 2022; 225:275893. [PMID: 35694963 DOI: 10.1242/jeb.243860] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2021] [Accepted: 06/08/2022] [Indexed: 11/20/2022]
Abstract
Small mammals undergo thermoregulatory adjustments in response to changing environmental conditions. Whereas small heterothermic mammals can employ torpor to save energy in the cold, homeothermic species must increase heat production to defend normothermia through the recruitment of brown adipose tissue (BAT). Here, we studied thermoregulatory adaptation in an obligate homeotherm, the African striped mouse (Rhabdomys pumilio), captured from a subpopulation living in a mesic, temperate climate with marked seasonal differences. Basal metabolic rate (BMR), non-shivering thermogenesis (NST) and summit metabolic rate (MSUM) increased from summer to winter, with NST and MSUM already reaching maximal rates in autumn, suggesting seasonal preparation to the cold. Typical of rodents, cold-induced metabolic rates positively correlate with BAT mass. Analysis of cytochrome c oxidase (COX) activity and UCP1 content, however, demonstrate that thermogenic capacity declines with BAT mass. This resulted in seasonal differences in NST being driven by changes in BMR. The increase in BMR is supported by a comprehensive anatomical analysis of metabolically active organs, revealing increased mass proportions in the cold season. The thermoregulatory response of R. pumilio is associated with the maintenance of body weight throughout the year (48.3±1.4 g), contrasting large summer-winter mass reductions often observed in Holarctic rodents. Collectively, bioenergetic adaptation of this Afrotropical rodent involves seasonal organ adjustments influencing BMR, combined with a constant thermogenic capacity dictated by trade-offs in thermogenic properties of BAT. Arguably, this high degree of plasticity was a response to unpredictable cold spells throughout the year. Consequently, the reliance on such a resource intensive thermoregulatory strategy may expose more energetic vulnerability in changing environments of food scarcity and extreme weather conditions due to climate change, with major ramifications for survival of the species.
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Affiliation(s)
- Shaun Welman
- Department of Zoology, Nelson Mandela University, Gqeberha, South Africa
| | - Martin Jastroch
- Department of Molecular Biosciences, The Wenner-Gren Institute, The Arrhenius Laboratories F3, Stockholm University, SE-106 91 Stockholm, Sweden.,Institute for Diabetes and Obesity, Helmholtz Zentrum München, German Research Center for Environmental Health, Munich-Neuherberg, Germany
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3
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Weil R, Pillay N, Rochais C. Characteristics influencing local enhancement in free-living striped mice. Behav Processes 2022; 197:104621. [PMID: 35301065 DOI: 10.1016/j.beproc.2022.104621] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2021] [Revised: 02/22/2022] [Accepted: 03/10/2022] [Indexed: 11/02/2022]
Abstract
Social learning is widespread across species; however, we still know little about the impact of individual differences in behaviour on social transmission. We aimed to investigate factors influencing social learning in free-living Rhabdomys pumilio, a group-living, arid-adapted mouse. We studied 52 mice in a lid opening task in a field laboratory. We created observer-demonstrator dyads with demonstrators either opening lids or not. We measured success of observers to open lids, their attention and latency to open and time spent interacting with the device. We also considered influences of observer age, sex, group size and personality traits. Demonstrator success did not influence observer success, although attention towards the demonstrator did impact the observers' time spent with the device. Males were more successful than females and more active/explorative observers interacted with the device faster and for a longer time compared to less active/explorative counterparts. We found no influence of age and group size on mouse success. Striped mice appeared to use cues from other individuals to learn how to solve the task and it was influenced by sex and personality. Striped mice in this studied population may use local enhancement to acquire information socially.
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Affiliation(s)
- Richard Weil
- School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa.
| | - Neville Pillay
- School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa
| | - Céline Rochais
- School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa
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4
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Neves CN, Pillay N. Sociability, but not spatial memory, is correlated with regional brain volume variation in the striped mouse Rhabdomys spp. Behav Brain Res 2022; 417:113567. [PMID: 34508770 DOI: 10.1016/j.bbr.2021.113567] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2021] [Revised: 08/25/2021] [Accepted: 08/26/2021] [Indexed: 11/02/2022]
Abstract
Local environmental conditions associated with different geographic areas may elicit variations in behavioural responses in animals, leading to concomitant differences in functional brain region volumes. We investigated the behavioural correlates of hippocampus and amygdala volumes in three sister taxa of the murid rodent genus Rhabdomys, occurring in different environments. We used a Barnes maze to test spatial memory, dyadic encounters to test social behaviour, and histological brain sections to calculate hippocampus and amygdala volumes. Arid-occurring R. pumilio made fewer errors and had shorter latencies in locating the escape tunnel compared to moist grassland-occurring R. d. dilectus and R. d. chakae in two probe trials, 48 and 96 h after the last learning trial. R. pumilio was more amicable than the R. dilectus subspecies in intra-specific dyadic encounters. R. pumilio had larger hippocampus and amygdala volumes than the other species. Smaller amygdala volumes were correlated with longer latencies in females for probe trial 1, but males showed similar latencies regardless of taxon. Higher amicability scores were correlated with larger amygdala volumes in all taxa. Higher amicability scores were correlated with larger hippocampus volumes in R. pumilio and R. d. chakae but smaller hippocampus volumes in R. d. dilectus. Correlative relationships between spatial memory and amygdala volume appeared 48 h, but not 96 h, after the last learning trial. Local environmental conditions may influence spatial navigation, but social correlates drive regional brain size within cryptic striped mouse taxa.
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Affiliation(s)
- Candice Nikita Neves
- School of Animal, Plant, and Environmental Sciences, University of the Witwatersrand, 1 Jan Smuts Ave, Private Bag 3, Johannesburg 2050, South Africa
| | - Neville Pillay
- School of Animal, Plant, and Environmental Sciences, University of the Witwatersrand, 1 Jan Smuts Ave, Private Bag 3, Johannesburg 2050, South Africa.
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5
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Generalist indigenous herbivores resist alien tree invasion: Rhabdomys pumilio limits establishment of Acacia cyclops. Biol Invasions 2022. [DOI: 10.1007/s10530-022-02728-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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6
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Harrison LM, Noble DWA, Jennions MD. A meta-analysis of sex differences in animal personality: no evidence for the greater male variability hypothesis. Biol Rev Camb Philos Soc 2021; 97:679-707. [PMID: 34908228 DOI: 10.1111/brv.12818] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2021] [Revised: 11/13/2021] [Accepted: 11/17/2021] [Indexed: 12/18/2022]
Abstract
The notion that men are more variable than women has become embedded into scientific thinking. For mental traits like personality, greater male variability has been partly attributed to biology, underpinned by claims that there is generally greater variation among males than females in non-human animals due to stronger sexual selection on males. However, evidence for greater male variability is limited to morphological traits, and there is little information regarding sex differences in personality-like behaviours for non-human animals. Here, we meta-analysed sex differences in means and variances for over 2100 effects (204 studies) from 220 species (covering five broad taxonomic groups) across five personality traits: boldness, aggression, activity, sociality and exploration. We also tested if sexual size dimorphism, a proxy for sex-specific sexual selection, explains variation in the magnitude of sex differences in personality. We found no significant differences in personality between the sexes. In addition, sexual size dimorphism did not explain variation in the magnitude of the observed sex differences in the mean or variance in personality for any taxonomic group. In sum, we find no evidence for widespread sex differences in variability in non-human animal personality.
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Affiliation(s)
- Lauren M Harrison
- Division of Ecology and Evolution, Research School of Biology, The Australian National University, 46 Sullivans Creek Road, Canberra, ACT, 2600, Australia
| | - Daniel W A Noble
- Division of Ecology and Evolution, Research School of Biology, The Australian National University, 46 Sullivans Creek Road, Canberra, ACT, 2600, Australia
| | - Michael D Jennions
- Division of Ecology and Evolution, Research School of Biology, The Australian National University, 46 Sullivans Creek Road, Canberra, ACT, 2600, Australia
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Kanyile SN, Pillay N, Schradin C. Bachelor groups form due to individual choices or environmental disrupters in African striped mice. Anim Behav 2021. [DOI: 10.1016/j.anbehav.2021.10.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Rochais C, Hotte H, Pillay N. Seasonal variation in reversal learning reveals greater female cognitive flexibility in African striped mice. Sci Rep 2021; 11:20061. [PMID: 34625648 PMCID: PMC8501043 DOI: 10.1038/s41598-021-99619-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2021] [Accepted: 09/27/2021] [Indexed: 11/09/2022] Open
Abstract
Cognitive flexibility describes the ability of animals to alter cognitively mediated behaviour in response to changing situational demands, and can vary according to prevailing environemental conditions and individual caracteristics. In the present study, we investigated (1) how learning and reversal learning performance changes between seasons, and (2) how cognitive flexibility is related to sex in a free-living small mammal. We studied 107 African striped mice, Rhabdomys pumilio, in an arid semi-desert, 58 during the hot dry summer with low food availability, and 49 during the cold wet winter with higher food availability. We used an escape box task to test for learning and reversal learning performance. We found that learning and reversal learning efficiency varied seasonally by sex: females tested in summer were faster at solving both learning and reversal tasks than males tested in winter. Performance varied within sex: males tested in winter showed faster learning compared to males tested in summer. During reversal learning, females tested in summer were more efficient and solve the task faster compared to females tested in winter. We suggest that seasonal cognitive performance could be related to sex-specific behavioural characteristics of the species, resulting in adaptation for living in harsh environmental conditions.
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Affiliation(s)
- Céline Rochais
- School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa.
| | - Hoël Hotte
- School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa.,ANSES, Plant Health Laboratory - Nematology Unit, Domaine de la Motte Au Vicomte, BP 35327, 35653, Le Rheu Cédex, France
| | - Neville Pillay
- School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa
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Trajectory assessment of the vulnerable marsupial Dromiciops gliroides in the Patagonian temperate forest. Mamm Biol 2021. [DOI: 10.1007/s42991-021-00106-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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10
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Rimbach R, Pillay N, Schradin C. Prolonged growth during the food-restricted dry season in a small African mammal. J Mammal 2021. [DOI: 10.1093/jmammal/gyaa169] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Abstract
Studying how different environmental parameters, such as resource availability and ambient temperature, affect growth rates aids to understand the evolution of different growth strategies. Low levels of food availability restrict growth, and high ambient temperature can constrain growth via trade-offs between body temperature maintenance and heat produced during digestion. We studied growth of African striped mice (Rhabdomys pumilio), a small mammal living in a seasonally arid habitat. Striped mice are born during spring with high food availability and low ambient temperature, and typically enter the food-restricted dry season before reaching adulthood. We predicted low food availability and high ambient temperature would negatively affect growth. We therefore expected an extended period of slow growth during the long dry season. We repeatedly measured body length of 369 free-living individuals, examined how ambient temperature and food availability influenced growth rate, and seasonal changes in growth rate. In addition, we investigated whether mice (N = 27) born in summer (atypical breeding season) have slower growth rates than those born in spring. Growth rate increased with increasing food availability and decreased with increasing ambient temperature. Individuals born in summer grew slower than those born in spring. Sexes reached asymptotic body length at 258 days (females) and 285 days (males), which is an unusually long growth period compared with other small rodents. As most striped mice live for less than 1 year, this period encompasses the entire life for most individuals, but stops at old age, which could indicate senescence. Our results demonstrate a positive influence of food availability on growth, a relationship mediated by ambient temperature. We conclude that striped mice enter the food-restricted dry season before postnatal growth is terminated, and early exposure to harsh environmental conditions during the long dry season likely explains the prolonged growth period in striped mice.
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Affiliation(s)
- Rebecca Rimbach
- School of Animal, Plant, and Environmental Sciences, University of the Witwatersrand, 1 Jan Smuts Avenue, Braamfontein 2001, Johannesburg, South Africa
| | - Neville Pillay
- School of Animal, Plant, and Environmental Sciences, University of the Witwatersrand, 1 Jan Smuts Avenue, Braamfontein 2001, Johannesburg, South Africa
| | - Carsten Schradin
- School of Animal, Plant, and Environmental Sciences, University of the Witwatersrand, 1 Jan Smuts Avenue, Braamfontein 2001, Johannesburg, South Africa
- Université de Strasbourg, CNRS, UMR 7178, Institut Pluridisciplinaire Hubert Curien, Département Écologie, Physiologie et Éthologie, 23, rue Becquerel, F-67000 Strasbourg, France
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11
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Criscuolo F, Pillay N, Zahn S, Schradin C. Seasonal variation in telomere dynamics in African striped mice. Oecologia 2020; 194:609-620. [DOI: 10.1007/s00442-020-04801-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2020] [Accepted: 11/05/2020] [Indexed: 02/08/2023]
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Pillay N, Rymer TL. Sons benefit from paternal care in African striped mice. Dev Psychobiol 2020; 63:662-675. [PMID: 33098084 DOI: 10.1002/dev.22050] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2020] [Revised: 09/27/2020] [Accepted: 10/01/2020] [Indexed: 12/26/2022]
Abstract
Mammalian paternal care is rare and is often linked to enhanced fitness under particular ecological conditions. The proximate consequences of paternal care on offspring are lacking, however. Here, we tested whether levels of paternal care predict the behavioural, cognitive and physiological development of sons in the naturally paternal African striped mouse (Rhabdomys pumilio). We focused on sons raised in two treatments: biparental (both parents) or uniparental (mother alone) families. We recorded levels of interactions between pups with both parents, and later assessed the behaviour, cognition and physiology of sons at three developmental stages: juvenile, sub-adult and adult (sexual maturity). Sons from biparental families showed (a) reduced anxiety as juveniles; (b) greater exploration and social interaction at different stages; (c) better cognition; and (d) reduced corticosterone concentrations than sons from uniparental families. In contrast, sons from uniparental families showed greater levels of paternal care, although prolactin concentrations did not differ between treatments. Paternal care in striped mice enhances fitness of males. Here, we also show that sons benefit psychologically and physiologically through interactions with their fathers. However, sons also trade-off such benefits against their own paternal care behaviour, suggesting that fathers influence the development of their son's phenotype in complex ways.
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Affiliation(s)
- Neville Pillay
- School of Animal, Plant and Environmental Science, University of the Witwatersrand, Johannesburg, South Africa
| | - Tasmin L Rymer
- School of Animal, Plant and Environmental Science, University of the Witwatersrand, Johannesburg, South Africa.,College of Science and Engineering, James Cook University, Cairns, QLD, Australia.,Centre for Tropical Environmental and Sustainability Sciences, James Cook University, Cairns, QLD, Australia
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Rimbach R, Blanc S, Zahariev A, Robin JP, Pillay N, Schradin C. Fat content of striped mice decreases during the breeding season but not during the food-restricted dry season. ACTA ACUST UNITED AC 2019; 222:jeb.208504. [PMID: 31727761 DOI: 10.1242/jeb.208504] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2019] [Accepted: 11/07/2019] [Indexed: 10/25/2022]
Abstract
Individuals that are capable of accumulating appropriate fat stores are assumed to have selective advantages when food becomes scarce. Similarly to species from temperate zones, some species inhabiting arid areas accumulate fat stores prior to periods of food limitation. Yet, we have little knowledge concerning seasonal variation in body composition and the relationship between fat store size and disappearance risk in species from arid habitats. Using the water dilution method, we examined the body composition of African striped mice (Rhabdomys pumilio) living in a seasonal habitat with a long food-restricted dry season. We tested for seasonal changes in body composition (N=159 measurements of 113 individuals) and whether dry season survival was related to fat mass (N=66 individuals). Fat stores were similar in size at the onset and the end of the dry season, but surprisingly smaller at the onset of the moist breeding season. Fat stores showed a negative relationship with food availability. Individual variation in fat stores was not associated with disappearance risk, but there was a positive association of disappearance risk with body mass. Increased disappearance risk of heavy individuals suggests elevated dispersal rates in competitive individuals. This study suggests that non-breeding philopatric striped mice do not accumulate large fat stores prior to the food-limited dry season but that they might mobilize fat stores at the onset of the breeding season to satisfy the energetic demands of reproduction and/or to decrease costs associated with larger fat stores, such as increased predation risk.
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Affiliation(s)
- Rebecca Rimbach
- School of Animal, Plant & Environmental Sciences, University of the Witwatersrand, Private Bag 3, WITS 2050, Johannesburg, South Africa
| | - Stéphane Blanc
- Université de Strasbourg, CNRS, IPHC UMR 7178, 67000 Strasbourg, France
| | | | | | - Neville Pillay
- School of Animal, Plant & Environmental Sciences, University of the Witwatersrand, Private Bag 3, WITS 2050, Johannesburg, South Africa
| | - Carsten Schradin
- School of Animal, Plant & Environmental Sciences, University of the Witwatersrand, Private Bag 3, WITS 2050, Johannesburg, South Africa.,Université de Strasbourg, CNRS, IPHC UMR 7178, 67000 Strasbourg, France
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How does cognitive performance change in relation to seasonal and experimental changes in blood glucose levels? Anim Behav 2019. [DOI: 10.1016/j.anbehav.2019.10.011] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Lloyd KJ, Vetter S. Generalist trophic ecology in a changing habitat: The case of the four‐striped mouse in a woody‐encroached savannah. Afr J Ecol 2019. [DOI: 10.1111/aje.12613] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Affiliation(s)
- Kyle J. Lloyd
- Department of Botany Rhodes University Grahamstown South Africa
| | - Susanne Vetter
- Department of Botany Rhodes University Grahamstown South Africa
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Rimbach R, Blanc S, Zahariev A, Pillay N, Schradin C. Daily energy expenditure of males following alternative reproductive tactics: Solitary roamers spend more energy than group-living males. Physiol Behav 2018; 199:359-365. [PMID: 30521878 DOI: 10.1016/j.physbeh.2018.12.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2018] [Revised: 10/25/2018] [Accepted: 12/03/2018] [Indexed: 12/21/2022]
Abstract
In many species, males follow alternative reproductive tactics (ARTs), where one tactic (called bourgeois) has much higher reproductive success than alternative tactics followed by males with lower competitive ability. The extent to which ARTs differ in energetic costs is unknown, but it is important to understand the fitness payoffs of ARTs. We studied male African striped mice (Rhabdomys pumilio) which follow one of three ARTs: heavy bourgeois males defend harems of females and have 10 times higher reproductive success than smaller roamers, which have ten times higher reproductive success than philopatric males, which remain in their natal group and are the smallest males. Bourgeois and philopatric males live in social groups that defend one territory, while roamers are solitary and roam over larger areas. We predicted that roamers will face higher energetic costs compared to group-living males because they do not gain thermoregulatory benefits of huddling in groups and might travel larger distances as they have larger home ranges. We measured daily energy expenditure (DEE) of 30 males, resting metabolic rate (RMR) of 79 males, travel distances and daily ranges of 31 males and changes in body mass of 51 males. Roamers had higher DEE and higher RMR than both types of group-living males. Philopatric males had shorter travel distances and smaller daily ranges than both roamers and bourgeois males, which did not differ from each other. This indicates that the higher DEE of roamers compared to bourgeois males cannot be explained by larger travel distances. Philopatrics gained body mass faster than bourgeois males and roamers, thereby increasing their competitive ability and thus the probability of later switching to a tactic of higher reproductive success. Our results suggest that roamers suffer energetic costs that might reduce their ability of gaining body mass and thus the likelihood of switching to the bourgeois tactic, indicating evolutionary trade-offs between investing energy into roaming versus gaining body mass.
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Affiliation(s)
- Rebecca Rimbach
- School of Animal, Plant & Environmental Sciences, University of the Witwatersrand, Private Bag 3, WITS, 2050 Johannesburg, South Africa.
| | - Stéphane Blanc
- IPHC, UNISTRA, CNRS, 23 rue du Loess, 67200 Strasbourg, France
| | | | - Neville Pillay
- School of Animal, Plant & Environmental Sciences, University of the Witwatersrand, Private Bag 3, WITS, 2050 Johannesburg, South Africa
| | - Carsten Schradin
- School of Animal, Plant & Environmental Sciences, University of the Witwatersrand, Private Bag 3, WITS, 2050 Johannesburg, South Africa; IPHC, UNISTRA, CNRS, 23 rue du Loess, 67200 Strasbourg, France
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Seasonal variation in energy expenditure in a rodent inhabiting a winter-rainfall desert. J Comp Physiol B 2018; 188:877-888. [PMID: 29948157 DOI: 10.1007/s00360-018-1168-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2018] [Revised: 05/23/2018] [Accepted: 05/29/2018] [Indexed: 12/20/2022]
Abstract
Animals that spend more energy than they obtain risk entering allostatic overload, reducing survival and fitness. They are predicted to adjust their daily energy expenditure (DEE) during periods of food scarcity. Adjustments of DEE to changes in food availability have been well-studied in species in temperate zones during winter, but less so in species enduring seasonal droughts. Likely mechanisms regulating DEE involve adjustments of activity and maintenance metabolism. Species that experience seasonal droughts and changes in food availability, like the African striped mouse (Rhabdomys pumilio), are appropriate model organisms to study the regulation of seasonal changes of DEE. We quantified DEE using the 'doubly labelled water' method, measured resting metabolic rate (RMR), and concomitantly determined activity levels using all-day focal observations of 69 free-living striped mice in the cold moist season with high food availability and the hot dry season with low food availability. Striped mice decreased their DEE in the food scarce dry season using multiple mechanisms, especially reductions in RMR, and reduced overall physical activity. This was further facilitated passively by reduced thermoregulatory costs. Our study demonstrates that animals reduce DEE via active and passive mechanisms in food-restricted environments, and highlights that several environmental factors should be considered simultaneously when aiming to understand how animals cope with harsh environments.
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Intra- and interspecific similarity in species composition of helminth communities in two closely-related rodents from South Africa. Parasitology 2017; 144:1211-1220. [DOI: 10.1017/s003118201700049x] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
SUMMARYTo reveal factors responsible for spatial variation in parasite community composition we studied patterns of similarity in helminth species composition in two closely-related rodents (Rhabdomys pumilioandRhabdomys dilectus) that differ in their social and spatial behaviour and live under different environmental conditions across 20 localities in South Africa. We asked whether the two hosts harbour similar assemblages, whether these are more dissimilar between than within hosts and if host social structure, behaviour or environment affects similarity patterns in helminth infracommunities within and among localities. We also investigated whether similarity in species composition of helminth component communities decreases with an increase of geographic distance between host populations. We found that the pattern of space use by the hosts rather than their social behaviour promotes differences in helminth species composition between host species as well as among host populations from different localities. The rate of distance decay of similarity in species composition of helminth component communities differed between the two hosts due to difference in the degree of environmental variation across their geographic ranges. We conclude that patterns of spatial variation in helminth species composition are driven mainly by host spatial behaviour and, to a lesser extent, by environment-associated factors.
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Jäger J, Schradin C, Pillay N, Rimbach R. Active and explorative individuals are often restless and excluded from studies measuring resting metabolic rate: Do alternative metabolic rate measures offer a solution? Physiol Behav 2017; 174:57-66. [PMID: 28283463 DOI: 10.1016/j.physbeh.2017.02.037] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2016] [Revised: 01/23/2017] [Accepted: 02/15/2017] [Indexed: 10/20/2022]
Abstract
It has often been proposed that bolder, more explorative or more active individuals also have a higher resting metabolic rate (RMR), indicating metabolic costs of these personality types. However, such individuals might often be restless and thus excluded from RMR datasets, leading to a significant sampling bias. We tested (1) whether such a bias occurs when animals are measured for a relatively common but short time period of 3h, and if so, (2) whether alternative measures of metabolic rate, that allow the incorporation of non-resting individuals, would reveal associations between metabolism and personality. For this, we studied free-living individuals of the African striped mouse (Rhabdomys pumilio) both during the moist season (N=25 individuals) with high food availability and the dry season (N=48 individuals) with low food availability. We assessed variation in the latency to explore a novel object, and the time spent active and time spent in the centre of a neutral arena. We examined links between personality and (i) RMR and (ii) four alternative metabolic rate (MR) metrics: average MR, highest MR, lowest MR and span of MR. Twenty-nine percent of the measured individuals had to be excluded from our RMR study because they remained restless during respirometry trials. Striped mice showed a behavioural syndrome where fast explorers also spent more time in centre and more time active than slow explorers. Individuals that did not rest during respirometry trials were faster explorers and in the moist season, they were also more active and spent more time in the centre than individuals that rested. We found no relationship between RMR and the behavioural syndrome, which might be due to the exclusion of individuals with a certain behavioural type, leaving a subset of compliant individuals. In the moist season, we found positive relationships between the behavioural syndrome and span of MR and lowest MR. In the dry season, low food availability may mask links between the behavioural syndrome and alternative MR measures due to reduced overall activity in striped mice. Our study demonstrated the importance to consider personality when measuring RMR and suggests that some alternative MRs may be useful to examine relationships between metabolism and personality when it is impossible to measure individuals over extended time periods.
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Affiliation(s)
- Jörg Jäger
- University of the Witwatersrand, School of Animal, Plant & Environmental Sciences, Private Bag 3, WITS, 2050 Johannesburg, South Africa
| | - Carsten Schradin
- University of the Witwatersrand, School of Animal, Plant & Environmental Sciences, Private Bag 3, WITS, 2050 Johannesburg, South Africa; IPHC, UNISTRA, CNRS, 23 rue du Loess, 67200 Strasbourg, France
| | - Neville Pillay
- University of the Witwatersrand, School of Animal, Plant & Environmental Sciences, Private Bag 3, WITS, 2050 Johannesburg, South Africa
| | - Rebecca Rimbach
- University of the Witwatersrand, School of Animal, Plant & Environmental Sciences, Private Bag 3, WITS, 2050 Johannesburg, South Africa.
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Rimbach R, Pillay N, Schradin C. Both thyroid hormone levels and resting metabolic rate decrease in African striped mice when food availability decreases. ACTA ACUST UNITED AC 2016; 220:837-843. [PMID: 27994044 DOI: 10.1242/jeb.151449] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2016] [Accepted: 12/12/2016] [Indexed: 01/13/2023]
Abstract
In response to variation in food availability and ambient temperature (Ta), many animals show seasonal adaptations in their physiology. Laboratory studies showed that thyroid hormones are involved in the regulation of metabolism, and their regulatory function is especially important when the energy balance of an individual is compromised. However, little is known about the relationship between thyroid hormones and metabolism in free-living animals and animals inhabiting seasonal environments. Here, we studied seasonal changes in triiodothyronine (T3) levels, resting metabolic rate (RMR) and two physiological markers of energy balance (blood glucose and ketone bodies) in 61 free-living African striped mice (Rhabdomys pumilio) that live in an semi-arid environment with food shortage during the dry season. We predicted a positive relationship between T3 levels and RMR. Further, we predicted higher T3 levels, blood glucose levels and RMR, but lower ketone body concentrations, during the moist season when food availability is high compared with summer when food availability is low. RMR and T3 levels were negatively related in the moist season but not in the dry season. Both RMR and T3 levels were higher in the moist than in the dry season, and T3 levels increased with increasing food availability. In the dry season, blood glucose levels were lower but ketone body concentrations were higher, indicating a change in substrate use. Seasonal adjustments in RMR and T3 levels permit a reduction of energy expenditure when food is scarce, and reflect an adaptive response to reduced food availability in the dry season.
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Affiliation(s)
- Rebecca Rimbach
- University of the Witwatersrand, School of Animal, Plant & Environmental Sciences, Private Bag 3, WITS 2050, Johannesburg, South Africa
| | - Neville Pillay
- University of the Witwatersrand, School of Animal, Plant & Environmental Sciences, Private Bag 3, WITS 2050, Johannesburg, South Africa
| | - Carsten Schradin
- University of the Witwatersrand, School of Animal, Plant & Environmental Sciences, Private Bag 3, WITS 2050, Johannesburg, South Africa.,IPHC, UNISTRA, CNRS, 23 rue du Loess, Strasbourg 67200, France
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Rimbach R, Willigenburg R, Schoepf I, Yuen CH, Pillay N, Schradin C. Young But Not Old Adult African Striped Mice Reduce Their Activity in the Dry Season When Food Availability is Low. Ethology 2016. [DOI: 10.1111/eth.12527] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Rebecca Rimbach
- School of Animal, Plant & Environmental Sciences; University of the Witwatersrand; Johannesburg South Africa
| | - Remco Willigenburg
- School of Animal, Plant & Environmental Sciences; University of the Witwatersrand; Johannesburg South Africa
- HAS Den Bosch; University of Applied Sciences; Den Bosch The Netherlands
| | - Ivana Schoepf
- School of Animal, Plant & Environmental Sciences; University of the Witwatersrand; Johannesburg South Africa
| | - Chi Hang Yuen
- School of Animal, Plant & Environmental Sciences; University of the Witwatersrand; Johannesburg South Africa
| | - Neville Pillay
- School of Animal, Plant & Environmental Sciences; University of the Witwatersrand; Johannesburg South Africa
| | - Carsten Schradin
- School of Animal, Plant & Environmental Sciences; University of the Witwatersrand; Johannesburg South Africa
- IPHC; UNISTRA; CNRS; Strasbourg France
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Rymer TL, Pillay N, Schradin C. RESILIENCE TO DROUGHTS IN MAMMALS: A CONCEPTUAL FRAMEWORK FOR ESTIMATING VULNERABILITY OF A SINGLE SPECIES. QUARTERLY REVIEW OF BIOLOGY 2016; 91:133-76. [PMID: 27405222 DOI: 10.1086/686810] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
ABSTRACT The frequency and severity of droughts in certain areas is increasing as a consequence of climate change. The associated environmental challenges, including high temperatures, low food, and water availability, have affected, and will affect, many populations. Our aims are to review the behavioral, physiological, and morphological adaptations of mammals to arid environments, and to aid research- ers and nature conservationists about which traits they should study to assess whether or not their study species will be able to cope with droughts. We provide a suite of traits that should be considered when making predictions about species resilience to drought. We define and differentiate between general adaptations, specialized adaptations, and exaptations, and argue that specialized adaptations are of little interest in establishing how nondesert specialists will cope with droughts. Attention should be placed on general adaptations of semidesert species and assess whether these exist as exaptations in nondesert species. We conclude that phenotypic flexibility is the most important general adaptation that may promote species resilience. Thus, to assess whether a species will be able to cope with increasing aridity, it is important to establish the degree offlexibility of traits identified in semidesert species that confer afitness advantage under drying conditions.
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Schoepf I, Pillay N, Schradin C. The pathophysiology of survival in harsh environments. J Comp Physiol B 2016; 187:183-201. [DOI: 10.1007/s00360-016-1020-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2016] [Revised: 06/16/2016] [Accepted: 07/09/2016] [Indexed: 12/20/2022]
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Nater CR, Canale CI, van Benthem KJ, Yuen CH, Schoepf I, Pillay N, Ozgul A, Schradin C. Interactive effects of exogenous and endogenous factors on demographic rates of an African rodent. OIKOS 2016. [DOI: 10.1111/oik.03384] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Chloé R. Nater
- Dept of Evolutionary Biology and Environmental Studies; Univ. of Zurich; Winterthurerstrasse 190 CH-8057 Zurich Switzerland
- Centre for Ecological and Evolutionary Synthesis (CEES), Dept of Biosciences; Univ. of Oslo; Blindern Oslo Norway
| | - Cindy I. Canale
- Dept of Evolutionary Biology and Environmental Studies; Univ. of Zurich; Winterthurerstrasse 190 CH-8057 Zurich Switzerland
| | - Koen J. van Benthem
- Dept of Evolutionary Biology and Environmental Studies; Univ. of Zurich; Winterthurerstrasse 190 CH-8057 Zurich Switzerland
| | - Chi-Hang Yuen
- School of Animal, Plant and Environmental Sciences; Univ. of the Witwatersrand; Braamfontein Johannesburg South Africa
| | - Ivana Schoepf
- School of Animal, Plant and Environmental Sciences; Univ. of the Witwatersrand; Braamfontein Johannesburg South Africa
| | - Neville Pillay
- School of Animal, Plant and Environmental Sciences; Univ. of the Witwatersrand; Braamfontein Johannesburg South Africa
| | - Arpat Ozgul
- Dept of Evolutionary Biology and Environmental Studies; Univ. of Zurich; Winterthurerstrasse 190 CH-8057 Zurich Switzerland
| | - Carsten Schradin
- School of Animal, Plant and Environmental Sciences; Univ. of the Witwatersrand; Braamfontein Johannesburg South Africa
- Inst. Pluridisciplinaire Hubert Curien; Dépt d'Ecologie Physiologie et Ethologie; Strasbourg France
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Maille A, Pillay N, Schradin C. Seasonal variation in attention and spatial performance in a wild population of the African striped mouse (Rhabdomys pumilio). Anim Cogn 2015; 18:1231-42. [DOI: 10.1007/s10071-015-0892-y] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2015] [Revised: 06/22/2015] [Accepted: 06/24/2015] [Indexed: 01/03/2023]
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Schoepf I, Schmohl G, König B, Pillay N, Schradin C. Manipulation of population density and food availability affects home range sizes of African striped mouse females. Anim Behav 2015. [DOI: 10.1016/j.anbehav.2014.10.002] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Schradin C, Raynaud J, Arrivé M, Blanc S. Leptin levels in free ranging striped mice (Rhabdomys pumilio) increase when food decreases: the ecological leptin hypothesis. Gen Comp Endocrinol 2014; 206:139-45. [PMID: 24992023 DOI: 10.1016/j.ygcen.2014.06.024] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/22/2014] [Revised: 06/13/2014] [Accepted: 06/21/2014] [Indexed: 11/29/2022]
Abstract
Leptin is a hormone informing the body about its fat stores, reducing appetite and foraging and as such reducing fattening of individuals. In laboratory rodents, leptin secretion is highly correlated to the amount of adipose tissue. We compared this to the alternative ecological leptin hypothesis, which based on the behavioural effects of leptin predicts that leptin levels are disassociated from adipose tissue when fattening is of evolutionary advantage to survive coming periods of low food availability. Studying a species that has to survive a dry season with low food availability, we tested the ecological leptin hypothesis, predicting low leptin levels when food availability and thus adiposity is high promoting foraging and fattening, but high leptin levels in the seasons of low food availability, reducing energetic costs due to foraging. We measured leptin levels in 154 samples of free living African striped mice (Rhabdomys pumilio). Striped mice gain significant body mass during the moist season to survive the following dry season with low food availability. We found a strong seasonal effect, with higher leptin levels in the dry season with low food availability, which was in contrast to the hypothesis deriving from studies on laboratory rodents, but in agreement with ecological leptin hypothesis: leptin levels remained low in the period of high food availability, allowing fattening, but increased during periods of low food availability, possibly suppressing energetically costly foraging in an environment where foraging success would have been very low. Leptin correlated significantly and negatively with testosterone levels, and high testosterone levels in the moist season could explain why leptin levels were low even though food availability was high. However, analysing samples from an experimental laboratory study where testosterone levels were increased via implants found no support for a suppressive role of testosterone on leptin. In sum, our study indicates that in a species with seasonal fattening, leptin levels might be uncoupled from the amount of adipose tissue.
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Affiliation(s)
- Carsten Schradin
- Université de Strasbourg, IPHC-DEPE, 23 rue Becquerel, 67087 Strasbourg, France; CNRS, UMR 7178, 67087 Strasbourg, France; School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa.
| | - Julien Raynaud
- Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Mathilde Arrivé
- Université de Strasbourg, IPHC-DEPE, 23 rue Becquerel, 67087 Strasbourg, France; CNRS, UMR 7178, 67087 Strasbourg, France
| | - Stéphane Blanc
- Université de Strasbourg, IPHC-DEPE, 23 rue Becquerel, 67087 Strasbourg, France; CNRS, UMR 7178, 67087 Strasbourg, France
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Schoepf I, Schradin C. Arginine vasopressin plasma levels change seasonally in African striped mice but do not differ between alternative reproductive tactics. Gen Comp Endocrinol 2014; 204:43-8. [PMID: 24842715 DOI: 10.1016/j.ygcen.2014.05.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/25/2014] [Revised: 04/30/2014] [Accepted: 05/02/2014] [Indexed: 11/20/2022]
Abstract
Arginine vasopressin (AVP) is an important hormone for osmoregulation, while as a neuropeptide in the brain it plays an important role in the regulation of social behaviors. Dry habitats are often the home of obligately sociable species such as meerkats and Damaraland mole-rats, leading to the hypothesis that high plasma AVP levels needed for osmoregulation might be associated with the regulation of social behavior. We tested this in a facultative sociable species, the African striped mouse (Rhabdomys pumilio). During the moist breeding season, both solitary- and group-living reproductive tactics occur in this species, which is obligatory sociable in the dry season. We collected 196 plasma samples from striped mice following different reproductive tactics both during the moist and the dry season. Solitary mice did not have lower AVP levels than sociable mice, rejecting the hypothesis that peripheral AVP is involved in the regulation of alternative reproductive tactics. However, we found significantly higher AVP levels during the dry season, with AVP levels correlated with the abundance of food plants, the main source of water for striped mice. Plasma AVP levels were not correlated with testosterone or corticosterone levels. Our study underlines the important role that AVP plays in osmoregulation, particularly for a free ranging mammal living under harsh arid conditions.
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Affiliation(s)
- Ivana Schoepf
- Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland; School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa
| | - Carsten Schradin
- Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland; School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa; Université de Strasbourg, IPHC-DEPE, 23 rue Becquerel, 67087 Strasbourg, France; CNRS, UMR7178, 67087 Strasbourg, France.
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Schradin C, Larke RH, Bales KL. Growing up in the family or growing up alone influences behavior and hormones, but not arginine vasopressin receptor 1a expression in male African striped mice. Physiol Behav 2014; 129:205-13. [PMID: 24631307 DOI: 10.1016/j.physbeh.2014.02.060] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2013] [Revised: 01/16/2014] [Accepted: 02/21/2014] [Indexed: 11/17/2022]
Abstract
In many species males display alternative reproductive tactics (ARTs). While males of different tactics differ behaviorally in the field, it is often not known whether these behavioral differences would also occur under standardized laboratory conditions, nor how ARTs are regulated by the brain. In the present study we kept male African striped mice (Rhabdomys pumilio) in captivity either in family groups or solitary, to mimic ARTs observed in the field. This allowed us to study these males behaviorally under standardized conditions, to replicate physiological findings from the field, and to study the expression of the arginine vasopressin 1a receptor (AVPR1a) in their brains. Changes in either peptide release or receptor expression (or both) might regulate ARTs with differential timelines, with peptide secretion being faster than receptor expression. As observed in the field, family living males had higher corticosterone but lower testosterone levels than singly housed males. Surprisingly, singly housed males were less aggressive while at the same time having higher testosterone levels. We found no differences in AVPR1a expression. In a previous study it was shown that singly housed males have higher levels of AVP stored in their brain, which potentially could be secreted when the social situation changes, for example to establish social bonds. Our study on AVPR1a suggests the hypothesis that, given that the receptor distribution and expression of singly housed males do not differ from that of family-living males, the brains of singly-housed males have a similar capacity to be responsive to AVP when given the chance to interact socially.
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Affiliation(s)
- Carsten Schradin
- Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland; School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa; Université de Strasbourg, IPHC-DEPE, 23 rue Becquerel, 67087 Strasbourg, France; CNRS, UMR7178, 67087 Strasbourg, France.
| | - Rebecca H Larke
- Department of Psychology, University of California, Davis, CA 95616, USA
| | - Karen L Bales
- Department of Psychology, University of California, Davis, CA 95616, USA
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Histology and ultrastructure of transitional changes in skin morphology in the juvenile and adult four-striped mouse (Rhabdomys pumilio). ScientificWorldJournal 2013; 2013:259680. [PMID: 24288469 PMCID: PMC3830898 DOI: 10.1155/2013/259680] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2013] [Accepted: 09/19/2013] [Indexed: 11/25/2022] Open
Abstract
The four-striped mouse has a grey to brown coloured coat with four characteristic dark stripes interspersed with three lighter stripes running along its back. The histological differences in the skin of the juvenile and adult mouse were investigated by Haematoxylin and Eosin and Masson Trichrome staining, while melanocytes in the skin were studied through melanin-specific Ferro-ferricyanide staining. The ultrastructure of the juvenile skin, hair follicles, and melanocytes was also explored. In both the juvenile and adult four-striped mouse, pigment-containing cells were observed in the dermis and were homogeneously dispersed throughout this layer. Apart from these cells, the histology of the skin of the adult four-striped mouse was similar to normal mammalian skin. In the juvenile four-striped mouse, abundant hair follicles of varying sizes were observed in the dermis and hypodermis, while hair follicles of similar size were only present in the dermis of adult four-striped mouse. Ultrastructural analysis of juvenile hair follicles revealed that the arrangement and differentiation of cellular layers were typical of a mammal. This study therefore provides unique transition pattern in the four-striped mouse skin morphology different from the textbook description of the normal mammalian skin.
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Schoepf I, Schradin C. Endocrinology of sociality: comparisons between sociable and solitary individuals within the same population of African striped mice. Horm Behav 2013; 64:89-94. [PMID: 23648775 DOI: 10.1016/j.yhbeh.2013.04.011] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/22/2012] [Revised: 04/20/2013] [Accepted: 04/25/2013] [Indexed: 10/26/2022]
Abstract
The social organization of species ranges from solitary-living to complex social groups. While the evolutionary reasons of group-living are well studied, the physiological mechanisms underlying alternative social systems are poorly understood. By studying group-living and solitary individuals of the same species, we can determine hormonal correlates of sociality without the problem of confounding phylogenetic factors. The African striped mouse (Rhabdomys pumilio) is a socially flexible species, which can be solitary or alternatively form complex family groups, depending on population density and the extent of reproductive competition. We predicted group-living striped mice to show signs of reproductive suppression and social stress, resulting in higher corticosterone but lower testosterone levels when compared to solitary-living individuals. To determine whether differences in social organization correlated with hormonal differences, we collected blood samples from free-living striped mice during four breeding seasons when we experimentally induced solitary-living in philopatric individuals by locally reducing population density. Striped mice that were group-living did not change their corticosterone or estosterone levels during the study, indicating that there was no temporal effect during the breeding season. Striped mice of both sexes had significantly lower corticosterone levels after switching from group- to solitary-living. Solitary males - but not solitary females - had higher testosterone levels than group-living conspecifics. Our results suggest that group-living results in physiological stress and can induce reproductive suppression, at least in philopatric males. The switch to solitary-living may thus be a tactic to avoid reproductive competition within groups, and is associated with decreased stress hormone levels and onset of independent reproduction.
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Affiliation(s)
- Ivana Schoepf
- Department of Animal Behaviour, Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Zurich, Switzerland.
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Raynaud J, Schradin C. Regulation of male prolactin levels in an opportunistically breeding species, the African striped mouse. J Zool (1987) 2013. [DOI: 10.1111/jzo.12040] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- J. Raynaud
- Institute of Evolutionary Biology and Environmental Studies; University of Zurich; Zurich Switzerland
| | - C. Schradin
- Université de Strasbourg; IPHC-DEPE; CNRS; Strasbourg France
- School of Animal, Plant and Environmental Sciences; University of the Witwatersrand; Johannesburg South Africa
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Extinction or Survival? Behavioral Flexibility in Response to Environmental Change in the African Striped Mouse Rhabdomys. SUSTAINABILITY 2013. [DOI: 10.3390/su5010163] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Schradin C, Kenkel W, Krackow S, Carter CS. Staying put or leaving home: endocrine, neuroendocrine and behavioral consequences in male African striped mice. Horm Behav 2013; 63:136-43. [PMID: 23079108 DOI: 10.1016/j.yhbeh.2012.10.004] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/12/2012] [Revised: 10/08/2012] [Accepted: 10/09/2012] [Indexed: 11/25/2022]
Abstract
Social flexibility occurs when individuals of both sexes can change their social and reproductive tactics, which in turn can influence the social system of an entire population. However, little is known regarding the extent to which individuals of socially flexible species vary in their social behavior and in the underlying physiological mechanisms that support different social tactics. The present study in African striped mice modeled in captivity three male tactics described from the field: (a) philopatric males remaining in the family; (b) solitary roamers; or (c) group-living breeding males. Sixteen pairs and their offspring were kept in captivity, while one male offspring from the family remained as singly housed after he reached 21 days of age. Differences in behavior, morphology, hormone and neuropeptide levels were tested, and physiological measurements were correlated with behavioral measurements. In standardized arena experiments group-living males (philopatrics and breeders) were significantly more aggressive than singly housed males, in agreement with previous data suggesting that group-living, but not roaming males, are territorial. Philopatric males showed signs of reproductive suppression, small testes, lower testosterone and higher corticosterone levels than their singly housed brothers. Higher levels of arginine vasopressin (AVP) were measured in the PVN and BNST of singly housed males compared to group-living males. Based on these findings we hypothesize that roamers are physiologically primed, and capable, if the opportunity to mate arises, to release AVP, form social bonds and become territorial, thus quickly adopting the tactic as breeding male which would yield a higher reproductive success.
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Affiliation(s)
- Carsten Schradin
- Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
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36
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Differences in social behaviour between group-living and solitary African striped mice, Rhabdomys pumilio. Anim Behav 2012. [DOI: 10.1016/j.anbehav.2012.08.019] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Ganem G, Meynard CN, Perigault M, Lancaster J, Edwards S, Caminade P, Watson J, Pillay N. Environmental correlates and co-occurrence of three mitochondrial lineages of striped mice (Rhabdomys) in the Free State Province (South Africa). ACTA OECOLOGICA-INTERNATIONAL JOURNAL OF ECOLOGY 2012. [DOI: 10.1016/j.actao.2012.01.003] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Schradin C, Eder S, Müller K. Differential investment into testes and sperm production in alternative male reproductive tactics of the African striped mouse (Rhabdomys pumilio). Horm Behav 2012; 61:686-95. [PMID: 22445749 DOI: 10.1016/j.yhbeh.2012.03.002] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/10/2011] [Revised: 03/06/2012] [Accepted: 03/07/2012] [Indexed: 11/25/2022]
Abstract
Males that follow alternative reproductive tactics might differ in their investment into testis development and sperm production. The resource-allocation hypothesis predicts that males following a sneaker tactic should invest more into sperm production than dominant territorial males which should invest more into mate guarding. This hypothesis is supported by studies in species where individual males cannot switch between tactics (fixed tactics). Here we present the first data for a species where males can switch between tactics (plastic tactics). We studied African striped mice (Rhabdomys pumilio) in captivity, mimicking three tactics observed in the field: philopatric group-living males, singly-housed males representing roaming males, and group-living breeding males. We measured quantitative and qualitative reproductive traits, as well as serum and testis hormone concentrations. We found no support for the resource-allocation hypothesis, since breeding and singly-housed males invested similarly in testes and sperm. However, philopatric males had significantly smaller testes and epididymides, lower sperm counts, lower testosterone and higher corticosterone levels than males of the two other tactics. Philopatric males did not reach a larger body mass than singly-housed males with well developed reproductive traits, indicating that they did not trade investment in sperm production against growth. Interestingly, testis testosterone concentrations of philopatric males did not differ from those of other males. Our data suggest that philopatric males are reproductively suppressed by the breeding male, but might be ready to increase their serum testosterone levels when social and environmental conditions allow for this physiological switch accompanying the behavioral switch between tactics.
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Affiliation(s)
- Carsten Schradin
- Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstr. 190, 8057 Zurich, Switzerland.
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Meynard CN, Pillay N, Perrigault M, Caminade P, Ganem G. Evidence of environmental niche differentiation in the striped mouse (Rhabdomys sp.): inference from its current distribution in southern Africa. Ecol Evol 2012; 2:1008-23. [PMID: 22837845 PMCID: PMC3399166 DOI: 10.1002/ece3.219] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2012] [Accepted: 02/03/2012] [Indexed: 11/10/2022] Open
Abstract
The aim of this study was to characterize environmental differentiation of lineages within Rhabdomys and provide hypotheses regarding potential areas of contact between them in the Southern African subregion, including the Republic of South Africa, Lesotho, and Namibia. Records of Rhabdomys taxa across the study region were compiled and georeferenced from the literature, museum records, and field expeditions. Presence records were summarized within a 10 × 10 km grid covering the study area. Environmental information regarding climate, topography, land use, and vegetation productivity was gathered at the same resolution. Multivariate statistics were used to characterize the current environmental niche and distribution of the whole genus as well as of three mitochondrial lineages known to occur in southern Africa. Distribution modeling was carried out using MAXENT in order to generate hypotheses regarding current distribution of each taxa and their potential contact zones. Results indicate that the two species within Rhabdomys appear to have differentiated across the precipitation/temperature gradient present in the region from east to west. R. dilectus occupies the wettest areas in eastern southern Africa, while R. pumilio occupies the warmer and drier regions in the west, but also penetrates in the more mesic central part of the region. We provide further evidence of environmental differentiation within two lineages of R. dilectus. Contact zones between lineages appear to occur in areas of strong environmental gradients and topographic complexity, such as the transition zones between major biomes and the escarpment area where a sharp altitudinal gradient separates coastal and plateau areas, but also within more homogeneous areas such as within grassland and savannah biomes. Our results indicate that Rhabdomys may be more specialized than previously thought when considering current knowledge regarding mitochondrial lineages. The genus appears to have differentiated along two major environmental axes in the study region, but results also suggest dispersal limitations and biological interactions having a role in limiting current distribution boundaries. Furthermore, the projection of the potential geographic distribution of the different lineages suggests several contact zones that may be interesting study fields for understanding the interplay between ecological and evolutionary processes during speciation.
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Schoepf I, Schradin C. Better off alone! Reproductive competition and ecological constraints determine sociality in the African striped mouse (Rhabdomys pumilio). J Anim Ecol 2012; 81:649-56. [PMID: 22220746 DOI: 10.1111/j.1365-2656.2011.01939.x] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Ivana Schoepf
- Department of Animal Behaviour, Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, Zurich 8057, Switzerland.
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Abu Baker MA, Brown JS. Variation of within-day foraging costs in the striped mouse (Rhabdomys pumilio). Mamm Biol 2011. [DOI: 10.1016/j.mambio.2011.02.005] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Schradin C, Lindholm AK. Relative fitness of alternative male reproductive tactics in a mammal varies between years. J Anim Ecol 2011; 80:908-17. [PMID: 21418210 DOI: 10.1111/j.1365-2656.2011.01831.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
1. In many species, males can use different behavioural tactics to achieve fertilization, so-called alternative reproductive tactics (ARTs). Few field studies have measured fitness consequences of ARTs under varying environmental conditions. 2. Here, we describe fitness consequences of three phenotypically plastic ARTs in the African striped mouse (Rhabdomys pumilio) and show that relative fitness of ARTs differs between years. Each year represents a different generation. 3. For the generation living under high population density, tactics differed in relative fitness in accordance with the theory of conditional strategies, with highly successful territorial breeding males having 10 times higher success than solitary roaming males and 102 times higher success than adult natally philopatric males. 4. For the generation living under intermediate population density, the territorial breeding and roaming tactics yielded similar fitness, which would be in agreement with the theory of mixed strategies. No philopatric males occurred. 5. For the generation living under low population density, roaming was the only tactic used and some roamers had very high fitness. 6. The main prediction of status-dependent selection for conditional strategies is a correlation between fitness and status, often measured as body mass, but we did not find this correlation within tactics when more than one tactic was expressed in the population. 7. Female distribution seems to have an effect on which reproductive tactics male chose: female defence polygyny when females are clumped (interference competition), but a searching tactic when females are dispersed (scramble competition). In contrast to predictions arising from theory on scramble competition, male body mass was important in determining fitness only in the year when females were dispersed, but not in other years. 8. Our results indicate that the differentiation between conditional and mixed strategies is not an absolute one. In many other species, environmental conditions might fluctuate temporally and spatially so that the normally suboptimal tactic yields similar fitness to the (usually) dominant tactic or that only a single tactic prevails. 9. We suggest the term single strategy, independent of current fitness consequences, for systems where tactics are not genetically determined, in contrast to genetically determined alternative strategies.
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Affiliation(s)
- Carsten Schradin
- Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstr. 190, 8057 Zurich, Switzerland.
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SOLMSEN N, JOHANNESEN J, SCHRADIN C. Highly asymmetric fine-scale genetic structure between sexes of African striped mice and indication for condition dependent alternative male dispersal tactics. Mol Ecol 2011; 20:1624-34. [DOI: 10.1111/j.1365-294x.2011.05042.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Abu Baker MA, Brown JS. Islands of fear: effects of wooded patches on habitat suitability of the striped mouse in a South African grassland. Funct Ecol 2010. [DOI: 10.1111/j.1365-2435.2010.01757.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Scantlebury M, Krackow S, Pillay N, Bennett N, Schradin C. Basking is affected by season and influences oxygen consumption in desert-living striped mice. J Zool (1987) 2010. [DOI: 10.1111/j.1469-7998.2010.00687.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Schradin C, Scantlebury M, Pillay N, König B. Testosterone levels in dominant sociable males are lower than in solitary roamers: physiological differences between three male reproductive tactics in a sociably flexible mammal. Am Nat 2010; 173:376-88. [PMID: 19199528 DOI: 10.1086/596535] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
The relative plasticity hypothesis predicts that alternative tactics are associated with changes in steroid hormone levels. In species with alternative male reproductive tactics, the highest androgen levels have usually been reported in dominant males. However, in sociable species, dominant males show amicable behaviors to gain access to females, which might conflict with high testosterone levels. We compared testosterone, corticosterone, and resting metabolic rate in male striped mice (Rhabdomys pumilio) following a conditional strategy with three different reproductive tactics: (i) philopatric group-living males, (ii) solitary-living roamers, (iii) dominant but sociable group-living territorial breeders. Philopatrics had the lowest testosterone but highest corticosterone levels, suggesting that they make the best of a bad job. Dominant territorial breeders had lower testosterone levels than roamers, which have a lower competitive status. Roamers had the highest testosterone levels, which might promote risky behavior, such as invading territories defended by territorial males. Roamers also had lower resting metabolic rates than either type of group-living males. Our results suggest that dominant males' testosterone levels reflect a trade-off between low testosterone amicable behavior and high testosterone dominance behavior.
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Affiliation(s)
- Carsten Schradin
- Institute of Zoology, University of Zurich, Winterthurerstrasse 190, Zurich, Switzerland.
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Schradin C, König B, Pillay N. Reproductive competition favours solitary living while ecological constraints impose group-living in African striped mice. J Anim Ecol 2010; 79:515-21. [PMID: 20059610 DOI: 10.1111/j.1365-2656.2009.01651.x] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
1. Social groups typically form due to delayed dispersal of adult offspring when no opportunities for independent breeding exist, or the costs of dispersal are higher than the costs of remaining philopatric. Ecological constraints are thought to be a main reason for group-living in animals. 2. Reproductive competition within groups can induce high costs of philopatry, and is thought to be a main reason for solitary living. 3. Experimental manipulation of reproductive competition is difficult. One solution is to compare sociality between periods with and without reproductive competition. 4. Here, we show empirically in a 8-year field study that striped mice (Rhabdomys pumilio) of both sexes were group-living during the breeding season when population density (PD) was high but solitary living when PD was low, supporting the ecological constraints model. 5. After the breeding season, in the absence of reproductive competition, the positive correlation between PD and percentage of group-living striped mice was absent. Almost all striped mice were group-living even under very low population densities. This supports the reproductive competition model. 6. Ambient temperature, food availability and predation pressure, did not influence sociality. 7. In captivity, the costs of reproductive competition in communal groups include female infanticide and aggression between females. 8. We conclude that group-living is favoured by constraints imposed through habitat saturation and by its benefits (improved thermoregulation by huddling, group-territoriality and predator avoidance), and that reproductive competition is a major force favouring solitary living in striped mice.
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Affiliation(s)
- Carsten Schradin
- Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstr. 190, 8057 Zurich, Switzerland.
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Schradin C, Schmohl G, Rödel HG, Schoepf I, Treffler SM, Brenner J, Bleeker M, Schubert M, König B, Pillay N. Female home range size is regulated by resource distribution and intraspecific competition: a long-term field study. Anim Behav 2010. [DOI: 10.1016/j.anbehav.2009.10.027] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Schradin C, Schneider C, Yuen CH. Age at puberty in male African striped mice: the impact of food, population density and the presence of the father. Funct Ecol 2009. [DOI: 10.1111/j.1365-2435.2009.01569.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Schubert M, Pillay N, Ribble DO, Schradin C. The Round-Eared Sengi and the Evolution of Social Monogamy: Factors that Constrain Males to Live with a Single Female. Ethology 2009. [DOI: 10.1111/j.1439-0310.2009.01684.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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