1
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Hart DW, Roberts E, O'Riain MJ, Millar RP, Bennett NC. The curious case of the hypothalamic-pituitary-gonadal axis dysfunction in subordinate female naked mole-rats (Heterocephalus glaber): No apparent role of opioids and glucocorticoids. J Neuroendocrinol 2024; 36:e13444. [PMID: 39279348 DOI: 10.1111/jne.13444] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/08/2024] [Revised: 08/13/2024] [Accepted: 08/25/2024] [Indexed: 09/18/2024]
Abstract
The naked mole-rat (Heterocephalus glaber) is a unique model mammal in which to study socially induced inhibition of the hypothalamic-pituitary-gonadal (HPG) axis. Naked mole-rat groups exhibit a high degree of reproductive bias in which breeding is restricted to one female (the queen) and one male, with subordinate non-breeding colony members rarely, if ever, having the opportunity to reproduce due to a dysfunctional HPG axis. It is posited that aggression directed at subordinates by the queen suppresses reproduction in these subordinates, yet the underlying physiological mechanisms causing this dysfunction are unknown. This study aimed to investigate the possible factors contributing to the dysfunction of the HPG axis in subordinate female naked mole-rats with a specific focus on the role of ovarian feedback and stress-related factors such as circulating glucocorticoid and endogenous opioid peptides. The results showed that stress-related factors appear to not mediate the suppression of reproductive function in subordinate female naked mole rats. Indeed, in some cases, the activation of the stress axis may lead to reproductive activation instead of deactivation. At the same time, the role of ovarian sex steroid feedback in reproductive suppression is likely limited and not clearly delineated. This study highlights the need for detailed studies to elucidate the mechanism of reproductive suppression in this unique model mammalian species which may shed light on, and reveal novel mechanisms, in the social regulation of reproduction.
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Affiliation(s)
- Daniel W Hart
- Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa
| | - E Roberts
- Department of Zoology, University of Cape Town, Cape Town, South Africa
| | - M J O'Riain
- Department of Zoology, University of Cape Town, Cape Town, South Africa
| | - R P Millar
- Centre for Neuroendocrinology, Department of Immunology, University of Pretoria, Pretoria, South Africa
- Department of Integrative Biomedical Sciences, Institute of Infectious Diseases and Molecular Medicine, University of Cape Town, Cape Town, South Africa
| | - N C Bennett
- Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa
- Mammal Research Institute, University of Pretoria, Pretoria, South Africa
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2
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Amari M, Mary A, Zablocki-Thomas P, Bourgeois A, Pouydebat E. Positive effect of a diggable substrate on the behaviour of a captive naked mole rat colony. Sci Rep 2024; 14:20138. [PMID: 39209873 PMCID: PMC11362154 DOI: 10.1038/s41598-024-64146-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2024] [Accepted: 06/05/2024] [Indexed: 09/04/2024] Open
Abstract
Naked mole rats (Heterocephalus galber) are eusocial mammals from East Africa. Their extraordinary social organisation is accompanied by remarkable adaptations to an underground lifestyle, extreme longevity and resistance to many diseases, making naked mole rats a highly relevant model for biological research. However, their living conditions in controlled environments do not allow them to express fundamental behaviours: digging galleries and exploring. This gap probably constitutes a bias to any behavioural or even medical study, because it represents a potential obstacle to their well-being. In this article, we tested the effects of the introduction of a diggable substrate on the behaviour of a colony of naked mole rats at the Menagerie, le Zoo du Jardin des Plantes, Paris. We measured individual exploratory latencies, the number of entries per minute and the frequency with which naked mole rats gnawed tunnels during observation trials. We found that: (i) young individuals explore more quickly, (ii) the introduction of a diggable substrate encourages exploration and digging behaviour, and (iii) could therefore be a relevant element to introduce under human care. This new environmental design could improve the welfare of naked mole rats by creating opportunities for cognitive challenges such as exploration and environmental control.
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Affiliation(s)
- Myriam Amari
- UMR 7179 MECADEV, CNRS/MNHN, Département Adaptations du Vivant, Mécanismes Adaptatifs et Evolution, Muséum National d'Histoire Naturelle, 57 Rue Cuvier, 75231, Paris, France.
- Département de Biologie, École normale supérieure, PSL Université Paris, 75005, Paris, France.
| | - Alma Mary
- UMR 7179 MECADEV, CNRS/MNHN, Département Adaptations du Vivant, Mécanismes Adaptatifs et Evolution, Muséum National d'Histoire Naturelle, 57 Rue Cuvier, 75231, Paris, France
| | - Pauline Zablocki-Thomas
- UMR 7179 MECADEV, CNRS/MNHN, Département Adaptations du Vivant, Mécanismes Adaptatifs et Evolution, Muséum National d'Histoire Naturelle, 57 Rue Cuvier, 75231, Paris, France
- Westfälische Wilhelms-Universität Münster, Münster, Germany
| | - Aude Bourgeois
- Ménagerie, Le Zoo du Jardin des Plantes, Muséum National d'Histoire Naturelle, 57 Rue Cuvier, 75005, Paris, France
| | - Emmanuelle Pouydebat
- UMR 7179 MECADEV, CNRS/MNHN, Département Adaptations du Vivant, Mécanismes Adaptatifs et Evolution, Muséum National d'Histoire Naturelle, 57 Rue Cuvier, 75231, Paris, France
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3
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Thorley J, Bensch HM, Finn K, Clutton-Brock T, Zöttl M. Damaraland mole-rats do not rely on helpers for reproduction or survival. Evol Lett 2023; 7:203-215. [PMID: 37475748 PMCID: PMC10355180 DOI: 10.1093/evlett/qrad023] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2022] [Revised: 03/23/2023] [Accepted: 05/05/2023] [Indexed: 07/22/2023] Open
Abstract
In eusocial invertebrates and obligate cooperative breeders, successful reproduction is dependent on assistance from non-breeding group members. Although naked (Heterocephalus glaber) and Damaraland mole-rats (Fukomys damarensis) are often described as eusocial and their groups are suggested to resemble those of eusocial insects more closely than groups of any other vertebrate, the extent to which breeding individuals benefit from the assistance of non-breeding group members is unclear. Here we show that, in wild Damaraland mole-rats, prospective female breeders usually disperse and settle alone in new burrow systems where they show high survival rates and remain in good body condition-often for several years-before being joined by males. In contrast to many obligate cooperative vertebrates, pairs reproduced successfully without non-breeding helpers, and the breeding success of experimentally formed pairs was similar to that of larger, established groups. Though larger breeding groups recruited slightly more pups than smaller groups, adult survival was independent of group size and group size had mixed effects on the growth of non-breeders. Our results suggest that Damaraland mole-rats do not need groups to survive and that cooperative breeding in the species is not obligate as pairs can-and frequently do-reproduce without the assistance of helpers. While re-emphasizing the importance of ecological constraints on dispersal in social mole-rats, the mixed effects of group size in our study suggest that indirect benefits accrued through cooperative behavior may have played a less prominent role in the evolution of mole-rat group-living than previously thought.
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Affiliation(s)
- Jack Thorley
- Corresponding author: Department of Zoology, Downing Street, University of Cambridge, Cambridge, CB2 3EJ, United Kingdom.
| | | | - Kyle Finn
- Kalahari Research Centre, Kuruman River Reserve, Van Zylsrus, South Africa
- Department of Zoology and Entomology, Mammal Research Institute, University of Pretoria, Pretoria, South Africa
| | - Tim Clutton-Brock
- Department of Zoology, University of Cambridge, Cambridge, United Kingdom
- Kalahari Research Centre, Kuruman River Reserve, Van Zylsrus, South Africa
- Department of Zoology and Entomology, Mammal Research Institute, University of Pretoria, Pretoria, South Africa
| | - Markus Zöttl
- Kalahari Research Centre, Kuruman River Reserve, Van Zylsrus, South Africa
- Department of Biology and Environmental Science, Linnaeus University, Kalmar, Sweden
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4
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Edwards PD, Toor I, Holmes MM. The Curious Case of the Naked Mole-Rat: How Extreme Social and Reproductive Adaptations Might Influence Sex Differences in the Brain. Curr Top Behav Neurosci 2023; 62:47-70. [PMID: 35301704 DOI: 10.1007/7854_2022_310] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Research in the neurobiology of sex differences is inherently influenced by the study species that are used. Some traditional animal research models, such as rats and mice, show certain sex differences in the brain that have been foundational to neurobiological research. However, subsequent work has demonstrated that these differences are not always generalizable, especially to species with different social structures and sex-associated roles or behaviors. One such example is the naked mole-rat (Heterocephalus glaber), which has an unusual social structure among mammals. Naked mole-rats live in large groups where reproduction is restricted to a dominant female, called the "queen," and often only one breeding male. All other animals in the group, the "subordinates," are socially suppressed from reproduction and remain in a prepubescent state as adults, unless they are removed from the presence of the queen. These subordinates show little to no sex differences in external morphology, neural morphology, or behavior. However, there are a suite of neurobiological differences between subordinate and breeding naked mole-rats. After naked mole-rats attain breeding status, many of the classically sexually differentiated brain regions increase in volume (paraventricular nucleus, medial amygdala, bed nucleus of the stria terminalis). There are additionally social status differences in sex hormone receptor expression in the brain, as well as other changes in gene expression, some of which also show sex differences - though not always in the predicted direction based on other rodent studies. Data from naked mole-rats show that it is critical to consider the evolved social structure of a species when studying sex differences in the brain.
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Affiliation(s)
- Phoebe D Edwards
- Department of Psychology, University of Toronto Mississauga, Mississauga, ON, Canada
| | - Ilapreet Toor
- Department of Psychology, University of Toronto Mississauga, Mississauga, ON, Canada
| | - Melissa M Holmes
- Department of Psychology, University of Toronto Mississauga, Mississauga, ON, Canada.
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5
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Toor I, Faykoo-Martinez M, Edwards PD, Boonstra R, Holmes MM. Hormones do not maketh the mole-rat: No steroid hormone signatures of subordinate behavioral phenotypes. Horm Behav 2022; 145:105236. [PMID: 35917594 DOI: 10.1016/j.yhbeh.2022.105236] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/27/2022] [Revised: 07/07/2022] [Accepted: 07/08/2022] [Indexed: 11/19/2022]
Abstract
In some cooperatively breeding groups, individuals have distinct behavioral characteristics that are often stable and predictable across time. However, in others, as in the eusocial naked mole-rat, evidence for behavioral phenotypes is ambiguous. Here, we study whether the naked mole-rat can be divided into discrete phenotypes and if circulating hormone concentrations underpin these differences. Naked mole-rat colonies consist of a single breeding female and large numbers of non-reproductive subordinates that in some cases can exceed several hundred in a colony. The subordinates can potentially be divided into soldiers, who defend the colony; workers, who maintain it; and dispersers, who want to leave it. We established six colonies de novo, tracked them over three years, and assessed the behavior and hormone concentrations of the subordinates. We found that soldiers tended to be from earlier litters and were higher ranked compared to workers, whereas dispersers were distributed throughout litters and rankings. There was no difference in estradiol, testosterone, or dehydroepiandrosterone (DHEA) concentrations among phenotypes. Progesterone concentrations were higher in soldiers, but this difference appeared to be driven by a few individuals. Principal component analysis demonstrated that soldiers separated into a discrete category relative to workers/dispersers, with the highest ranked loadings being age, body mass, and testosterone concentrations. However, the higher testosterone in soldiers was correlated with large body size instead of strictly behavioral phenotype. Workers and dispersers have more overlap with each other and no hormonal differences. Thus the behavioral variation in subordinate naked mole-rats is likely not driven by circulating steroid hormone concentrations, but rather it may stem from alternative neural and/or neuroendocrine mechanisms.
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Affiliation(s)
- Ilapreet Toor
- Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada
| | | | - Phoebe D Edwards
- Psychology, University of Toronto Mississauga, Mississauga, ON, Canada
| | - Rudy Boonstra
- Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada
| | - Melissa M Holmes
- Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada; Cell and Systems Biology, University of Toronto, Toronto, ON, Canada; Psychology, University of Toronto Mississauga, Mississauga, ON, Canada
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6
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Ragland NH, Compo NR, Wiltshire N, Shepard A, Troutman S, Kissil JL, Engelman RW. Housing and Husbandry Alternatives for Naked Mole Rat Colonies Used in Research Settings. JOURNAL OF THE AMERICAN ASSOCIATION FOR LABORATORY ANIMAL SCIENCE : JAALAS 2022; 61:412-418. [PMID: 35944976 PMCID: PMC9536831 DOI: 10.30802/aalas-jaalas-22-000035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Naked mole rats (Heterocephalus glaber) are a unique rodent species originating in Africa and are increasingly being used in research. Their needs and characteristics differ from those of other rodents used in research. Unique housing systems are necessary to address the special macro- and microenvironmental requirements of NMRs. Naked mole rats are one of the 2 known eusocial mammalian species, are extremely long-living, are active burrowers, and are accustomed to a subterranean environment. Unlike typical rats and mice, naked mole rats need specific, unique housing systems that mimic their natural subterranean environment to support health and longevity. Here we provide an overview of naked mole rats and a housing method that can be used in research settings.
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Affiliation(s)
- Natalie H Ragland
- Department of Biomedical Sciences, Ross University School of Veterinary Medicine, Basseterre, Saint Kitts and Nevis,Corresponding author.
| | - Nicole R Compo
- Department of Comparative Medicine, University of South Florida, Tampa, Florida,,H. Lee Moffitt Cancer Center & Research Institute, Tampa, Florida
| | - Norman Wiltshire
- Department of Comparative Medicine, University of South Florida, Tampa, Florida,,H. Lee Moffitt Cancer Center & Research Institute, Tampa, Florida
| | - Alyssa Shepard
- H. Lee Moffitt Cancer Center & Research Institute, Tampa, Florida
| | - Scott Troutman
- H. Lee Moffitt Cancer Center & Research Institute, Tampa, Florida
| | - Joseph L Kissil
- H. Lee Moffitt Cancer Center & Research Institute, Tampa, Florida
| | - Robert W Engelman
- Department of Comparative Medicine, University of South Florida, Tampa, Florida,,H. Lee Moffitt Cancer Center & Research Institute, Tampa, Florida
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7
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Fitzpatrick CR, Toor I, Holmes MM. Colony but not social phenotype or status structures the gut bacteria of a eusocial mammal. Behav Ecol Sociobiol 2022. [DOI: 10.1007/s00265-022-03230-5] [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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8
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Parthasarathy B, Müller M, Bilde T, Schneider JM. Hunger state and not personality determines task participation in a spider society. Anim Behav 2022. [DOI: 10.1016/j.anbehav.2022.06.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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9
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Gilbert JD, Rossiter SJ, Bennett NC, Faulkes CG. The elusive role of prolactin in the sociality of the naked mole-rat. Horm Behav 2022; 143:105196. [PMID: 35597054 DOI: 10.1016/j.yhbeh.2022.105196] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/10/2021] [Revised: 04/13/2022] [Accepted: 05/05/2022] [Indexed: 12/01/2022]
Abstract
Despite decades of research into the evolutionary drivers of sociality, we know relatively little about the underlying proximate mechanisms. Here we investigate the potential role of prolactin in the highly social naked mole-rat. Naked mole-rats live in large social groups but, only a small number of individuals reproduce. The remaining non-breeders are reproductively suppressed and contribute to burrow maintenance, foraging, and allo-parental care. Prolactin has well-documented links with reproductive timing and parental behaviour, and the discovery that non-breeding naked mole-rats have unusually high prolactin levels has led to the suggestion that prolactin may help maintain naked mole-rat sociality. To test this idea, we investigated whether urinary prolactin was correlated with cooperative behaviour and aggression. We then administered the prolactin-suppressing drug Cabergoline to eight female non-breeders for eight weeks and assessed the physiology and behaviour of the animals relative to controls. Contrary to the mammalian norm, and supporting previous findings for plasma, we found non-breeders had elevated urinary prolactin concentrations that were similar to breeding females. Further, prolactin levels were higher in heavier, socially dominant non-breeders. Urinary prolactin concentrations did not explain variation in working behaviour or patterns of aggression. Furthermore, females receiving Cabergoline did not show any behavioural or hormonal (progesterone) differences, and urinary prolactin did not appear to be suppressed in individuals receiving Cabergoline. While the results add to the relatively limited literature experimentally manipulating prolactin to investigate its role in reproduction and behaviour, they fail to explain why prolactin levels are high in non-breeding naked mole-rats, or how female non-breeding phenotypes are maintained.
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Affiliation(s)
- James D Gilbert
- School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, United Kingdom of Great Britain and Northern Ireland.
| | - Stephen J Rossiter
- School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, United Kingdom of Great Britain and Northern Ireland
| | - Nigel C Bennett
- Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa
| | - Christopher G Faulkes
- School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, United Kingdom of Great Britain and Northern Ireland.
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10
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Zöttl M, Bensch HM, Finn KT, Hart DW, Thorley J, Bennett NC, Braude S. Capture Order Across Social Bathyergids Indicates Similarities in Division of Labour and Spatial Organisation. Front Ecol Evol 2022. [DOI: 10.3389/fevo.2022.877221] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The social mole-rats of the family Bathyergidae show elaborate social organisation that may include division of labour between breeders and non-breeders as well as across non-breeders within their groups. However, comparative behavioural data across the taxa are rare and contrasts and similarities between species are poorly understood. Field studies of social bathyergids usually involve capturing all group members until the entire group is captured. Because each animal is only captured once and traps are typically placed in close proximity to active foraging areas, the order in which animals are captured provides an indication of the foraging activity of different individuals and of the spatial organisation of the group within the burrow system. Here, we compare the association of capture order with breeding status, sex, and body mass in four species and subspecies of social bathyergids, which vary in group size and represent all three social genera within the family Bathyergidae. We show that in naked and Damaraland mole-rats (Heterocephalus glaber and Fukomys damarensis), male and female breeders are captured later than non-breeders, whereas in two different subspecies of the genus Cryptomys only female breeders are captured later than non-breeders. The effect sizes vary largely and are 10 times larger in naked mole-rats as compared to Fukomys and 3–4 times larger than in Cryptomys. Among non-breeders, sex effects are notably absent in all species and body mass predicted capture order in both naked and Damaraland mole-rats. In naked mole-rats, larger non-breeders were captured earlier than smaller ones, whereas in Damaraland mole-rats intermediate-sized non-breeders were captured first. Our data suggest that there are similarities in behavioural structure and spatial organisation across all social bathyergid species, though the most pronounced differences within groups are found in naked mole-rats.
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11
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Fukuhara A, Gunji M, Masuda Y. Comparative anatomy of quadruped robots and animals: a review. Adv Robot 2022. [DOI: 10.1080/01691864.2022.2086018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022]
Affiliation(s)
- Akira Fukuhara
- Research Institute of Electrical Communication, Tohoku University, Sendai, Japan
| | - Megu Gunji
- Department of Life Sciences, Faculty of Life Sciences, Toyo University, Gunma, Japan
| | - Yoichi Masuda
- Department of Mechanical Engineering, Osaka University, Osaka, Japan
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12
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Toor I, Maynard R, Peng X, Beery AK, Holmes MM. Naked Mole-Rat Social Phenotypes Vary in Investigative and Aggressive Behavior in a Laboratory Partner Preference Paradigm. Front Ecol Evol 2022. [DOI: 10.3389/fevo.2022.860885] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Here we employed the partner preference test (PPT) to examine how naked mole-rat non-breeding individuals of different behavioral phenotypes make social decisions. Naked mole-rats from six colonies were classified into three behavioral phenotypes (soldiers, dispersers, and workers) using a battery of behavioral tests. They then participated in a 3 h long PPT, where they could freely interact with a tethered familiar or tethered unfamiliar conspecific. By comparing the three behavioral phenotypes, we tested the hypothesis that the PPT can be used to interrogate social decision-making in this species, revealing individual differences in behavior that are consistent with discrete social phenotypes. We also tested whether a shorter, 10 min version of the paradigm is sufficient to capture group differences in behavior. Overall, soldiers had higher aggression scores toward unfamiliar conspecifics than both workers and dispersers at the 10 min and 3 h comparison times. At the 10 min comparison time, workers showed a stronger preference for the familiar animal’s chamber, as well as for investigating the familiar conspecific, compared to both dispersers and soldiers. At the 3 h time point, no phenotype differences were seen with chamber or investigation preference scores. Overall, all phenotypes spent more time in chambers with another animal vs. being alone. Use of the PPT in a comparative context has demonstrated that the test identifies species and group differences in affiliative and aggressive behavior toward familiar and unfamiliar animals, revealing individual differences in social decision-making and, importantly, capturing aspects of species-specific social organization seen in nature.
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13
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Siegmann S, Feitsch R, Hart DW, Bennett NC, Penn DJ, Zöttl M. Naked mole‐rats (
Heterocephalus glaber
) do not specialise in cooperative tasks. Ethology 2021. [DOI: 10.1111/eth.13160] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Affiliation(s)
- Susanne Siegmann
- Konrad Lorenz Institute of Ethology University of Veterinary Medicine Vienna Austria
| | - Romana Feitsch
- Konrad Lorenz Institute of Ethology University of Veterinary Medicine Vienna Austria
| | - Daniel W. Hart
- Department of Zoology and Entomology Mammal Research Institute University of Pretoria Pretoria South Africa
| | - Nigel C. Bennett
- Department of Zoology and Entomology Mammal Research Institute University of Pretoria Pretoria South Africa
| | - Dustin J. Penn
- Konrad Lorenz Institute of Ethology University of Veterinary Medicine Vienna Austria
| | - Markus Zöttl
- Ecology and Evolution in Microbial Model Systems EEMiS Department of Biology and Environmental Science Linnaeus University Kalmar Sweden
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14
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Loftus JC, Perez AA, Sih A. Task syndromes: linking personality and task allocation in social animal groups. Behav Ecol 2021; 32:1-17. [PMID: 33708004 PMCID: PMC7937036 DOI: 10.1093/beheco/araa083] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2018] [Revised: 08/04/2020] [Accepted: 08/07/2020] [Indexed: 11/12/2022] Open
Abstract
Studies of eusocial insects have extensively investigated two components of task allocation: how individuals distribute themselves among different tasks in a colony and how the distribution of labor changes to meet fluctuating task demand. While discrete age- and morphologically-based task allocation systems explain much of the social order in these colonies, the basis for task allocation in non-eusocial organisms and within eusocial castes remains unknown. Building from recent advances in the study of among-individual variation in behavior (i.e., animal personalities), we explore a potential mechanism by which individuality in behaviors unrelated to tasks can guide the developmental trajectories that lead to task specialization. We refer to the task-based behavioral syndrome that results from the correlation between the antecedent behavioral tendencies and task participation as a task syndrome. In this review, we present a framework that integrates concepts from a long history of task allocation research in eusocial organisms with recent findings from animal personality research to elucidate how task syndromes and resulting task allocation might manifest in animal groups. By drawing upon an extensive and diverse literature to evaluate the hypothesized framework, this review identifies future areas for study at the intersection of social behavior and animal personality.
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Affiliation(s)
- J C Loftus
- Department of Anthropology, University of California at Davis, Davis, CA, USA.,Department for the Ecology of Animal Societies, Max Planck Institute of Animal Behavior, Radolfzell, Germany.,Department of Biology, University of Konstanz, Konstanz, Germany.,Centre for the Advanced Study of Collective Behaviour, University of Konstanz, Konstanz, Germany
| | - A A Perez
- Department of Entomology, University of California at Davis, Davis, CA, USA
| | - A Sih
- Department of Environmental Science and Policy, University of California at Davis, Davis, CA, USA
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15
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Social Behavior in Naked Mole-Rats: Individual Differences in Phenotype and Proximate Mechanisms of Mammalian Eusociality. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2021; 1319:35-58. [PMID: 34424512 DOI: 10.1007/978-3-030-65943-1_2] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Naked mole-rats (Heterocephalus glaber) are small rodents native to east Africa, living in subterranean colonies of up to 300 individuals. Within each colony, reproduction is restricted to a single breeding female and 1-3 breeding males; all other colony members are reproductively suppressed and socially subordinate unless removed from the suppressive cues of the colony. Due to their striking reproductive skew, naked mole-rats are often considered eusocial mammals. Consistent with this idea, there are behavioral specializations and at least some evidence for morphological distinctions within and between the breeding and non-breeding members of the colony. Importantly, naked mole-rats show plasticity in their behavioral phenotype whereby changes in the social environment influence expression of both type and amount of social behavior. Thus, naked mole-rats provide the opportunity to examine the proximate mechanisms controlling individual differences in social behavior, shedding light on how mammals live in complex social groups.
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16
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Social Evolution in African Mole-Rats - A Comparative Overview. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2021; 1319:1-33. [PMID: 34424511 DOI: 10.1007/978-3-030-65943-1_1] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The African mole-rat superfamily are a unique group of subterranean rodents that are remarkable for their adaptations to a subterranean lifestyle and their range in sociality, spanning strictly solitary species to the naked mole-rat, the most social of all rodents. Widely distributed through sub-Saharan Africa their occurrence is associated with the presence of food resources in the form of underground roots, bulbs and tubers, which form their staple diet. African mole-rats have an ancient Oligocene/Eocene origin, with the naked mole-rat, the extant species with the earliest divergence from the common ancestor of the clade. As a consequence of its early evolution the naked mole-rat appears to have acquired many extraordinary biological features, even when compared with other mole-rats. Molecular phylogenies indicate that complex sociality and cooperative breeding has been convergently gained and/or lost more than once among African mole-rats, making them a fascinating group for comparative studies of social evolution. Ultimately, ecological constraints on digging and finding food have played a role in increasing cooperative behavior and social complexity, from what was most likely a monogamous ancestor living in family groups. Phylogenetically controlled comparisons suggest that proximate control of their lifestyle shows both conservation and divergence in the underlying mechanisms.
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Braude S, Holtze S, Begall S, Brenmoehl J, Burda H, Dammann P, Marmol D, Gorshkova E, Henning Y, Hoeflich A, Höhn A, Jung T, Hamo D, Sahm A, Shebzukhov Y, Šumbera R, Miwa S, Vyssokikh MY, Zglinicki T, Averina O, Hildebrandt TB. Surprisingly long survival of premature conclusions about naked mole‐rat biology. Biol Rev Camb Philos Soc 2020; 96:376-393. [DOI: 10.1111/brv.12660] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2020] [Revised: 10/06/2020] [Accepted: 10/13/2020] [Indexed: 12/11/2022]
Affiliation(s)
- Stan Braude
- Biology Department Washington University, One Brookings Drive St. Louis MO 63130 U.S.A
| | - Susanne Holtze
- Department of Reproduction Management Leibniz‐Institute for Zoo and Wildlife Research Berlin 10315 Germany
| | - Sabine Begall
- Department of General Zoology, Faculty of Biology University of Duisburg‐Essen, Universitätsstr Essen 45147 Germany
| | - Julia Brenmoehl
- Institute for Genome Biology Leibniz‐Institute for Farm Animal Biology Dummerstorf 18196 Germany
| | - Hynek Burda
- Department of Game Management and Wildlife Biology, Faculty of Forestry and Wood Sciences Czech University of Life Sciences Praha 16500 Czech Republic
| | - Philip Dammann
- Department of General Zoology, Faculty of Biology University of Duisburg‐Essen, Universitätsstr Essen 45147 Germany
- University Hospital Essen Hufelandstr Essen 45141 Germany
| | - Delphine Marmol
- Molecular Physiology Research Unit (URPhyM), NARILIS University of Namur Namur 5000 Belgium
| | - Ekaterina Gorshkova
- Engelhardt Institute of Molecular Biology Russian Academy of Sciences, Vavilova str. 32 Moscow 119991 Russia
- Faculty of Biology Lomonosov Moscow State University Moscow 119991 Russia
| | - Yoshiyuki Henning
- University Hospital Essen Hufelandstr Essen 45141 Germany
- Institute of Physiology Department of General Zoology University of Duisburg Essen Germany
| | - Andreas Hoeflich
- Division Signal Transduction Institute for Genome Biology, Leibniz‐Institute for Farm Animal Biology, FBN Dummerstorf, Wilhelm‐Stahl‐Allee 2 Dummerstorf 18196 Germany
| | - Annika Höhn
- Department of Molecular Toxicology German Institute of Human Nutrition (DIfE) Potsdam‐Rehbrücke Nuthetal 14558 Germany
- German Center for Diabetes Research (DZD) München‐Neuherberg 85764 Germany
| | - Tobias Jung
- Department of Molecular Toxicology German Institute of Human Nutrition (DIfE) Potsdam‐Rehbrücke Nuthetal 14558 Germany
| | - Dania Hamo
- Charité ‐ Universitätsmedizin Berlin Berlin Institute of Health Center for Regenerative Therapies (BCRT) Berlin 13353 Germany
- German Rheumatism Research Centre Berlin (DRFZ) Berlin 10117 Germany
| | - Arne Sahm
- Computational Biology Group Leibniz Institute on Aging – Fritz Lipmann Institute Jena 07745 Germany
| | - Yury Shebzukhov
- Engelhardt Institute of Molecular Biology Russian Academy of Sciences, Vavilova str. 32 Moscow 119991 Russia
- Charité ‐ Universitätsmedizin Berlin Berlin Institute of Health Center for Regenerative Therapies (BCRT) Berlin 13353 Germany
| | - Radim Šumbera
- Faculty of Science University of South Bohemia České Budějovice 37005 Czech Republic
| | - Satomi Miwa
- Biosciences Institute, Edwardson building, Campus for Ageing and Vitality Newcastle University Newcastle upon Tyne NE4 5PL U.K
| | - Mikhail Y. Vyssokikh
- Belozersky Institute of Physico‐Chemical Biology Lomonosov Moscow State University Moscow 119991 Russia
| | - Thomas Zglinicki
- Biosciences Institute, Edwardson building, Campus for Ageing and Vitality Newcastle University Newcastle upon Tyne NE4 5PL U.K
| | - Olga Averina
- Belozersky Institute of Physico‐Chemical Biology Lomonosov Moscow State University Moscow 119991 Russia
| | - Thomas B. Hildebrandt
- Department of Reproduction Management Leibniz‐Institute for Zoo and Wildlife Research Berlin 10315 Germany
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Francioli Y, Thorley J, Finn K, Clutton-Brock T, Zöttl M. Breeders are less active foragers than non-breeders in wild Damaraland mole-rats. Biol Lett 2020; 16:20200475. [PMID: 33023382 DOI: 10.1098/rsbl.2020.0475] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Eusocial societies are characterized by a clear division of labour between non-breeding workers and breeding queens, and queens often do not contribute to foraging, defence and other maintenance tasks. It has been suggested that the structure and organization of social mole-rat groups resembles that of eusocial insect societies. However, the division of labour has rarely been investigated in wild mole-rats, and it is unknown whether breeders show decreased foraging activity compared with non-breeding helpers in natural groups. Here, we show that, in wild Damaraland mole-rats (Fukomys damarensis), breeders show lower activity in foraging areas than non-breeding group members. Both breeders and non-breeders displayed variation in activity across the different seasons. Our results suggest that group living allows social mole-rat breeders to reduce their investment in energetically costly behaviour, or alternatively, that the high cost of reproduction in this species forces a behavioural trade-off against foraging investment.
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Affiliation(s)
- Yannick Francioli
- Ecology and Evolution in Microbial Model Systems, EEMiS, Department of Biology and Environmental Science, Linnaeus University, Kalmar, Sweden
| | - Jack Thorley
- Department of Zoology, University of Cambridge, Cambridge, UK
| | - Kyle Finn
- Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, South Africa
| | - Tim Clutton-Brock
- Department of Zoology, University of Cambridge, Cambridge, UK.,Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, South Africa
| | - Markus Zöttl
- Ecology and Evolution in Microbial Model Systems, EEMiS, Department of Biology and Environmental Science, Linnaeus University, Kalmar, Sweden
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Gilbert JD, Rossiter SJ, Faulkes CG. The relationship between individual phenotype and the division of labour in naked mole-rats: it's complicated. PeerJ 2020; 8:e9891. [PMID: 33062418 PMCID: PMC7531346 DOI: 10.7717/peerj.9891] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2020] [Accepted: 08/17/2020] [Indexed: 11/20/2022] Open
Abstract
Background The naked mole-rat (Heterocephalus glaber) is among the most social mammals on the planet, living in eusocial groups of up to 300 individuals that contain a single reproductive female and up to three reproductive males. A critical aspect of their complex social system is the division of labour that allows non-breeders to form an effective workforce. Age- or weight-based polyethisms are widely cited as explanations for how labour is divided, but evidence in support of these hypotheses has been equivocal. Methods To assess the extent to which individual working behaviour is determined by sex, age, weight and social rank, we studied the behaviours of 103 animals from eight captive colonies. We performed focal sampling and ran mixed-effects models to assess which factors explained variation in working behaviour during six ten-minute observation periods per individual. Results Contrary to widely-held beliefs, we found that working behaviour did not decrease linearly with weight, although polynomial regressions indicated younger and medium-sized individuals worked most frequently, while high-ranking individuals worked for the shortest periods of time. Working behaviour and its relationship with individual characteristics also varied between colonies. Conclusions While age- or size-based polyethisms may have some influence on working behaviour, we argue that other characteristics of the individual and colony are also important. In particular, the interactions of individual, social and environmental factors must be considered in order to understand the emergence and effectiveness of the division of labour that is so critical to many social organisms.
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Affiliation(s)
- James D Gilbert
- School of Biological and Chemical Sciences, Queen Mary University of London, London, United Kingdom
| | - Stephen J Rossiter
- School of Biological and Chemical Sciences, Queen Mary University of London, London, United Kingdom
| | - Chris G Faulkes
- School of Biological and Chemical Sciences, Queen Mary University of London, London, United Kingdom
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20
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Poulson SJ, Aldarraji A, Arain II, Dziekonski N, Motlana K, Riley R, Holmes MM, Martin LJ. Naked mole-rats lack cold sensitivity before and after nerve injury. Mol Pain 2020; 16:1744806920955103. [PMID: 32880221 PMCID: PMC7475789 DOI: 10.1177/1744806920955103] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Neuropathic pain is a chronic disease state resulting from injury to the nervous system. This type of pain often responds poorly to standard treatments and occasionally may get worse instead of better over time. Patients who experience neuropathic pain report sensitivity to cold and mechanical stimuli. Since the nociceptive system of African naked mole-rats contains unique adaptations that result in insensitivity to some pain types, we investigated whether naked mole-rats may be resilient to sensitivity following nerve injury. Using the spared nerve injury model of neuropathic pain, we showed that sensitivity to mechanical stimuli developed similarly in mice and naked mole-rats. However, naked mole-rats lacked sensitivity to mild cold stimulation after nerve injury, while mice developed robust cold sensitivity. We pursued this response deficit by testing behavior to activators of transient receptor potential (TRP) receptors involved in detecting cold in naïve animals. Following mustard oil, a TRPA1 activator, naked mole-rats responded similarly to mice. Conversely, icilin, a TRPM8 agonist, did not evoke pain behavior in naked mole-rats when compared with mice. Finally, we used RNAscope to probe for TRPA1 and TRPM8 messenger RNA expression in dorsal root ganglia of both species. We found increased TRPA1 messenger RNA, but decreased TRPM8 punctae in naked mole-rats when compared with mice. Our findings likely reflect species differences due to evolutionary environmental responses that are not easily explained by differences in receptor expression between the species.
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Affiliation(s)
- Sandra J Poulson
- Department of Psychology, University of Toronto Mississauga, Mississauga, ON, Canada
| | - Ahmed Aldarraji
- Department of Psychology, University of Toronto Mississauga, Mississauga, ON, Canada
| | - Iqra I Arain
- Department of Psychology, University of Toronto Mississauga, Mississauga, ON, Canada
| | - Natalia Dziekonski
- Department of Psychology, University of Toronto Mississauga, Mississauga, ON, Canada
| | - Keza Motlana
- Department of Psychology, University of Toronto Mississauga, Mississauga, ON, Canada
| | - Rachel Riley
- Department of Psychology, University of Toronto Mississauga, Mississauga, ON, Canada
| | - Melissa M Holmes
- Department of Psychology, University of Toronto Mississauga, Mississauga, ON, Canada.,Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada.,Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, ON, Canada
| | - Loren J Martin
- Department of Psychology, University of Toronto Mississauga, Mississauga, ON, Canada.,Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada
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21
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Nest defence and offspring provisioning in a cooperative bird: individual subordinates vary in total contribution, but no division of tasks among breeders and subordinates. Behav Ecol Sociobiol 2020. [DOI: 10.1007/s00265-020-02877-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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22
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Edwards PD, Mooney SJ, Bosson CO, Toor I, Palme R, Holmes MM, Boonstra R. The stress of being alone: Removal from the colony, but not social subordination, increases fecal cortisol metabolite levels in eusocial naked mole-rats. Horm Behav 2020; 121:104720. [PMID: 32081743 DOI: 10.1016/j.yhbeh.2020.104720] [Citation(s) in RCA: 31] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/10/2019] [Revised: 02/06/2020] [Accepted: 02/14/2020] [Indexed: 12/15/2022]
Abstract
In many social species, hierarchical status within the group is associated with differences in basal adrenocortical activity. We examined this relationship in naked mole-rats (Heterocephalus glaber), eusocial rodents with arguably the most extreme social hierarchies of all mammals. This species lives in colonies where breeding is restricted to one socially dominant 'queen' and her male consorts, and all other individuals are reproductively suppressed 'subordinates'. The relationship between cortisol and social status in naked mole-rats has not fully been elucidated, as prior results on this topic have been contradictory. We used non-invasive feces sampling to measure baseline cortisol levels in eight laboratory colonies of naked mole-rats, to either replicate or reject rank differences. First, we successfully validated an assay to measure fecal cortisol metabolites (FCMs). Removal from the colony for the validation experiment, either alone or with an opposite sex conspecific, induced prolonged elevation of FCM levels on a scale of days to weeks. This increase in cortisol did not prevent the removed animals from sexually maturing. In colony-housed animals, we found no relationship between rank in the social hierarchy and FCM levels. Further, queens, breeding males, and reproductively suppressed subordinates all had equivalent FCM levels. We conclude that this species shows little evidence of the 'stress of dominance' or 'stress of subordination' and that reproductive suppression in naked mole-rats is not driven by elevated cortisol levels.
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Affiliation(s)
- Phoebe D Edwards
- Dept. of Psychology, University of Toronto Mississauga, Mississauga, ON L5L 1C6, Canada; Dept. of Ecology & Evolutionary Biology, University of Toronto, Toronto, ON M5S 3B2, Canada; Centre for the Neurobiology of Stress, Dept. of Biological Sciences, University of Toronto Scarborough, Toronto, ON M1C 1A4, Canada.
| | - Skyler J Mooney
- Dept. of Psychology, University of Toronto Mississauga, Mississauga, ON L5L 1C6, Canada
| | - Curtis O Bosson
- Centre for the Neurobiology of Stress, Dept. of Biological Sciences, University of Toronto Scarborough, Toronto, ON M1C 1A4, Canada
| | - Ilapreet Toor
- Dept. of Ecology & Evolutionary Biology, University of Toronto, Toronto, ON M5S 3B2, Canada
| | - Rupert Palme
- Dept. of Biomedical Sciences, University of Veterinary Medicine, 1210 Vienna, Austria
| | - Melissa M Holmes
- Dept. of Psychology, University of Toronto Mississauga, Mississauga, ON L5L 1C6, Canada; Dept. of Ecology & Evolutionary Biology, University of Toronto, Toronto, ON M5S 3B2, Canada; Dept. of Cell & Systems Biology, University of Toronto, Toronto, ON M5S 3G5, Canada
| | - Rudy Boonstra
- Dept. of Ecology & Evolutionary Biology, University of Toronto, Toronto, ON M5S 3B2, Canada; Centre for the Neurobiology of Stress, Dept. of Biological Sciences, University of Toronto Scarborough, Toronto, ON M1C 1A4, Canada
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23
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Stress in groups: Lessons from non-traditional rodent species and housing models. Neurosci Biobehav Rev 2020; 113:354-372. [PMID: 32278793 DOI: 10.1016/j.neubiorev.2020.03.033] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2019] [Revised: 03/06/2020] [Accepted: 03/31/2020] [Indexed: 02/06/2023]
Abstract
A major feature of life in groups is that individuals experience social stressors of varying intensity and type. Social stress can have profound effects on health, social behavior, and ongoing relationships. Relationships can also buffer the experience of exogenous stressors. Social stress has most commonly been investigated in dyadic contexts in mice and rats that produce intense stress. Here we review findings from studies of diverse rodents and non-traditional group housing paradigms, focusing on laboratory studies of mice and rats housed in visible burrow systems, prairie and meadow voles, and mole-rats. We argue that the use of methods informed by the natural ecology of rodent species provides novel insights into the relationship between social stress, behavior and physiology. In particular, we describe how this ethologically inspired approach reveals how individuals vary in their experience of and response to social stress, and how ecological and social contexts impact the effects of stress. Social stress induces adaptive changes, as well as long-term disruptive effects on behavior and physiology.
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24
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Abstract
Evolutionary transitions in individuality (hereafter, ETIs), such as the transition to multi-cellularity and the transition to social colonies, have been at the centre of evolutionary research, but only few attempts were made to systematically operationalize this concept. Here, we devise a set of four indicators intended to assess the change in complexity during ETIs: system size, inseparability, reproductive specialization and non-reproductive specialization. We then conduct a quantitative comparison across multiple taxa and ETIs. Our analysis reveals that inseparability has a crucial role in the process; it seems irreversible and may mark the point where a group of individuals becomes a new individual at a higher hierarchical level. Interestingly, we find that disparate groups demonstrate a similar pattern of progression along ETIs.
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Affiliation(s)
- Yohay Carmel
- Faculty of Civil and Environmental Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel
| | - Ayelet Shavit
- Department of Environmental Sciences, Tel Hai College, Tel-Hai 12208, Israel
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25
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Van Daele PA, Desmet N, Šumbera R, Adriaens D. Work behaviour and biting performance in the cooperative breeding Micklem’s mole-rat Fukomys micklemi (Bathyergidae, Rodentia). Mamm Biol 2019. [DOI: 10.1016/j.mambio.2019.02.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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26
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Faykoo-Martinez M, Mooney SJ, Holmes MM. Oxytocin Manipulation Alters Neural Activity in Response to Social Stimuli in Eusocial Naked Mole-Rats. Front Behav Neurosci 2018; 12:272. [PMID: 30515085 DOI: 10.3389/fnbeh.2018.00272] [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: 07/12/2018] [Accepted: 10/23/2018] [Indexed: 12/28/2022] Open
Abstract
The social decision-making network (SDMN) is a conserved neural circuit that modulates a range of social behaviors via context-specific patterns of activation that may be controlled in part by oxytocinergic signaling. We have previously characterized oxytocin's (OT) influence on prosociality in the naked mole-rat, a eusocial mammalian species, and its altered neural distribution between animals of differing social status. Here, we asked two questions: (1) do patterns of activation in the SDMN vary by social context and (2) is functional connectivity of the SDMN altered by OT manipulation? Adult subordinate naked mole-rats were exposed to one of three types of stimuli (three behavioral paradigms: familiar adult conspecific, unfamiliar adult conspecific, or familiar pups) while manipulating OT (three manipulations: saline, OT, or OT antagonist). Immediate early gene c-Fos activity was quantified using immunohistochemistry across SDMN regions. Network analyses indicated that the SDMN is conserved in naked mole-rats and functions in a context-dependent manner. Specific brain regions were recruited with each behavioral paradigm suggesting a role for the nucleus accumbens in social valence and sociosexual interaction, the prefrontal cortex in assessing/establishing social dominance, and the hippocampus in pup recognition. Furthermore, while OT manipulation was generally disruptive to coordinated neural activity, the specific effects were context-dependent supporting the hypothesis that oxytocinergic signaling promotes context appropriate social behaviors by modulating co-ordinated activity of the SDMN.
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Affiliation(s)
| | - Skyler J Mooney
- Department of Psychology, University of Toronto, Toronto, ON, Canada
| | - Melissa M Holmes
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada.,Department of Psychology, University of Toronto, Toronto, ON, Canada.,Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada
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Abstract
The specialization of individuals in specific behavioural tasks is often attributed either to irreversible differences in development, which generate functionally divergent cooperative phenotypes, or to age-related changes in the relative frequency with which individuals perform different cooperative activities; both of which are common in many insect caste systems. However, contrasts in cooperative behaviour can take other forms and, to date, few studies of cooperative behaviour in vertebrates have explored the effects of age, adult phenotype and early development on individual differences in cooperative behaviour in sufficient detail to discriminate between these alternatives. Here, we used multinomial models to quantify the extent of behavioural specialization within nonreproductive Damaraland mole-rats, Fukomys damarensis, at different ages. We showed that, although there were large differences between individuals in their contribution to cooperative activities, there was no evidence of individual specialization in cooperative activities that resembled the differences found in insect societies with distinct castes where individual contributions to different activities are negatively related to each other. Instead, individual differences in helping behaviour appeared to be the result of age-related changes in the extent to which individuals committed to all forms of helping. A similar pattern is observed in cooperatively breeding meerkats, Suricata suricatta, and there is no unequivocal evidence of caste differentiation in any cooperative vertebrate. The multinomial models we employed offer a powerful heuristic tool to explore task specialization and developmental divergence across social taxa and provide an analytical approach that may be useful in exploring the distribution of different forms of helping behaviour in other cooperative species. Cooperative behaviours do not trade off against one another. Individuals differ in overall commitment to cooperation. Sex differences in behaviour are minimal. Cooperative contributions vary with age and relative size.
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Sociality does not drive the evolution of large brains in eusocial African mole-rats. Sci Rep 2018; 8:9203. [PMID: 29907782 PMCID: PMC6003933 DOI: 10.1038/s41598-018-26062-8] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2017] [Accepted: 05/02/2018] [Indexed: 11/15/2022] Open
Abstract
The social brain hypothesis (SBH) posits that the demands imposed on individuals by living in cohesive social groups exert a selection pressure favouring the evolution of large brains and complex cognitive abilities. Using volumetry and the isotropic fractionator to determine the size of and numbers of neurons in specific brain regions, here we test this hypothesis in African mole-rats (Bathyergidae). These subterranean rodents exhibit a broad spectrum of social complexity, ranging from strictly solitary through to eusocial cooperative breeders, but feature similar ecologies and life history traits. We found no positive association between sociality and neuroanatomical correlates of information-processing capacity. Solitary species are larger, tend to have greater absolute brain size and have more neurons in the forebrain than social species. The neocortex ratio and neuronal counts correlate negatively with social group size. These results are clearly inconsistent with the SBH and show that the challenges coupled with sociality in this group of rodents do not require brain enlargement or fundamental reorganization. These findings suggest that group living or pair bonding per se does not select strongly for brain enlargement unless coupled with Machiavellian interactions affecting individual fitness.
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29
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Junghanns A, Holm C, Schou MF, Sørensen AB, Uhl G, Bilde T. Extreme allomaternal care and unequal task participation by unmated females in a cooperatively breeding spider. Anim Behav 2017. [DOI: 10.1016/j.anbehav.2017.08.006] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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30
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RFamide-related peptide-3 (RFRP-3) suppresses sexual maturation in a eusocial mammal. Proc Natl Acad Sci U S A 2017; 114:1207-1212. [PMID: 28096421 DOI: 10.1073/pnas.1616913114] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Neuroendocrine mechanisms underlying social inhibition of puberty are not well understood. Here, we use a model exhibiting the most profound case of pubertal suppression among mammals to explore a role for RFamide-related peptide-3 [RFRP-3; mammalian ortholog to gonadotropin-inhibitory hormone (GnIH)] in neuroendocrine control of reproductive development. Naked mole rats (NMRs) live in sizable colonies where breeding is monopolized by two to four dominant animals, and no other members exhibit signs of puberty throughout their lives unless they are removed from the colony. Because of its inhibitory action on the reproductive axis in other vertebrates, we investigated the role of RFRP-3 in social reproductive suppression in NMRs. We report that RFRP-3 immunofluorescence expression patterns and RFRP-3/GnRH cross-talk are largely conserved in the NMR brain, with the exception of the unique presence of RFRP-3 cell bodies in the arcuate nucleus (Arc). Immunofluorescence comparisons revealed that central expression of RFRP-3 is altered by reproductive status, with RFRP-3 immunoreactivity enhanced in the paraventricular nucleus, dorsomedial nucleus, and Arc of reproductively quiescent NMRs. We further observed that exogenous RFRP-3 suppresses gonadal steroidogenesis and mating behavior in NMRs given the opportunity to undergo puberty. Together, our findings establish a role for RFRP-3 in preserving reproductive immaturity, and challenge the view that stimulatory peptides are the ultimate gatekeepers of puberty.
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31
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Šklíba J, Lövy M, Burda H, Šumbera R. Variability of space-use patterns in a free living eusocial rodent, Ansell's mole-rat indicates age-based rather than caste polyethism. Sci Rep 2016; 6:37497. [PMID: 27922127 PMCID: PMC5138616 DOI: 10.1038/srep37497] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2016] [Accepted: 10/10/2016] [Indexed: 11/15/2022] Open
Abstract
Eusocial species of African mole-rats live in groups cooperating on multiple tasks and employing division of labour. In captivity, individuals of the same group differ in cooperative contribution as well as in preference for a particular task. Both can be viewed as polyethism. However, little information is available from free-ranging mole-rats, which live in large burrow systems. We made an attempt to detect polyethism in the free-living Ansell's mole-rat (Fukomys anselli) as differences in individuals' space-use patterns. We radio-tracked 17 adults from five groups. Large individuals, including breeding males, spent more time inside the nest than smaller individuals. Breeding females were more often located <10 m from the nest in comparison to non-breeding females, who were relatively more often located 30-90 m and exclusively >90 m from the nest. One non-breeding female even conducted a brief intrusion into a neighbouring group's territory via an open tunnel connection. A significant part of the variability in mole-rat space-use patterns was explained by body mass which is probably related to age in this species. This result can therefore be attributed to age polyethism. There was no apparent discontinuity in the space-use patterns of non-breeders that would indicate existence of castes.
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Affiliation(s)
- Jan Šklíba
- Department of Zoology, Faculty of Science, University of South Bohemia, Branišovská 1760, 370 05 České Budějovice, Czech Republic
- Institute of Entomology, Biology Centre CAS, Branišovská 1160, 370 05 České Budějovice, Czech Republic
| | - Matěj Lövy
- Department of Zoology, Faculty of Science, University of South Bohemia, Branišovská 1760, 370 05 České Budějovice, Czech Republic
| | - Hynek Burda
- Department of General Zoology, Faculty of Biology, University of Duisburg-Essen, 45117 Essen, Germany
| | - Radim Šumbera
- Department of Zoology, Faculty of Science, University of South Bohemia, Branišovská 1760, 370 05 České Budějovice, Czech Republic
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Differences in cooperative behavior among Damaraland mole rats are consequences of an age-related polyethism. Proc Natl Acad Sci U S A 2016; 113:10382-7. [PMID: 27588902 DOI: 10.1073/pnas.1607885113] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In many cooperative breeders, the contributions of helpers to cooperative activities change with age, resulting in age-related polyethisms. In contrast, some studies of social mole rats (including naked mole rats, Heterocephalus glaber, and Damaraland mole rats, Fukomys damarensis) suggest that individual differences in cooperative behavior are the result of divergent developmental pathways, leading to discrete and permanent functional categories of helpers that resemble the caste systems found in eusocial insects. Here we show that, in Damaraland mole rats, individual contributions to cooperative behavior increase with age and are higher in fast-growing individuals. Individual contributions to different cooperative tasks are intercorrelated and repeatability of cooperative behavior is similar to that found in other cooperatively breeding vertebrates. Our data provide no evidence that nonreproductive individuals show divergent developmental pathways or specialize in particular tasks. Instead of representing a caste system, variation in the behavior of nonreproductive individuals in Damaraland mole rats closely resembles that found in other cooperatively breeding mammals and appears to be a consequence of age-related polyethism.
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Hathaway GA, Faykoo-Martinez M, Peragine DE, Mooney SJ, Holmes MM. Subcaste differences in neural activation suggest a prosocial role for oxytocin in eusocial naked mole-rats. Horm Behav 2016; 79:1-7. [PMID: 26718226 DOI: 10.1016/j.yhbeh.2015.12.001] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/10/2015] [Revised: 11/24/2015] [Accepted: 12/19/2015] [Indexed: 10/22/2022]
Abstract
The neuropeptide oxytocin (OT) influences prosocial behavior(s), aggression, and stress responsiveness, and these diverse effects are regulated in a species- and context-specific manner. The naked mole-rat (Heterocephalus glaber) is a unique species with which to study context-dependent effects of OT, exhibiting a strict social hierarchy with behavioral specialization within the subordinate caste: soldiers are aggressive and defend colonies against unfamiliar conspecifics while workers are prosocial and contribute to in-colony behaviors such as pup care. To determine if OT is involved in subcaste-specific behaviors, we compared behavioral responses between workers and soldiers of both sexes during a modified resident/intruder paradigm, and quantified activation of OT neurons in the hypothalamic paraventricular nucleus (PVN) and supraoptic nucleus (SON) using the immediate-early-gene marker c-fos co-localized with OT neurons. Resident workers and soldiers were age-matched with unfamiliar worker stimulus animals as intruders, and encounters were videorecorded and scored for aggressive behaviors. Colony-matched controls were left in their home colony for the duration of the encounters. Brains were extracted and cell counts were conducted for OT immunoreactive (ir), c-fos-ir, and percentage of OT-c-fos double-labeled cells. Results indicate that resident workers were less aggressive but showed greater OT neural activity than soldiers. Furthermore, a linear model including social treatment, cortisol, and subcaste revealed that subcaste was the only significant predictor of OT-c-fos double-labeled cells in the PVN. These data suggest that in naked mole-rats OT promotes prosocial behaviors rather than aggression and that even within subordinates status exerts robust effects on brain and behavior.
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Affiliation(s)
- Georgia A Hathaway
- Department of Psychology, University of Toronto Mississauga, Mississauga, ON L5L 1C6, Canada
| | - Mariela Faykoo-Martinez
- Department of Psychology, University of Toronto Mississauga, Mississauga, ON L5L 1C6, Canada
| | - Deane E Peragine
- Department of Psychology, University of Toronto Mississauga, Mississauga, ON L5L 1C6, Canada
| | - Skyler J Mooney
- Department of Psychology, University of Toronto Mississauga, Mississauga, ON L5L 1C6, Canada
| | - Melissa M Holmes
- Department of Psychology, University of Toronto Mississauga, Mississauga, ON L5L 1C6, Canada; Departments of Cell & Systems Biology and Ecology & Evolutionary Biology, University of Toronto, Toronto, ON M5S 3G5, Canada.
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