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Gómez‐López G, Sanz‐Aguilar A, Carrete M, Arrondo E, Benítez JR, Ceballos O, Cortés‐Avizanda A, de Pablo F, Donázar JA, Frías Ó, Gangoso L, García‐Alfonso M, González JL, Grande JM, Serrano D, Tella JL, Blanco G. Insularity determines nestling sex ratio variation in Egyptian vulture populations. Ecol Evol 2023; 13:e10371. [PMID: 37529590 PMCID: PMC10385291 DOI: 10.1002/ece3.10371] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2023] [Revised: 07/04/2023] [Accepted: 07/11/2023] [Indexed: 08/03/2023] Open
Abstract
Variation in offspring sex ratio, particularly in birds, has been frequently studied over the last century, although seldom using long-term monitoring data. In raptors, the cost of raising males and females is not equal, and several variables have been found to have significant effects on sex ratio, including food availability, parental age, and hatching order. Sex ratio differences between island populations and their mainland counterparts have been poorly documented, despite broad scientific literature on the island syndrome reporting substantial differences in population demography and ecology. Here, we assessed individual and environmental factors potentially affecting the secondary sex ratio of the long-lived Egyptian vulture Neophron percnopterus. We used data collected from Spanish mainland and island populations over a ca. 30-year period (1995-2021) to assess the effects of insularity, parental age, breeding phenology, brood size, hatching order, type of breeding unit (pairs vs. trios), and spatial and temporal variability on offspring sex ratio. No sex bias was found at the population level, but two opposite trends were observed between mainland and island populations consistent with the island syndrome. Offspring sex ratio was nonsignificantly female-biased in mainland Spain (0.47, n = 1112) but significantly male-biased in the Canary Islands (0.55, n = 499), where a male-biased mortality among immatures could be compensating for offspring biases and maintaining a paired adult sex ratio. Temporal and spatial variation in food availability might also have some influence on sex ratio, although the difficulties in quantifying them preclude us from determining the magnitude of such influence. This study shows that insularity influences the offspring sex ratio of the Egyptian vulture through several processes that can affect island and mainland populations differentially. Our research contributes to improving our understanding of sex allocation theory by investigating whether sex ratio deviations from parity are possible as a response to changing environments comprised by multiple and complexly interrelated factors.
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Affiliation(s)
- Guillermo Gómez‐López
- Department of Evolutionary Ecology, National Museum of Natural SciencesSpanish National Research CouncilMadridSpain
- Department of Biodiversity, Ecology and Evolution, Faculty of BiologyComplutense University of MadridMadridSpain
| | - Ana Sanz‐Aguilar
- Animal Demography and Ecology GroupInstitut Mediterrani d'Estudis Avançats, Spanish National Research CouncilMallorcaSpain
- Applied Zoology and Conservation GroupUniversitat de les Illes BalearsPalmaSpain
| | - Martina Carrete
- Department of Physical, Chemical and Natural SystemsPablo de Olavide UniversitySevillaSpain
| | - Eneko Arrondo
- Department of ZoologyUniversity of GranadaGranadaSpain
- Department of Applied BiologyMiguel Hernández UniversityElcheSpain
| | - José Ramón Benítez
- Department of BiodiversityAgencia de Medioambiente y Agua, Junta de AndalucíaSevillaSpain
| | | | - Ainara Cortés‐Avizanda
- Department of Plant Biology and EcologyUniversity of SevilleSevillaSpain
- Department of Conservation BiologyDoñana Biological Station, Spanish National Research CouncilSevillaSpain
| | - Félix de Pablo
- Department of Environment and Biosphere ReserveConsell Insular de Menorca, PlazaMaóSpain
| | - José Antonio Donázar
- Department of Conservation BiologyDoñana Biological Station, Spanish National Research CouncilSevillaSpain
| | - Óscar Frías
- Department of Physical, Chemical and Natural SystemsPablo de Olavide UniversitySevillaSpain
| | - Laura Gangoso
- Department of Biodiversity, Ecology and Evolution, Faculty of BiologyComplutense University of MadridMadridSpain
| | - Marina García‐Alfonso
- Department of Conservation BiologyDoñana Biological Station, Spanish National Research CouncilSevillaSpain
| | - José Luis González
- Department of Evolutionary Ecology, National Museum of Natural SciencesSpanish National Research CouncilMadridSpain
| | | | - David Serrano
- Department of Conservation BiologyDoñana Biological Station, Spanish National Research CouncilSevillaSpain
| | - José Luis Tella
- Department of Conservation BiologyDoñana Biological Station, Spanish National Research CouncilSevillaSpain
| | - Guillermo Blanco
- Department of Evolutionary Ecology, National Museum of Natural SciencesSpanish National Research CouncilMadridSpain
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2
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Brood sex ratio variation in a colonial raptor, the Eleonora's falcon, Falco eleonorae. Anim Behav 2022. [DOI: 10.1016/j.anbehav.2022.11.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
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3
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Mermoz ME, Villarruel C, de la Colina A, Mahler B. Fledgling sex-ratio is biased towards the helping sex in a Neotropical cooperative breeder, the brown-and-yellow marshbird (Pseudoleistes virescens). BEHAVIOUR 2021. [DOI: 10.1163/1568539x-bja10061] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Abstract
In many cooperatively breeding species, helpers increase the breeding success of their parents. The repayment hypothesis predicts a skewed sex-ratio towards the helping sex at population level; at individual level bias would increase in broods attended by a smaller number of helpers. We studied a brown-and-yellow marshbird (Pseudoleistes virescens) population during 11 breeding seasons. We found that 90% of helpers were males and that they increased nestling survival, although this effect disappeared in presence of parasitic shiny cowbirds. Helpers sometimes helped at nests of adults other than their parents. Population sex-ratio of fledglings was highly skewed towards males (1.4:1). At individual level, male-biased sex-ratio of fledglings was more pronounced early in the season and increased with brood losses but was not affected by number of helpers. Marshbirds feed at communal areas so retaining helpers would not be costly. Therefore, a general skew towards males might be the best adaptive strategy.
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Affiliation(s)
- Myriam E. Mermoz
- Instituto de Ecología, Genética, y Evolución de Buenos Aires (UBA-CONICET), Intendente Güiraldes 2160 — Ciudad Universitaria — C1428EGA, CABA, Argentina
- Departamento de Ecología, Genética, y Evolución, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Intendente Güiraldes 2160 — C1428EGA Ciudad Universitaria, CABA, Argentina
| | - Cecilia Villarruel
- Departamento de Ecología, Genética, y Evolución, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Intendente Güiraldes 2160 — C1428EGA Ciudad Universitaria, CABA, Argentina
- Current address: Instituto de Fisiología, Biología Molecular y Neurociencias (UBA-CONICET), Intendente Güiraldes 2160 — C1428EGA Ciudad Universitaria, CABA, Argentina
| | - Alicia de la Colina
- Instituto de Ecología, Genética, y Evolución de Buenos Aires (UBA-CONICET), Intendente Güiraldes 2160 — Ciudad Universitaria — C1428EGA, CABA, Argentina
- Current address: Departamento de Conservación e Investigación, Fundación Temaikèn — B1625 Escobar, Prov. de Buenos Aires, Argentina
| | - Bettina Mahler
- Instituto de Ecología, Genética, y Evolución de Buenos Aires (UBA-CONICET), Intendente Güiraldes 2160 — Ciudad Universitaria — C1428EGA, CABA, Argentina
- Departamento de Ecología, Genética, y Evolución, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Intendente Güiraldes 2160 — C1428EGA Ciudad Universitaria, CABA, Argentina
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Tschumi M, Humbel J, Erbes J, Fattebert J, Fischer J, Fritz G, Geiger B, van Harxen R, Hoos B, Hurst J, Jacobsen LB, Keil H, Kneule W, Michel VT, Michels H, Möbius L, Perrig M, Rößler P, Schneider D, Schuch S, Stroeken P, Naef-Daenzer B, Grüebler MU. Parental sex allocation and sex-specific survival drive offspring sex ratio bias in little owls. Behav Ecol Sociobiol 2019. [DOI: 10.1007/s00265-019-2694-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Equitable Chick Survival in Three Species of the Non-Migratory Shorebird Despite Species-Specific Sexual Dimorphism of the Young. Animals (Basel) 2019; 9:ani9050271. [PMID: 31126098 PMCID: PMC6562553 DOI: 10.3390/ani9050271] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2019] [Revised: 05/13/2019] [Accepted: 05/21/2019] [Indexed: 11/22/2022] Open
Abstract
Simple Summary We aimed to determine whether seasonal brood sex-ratio, sex-biased chick survival, and sex specific dimorphism at hatching or during growth occurs among three species of resident Australian shorebird. Our results describe no sex-bias in chick production, survival or growth rates between sexes for any of the three species studied. Abstract Sex-biases in populations can have important implications for species’ social biology, population demography and mating systems. It has recently been suggested that in some shorebirds, sex-specific bias in survival of precocial young may occur. This may be driven by variation in the brood sex-ratio and/or the sexual size dimorphism of young birds, which may influence predator escape capacity. Understanding the survival of young birds remains a significant knowledge gap for many taxa, especially when young birds are mobile and cryptic. Our aims were to estimate the sex-ratio variation in three species of Australian resident shorebird, specifically to determine: (1) whether seasonal brood sex-ratio variation at hatching is occurring, (2) the extent of any sex-biased chick survival, (3) if sex specific dimorphism at hatching or during growth occurs; and, (4) whether escape capacity differs between the sexes. We radio-tracked 50 Masked Lapwing Vanellus miles, 42 Red-capped Plover Charadrius ruficapillus and 27 Hooded Plover Thinornis cucullatus chicks from individual broods, examined the likelihood of hatchlings being male or female based on the hatching date within the breeding season, and compared size at hatching, growth and mortality of chicks of different sexes. There was no sex-bias with the hatching date across the breeding season, nor were there differences in survival or growth rates between sexes for any of the three species studied. In one species, male hatchlings had longer tarsi than females, but this did not result in differential escape propensity or improved survival. In conclusion, the hatching date, survival and growth of chicks from three species of resident shorebird was not influenced by their sex.
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Reynolds RT, Lambert JS, Flather CH, White GC, Bird BJ, Baggett LS, Lambert C, Bayard De Volo S. Long-term demography of the Northern Goshawk in a variable environment. WILDLIFE MONOGRAPHS 2017. [DOI: 10.1002/wmon.1023] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Richard T. Reynolds
- Rocky Mountain Research Station; 240 West Prospect Road Fort Collins CO 80526 USA
| | - Jeffrey S. Lambert
- Rocky Mountain Research Station; 240 West Prospect Road Fort Collins CO 80526 USA
| | - Curtis H. Flather
- Rocky Mountain Research Station; 240 West Prospect Road Fort Collins CO 80526 USA
| | - Gary C. White
- Department of Fisheries and Wildlife and Conservation Biology; Colorado State University; Fort Collins CO 80523 USA
| | - Benjamin J. Bird
- Rocky Mountain Research Station; 240 West Prospect Road Fort Collins CO 80526 USA
| | - L. Scott Baggett
- Rocky Mountain Research Station; 240 West Prospect Road Fort Collins CO 80526 USA
| | - Carrie Lambert
- Rocky Mountain Research Station; 240 West Prospect Road Fort Collins CO 80526 USA
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Schwanz LE, Cordero GA, Charnov EL, Janzen FJ. Sex-specific survival to maturity and the evolution of environmental sex determination. Evolution 2016; 70:329-41. [DOI: 10.1111/evo.12856] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2015] [Revised: 12/11/2015] [Accepted: 12/09/2015] [Indexed: 11/30/2022]
Affiliation(s)
- Lisa E. Schwanz
- School of Biological, Earth and Environmental Sciences; University of New South Wales; Sydney NSW 2052 Australia
- Research School of Biology; Australian National University; Canberra ACT Australia
| | - Gerardo A. Cordero
- Department of Ecology, Evolution and Organismal Biology; Iowa State University; Ames Iowa 50011
| | - Eric L. Charnov
- Department of Fisheries and Wildlife; Oregon State University; Corvallis Oregon 97331
| | - Fredric J. Janzen
- Department of Ecology, Evolution and Organismal Biology; Iowa State University; Ames Iowa 50011
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8
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Seasonal sex ratios and the evolution of temperature-dependent sex determination in oviparous lizards. Evol Ecol 2016. [DOI: 10.1007/s10682-016-9820-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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9
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Bowers EK, Thompson CF, Sakaluk SK. Within-female plasticity in sex allocation is associated with a behavioural polyphenism in house wrens. J Evol Biol 2016; 29:602-16. [PMID: 26687708 DOI: 10.1111/jeb.12810] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2015] [Revised: 12/07/2015] [Accepted: 12/14/2015] [Indexed: 01/14/2023]
Abstract
Sex allocation theory assumes individual plasticity in maternal strategies, but few studies have investigated within-individual changes across environments. In house wrens, differences between nests in the degree of hatching synchrony of eggs represent a behavioural polyphenism in females, and its expression varies with seasonal changes in the environment. Between-nest differences in hatching asynchrony also create different environments for offspring, and sons are more strongly affected than daughters by sibling competition when hatching occurs asynchronously over several days. Here, we examined variation in hatching asynchrony and sex allocation, and its consequences for offspring fitness. The number and condition of fledglings declined seasonally, and the frequency of asynchronous hatching increased. In broods hatched asynchronously, sons, which are over-represented in the earlier-laid eggs, were in better condition than daughters, which are over-represented in the later-laid eggs. Nonetheless, asynchronous broods were more productive later within seasons. The proportion of sons in asynchronous broods increased seasonally, whereas there was a seasonal increase in the production of daughters by mothers hatching their eggs synchronously, which was characterized by within-female changes in offspring sex and not by sex-biased mortality. As adults, sons from asynchronous broods were in better condition and produced more broods of their own than males from synchronous broods, and both males and females from asynchronous broods had higher lifetime reproductive success than those from synchronous broods. In conclusion, hatching patterns are under maternal control, representing distinct strategies for allocating offspring within broods, and are associated with offspring sex ratios and differences in offspring reproductive success.
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Affiliation(s)
- E K Bowers
- Behavior, Ecology, Evolution, and Systematics Section, School of Biological Sciences, Illinois State University, Normal, IL, USA
| | - C F Thompson
- Behavior, Ecology, Evolution, and Systematics Section, School of Biological Sciences, Illinois State University, Normal, IL, USA
| | - S K Sakaluk
- Behavior, Ecology, Evolution, and Systematics Section, School of Biological Sciences, Illinois State University, Normal, IL, USA
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10
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Chakarov N, Pauli M, Mueller AK, Potiek A, Grünkorn T, Dijkstra C, Krüger O. Territory Quality and Plumage Morph Predict Offspring Sex Ratio Variation in a Raptor. PLoS One 2015; 10:e0138295. [PMID: 26445010 PMCID: PMC4596812 DOI: 10.1371/journal.pone.0138295] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2015] [Accepted: 08/29/2015] [Indexed: 11/19/2022] Open
Abstract
Parents may adapt their offspring sex ratio in response to their own phenotype and environmental conditions. The most significant causes for adaptive sex-ratio variation might express themselves as different distributions of fitness components between sexes along a given variable. Several causes for differential sex allocation in raptors with reversed sexual size dimorphism have been suggested. We search for correlates of fledgling sex in an extensive dataset on common buzzards Buteo buteo, a long-lived bird of prey. Larger female offspring could be more resource-demanding and starvation-prone and thus the costly sex. Prominent factors such as brood size and laying date did not predict nestling sex. Nonetheless, lifetime sex ratio (LSR, potentially indicative of individual sex allocation constraints) and overall nestling sex were explained by territory quality with more females being produced in better territories. Additionally, parental plumage morphs and the interaction of morph and prey abundance tended to explain LSR and nestling sex, indicating local adaptation of sex allocation However, in a limited census of nestling mortality, not females but males tended to die more frequently in prey-rich years. Also, although females could have potentially longer reproductive careers, a subset of our data encompassing full individual life histories showed that longevity and lifetime reproductive success were similarly distributed between the sexes. Thus, a basis for adaptive sex allocation in this population remains elusive. Overall, in common buzzards most major determinants of reproductive success appeared to have no effect on sex ratio but sex allocation may be adapted to local conditions in morph-specific patterns.
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Affiliation(s)
- Nayden Chakarov
- Department of Animal Behaviour, Bielefeld University, PO Box 10 01 31, 33501, Bielefeld, Germany
- * E-mail:
| | - Martina Pauli
- Department of Animal Behaviour, Bielefeld University, PO Box 10 01 31, 33501, Bielefeld, Germany
| | - Anna-Katharina Mueller
- Department of Animal Behaviour, Bielefeld University, PO Box 10 01 31, 33501, Bielefeld, Germany
| | - Astrid Potiek
- Department of Animal Behaviour, Bielefeld University, PO Box 10 01 31, 33501, Bielefeld, Germany
| | | | - Cor Dijkstra
- Behavioural Biology, University of Groningen, PO Box 11103, 9700 CC, Groningen, The Netherlands
| | - Oliver Krüger
- Department of Animal Behaviour, Bielefeld University, PO Box 10 01 31, 33501, Bielefeld, Germany
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11
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Romano A, Romano M, Caprioli M, Costanzo A, Parolini M, Rubolini D, Saino N. Sex allocation according to multiple sexually dimorphic traits of both parents in the barn swallow (Hirundo rustica). J Evol Biol 2015; 28:1234-47. [PMID: 25913917 DOI: 10.1111/jeb.12650] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2015] [Revised: 04/21/2015] [Accepted: 04/23/2015] [Indexed: 01/10/2023]
Abstract
Parents should differentially invest in sons or daughters depending on the sex-specific fitness returns from male and female offspring. In species with sexually selected heritable male characters, highly ornamented fathers should overproduce sons, which will be more sexually attractive than sons of less ornamented fathers. Because of genetic correlations between the sexes, females that express traits which are under selection in males should also overproduce sons. However, sex allocation strategies may consist in reaction norms leading to spatiotemporal variation in the association between offspring sex ratio (SR) and parental phenotype. We analysed offspring SR in barn swallows (Hirundo rustica) over 8 years in relation to two sexually dimorphic traits: tail length and melanin-based ventral plumage coloration. The proportion of sons increased with maternal plumage darkness and paternal tail length, consistently with sexual dimorphism in these traits. The size of the effect of these parental traits on SR was large compared to other studies of offspring SR in birds. Barn swallows thus manipulate offspring SR to overproduce 'sexy sons' and potentially to mitigate the costs of intralocus sexually antagonistic selection. Interannual variation in the relationships between offspring SR and parental traits was observed which may suggest phenotypic plasticity in sex allocation and provides a proximate explanation for inconsistent results of studies of sex allocation in relation to sexual ornamentation in birds.
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Affiliation(s)
- A Romano
- Department of Biosciences, University of Milan, Milan, Italy
| | - M Romano
- Department of Biosciences, University of Milan, Milan, Italy
| | - M Caprioli
- Department of Biosciences, University of Milan, Milan, Italy
| | - A Costanzo
- Department of Biosciences, University of Milan, Milan, Italy
| | - M Parolini
- Department of Biosciences, University of Milan, Milan, Italy
| | - D Rubolini
- Department of Biosciences, University of Milan, Milan, Italy
| | - N Saino
- Department of Biosciences, University of Milan, Milan, Italy
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12
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Aggressive behavior of the male parent predicts brood sex ratio in a songbird. Naturwissenschaften 2014; 101:653-60. [DOI: 10.1007/s00114-014-1204-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2014] [Revised: 06/13/2014] [Accepted: 06/19/2014] [Indexed: 01/22/2023]
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13
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Székely T, Weissing FJ, Komdeur J. Adult sex ratio variation: implications for breeding system evolution. J Evol Biol 2014; 27:1500-12. [DOI: 10.1111/jeb.12415] [Citation(s) in RCA: 141] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2013] [Revised: 04/16/2014] [Accepted: 04/16/2014] [Indexed: 11/28/2022]
Affiliation(s)
- T. Székely
- Biodiversity Lab; Department of Biology & Biochemistry; University of Bath; Bath UK
- Theoretical Biology; Centre for Ecological and Evolutionary Studies; University of Groningen; Groningen The Netherlands
- Behavioural Ecology and Self-organization; Centre for Ecological and Evolutionary Studies; University of Groningen; Groningen The Netherlands
| | - F. J. Weissing
- Theoretical Biology; Centre for Ecological and Evolutionary Studies; University of Groningen; Groningen The Netherlands
| | - J. Komdeur
- Behavioural Ecology and Self-organization; Centre for Ecological and Evolutionary Studies; University of Groningen; Groningen The Netherlands
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14
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Saalfeld ST, Conway WC, Haukos DA, Johnson WP. Seasonal Variation in Offspring Sex Ratio in the Snowy Plover. WEST N AM NATURALIST 2013. [DOI: 10.3398/064.073.0106] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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15
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Kristensen DL, Erikstad KE, Reiertsen TK, Moum T, Barrett RT, Jenni-Eiermann S. Are female offspring from a single-egg seabird more costly to raise? Behav Ecol 2012. [DOI: 10.1093/beheco/ars144] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
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16
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Progeny sex ratios in a short-lived lizard: seasonal invariance despite sex-specific effects of hatching date on fitness. Evol Ecol 2012. [DOI: 10.1007/s10682-012-9575-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
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17
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Barclay RMR. Variable variation: annual and seasonal changes in offspring sex ratio in a bat. PLoS One 2012; 7:e36344. [PMID: 22570704 PMCID: PMC3343075 DOI: 10.1371/journal.pone.0036344] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2012] [Accepted: 04/05/2012] [Indexed: 11/18/2022] Open
Abstract
Many organisms produce offspring with sex-ratios that deviate from equal numbers of males and females, and numerous adaptive explanations have been proposed. In some species, offspring sex-ratio varies across the reproductive season, again with several explanations as to why this might be adaptive. However, patterns for birds and mammals are inconsistent, and multiple factors are likely involved. Long-term studies on a variety of species may help untangle the complexity. I analyzed a long-term data set on the variation in offspring sex-ratio of the big brown bat, Eptesicus fuscus, a temperate-zone, insectivorous species. Sex ratio varied seasonally, but only in some years. Births early in the season were significantly female biased in years in which parturition occurred relatively early, but not in years with late parturition. Survival of female pups increased with earlier median birth date for the colony, and early-born females were more likely to survive and reproduce as one-year olds, compared to later-born pups. I argue that, due to the unusual timing of reproductive activities in male and female bats that hibernate, producing female offspring early in the year increases their probability of reproducing as one year olds, but this is not the case for male offspring. Thus, mothers that can give birth early in the year, benefit most by producing a female pup. The relative benefit of producing female or male offspring varies depending on the length of the growing season and thus the time available for female pups to reach sexual maturity. This suggests that not only does sex-ratio vary seasonally and among years, depending on the condition of the mother and the environment, but also likely varies geographically due to differences in season length.
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Affiliation(s)
- Robert M R Barclay
- Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada.
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19
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Pryke SR, Rollins LA, Griffith SC. CONTEXT-DEPENDENT SEX ALLOCATION: CONSTRAINTS ON THE EXPRESSION AND EVOLUTION OF MATERNAL EFFECTS. Evolution 2011; 65:2792-9. [DOI: 10.1111/j.1558-5646.2011.01391.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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20
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Schrand BE, Stobart CC, Engle DB, Desjardins RB, Farnsworth GL. Nestling Sex Ratios in Two Populations of Northern Mockingbirds. SOUTHEAST NAT 2011. [DOI: 10.1656/058.010.0215] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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21
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Dijkstra C, Riedstra B, Dekker A, Goerlich VC, Daan S, Groothuis TGG. An adaptive annual rhythm in the sex of first pigeon eggs. Behav Ecol Sociobiol 2010; 64:1393-1402. [PMID: 20730075 PMCID: PMC2920424 DOI: 10.1007/s00265-010-0954-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2009] [Revised: 03/29/2010] [Accepted: 04/01/2010] [Indexed: 11/03/2022]
Abstract
When the reproductive value of male and female offspring varies differentially, parents are predicted to adjust the sex ratio of their offspring to maximize their fitness (Trivers and Willard, Science 179:90-92, 1973). Two factors have been repeatedly linked to skews in avian offspring sex ratio. First, laying date can affect offspring sex ratio when the sexes differ in age of first reproduction, such that the more slowly maturing sex is overproduced early in the season. Second, position of the egg in the laying sequence of a clutch may affect sex ratio bias since manipulating the sex of the first eggs may be least costly to the mother. We studied both factors in two non-domesticated pigeon species. Both the Wood pigeon (Columba palumbus) and the Rock pigeon (Columba livia) have long breeding seasons and lay two-egg clutches. In the field, we determined the sex of Wood pigeon nestlings. In Rock pigeons, housed in captivity outdoors, we determined embryo sex after 3 days of incubation. On the basis of their sex-specific age of first reproduction, we predicted that males, maturing at older age than females, should be produced in majority early and females later in the year. This was confirmed for both species. The bias was restricted to first eggs. Rock pigeons produced clutches throughout the year and show that the sex of the first egg followed an annual cycle. To our knowledge, this study presents the first evidence of a full annual rhythm in adaptive sex allocation in birds. We suggest that this reflects an endogenous seasonal program in primary sex ratio controlled by a preovulatory mechanism.
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Affiliation(s)
- Cor Dijkstra
- Behavioural Biology, University of Groningen, P.O. Box 14, 9750 AA Haren, The Netherlands
| | - Bernd Riedstra
- Behavioural Biology, University of Groningen, P.O. Box 14, 9750 AA Haren, The Netherlands
| | - Arjan Dekker
- Behavioural Biology, University of Groningen, P.O. Box 14, 9750 AA Haren, The Netherlands
| | - Vivian C. Goerlich
- Behavioural Biology, University of Groningen, P.O. Box 14, 9750 AA Haren, The Netherlands
| | - Serge Daan
- Behavioural Biology, University of Groningen, P.O. Box 14, 9750 AA Haren, The Netherlands
| | - Ton G. G. Groothuis
- Behavioural Biology, University of Groningen, P.O. Box 14, 9750 AA Haren, The Netherlands
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22
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Rosivall B, Szöllősi E, Hasselquist D, Török J. Males are sensitive — sex-dependent effect of rearing conditions on nestling growth. Behav Ecol Sociobiol 2010. [DOI: 10.1007/s00265-010-0969-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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23
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Isaksson C, Magrath MJL, Groothuis TGG, Komdeur J. Androgens during development in a bird species with extremely sexually dimorphic growth, the brown songlark, Cinclorhamphus cruralis. Gen Comp Endocrinol 2010; 165:97-103. [PMID: 19539628 DOI: 10.1016/j.ygcen.2009.06.015] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/12/2009] [Revised: 06/06/2009] [Accepted: 06/12/2009] [Indexed: 11/27/2022]
Abstract
In birds, early exposure to androgens has been shown to influence offspring growth and begging behaviour, and has been proposed as a mechanism for the development of sexual size dimorphism (SSD). Sex specific effects during development can occur due to sex-specific allocation of maternal androgens, sensitivity to, or synthesis of, androgens. In addition, maternal hormones have been suggested as a mechanism to skew brood sex ratio. This study uses one of the world's most extreme SSD species, the brown songlark Cinclorhamphus cruralis, to investigate (1) sex-specific differences of androgens in yolk and chick plasma and (2) the relationship between androgens and sex ratio bias. The study reveals no indication of sex-specific maternal allocation, but a modest sex effect during the later stages of incubation when the embryo starts to produce its own androgens. Moreover, there was a strong seasonal sex ratio bias: female-biased early and male-biased later in the season, but yolk testosterone (T) did not show a seasonal trend. Taken together these results suggest that if androgens, from any source, have a significant role in development of SSD in this species it is most likely via sex-specific sensitivity or synthesis rather than differential maternal transfer to the egg.
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Affiliation(s)
- C Isaksson
- Centre for Ecological and Evolutionary Studies, University of Groningen, Haren, The Netherlands.
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24
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Navara K, Workman J, Oberdick J, Nelson R. Short Day Lengths Skew Prenatal Sex Ratios toward Males in Siberian Hamsters. Physiol Biochem Zool 2010; 83:127-34. [DOI: 10.1086/648487] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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25
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Schwanz LE, Janzen FJ, Proulx SR. SEX ALLOCATION BASED ON RELATIVE AND ABSOLUTE CONDITION. Evolution 2010; 64:1331-45. [DOI: 10.1111/j.1558-5646.2009.00916.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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26
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Maternal characteristics and the production and recruitment of sons in the eastern kingbird (Tyrannus tyrannus). Behav Ecol Sociobiol 2009. [DOI: 10.1007/s00265-009-0787-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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27
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Prenatal environmental influences on the production of sex-specific traits in mammals. Semin Cell Dev Biol 2009; 20:313-9. [DOI: 10.1016/j.semcdb.2008.12.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2008] [Revised: 12/08/2008] [Accepted: 12/09/2008] [Indexed: 11/22/2022]
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28
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Evolution of "determinants" in sex-determination: a novel hypothesis for the origin of environmental contingencies in avian sex-bias. Semin Cell Dev Biol 2008; 20:304-12. [PMID: 19073270 DOI: 10.1016/j.semcdb.2008.11.013] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2008] [Revised: 11/18/2008] [Accepted: 11/19/2008] [Indexed: 11/23/2022]
Abstract
Sex-determination is commonly categorized as either "genetic" or "environmental"-a classification that obscures the origin of this dichotomy and the evolution of sex-determining factors. The current focus on static outcomes of sex-determination provides little insight into the dynamic developmental processes by which some mechanisms acquire the role of sex determinants. Systems that combine "genetic" pathways of sex-determination (i.e., sex chromosomes) with "environmental" pathways (e.g., epigenetically induced segregation distortion) provide an opportunity to examine the evolutionary relationships between the two classes of processes and, ultimately, illuminate the evolution of sex-determining systems. Taxa with sex chromosomes typically undergo an evolutionary reduction in size of one of the sex chromosomes due to suppressed recombination, resulting in pronounced dimorphism of the sex chromosomes, and setting the stage for emergence of epigenetic compensatory mechanisms regulating meiotic segregation of heteromorphic sex chromosomes. Here we propose that these dispersed and redundant regulatory mechanisms enable environmental contingency in genetic sex-determination in birds and account for frequently documented context-dependence in avian sex-determination. We examine the evolution of directionality in such sex-determination as a result of exposure of epigenetic regulators of meiosis to natural selection and identify a central role of hormones in integrating female reproductive homeostasis, resource allocation to oocytes, and offspring sex. This approach clarifies the evolutionary relationship between sex-specific molecular genetic mechanisms of sex-determination and non-sex-specific epigenetic regulators of meiosis and demonstrates that both can determine sex. Our perspective shows how non-sex-specific mechanisms can acquire sex-determining function and, by establishing the explicit link between physiological integration of oogenesis and sex-determination, opens new avenues to the studies of adaptive sex-bias and sex-specific resource allocation in species with genetic sex-determination.
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ULLER T, ODIERNA G, OLSSON M. Sex ratio variation and sex determination in the mallee dragonCtenophorus fordi. Integr Zool 2008; 3:157-65. [DOI: 10.1111/j.1749-4877.2008.00109.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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31
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Cordero PJ, Viñuela J, Aparicio JM, Veiga JP. Seasonal variation in sex ratio and sexual egg dimorphism favouring daughters in first clutches of the spotless starling. J Evol Biol 2008. [DOI: 10.1046/j.1420-9101.2001.00320.x] [Citation(s) in RCA: 105] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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32
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Fitness effects of the timing of hatching may drive the evolution of temperature-dependent sex determination in short-lived lizards. Evol Ecol 2007. [DOI: 10.1007/s10682-007-9222-4] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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33
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Olsson M, Schwartz T, Uller T, Healey M. Sons are made from old stores: sperm storage effects on sex ratio in a lizard. Biol Lett 2007; 3:491-3. [PMID: 17650477 PMCID: PMC2391176 DOI: 10.1098/rsbl.2007.0196] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Sperm storage is a widespread phenomenon across taxa and mating systems but its consequences for central fitness parameters, such as sex ratios, has rarely been investigated. In Australian painted dragon lizards (Ctenophorus pictus), we describe elsewhere that male reproductive success via sperm competition is largely an effect of sperm storage. That is, sperm being stored in the female reproductive tract out-compete more recently inseminated sperm in subsequent ovarian cycles. Here we look at the consequences of such sperm storage for sex allocation in the same species, which has genetic sex determination. We show that stored sperm have a 23% higher probability of producing sons than daughters. Thus, shifts in sex ratio, for example over the reproductive season, can partly be explained by different survival of son-producing sperm or some unidentified female mechanism taking effect during prolonged storage.
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Affiliation(s)
- Mats Olsson
- School of Biological Sciences, University of Wollongong, Wollongong, New South Wales 2522, Australia.
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34
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Cockburn A, Double MC. Cooperatively breeding superb fairy-wrens show no facultative manipulation of offspring sex ratio despite plausible benefits. Behav Ecol Sociobiol 2007. [DOI: 10.1007/s00265-007-0492-1] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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35
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Warner DA, Shine R. Fitness of juvenile lizards depends on seasonal timing of hatching, not offspring body size. Oecologia 2007; 154:65-73. [PMID: 17653771 DOI: 10.1007/s00442-007-0809-9] [Citation(s) in RCA: 137] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2007] [Accepted: 06/27/2007] [Indexed: 11/28/2022]
Abstract
To understand how selection shapes life-history traits, we need information on the manner in which offspring phenotypes influence fitness. Life-history allocation models typically assume that "bigger offspring are better", but field data paint a more complex picture: larger offspring size sometimes enhances fitness, and sometimes not. Additionally, higher survival and faster growth of larger offspring might be due to indirect maternal effects (e.g., mothers allocate hormones or nutrients differently to different-sized eggs), and not to offspring size per se. Alternative factors, such as seasonal timing of hatching, may be more important. We examined these issues using 419 eggs from captive jacky dragon lizards (Amphibolurus muricatus). The mothers were maintained under standardized conditions to minimize variance in thermal and nutritional history, and the eggs were incubated under controlled conditions to minimize variance in offspring phenotypes due to incubation temperature and moisture. We reduced the size of half the eggs (and, thus, the size of the resultant hatchlings) from each clutch by yolk extraction. The hatchlings were marked and released at a field site over a 3-month period, with regular recapture surveys to measure growth and survival under natural conditions. Growth rates and survival were strongly enhanced by early-season hatching, but were not affected by hatchling body size.
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Affiliation(s)
- Daniel A Warner
- School of Biological Sciences, University of Sydney, Sydney, NSW, 2006, Australia.
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36
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Uller T, Olsson M. NO SEASONAL SEX-RATIO SHIFT DESPITE SEX-SPECIFIC FITNESS RETURNS OF HATCHING DATE IN A LIZARD WITH GENOTYPIC SEX DETERMINATION. Evolution 2007. [DOI: 10.1111/j.0014-3820.2006.tb01850.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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37
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Ward SJ. Test of the First-Cohort Advantage Hypothesis with Feathertail Gliders (Marsupialia). J Mammal 2007. [DOI: 10.1644/06-mamm-a-100r1.1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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38
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Sockman KW, Sharp PJ, Schwabl H. Orchestration of avian reproductive effort: an integration of the ultimate and proximate bases for flexibility in clutch size, incubation behaviour, and yolk androgen deposition. Biol Rev Camb Philos Soc 2007. [DOI: 10.1111/j.1469-185x.2006.tb00221.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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39
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Tobler M, Granbom M, Sandell MI. Maternal androgens in the pied flycatcher: timing of breeding and within-female consistency. Oecologia 2007; 151:731-40. [PMID: 17216215 DOI: 10.1007/s00442-006-0610-1] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2006] [Accepted: 11/02/2006] [Indexed: 11/29/2022]
Abstract
Maternal hormones can have substantial phenotypic effects in the progeny of many vertebrates. It has been proposed that mothers adaptively adjust hormone levels experienced by particular young to optimize their reproductive output. In birds, systematic variation in egg hormone levels has been related to different female reproductive strategies. Because in many bird species prospects of the offspring change seasonally and with brood number, strategic adjustment of yolk androgen levels would be expected. To test this idea, we induced pied flycatcher (Ficedula hypoleuca) females to nest twice during the same season by removing their first clutches shortly after clutch completion. We collected eggs of first and replacement clutches to measure yolk concentrations of androstenedione (A4) and testosterone (T) and captured the females that laid these clutches for phenotypic measurements. Although average egg androgen levels were remarkably consistent within females, hormone patterns differed considerably between first and replacement clutches. Eggs of replacement clutches were heavier with larger yolks compared to first clutches, but they contained on average lower levels of androgens. Within clutches, androgen concentration increased over the laying sequence in the first clutch, but decreased or remained more constant over the laying sequence in the replacement clutch. Mean yolk T, but not A4 levels, were negatively associated with laying date for both breeding attempts. Moreover, females in good body condition produced eggs containing lower levels of androgens than females in poor condition. Our results are consistent with the idea that differences in yolk androgen levels may be one mechanism underlying seasonal variation in reproductive success and it is possible that changes in egg androgen patterns may reflect a change in female reproductive strategy. High within-female consistency also highlights the possibility that there may be some underlying genetic variation in yolk androgen levels.
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Affiliation(s)
- Michael Tobler
- Department of Animal Ecology, Lund University, Lund, Sweden.
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40
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Blanchard P, Hanuise N, Dano S, Weimerskirch H. Offspring sex ratio in relation to parental structural size and body condition in the long-lived wandering albatross (Diomedea exulans). Behav Ecol Sociobiol 2006. [DOI: 10.1007/s00265-006-0307-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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41
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Badyaev AV, Hamstra TL, Oh KP, Acevedo Seaman DA. Sex-biased maternal effects reduce ectoparasite-induced mortality in a passerine bird. Proc Natl Acad Sci U S A 2006; 103:14406-11. [PMID: 16983088 PMCID: PMC1599976 DOI: 10.1073/pnas.0602452103] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2006] [Indexed: 11/18/2022] Open
Abstract
Duration of developmental stages in animals evolves under contrasting selection pressures of age-specific mortality and growth requirements. When relative importance of these effects varies across environments, evolution of developmental periods is expected to be slow. In birds, maternal effects on egg-laying order and offspring growth, two proximate determinants of nestling period, should enable rapid adjustment of developmental periods to even widely fluctuating mortality rates. We test this hypothesis in a population of house finches (Carpodacus mexicanus) breeding under two contrasting mortality risks: (i) a nest mite-free condition when selection on offspring survival favors a longer time in the nest; and (ii) a mite infestation when selection favors a shorter nest tenure. Mites affected survival of sons more than daughters, and females breeding under mite infestation laid male eggs last and female eggs first in the clutch, thereby reducing sons' exposure to mites and associated mortality. Strong sex bias in laying order and growth patterns enabled mite-infested offspring to achieve similar fledging size, despite a shorter nest tenure, compared with mite-free conditions. In mite-infested nests, male nestlings hatched at larger sizes, completed growth earlier, and had faster initial growth compared with mite-free nests, whereas mite-infested females grew more slowly but for a longer period of time. A combination of heavily sex-biased laying order and sex differences in growth patterns lowered mite-induced mortality by >10% in both sexes. Thus, strong maternal effects can account for frequently observed, but theoretically unexpected, concordance of mortality risks and growth patterns, especially under fluctuating ecological conditions.
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Affiliation(s)
- Alexander V Badyaev
- Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA.
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42
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McLean N, Handasyde KA. Sexual maturity, factors affecting the breeding season and breeding in consecutive seasons in populations of overabundant Victorian koalas (Phascolarctos cinereus). AUST J ZOOL 2006. [DOI: 10.1071/zo06015] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
It is important to have knowledge of basic population parameters to understand how these vary geographically and temporally and how they contribute to population dynamics. This paper investigates three of these parameters in Victorian koala populations: sexual maturity, aspects of the breeding season, and the continuity of individuals’ breeding. The investigation was carried out in koalas of known-age in two free-living (Redbill Creek on French Island and Brisbane Ranges) and one semi-captive (the Koala Conservation Centre on Phillip Island) population as well as koalas of unknown age in four Victorian populations of overabundant koalas: Mt Eccles and Framlingham in south-west Victoria, French Island in Western Port and Snake Island in south Gippsland. At sexual maturity, female koalas had a mean age (±95% confidence interval) of 24.4 months (23.5–25.3 months), a mean head length of 125 mm (124–127 mm) and a mean body mass of 6.6 kg (6.3–6.8 kg). Only 7.4% of independent females (of unknown age) were carrying young when they weighed less than 6 kg. The breeding season was more restricted in the south-west populations. At Framlingham and Mt Eccles 85% and 91% of births, respectively, occurred between December and March. At Snake and French Islands only 46% and 53% of births, respectively, were recorded in the same period. In the Chlamydia-free population (Red Bill Creek) none of the koalas that were monitored stopped breeding and then resumed breeding in a subsequent season whereas many females from Chlamydia-infected populations (Brisbane Ranges and the Koala Conservation Centre) did so. This variation in reproductive patterns is likely to make an important contribution to the variation in the demography observed in different koala populations.
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43
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Uller T, Olsson M. NO SEASONAL SEX-RATIO SHIFT DESPITE SEX-SPECIFIC FITNESS RETURNS OF HATCHING DATE IN A LIZARD WITH GENOTYPIC SEX DETERMINATION. Evolution 2006. [DOI: 10.1554/06-241.1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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44
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Janssen K, Erikstad KE, Bensch S. Offspring sex ratio allocation in the parasitic jaeger: selection for pale females and melanic males? Behav Ecol 2005. [DOI: 10.1093/beheco/arj015] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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45
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Egg size in relation to sex of embryo, brood sex ratios and laying sequence in northern lapwings ( Vanellus vanellus ). J Zool (1987) 2005. [DOI: 10.1017/s0952836905007260] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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46
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Vedder O, Dekker AL, Visser GH, Dijkstra C. Sex-specific energy requirements in nestlings of an extremely sexually size dimorphic bird, the European sparrowhawk (Accipiter nisus). Behav Ecol Sociobiol 2005. [DOI: 10.1007/s00265-005-0926-6] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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47
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Stauss M, Segelbacher G, Tomiuk J, Bachmann L. Sex ratio ofParus majorandP. caeruleusbroods depends on parental condition and habitat quality. OIKOS 2005. [DOI: 10.1111/j.0030-1299.2005.13333.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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48
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Krüger O, Radford AN, Anderson C, Liversidge R. Successful sons or superior daughters: sex-ratio variation in springbok. Proc Biol Sci 2005; 272:375-81. [PMID: 15734691 PMCID: PMC1634982 DOI: 10.1098/rspb.2004.2943] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2004] [Accepted: 09/16/2004] [Indexed: 11/12/2022] Open
Abstract
Mothers would often benefit from producing more offspring of one sex than the other. Although some species show an astonishing ability to skew their sex ratio adaptively, the trends found in many studies on vertebrates have proved inconsistent. Furthermore, evidence for a mechanism by which such a bias is achieved is equivocal at best. Here, we examine sex-ratio variation over 30 years, both at an individual and a population level, in the highly polygynous, size-dimorphic springbok (Antidorcas marsupialis). Many previous studies of similar species have shown that mothers in superior condition preferentially produce sons, whereas those in poorer condition produce more daughters. We found the opposite to be true in springbok, perhaps because daughters provide mothers in superior condition with a more rapid and secure fitness return. This theory was supported by the findings that earlier-conceived offspring tended to be female and that an increased proportion of daughters were produced with increasing rainfall (which was likely to reduce nutritional stress). We also show that selective reabsorption of embryos is unlikely to be the main mechanism by which deviations from an equal sex ratio are achieved. Hence, either differential implantation occurs or females are able to influence the sex of the sperm fertilizing an egg.
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Affiliation(s)
- O Krüger
- Department of Zoology, University of Cambridge, Dowing Street, Cambridge CB2 3EJ, UK.
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49
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Hipkiss T, H�rnfeldt B. High interannual variation in the hatching sex ratio of Tengmalm?s owl broods during a vole cycle. POPUL ECOL 2004. [DOI: 10.1007/s10144-004-0195-7] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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50
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Veiga JP, Viñuela J, Cordero PJ, Aparicio JM, Polo V. Experimentally increased testosterone affects social rank and primary sex ratio in the spotless starling. Horm Behav 2004; 46:47-53. [PMID: 15215041 DOI: 10.1016/j.yhbeh.2004.01.007] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/22/2003] [Revised: 01/06/2004] [Accepted: 01/22/2004] [Indexed: 11/27/2022]
Abstract
It has been suggested that the amount of maternal testosterone allocated into the eggs might be implicated in the process of sex determination. However, recent findings on the effect that female social rank has on the level of egg testosterone suggest that reported associations between male-biased sex ratios and yolk testosterone may represent an indirect hormonal effect mediated by the interdependence among maternal hormones, female social rank, and sex ratio. Here, we report the results of a field experiment in which we manipulated the circulating levels of testosterone in female spotless starlings (Sturnus unicolor) before egg formation. Focal females were controlled in subsequent years to explore possible delayed effects of hormone manipulation on primary sex ratio and social status that could persist because of permanent hormonal change or through hormone-dominance interactions. The results indicate that testosterone-implanted females (T-females) produced significantly more sons than control females (C-females) in the year in which they were manipulated. These differences in offspring sex ratio between T- and C-females persisted in the next 3 years, although no additional hormone treatments were given. These results were not mediated by an eventual effect of testosterone treatment on the quality of the females' mates. A similar proportion of T- and C-females acquired a nest box and bred either in the manipulation year or in Year 1 after manipulation, but T-females tended to be more successful in acquiring a nest box than C-females in Years 2 and 3 after manipulation. These results suggest that added testosterone had a direct role on the acquisition and maintenance of high social rank. Delayed effects of testosterone on primary sex ratio might have been caused by altered endogenous production of T-females. Alternatively, the maintenance of sex ratio differences between T- and C-females long after having being implanted might be attributed to the positive effect that enhanced social rank of T-females has on their circulating testosterone levels.
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Affiliation(s)
- José P Veiga
- Museo Nacional de Ciencias Naturales, CSIC, José Gutiérrez Abascal 2, 28006 Madrid, Spain.
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