Mate choice for neutral and MHC genetic characteristics in Alpine marmots : different targets in different contexts?

We warmly thank all students and Earthwatch volunteers involved in catching the marmots and the authorities of the Vanoise National Park for granting us permission to work in the Grande Sassière Nature Reserve. We thank M. Harrington for English editing and Dr. E. Rajon for helpful discussions on the manuscript. This work was supported by the "Agence Nationale de la Recherche" (ANR, project ANR-08-BLAN-0214-03, ANR-13-JSV7-0005), the "Centre National de la Recherche Scientifique" (CNRS), the "FR41 BioEnvironnement et Santé de l'Université de Lyon" and the "Earthwatch Institute", the scholarship for postgraduate studies "Obra Social Fundació La Caixa" and Vetagro-Sup.Sexual selection through female mate choice for genetic characteristics has been suggested to be an important evolutionary force maintaining genetic variation in animal populations. However, the genetic targets of female mate choice are not clearly identified and whether female mate choice is based on neutral genetic characteristics or on particular functional loci remains an open question. Here, we investigated the genetic targets of female mate choice in Alpine marmots (Marmota marmota), a socially monogamous mammal where extra-pair paternity (EPP) occurs. We used 16 microsatellites to describe neutral genetic characteristics and two MHC loci belonging to MHC class I and II as functional genetic characteristics. Our results reveal that (1) neutral and MHC genetic characteristics convey different information in this species, (2) social pairs show a higher MHC class II dissimilarity than expected under random mate choice, and (3) the occurrence of EPP increases when social pairs present a high neutral genetic similarity or dissimilarity but also when they present low MHC class II dissimilarity. Thus, female mate choice is based on both neutral and MHC genetic characteristics, and the genetic characteristics targeted seem to be context dependent (i.e., the genes involved in social mate choice and genetic mate choice differ). We emphasize the need for empirical studies of mate choice in the wild using both neutral and MHC genetic characteristics because whether neutral and functional genetic characteristics convey similar information is not universal

Early and Adult Social Environments Shape Sex-Specific Actuarial Senescence Patterns in a Cooperative Breeder

Sociality modulates life-history traits through changes in resource allocation to fitness-related traits. However, how social factors at different stages of the life cycle modulate senescence remains poorly understood. To address this question, we assessed the influence of social environment in both early life and adulthood on actuarial senescence in the Alpine marmot, a cooperative breeder. The influence of helpers on actuarial senescence strongly differed depending on when help was provided and on the sex of the dominant. Being helped when adult slowed down senescence in both sexes. However, the effect of the presence of helpers during the year of birth of a dominant was sex specific. Among dominants helped during adulthood, females born in the presence of helpers senesced slower, whereas males senesced faster. Among dominants without helpers during adulthood, females with helpers at birth senesced faster. Social environment modulates senescence but acts differently between sexes and life stages

Sex differences in adult lifespan and aging rates of mortality across wild mammals

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Sex ratio variation in the cooperatively breeding alpine marmot Marmota marmota

In cooperatively breeding vertebrate species, a clear theoretical prediction about the direction of sex ratio adjustment can be made: mothers should bias the sex ratio of their offspring towards the helping sex when helpers are absent. A consistent trend in the direction predicted by theory exists in cooperative birds, but theory is still poorly tested in cooperative mammals. Here, multivariate analyses are applied to a long-term data set to test this prediction in two ways in the alpine marmot: (1) across females in a population and (2) in individual females across multiple years. It was shown that in the alpine marmot offspring sex ratio was biased towards the helping sex (males) when helpers were absent, whereas helped mothers produced unbiased sex ratio. Unhelped mothers did not adjust the litter size but produced more sons and fewer daughters than helped mothers. These results support the theoretical prediction and explain well the male bias observed among juvenile alpine marmots at the population level. The occurrence of possible sex ratio manipulations in cooperatively breeding vertebrates is also discussed. Copyright 2004.cooperative breeders; generalized linear models; Marmota marmota; sex ratio variation

Evolution et typologie des régimes d'appariement.

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Is there an optimal number of helpers in alpine marmot family groups?

The consequence of helping behavior on breeders fitness is still controversial. We used multivariate analyses to investigate for the effects of male and female subordinates on breeders ’ components of fitness in the Alpine marmot, Marmota marmota. We found that male and female subordinates, respectively, increased and decreased juvenile survival during winter. Thus, we give evidence that male subordinates should be considered as helpers, and that helpers provided breeders with immediate reproductive success gains, whereas subordinates females were costly. Helpers had no positive effects on female body condition, on persistence (future survival) of dominants, and on future reproduction (occurrence and size of a litter). Helpers thus did not provide breeders with delayed fitness benefits, and therfore, the load-lightening hypothesis was not supported. On the contrary, helpers had delayed fitness cost for dominant males and, consequently, for dominant females. Immediate benefits counterbalanced by delayed costs suggested an optimal number of helpers in the family group both from male and female perspectives. An optimality model well predicted the observed mean number of helpers in Alpine marmot family groups. Optimal numbers of helpers were slightly different for males and females, suggesting a potential conflict of interest between dominants. We finally discuss the possible mechanisms of helping that may explain the observed pattern in the Alpine marmot. Key words: cooperative breeding, load-lightening hypothesis, Marmota marmota, mixed models, optimality. [Behav Ecol 15:916–924 (2004)] The evolution of cooperative breeding has stimulatedtheoretical and empirical work and remains an open field of research (Cockburn, 1998). The fitness consequences of cooperative breeding have been considered both for helper

La sélection sexuelle

36 page