Faithful or not: direct and indirect effects of climate on extra-pair paternities in a population of Alpine marmots

Abstract

Despite being identified an area that is poorly understood regarding the effects of climate change, behavioural responses to climatic variability are seldom explored. Climatic variability is likely to cause large inter-annual variation in the frequency of extra-pair litters produced, a widespread alternative mating tactic to help prevent, correct or minimize the negative consequences of sub-optimal mate choice. In this study, we investigated how climatic variability affects the inter-annual variation in the proportion of extra-pair litters in a wild population of Alpine marmots. During 22 years of monitoring, the annual proportion of extra-pair litters directly increased with the onset of earlier springs and indirectly with increased snow in winters. Snowier winters resulted in a higher proportion of families with sexually mature male subordinates and thus, created a social context within which extra-pair paternity was favoured. Earlier spring snowmelt could create this pattern by relaxing energetic, movement and time constraints. Further, deeper snow in winter could also contribute by increasing litter size and juvenile survival. Optimal mate choice is particularly relevant to generate adaptive genetic diversity. Understanding the influence of environmental conditions and the capacity of the individuals to cope with them is crucial within the context of rapid climate change.

Estimating a Key Parameter of Mammalian Mating Systems: The Chance of Siring Success for a Mated Male

“…For example, Alpine marmots exhibit a socially monogamous mating system, but about 20% of litters have young produced by the paired male and one or more males other than the social male partner . The rate at which the genetic pattern of mating differs from social monogamy is influenced by the social setting, specifically the number of subordinate males nearby, and even by conditions associated with climate change …”

Extrinsic and intrinsic constraints interact to drive extra‐pair paternities in the Alpine marmot

“…In the Alpine marmots, female social mate choice is strongly constrained (Lardy et al ., ) and we only found an impact of the females’ genetic makeup on the proportion of EPY when sexually mature males were present in the family groups. In this species, abiotic and biotic factors interact to strongly constrain extra‐pair mating opportunities (Bichet et al ., ). The annual proportion of extra‐pair litters increases directly with earlier springs and indirectly with increased snow in winters.…”

“…Earlier spring snowmelt is expected to relax energetic, movement and time constraints linked to mate searching. Snowier winters result in a higher proportion of families with sexually mature male subordinates (Bichet et al ., ; Rézouki et al ., ), and further create a social context within which extra‐pair paternity is favoured (Bichet et al ., ). Indeed, the presence of sexually mature males increases the cost of reproductive monopolization for dominant males and facilitates that dominant females escape mate guarding (Cohas et al ., ; Lardy et al ., ).…”

“…The majority of the extra‐pair fathers are within‐group mature male subordinates and the others are transient males, dispersing in search for a breeding vacancy, or are dominant males from another neighbouring family (Cohas et al ., ; Bichet et al ., ; Appendix S1). The occurrence of EPP is associated with social factors and more precisely increases with the presence and the number of mature male subordinates in the family group (Cohas et al ., ; Bichet et al ., ). Extra‐pair behaviours are also associated with genetic characteristics, especially the relatedness of the dominant pair measured with microsatellites.…”

“…Marmots live in families, and the social context is an extrinsic factor strongly constraining the proportion of extra‐pair young (EPY) (Cohas et al ., ). In the Alpine marmot, previous findings indicated that the occurrence of extra‐pair paternity is driven by both genetic characteristics, especially the within‐pair relatedness (Cohas et al ., ), and the presence of mature male subordinates (Cohas et al ., , ; Bichet et al ., ). Thus, we predict that females with longer Avpr‐1a microsatellites should have a higher propensity to mate switching (as found in female prairie voles) and therefore should obtain a higher proportion of EPY, especially under a permissive social context (i.e.…”