Population Resilience Under Environmental Deterioration in Socially Monogamous Systems with Mutual Mate Choice

Rapid environmental change and biodiversity loss make it increasingly important to identify factors influencing population extinction risk. Previous studies examining how mating systems can affect persistence of populations under environmental stress generally report higher extinction risks in monogamous than polygynous systems but have largely ignored extra-pair copulations (EPC) and paternity (EPP), despite the prevalence of genetic polyandry in socially monogamous species. Here, using an individual-based model, we study how EPP in socially monogamous systems affects population resilience under directional environmental change. We assume that in socially monogamous species, both sexes carry costly sexual ornaments, the elaboration of which depends on the strength of preference. The effect of EPPs on extinction risk depended on the strength of mate preference, population size, and the degree to which homozygosity affected fitness. Systems with EPCs are not simply intermediate in resilience between strict monogamy and polygyny: the preference strength interacts with mating system, leading to superior resilience of EPC systems compared to strictly monogamous and polygynous systems when choosiness and the negative consequences of heterozygosity loss are low, and EPP rates are high. However, this benefit was reduced in small populations due to faster loss of heterozygosity. At high choosiness, EPC systems exhibited lower resilience than socially polygynous choice systems because the higher reproductive skew of the latter system allowed them to adapt faster while not suffering from the demographic consequences of sexual signaling costs borne by females. Overall, our results suggest that EPCs can enhance population resilience when females obtain fertilizations from higher-condition extra-pair males compared to systems without EPC.