Examining the social landscapes of alternative reproductive strategies

Abstract

Social environments are inherently dynamic, often changing depending on the frequency and outcomes of conspecific interactions - they can be simultaneously the targets and agents of selection. Understanding how organisms settle in heterogeneous social environments and the effects this has on reproductive success is vital to our understanding of the selective forces at work in wild populations. From an intensive behavioural and ecological study of territoriality in the polymorphic white-throated sparrow (Zonotrichia albicollis), we demonstrate that males of the two morphs inhabit social niches that correspond to their respective alternative reproductive strategies. By integrating molecular ecology and Geographic Information Systems, we generated continuous, socio-spatial models of local conspecific density and cuckoldry risk. Our results suggest that the morphs segregate their territories based on socio-spatial variables, creating a heterogeneous social landscape that matches each behavioural phenotype with a favourable social environment. Specifically, the monogamous tan males tended to settle in low-density areas that were also low for cuckoldry risk, while the opposite was true for the promiscuous white males. This pattern of socio-spatial heterogeneity, combined with the social niche partitioning we observed, might act as a social niche polymorphism, and play an important role in maintenance of the alternative reproductive strategies of the white-throated sparrow. Socio-spatial factors, similar to those observed in the white-throated sparrow, may play important roles in the evolution of mating systems in other species, even those with more continuous or cryptic variation.