“Ecological and social factors constrain spatial and temporal opportunities for mating in a migratory songbird”

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Sara A. Kaiser, Benjamin B. Risk, T. Scott Sillett, and Michael S. Webster

Ecological and social factors affect the spatial and temporal opportunities for extra-pair paternity sexual selection

Environmental constraints on extrapair mating could have overlooked consequences for the evolution of sexual traits

Female black-throated blue warbler (Setophaga caerulescens).
(Credit: Rebecca Koch)

In socially monogamous species, extrapair paternity – mating outside of social pair bonds – may increase the strength of sexual selection when males with preferred characteristics monopolize these matings. However, most studies of sexual selection have found weak associations between male sexual traits and their extrapair mating success. New research on a North American songbird shows that environmental heterogeneity generates variation in opportunities for extrapair mating, which could moderate the strength of sexual selection shaping sexual traits in natural populations and thus can explain why such strong associations are rarely found.

Hubbard Brook Experimental Forest.
(Credit: Alisa Muniz)

In a study appearing in The American Naturalist, a team of researchers from Cornell University, the Cornell Lab of Ornithology, and the Smithsonian Migratory Bird Center examine how ecological and social conditions affect a male’s opportunity for extrapair paternity. The authors use genetic parentage data collected from an intensively studied population of black-throated blue warblers at the Hubbard Brook Experimental Forest in New Hampshire to construct spatial networks of breeding individuals, which included over 5,000 possible female–male pairings over four years.

Male black-throated blue warbler (S. caerulescens).
(Credit: Robert Royse)

The data revealed that most males mated with extrapair females in their local neighborhood and when their social mate was incubating her eggs. These spatial and temporal constraints on extrapair mating opportunities were stronger for males on food-abundant territories. This research sheds new light on the evolution of sexual traits, and shows that the ecological and social conditions under which sexual traits evolve are likely to be more constrained by the environment than previously appreciated. Read the Article