Co-divergence of sexual traits and mate preferences can lead to assortative mating and subsequently reproductive isolation. However, mate choice rarely operates without intrasexual competition, and the effects of the latter on speciation are often overlooked. Maintaining trait polymorphisms despite gene flow and limiting assortative female preferences for less-competitive male phenotypes are two important roles that male-male competition may play in the speciation process. Both roles rely on the assumption that male-male competition limits the expression of divergent female preferences. We tested this assumption in the highly color-polymorphic strawberry poison frog (Oophaga pumilio). Females prefer males of the local color, suggesting that reproductive isolation may be evolving among color morphs. However, this inference does not account for male-male competition, which is also color-mediated. We housed females with two differently-colored males, and compared reproductive patterns when the more attractive male was the territory holder versus when he was the non-territorial male. Females mated primarily with the territory winner, regardless of coloration, suggesting that when a choice must be made between the two, male territoriality overrides female preferences for male coloration. Our results highlight the importance of considering the combined effects of mate choice and intrasexual competition in shaping phenotypic divergence and speciation.

The experiments were done in the Oophaga pumilio colony at University of Pittsburgh. Behavioral and reproductive data was collected by YY and numerous undergrads in the lab, curated by YY. Microsatillite analysis and curation was done by YY. R code for analysis by YY.

The R markdown file contains the code and annotation for all analyses and figures presented in the manuscript.