Multimodal flight display of a neotropical songbird predicts social pairing but not extrapair mating success

Abstract

Models of sexual selection predict that socially monogamous females may gain direct or indirect (genetic) benefits by mating with multiple males. We addressed current hypotheses by investigating how, in the socially monogamous blue-black grassquit (Volatinia jacarina), male courtship and territory quality varied with social and extrapair paternity. Males of this tropical granivorous passerine exhibit multimodal displays integrating motor (leap displays) and acoustic components. Across 3 years, we found that extrapair paternity ranged from 8 to 34 % of all nestlings and from 11 to 47 % of all broods. Extrapair and socially paired male territories had similar seed densities. Females preferred to pair socially with males executing higher leaps, but no other male display characteristic associated with paternity loss and extrapair fertilizations. Extrapair and social mates did not differ in genetic similarity to female partners nor in inbreeding levels. Additionally, inbreeding and body condition of extrapair and within-pair nestlings did not differ. Thus, not only did we reject the direct benefits hypothesis for extrapair copulations, but our results also did not support the additive and nonadditive genetic benefits hypotheses. Instead, we found support for benefits through selection of potentially “good fathers,” specifically for females that chose to pair socially with males exhibiting enhanced performance in their displays. Multiple mating by females is intriguing because resulting advantages seem improbable. However, access to resources, genetic compatibility with the sexual partner and good gene transmission to the offspring are possible explanations for this behavior in several animals, including socially monogamous species. We investigated potential benefits in a socially monogamous neotropical bird, the blue-black grassquit. Males attract females using a sexual display of repeated leap flights synchronized with a song. We found that when selecting social mates, females favor higher-leaping males, an attribute associated with enhanced body condition that could indicate the capacity for better parenting and also be inherited by the offspring. Yet, when choosing extrapair males, females did not appear to base choices on leap parameters, vocal attributes, and genetic compatibility. These results do not suggest benefits for multiple mating by females, but show that selection of males in good physical condition can influence choice for social mates.