Elements of male song performance and complexity are associated with reduced risk of paternity loss in a South American passerine.

Many passerines have elaborated songs hypothesized to have evolved through sexual selection. Extra-pair mating can be a contributing factor in the evolution of complex songs by increasing the variance in male fitness. We investigated this by quantifying the relationship between male song performance and complexity and levels of paternity loss through extra-pair mating by their female mates in the grass wren (), a socially monogamous passerine with elaborate songs. We conducted fieldwork in the Uspallata Valley, Mendoza, Argentina over two breeding seasons and recorded the songs of 30 focal males during the egg-laying stage of their social mate. We collected blood samples from adults and nestlings and used ddRAD sequencing SNP data to determine parentage. We assessed the extra-pair mating behaviour of females by measuring paternity loss of their social partner and examined whether variation in paternity loss was associated with structural characteristics of that male's songs. We found relationships between paternity loss and song duration, syllable diversity and duty cycle. Our findings indicate that some specific traits of male song are associated with lower levels of paternity loss and therefore potentially higher fitness. Future studies should determine whether this relationship is a result of female preference (intersexual selection), effective male mate guarding or territory defence (intrasexual selection) or both.