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. 31 Extra-pair mating can be a contributing factor in the evolution of complex songs by increasing 32 the variance in male fitness. We investigated this by quantifying the relationship between male 33 song performance and complexity and levels of paternity loss through extra-pair mating by 34 their female mates in the Grass Wren (Cistothorus platensis), a socially monogamous passerine 35 with elaborate songs. We conducted fieldwork in the Uspallata Valley, Mendoza, Argentina 36 over two breeding seasons and recorded the songs of 30 focal males during the egg-laying stage 37 of their social mate. We collected blood samples from adults and nestlings and used ddRAD 38 sequencing SNP data to determine parentage. We assessed extra-pair mating behaviour of 39 females by measuring paternity loss of their social partner and examined whether variation in 40 paternity loss was associated with structural characteristics of that male’s songs. We found 41 relationships between paternity loss and song duration, syllable diversity, and duty cycle. Our 42 findings indicate that some specific traits of male song are associated with lower levels of 43 paternity loss and therefore potentially higher fitness. Future studies should determine whether 44 this relationship is a result of female preference (intersexual selection), effective male mate 45 guarding or territory defence (intrasexual selection), or both.