Male age is associated with extra-pair paternity, but not with extra-pair mating behaviour

Abstract

21Extra-pair paternity is the result of copulation between a female and a male other than 22 her social partner. In socially monogamous birds, old males are most likely to sire 23 extra-pair offspring. The male manipulation and female choice hypotheses predict that 24 age-specific male mating behaviour could explain this old-over-young male 25advantage. These hypotheses have been difficult to test because copulations and the 26 individuals involved are hard to observe. Here, we studied the mating behaviour and 27 pairing contexts of captive house sparrows, Passer domesticus. Our set-up mimicked 28 the complex social environment experienced by wild house sparrows. We found that 29 middle-aged males, that would be considered old in natural populations, gained most 30 extra-pair paternity. However, both female solicitation behaviour and subsequent 31 extra-pair matings were unrelated to male age. Further, copulations were more likely 32 when solicited by females than those initiated by males (i.e. unsolicited copulations), 33 and unsolicited within-pair copulations were more common than unsolicited extra-34 pair copulations. To conclude, our results did not support either hypotheses regarding 35 age-specific male mating behaviour. Instead, female choice, independent of male age, 36 governed copulation success, especially in an extra-pair context and post-copulatory 37 mechanisms might determine why older males sire more extra-pair offspring. 38 39

Individual Quality and Extra‐Pair Paternity in the Blue Tit: Sexy Males Bear the Costs

“…In fact, in season 2, only males second year or older gained extra-pair paternity. Similar results have been found in other avian mating systems (Delhey et al 2006a;Vedder et al 2011;Girndt et al 2018;Michálková et al 2019). However, the opposite was found in another blue tit population, with extra-pair paternity being almost absent in older males (Johannessen et al 2005).…”

Male age and its association with reproductive traits in captive and wild house sparrows

“…Instead, we found that in captivity, the number of old males’ sperm in the eggs of females was almost three times higher than the number of young males’ sperm. Our result is intriguing because neither the number of mating attempts, the number of copulations nor female choice are explained by male age in this population (Girndt et al., ). Hence, precopulatory differences do not seem to explain the age‐related difference in extra‐pair copulation success and it is tempting to suggest age‐related post‐copulatory differences between old and young males.…”

“…All birds were fitted with a unique numbered metal ring and combination of colour rings for identification. The specific husbandry under semi‐natural conditions has been described and illustrated previously (Girndt et al., , ).…”

“…Further, we estimated standardized multi‐locus heterozygosity (hereafter sMLH) as a proxy for the degree of inbreeding from genetic marker data, using the R package inbreedR version 0.3.2 (Stoffel et al., ), to account for potential inbreeding affecting sperm morphology. The identity and details of the genetic markers were published previously (Dawson et al., ; Girndt et al., ). We added sampling years (levels: 2014 and 2015) and the method of sperm collection (captive house sparrow data only) as explanatory variables (levels: abdominal massage and faeces).…”

“…The hypothesis predicts further that females are indifferent to male age during mate choice and old males are worse sperm competitors than young males (Radwan, ). A recent study found no evidence that female house sparrows preferred old males for mating (Girndt, Chng, Burke, & Schroeder, ) but, like in other birds, old captive and wild house sparrow males also achieve most extra‐pair paternity (Girndt et al., ; Hsu, Schroeder, Winney, Burke, & Nakagawa, ). These are intriguing findings because if old males achieve most extra‐pair paternity but are not preferred in extra‐pair matings, it is unlikely that old males are worse sperm competitors than young males like the polyandry hypothesis suggests.…”