Older male reed buntings are more successful at gaining extrapair fertilizations

Abstract

The importance of extrapair paternity (EPP) as an aspect of mixed reproductive strategies is currently the focus of many studies. Since females have at least some control over the occurrence of inseminations, they are expected to engage in extrapair copulations only if they benefit, for instance through gaining highquality or compatible genes for their offspring, or insurance against infertility. To distinguish between these benefits, we studied characteristics related to intermale variation in fertilization success as well as differences in fitness between half-siblings in the reed bunting, Emberiza schoeniclus, a socially monogamous passerine with high levels of EPP (50% of young). We found that older males were more successful at siring offspring in other broods and a nonsignificant tendency for them to be less cuckolded in their own broods. The success of older males does not support the fertility insurance hypothesis: a male's sperm storage capacity did not predict his fertilization success, the occurrence of infertile eggs was unrelated to the occurrence of EPP in a nest and older males had more infertile eggs in nests with no EPP. Extrapair young had longer tarsi at fledging than their maternal half-siblings, but we found no other differences between maternal or paternal half-siblings in several presumed quality traits. Owing to the absence of long-term fitness data, we are unable to determine whether the difference in tarsus length is related to a difference in fitness benefits. At this time, we cannot exclude the possibility that females do gain genetic benefits through EPP.

Reed bunting females increase fitness through extra-pair mating with genetically dissimilar males

“…Weight has been shown to be important for fledgling survival (Magrath 1991;Naef-Daenzer et al 2001). Longer tarsi of EPY compared with WPY have also been found in a population of reed buntings in The Netherlands (Bouwman et al 2007) as well as in However, the size differences between extra-and within-pair nestlings could be based on other than genetic factors. The first eggs laid in a clutch might be more likely to contain EPY and therefore hatch earlier (Krist et al 2005), but see Westneat et al (1995), Whittingham et al (2003) and Barber & Robertson (2007).…”

“…Studies on reed bunting populations in Norway and The Netherlands did not reveal differences in heterozygosity between EPY and WPY Bouwman et al 2007). However, the authors were focusing on mixed broods.…”

“…In the reed bunting, it has been shown that mainly old males gain extra-pair paternity (Bouwman et al 2007). The fact that old males have shown their ability to survive might be an indicator of their good genes (Kokko & Lindstrom 1996;Brooks & Kemp 2001).…”

A distinct reed bunting dawn song and its relation to extrapair paternity

“…An earlier study on reed buntings showed that older males sing actively during the day and are more successful at gaining EPP (Bouwman et al 2007). In our study too, old males were more successful at gaining EPP than young males (Table 3).…”

“…Males were categorized as old males when they were at least in their second breeding season (2005: N ¼ 10, 2006: N ¼ 13). We assumed unringed adults that were breeding for the first time on our study area in 2005 (N ¼ 16) and 2006 (N ¼ 21) to be young males (following Bouwman et al 2007). Year was excluded from the final GLMs as it showed no effect in the initially expanded models.…”