Parental investment and reproductive success in the reed bunting (Emberiza schoeniclus), investigated by DNA fingerprinting.

This study investigated the mating behaviour and parental behaviour of reed buntings (Emberiza schoeniclus), at Rutland Water, Leicestershire. The study integrated behavioural, molecular and anatomical approaches to examine the evolutionary consequences of sperm competition in the species. The frequency of extra-pair paternity (EPP) was extremely high in the study population. 86% (50/58) of broods held at least one extra-pair offspring, whilst 55% (118/216) of young were extra-pair young (EPY). Female participation in extra-pair copulations (EPCs) was virtually ubiquitous at 97% (33/34). Most, i.e., 83% (98/118), EPY were sired by males from an adjacent territory. This pattern of extra-pair paternity was best explained by the indiscriminate female copulatory behaviour associated with the 'genetic diversity' hypothesis. DNA fingerprinting revealed that just over half the males (15/28) breeding in the core study population obtained at least one extra-pair fertilisation (EPFs), and that EPFs accounted for an average of 40% (range 0 - 100%) of a male's reproductive success. There was no relationship between a male's paternity in his own nest and the number of EPFs achieved. Neither was there any consistency in the level of paternity among broods of multiple-brooded pairs. Old males had more EPY in their own nests than young males. There was no relationship between male reproductive success and any of the male phenotypic characters tested in a multivariate analysis. An examination of the paternity protection behaviour of male reed buntings revealed that males did not attempt to expand their territory during the female's fertile period in order to reduce the risk of cuckoldry. There was some evidence of weak mate guarding in the species. It is proposed that the primary paternity guard in the species is through frequent copulations. In the study population, 27% (8/30) of males were polygynous. Males benefit from polygyny through an increased reproductive output on their territories, though not to a significant extent due to a higher level of EPY in secondary nests. Polygynous males fed at only one nest on a territory, thus secondary females incurred a potential cost in terms of increased parental effort. Male and female reed buntings exhibit morphological adaptations associated with a high degree of sperm competition. Males have larger cloacal protuberances, testis and sperm than expected for a bird of comparable size. Females have extremely long sperm storage tubules. Analysis of provisioning behaviour revealed that male feeding rate was significantly related to their level of paternity in the brood. It is proposed that males can assess the confidence of paternity and adjust their feeding rate accordingly. This indicates that there is a potential cost to females of participating in EPCs.