Extra-pair paternity in two sympatric Aegithalos tits: patterns and implications

Abstract

The explanation for extra-pair paternity (EPP) variation continues to attract research interest in the area of avian breeding systems. Comparisons among closely related species are recommended to explore factors that affect EPP rate variations. We utilised microsatellite markers to investigate extra-pair paternity in two sympatric populations of congeneric Black-throated Tits, Aegithalos concinnus, and Silver-throated Tits, A. glaucogularis. The two species share a similar breeding period at our study site and have helpers during breeding at some nests. The results suggest that the two species had low levels of extra-pair paternity: 5.7 % of the offspring in the Black-throated Tits and 6.8 % of the offspring in the Silver-throated Tits. The proportion of broods with extra-pair paternity in the Silver-throated Tits (33.3 %) was higher overall than the Black-throated Tits (17.2 %). This difference is consistent with the prediction by their different male attendance of incubation, but failed to be explained by major ecological factors. On the one hand, we conducted the study at the same site during the same time, which therefore limited the potential effect of different environmental conditions and habitat on their EPP incidence. On the other hand, other factors such as the inter-nest distances failed to explain the observed pattern. Current results also could not rule out an effect of evolutionary history on the EPP patterns of these two related species. Our research on their cooperative breeding system found a low proportion of cooperative breeding nests with offspring sired by helpers (Black-throated Tit, 8.3 % and Silver-throated Tit, 25.0 %), indicating that a direct reproductive benefit is not a likely major reason for the existence of the helpers in these two species.