Female in-nest attendance predicts the number of ectoparasites in Darwin's finch species

Selection should act on parental care and favour parental investment decisions that optimize the number of offspring produced. Such predictions have been robustly tested in predation risk contexts, but less is known about alternative functions of parental care under conditions of parasitism. The avian vampire fly ( Philornis downsi ) is a myasis-causing ectoparasite accidentally introduced to the Galápagos Islands, and one of the major mortality causes in Darwin's finch nests. With an 11-year dataset spanning 21 years, we examine the relationship between parental care behaviours and number of fly larvae and pupae in Darwin's finch nests. We do so across three host species ( Camarhynchus parvulus , C. pauper , Geospiza fuliginosa ) and one hybrid Camarhynchus group. Nests with longer female brooding duration (minutes per hour spent sitting on hatchlings to provide warmth) had fewer parasites, and this effect depended on male food delivery to chicks. Neither male age nor number of nest provisioning visits were directly associated with number of parasites. While the causal mechanisms remain unknown, we provide the first empirical study showing that female brooding duration is negatively related to the number of ectoparasites in nests. We predict selection for coordinated host male and female behaviour to reduce gaps in nest attendance, especially under conditions of novel and introduced ectoparasites.

Enzymatic antioxidants but not baseline glucocorticoids mediate the reproduction–survival trade-off in a wild bird

The trade-off between reproductive investment and survival is central to life-history theory, but the relative importance and the complex interactions among the physiological mechanisms mediating it are still debated. Here we experimentally tested whether baseline glucocorticoid hormones, the redox system or their interaction mediate reproductive investment–survival trade-offs in wild great tits ( Parus major ). We increased the workload of parental males by clipping three feathers on each wing, and 5 days later determined effects on baseline corticosterone concentrations (Cort), redox state (reactive oxygen metabolites, protein carbonyls, glutathione peroxidase [GPx], total non-enzymatic antioxidants), body mass, body condition, reproductive success and survival. Feather-clipping did not affect fledgling numbers, chick body condition, nest provisioning rates or survival compared with controls. However, feather-clipped males lost mass and increased both Cort and GPx concentrations. Within feather-clipped individuals, GPx increases were positively associated with reproductive investment (i.e. male nest provisioning). Furthermore, within all individuals, males that increased GPx suffered reduced survival rates. Baseline Cort increases were related to mass loss but not to redox state, nest provisioning or male survival. Our findings provide experimental evidence that changes in the redox system are associated with the trade-off between reproductive investment and survival, while baseline Cort may support this trade-off indirectly through a link with body condition. These results also emphasize that plastic changes in individuals, rather than static levels of physiological signals, may mediate life-history trade-offs.

Site fidelity and long-distance homing by males of solitary parasitic wasps (Hymenoptera: Scoliidae)

Site fidelity and long-distance homing are known to occur in nesting female Hymenoptera. We report here on the site fidelity and homing ability in males of five species of scoliid wasps (Hymenoptera: Scoliidae), a group whose females do not make nests but are ectoparasitoids of scarabaeid beetles (Coleoptera: Scarabaeoidea). The males of these wasp species patrol female emergence areas searching for mates. Based on mark-recapture data, we found that between 40% and 100% of marked males left the release area and travelled 50–800 m from the point of capture returning to their original patrol area. We discuss the adaptive significance of site fidelity and homing behaviour in Scoliidae, and propose hypotheses about the evolution of the homing behaviour in Hymenoptera. The homing ability of these primitive Aculeata may represent a case of convergent evolution with other Hymenoptera in which males patrol emergence areas in search of females. Additionally, this homing ability may serve as a preadaptation for the evolution of nest-provisioning and nesting habits in Hymenoptera.