No abstract

As a consequence of the deleterious e¡ects of parasites on host ¢tness, hosts have evolved responses to minimize the negative impact of parasite infection. Facultative parasite-induced responses are favoured when the risk of infection is unpredictable and host responses are costly. In vertebrates, induced responses are generally viewed as being adaptive, although evidence for ¢tness bene¢ts arising from these responses in natural host populations is lacking. Here we provide experimental evidence for direct reproductive bene¢ts in £ea-infested great tit nests arising from exposure during egg production to £eas. In the experiment we exposed a group of birds to £eas during egg laying (the exposed group), thereby allowing for induced responses, and kept another group free of parasites (the unexposed group) over the same time period. At the start of incubation, we killed the parasites in both groups and all nests were reinfested with £eas. If induced responses occur and are adaptive, we expect that birds of the exposed group mount earlier responses and achieve higher current reproductive success than birds in the unexposed group. In agreement with this prediction, our results show that birds with nests infested during egg laying have (i) fewer breeding failures and raise a higher proportion of hatchlings to £edging age; (ii) o¡spring that reach greater body mass, grow longer feathers, and £edge earlier, and (iii) a higher number of recruits and ¢rst-year grandchildren than unexposed birds. Flea reproduction and survival did not di¡er signi¢cantly between the two treatments. These results provide the ¢rst evidence for the occurrence and the adaptiveness of induced responses against a common ectoparasite in a wild population of vertebrates.

No abstract

Dispersal patterns of organisms are a fundamental aspect of their ecology, modifying the genetic and social structure of local populations. Parasites reduce the reproductive success and survival of hosts and thereby exert selection pressure on host life-history traits, possibly affecting host dispersal. Here we test experimentally whether infestation by hen fleas, Ceratophyllus gallinae, affects sex-related recruitment of great tit, Parus major, fledglings. Using sex-specific DNA markers, we show that flea infestation led to a higher proportion of male fledglings recruiting in the local population in one year. In infested broods, the proportion of male recruits increased with brood size over a three year period, whereas the proportion of male recruits from uninfested broods decreased with brood size. Natal dispersal distances of recruits from infested nests were shorter than those from uninfested nests. To our knowledge, this study provides the first evidence for parasite-mediated host natal dispersal and local recruitment in relation to sex. Current theory needs to consider parasites as potentially important factors shaping life-history traits associated with host dispersal.