Benefits of induced host responses against an ectoparasite

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.

Ectoparasite–modulated deposition of maternal androgens in great tit eggs

“…This adjustment might promote the development of the offspring's immune system (Martin 2000) and lower the negative impact of parasites on the offspring after hatching. Two previous studies demonstrated maternal effects that reduce negative impact of hen fleas on great tit nestlings (Heeb et al 1998;Buechler et al 2002). Hen fleas inflicted less negative effects on nestling body mass when their mother was exposed to ectoparasites prior to egg laying.…”

Sex-biased maternal effects reduce ectoparasite-induced mortality in a passerine bird

“…Exposure to ectoparasites before egg-laying and associated endocrinological changes in breeding females can be one proximate mechanism enabling or triggering modifications in laying order and offspring growth (15,21,38). Although ectoparasite exposure of breeding females can induce greater egg allocation of maternal steroids that facilitate nestling growth or begging, such allocation can have detrimental effects on growth of the sexes if male and female offspring differ in growth requirements (39)(40)(41).…”

Immune function across generations: integrating mechanism and evolutionary process in maternal antibody transmission

“…inducible defences involve trade-offs (Frost 1999). Therefore, we would expect that elevated maternal antibody transmission would necessitate reproductive trade-offs for females (Heeb et al 1998 (a) Environmental determinants of variation in maternal antibody transmission The diversity and quantity of specific antibodies transmitted to offspring have been shown to reflect differences in the local disease environment experienced by females prior to antibody transmission (Lemke & Lange 1999;Lundin et al 1999;Gasparini et al 2001). Females not exposed to particular pathogens prior to transmission will not transfer antibodies to those pathogens, leaving their offspring susceptible to infection Leitner et al 1990).…”

“…Consequently, increased maternal antibody transmission may entail both positive and negative fitness effects for offspring. Despite the potential costs, maternal antibodies are generally believed to provide net benefits to offspring (Solomon 1971b;Lemke & Lange 1999), however, very little is known about the protective effects of maternal antibodies in natural systems (Heeb et al 1998).…”