JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to Journal of Animal Ecology. Summary 1. The effect of a haematophageous ectoparasite, the hen flea, on quality and number of offspring was experimentally investigated in the great tit. The experiment consisted of a controlled infestation of a random sample of nests with the parasitic flea and of a regular treatment of control nests with microwaves in order to eliminate the naturally occurring fleas. 2. To assess the effects of fleas on variables related to offspring number, we considered the number of hatchlings and fledglings, the mortality between hatching and fledging, and the hatching and fledging success. For assessment of offspring quality, we measured body mass, tarsus and wing length, and calculated the nutritional condition of nestlings as the ratio of body mass to tarsus length. A physiological variable, the haematocrit level, was also measured. 3. Hatching success and hatchling numbers did not differ between the two experimental groups. Offspring mortality between hatching and fledging was significantly higher in the infested broods (x = 022 chicks dead per day) than in the parasitefree broods (x = 007 dead per day). Fledging success was 83% in the parasite-free broods, but only 53% in the infested ones. The number of fledglings in infested broods (x = 3-7 fledglings ?2 1 SD) was significantly lower than in the parasite-free (x = 4 9 + 1-1 SD) broods. 4. Body mass of chicks in the infested broods was significantly smaller than in the parasite-free broods both 14 days and 17 days after hatching. The chicks in the infested broods reached a significantly smaller tarsus length than the ones in the parasite-free broods. Close to fledging, the nutritional condition of chicks was significantly lower in infested broods. Haematocrit levels were significantly lower in the infested broods. 5. Brood size correlated differently with body mass and condition of chicks in infested and parasite-free nests. In parasite-free broods both body mass and condition of chicks at age 17 days, i.e. close to fledging, were significantly higher in small broods than in large ones. However, in the infested broods chicks were of the same body mass and condition in large as in small broods. Therefore, in parasitefree broods fitness can potentially be gained through offspring quality or number or both, whereas in infested broods it can be gained through offspring quantity only. In other words, a trade-off between quality and number of offspring is feasible only in the absence of the parasitic hen flea. 6. These results emphasize the need to study the effects of ectoparasites on ecological, behavioural and ev...

Ectoparasites are a ubiquitous environmental component of breeding birds, and it has repeatedly been shown that hematophagous ectoparasites such as fleas and mites reduce the quality and number of offspring of bird hosts, thereby lowering the value of a current brood. Selection acting on the hosts will favor physiological and behavioral responses that will reduce the parasites' impact. However, the results of the few bird studies that addressed the question of whether parasitism leads to a higher rate of food provisioning are equivocal, and the begging response to infestation has rarely been quantified. A change in begging activity and parental rate of food provisioning could be predicted in either direction: parents could reduce their investment in the brood in order to invest more in future broods, or they could increase their investment in order to compensate for the parasites' effect on the current brood. Since the nesdings are weakened by the ectoparasites they may beg less, but on the other hand they may beg more in order to obtain more food. In this study we show experimentally that (1) hen fleas (Ceratophyllus galtinae) reduce the body mass and size of great tit (Parus major) nestlings, (2) nesdings of parasitized broods more than double their begging rate, (3) die male parents increase the frequency of feeding trips by over 50%, (4) the females do not adjust feeding rate to the lowered nutritional state of nestlings, and (5) food competition among siblings of parasitized broods is increased. Ultimately the difference in the parental feeding response may be understood as the result of a sex-related difference in die trade-off of investing in current versus future broods.

Both reproduction and parasite defense can be costly, and an animal may face a trade-off between investing in offspring or in parasite defense. In contrast to the findings from nonexperimental studies that the poorly reproducing individuals are often the ones with high parasite loads, this life-history view predicts that individuals with high reproductive investment will show high parasite prevalence. Here we provide an experimental confirmation of a positive association between parental investment levels of male great tits Parus major and the prevalence of Plasmodium spp, a hematozoa causing malaria in various bird species. We manipulated brood size, measured feeding effort of both males and females, and assessed the prevalence of the hemoparasite from blood smears. In enlarged broods the males, but not the females, showed significantly higher rates of food provisioning to the chicks, and the rate of malarial infection was found to be more than double in male, but not female, parents of enlarged broods. The findings show that there may be a trade-off between reproductive effort and parasite defense of the host and also suggest a mechanism for the well documented trade-off between current reproductive effort and parental survival.What is the cost of working hard for one's offspring? For birds and mammals it has been shown that a high parental investment in the current offspring can affect survival of the parents (1-4), their future fecundity (5), or both (6). Both reproduction and parasite defense are costly (7-10), and a fitness reduction through reduced survival or fecundity may arise if there is a coupling between investment levels and parasite prevalence in a host-that is, if increased levels of investment render hosts more susceptible to parasites or increase their exposure to the parasite vector. For an experimental test of this hypothesis we manipulated parental effort of great tits and assessed the prevalence of a common hemoparasite, Plasmodium spp., in our host population. Because the sexes can differ in several ways that could affect their parasite load (11), including their readiness to work harder for a larger brood, their exposure to the parasites or to the vectors (12), or their endocrine types and endocrine levels that may interact with immunocompetence (13-16), we assessed both maternal and paternal efforts for all manipulated broods and recorded the prevalence of the hemoparasite in male and female parents. METHODSIn our study population of great tits (Parus major) near Lausanne, Switzerland, we manipulated, in spring 1993, the brood size of great tits on the day of hatching by removing two chicks from a brood and adding them to a brood that hatched within a few hours of the first brood. When an odd number of broods hatched the same day, these extra broods were left unmanipulated and were monitored for comparison with the reduced and enlarged broods. By this exchange of two chicks between broods we created enlarged broods that held significantly more chicks than the reduced broods (9.5 ...

We investigated the effect of water constraints on yearling Lacerta vivipara, a widespread species of lizard inhabiting European peat bogs and heath land. We conducted a laboratory experiment to investigate plasticity of growth rate, activity level and preferred body temperature. We subjected individuals of two source habitats (dry vs humid) to two laboratory conditions of water supply resulting in different air relative humidity and water availability (high vs low). We observed that a low water supply induced a lower growth rate and lower activity level, suggesting that growth limitation is correlated with adaptive responses to avoid dehydration. However, individuals from the two habitats selected different body temperatures when restricted in water and showed different ratios between growth and activity. This suggests that there is population variability in phenotypic plasticity with respect to water availability in the habitat. Field observations conducted in six natural populations, classified into two groups (dry vs humid habitat) also suggest that growth rate in nature is constrained by water availability.

Social organisms are exposed to many pathogens, and have evolved various defence mechanisms to limit the cost of parasitism. Here we report the first evidence that ants use plant compounds as a collective mean of defence against microorganisms. The wood ants Formica paralugubris often incorporate large quantities of solidified conifer resin into their nests. By creating resin-free and resin-rich experimental nests, we demonstrate that this resin inhibits the growth of microorganisms in a context mimicking natural conditions. Such a collective medication probably confers major ecological advantages, and may be an unrecognized yet common feature of large, complex and successful societies.