Paternal investment affects prevalence of malaria.

Abstract

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 ...

Associations between malaria and MHC genes in a migratory songbird

“…In the great tit (Parus major), females with Plasmodium malaria infections lay smaller egg clutches (Richner et al 1995;Oppliger et al 1996). In feral pigeons (Columba livia), young birds that were infected with Haemoproteus columbae had a lower probability of surviving until adulthood compared with uninfected birds (Sol et al 2003).…”

“…A number of studies from wild bird populations have shown that there are severe fitness costs associated with the acute phase of avian malaria (Richner et al 1995;Oppliger et al 1996;Atkinson et al 2001;Sol et al 2003). In the great tit (Parus major), females with Plasmodium malaria infections lay smaller egg clutches (Richner et al 1995;Oppliger et al 1996).…”

Twofold cost of reproduction: an increase in parental effort leads to higher malarial parasitaemia and to a decrease in resistance to oxidative stress

“…A negative relationship between reproductive effort and immune defences or parasite susceptibilities has been shown in both mammals [14,15] and birds [6,16,17], and has been mainly interpreted as the results of immunosupression during the reproductive period. Immunosuppression would be either the result of an energetic trade-off between immune defences and physical workload or an adaptive response to avoid physiological disorders such as oxidative stress or immunopathology during this intense period, ultimately impairing future survival [18,19].…”

“…Brood size manipulation in experimental bird studies is commonly used to manipulate current investment in reproduction [5,6]. As period of rearing nestlings represent high levels of energy expenditure, especially for parents with an enlarged brood, metabolic rates increase dramatically during this phase [5].…”

Evolution of Paternal Investment

“…Support is found in the relation between paternal investment and childrenʹs well-being in extant populations and the historical record (Hill & Hurtado, 1996;Richner, Christe, & Oppliger, 1995;Schultz, 1991).…”