The quantitative genetic basis of offspring solicitation and parental response in a passerine bird with biparental care

The coevolution of parental investment and offspring solicitation is driven by partly different evolutionary interests of genes expressed in parents and their offspring. In species with biparental care, the outcome of this conflict ma!: be influenced by the sexual conflict over parental investment, Models for the resolution of such family conflicts have made so far untested assumptions about genetic variation and covariation in the parental resource provisioning response and the level of offspring solicitation. Using a combination of cross-fostering and begging playback experiments, we show that, in the great tit (Parus major), (i) the begging call intensity of nestlings depends on their common origin, suggesting genetic variation for this begging display, (ii) only mothers respond to begging calls by increased food provisioning, and (iii! the size of the parental response is positively related to the begging call intensity of nestlings in the maternal but not paternal line. This study indicates that genetic covariation, its differential expression in the maternal and paternal lines and/or early environmental and parental effects need to be taken into account when predicting the phenotypic outcome of the conflict over investment between genes expressed in each parent and the offspring. [References: 36]

Host condition and host immunity affect parasite fitness in a bird-ectoparasite system

1. Parasites might preferentially feed on hosts in good nutritional condition as such hosts provide better resources for the parasites' own growth, survival and reproduction. However, hosts in prime condition are also better able to develop costly immunological or physiological defence mechanisms, which in turn reduce the parasites' reproductive success. The interplay between host condition, host defence and parasite fitness will thus play an important part in the dynamics of host-parasite systems.;2. In a 2 x 2 design, we manipulated both the access to food in great tit Parus major broods and the exposure of the nestlings to hen fleas Ceratophyllus gallinae, a common ectoparasite of hole-breeding birds. We subsequently investigated the role of manipulated host condition, host immunocompetence, and experimentally induced host defence in nestlings on the reproductive success of individual hen flea females.;3. The food supplementation of the nestlings significantly influenced the parasites' reproductive success. Female fleas laid significantly more eggs when feeding on food-supplemented hosts.;4. Previous parasite exposure of the birds affected the reproductive success of fleas. However, the impact of this induced host response on flea reproduction depended on the birds' natural level of immunocompetence, assessed by the phytohaemagglutinin (PHA) skin test. Flea fecundity significantly decreased with increasing PHA response of the nestlings in previously parasite-exposed broods. No relationship between flea fitness and host immunocompetence was, however, found in previously unexposed broods. The PHA response thus correlates with the nestlings' ability to mount immunological or physiological defence mechanisms against hen fleas. No significant interaction effect between early flea exposure and food supplementation on the parasites' reproductive success was found.;5. Our study shows that the reproductive success of hen fleas is linked to the hosts' food supply early in life and their ability to mount induced immunological or physiological defence mechanisms. These interactions between host quality and parasite fitness are likely to influence host preference, host choice and parasite virulence and thus the evolutionary dynamics in host-parasite systems.

Maternal modulation of natal dispersal in a passerine bird: An adaptive strategy to cope with parasitism?

The decision of how far to disperse from the natal territory has profound and long-lasting consequences for young animals, yet the optimal dispersal behavior often depends on environmental factors that are difficult or impossible to assess by inexperienced juveniles. Natural selection thus favors mechanisms that allow the adaptive and flexible adjustment of the offspring's dispersal behavior by their parents via either paternal or maternal effects. Here we show that different dispersal strategies maximize the reproductive success of young great tits (Parus major) originating from a parasite-infested or a parasite-free nest and demonstrate that differential transfer of maternal yolk androgens in response to parasitism can result in a modification of the offspring's dispersal behavior that appears adaptive. It demonstrates that prenatal maternal effects are an important yet so far neglected determinant of natal dispersal and highlights the potential importance of maternal effects in mediating coevolutionary processes in host-parasite systems.