Repeatability of parental effort in male and female Pied Flycatchers as measured with doubly labeled water

Intensity of parental care is one of the critical factors affecting offspring growth and final size and thus is a key variable in life-history evolution. In the study population of Pied Flycatchers (Ficedula hypoleuca), it was previously shown that maternal daily energy expenditure was an important source of variance in offspring size and likelihood of infection by blood parasites. Thus, energy expenditure may be considered a parental-performance effect, and variation among females in the intensity of parental care they provide might itself be influenced by genetic differences, affording the opportunity for evolutionary change. To address whether parental work load is a consistent trait and thus may retain additive genetic variance, the same individuals were scored for mass-independent daily energy expenditure (DEE) across two consecutive breeding seasons, while feeding nestlings close to fledging. While DEE of females was significantly repeatable between years, this was not the case for males. DEE may retain additive genetic variance in females, although its expression may be obscured in males by their less constrained activity budgets and lower confidence of paternity.

Growth, nutrition, and blow fly parasitism in nestling Pied Flycatchers

The nutritional status of the host may play a major role in mediating the detrimental effects of parasites. We performed an experiment with the aim of determining whether increased food availability can compensate for the effects of ectoparasites on growth during the late nestling period, final size, and survival until fledging of Pied Flycatcher (Ficedula hypoleuca) nestlings. Nests were provided with supplementary food, treated with insecticide, given both treatments, or given neither treatment (control). Differences in the number of blood-sucking, ectoparasitic blow fly larvae (Protocalliphora azurea) occurred between treated nests. Nestlings in the group given supplementary food and with low numbers of parasites grew faster and had a higher haematocrit value than those in groups that were fumigated and given supplementary food, with nestlings from control nests attaining the lowest values. Nestling measurements did not differ between fumigated and food-supplemented groups. Although the final sizes attained did not differ among nestlings from the different experimental groups, there was a significant difference in the rates of increase in size among groups. Nestlings in nests fumigated and provided with extra food were (nonsignificantly) smaller and leaner than nestlings from the other groups at the beginning of the experiment, but were slightly larger and heavier (again nonsignificantly) at the end of the experiment. Thus, their growth was faster than that of the other groups. The results are discussed, highlighting problems related to the function linking intensity of parasit ism to host fitness and variation in external (climate, food) conditions.

Blood parasites of passerine birds from central Spain

Sixteen species of passerine birds captured during a 2.5 yr period in Central Spain were examined for hematozoa. Haemoproteus spp., Leucocytozoon spp., Trypanosoma spp., Plasmodium spp., and microfilariae were observed. The most prevalent species were in the genus Leucocytozoon. The majority of the records are new for Spain and some represent new host records. More than one-half of the birds examined were infected with at least one parasite species. These records are similar to those reported from other areas in northern Europe and the Iberian Peninsula.

Maternal effort mediates the prevalence of trypanosomes in the offspring of a passerine bird

The relationships between parental effort, offspring growth, and offspring blood parasitemias are poorly known. We examined the effect of parental effort on offspring size and prevalence of trypanosomes in peripheral blood of nestling Pied Flycatchers Ficedula hypoleuca aged 13 days. Trypanosome infections were likely to be shared by siblings, indicating the role of a common environment and/or shared genes in the susceptibility to infection. Broods infected by trypanosomes had reduced growth, but this was due to decreased parental, especially maternal, energy expenditure in broods with nestlings infected by trypanosomes. There was no association between parental infection with trypanosomes and both their energy expenditure and the infection of their broods. Under stressful conditions caused by low maternal energy expenditure, the immune response of nestlings during growth was probably impaired, in a way analogous to the relapses of blood parasitemias with reproductive effort in breeding animals.

Heritability estimates and maternal effects on tarsus length in pied flycatchers, Ficedula hypoleuca

Tarsus length has previously been shown to have an additive genetic component in some pied flycatcher populations. In addition to estimation of additive genetic variation by means of repeatability analyses at various ontogenetic stages and degrees of genetic resemblance, we explore in this paper variation among parent-offspring regressions between sexes and years, as well as the influence of hatching date, ectoparasite abundance, egg volume, and male and female condition on the tarsus length of their offspring. Mother-offspring regressions gave heritability estimates consistently higher than father-offspring regressions, although variation among years was large and both types of estimates yielded lower heritability values than those estimated by means of full-sib resemblance. This indicates that common environmental effects were inflating heritability estimates. There existed maternal effects via egg size, larger eggs fledging chicks with larger tarsi. Mean tarsus length of broods decreased with hatching date and, independently, with high loads of ectoparasitic, blood-feeding mites (Acari). The maternal effect via egg size persisted into the adulthood, and confounded the interpretation of differences between heritability slopes. We address the method of examining differences in parent-offspring regressions as a shorthand for estimating extra-pair copulation (EPC) rates. In our population, this method would give an EPC rate of 0-59%, depending on whether the analysis is performed with fledglings recruited to the breeding population or with offspring at the nest.

Environmental, ontogenetic, and genetic variation in egg size of Pied Flycatchers

Ontogenetic, genetic, and environmental variation in egg length, breadth, and volume were investigated in the Pied Flycatcher across four breeding seasons in central Spain. Egg length and breadth were poorly correlated and did not vary with laying date. There was an indication of decreasing egg breadth with increasing clutch size that may indicate a trade-off between both variables. Egg size increased with female condition and, independently, with territory quality. Mean egg size decreased with advancing female age, which is perhaps related to the increase of clutch size with age in this species. There were high, significant repeatabilities of almost all egg dimensions, including relative volumes of first and last eggs, among females, both within and between years. Also, nest boxes were repeatable in the relative volume of the last eggs of (different) females laying in them, suggesting an influence of territory quality on relative egg size. Territory quality also had positive influences on some egg measurements that were independent of female condition. Heritability, estimated by mother–daughter regression, was significant only for egg length. These results are discussed in relation to proximate constraints on egg formation, predictions from the brood-survival hypothesis, and a possible trade-off between clutch and egg sizes.