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.