Continuous variation rather than specialization in the egg phenotypes of Cuckoos (Cuculus canorus) parasitizing two sympatric reed warbler species

The evolution of brood parasitism has long attracted considerable attention among behavioural ecologists, especially in the common cuckoo system. Common cuckoos (Cuculus canorus) are obligatory brood parasites, laying eggs in nests of passerines and specializing on specific host species. Specialized races of cuckoos are genetically distinct. Often in a given area, cuckoos encounter multiple hosts showing substantial variation in egg morphology. Exploiting different hosts should lead to egg-phenotype specialization in cuckoos to match egg phenotypes of the hosts. Here we test this assumption using a wild population of two sympatrically occurring host species: the great reed warbler (Acrocephalus arundinaceus) and reed warbler (A. scirpaceus). Using colour spectrophotometry, egg shell dynamometry and egg size measurements, we studied egg morphologies of cuckoos parasitizing these two hosts. In spite of observing clear differences between host egg phenotypes, we found no clear differences in cuckoo egg morphologies. Interestingly, although chromatically cuckoo eggs were more similar to reed warbler eggs, after taking into account achromatic differences, cuckoo eggs seemed to be equally similar to both host species. We hypothesize that such pattern may represent an initial stage of an averaging strategy of cuckoos, that – instead of specializing for specific hosts or exploiting only one host – adapt to multiple hosts

PARENTAL CARE OF NESTLINGS IN THE SLATY-BACKED NIGHTINGALE-THRUSH (CATHARUS FUSCATER) IN EASTERN ECUADOR

No abstract

Sex Allocation in Relation to Host Races in the Brood-Parasitic Common Cuckoo (Cuculus canorus)

Sex allocation theory and empirical evidence both suggest that natural selection should favour maternal control of offspring sex ratio in relation to their ability to invest in the offspring. Generalist parasites constitute a particularly interesting group to test this theory as different females commonly utilize different host species showing large variation in provisioning ability. The common cuckoo (Cuculus canorus) is a generalist brood parasite that lays its eggs in the nest of many different passerine birds, but each female tends to specialize on one particular host species giving rise to highly specialized host races. The different host species show large variation in their ability to invest in the parasitic offspring, presenting an opportunity for female cuckoos to bias offspring sex ratio in relation to host species quality. Here, we investigate host-race specific sex allocation controlling for maternal identity in the common cuckoo. We found no evidence of any significant relationship between host race and sex ratio in one sympatric population harbouring three different host races, or in a total of five geographically separated populations. There was also no significant association between host quality, as determined by species-specific female host body mass, and cuckoo sex ratio. Finally, we found no significant relationship between individual cuckoo maternal quality, as determined by her egg volume, and sex ratio within each host race. We conclude that the generalist brood-parasitic common cuckoo show no significant sex-ratio bias in relation to host race and discuss this finding in light of gene flow and host adaptations

Wstępne obserwacje nad ptakami Karkonoskiego parku narodowego =Preliminary birds observations in Karkonosze National Park

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Between monogamy and promiscuity - how does behavioural ecology explain the diversity of avian mating systems?

The evolution of diversity and complexity of avian mating systems can be explained basing on sociobiological assumption that individuals maximize their fitness (selection acts on the level of individuals or genotype but not population) and no behaviour could have evolved for "the good of a species". As a result there is a conflict between sexes and a mating system is the outcome of this conflict. Within a small genus Acrocephalus the whole spectrum of mating systems from monogamy to promiscuity has been described. The social relationships roughly reflect genetic links (genetic paternity and maternity), but no species is in 100% genetically monogamous. The diversity of mating systems can be found not only while comparing different species but also within a species. In various populations of the same species genetic monogamy or polygyny can dominate. Moreover, such differences can be found in the same population in different years. This suggests the influence of environmental factors. These facts contradict the hypothesis that closely related species have similar mating systems as a result of common evolutionary history. For example, two closely related species from the genus Acrocephalus (in the past considered as sibling species): sedge warbler and aquatic warbler have completely different mating systems. Among environmental factors most important seem to be potential food resources. In general, the diversity of mating systems in the genus Acrocephalus supports the hypothesis that non-monogamous mating systems occur in habitats rich in food resources in which males can partly (sedge warbler, great reed warbler) or totally (aquatic warbler) be emancipated from parental duties