The attractiveness hypothesis predicts that females should bias the sex ratio of their offspring towards sons when mated to attractive males. Females of many socially monogamous bird species commonly engage in extra-pair fertilizations (EPFs). Assuming that extra-pair males are more attractive to females than their social partners, and that sons inherit superior traits from their fathers, extra-pair young should be more likely males. According to the maternal condition hypothesis male-biased sex ratio in offspring should be also associated with better female body condition. We evaluated these ideas in the scarlet rosefinch (Carpodacus erythrinus), socially monogamous songbird with moderate level of extra-pair fertilizations. Contrary to the attractiveness hypothesis we have found no significant effect of paternity (within-pair or extra-pair) on the sex of individual offspring. Furthermore, data did not suggest that females mated to males with more elaborated plumage colour were more likely to produce sons. However, consistently with the maternal condition hypothesis, high-quality females produced more sons than daughters. Our results indicate that scarlet rosefinch females may not be able to manipulate the primary sex ratio of their offspring in relation to the attractiveness of their mate, but they may adjust it according to their own condition.
Adaptive immunity is commonly viewed as a unique vertebrate feature. A misleading view on vertebrate longevity compared to non-vertebrate animals together with oversimplification of ‘invertebrate’ phylogeny sometimes serves for justifying the limitation of adaptive immunity exclusively to vertebrates. However, here we emphasise that the borderline for differentiation between ‘innate’ and ‘adaptive’ immunity may be fuzzy and artificial. In each taxon, the feature of bearing a particular immunological mechanism should reflect its costs and benefits in a given ecological context. Hence, in invertebrates with a long lifespan some kind of acquired immunity could be expected. Indeed, several recent studies support this view. We therefore stress that the definition of ‘adaptivity’ of immune response should reflect the system function instead of a certain molecular mechanism adopted. If these altered criteria are considered then several pieces of recent evidence indicate that the adaptive immunity in animals might have arisen several times independently and in very different forms.
In the last decade a great effort has been devoted in animal evolutionary ecology to searching for interindividual and interspecific differences in anti-parasite resistance. Although many examples of variability in health-related traits were described in natural animal populations, our knowledge about the underlying genetic features dermining this variance is only limited. It has been shown in numerous examples in laboratory animals, domestic animals and humans that variation in the Major histocompatibility complex (MHC) is unable to explain all known genetically determined immunological variation in animals. Still MHC is so far the only gene cluster studied in ecological immunology of free-living animals. In this review we therefore map the potential importance of another group of immunity genes, the Toll-like receptors (TLRs). These innate immunity receptors belong among the most essential components of animal pathogen-recognition system and being reasonably polymorphic they might be responsible for substantial part of variation in disease-resistance in animals.