Digit ratios have poor indicator value in a wild bird population

Early androgen exposure is known to have long-lasting effects on phenotype, behaviour and even fitness, but difficulties in measuring the exposure hinders the study of its importance in evolutionary context. Digit ratios have been highlighted as a potential easy-to-measure indicator of early steroid exposure, as they have been suggested to reflect steroid, mainly testosterone levels during prenatal development. However, evidence for digit ratios reflecting early steroid levels is weak, as experimental studies, especially in wild populations, are scarce. We studied the association between maternally derived yolk androgens and digit ratios (2D:4D, 2D:3D and 3D:4D) using both correlative data and a rather high level of experimental elevation of yolk androgens in a passerine bird, the pied flycatcher (Ficedula hypoleuca). We also examined whether digit ratios have indicator value in an evolutionary context by studying correlations between digit ratios and reproductive traits, secondary sexual traits and exploratory behaviour. We did not find any association between digit ratios and yolk androgen level either in correlative or experimental data. Digit ratios were neither related to any of the reproductive and secondary sexual traits or exploratory behaviour measured. There was, however, a sex difference in 2D:3D and 3D:4D of adult birds (due to second and fourth digits being shorter in females), which was not apparent in fledglings or captivity-raised juveniles. This suggests that either the sex difference may develop as late as during the sexual maturation for breeding. These results indicate that, in this species, digit ratios are not reliable markers of maternally derived yolk androgen exposure and that they bear little relevance as correlates of the adaptive traits we measured

Adults’ Reactions to Infant Cry and Laugh: A Multilevel Study

Starting from the assumption that caregiving behaviours are regulated at different levels, the aim of the present paper was to investigate adults’ reaction to salient infant cues by means of a multilevel approach. To this aim, psychophysiological responses (Heart Rate Variability), implicit associations (SC-IAT-A), and explicit attitudes (semantic differential) toward salient infant cues were measured on a sample of 25 non-parents adults (14 females, 11 males). Moreover, the trait anxiety and the individual noise sensitivity were considered as controlling factors. Results showed that adults’ responses were moderated by the specific measure considered, and that responses at the different levels were only partially consistent. Theoretical and practical implications were discussed