Gabriel J. Castaño-Villa

Baseline corticosterone and stress response in the Thorn-tailed Rayadito (Aphrastura spinicauda) along a latitudinal gradient.

Glucocorticoids are essential for life and their secretion is regulated by the hypothalamic-pituitary-adrenal axis (HPA). The HPA axis is often divided into two components: baseline glucocorticoids levels and stress response glucocorticoids levels, which are affected by changes in ambient temperature and productivity among others factors. An approximation to evaluate how a species copes with these changes is to evaluate differences of this hormone amongst populations of the same species that inhabit places ideally presenting all the possible combinations of temperature and productivity. We aimed to evaluate whether environmental temperature or productivity, represent challenges in terms of stress in the Thorn-tailed Rayadito (Aphrastura spinicauda). We examined circulating baseline levels of CORT and stress responses from three populations, covering the whole geographic distribution of the species across large gradients in weather conditions. If low temperature influences baseline CORT levels, we expect higher levels of this hormone in the southernmost population (higher latitude). However, if productivity is the factor that influences baseline CORT levels, we expect the contrary pattern, that is, lower values of this hormone in the southernmost population (more productive environment). We observed that baseline CORT levels presented lower values in the southernmost population, supporting the environmental productivity hypothesis. Secondly, we tested the hypothesis that individuals breeding at higher latitudes should have a lower stress response than individuals breeding at lower latitudes. Contrary to our expectations, we found that stress response did not vary among populations in any of the three years. We concluded that low environmental temperatures did not represent a stress situation for the Thorn-tailed Rayadito if food abundance was sufficient to support energetic demands.

Isolation and characterisation of eight microsatellite markers of the thorn-tailed Rayadito Aphrastura Spinicauda

Summary. Eight novel microsatellites were isolated and characterised in the thorn-tailed rayadito Aphrastura spinicauda in order to evaluate genetic diversity in three contrasting populations, two of them at the boundaries of the geographic range of the species. All loci were found to be polymorphic and 3–15 alleles were found per locus. Expected and observed heterozygosity ranged from 0.26 to 0.89 and from 0.27 to 0.87, respectively. Global and pairwise Weir and Cockerhams Fst showed that genetic differentiation was greater between the northern population and the ones in central and southern Chile. The eight markers developed will be useful to study the genetic diversity of the thorn-tailed rayadito across its distribution.

Sex-specific provisioning of nutritious food items in relation to brood sex ratios in a non-dimorphic bird

In birds, the frequency with which the parents feed the young can vary considerably. Because of sexual differences in the begging behaviour and/or differences in the food requirements of the nestlings, brood sex ratio (BSR) is an important factor that may influence parental provisioning behaviour. Disparities in the quantity and quality of prey received by the sexes have been reported in a range of sexually size-dimorphic birds. However, to our knowledge, no study has evaluated prey composition delivery to nestlings in relation to BSR in a non-dimorphic size bird species. Because BSR influences provisioning rate in dimorphic and non-size dimorphic species and because in dimorphic species, BSR influences prey composition delivered to the nest, we hypothesised that similar to dimorphic species, BSR may influence prey composition delivered to nestlings in non-size dimorphic species. We quantify parental provisioning rate and prey composition of prey delivered to nestlings in relation to BSR in the Thorn-tailed Rayadito (Aphrastura spinicauda) a non-dimorphic and altricial passerine bird. At the population level, we found that Thorn-tailed Rayadito mothers delivered more insect larvae to the nest when compared to the father, who provided the brood with a diet more diverse in composition. However, when we considered BSR, mothers delivered a greater quantity of arachnida and lepidoptera items (high-quality foods) in male-biased BSR. In addition, nestling weight gain increased in line with the proportion of high-quality food in the diet. Our results suggest that when considering non-dimorphic species, there may be more subtle, but nevertheless important, differences, in explaining parental care behaviour in species with bi-parental care.Significance statementIn birds, the frequency with which the parents feed the young can vary considerably. Because of sexual differences in the begging behaviour and/or differences in the food requirements of the nestlings, brood sex ratio is an important factor that may influence parental provisioning behaviour in sexual size species. For the first time, we evaluated prey composition delivery to nestlings in relation to BSR in a non-size dimorphic bird species. We found that the mother of the Thorn-tailed Rayadito delivered a greater quantity of lepidoptera and arachnida (high-quality food) items in a male-biased brood. In addition, nestling weight gain increased with the proportion of high-quality food in the diet. Our results suggest that in non-dimorphic species, there may be more subtle, but nevertheless important, differences in explaining parental care behaviour in species with bi-parental care.