Super-normal length song preferences of female zebra finches (Taeniopygia guttata) and a theory of the evolution of bird song

Two way choice tests show a preference of female zebra finches for male songs four standard deviations longer than normal song. Further tests show the ontogeny of this preference to parallel song learning in general as well as a preference for songs with entirely heterogeneous notes compared to songs with four note repeats. These findings are discussed in relation to a theory of the evolution of bird song from bird calls due to female preferences for longer, more complex vocalizations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Distribution of the nuclear receptor for vitamin D in female and male zebra finches,Taeniopygia guttata

In this study, we describe the distribution of high affinity binding sites for 1,25(OH)₂-vitamin D₃ (1,25-D₃) in the zebra finch (Taeniopygia guttata). Four hours following the injection of tritiated 1,25-D₃, binding of the steroid hormone was found primarily in the cell nuclei of a variety of differnt organs. Neurons in numerous discrete regions of the forebrain were labeled. These forebrain regions included the nucleus accumbens, nucleus dorsomedialis posterior thalami, lobus parolfactorius, nucleus septalis lateralis and medialis, nucleus septalis, lamina medullaris dorsalis, nucleus striae terminalis, palaeostriatum augmentatum, and stratum griseum. The choroid plexuses, however, remained clear. Labeled cells were seen in several organs of the alimentary canal, in both the exocrine and the endocrine pancreas, in the proximal tubules of the kidney, in the spleen, in the bursa of Fabricius, and in the heart. The basal cells of the uropygial gland were also labeled. No specific retention was evident in the gonads of either sex. Vitamin D is thus bound by cells in systems with widely different functions. Since several of the labeled tissues are not primarily involved in calcium homeostasis, the data support the concept that vitamin D-soltriol is a steroid hormone that acts as a seasonal neuroendocrine-endocrine regulator and somatotrophic modulator.     

Costly steroids: egg testosterone modulates nestling metabolic rate in the zebra finch

The transfer of non-genetic resources from mother to the offspring often has considerable consequences for offspring performance. In birds, maternally derived hormones are known to influence a variety of morphological, physiological and behavioural traits in the chick. So far, the range of these hormonal effects involves benefits in terms of enhanced growth and competitive ability as well as costs in terms of immunosuppression. However, since yolk hormones can enhance growth and begging activity, high levels of these hormones may also involve energetic costs. Here, we show experimentally that elevated levels of prenatal testosterone increase resting metabolic rate in nestling zebra finches (Taeniopygia guttata). Surprisingly, however, elevation of prenatal testosterone did not result in higher growth rates and, thus, differences in resting metabolism do not seem to be linked to nestling growth. We conclude that apart from immunosuppressive effects, high levels of egg steroids may also entail costs in terms of increased energy expenditure.     

Adrenocortical responses in zebra finches (Taeniopygia guttata): individual variation, repeatability, and relationship to phenotypic quality

Although individual variation is a key requirement for natural selection, little is known about the magnitude and patterns of individual variation in endocrine systems or the functional significance of that variation. Here we describe (1) the extent and repeatability of inter-individual variation in adrenocortical responses and (2) its relationship to sex-specific phenotypic quality, such as song duration and frequency and timing of egg laying. We measured adrenocortical responses to a standardized stressor in zebra finches (Taeniopygia guttata) at two life history stages: approximately day 16 (nestlings) and 3 months of age (sexually mature adults). Subsequently, we assessed phenotypic (reproductive) quality of all individuals as adults. Marked inter-individual variation in the adrenocortical response was seen in both sexes and ages, e.g., stress-induced corticosterone ranged from 2.2 to 62.5 ng/mL in nestlings and 5.0-64.0 ng/mL in adults. We found sex differences in (a) inter-individual variation in the adrenocortical response, (b) repeatability, and (c) relationships between corticosterone levels and phenotypic quality. In males, variation in nestling corticosterone was weakly but positively correlated with brood size and negatively correlated with nestling mass (though this relationship was dependent on one individual). There was no significant correlation of adrenocortical responses between two stages in males and adult phenotypic quality was significantly correlated only with adult corticosterone levels. In contrast, in females there was no relationship between nestling corticosterone and brood size or mass but adrenocortical response was repeatable between two stages (r2=0.413). Phenotypic quality of adult females was correlated with nestling baseline and adrenocortical response.     

Environmental transmission of a personality trait: foster parent exploration behaviour predicts offspring exploration behaviour in zebra finches

Consistent behavioural differences among individuals are common in many species and can have important effects on offspring fitness. To understand such ‘personality’ variation, it is important to determine the mode of inheritance, but this has been quantified for only a few species. Here, we report results from a breeding experiment in captive zebra finches, Taeniopygia guttata, in which we cross-fostered offspring to disentangle the importance of genetic and non-genetic transmission of behaviour. Genetic and foster-parents’ exploratory type was measured in a novel environment pre-breeding and offspring exploratory type was assessed at adulthood. Offspring exploratory type was predicted by the exploratory behaviour of the foster but not the genetic parents, whereas offspring size was predicted by genetic but not foster-parents’ size. Other aspects of the social environment, such as rearing regime (uni- versus biparental), hatching position, brood size or an individual''s sex did not influence offspring exploration. Our results therefore indicate that non-genetic transmission of behaviour can play an important role in shaping animal personality variation.