Molecular techniques and avian reproductive biology: Integrating field and laboratory investigations

Understanding precise molecular mechanisms that wild animals rely upon to cope with their environment is uncommon because molecular techniques have been primarily used in carefully controlled circumstances, such as the laboratory. Additionally, many wild animals are not known well enough to use them as molecular model systems. Nevertheless, gaining a deeper knowledge about life processes in other creatures provides a clearer understanding of human biology, and molecular techniques are the most powerful and direct tools available for this purpose. Despite these practical limitations, some animals, particularly birds, can reveal biologically relevant information. For example, white-crowned sparrows, Zonotrichia leucophrys, are among the best-known bird species: They are accessible both as free-living and captive individuals and can thus serve as a model system for a variety of questions.; Described here are two molecular studies used to investigate reproductive biology in free-living and captive populations of white-crowned sparrows. Additionally, the applicability of some of these techniques was demonstrated for other avian species.; Ultimate environmental signals have overt effects upon animals by causing adaptive changes in behavior, physiology, and morphology. Proximate environmental factors also intimately affect the internal hormonal milieu. Changes in hormone concentrations are correlated with biologically appropriate behavioral, physiological and morphological responses.; The presence or absence of certain hormones or hormone combinations can trigger functional responses in animals. However, other adaptive responses are mediated through discrete plasma concentrations of a single hormone. For example, three distinct plasma concentrations of testosterone have been described in white-crowned sparrows, Zonotrichia leucophrys, and each level corresponds with distinct physiological, morphological and behavioral responses in these birds.; Androgens mediate genomic effects through binding to a cytosolic ligand-dependent transcription factor, the androgen receptor (AR). When “activated”, this receptor binds the genome, altering gene expression. This differential expression of particular genes is correlated with observed alterations in physiology, morphology and behavior. But the precise mechanisms of how different plasma concentrations of androgens are translated into different functional responses remain mysterious.; To study monomorphic birds, identifying sex accurately and quickly can pose problems. To address that issue, several molecular methods for identifying sex in birds, particularly white-crowned sparrows, were compared.