For most bird species reproduction is seasonal and breeding is regulated by environmental cues including photoperiod, food availability, temperature, and social interactions. My research interests lie in understanding how these environmental factors coordinate both the timing and the progression of reproduction and associated behaviour. I will give an overview of recent research giving examples from both wild free-living passerines and domesticated species. The change in day length is one key environmental factor used by birds to determine the time of year to breed. Birds use extraretinal photoreceptors and their circadian system to interpret the light:dark signal and here I will describe some recent findings relating to the mechanisms of photoperiodic internal timing that are critical for stimulating gonadal growth. Gonadal development is under the control of gonadotrophin secretion from the pituitary gland and under increasing day lengths thyrotrophin triggers a flow of molecular events in the mediobasal hypothalamus to increase the synthesis of triiodothyronine which ultimately leads to gonadotrophin-releasing hormone synthesis and release until photorefractoriness. Nonetheless there is inherent flexibility for precisely when birds transition from their reproductive states. For example at the beginning of the breeding season temperature and rainfall give wild free living song sparrows, precise information about the timing of food peaks which are critical for their offspring’s survival; interestingly these same environmental factors also contribute to determining feather moult at the end of the breeding season. Investigations into the neurobiology of annual changes in song sparrow territorial and reproductive behaviour reveal changes in aromatase and testosterone sensitivity and neural activity in brain regions that form part of the social behaviour network. Sex steroids play a key role in regulating other reproductive behaviours such as sexual behaviour, but other neuroendocrine systems significantly contribute to reproductive success. Recent investigations into the neural mechanisms underlying complex social and parental care have highlighted the importance of the central mesotocin and vasotocin systems. Neurophysiological studies in zebra finches and Silkie bantam chickens have been particularly useful in elucidating brain mechanisms responsible for behaviours such as nest building, incubation and care of the chicks. There is also evidence that neuroendocrine adaptations underlie the unique behaviour required to maximize survival and reproductive success in capricious environments, e.g. in arctic-breeding passerines like the socially monogamous white-crowned sparrow and the polygynandrous Smith’s longspur. These species rapidly modulate their stress response and adapt their behaviour to optimise reproductive success in a very short breeding season which is often fraught with inclement weather events. Indeed the white-crowned sparrow is behaviourally insensitive to experimentally elevated testosterone and this insensitivity requires rapid and dynamic changes in the neuroendocrine system. With such wonderful examples of environmental adaptations and regulation, avian behavioural neuroendocrinologists are entering an exciting period. Using the annotation of many more avian species’ genomes to devise comparative genomic approaches and species-specific genetic tools, the identification of the genes responsible for integrating environmental information, neuroendocrine signals and reproductive behaviour is within our reach. Research supported by the BBSRC and NSF.
|Conference||Eleventh International Symposium on Avian Endocrinology|
|Period||11/10/16 → 14/10/16|