GENES ON THE MOVE: CANDIDATE GENES AND LONG-DISTANCE MIGRATION IN BIRDS
Creators: name: BAZZI, GAIA
Publisher: name: Universit� degli Studi di Milano
Year: 2016

description: Bird migration is an adaptive strategy evolved to exploit the seasonal changes of resources by moving to different areas at different times of the year, as these become suitable. Migratory birds reach the breeding grounds when the food supplies enable them to breed and leave towards more suitable areas before the ecological conditions deteriorate; to this end, they must anticipate the changes in ecological conditions by weeks or even months to prepare for migration. Tis is allowed by the by the existence of an endogenous control of the annual schedule, that is kept in phase with seasons by means of external cues, such as photoperiod. The occurrence of a tight endogenous control of migration hint that migration is under a strong genetic influence and the broad among-species, -populations and -individuals differences in migratory traits are partly triggered by variation at genes controlling migratory behaviour. Identifying which genes underline the phenotypic variation observed in natural populations, and to which extent, is of broad evolutionary and conservation interest. It has been suggested that variation in migratory traits could be the outcome of polymorphism at relatively few regions or loci with additive effects on a variety other genes. Hence, in recent years, several studies have focused on the polymorphism of phenological candidate genes, that may explain the variability of behavioural traits. Most of the phenological candidate genes studied so far are involved in the ?core circadian oscillator? (CCO), an auto-regulated negative feedback loop that modulates the photoperiodic response and sets the circadian and circannual rhythms. The Clock and Adcyap1 genes are among the best studied candidate genes involved in the photoperiodic response and in the circannual rhythmicity. Both the genes show a polymorphism in short tandem repeat sequences that may affect the gene function or the post-transcriptional processes and that have been linked to variation in the timing of seasonal events and other behavioural traits in several vertebrate species. However, no study has investigated the effect of Clock and Adcyap1 genotype on migration phenology and on migration distance directly in wild birds. Hence, the aim of this thesis is to investigate whether polymorphism at candidate genes affects the timing of migration and the migration distance in avian species, with particular reference to Clock and Adcyap1 genes. I found Clock allele size to predict the timing the timing of migration in different long-distance migratory bird species. The direction of the association was coherent with previous studies and across species (longer allele being associated with a delayed phenology), the only exception being the willow warbler (Phylloscopus trochilus). Moreover, Adcyap1 allele size was associated with the migration distance in a Nearctic-Neotropical migratory bird. In such species the genotype-phenotype association was stronger among the northern, long-distance migratory populations than among the southern ones. Finally, I found that Clock allele size increased with breeding latitude across species and that Clock gene diversity was depleted among the species migrating over longer distances, that show delayed and more concentrated migration periods. To conclude, the findings from this thesis deepen our understanding of the role of polymorphism at candidate gene in shaping avian behaviour, by highlighting that Clock and Adcyap1 polymorphisms are involved in the control of migration.