Seasonal migration is one of the most amazing biological phenomena, involving billions of individuals each year. Songbirds undergo one of the most iconic migrations; they can weigh as little as 3 grams, migrate up to 15,000 km and complete this trek at night.
Considerable variation has been documented in this behaviour, in both the propensity to migrate and the selection of migratory routes (i.e., migratory orientation). During my Postdoc I am examining the role hard- and soft-coded changes could play in generating this variation. Hard-coded changes could involve changes in the DNA sequence or gene expression; soft-coded changes could be epigenetic and involve changes in DNA methylation. I will focus on the European blackcap for this work. This species is iconic for studies of migration; it exhibits tremendous variation in migratory behaviour and some of the first selection and cross-breeding experiments were conducted on this species. Accordingly, it provides the perfect setting to begin examining the genetic and epigenetic basis of variation in this behaviour. Photo credit Wikipedia.
I conducted most of this work in a migratory divide between inland and coastal Swainson’s thrushes. Migratory divides are contact zones between populations that breed adjacent to one another but use different routes on migration. Swainson’s thrushes breed next to one another in western North America, the coastal group migrates south to Mexico and Central America while the inland group migrates southeast to South America. Using recently miniaturized light-level geolocators, we showed that hybrids between these groups take intermediate routes on migration over mountain chains and arid regions that pure forms avoid. These areas are likely difficult to navigate, leading to a reduction in hybrid survival and helping to maintain reproductive isolation between Swainson’s thrushes. We used next-generation sequencing techniques to describe the genomic landscape of differentiation between these groups and identify process that could generate the patterns we saw. We also used museum collections to conduct a comaarative analysis examining migration’s role in the speciation of North American birds in general.
Work for my Masters focused on a hybrid zone between brown lemurs in southeastern Madagascar. Research at the center of the hybrid zone suggested that it was stable. We collected morphological, genetic and climate data along a transect through this zone to confirm this suggestion and show that ecological selection may actually favour hybrids at the center of the zone. Some of the strongest support for this suggestion came from the observation that hybrids are equally as fit as parental forms and occur in novel or transitional habitats. In addition, estimates of linkage disequilibrium were not elevated at the zone’s center. This was the first time molecular genetic evidence had been used to show that hybrids may actually be favoured in intermediate habitats. In addition, the white-collared lemur is listed as endangered on the IUCN Red List; hybridization with the more abundant red-fronted lemur could have had a large, negative impact on this species.
As is often the case when undertaking field work in remote areas, we uncovered a few of Madagascar’s secrets along the way, including the presence of the golden bamboo lemur in the Andringitra region. At the time, this species was down to 300 individuals and is currently of major conservation concern.