Search

Penguins in Antarctica and the sub-Antarctic have survived multiple glacial to inter-glacial transitions. However, anthropogenic climate change may exceed this natural variability in the rate and extent of warming. To accurately monitor the effects of climate change on natural populations, predict their local or global extinction risk, and design effective conservation management plans, we must first be able to define the borders of breeding populations. Regular dispersal of individuals from their natal colony to breed at another colony may mean that multiple colonies constitute a breeding population. By investigating patterns of intraspecific genetic variation, we can estimate the dispersal of individuals between colonies and identify any barriers to gene flow. Barriers to gene flow may be permanent or transient. Permanent barriers to gene flow may ultimately lead to speciation if populations diverge sufficiently, and so by investigating intraspecific population differentiation, we can potentially gain a window into the speciation process. Using both mitochondrial and nuclear genomic markers (single nucleotide polymorphisms, SNPs), and by comparing closely related species with different life histories across a range of habitats, I identify the historical and contemporary barriers to gene flow in emperor, king, gentoo, chinstrap and Adélie penguins. I find that historical glaciation during the last glacial period was significant in driving population divergence among small, refugial populations of Antarctic emperor penguins, but there was no evidence for this in their congener the sub- Antarctic king penguin. This is likely a result of the greater effects of glaciation in the Antarctic compared to the sub-Antarctic. I also show that high levels of contemporary dispersal among emperor penguin colonies has created at least four metapopulations, which span thousands of kilometres of coastline, and that dispersal between these metapopulations has largely eroded the historical population differentiation. King, chinstrap, and Adélie penguins also showed high levels of dispersal across distances of thousands of kilometres. This is in stark contrast to the gentoo penguin, in which colonies separated by less than 50 km were genetically differentiated, and large stretches of open-ocean appear to form permanent barriers to gene flow, promoting allopatric speciation in gentoo penguins. I find that the at-sea range of these species appears to determine these dispersal patterns. The pelagic foraging emperor, king, chinstrap and Adélie penguins, which range from hundreds to thousands of kilometres away from their colonies during the nonbreeding season, show high levels of dispersal and gene flow between colonies. However the coastal foraging gentoo penguin, which is resident at or near colonies year-round, shows very little dispersal and gene flow between colonies. Other barriers to gene flow identified were the Polar Front, which restricts gene flow among king and gentoo penguin colonies, and natal philopatry, which also appears to play a role in restricting gene flow among gentoo penguin colonies. The implications of these patterns of dispersal are discussed with respect to monitoring and management, and taxonomic revision is advised to recognise the incipient allopatric speciation identified between populations of gentoo penguins.