Two recent studies use different genetic approaches to uncover the past and present population structure of several penguin species.
Penguin colonies are a goldmine for nature documentaries. Many viewers have followed the life story of an adolescent Emperor Penguin (Aptenodytes forsteri) or the romantic escapades of Adélie penguins (Pygoscelis adeliae). But did you ever wonder about the dynamics between different colonies of the same species? Do individuals move between breeding grounds or do they remain loyal to their colonies? A recent study in Molecular Ecology mapped the genetic structure across five penguin species, representing 32 colonies.
Four of the five species showed low levels of genetic differentiation between the colonies, which could be thousands of kilometers apart. It concerns Emperor Penguin, King Penguin (Aptenodytes patagonicus), Chinstrap Penguin (Pygoscelis antarcticus) and Adélie penguin. All these species are pelagic, they spend at least some part of their life in the open ocean. This behavior facilitates exchange between colonies, resulting in gene flow which prevents genetic differentiation.
The fifth species in this study – the Gentoo Penguin (Pygoscelis papua) – showed high levels of genetic differentiation between the colonies. These penguins have a coastal lifestyle, they rarely swim into the open ocean but prefer to stay close to the shore. In addition Gentoo Penguins tend to breed where they were born (biologists call this natal philopatry). These characteristics result in low levels of gene flow between the colonies, leading to genetic differentiation.
Apart from life history traits, environmental factors can also determine patterns of gene flow. The Antarctic Polar Front is the boundary between cold Antarctic waters and warmer sub-Antarctic waters. This front acts as a barrier to dispersal for several penguin species, which is reflected in the genetic patterns. For example, King Penguins from South Georgia (the only breeding colony south of the front in this study) were the most divergent even though they were not the most distant colony in this species. Penguins from distant colonies, such as Crozet and the Falkland Islands (about 7500 km apart) were genetically more similar each other than each colony was to the penguins on South Georgia.
Another recent study, published in the journal Molecular Phylogenetics and Evolution, focused on population dynamics of the genus Eudyptes in New Zealand. The ranges of these penguins have contracted over the years, possibly affecting their population sizes. Here, the researchers took a different approach. Instead of sequencing only contemporary populations, they obtained ancient mtDNA from several bone samples and compared the results with present-day penguins.
Looking at the distribution of haplotypes over time revealed no loss of genetic diversity. Moreover, the reconstructed population history of one species, the Fiordland Crested Penguin (Eudyptes pachyrhynchus), indicated constant population size over the last millennium. Despite range contractions, the penguin populations seems to be doing fine. The authors write that “importantly, in cases where populations are genetically well connected, range contractions do not necessarily result in substantially reduced population sizes and genetic diversity.”
Conservation of Penguins
Both studies provide important insights for penguin conservation. Pinpointing the barriers of dispersal can inform which populations are connected by gene flow and could potentially be managed as one unit. In addition, the use of ancient DNA can provide a perspective on the evolutionary history of population and how it has dealt with previous changes. Together these approaches can improve the way conservationists make decisions.
Clucas, G. V., Younger, J. L., Kao, D., Emmerson, L., Southwell, C., Wienecke, B., Rogers, A.D., Bost, C.-A., Miller, G.D., Polito, M.J., Lelliot, P., Handley, J., Crofts, S., Philips, R.A., Dunn, M.J., Miller, K.J. & Hart, T. (2018). Comparative population genomics reveals key barriers to dispersal in Southern Ocean penguins. Molecular ecology, 27(23), 4680-4697.
Cole, T.L., Rawlence, N.J., Dussex, N., Ellenberg, U., Houston, D.M., Mattern, T., Miskelly, C.M., Morrison, K.W., Paul Scofield, R., Tennyson, A.J.D., Thompson, D.R., Wood, J.R., Waters, J.M. (2018) Ancient DNA of crested penguins: Testing for temporal genetic shifts in the world’ s most diverse penguin clade. Molecular Phylogenetics and Evolution.