Phylogeographic studies of a species aim to uncover how historical processes could account for their geographical distribution, considering the genetic patterns within that species. Fossil records can provide a window into their ancient distributions and have shown that the widespread distribution of the red fox across Eurasia and North America has notably been maintained through the ages to the modern day. However a comprehensive study of the phylogeography of the red fox across its entire geographic distribution has been lacking. Frank Hailer and Verena Kutschera, from the Biodiversity and Climate Research Centre, Germany, and colleagues set about filling in the phylogeographic gaps in our knowledge of the red fox using mitochondrial DNA sequences, as published in a recent article in BMC Evolutionary Biology. Hailer and Kutschera told us more about what their findings revealed.
Why is studying the phylogeography of the red fox important?
The red fox is the most widely distributed carnivore in the world and highly flexible with regard to habitat choice. Red foxes are able to adapt not only to natural habitats like forests, grasslands, mountains, and deserts, but also to environments that have been strongly shaped by humans: even city-fox populations are successfully established in highly urbanized areas, for example in Zurich or Melbourne. The basis for studying adaptation to such different habitats is to investigate the phylogeography of the red fox, to identify regionally restricted genetic lineages that might be phenotypically adapted to their region-specific niche.
What did your study set out to investigate and how?
Our aim was to study range-wide phylogeographic processes in the red fox, by adding new data from a region previously not studied (Central Siberia) and from European populations in addition to those previously published, as well as using existing publicly available data. Utilizing mitochondrial DNA fragments from a total of 729 red foxes, we have analyzed phylogeographic patterns over the whole distribution range of the red fox. Based on these findings, we have established the first timeline of the main evolutionary events in red foxes, using a modern Bayesian coalescence approach with several fossil calibration points. This timeline enabled us to get a better understanding of migration events of red foxes during glacial periods, when land bridges were formed due to sea-level changes.
Although you generally found wide ranging gene flow across the areas you studied, you also identified some areas with restricted gene flow. Which areas were these? Do foxes here show particular phenotypic adaptations?
It was not a huge surprise to find that red foxes, a species that we know is capable of far ranging movements in the landscape, showed strong signals of gene flow across vast geographic distances. It makes sense that you would not see a lot of population structuring in such a species. We did however observe that gene flow in some regions had been interrupted, in particular on islands. Once a terrestrial species reaches an island – in foxes this likely happened at glacial times, when sea levels were lower and those islands were physically connected to the mainland – it typically gets isolated from mainland populations and develops particular characteristics.
We see genetic signals of several such events of isolation on islands. First, red foxes crossed the Bering strait and colonized the North American continent (a very big ‘island’, if you wish), at some point since the mid Pleistocene epoch. Red foxes also colonized Japan with at least 3-4 different genetic lineages. One lineage arrived in the mid or late Pleistocene to the more southern islands of Honshu and Kyushu. Later in the Pleistocene, additional lineages colonized the more northern Japanese island of Hokkaido.
A recent study by Ceiridwen Edwards from the University of Oxford, UK and colleagues showed a very similar picture for red foxes on the British Isles. Even more fascinating are findings a few years ago by Benjamin Sacks from University of California, Davis, USA and colleagues. They demonstrated that red foxes in the Sacramento Valley in California are not only genetically distinct, but also show particular adaptations to their environment. This shows that, despite their far-ranging individual movements, red foxes do adapt to local conditions. Similar results have been obtained from other highly dispersive species like coyotes and wolves.
What excited you the most when you were looking at your data?
There are only a few other species with a similar distribution, mobility, and ecological flexibility as the red fox; for example the brown bear and the grey wolf. All three species occur in an area that spans climatic zones from the arctic to the deserts. We were therefore very excited when we realized that the phylogeographic patterns of the three carnivores were also very similar. All three species have one range-wide distributed genetic lineage and only a few regionally restricted lineages. These results are a great demonstration of the principle that ecologically similar species react similarly to climatic and habitat changes.
How do you think your study will inform future work?
We evolutionary geneticists live in a very exciting era, with new developments in sequencing technology and advances in statistical analysis techniques that allow us to address questions that were impossible to address just a decade ago. In particular, we can link specific phenotypic traits of a species to a genetic trait, and finally get at the core of evolutionary processes. We hope that our timeline of major phylogeographic events in red foxes will serve as a backbone for future studies that will investigate population structuring and adaptive processes in red foxes. Red foxes can be reared in captivity, and non-invasive monitoring techniques allow collection of genetic as well as physiological data in the field. It will be interesting to link such research areas in the future.