Into Africa: The biogeography of the genus Python in Africa

Most of the nine genera and 38 species in the family Pythonidae occur in south-east Asia and Australasia, but the genus Python is distinctive in that it also occurs in sub-Saharan Africa. There is a large distribution gap for Python between Africa and south-east Asia, but fossil evidence suggests Python once occurred in this gap, as well as in Europe until the mid-Miocene. However, because all African species have not previously been included in any previously published phylogeny, their monophyly has not been established. Further, it has been suggested that the genus Python may have an Asian origin, and this scenario would require the African species to be monophyletic. Otherwise, multiple independent dispersals into Africa would be required to explain current day biogeographic patterns. To test these competing hypotheses, a dated phylogeny was constructed based on one nuclear and two mitochondrial genes and biogeographic scenarios evaluated using ancestral range reconstruction. In addition, fossil evidence was appraised as supporting evidence for their paleo-distribution but also to evaluate the hypothesis that large pythons (e.g., > 6 m in body length) are restricted to warmer climatic zones, and we suggest this influenced their paleo- and present-day distributions. The dated phylogeny indicates monophyly for the African species, diverging from the Asian species approximately 33 Mya. Ancestral area reconstruction supports an Asian origin for the genus, with a single dispersal event to Africa after which species diversified across the continent. We find no support for multiple dispersal events into Africa. Accounting for the distribution of fossils, it appears that Python, including large-bodied species, were once more widespread, but ranges contracted in response to global cooling since the mid-Miocene, and they are now excluded from temperate (i.e., Europe, Iranian plateau) as well as hyper-arid areas (i.e., Arabian, Saharan and Namib deserts). The genus Python originated in Asia, with a single ancestral lineage entering Africa around 33 Mya where it diversified into four extant species. Fossil evidence reveals that Python was much more widespread but with mid to late Miocene global cooling, the African and south-east Asian clades became isolated geographically from each other. Large body size may have had an important influence on geographic range, limiting species to the warmer areas. Long-term global cooling has presumably driven range contractions, creating the distribution gap, and possibly causing extinctions of Python species.