A review of the systematics and taxonomy of Pythonidae: an ancient serpent lineage

Abstract

Here we review research over the past quarter century regarding the systematics and taxonomy of an ancient, popular and economically valuable group of snakes referred to as pythons (Serpentes, Pythonidae). All recent phylogenetic studies recognize the pythons as monophyletic; however, the phylogenetic relationships at supraspecific levels are conflicting, and many of the relationships recovered are paraphyletic. We identify several taxonomic changes as necessary to clarify supraspecific relationships and which resolve the issue of paraphyly recovered in several studies. Overall, our review of the phylogenetic systematics of pythons points to considerable incongruence among recovered relationships. Instances of paraphyly emerge, low node support is detected, and terminal taxa are unstable across phylogenetic hypotheses. We thus recognize that pythonid gene trees have been unable, for various reasons, to reveal the true species tree. This occurrence is not unexpected and can arise from incomplete taxon sampling, long-branch attraction and repulsion, homoplasy, ancestral polymorphism, and, more notably, the anomaly zone. These phenomena ultimately yield incomplete lineage sorting, or the failure of lineages to coalesce over evolutionary time. We discuss future directions to resolve these troubling issues. Without resolution, adaptive hypotheses about pythons will be limited, including hypotheses of geographic origin. Analyses that recover the clade Python as sister to the Indo-Australian clade are interpreted to support a Laurasian origin of Pythonidae. In contrast, a Gondwanan origin is supported when the Indo-Australian clade is recovered as basal to the Python clade. We describe the morphology of two recently proposed genera. Finally, we designate and describe the neotype for Morelia azurea and offer a list of the currently accepted python species and their taxonomy.

Evolution of extreme ontogenetic allometric diversity and heterochrony in pythons, a clade of giant and dwarf snakes

“…They exhibit their maximum taxonomic, phenotypic, and ecological diversity in the Australasian region (Barker et al. ). Several aspects of this family make them an excellent model for the study of morphological diversity, adaptation, and allometry.…”

Facultative thermogenesis during brooding is not the norm among pythons

“…The Pythonidae is divided between two primary phylogenetic clades, an Afro-Asian clade with two major lineages and an Indo-Australian clade with eight major lineages (Reynolds et al 2014; for recent review, see Barker et al 2015). The two species with confirmed facultative thermogenesis are in the different clades-P. molurus within the Afro-Asian group and M. spilota within the Indo-Australian group.…”

“…Pythons are ectothermic throughout most of life, but during brooding the females of some species are known to increase their metabolic rate and exhibit muscular twitching, termed facultative thermogenesis. While widely accepted as a trait of pythons in general, of the 44 extant python species (Barker et al 2015), facultative thermogenesis has been confirmed in only two species: the Burmese python (Python molurus) (Vinegar et al 1970), which has since been broken into two species (P. molurus and P. bivitattus, Jacobs et al 2009) and two subspecies of the carpet python (Morelia spilota spilota) (Slip and Shine 1988); (M. s. imbricata) (Pearson et al 2003). In Abstract Facultative thermogenesis is often attributed to pythons in general despite limited comparative data available for the family.…”

Birds in a bush: Toward an avian phylogenetic network

“…Several studies using multilocus data reported high levels of incomplete lineage sorting, hampering the estimation of species trees (e.g., Pollard et al 2006, Willis et al 2007, Kutschera et al 2014, Barker et al 2015. So, along with reticulation, incomplete lineage sorting results in a deviation from a tree-like depiction of evolutionary histories in a species tree.…”