Phylogeography in Response to Reproductive Strategies and Ecogeographic Isolation in Ant Species on Madagascar: Genus Mystrium (Formicidae: Amblyoponinae)

Purpose of the Study: Madagascar is a region of great biological diversity and complex microendemism patterns. Ants (Formicidae) are a hyperdiverse group, which afford finer scale information regarding microendemism than vertebrates, in part because of their reduced vagility. The purpose of this study is to use molecular phylogenetic methods along with geographic and habitat data to examine the diversification of a particular group of ants on the island of Madagascar. Procedure: We have assembled a nuclear and mitochondrial phylogeny of a genus of ants, Mystrium, from Madagascar. Species within the genus Mystrium display two different colonial reproductive strategies; six Mystrium species endemic to the island of Madagascar use dependent colony foundation (DCF) and have wingless ergatoid queens. Conversely, four species of Mystrium, two which are endemic to the island reproduce via independent colony foundation (ICF) and have winged queens. Thus, we are able to assess complex microendemism patterns and recent vertebrate derived species diversification hypotheses using an arthropod system with contrasting vagility. Findings: Among Mystrium species which use DCF there is a deep phylogenetic split between species which occur in more mesic conditions of the eastern rainforest and the more arid conditions of the western tropical dry-forest and southern spiny desert. While examining the phylogeographic signal of conspecifics, Mystrium species which reproduce by DCF display deep mitochondrial phylogenetic divergence. Mystrium species which reproduce by ICF display shallow mitochondrial phylogenetic divergence. Tropical rainforest Mystrium species also appear to be diverging due to isolation on mountains during periods of paleoclimatic change. Conclusions: There are other patterns which emerge from the arthropod data set; particularly there are regions of the island which contain unique assemblages of Mystrium associated with microhabitat such as Tsingy formations. Overall, Mystrium species provide insight into how reproductive strategy impacts species diversification across a region with high microendemism.