Coastal-inland divergence and postglacial expansion in the populations of the orchid bee Euglossa annectans

Biogeographic patterns in the southernmost portion of the Atlantic Forest (AF) are still elusive for a high number of endemic species where the main phylogeographic hypothesis in AF (e.g., CM model or AF expansion) fails to predict refuges during the Last Glacial Maximum (LGM). Euglossa annectans is an orchid bee species endemic to AF, distributed throughout the longitudinal edges of the southern portions of this biome. Combining ecological niche modelling and genetic analysis, we investigated whether the Pleistocene climate fluctuations played some role in the population structure of this species. We analysed 640 bp of the Cytb gene and eight microsatellite loci from males sampled from twelve localities along E. annectans distribution. Microsatellite markers indicated two main groups with a disjunction between inland and coastal areas. Although mitochondrial data showed no spatial structure, we found signals of a bottleneck followed by population expansion after the LGM. Pleistocene climatic models revealed a fragmented scenario with suitable areas concentrated at the coastal continental shelf and the northern-west inland areas, both in line with the genetic nuclear markers' structure and synchronic with the mitochondrial bottleneck at the LGM. The climatic instability along the Pleistocene has played a central role in determining the phylogeographic and demographic patterns of the E. annectans, resulting in a genetic structure reported for the first time in this area.