Abstract
Aim
The North American Coastal Plain is currently recognized as a global biodiversity hotspot. However, the mechanisms driving high levels of species richness in a region with relatively low topographic relief and homogeneous climate are unclear. We investigated the evolutionary processes driving ancestral area evolution and diversification in a biodiversity hotspot from both a systematic and biogeographical context using a clade endemic to the hotspot.
Location
North American Coastal Plain.
Taxon
The Scrub Mint clade (SMC) comprises Dicerandra, Conradina, Piloblephis, Stachydeoma and four species of Clinopodium (Mentheae; Lamiaceae), almost all of which are endemic to the North American Coastal Plain.
Methods
We generated a dated phylogeny using a target enrichment/capture dataset and then calculated ancestral area using biogeographical models. We uncovered neo- and palaeo-endemism hotspots and inferred ancestral potential ranges at each node based on ancestral niche reconstructions and palaeoclimatic data to understand the geographical range evolution of subclades.
Results
Ancestral area for the SMC was inferred to be the Florida Panhandle/Apalachicola River basin. A diversification event likely happened around the mid-Pleistocene Transition. Endemism hotspots were recovered in NE Florida, the Atlantic Coastal Ridge, and along the Lake Wales Ridge. Reconstructions of potential ranges support biogeographical findings, with the ancestor of the SMC likely located in the vicinity of the northeastern Gulf Coast during interglacial and glacial periods.
Main Conclusions
The timing of diversification events and colonization of new areas by ancestors of the SMC are consistent with the timing of major geological events in the region. The presence of multiple types of endemism highlights the complexity of evolutionary and ecological processes that foster the large number of endemic taxa found in this region. Efforts to identify hotspots in this region will be critical to preserving the remaining pockets of biodiversity threatened by global change.