TOPOGRAPHY AND BIOGEOGRAPHIC CHANGES OF MONTANE FORESTS IN THE “SKY ISLANDS” OF SOUTHEASTERN ARIZONA AND THE ASSOCIATED GENETIC DIVERGENCE OF SCAPHINOTUS PETERSI DURING THE QUATERNARY
Molecular clock analysis indicates that divergence between the beetle populations occurred between 25 and 260 Kya, depending on the particular combination of populations analyzed. Furthermore, the genetic data are consistent with genetic separation due to habitat segmentation as opposed to dispersal. A preliminary model relating forest hysometry to past and present T° and P indicates that LGM paleoclimate conditions were likely wet and cool enough for montane forests to coalesce at lower altitudes. However, the age of divergence of Scaphinotus populations is correlated with neither the distance of geographic separation (90-215 km), nor the forest biome altitude depression necessary to link populations (750-1000 m). Furthermore, common ancestors between some populations, and thus the maximum date of separation, long predate the LGM. The complex relationship between the paleoclimate and paleoecology record and the genetic divergence data indicate that 1) a simple model of upslope biome migration since the LGM or YD is not sufficient, 2) the paleobiogeography of beetle populations differs from their current forest habitat, and/or 3) there is a multi-stage pattern of localized beetle extinction and re-population throughout the Pleistocene and Holocene.