Past and future sky-island dynamics of tropical mountains: A model for two Geotrupes (Coleoptera: Geotrupidae) species in Oaxaca, Mexico

Recent collecting and taxonomic studies of dung beetles of the genus Geotrupes Latreille (Coleoptera: Geotrupidae) in the mountains of Oaxaca have evidenced the existence of a vicariant speciation pattern, where one species occupies the northern mountain system and the other one the southern mountain range. A study of this possible vicariant speciation mechanism is presented using a paleobiogeographic mapping analysis of both Geotrupes species distribution during Late Quaternary glaciation events. Based on these paleomaps a possible speciation mechanism (vicariant speciation) is suggested, in which one common ancestor (mother species) lived at the bottom of the Valle de Oaxaca (Oaxaca Valley) during the last local glacial maximum (LLGM, 21-17.5 kyr) and whose possible continuous distribution was broken into two (or more) separated areas on mountaintops as the climate became warmer toward the present. We propose that the fragmentation and isolation of habitats may have promoted genetic differentiation of populations resulting in vicariant speciation, as suggested by a sky-island dynamic process. The example of a possible effect of the Little Ice Age in the mountains of Oaxaca is also discussed. Finally, a projection is made into the XXII century, based on climatic modeling predictions. These last results suggest the possible disappearance of the sky-island dynamic process through the accelerated speed of climatic change.