Molecular evolution of martens (genus Martes)

Abstract

Molecular studies provide the opportunity to re-evaluate and further investigate hypotheses such as those related to phylogenetic relationships, inter- and intra-continental colonizations, population differentiation, and the dynamics of hybrid zones. Three sets of molecular markers, nuclear and mitochondrial, were used to examine phylogenetic relationships among species within a holarctically distributed genus (Martes), and intraspecific diversification and population differentiation within American marten (Martes americana). In American marten, two morphological groups ('americana' and 'caurina') have been recognized, though the level of distinctiveness between them has been debated. My data supported the fossil record's indication that early radiations gave rise to two subgenera of the genus Martes (Pekania and Charronia) and that a more recent, possibly rapid, radiation gave rise to species of the third subgenus (Martes). Two colonizations of North America are evident, one by members of the subgenus Pekania, and another by the subgenus Martes. However, contrary to hypotheses based on morphological evidence, the 'americana' and 'caurina' subspecies groups of Martes americana represent only one colonization. Cytochrome b data were consistent with the recognition of these as monophyletic clades; however, aldolase C sequences and microsatellite data indicated that these generaly parapatric groups interbreed in at least one region of limited geographic overlap. These clades probably were isolated during the late Pleistocene in eastern and western refugia, but geographic separation apparently has not led to reproductive isolation. My data also indicated two colonization events for the Pacific Northwest by American martens (one by each clade). Due to patterns of genetic variation, I hypothesize that the 'caurina' clade spread along the North Pacific Coast, including southeastern Alaska, earlier than the 'americana' clade, and that these clades have now formed a zone of secondary contact on Kuiu Island in southeastern Alaska. Microsatellite data revealed population differentiation among many island populations in the Pacific Northwest, but possible gene flow among several near-shore island and mainland populations was suggested. Analyses of genetic and geographic distances suggested that colonization history had a strong effect on present day population structure and that oceanic straits and possibly other physiographic features posed significant barriers to gene flow.