Phylogenetic structuring in skull variation of Apodemus species (Rodentia: Muridae)

Abstract

We studied phenetic and phylogenetic relationships among Apodemus species of the Western Paleartic region. The sample comprised eight filed mice species from three subgenera Sylvaemus (A. alpicola, A. flavicollis, A. sylvaticus, A. uralensis, A. witherbyi), Karstomys (A. epimelas, A. mystacinus) and Apodemus (A. agrarius). Two species were each represented by two geographically distinct populations, A. flavicollis from Slovenia and Türkiye in Asia, and A. uralensis from the Czech Republic and Türkiye. The study of skull variation with geometric morphometric methods included the ventral cranium, mandible and upper molars. The analyzed skull structures were the largest in A. mystacinus and A. epimelas and the smallest in A. uralensis. The most distinctive in the mandible shape were A. mystacinus, A. epimelas, A. alpicola and A. agrarius. Apodemus mystacinus, A. epimelas and A. alpicola showed most unique cranium shape while A. agrarius was the most distinct in the molar shape. Mapping the geometric morphometric data to a phylogenetic tree of Apodemus species based on mtDNA cytochrome b sequences showed a phylogenetic signal in size variation in all the studied skull structures. The presence of a phylogenetic signal in shape variation was recorded for the mandible and molars. For the cranium, the permutation test showed the absence of a phylogenetic structure in shape variation. These results confirm the idea that different skull structures have diverse developmental pathways and different functional roles and respond differently to phylogenetic constraints and selective pressures. Nevertheless, contrary to the expectations, the cranial shape variation of the studied Apodemus species did not contain phylogenetic structuring.