Speciation of two stingrays with antitropical distributions: low levels of divergence in mitochondrial DNA and morphological characters suggest recent evolution

Disjunct geographic distributions across the equator (antitropicality) occur in many marine and terrestrial taxa. However, their origin and role in forming new species is still poorly understood. Here we examine the phylogenetic relationships and levels of genetic and morpho- logical divergence in 2 stingray species, the Southern Hemisphere Dasyatis brevicaudata and the Northern Hemisphere D. matsubarai, with antitropical distributions and suspected conserved morphological traits. Analyses of concatenated mtDNA sequences (3160 bp dataset: CO1, cytochrome b, control region) suggest D. brevicaudata and D. matsubarai are closely related sister lineages, with low levels of sequence divergence more akin to intra- rather than interspecific com- parisons. Multivariate analyses of morphological traits are largely consistent with the genetic data in showing small but discrete differences in morphometric characteristics, allowing Northern and Southern Hemisphere individuals to be separated into 2 groups. We suggest that D. brevicaudata and D. matsubarai are closely related sister taxa that may represent an early stage in the process of allopatric speciation.