Evolutionary diversification of spiny rats (genus Trinomys, Rodentia : Echimyidae) in the Atlantic Forest of Brazil

Phylogenetic and phylogeographic relationships within and among species of the Atlantic Forest spiny rat Trinomys (family Echimyidae) were examined us ing cytochrome b sequence data. Levels of sequence divergence among species of Trinomys are as high as those found among taxa of echimyids that are re cognized as different genera. Trinomys contains three distinct monophyletic clades that show a striking concordance with vegetational distribution. Ha plotypes of clade 1 are distributed along the coastal margins of southeaste rn Brazil, following the moist tropical forest. Members of clade 2 are foun d in the semi-deciduous tropical forest. T. albispinus represents clade 3 a nd is found in a more xeric vegetation. Estimate so divergence times separa ting the three clades are very deep and range from 1.6 to 7.4 millions of y ears, predating the climatic fluctuations of the Pleistocene. Therefore, th e proposed Late Pleistocene refugia in the Atlantic Forest cannot account f or the divergence of the clades of Trinomys, but most likely shaped the mod ern distribution of species. The current taxonomy of this group does not re flect the diversity and phylogenetic relationships of the named species. Ho wever, morphological characters are congruent with the phylogeny uncovered by the molecular data. An extensive taxonomic rearrangement is suggested, r eflecting phylogenetic relationships of monophyletic entities within the ge nus Trinomys, degree of sequence differences, and morphological diagnosabil ity. (C) 1999 The Linnean Society of London.