New Karyotype Information for Ctenomys (Rodentia: Ctenomyidae) from Midwest and Northern Brazil

Abstract

<b><i>Introduction:</i></b> Its wide karyotypic variation characterizes the genus <i>Ctenomys</i>, and in Brazil, the genus is distributed in the country’s southern, Midwest, and northern regions. Recently, populations of <i>Ctenomys</i> have been found in the Midwest and northern Brazil, with two new lineages named <i>C.</i> sp. “xingu” and <i>C.</i> sp. “central.” <b><i>Methods:</i></b> This work combines classical cytogenetic and molecular analyses to provide new chromosomal information on the <i>boliviensis</i> group distributed in northern and Midwestern Brazil. This includes the validation of the karyotype of <i>C. bicolor</i> and <i>C. nattereri</i> and the description of the karyotype of <i>C.</i> sp. “xingu” and <i>C.</i> sp. “central.” <b><i>Results:</i></b> We found three different karyotypes: 2<i>n</i> = 40 for <i>C. bicolor</i>; 2<i>n</i> = 36 for <i>C. nattereri</i>, and specimens from a locality belonging to <i>C.</i> sp. “central”; 2<i>n</i> = 34 for the lineage <i>C.</i> sp. “xingu” and specimens from a locality belonging to <i>C.</i> sp. “central.” Furthermore, GTG banding revealed homologous chromosomes between species/lineages and allowed the identification of the rearrangements that occurred, which proved the occurrence of fissions. <b><i>Conclusion:</i></b> Considering our results on the variation of 2<i>n</i> in the <i>boliviensis</i> group, we found two possibilities: the first, deduced by parsimony, is that 2<i>n</i> = 36 appeared initially, and two fissions produced gave rise to 2<i>n</i> = 40, and an independent fusion gave rise to 2<i>n</i> = 34 from 2<i>n</i> = 36; moreover, the second explanation is that all karyotypes arose independently.