Investigating the evolutionary dynamics of diploid number variation in Ctenomys (Ctenomyidae, Rodentia)

Abstract

Contrary to predictions from classical hybrid sterility models of chromosomal speciation, some organisms display high rates of karyotype variation. Ctenomys are the current mammals with the greatest interspecific and intraspecific chromosomal variation. A large number of species have been studied cytogenetically. The diploid numbers of chromosomes range from 2n = 10 to 2n = 70. Here, we analyzed karyotype evolution in Ctenomys using comparative phylogenetic methods. We found a strong phylogenetic signal with chromosome number. This refutes the chromosomal megaevolution model, which proposes the independent accumulation of multiple chromosomal rearrangements in each closely related species. We found that Brownian motion (BM) described the observed characteristic changes more thoroughly than the Ornstein-Uhlenbeck and Early-Burst models. This suggests that the evolution of chromosome numbers occurs by a random walk along phylogenetic clades. However, our data indicate that the BM model alone does not fully characterize the chromosomal evolution of Ctenomys .

A Cryptic Subterranean Mammal Species, the Lesser Blind Mole Rat (Nannospalax leucodon syrmiensis)—Retreated but Not Extinct

“…Chromosomal speciation and cryptic species in the genus Nannospalax —Chromosomal rearrangements are common in rodents, especially in the two most species-rich families, the Cricetidae and Muridae [ 48 ], and in the Ctenomyidae [ 49 ]. The theoretical basis for speciation mechanism through chromosomal rearrangements is described in detail.…”