Karyotypic Repatterning as One Triggering Factor in Cases of Explosive Speciation

Karyotype composition of some rodents and marsupials from Chapada Diamantina (Bahia, Brasil)

“…On the other hand, Neotropical rodents (Cricetidae, Sigmodontinae in particular) present chromosomal variation within and among populations, species and genera (e.g. Baker et al, 1983;Bianchi et al, 1983;Geise, 1995;Geise et al, 1998;Patton and Sherwood, 1983;Reig, 1989). The association between chromosomal variation and species diversity in rodents means that karyological diversity is related to the differentiation of populations and constitutes an adaptative component in the phyletic evolution (Corti and Rohlf, 2001;Patton and Sherwood, 1983).…”

The dental evidence on the differentiation of the ctenomyine rodents (Caviomorpha, Octodontidae, Ctenomyinae)

“…Pascual (1967) linked Chasichimys with the Santacruzian octodontoid Acarechimys on one hand, and with the living echimyid "Cercomys" (= Thrichomys) on the other. The latter was mentioned by Reig (1989) as a possible senior synonym of Chasichimys. Reviewing the materials from Chasico we could verify that the only described species of this genus, Chasichimys bonaerense Pascual, 1967, is a composite taxon.…”

“…scagliai was originally considered a Heteropsomyine echimyid, linked with the "Proechimys group" (see the extension of this group in Pascual 1967). Afterwards, Reig (1989) proposed Chasichimys and Pattersomys as the most ancient Eumysopinae (Rusconi 1935). This subfamily of Echimyidae was revalidated by Patton and Reig (1989) to separate these genera, and others previously included within the Heteropsomyinae, from the Antillean genera Heteropsomys, Boromys and Brotomys.…”

“…However, those taxa of Deseadan to Friasian Age (Middle Oligocene-Middle Miocene) have doubtful taxonomic relationships (Reig 1986, 1989. Only since the Chasicoan Age (Late Miocene), can undisputed Octodontidae, with hypsodont molars and increasingly simplified occlusal designs, be recognized.…”

“…In the Pliocene, Ctenomyinae was characterized by low species richness, although it reached its highest diversity of adaptive types; four genera (Xenodontomys, Actenomys, Eucelophorus, and Praectenomys) were recognized, whose differentiation involved varied strategies of adaptation to the subterranean life (Reig and Quintana 1992, Quintana 1994b, Verzi 1994. In the Pleistocene, long-biochron genera disappeared (Tonni et al 1995, Vucetich and and the explosive speciation of Ctenomys began, leading to the present state (Reig 1989, Reig and Quintana 1992, Verzi 1994. In the living fauna, the highly polytypic genus Ctenomys includes nearly 56 species {fide ) of subterranean rodents (approximately 30 % of the total species of South American caviomorphs).…”