Cryptic Species in <b><i>Proechimys goeldii </i></b>(Rodentia, Echimyidae)? A Case of Molecular and Chromosomal Differentiation in Allopatric Populations

Abstract

The spiny rats of the genus Proechimys have a wide distribution in the Amazon, covering all areas of endemism of this region. We analyzed the karyotype and cytochrome b (Cyt b) sequences in Proechimys goeldii from 6 localities representing 3 interfluves of the eastern Amazon. A clear separation of P. goeldii into 2 monophyletic clades was observed, both chromosomally and based on Cyt b sequences: cytotype A (2n = 26♀/27♂, NF = 42) for samples from the Tapajos-Xingu interfluve and cytotype B (2n = 24♀/25♂, NF = 42) for samples from the Xingu-Tocantins interfluve and east of the Tocantins River. The karyotypes differ in a pericentric inversion and a centric fusion/fission and an average nucleotide divergence of 6.1%, suggesting cryptic species. Meiotic analysis confirmed the presence of a XX/XY₁Y₂ multiple sex chromosome determination system for both karyotypes. The karyotypes also vary from the literature (2n = 24, NF = 42, XX/XY). The autosome translocated to the X chromosome is different both in size and morphology to P. cf. longicaudatus, which also has a multiple sex chromosome determination system (2n = 14♀/15♀♂/16♀/17♂, NF = 14). The Xingu River is a barrier that separates populations of P. goeldii, thus maintaining their allopatric nature and providing an explanation for the molecular and cytogenetic patterns observed for the Xingu River but not the Tocantins River.

Chromosomal diversity and molecular divergence among three undescribed species of Neacomys (Rodentia, Sigmodontinae) separated by Amazonian rivers

“…The geographical barrier of the Amazonian rivers [ 6 ] explains the lack of gene flow between interpluvial regions in Amazon, and confines some species to a single endemic area [ 5 ], as described for several groups of terrestrial vertebrates, including primates [ 53 ], birds [ 54 ] and rodents [ 55 ]. In the Neacomys genus, some species occur in more than one endemic area [ 2 , 24 – 28 ], which is in disagreement with the pattern observed for the three undescribed species of Neacomys , who have isolated distributions: Neacomys sp.…”

Centric Fusions behind the Karyotype Evolution of Neotropical Nannostomus Pencilfishes (Characiforme, Lebiasinidae): First Insights from a Molecular Cytogenetic Perspective

“…As another layer of evidence supporting the significant contribution of fusions in the karyotype dynamics of Nannostomus, the large blocks of constitutive heterochromatin flanking the centromeres of rather large-sized metacentric chromosomes, as found in the karyotypes of N. marginatus and N. unifasciatus, may be potentially considered as relics of two previously independent centromeres linked together by the process of fusion. In fact, such a situation has been repeatedly observed in many teleost species (sometimes, again, accompanied by the presence of rDNA sites in the fusion points) [49][50][51][52][53][54] and it was reported also in other animal taxa, e.g., amphibians [55] or mammals [56,57]. Nonetheless, other studies show that the large pericentromeric heterochromatic blocks can also be found evenly distributed throughout the karyotype regardless of the fusion events (see, e.g., Houck et al [57] and Sousa et al [58]).…”

New karyotype records for the genus Proechimys (Rodentia: Echimyidae) from Brazilian Amazonia

“…In the family Echimiydae, the mapping of repetitive DNA sequences is limited to the location of the 45S rDNA and telomeric sequences in six species: Phyllomys lamarum and Phyllomys sp. from northern Minas Gerais, Brazil (Araújo et al, 2014); and Proechimys guyannensis, Proechimys cuvieri (Silva et al, 2012), Proechimys longicau-datus (Amaral et al, 2013), and two cytotypes of P. goeldii (Rodrigues da Costa et al, 2016), collected in Brazilian Amazonia.…”