Proechimys (Rodentia, Echimyidae): characterization and taxonomic considerations of a form with a very low diploid number and a multiple sex chromosome system

Abstract

BackgroundProechimys is the most diverse genus in family Echimyidae, comprising 25 species (two of which are polytypic) and 39 taxa. Despite the numerous forms of this rodent and their abundance in nature, there are many taxonomic problems due to phenotypic similarities within the genus and high intraspecific variation. Extensive karyotypic variation has been noted, however, with diploid numbers (2n) ranging from 14 to 62 chromosomes. Some heteromorphism can be found, and 57 different karyotypes have been described to date.ResultsIn the present work, we describe a cytotype with a very low 2n. Specimens of Proechimys cf. longicaudatus were collected from two different places in northern Mato Grosso state, Brazil (12°54″S, 52°22″W and 9°51′17″S, 58°14′53″W). The females and males had 16 and 17 chromosomes, respectively; all chromosomes were acrocentric, with the exception of the X chromosome, which was bi-armed. The sex chromosome system was found to be XY1Y2, originating from a Robertsonian rearrangement involving the X and a large acrocentric autosome. Females had two Neo-X chromosomes, and males had one Neo-X and two Y chromosomes. NOR staining was found in the interstitial region of one autosomal pair.ConclusionsComparison of this karyotype with those described in the literature revealed that Proechimys with similar karyotypes had previously been collected from nearby localities. We therefore suggest that this Proechimys belongs to a different taxon, and is either a new species or one that requires reassessment.

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

“…longicaudatus (Jacareacanga and Itaituba; fig. 1 , localities 6 and 7) present the same karyotype (2n = 16 ♀ /17 ♂ , FN = 14) as the sample described by Amaral et al [2013] which was obtained near the Juruena River in Cotriguaçu northwest and Querên-cia northeast Mato Grosso ( fig. 1 , localities 10 and 11).…”

“…commun. ); 9 = Juruena town, Mato Grosso, Machado et al [2005]; 10 = Cotriguaçu town, Mato Grosso, Amaral et al [2013]; 11 = Querência town, Mato Grosso, Amaral et al [2013]. Each square corresponds to 3 degrees of latitude and longitude.…”

“…1 , localities 10 and 11). According to Amaral et al [2013], the karyotype de- fig. 1 , locality 9) should belong to the P. longicaudatus group instead of the P. goeldii group.…”

“…Of the 57 karyotypic forms described for the genus, only P. cf. longicaudatus (2n = 14 ♀ /15 ♀ ♂ /16 ♀ /17 ♂ , FN = 14) has a multiple sex chromosome determination system [Amaral et al, 2013]. In contrast, the other species have simple systems [Weksler et al, 2001;Eler et al, 2012].…”

“…Proechimys displays intense karyotypic variation for the 25 recognized species with 57 different karyotypic forms [Wilson and Reeder, 2005;Eler et al, 2012;Amaral et al, 2013]. This genus shows variations in diploid number (2n) of 14-62, and many species within this genus are characterized by more than one diploid number and/or number of autosomal chromosome arms (FN), which in a few cases is also observed in sympatric animals [Barros, 1978;Weksler et al, 2001;Eler et al, 2012].…”