A New Allopatric Lineage of the Rodent <i>Deltamys</i> (Rodentia: Sigmodontinae) and the Chromosomal Evolution in <i>Deltamys kempi</i> and <i>Deltamys</i> sp.

Abstract

Deltamys Thomas 1917 is a poorly studied and rarely collected taxon of Akodontini (Sigmodontinae). The single described species, Deltamys kempi (DKE), has a basic karyotype with a diploid number of 2n = 37 in males and 2n = 38 in females, a fundamental number FN = 38 for both sexes, and an X₁X₁X₂X₂/X₁X₂Y sex determination system. Herein, a new allopatric form, Deltamys sp. (DSP), is reported, based on specimens from southern Brazil, with 2n = 40, FN = 40 and XX/XY sex chromosomes. We describe the karyotype and mechanism of chromosomal differentiation between both Deltamys complements. Phylogenetic analyses, based on the complete sequence (1,140 bp) of the mitochondrial cytochrome b gene, grouped Deltamys sp. as sister species to D. kempi, with up to 12% genetic divergence between them. The GTG-banding patterns show complete autosomal correspondence between D. kempi and Deltamys sp. and identify a tandem rearrangement involving DSP7, DSP19 and DKE4 that is responsible for the differences in 2n and FN. Chromosome painting with Akodon paranaensis chromosome 21 (a small metacentric akodont marker) paint revealed total homology with the smallest acrocentric Deltamys sp. chromosome, DSP19. This suggests the occurrence of a pericentric inversion or centromeric shift when compared to other akodontines, with a posterior tandem rearrangement giving rise to DKE4. In DKE, large blocks of pericentromeric constitutive heterochromatin are present on the autosomes and the X, and the Y/autosome has an entirely heterochromatic short arm. In DSP, small heterochromatic blocks are observed on autosomes and X, and the Y is a very small, mostly heterochromatic acrocentric. The cytogenetic analyses suggest that the Deltamys sp. karyotype is ancestral, with the derived condition resulting from a tandem fusion (DSP7 + DSP19) and the Y/autosome translocation giving rise to the multiple sex chromosome system. The autosomal rearrangements, the differences in CBG-banding patterns and Ag-NOR localization, as well as the presence of X₁X₁X₂X₂/X₁X₂Y and XX/XY sex determination mechanisms, possibly acting as a reproductive barrier, and the phylogenetic position within the Deltamys genus, with high genetic divergence, call for a taxonomic review of the genus.

DNA Barcoding of Sigmodontine Rodents: Identifying Wildlife Reservoirs of Zoonoses

“…The diploid number of this putatively new species is 2n=34, whereas D. kempi has a multiple sex chromosome system with 2n= 35, 36, 37, 38 [ 71 – 73 ]. Recently, a new allopatric lineage of Deltamys was proposed [ 74 ], with a diploid number of 2n=40. Akodon and Deltamys belong to the same tribe (Akodontini), and are sister genera according to nuclear and mitochondrial genes [ 39 ]; they can be distinguished by a single small chromosome pair that is present only in Akodon.…”

Variable patterns of Y chromosome homology in Akodontini rodents (Sigmodontinae): a phylogenetic signal revealed by chromosome painting

“…serrensis, 2n 046, Necromys lasiurus (NLA), 2n 034, Deltamys sp. (DSP), 2n040 (see Ventura et al 2011), Thalpomys lasiotis (TLA), 2n038, Thaptomys sp. (TSP), 2n050, Thaptomys nigrita (TNI), 2n052, Oxymycterus amazonicus (OAM), 2n054, Blarinomys breviceps (BBR), 2n043, Brucepattersonius soricinus (BSO), 2n052, Scapteromys tumidus (STU), 2n 034 and Kunsia tomentosus (KTO), 2n044.…”

“…Knowledge about the tribe systematics and taxonomy is still being developed since new taxa are still being discovered (Ventura et al 2004(Ventura et al , 2010(Ventura et al , 2011, demanding new studies and discussion based on different sources of data.…”

The emergence of a new sex-system (XX/XY1Y2) suggests a species complex in the “monotypic” rodent Oecomys auyantepui (Rodentia, Sigmodontinae)

“…1 ), validating the emergence of a new sex system (XX/XY 1 Y 2 ) in O. auyantepui (2n = 64♀65♂/FNa = 84). Regarding Sigmodontinae rodents, this is the first record of a multiple sex system in Oryzomyini, since this type of sex determination system has previously been reported only in representatives of Akodontini (X 1 X 1 X 2 X 2 /X 1 X 2 Y) 42 , Phyllotini (XY 1 Y 2 ) 43 and Reithrodontini (XY 1 Y 2 and Neo-XY) 44 tribes.…”

“…In Lonchothrix emiliae , the multiple sex system was identified based on classic banding 38 , while in the Proechimys taxa it was detected by FISH (Fluorescence In Situ Hybridization) with whole chromosome probes (chromosome painting) from P. roberti and P. goeldii 35 . In Sigmodontinae rodents (Rodentia, Cricetidae), the Oryzomyini tribe currently comprises 29 genera and is the most diverse of the 11 tribes within the subfamily 39 – 41 , but multiple sex systems are acknowledged solely in representatives of the Akodontini, Phyllotini and Reithrodontini tribes: Deltamys kempi (Akodontini) exhibits a X 1 X 1 X 2 X 2 /X 1 X 2 Y sex system due to a translocation involving chromosomes 2 and Y 42 ; Salinomys delicatus (Phyllotini) shows a XY 1 Y 2 system 43 ; and Reithrodon (Reithrodontini) exhibits a XY 1 Y 2 system (Uruguay population) and a Neo-XY system (Brazil population) 44 .…”