Trinomys albispinus (I. Geoffroy, 1838)

Gutierrez, Eliecer E. & Marinho-Filho, Jader, 2017, The mammalian faunas endemic to the Cerrado and the Caatinga, ZooKeys 644, pp. 105-157 : 125

Trinomys albispinus (I. Geoffroy, 1838)

Distribution.

Trinomys albispinus is endemic to the Cerrado and the Caatinga (contra Carmignotto et al. 2012, Paglia et al. 2012), and has been recorded in the Brazilian states of Bahia, Minas Gerais, and Sergipe ( Souza et al. 2006, Pessôa et al. 2015b).

Taxonomy.

The recently published synopsis of the genus Trinomys by Pessôa et al. (2015b) followed the views of Reis and Pessôa (1995) and Souza et al. (2006) in treating Trinomys minor as a subspecies of Trinomys albispinus (i.e., Trinomys albispinus minor). Reis and Pessôa (1995) did not discuss the biogeographic context they presumably considered to designate minor as a subspecies of Trinomys albispinus (then allocated in the genus Proechimys ) instead of a valid species. Souza et al. (2006) considered minor as a subspecies of Trinomys albispinus due to the fact that karyotypes that they and Leal-Mesquita et al. (1992) attributed to albispinus and minor , respectively, shared the same diploid and autosomal fundamental numbers (2n=60, FNa=116), morphology of the sex chromosomes, and size of the first and second pairs of autosomes. Pessôa et al. (2015b) textually described a topology presumably resulting from phylogenetic analyses based on cytochrome-b sequences by Souza (2011 [an unpublished Ph.D. dissertation]) in which samples attributed to minor were nested within a haplogroup formed by samples attributed to Trinomys albispinus sertonius (= Trinomys albispinus albispinus [sensu Pessôa et al. 2015b and references therein]). We currently lack access to both the sequence data and the analyses that formed the basis of Pessôa et al.'s (2015b) views. Regardless, we argue that Trinomys minor and Trinomys albispinus represent different, valid species, for the following reasons: (1) the two species occur in a geographic context in which no clear barrier to dispersal separate them (see map in Pessôa et al. 2015b: 1004), and records of both species exists at only 30 km away from each other (see Souza et al. 2006); (2) the two species present well marked morphological differences (Reis and Pessôa 1995, Pessôa and Strauss 1999, Souza et al. 2006), and specimens with intermedium morphological characteristics have not been reported. These aspects strongly suggest that minor and albispinus do not constitute different subspecies of a single species, but rather that they are valid biological species, able to maintain their morphological differences in close geographic proximity and in absence of barriers to dispersal (i.e., virtually in sympatry) - even if they share the same karyotype and shallow genetic divergences. According to Pessôa et al. (2015b), Iack-Ximenes (2005 [an unpublished Ph.D. dissertation]) also recommends treating Trinomys minor as a species rather than as a subspecies of Trinomys albispinus . A number of potential causes could explain the yet-to-be-confirmed topology described in the species account by Pessôa et al. (2015b), including incomplete lineage sorting and other more technical aspects of the analyses and/or data (e.g., saturation of sequences, biases in nucleotide composition). Addressing these possibilities is pending from future publication of the sequence data used in those analyses and from future efforts to obtain nuclear sequence data from populations of Trinomys minor and Trinomys albispinus .

Conservation status.

The red list of the IUCN ver. 3.1 assigned the category "Least Concern" to Trinomys albispinus (see Bonvicino et al. 2016). The species was not included in the official list of threatened species of Brazil ( ICMBIO-MMA 2016).