Ctenomys

Tammone, Mauro N., Lacey, Eileen A. & Pardiñas, Ulyses F. J., 2022, A century of stasis: Taxonomy of Ctenomys (Rodentia: Hystricomorpha) populations in northeastern Patagonia limits, Argentina, Zoologischer Anzeiger 298, pp. 136-147 : 142-143

4.1. Taxonomy of Ctenomys in Patagonia

The results of our phylogenetic analyses confirm previous suggestions that the “ magellanicus ” lineage is composed of three major subclades (Teta and D’ Elía 2020). The northernmost subclade is widespread in southern Mendoza, Neuqu´en and Río Negro Provinces, but also includes an apparently isolated portion of Península Vald´es in Chubut Province. Currently, the only named species in this subclade is C. bidaui , which is known from eastern Patagonia (Teta and D’ Elía 2020). Also included in this subclade are at least two undescribed forms from western Patagonia: one from the vicinity of the Río Grande near Bardas Blancas in Mendoza Province and the other from Laguna Blanca National Park in Neuqu´en Province ( Tammone et al. 2021). As revealed by this study, Cytb sequence data indicate that both unnamed forms diverge from all other Patagonian Ctenomys by> 3.00%; specimens from Bardas Blancas also differ morphologically from other members of the “ magellanicus ” lineage. Based on geographic location, previous work had suggested that the specimen from Anelo ˜belonged to the “ mendocinus ” lineage (Tammone and Pardi˜nas 2021a); our findings indicate that this animal is unambiguously nested within the “ magellanicus ” lineage as sister to C. bidaui . Thus, the “ magellanicus ” and “ mendocinus ” lineages appear to be parapatric in northwestern Neuqu´en Province. These findings are consistent with previous studies by Thomas (1927), Thomas and Saint Leger (1926), Pearson (1984) and Tiranti (1996) in suggesting a biogeographically complex taxonomy for Ctenomys in northwestern Patagonia that includes species (e.g., C. haigi , C. maulinus , C. mendocinus ) assigned to what are now recognized as distinct lineages within this genus.

The second subclade within the “ magellanicus ” lineage is widely distributed across central and southern Patagonia. This subclade is polytypic and includes populations that have previously been identified as C. haigi , C. sericeus , C. contrerasi , and C. thalesi (Teta and D’ Elía 2020) . Our analyses indicate that specimens from Aguada Cecilio and Playas Doradas in Río Negro Province and those from Puerto Madryn and Bahia Cracker in northeastern Chubut Province are associated with C. contrerasi , while those from Cabo Raso and Pico Salamanca along the southeastern coast of Chubut are associated with C. thalesi . In contrast, Thomas (1929) concluded that all Ctenomys in eastern Patagonia – from the Río Negro south to the Deseado basin in Santa Cruz Province – likely belong to a single species for which the name of C. sericeus was available. Although a formal taxonomic assessment is required, the marked lack of morphological variation among members of the central subclade reported here and by Teta et al. (2020) is consistent with this hypothesis. Indeed, differentiation within the central subclade has only recently been detected using integrative analyses of morphological, molecular, and karyotipic data ( Bidau et al. 2003; Teta and D’ Elía 2020).

With regard to diversity within the central clade, we concur with Teta et al. (2020) that based on both the Cytb haplotype assigned to C. fodax (HM777475, see Parada et al. 2011) and morphological comparisons, this specimen is most likely C. sericeus (including C. coyhaiquensis as a junior synonym; Teta and D’ Elía 2020), suggesting that formal taxonomic revision of C. fodax is needed. As noted above, the specimens assigned to C. haigi , including the newly sampled locality at Pillahuinco and the specimen from Bariloche (both in Río Negro Province), do not form a monophyletic group (see Parada et al. 2011). This outcome is due to a sequence (HM77476) reported by Parada et al. (2011) as being from the type locality for C. haigi at El Mait´en, Chubut Province (see Thomas 1919), that is paraphyletic to all other specimens identified as belonging to this species. We suggest that a re-examination of this collecting locality as well as additional sequence analyses and morphological comparisons are needed to resolve the apparent paraphyly of C. haigi (see Teta and D’ Elía 2020). The specimen from El Mait´en, a reported topotype that was not examined in this study, is part of the same Genbank accession as the specimen of C. fodax mentioned above, underscoring the need for a re-examination of these materials. Vast portions of Patagonia – particularly the central basaltic plateaus in Río Negro and Chubut Provinces – remain virtually unexplored with regard to their small mammal faunas and thus it is possible that these taxonomic issues reflect previously unrecognized diversity among the Ctenomys of this region.

The third subclade identified here is the southernmost in distribution, both for the “ magellanicus ” lineage and for the genus Ctenomys . The single species C. magellanicus is recognized, although many subspecies have been proposed ( Osgood 1943; Teta et al. 2020; Texera 1975). Morphological analyses suggest that C. fodax is most closely allied with C. magellanicus ( Thomas 1910; but see Teta et al. 2020) and, indeed, it has been considered synonymous with C. magellanicus osgoodi ( Osgood 1943) , although genetic analyses are needed to evaluate this hypothesis. Based on an animal collected by Henry Dunford near the Atlantic coast, Thomas (1898) reported the apparent occurrence of C. magellanicus at Punta Tombo in eastern Chubut Province, a locality that is substantially further northeast than the currently recognized range of this species. Initial identification of this specimen, a subadult, was somewhat tentative, likely due to the status of taxonomic knowledge of the genus at the end of the19 th century, leading Thomas to associate this individual with the single Patagonian species known at this time (i.e., C. magellanicus after Bennett, 1835; but published in 1836, see Duncan 1937). Bidau (2015: 847) rejected this assignment on the basis of geographic locality. In contrast to Thomas, our analyses suggest that populations of Ctenomys from coastal portions of Chubut Province belong to C. thalesi . This outcome implies that in eastern Patagonia, C. magellanicus is limited to south of the Río Santa Cruz. Thus, although the record of C. magellanicus in Punta Tombo ( Thomas 1898) can prima facie be referred to C. thalesi , a direct inspection of the original material collected by Dunford is required.