Akodon sylvanus Thomas, 1921

J. Pablo Jayat, Pablo E. Ortiz, Jorge Salazar-Bravo, Ulyses F. J. Pardiñas & Guillermo D’Elía, 2010, The Akodon boliviensis species group (Rodentia: Cricetidae: Sigmodontinae) in Argentina: species limits and distribution, with the description of a new entity, Zootaxa 2409, pp. 1-61 : 32-34

Akodon sylvanus Thomas, 1921

Akodon sylvanus Thomas, 1921 . Annals and Magazine of Natural History, 9 (7):184.

Holotype: B.M. 21.1.1.27, an old male.

Type locality: “Sierra de Santa Barbara, S.E. Jujuy. Type from Sunchal, 1200 m ” ( Thomas 1921:185). Sunchal is located in Santa Bárbara Department, Jujuy Province (24º 15’ S, 64º 26’ W, 1454 m).

Description: We summarize here the most relevant characters for comparison and refer the reader to Jayat et al. (2007a) who redescribe this species in detail. The dorsal coloration is uniform, olivaceous brown finely spattered with black hairs, not well contrasting with ventral region. Ears with the same color as the dorsum. Eye rings absent or poorly developed. White spot on the chin barely developed. Tail slightly bicolored, ventrally clearer. Skull relatively narrow and elongated, with prominent rostrum. Zygomatic notches not particularly broad nor deep. Zygomatic arches comparatively slightly expanded and braincase poorly inflated. Interobital region with rounded margins. Mesopterygoyd fossa relatively narrow, with anterior border rounded or squared, without medial process. Upper incisors orthodont. The molars are the most hypsodont among the species of the boliviensis group. M1 with well developed anteroloph-parastyle. In some specimens the mesoloph extends to the lateral margin of the teeth. Mesoloph and paraflexus of M2 less developed than M1. M3 with poorly developed paraflexus and conspicuous hypoflexus. Protostylid of m1 well developed but the metastylid, mesolophid and mesostylid are tiny. In m2 there is no evidence of either an ectolophid (ectostylid) or mesolophid. The m3 shows hipoflexid and mesoflexid well developed.

Karyotype: Unknown.

Variation: Individuals near the type locality are uniform in color with some specimens with a more intense hue. Most variation in cranial morphology is age-dependent: young specimens present proportionally broad braincases and frontal sinuses but less developed zygomatic notches. Notwithstanding, the breadth of the zygomatic plate is highly variable among individuals of the same age class. The hamular process of the squamosal also is variable, from extremely thin to relatively broad and the capsular projection in mandible can be a slight elevation or a distinctive capsule.

Comparisons: Comparisons of Akodon sylvanus with A. boliviensis , A. caenosus , and A. spegazzinii are given in the treatment of these species. In addition, Jayat et al. (2007a) distinguished A. sylvanus from A. azarae and other species of Akodon present in northwestern Argentina. Detailed comparisons between A. sylvanus and the new species are described below.

Distribution: Akodon sylvanus is restricted to Sierra de Santa Barbara and neighboring areas in Jujuy province ( Fig. 6 ).

Habitat: the species has been recorded at all altitudinal belts of the Yungas forest, from 700 m, in transitional pedemontane forest, to 2300 m in cloud highland grasslands. Additional specimens were collected in grasslands associated with Chacoan environments at 1400 m ( Jayat et al. 2006, 2007a, 2008a)

Natural History: most of the individuals caught in winter (June) were reproductively inactive; sexual activity appears to start in late August. Akodon sylvanus was caught with other 10 sigmodontine species. In La Herradura, a few kilometers from the type locality, A. sylvanus was registered in sympatry with Akodon caenosus , A. simulator , Oligoryzomys cf. O. flavescens , Oligoryzomys sp. and Oxymycterus paramensis . In El Piquete, pedemontane forest in Sierra de Santa Bárbara, A. sylvanus is sympatric with A. simulator , Oligoryzomys chacoensis , Oligoryzomys cf. O. flavescens , Oligoryzomys sp., Euryoryzomys legatus , Rhipidomys austrinus and Calomys cf. C. fecundus . In cloud highlands grasslands in Sierra del Centinela, A. sylvanus coexists with Necromys lactens , Oligoryzomys cf. O. flavescens , O. paramensis and Phyllotis osilae nogalaris . In their distributional range A. sylvanus is frequently caught, with 40 to 60% of all sigmodontine individuals in La Herradura (n = 50) and Sierra del Centinela (n = 46).

Comments: Thomas (1921) described Akodon sylvanus from southeastern Jujuy province and later erected A. sylvanus pervalens , from Tarija Department, Bolivia ( Thomas, 1925). The taxonomic status of both taxa has fluctuated since then. Yepes (1933) indicated the presence of pervalens in Argentina, from Aguaray (northern Salta Province), listing both subspecies in Argentina ( Yepes 1935). Cabrera (1961) included sylvanus in the synonymy of A. azarae (Fischer) whereas pervalens was synonymyzed with A. varius Thomas. Myers (1989) tentatively treated azarae and sylvanus as different species and considered pervalens different from varius . Musser & Carleton (1993) considered sylvanus as a valid species (with pervalens as a subspecies). Díaz (1999), Musser & Carleton (2005) and Pardiñas et al. (2006) considered sylvanus as a valid species and different from pervalens. Recently, Jayat et al. (2007a), based on both genetic and morphologic analyses, validated A. sylvanus and incorporated it in the boliviensis group.

Recently, we erroneously assigned individuals from the area of Parque Nacional Baritú and Las Capillas to Akodon sylvanus ( Jayat et al. 2007a) . Morphological and molecular studies of more complete series of specimens of these areas indicate that they belong to A. fumeus . Consequently, some of the morphological, morphometric and distributional observations of Jayat et al. (2007a) are corrected here. Some characters previously considered as variations of A. sylvanus , such as a reddish hue and a broad mesopterygoid fossa, correspond to character states of A. fumeus specimens. Moreover, the smaller general size of these specimens lowered the average size of some of the measurements given by Jayat et al. (2007a) (compare Tables 1 and 2 of Jayat et al. [2007a] with Table 1 herein). In view of these amendments, the known distribution of A. sylvanus is restricted to southeastern Jujuy, in the vicinity of Sierra de Santa Barbara.

Figures

FIGURE 6. Recorded localities of A. boliviensis (square) and A. sylvanus (circles) in Northwestern Argentina. Localities and geographic position in Appendix II.