Thylamys pallidior ( Thomas, 1902 )

Giarla, T. C., Voss, R. S. & Jansa, S. A., 2010, Species Limits And Phylogenetic Relationships In The Didelphid Marsupial Genus Thylamys Based On Mitochondrial Dna Sequences And Morphology, Bulletin of the American Museum of Natural History 2010 (346), pp. 1-67 : 46-49

Thylamys pallidior ( Thomas, 1902)

SYNONYMS: coquimbensis Tate, 1931; fenestrae Marelli, 1932.

DISTRIBUTION: As recognized in this report, Thylamys pallidior occurs from eastern Arequipa and Tacna departments in southwestern Peru eastward and southward into Bolivia (Oruro, Chuquisaca, Tarija) and northern Chile (Antofagasta, Atacama, Coquimbo, Tarapacá) to Argentina. In Argentina, Thylamys pallidior ranges from Jujuy province southward to Chubut ( Flores et al., 2007). Specimens that we examined document an altitudinal range from near sea level to 3750 m. Misidentified material that has been reported from extralimital localities is discussed under Remarks (below).

The known geographic range of Thylamys pallidior overlaps that of T. sponsorius in northwestern Argentina, where the two species have been collected sympatrically near Barcena (gazetteer locality 11) in Jujuy province. The range of T. pallidior also overlaps that of T. pusillus , as described in the account of the latter species (above). Although the ranges of T. pallidior and T. venustus also overlap in northwestern Argentina, these species have apparently not been collected sympatrically. Sympatry between T. pallidior and T. elegans is to be expected in the Coquimbo region of Chile, where their known geographic ranges are closely juxtaposed (see Remarks for T. elegans , above).

MORPHOLOGICAL DIAGNOSIS: Body pelage tricolored (abrupt line of transition from darker middorsal to paler lateral coloration present); ventral pelage entirely self-white or with narrow lateral zones of gray-based hairs; plantar pads of manus separate, surrounding concave central palmar surface, and with well-developed dermatoglyphs; manual claws long, extending well beyond the fleshy apical pads of digits; tail longer than combined length of head and body (LT/HBL X 100 5 112%; N 5 41), without pale tip; prehensile ventral surface of tail tip well developed. Nasal bones variable in length (without any clearly modal condition; table 7); lacrimal foramina often partially exposed on orbital rim; infraorbital foramen usually above M1 but sometimes above P3/M1 commissure (apparently never above P3); nasolabial fossa shallow; supraorbital margins usually round- ed or squared; maxillary fenestrae almost always absent; crown of second upper incisor (I2) consistently smaller than crown of I3; stylar cusp C almost always absent on M1 and M2; metaconule usually absent on M3.

COMPARISONS: Comparisons of Thylamys pallidior with T. pusillus and T. elegans are summarized in the preceding species accounts. Thylamys pallidior differs from the only other currently recognized species in the Elegans Group, T. tatei , in size and qualitative characters. Although pallidior is, on average, smaller than tatei in all measured dimensions, age-invariant molar measurements provide the best univariate index for this comparison: mean length of the upper molar row (LM, see fig. 2) is 5.7 ± 0.2 mm S.D. (observed range: 5.3–6.0 mm; N 5 51) in pallidior and 6.2 ± 0.2 mm (observed range: 5.9–6.4 mm; N 5 11) in tatei . Qualitatively, these species are most readily distinguished by their ventral pelage (almost completely self-white in pallidior , with broad lateral zones of gray-based hairs in tatei ) and by upper incisor morphology (the crown of I2 is consistently smaller than or about the same size as the crown of I 3 in pallidior , whereas the crown of I2 is consistently larger than the crown of I 3 in tatei ; fig. 17).

REMARKS: As previously reported by Braun et al. (2005), cytochrome- b sequence variation in this species is geographically structured. In particular, our results confirm those authors’ discovery of two allopatric haplotype groups with distributions that are juxtaposed at or near the border between Bolivia and Argentina ( fig. 5). Although this basal dichotomy is moderately well support- ed by nodal statistics ( fig. 4), we are unable to distinguish representative voucher specimens by any morphological criterion (univariate metrical comparisons are summarized in table 20), and we therefore treat these haplogroups as conspecific. Nevertheless, names are available for each of them should future research justify their recognition as distinct taxa. In that event, pallidior (based on a Bolivian specimen; table 14) unambiguously applies to haplogroup A, and fenestrae (based on an Argentinian specimen) could be used for haplogroup B. According to Martin (2009), however, fenestrae is a distinct species restricted to the Argentinian provinces of Buenos Aires, Córdoba, and La Pampa. Our only tissue samples from these

TABLE 20

Measurements (mm) of Sequenced Adult Specimens of Thylamys pallidior a

areas (AC 47, LTU 77) are vouchered by morphological specimens that we have not examined, but the sequences we obtained from them are intermingled in our tree ( fig. 4) with sequences from specimens collected in other provinces. Although we have not examined any of the morphological material that Martin (2009) referred to fenestrae, our results suggest that the application of this name merits closer scrutiny.

Specimens of other Thylamys species have sometimes been misidentified as T. pallidior . For example, Anderson’s (1997: 29) key does not reliably distinguish T. pallidior from other Bolivian congeners, and his range maps include several records that fall outside the range of that species as we recognize it. Although we were not able to see every Bolivian specimen that Anderson identified as T. pallidior , all of those that we examined from the departments of Cochabamba (e.g., AMNH 275427, MSB 87109), La Paz (e.g., AMNH 248704), and Santa Cruz (e.g., AMNH 260030) are unambiguously referable to T. venustus (see below).

Among the Peruvian specimens that Solari (2003) referred to Thylamys pallidior (and which were mapped as such by Brown, 2004: fig. 87) are several that appear to represent undescribed taxa (table 1). Some of these (e.g., MVZ 116614; from 3 mi W Atico in Arequipa department; fig. 5, locality 98) are morphologically similar to pallidior (with mostly self-white underparts), whereas others (e.g., MVZ 137585; from Lima department; fig. 5, locality 103) differ from typical pallidior by having broad lateral zones of graybased hairs bordering a narrower median streak of self-white fur. Cytochrome- b sequences that we amplified from museum skins of these and other unidentified specimens from southwestern Peru are highly divergent from pallidior and form a monophyletic group with two sequences of T. tatei ( fig. 4). Indeed, one of these specimens (MVZ 119913; also from Lima department; fig. 5, locality 102) resembles tatei and differs from other (more pallidior -like) Peruvian specimens by having a white-tipped tail and very long nasal bones. Although these results are

hard to interpret taxonomically with the sparse material at hand, they do suggest that the systematics of Peruvian Thylamys is likely to reward further study. Other researchers are currently working on this problem using freshly collected material (E. Palma, personal commun.), and we await their results with the greatest interest.

SPECIMENS EXAMINED (N 5 69): Argentina — Catamarca, 17 km N Barranca Larga ( OMNH 29964 ), 34.6 km by road W Fiambala ( OMNH 34903 ), 7 km SW Los Morteros ( OMNH 32556 ) ; Chubut, ca. 208 km W Dolavon ( MMNH 15709 , 15712–15714 ), Estancia La Escondida ( MMNH 17323 , 17324 , 17366 ), Istmoameghino ( MMNH 15722 ) ; Jujuy, 9 km NW Barcena ( OMNH 29963 ), 11 km E Humahuaca and 2 km E Pucará on road to Cianzo ( OMNH 29957 ), 8.2 km S Sey ( OMNH 34911 ) ; Mendoza, Ñacuñán Reserve ( UWBM 72195 ), 49.2 road km N Mendoza ( UWBM 72224 ) ; 3 km W Refugio Militar General Alvarado ( OMNH 23482 ), Salinas del Diamante RR Station ( OMNH 23480 ) ; Neuquén, 16 km SE La Rinconada ( MVZ 163772 ) ; Río Negro, General Roca ( USNM 236331 ) ; Salta, 16 km S and 1.8 km W Barrancas along Río de las Burras ( OMNH 34908 , 34909 ), 17 km NW Cachi ( OMNH 32559 ), Los Sauces ( OMNH 32544 ) ; San Juan, Castaño Nuevo ( OMNH 23485 ), 8 km W Complejo Astronómico El Leoncito ( OMNH 32571 ), Quebrada de los Flores ( OMNH 29961 , 29962 ) ; San Luis, 7 km E San Francisco del Monte de Oro ( OMNH 23489 ), 12 km by road N Varela ( OMNH 23490 ), 15 km E Salinas del Bebedero ( OMNH 23488 ) ; Tucumán, Tafí del Valle ( AMNH 41723–41727 ; FMNH 41397 , 41398 ). Bolivia — Chuquisaca, 68 km by road N Camargo ( AMNH 262405–262407 , MSB 57003) ; Oruro, Challapata ( BMNH 2.2 .2.116 [holotype of pallidior ], USNM 121157 ), ca. 10 km by road SW Pazña ( UMMZ 155830 , 155831 , 156015 ) ; Tarija, 1 km E Iscayachi ( AMNH 262408 ), 2 km SE Cieneguillas ( FMNH 162495 ), Serranía Sama ( MSB 87099). Chile — Antofagasta, Muelle de Piedra E of Taltal ( AMNH 143240 ) ; Atacama, Altamira ( USNM 391776 ), El Transito ( USNM 391775 ) ; Coquimbo, Paiguano ( FMNH 22302 [holotype of coquimbensis]) ; Tarapaca´, 5 km S Belén ( USNM 541600 ), 1 km W Belén ( USNM 541595 , 541596 ), Camarones Valley ( USNM 391777 ), Chapiquiña ( USNM 541599 ), Enquelga ( MSB 133108 ), 7 km SE Socorama ( USNM 541593 , 541594 ). Peru — Arequipa, 1 km N Chivay ( MVZ 173937–173939 ), 3 mi N Mollendo ( MVZ 145531 ) ; Tacna, 1.5 mi N Tarata ( MVZ 139215 ), 4 km N Tarata ( MVZ 115634 ), 65 km W Tacna ( MVZ 143695 , 143696 ) .