Thylamys sponsorius ( Thomas, 1921 )

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 : 51-56

Thylamys sponsorius ( Thomas, 1921)

SYNONYMS: janetta Thomas, 1926 .

DISTRIBUTION: Based on specimens that we sequenced, Thylamys sponsorius occurs along the eastern slopes and foothills of the Andes from southern Bolivia (Tarija) to northwestern Argentina (Jujuy, Salta, Tucumán, Catamarca; fig. 9) with recorded elevations ranging from 515 to 3750 m. Although T. sponsorius and T. venustus have broadly overlapping horizontal and vertical distributions, our only sympatric samples are from 3 km SE Cuyambuyo, at 900 m elevation in the Bolivian department of Tarija ( fig. 9, gazetteer locality 74). The known geographic range of Thylamys sponsorius also overlaps that of T. pallidior as previously described in the account of the latter species (above).

MORPHOLOGICAL DIAGNOSIS: Body pelage tricolored (abrupt line of transition from darker middorsal to paler lateral coloration present); ventral pelage gray-based yellowish or whitish, except in some old adults from

TABLE 22 Results of Linear Discriminant Analysis of Sequenced Venustus Group Specimens and Three Unknowns a

Carlazo, Bolivia (type series and topotypes of ‘‘janetta’’), which have mostly self-whitish venters; plantar pads of manus separate, surrounding a concave central palmar surface; manual claws short, not extending much if at all beyond fleshy apical pads of digits; tail substantially longer than the combined length of head and body (LT/HBL X 100 5 136%; N 5 13), without pale tip; prehensile ventral surface of tail tip well developed.

TABLE 23 Coefficients of Linear Discriminant Function Separating Thylamys sponsorius from T. venustus

Nasal bones usually extending posteriorly as far as or behind lacrimals; lacrimal foramina usually concealed or only partially exposed on orbital rim; infraorbital foramen often over P3/M1 commissure, but sometimes over P3 or M1; nasolabial fossa shallow; supraorbital margins rounded or squared, with weak beads in some old adults but apparently never with distinct processes; maxillary fenestrae consistently present; crown of second upper incisor (I2) consistently smaller than or subequal to crown of I3; stylar cusp C almost always absent on M1 and M2; metaconule indistinct or absent on M3.

COMPARISONS: Sequenced material of Thylamys sponsorius seems to be indistinguishable from that of T. venustus in external morphological characters. Voucher specimens of both clades have brownish-gray dorsal fur that tends to be darker at lower elevations and paler in the highlands (. 2000 m). The ventral fur is predominantly gray based in most specimens, although the fur of the chin and throat is often selfcolored, and many specimens of both species have self-colored pectoral markings; the selfcolored ventral fur (if any) and the tips of the gray-based ventral hairs are white or offwhite (cream) in most highland specimens but yellowish in lowland material. The hind feet of T. sponsorius seem a little darker, on average, than those of T. venustus , but the difference is not sufficiently marked to sort skins, and it is probably useless for field identification.

Sequenced specimens of Thylamys sponsorius and T. venustus are likewise indistinguishable by any qualitative craniodental character that we examined, nor are they consistently diagnosable by any combination of qualitative craniodental traits. Tests for craniodental trait frequency differences (as recorded in tables 7–13) are statistically significant only for the presence/absence of stylar cusp C, which is not present on M 2 in any sequenced specimen of sponsorius , but which occurs on that tooth in a substantial number of sequenced specimens of venustus (table 12; p, 0.01 by Fisher’s exact test). Among traits that we did not formally score for statistical analysis, small postorbital processes were observed on several sequenced specimens of venustus (e.g., AMNH 186948; MSB 63260, 67005) but not on any sequenced specimen of sponsorius .

Sequenced adult specimens of Thylamys sponsorius and T. venustus differ significantly in most measured dimensions. Two-tailed t - tests for species differences among males, the sex most abundantly represented among our adult tissue vouchers, are significant at the 5% level for all measurements except HBL, Ear, NL, BW, and IBW (table 24). In every case where a significant difference was found, sponsorius is the larger species. Unfortunately, observed ranges of the two species overlap for every measurement, so none is diagnostic. In the absence of other criteria, provisional identifications of unsequenced specimens can be based on discriminant scores (computed as the dot product of the coefficients in table 23 and loge- transformed craniodental measurement values). If our hypothesis of species status for these clades is correct, then the scores of unsequenced specimens (of which several hundred are preserved in museum collections) should have a distinctly bimodal distribution.

REMARKS: This taxon was originally described as Marmosa elegans sponsoria , but Tate (1933) treated sponsoria as a subspecies of M. venusta , and Cabrera (1958) synonymized it with M. e. cinderella . Gardner (1993) listed cinderella , sponsorius , and venustus as synonyms of Thylamys elegans , but allozyme data reported by Palma and Yates (1998) suggested that venustus —the name they used for Bolivian populations of ‘‘ elegans ’’ (sensu

Fig. 18. Results of linear discriminant function analysis of craniodental measurement data from sequenced specimens of the Venustus Group belonging to the ‘‘large’’ (•) and ‘‘small’’ (O) clades. Unsequenced specimens (gray stars) were treated as unknowns (see table 22). Two specimens of known clade membership but with equivocal posterior probabilities are labeled with their museum catalog numbers.

Gardner, 1993)—was a distinct species. Subsequently, Flores et al. (2000) recognized three Argentine species of Thylamys with gray-based ventral fur, for which they used T. cinderella , T. sponsorius , and T. venustus as valid binomials. However, cinderella and sponsorius were synonymized again by Braun et al. (2005), who found genetic evidence for only two Argentine species of Thylamys with gray-based ventral fur, one corresponding to the phenotype that Flores et al. called venustus and the other containing specimens that Flores et al. had identified as cinderella and sponsorius . Gardner (2005) and Creighton and Gardner (2008) recognized T. cinderella , T. sponsorius , and T. venustus (including janetta ) as valid following Flores et al. (2000), but Voss and Jansa (2009) followed Braun et al. (2005) in recognizing only T. cinderella (including sponsorius ) and T. venustus (including janetta ) as valid species.

Our use of the name sponsorius is based on the morphometric analysis described above, which unambiguously associates the holotype ( BMNH 21.1 .1.85, an adult male from Sunchal , in the Sierra de Santa Bárbara of southeastern Jujuy, Argentina; Thomas, 1921) with the cytochrome- b clade that has larger average measurements. Because the

TABLE 24

Measurements (mm) of Sequenced Adult Specimens of Thylamys sponsorius and T. venustus a

same analysis assigned the holotype of cinderella (BMNH 0.7.9.20, an adult female from ‘‘ Tucuman,’’ Argentina; Thomas, 1902) to the clade with smaller average measurements, we conclude that these names are not synonymous. Instead, the only synonym of sponsorius that we are currently able to identify as such is a Bolivian form ( janetta ) whose relationships have long been controversial.

Marmosa janetta was originally described on the basis of 12 specimens collected at elevations ranging from 1700 to 2300 m in Tarija department, Bolivia, by Thomas (1926), who thought it was related to M. verax (a junior synonym of Thylamys pusillus ; see above). Tate (1933: 221) also recognized M. janetta as a valid species and said that it was ‘‘the mountain representative of the marmota radiation’’ (marmota being an unavailable synonym of T. macrurus ; see Voss et al., 2009). Subsequently, Cabrera (1958) included janetta without comment in the synonymy of M. elegans venusta . Most subsequent authors (e.g., Solari, 2003; Gardner, 2005; Creighton and Gardner, 2008) have listed janetta as a synonym of T. venustus , but the justification for this synonymy has never been explained.

We examined the holotype of janetta (BMNH 26.1.1.167, from Carlazo), several topotypic paratypes (BMNH 26.1.1.166, 26.1.1.168–26.1.1.170; FMNH 29169, 29170) and several recently collected topotypes (UMMZ 155836, 156034–156036). Oddly, all of these specimens are very old adults with heavily worn molars. The advanced age of these specimens plausibly explains the large size attributed to janetta by Thomas (1926) and Tate (1933); this conclusion is supported by the fact that whereas continuously growing dimensions seem unusually large in this series (e.g., CBL: 29.7–31.6 mm), age-invariant measurements do not (e.g., LM: 5.7–6.0 mm). Other distinctive attributes of this nominal species, however, are harder to explain as age-related, including its mostly self-white ventral coloration, white hind feet, and short posterolateral palatal foramina (which, unlike most other Thylamys , do not extend anteriorly to the level of the protocone of M4). In other respects, janetta resembles other forms that we assign to the Venustus Group; for example, the type and all examined topotypes have short claws, and maxillary fenestrae are bilaterally present.

Our primary justification for synonymizing janetta with sponsorius are partial (609– 812 bp) cytochrome- b sequences amplified from a paratype (FMNH 29170) and a topotype (UMMZ 155836) of janetta . Despite the unusual features of their morphological vouchers (as noted above), the sequences we obtained from FMNH 29170 and UMMZ 155836 cluster with other Tarija sequences that we obtained from phenotypically sponsorius -like specimens ( fig. 8). Although we are not able to confidently explain all of the odd traits that characterize examined specimens from Carlazo, we assume that they are ontogenetic artifacts and/or local peculiarities, perhaps of a small and closely inbred population.

Flores et al. (2000, 2007) recognized Thylamys cinderella , T. sponsorius , and T. venustus as distinct species that could be identified by diagnostic morphometric and qualitative criteria. However, none of their relevant key couplets ( Flores et al., 2000: 334) accurately distinguish voucher specimens representing the two mitochondrial clades recovered in our analysis of cytochrome- b sequence data. Additionally, we sequenced one specimen that they identified as T. sponsorius (AMNH 185323) and another that they identified as T. cinderella (AMNH 186948); according to our phylogenetic analyses, both specimens belong to haplogroup C of the species we identify as T. venustus .

SPECIMENS EXAMINED (N 5 29): Argentina — Catamarca, 5 km S Las Higuerillas on Hwy 9 ( OMNH 29965 ) ; Jujuy, 9 km NW Barcena ( OMNH 29974 ), 24.8 km E Santa Clara ( OMNH 34534 ), 10 km W Tiraxi on Hwy 29 ( OMNH 29970 ) ; Salta, 5 km NW Pulares ( OMNH 32545 ), 25 km SE La Viña ( OMNH 32548 ) ; Tucumán, 5 km N Las Higuerillas on Hwy 308 ( OMNH 29967 ), Km 42 on Hwy 364 S of San Pedro de Colalao ( OMNH 32566 ), 7 km W Ibatín ( OMNH 29977 ), 5 km SW Siambón ( OMNH 32553 ). Bolivia — Tarija, Carlazo ( BMNH 26.1 .1.166, 26.1.1.167 [type of janetta ], 26.1.1.168–26.1.1.170; FMNH 29169, 29170; UMMZ 155836 , 156034–156036 ), Chuquiaca ( FMNH 162505 ), 3 km SE Cuyambuyo ( MSB 67014, 67015 ), 5 km NNW Entre Ríos ( AMNH 275437 ; MSB 67010, 67012 ), ca. 10 km by road W Narvaez ( FMNH 162507 ), 1 km E Tucumilla ( MSB 67009) .