Mabuya cochabambae Dunn

Harvey, Michael B., Aguayo, Rodrigo & Miralles, Aurélien, 2008, Redescription and biogeography of Mabuya cochabambae Dunn with comments on Bolivian congeners (Lacertilia: Scincidae), Zootaxa 1828, pp. 43-56 : 45-51

Mabuya cochabambae Dunn

( Fig. 1 , 2 )

Mabuya frenata cochabambae Dunn, 1935: 553 . Holotype (UMMZ 68094) from “Pocona” Cochabamba, Bolivia. Paratypes UMMZ 68098, UMMZ 172577 (originally 68094 b), 172578 (originally 68094 d), and MCZ 46532 (originally UMMZ 68094 c). Peters & Donoso-Barros, 1970:198.

Mabuya cochabambae Dunn : Fugler, 1989: 66; De la Riva et al., 1992: 216; Dirksen & De la Riva, 1999: 204; Mausfeld & Lötters, 2001: 50; Pincheira-Donoso, 2002: 20; Aguayo et al., 2007: 134.

Diagnosis. A medium-size species of Mabuya reaching at least 76 mm SVL and distinguished from congeners by the following combination of characters: (1) prefrontals paired, usually separated medially; (2) frontoparietals fused; (3) parietals usually in contact with each other behind interparietal; (4) secondary nuchals absent; (5) supraciliaries usually three, first longer than combined second and third; (6) palm and sole usually darkly pigmented (rarely pale); (7) narrow vertebral and paravertebral brown stripes present dorsally; lateral black band edged dorsally and ventrally by prominent pale stripes; (9) lamellae under fourth finger 10–13; (11) lamellae under fourth toe 13–16; (12) limbs relatively short; fourth toe just reaching wrist when legs pressed against flanks; (13) supraoculars three, the first larger than remaining two combined; (14) supralabials 6–7, the fifth or sixth largest and positioned under eye; (15) internasals (=supranasals) usually in contact; (16) postmental entire.

Description. Snout relatively short and blunt; snout-vent length among eight adult specimens 55–76 mm (65 ± 8, CBGR 125 largest in series; sample likely contains various age classes), among two juveniles 37–38 mm; head length 18.3–22.4% (20.7 ± 1.6, n = 10) of SVL; tail 1.3–1.8 (1.6 ± 0.3, n = 3) times as long as SVL; limbs relatively short; fourth toe just reaching wrist when legs pressed against flanks.

Rostral visible from above, almost twice as wide as high, slightly narrower than mental; medial contact of internasals usually (94%, n = 16, separate in UMMZ 68094a; Dunn, 1935) separating rostral from frontonasal; accessory frontonasals (sensu Rebouças-Spieker, 1974) absent; prefrontals paired, separated by contact between frontal and frontonasal (100%, n = 16); frontal usually five-sided and about twice as long as wide; frontoparietals fused; parietals in contact behind interparietal (100%, n = 16); parietal eye visible; pair of primary nuchals; secondary nuchals (sensu Miralles, 2006) absent; supraoculars three (100%, n = 32), first about as large as second and third combined and in wide contact with frontal; supraoculars 2 and 3 not contacting frontal (i.e., the first supraocular is the last supraocular to contact the frontal; Greer & Broadley, 2000); supraciliaries usually 3/3 (92%, n = 24), first larger than other two combined (except in CBG R-323 where the first supraciliary is divided on both sides, 4/4 total. The first supraciliary is still the largest in this specimen).

Nasal tear-shaped with nostril positioned near posterior edge of scale; small postnasal separating internasal from supralabials; two loreals between postnasal and preocular scales; anterior loreal contacting internasal and frontonasal; posterior loreal contacting prefrontal and first supraciliary; lower eyelid with transparent disc; one row of palpebrals separating disc from upper edge of eyelid; pretemporals (sensu Greer & Broadley, 2000) two; single primary temporal contacting last supralabial and lower pretemporal; larger upper secondary temporal broadly contacting lower secondary temporal; temporal not overlapping parietal (Greer & Nussbaum, 2000); supralabials six (59%, n = 32) or seven (41%, n = 32) with, respectively, fifth or sixth supralabial largest and positioned below eye (i.e., single supralabial behind eye, without exception); infralabials five (8%, n = 24), six (84%, n = 24), or seven (8%, n = 24); postmental entire, followed by two pairs of chinshields, first pair in contact medially and each contacting infralabials; second pair of chinshields separated medially by first gular scale; preauricular margin lacking denticles.

Scales of palm and sole round in transverse and vertical aspect, subequal except for enlarged scales along pre and postaxial margins; most proximal scale of foot and hand greatly enlarged relative to others; all digits clawed; Finger 3 = 4> 5 = 2> 1; Toe 4> 3> 5 = 2> 1; subdigital lamellae of fourth finger 10–13 (12 ± 1.0, n = 14); subdigital lamellae of fourth toe 13–17 (15 ± 1.0, n = 14); dorsals smooth, those on tail not noticeably enlarged relative to dorsals on body, 57–62 (60 ± 1.9, n = 14) from first scale behind nuchals to posterior margin of thigh; scales at midbody 28–32 (31 ± 1.1, n = 16); ventrals 34–43 (39 ± 2.6, n = 13) from anterior margin of arm to anterior margin of thigh.

Coloration in preservative (70% ethanol after unbuffered 10% formalin). The dorsal surface of the head and dorsal field (about four dorsals wide) of the body and tail are bronze. A vertebral black stripe about onehalf scale wide begins behind the nuchals and extends to the base of the tail. It straddles the medial margins of two dorsal scales. Positioned along the lateral margins of these same scales are two fainter and more narrow, paravertebral brown stripes. A lightly pigmented stripe begins just behind the nostril and edges the black lateral band dorsally onto the tail. This sharp, prominent stripe is about one-half scale wide, pale bronze on the head and white behind the nuchals. Behind the parietals, it is edged by a slightly wider black stripe. A black, lateral band, about three scales high at midbody, extends from the nostril, through the eye, over the ear, and onto the tail. It is edged ventrally by another white stripe extending from the rostral, under the ear, over the limbs, and onto the tail. However, the supralabials are cream rather than white. Both white stripes appear finely serrated behind the arm and, in the case of the ventrolateral stripe, for a short distance on the neck. Black dorsoposterior apexes of the lower row of scales within the stripe create the serrated effect. Below the ventrolateral white stripe, three rows of scales on the lower flanks have thick black edges. The row just below the white stripe is almost entirely black from about midbody to the ear. Although the palpebrals lie within the lateral band and, thus, are mostly entirely black, those edging the ocular aperture are light bronze. The disc of the lower eyelid is not entirely clear, but rather smoke-colored. The ventral body and head are immaculate white (most adults) or dark gray (three specimens in CBG). UMMZ 172577 and ZFMK 72151 have pale palms and soles; however, the palms and soles are charcoal in the other adult specimens.

In specimens with regenerated tails (such as UTA 55805), the regenerated portion of the tail assumes quite a different coloration from the rest of the tail. The bold white and black stripes abruptly stop and are replaced by four rows of blotches along the sides of the otherwise brown regenerated portion of the tail. Whereas the ventral surface of the unregenerated portion is white, the ventral surface of the regenerated portion is brown.

Coloration in life (based on field notes by MBH regarding CBF 2900–2901 and UTA 55805). The palpebrals edging the ocular aperature, lower edge of the rostral, labials, mental, and postmental were orange. In UTA 55805 the ventral surface of the regenerated portion of the tail was also orange. Anteriorly, the white stripes became orange on the head. The ventral body, limbs, and unregenerated portion of the tail were pale yellow; the gular region was cream. The tongue and iris were black.

Mabuya cochabambae undergoes relatively little changes in color during ontogeny and the sexes are similarly colored (at least, in preservative). Juveniles possess orange labials and look like adults although the ventral surface of the tail is black and the palms and soles are cream-colored. Nonetheless, the ventral surfaces of the fingers and toes of juveniles are charcoal and distinctly darker than the venter.

Distribution and Natural History. The known range of Mabuya cochabambae extends for only about 235 km (airline) along the southwestern slopes of the Andes in Cochabamba and Santa Cruz ( Fig. 3 ). Due to rain shadow effects, the southwestern slopes and valleys are relatively xeric and mostly covered in brush and deciduous forest. Nonetheless, where clouds just cross the peaks of some mountains, evergreen cloud forest and a humid ecotone between cloud forest and dry forest occurs. Sunny, relatively open areas within this ecotone appear to be the preferred habitat of M. cochabambae . Like some anurans usually associated with more humid, montane environments, M. cochabambae appears to use streams and rivers as humid corridors to reach slightly lower, more xeric locations such as the type locality, Pocona.

We have encountered Mabuya cochabambae in Polylepis forest, in humid grassland and farmland adjacent to cloud forest, among the brushy vegetation of the semihumid prepuna, and along the margins of rivers and creeks through slightly drier habitats. A series collected by M. B. Harvey in the early afternoon of a sunny day in January, 2008, came from cultivated fields adjacent to cloud forest on the northwestern slopes of the Serranía de Siberia. The species appeared to be quite common at this locality, although the skinks were extremely wary and difficult to catch. Two experienced collectors were able to collect about one specimen per hour with about twice as many escaping. At the first sign of danger, foraging or sunning individuals of M. cochabambae immediately fled into tall grass or into large piles of rocks. Field notes and our observations indicate that this species is active from 0900–1500 hrs during sunny periods of the day (M. B. Harvey, personal observation, Aguayo et al., 2007).

The known vertical distribution of this species is 2700 m (at Pocona) to 3900 m (at Infernillo). Mausfeld & Lötters (2001) thought that it occurred much lower, perhaps reaching 1300 m based on a specimen (ZFMK 72151) from the “vicinity of Pampagrande.” We suspect that the ZFMK specimen came from higher elevations on the adjacent Andean slopes. Over the last ten years or so, local collectors supplied thousands of reptile specimens from Pampagrande and the surrounding valley to the Museo Noel Kempff Mercado. These collections contain remarkable series of otherwise rare lizards and snakes such as Micrurus serranus ( Harvey et al., 2003) and Apostolepis multicincta ( Embert & Reichle, 2003; Harvey, 1999). Not a single specimen of Mabuya was included in these samples ( Gonzales et al., 2004; L. Gonzales, in litt.), and a herpetologist from the Museo Noel Kempff Mercado who grew up in Pampagrande (R. Sosa) has never seen a skink in the town’s immediate vicinity. The original collector (Mr. Langer, a priest whose parish includes Pampagrande, but also adjacent areas in Santa Cruz and Cochabamba) does not recall where the specimen was collected (L. Gonzales, in litt.).

Remarks. We considered the possibility that ZFMK 72151 might be Mabuya dorsivittata , since many Chacoan species occur at lower elevations in the dry valleys. W. Böhme and P. Wagner of the ZFMK kindly examined the specimen for us and supplied photos of it. ZFMK 72151 is unusual in having pale soles and palms and four supraciliaries on one side. Both of these characters can ordinarily be used to distinguish M. dorsivittata from M. cochabambae . Unlike M. dorsivittata , ZFMK 72151 has fused frontoparietals. The first supraciliary of M. dorsivittata is a small, squarish scale, whereas on both sides of ZFMK 72151 the first supraciliary is longest. CBG 323 from Siberia also has 4/4 supraciliaries, the first longest on both sides. Although most M. cochabambae have charcoal palms and soles, distinctly darker than the venter, UMMZ 172577 from Pocona also has pale soles and palms. Thus, although ZFMK 72151 shares two ordinarily diagnostic traits with M. dorsivittata , these traits also occur in some other specimens of M. cochabambae ; they are polymorphic traits and the specimen was correctly identified by Mausfeld & Lötters (2001) as M. cochabambae .

Mabuya cochabambae in Bolivia and M. meridensis in Venezuela are the only described species of Mabuya inhabiting the Andes above 2000 m (Miralles et al., 2005). Nonetheless, these distantly allopatric species are probably not closely related. Recent molecular phylogenetic studies of Mabuya ( Carranza & Arnold 2003; Whiting et al. 2006) did not include Mabuya cochabambae . Mausfeld and Lötters (2001) found M. cochabambae to be more closely related to M. dorsivittata than to M. frenata , but these three were the only species included in their analysis. When compared to other species ( Table 2 ), the genetic distances between M. cochabambae and M. dorsivittata are extremely low. They are even lower than some intraspecific distances between some specimens of M. guaporicola and between some specimens of M. frenata . Both morphological similarity and pairwise comparisons of genetic distances ( Table 2 ) indicate that M. cochabambae and M. dorsivittata likely diverged from a common ancestor quite recently. Biogeographically, this result is not surprising. The dry valley ecosystem extends from Cochabamba through Santa Cruz and Chuquisaca to Tarija. Its herpetofauna is dominated by species from the Gran Chaco rather than species from the lowland rainforests and savannas on the other side of the Andes in Cochabamba and Santa Cruz. Regarding species endemic to the dry valleys, Harvey et al. (2003) noted the existence of pairs of species, the endemic species almost invariably being the apparent sister taxon of a species in the Gran Chaco of Argentina and southern Bolivia. Some examples include Apostolepis multicincta and A. dorbignyi , Micrurus serranus and M. baliocoryphus , and Amphisbaena cegei and A. darwinii . Mabuya dorsivittata is widely distributed in northern Argentina ( Cei, 1993; Gallardo, 1968) and, together with M. cochabambae , can be added to this list of pairs of species with similar distributional patterns.

The distribution of Mabuya cochabambae in humid habitats and its apparent use of riparian areas as humid corridors into drier environments of the valleys also recalls the ecology of M. dorsivittata . Although ranging across the xeric Gran Chaco, M. dorsivittata is frequently found in humid habitats ( Gallardo, 1968). Reviewing locality data for specimens in Uruguayan museums, Gudynas and Pebé (1978) found that about half of the specimens were collected in humid environments, usually adjacent to water courses. These authors supplemented their survey with observations on a captive animal that spent about half of its time partially submerged or swimming in water.

Figures

FIGURE 1. Mabuya cochabambae (UTA 55805, adult male, SVL 69.6 mm) from the Serranía de Siberia, Cochabamba, Bolivia.

FIGURE 2. Morphology of Mabuya cochabambae (UMMZ 68098, paratype, scale bars 2 mm) from Santa Cruz Department, Bolivia.

FIGURE 3. Distribution of Mabuya cochabambae (black circles) in the Andes of Cochabamba and Santa Cruz, Bolivia.