Spondylurus powelli, Hedges & Conn, 2012

Hedges, S. Blair & Conn, Caitlin E., 2012, A new skink fauna from Caribbean islands (Squamata, Mabuyidae, Mabuyinae) 3288, Zootaxa 3288 (1), pp. 1-244 : 190-194

Spondylurus powelli sp. nov.

Anguilla Bank Skink

( Figs. 73C , 76A , 77 )

Mabuya mabouya mabouya — Schwartz & Thomas, 1975:141 (part).

Mabuya mabouya mabouya — MacLean et al., 1977:36 (part).

Mabuya mabouya mabouya — Schwartz & Henderson, 1988:150 (part).

Mabuya mabouya mabouya — Schwartz & Henderson, 1991:457 (part).

Mabuya bistriata — Powell et al., 1996:82 (part).

Mabuya sloanii — Mayer & Lazell, 2000:883 (part).

Mabuya mabouya — Breuil, 2002:267 (part).

Mabuya sp. Hodge et al., 2003:43.

Mabuya sloanii — Henderson & Powell, 2009:293 (part).

Holotype. MCZ R-74343, an adult male, collected 29 May 1963 in Shannon Hill (North of Sandy Ground), Anguilla, by James D. Lazell.

Paratypes (n = 15). Anguilla. BWMC 06754–55 , Robert Powell and Avila REU, Junk’s Hole, 17 June 2000; CM 115518 and CM 115480 , Ellen J. Censky, Brimegin , 1987 ; CM 115481 , Ellen J. Censky, no specific locality, 1987; MPM 23178 , R. A. Sajdak, North Hill, 1987; RT 8335–37, Ava Gaa and Richard Thomas, Shoal Bay, January 1980. St. Barts . KU 242090–92 , Albert Schwartz, Baie de St. John (no collection dates available) ; MNHN 1997.6064 , M. Breuil, no specific locality, 1997; MNHN 2003.0844 , M. Magras, no specific locality, 2003; MPM 23055 , 0.5 km E L'Orient Beach (no collection date available) .

Diagnosis. Spondylurus powelli sp. nov. is characterized by (1) maximum SVL in males, 71.7 mm; (2) maximum SVL in females, 69.8 mm; (3) snout width, 2.28–3.02% SVL; (4) head length, 15.6–18.4% SVL; (5) head width, 11.7–14.4% SVL; (6) ear length, 1.36–2.64% SVL; (7) toe-IV length, 8.45–11.5% SVL; (8) prefrontals, two; (9) supraoculars, two (6%), three (13%), four (81%); (10) supraciliaries, three (6%), four (94%); (11) frontoparietals, two; (12) supralabial below the eye, five (31%), six (69%); (13) nuchal rows, one (19%), two (63%), three (19%); (14) dorsals, 59–65; (15) ventrals, 62–67; (16) dorsals + ventrals, 121–132; (17) midbody scale rows, 32–34; (18) finger-IV lamellae, 11–14; (19) toe-IV lamellae, 14–18; (20) finger-IV + toe-IV lamellae, 25–32; (21) supranasal contact, Y (19%), N (81%); (22) prefrontal contact, Y (25%), N (75%); (23) supraocular-1/ frontal contact, Y (38%), N (63%); (24) parietal contact, Y; (25) pale middorsal stripe, Y; (26) dark dorsolateral stripe, Y; (27) dark lateral stripe, Y; (28) pale lateral stripe, N (or barely evident on side of neck); and (29) palms and soles, pale ( Tables 3–5).

Within the Genus Spondylurus , S. powelli sp. nov. is separated from S. anegadae sp. nov., S. culebrae sp. nov., S. monae sp. nov., S. monitae sp. nov., S. semitaeniatus , and S. sloanii by having a lower dark dorsolateral stripe width/middorsal stripe width ratio (0.232 –0.762 versus 0.874–3.79 in those other species). It differs from S. caicosae sp. nov., S. culebrae sp. nov., S. fulgidus , S. haitiae sp. nov., S. lineolatus , S. magnacruzae sp. nov., S. martinae sp. nov., S. monae sp. nov., S. monitae sp. nov., S. nitidus , S. semitaeniatus , and S. spilonotus by lacking a pale lateral stripe. It is separated from S. haitiae sp. nov. by having a larger ear (2.28–3.02% SVL versus 1.19% SVL in S. haitiae sp. nov.) and by having fewer ventrals (62–67 versus 69–72 in S. haitiae sp. nov.). It differs from S. fulgidus by having fewer supraciliaries (3–4 versus five in S. fulgidus ) and more dorsals + ventrals (121–132 versus 108–120). It is distinguished from S. lineolatus by having a larger head (head length 15.6–18.4% SVL versus 12.9–14.4% SVL in S. lineolatus ), a higher number of midbody scale rows (32–34 versus 26–28 in S. lineolatus ), and four dark stripes instead of 10. From S. macleani , it is distinguished by having a darker middorsal stripe (zone) versus middorsal stripe similar to pale dorsolateral stripes in S. macleani . It is separated from S. martinae sp. nov. by having fewer ventrals (62–67 versus 68–71 in S. martinae sp. nov.). It differs from S. turksae sp. nov. by having a higher number of midbody scale rows (32–34 versus 30).

In terms of slightly overlapping (frequency) traits, Spondylurus powelli sp. nov. differs from S. anegadae sp. nov., S. culebrae sp. nov., S. semitaeniatus , and S. sloanii by having a lower frequency of supranasal contact (no contact in 81% of specimens versus contact in 80–100% of specimens belonging to those other species). From S. martinae sp. nov. and S. nitidus , it differs by having fewer finger-IV + toe-IV lamellae (25–28 in 81% of specimens versus 29–36 in 80–89% of specimens belonging to those other species). It differs from S. caicosae sp. nov. by having a higher number of midbody scale rows (32–34 versus 27–31 in 94% of specimens belonging to S. caicosae sp. nov.) and by having a higher number of dorsal + ventral scales (125–132 in 93% of specimens versus 113–124 in 85% of specimens belonging to S. caicosae sp. nov.).

Description of holotype ( Figs . 76A, 77A–B ). An adult male in excellent state of preservation, without injuries and without an abdominal slit. SVL 69.5 mm; tail length not measured; HL 12.1 mm; HW 10.0 mm; SW 2.06 mm; EL 1.55 mm; and toe-IV length 7.31 mm; ear-opening average in size and oval; toe length in the following order: I <V <II <III <IV.

Head scalation. Rostral wider than high, contacting first supralabials, nasals and supranasals. Paired supranasals not in median contact, contacting anteriormost loreal. Frontonasal heptagonal, near-diamond-shaped, wider than long, laterally in contact with anterior loreal scale. A pair of quadrilateral prefrontals, in contact medially, and in contact with frontonasal, both anterior and posterior loreals, first supraciliary, first supraoculars and frontal. Frontal tetragonal and lanceolate, in contact with the second supraoculars and paired frontoparietals. Frontoparietals also in contact with parietals and interparietal. Interparietal acorn- or shield-shaped, separated from nuchals by parietals; parietal eye distinct. Parietals in contact with upper secondary and tertiary temporal scales. Four supraoculars, the second one being the largest. Four supraciliaries, the second the longest. Nostril in posterior part of the nasal. A small postnasal, bordered by supranasal, anterior loreal and first supralabial. Anterior and posterior loreals rectangular with posteromedial projection on latter. Two upper preoculars and two lower preoculars. Eight supralabials, the sixth being the widest and forming the lower border of the eyelid. Five moderately enlarged scales behind eye comprising the postoculars; similar to temporal scales but smaller. One primary temporal, two secondary temporals, and three tertiary temporals; all imbricate, smooth, cycloid, not distinctly delimited from the scales on the nape and the sides of the neck. Seven infralabials. Mental scale wider than long, posterior margin straight. Postmental scale and one pair of adjoining chin shields in contact with anterior infralabials. First pair of chin shields in contact medially; second pair separated by a smaller cycloid scale.

Body and limb scalation. Three rows of nuchal scales, all paired except the last. Other scales on nape similar to dorsals. On lateral sides of neck, scales slightly smaller. Dorsal scales cycloid, imbricate, smooth, 59 in a longitudinal row; ventrals similar to dorsals; 62 in a longitudinal row; 32 scales around midbody. No distinct boundaries between dorsals, laterals and ventrals. Scales on tail and limbs similar to dorsals, except smaller on limbs. Palmar and plantar regions with small tubercles, subequal in size and delimited by a surrounding region of flatter scales. Subdigital lamellae smooth, single, 12 under finger-IV and 14 under toe-IV. Four preanals larger than adjacent ventral scales. No enlarged median subcaudal scales on tail.

Pattern and coloration. Dorsal ground color medium grayish-green with small dark brown flecks, sparsely distributed on body, tail, and limbs. Limbs darker than body. Dark dorsolateral stripes present, narrow (1.49 mm), dark brown, extending from tip of snout to first third of body. Dark lateral stripes present, dark brown with pale spots, extending from loreal region to first third of body. Pale middorsal stripe present, wide (2.73 mm), grayishgreen, extending from tip of snout to first third of body. Pale dorsolateral stripes present, pale gray, extending from tip of snout to first third of body. Pale lateral stripes barely evident, whitish, extending from below ear to forelimbs,

Variation. In coloration and scalation, other specimens resembled the holotype, although pale lateral stripe weak or absent in most ( Tables 4–5). Juveniles of this species, at least on St. Barts but presumably on Anguilla as well, have blue tails in life ( Fig. 77G ). No adult has been observed with a blue tail on either island, suggesting that the blue tail coloration is lost in adults. Other mabuyine species with blue tails, of which we are aware, are Panopa carvalhoi , P. croizati , and Spondylurus lineolatus .

Distribution. The species is distributed on Anguilla (91 km 2), including Dog Island (literature record), and Saint-Barthélemy (also called St. Barts, 21 km 2). All are part of the Anguilla Bank in the northern Lesser Antilles ( Fig. 11A ). However it is absent from St. Martin, which is also on that bank and is inhabited by another species, Spondylurus martinae sp. nov.

Ecology and conservation. Skinks are considered to be common on Anguilla ( Hodge et al. 2003) and St. Barts ( Breuil 2002), undoubtedly because the mongoose is absent. In that sense these islands share with Dominica ( Mabuya dominicana ) and a few other islands the striking contrast between islands lacking the mongoose —and having seemingly healthy populations of skinks —and those where skinks have been severely decimated by the introduction of the mongoose, such as nearby St. Martin. On Anguilla skinks have been found on and in loosely constructed rock walls ( Hodge et al. 2003). On St. Barts skinks have been found in sunny situations on cacti and in tall grass, and sometimes in houses ( Breuil 2002). Anguilla and St. Barts are not large islands, and threats to the survival of Spondylurus powelli sp. nov. are numerous. Invasive species, including competitors and predators, are of snakes by locals on these islands has led to the killing of not only the native snakes but also the skinks, which are sometimes mistaken for snakes ( Breuil 2002; Hodge et al. 2003).

Based on IUCN Redlist criteria ( IUCN 2011), we assess the conservation status of Spondylurus powelli sp. nov. as Vulnerable (VU A2ce). It faces a primary threat from predation by introduced mammals, including black rats, and a secondary threat from habitat alteration as a result of urbanization and tourism. Studies are needed to determine the health of any remaining populations, and threats to the survival of the species.

Reproduction. No data on reproduction are available for this species.

Etymology. The species name ( powelli ) is in honor of Robert Powell for his contributions to West Indian herpetology.

Remarks. DNA sequences of specimens from Anguilla and St. Barts are virtually identical ( Figs. 5–6 ). Also, morphologically, there is no detectable difference between the Anguilla and St. Barts populations. This was surprising given that the two islands are separated by 25 km and by the large island of St. Martin, which has a separate, endemic species ( Spondylurus martinae sp. nov.). Any vicariance from the isolation of previously connected land areas of the Anguilla bank, during the Pleistocene and Holocene, would be expected to be reflected in at least some genetic divergence at this relatively fast evolving gene (Cytochrome b). If this low sequence divergence was caused by natural dispersal on flotsam—based on currents, only from St. Barts to Anguilla —that dispersal event must have occurred very recently. Movement between the two islands by humans is a more likely explanation for this low sequence divergence, instead of recent, natural dispersal. Yet another explanation, that they are both recent colonists from another location, is unlikely because there is no other island known with this species. Phylogeographic studies using microsatellites or other fast-evolving markers might be able to resolve which of the two island populations, Anguilla or St. Barts, or both, is native and which (if either) is introduced.

Figures

FIGURE 5 (continued on the next page)

FIGURE 6. Phylogenetic tree of Neotropical skinks (Mabuyidae, Mabuyinae) showing linearized branch lengths (GTR +

FIGURE 11. Map showing the distribution of mabuyine skinks occurring in the Lesser Antilles and Trinidad and Tobago. See Fig. 1 for location of the islands. The islands and species are: (A) Anguilla, Dog Island, and St. Barts (Spondylurus powelli sp. nov., squares), and St. Martin (S. martinae sp. nov., circle); (B) Guadeloupe: Basse-Terre (Mabuya guadeloupae sp. nov., square), Grande-Terre (Mabuya grandisterrae sp. nov., triangle), Îlet à Cochons (Mabuya cochonae sp. nov., star), La Désirade and Terre de Bas, Petite-Terre (Mabuya desiradae sp. nov., diamonds), and Marie-Galante (Capitellum mariagalantae sp. nov., circle); (C) Martinique (Mabuya mabouya, circles; Capitellum metallicum, triangle); (D) St. Vincent, the Grenadines, and Grenada (Copeoglossum aurae sp. nov., circles; Marisora aurulae sp. nov., triangles); (E) Redonda (Copeoglossum redondae sp. nov., circle) and Montserrat (Mabuya montserratae sp. nov., square); (F) Dominica (Mabuya dominicana); (G) St. Lucia (Alinea luciae), (H) Barbados (Alinea lanceolata); (I) Trinidad (Copeoglossum aurae sp. nov., circles; Marisora aurulae sp. nov., triangle), and (J) Tobago (Copeoglossum aurae sp. nov., circles; Marisora aurulae sp. nov., triangles). Hollow symbols in A and J are literature records (specimens not examined). Where no specific localities within an island are known for a species, a symbol is placed centrally on the island: Alinea luciae, Capitellum mariagalantae, Capitellum metallicum, and Copeoglossum redondae sp. nov. The scale in (A) applies to all islands.

FIGURE 73. Representative patterns in species of the Genus Spondylurus (top, dorsal view; bottom, side view). (A) S. monitae sp. nov.; (B) S. nitidus; (C) S. powelli sp. nov.; (D) S. semitaeniatus; (E) S. sloanii; (F) S. spilonotus; and (G) S. turksae sp. nov.

FIGURE 76. Head scalation in species of the Genus Spondylurus (left, side view; right, dorsal view). (A) S. powelli sp. nov. (MCZ R-74343, holotype); (B) S. semitaeniatus (UMMZ 80585); (C) S. sloanii (USNM 576305); and (D) S. spilonotus

FIGURE 77. Spondylurus powelli sp. nov., from Anguilla and Barthélemy. (A–B) MCZ R-74343, holotype, Shannon Hill, Anguilla. (C–E) uncataloged, Anguilla (live individuals, photographed by Robert Powell). (F–G) uncataloged, St. Barthélemy (live individuals, photographed by Karl Questal).