Spondylurus macleani ( Mayer & Lazell 2000 ) Hedges, S. Blair & Conn, Caitlin E., 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 : 167-169

Spondylurus macleani ( Mayer & Lazell 2000) comb. nov.

Carrot Rock Skink

( Figs. 55G , 64C , 67 )

Mabuya mabouya sloanii — Mayer & Lazell, 1988:23 (part).

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

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

Mabuya macleani — Mayer & Lazell, 2000:871. Holotype: MCZ R-170884, Carrot Rock , south of Peter Island, British Virgin Islands, 18° 19' 45" N, 64° 34' 18" W, James D. Lazell, Jr., 13 July 1985.

Mabuya macleani —Miralles, 2005:51.

Mabuya macleani — Henderson & Powell, 2009:293.

Material examined (n = 5). Carrot Rock, British Virgin Islands. MCZ R-176728 (paratype), M. Hernandez and F. Krause, 26 October 1991 ; MCZ R-182270–72 (paratype) , R. Jenkins and L. Drew, 17 July 1988 ; USNM 576303 , June 2007 .

Diagnosis. Spondylurus macleani is characterized by (1) maximum SVL in males, 75.5 mm; (2) maximum SVL in females, 79.6 mm; (3) snout width, 2.47–3.09% SVL; (4) head length, 16.0–17.5% SVL; (5) head width, 12.1–13.8% SVL; (6) ear length, 1.29–1.52% SVL; (7) toe-IV length, 8.22–10.5% SVL; (8) prefrontals, two; (9) supraoculars, four; (10) supraciliaries, three (20%), four (60%), five (20%); (11) frontoparietals, two; (12) supralabial below the eye, five (40%), six (60%); (13) nuchal rows, one (20%), two (80%); (14) dorsals, 62–65; (15) ventrals, 62–64; (16) dorsals + ventrals, 125–127; (17) midbody scale rows, 32–34; (18) finger-IV lamellae, 12–14; (19) toe-IV lamellae, 15–18; (20) finger-IV + toe-IV lamellae, 28–31; (21) supranasal contact, Y (60%), N (40%); (22) prefrontal contact, N; (23) supraocular-1/frontal contact, Y (20%), N (80%); (24) parietal contact, Y; (25) pale middorsal stripe, Y; (26) dark dorsolateral stripe, Y (faint); (27) dark lateral stripe, Y (very faint); (28) pale lateral stripe, N; and (29) palms and soles, pale ( Tables 3–5).

Within the Genus Spondylurus , S. macleani differs from all other species except S. anegadae sp. nov. and S. turksae sp. nov. by having short and faded dorsolateral and dark lateral stripes, and essentially no dorsal pattern posterior to those stripes. From S. anegadae sp. nov., S. culebrae sp. nov., S. monae sp. nov., S. monitae sp. nov., S. semitaeniatus , and S. sloanii , it differs by having a wider middorsal stripe (3.14–3.96% SVL versus 0.953– 2.81% in those other species). It differs from S. haitiae sp. nov. and S. fulgidus by having a higher number of dorsal scales (62–65 versus 52–60 in those other species). It differs from S. magnacruzae sp. nov. and S. spilonotus by having a higher dark dorsolateral stripe width/middorsal dark stripe width ratio (0.608 –0.916 versus 0.276 –0.464 in those other species). From S. culebrae sp. nov., it differs by having a lower dark dorsolateral stripe width/ middorsal stripe width ratio (0.608 –0.916 versus 0.953–2.24 in S. culebrae sp. nov.). It is distinguished from S. lineolatus by having a higher number of finger-IV lamellae (12–14 versus 8–11 in S. lineolatus ). It is separated from S. martinae sp. nov. by having a lower number of ventrals (62–64 versus 68–71 in S. martinae sp. nov.). It differs from S. turksae sp. nov. in having more midbody scale rows (32–34 versus 30).

Frequency differences also separate Spondylurus macleani from other species within the genus. It is separated 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.). It differs from S. monitae sp. nov. by having a lower frequency of supraocular-1/frontal contact (no contact in 80% of specimens versus contact in 86% of specimens belonging to S. monitae sp. nov.). It is separated from S. nitidus by having a smaller head (head length 16.0–17.0% SVL in 80% of specimens versus 17.4–20.7% SVL in 87% of specimens belonging to S. nitidus ) and by having a shorter toe-IV (toe-IV length 8.22%–9.26% SVL in 80% of specimens versus 10.1–12.7% SVL in 93% of specimens belonging to S. nitidus ). It is distinguished from S. powelli sp. nov. by having a higher dark dorsolateral stripe width/middorsal stripe width ratio (0.608 –0.916 versus 0.232 –0.606 in 87% of specimens belonging to S. powelli sp. nov.).

Description of material. Three adult females and two adult males in excellent state of preservation, without injuries and with an abdominal slit. SVL 64.5–79.6 mm, our measurements differing only slightly from those of Mayer and Lazell (2000); tail length 10.7–76.2 mm (regenerated, broken, or complete); HL 10.8–13.2 mm; HW 8.67–10.4 mm; SW 1.73–2.33 mm; EL 0.83–1.17 mm; toe-IV length 5.90–7.11 mm; ear-openings average in size and round; fingers and toes clawed; toe length in the following order: I <V <II <III <IV or I <V = II <III <IV.

Head scalation. Rostral wider than high, contacting first supralabials, nasals and supranasals. Paired supranasals in or not in median contact, contacting anteriormost loreal. Frontonasal diamond-shaped, wider than long, laterally in contact with anterior loreal scale. A pair of quadrilateral prefrontals, separated medially, and in contact with frontonasal, both anterior and posterior loreals, first supraciliary (in some cases), first (and sometimes second) supraoculars, and frontal. Frontal heptagonal, in contact with the second (and sometimes first) supraoculars and paired frontoparietals. Frontoparietals also in contact with parietals and interparietal. Interparietal tetragonal and lanceolate or acorn-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 longest and largest. Three to five supraciliaries, the first or 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 squarish or rectangular with posterodorsal or posteromedial projection on latter (in some cases). Two or three upper preoculars and two lower preoculars. Seven or eight supralabials, the fifth or 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, chin shields in contact with anterior infralabials. First two pairs of chin shields in contact medially; third pair separated by a smaller cycloid scale (if it is present).

Body and limb scalation. One or two rows of paired or unpaired nuchal scales. Other scales on nape similar to dorsals. On lateral sides of neck, scales slightly smaller. Dorsal scales cycloid, imbricate, smooth, 62–65 in a longitudinal row; ventrals similar to dorsals; 62–64 in a longitudinal row; 32–34 scales around midbody. No distinct boundaries between dorsals, laterals and ventrals. Scales on tail and limbs similar to dorsals, except smaller on limbs. On regenerated portions of tails, one enlarged row each of middorsal and midventral scales and lateral rows on each side similar to dorsals and ventrals. Palmar and plantar regions with small tubercles, subequal in size and delimited by a surrounding region of flatter scales. Subdigital lamellae smooth, single, 12–14 under finger-IV and 15–18 under toe-IV. Preanal scales similar to ventrals. Enlarged or no enlarged median subcaudal scales on tail.

Pattern and coloration. Dorsal ground color pale bluish-gray without dark brown spots. Dark dorsolateral stripes present, narrow (1.52–2.08 mm), dark brown, extending from nuchal area to forelimbs. Dark lateral stripes, tan and weakly defined, extending from loreal region to forelimbs or first third of body. Pale middorsal stripe present, wide (2.27–3.04 mm), pale bluish-gray, extending from nuchal area to forelimbs. Pale dorsolateral stripes present, pale bluish-gray, extending from top of head to forelimbs. Pale lateral stripes absent. Ventral surface of body without pattern. Palmar and plantar surfaces unpigmented.

Color in life: The holotype, in life, was described by Mayer and Lazell (2000) as being pallid beige-gray with lead-gray dark dorsolateral stripes. That color description applies to another live individual ( Fig. 67D–E ) and indicates that the bluish color of preserved specimens is an artifact of preservation.

Distribution. The species is known only from Carrot Rock (0.013 km 2, 25 m) in the British Virgin Islands ( Fig. 10E ).

Ecology and conservation. Carrot Rock is a tiny jumble of rocks with a few small clumps of vegetation, including small trees (Sea Grape, Coccoloba uvifera Linnaeus ), several species of cacti, and some vines and grass ( Lazell 1983; Mayer & Lazell 2000). The observation by Grant (1932a), for Puerto Rico, that the favorite hiding place of mabuyine skinks is in dense clumps of cactus, probably applies here as well. In 1988, the total number of individuals of this species was estimated to be 520, based on extrapolation from a sample of eight ( Mayer & Lazell 2000). Skink abundance plummeted by the mid-1990s as a result of severe droughts and hurricanes, and population levels never fully recovered. Subsequently, only 2–3 individuals have been sighted during two-hour visits to the island ( Mayer & Lazell 2000). Based on this anecdotal evidence, the total number of individuals of Spondylurus macleani is likely less than 200 (James D. Lazell, personal communication). Given the existing small population size, any future climate change is likely to cause major changes in the skink population as well, and enhanced change as a result of anthropogenic factors could lead to extinction. Also, the probability of human introduction of pests (e.g., rats, invertebrates) that might cause direct or indirect negative effects on the skink population is not insignificant given the proximity of the island to Peter Island (400 m away) and the prevailing winds and currents. The island is currently unprotected, and anyone can visit it.

Based on IUCN Redlist criteria ( IUCN 2011), we assess the conservation status of Spondylurus macleani as Endangered (EN D). It faces a primary threat from predation by invasive mammals, including black rats, and other pests likely to colonize the island, and a secondary threat from habitat alteration resulting from human activities (the island is unprotected) and from global warming in coming decades. Studies are needed to determine the health of the population, and threats to the survival of the species. Captive breeding programs should be considered.

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

Etymology. The species ( macleani ) was named in honor of William P. MacLean III (1943–1991) for his contributions to the herpetology of the Virgin Islands ( Mayer & Lazell 2000).

Remarks. The small island of Carrot Rock may be no more than 3000 years old ( Lazell 1983; Mayer & Lazell 2000). This might seem like too short a time for an endemic species of lizard to evolve, but the island is also the only known locality for another distinct lizard species, Anolis ernestwilliamsi Lazell (1983) . The simplest and most likely hypothesis is that they evolved in isolation on Carrot Rock in the last few thousand years. An alternative, but more complex, hypothesis is that they are relict populations of widely distributed species that have since disappeared elsewhere. The timetree ( Fig. 7 ) shows that S. macleani split from other species in the Puerto Rico region in the Pleistocene (0.7 Ma), not Holocene, but the Bayesian credibility interval is wide, as expected given

Figures

FIGURE 7. Timetree of Neotropical skinks (Mabuyidae, Mabuyinae) using the data and topology of the full (four-gene) data set from Fig. 5. Divergence times (indicated on nodes) are in millions of years and are averages of the results of two Bayesian analyses (independent and autocorrelated rates). Bayesian credibility intervals (gray bars) are composites of the intervals derived from the two analyses. Three African species (Mabuyidae, Trachylepidinae subfam. nov.) are included to estimate the time of the trans-Atlantic dispersal event. Blue vertical bars indicate taxa occuring on Caribbean islands.

FIGURE 10. Map showing the distribution of mabuyine skinks occurring on islands in the greater Puerto Rico region. See Figure 1 for location of the islands. The islands and species are: (A) Puerto Rico (Spondylurus nitidus); (B) Mona (Spondylurus monae sp. nov., squares) and Monito (Spondylurus monitae sp. nov., circle); (C) Desecheo (Spondylurus nitidus); (D) Vieques (Spondylurus nitidus, circle), Culebra (Spondylurus nitidus, circles; Spondylurus culebrae sp. nov., squares), Cayo Luis Peña and Cayo Norte (S. nitidus, circles); (E) most of the U.S. and British Virgin Islands (Spondylurus macleani, diamond; Spondylurus sloanii, squares; Spondylurus semitaeniatus, circles; Spondylurus spilonotus, triangles); (F) Anegada (Spondylurus anegadae sp. nov.); and (G) St. Croix and Green Cay (Capitellum parvicruzae sp. nov., circle; Spondylurus magnacruzae sp. nov.,

FIGURE 55. Representative patterns in species of the Genus Spondylurus (top, dorsal view; bottom, side view). (A) S. anegadae sp. nov.; (B) S. caicosae sp. nov.; (C) S. culebrae sp. nov.; (D) S. fulgidus; (E) S. haitiae sp. nov.; (F) S. lineolatus; (G) S. macleani; (H) S. magnacruzae sp. nov.; (I) S. martinae sp. nov.; and (J) S. monae sp. nov.

FIGURE 64. Head scalation in species of the Genus Spondylurus (left, side view; right, dorsal view). (A) S. haitiae sp. nov. (MCZ R-3617, holotype); (B) S. lineolatus (MCZ R-156938); (C) S. macleani (MCZ R-182270, paratype); and (D) S.

FIGURE 67. Spondylurus macleani, from Carrot Rock, British Virgin Islands. (A–C) MCZ R-182270, paratype, Carrot Rock (no specific locality). (D–E) uncataloged (live individual, photographed by A. Sanchez).