Microlophus slevini, Torres-Carvajal, 2024

Torres-Carvajal, Omar, 2024, A new species of lava lizard (Iguanidae: Tropidurinae: Microlophus) from the Galápagos, Zootaxa 5428 (1), pp. 58-74 : 63-69

Microlophus slevini sp. nov.

https://zoobank.org/NomenclaturalActs/ F7C84D25-0BA5-46B3-A455-E3BF5B6C4A91

Tropidurus grayii (part)— van Denburgh & Slevin (1913):164.

Microlophus grayii (part)— Benavides et al. (2009):1608.

Proposed standard English name: Slevin’s lava lizards

Proposed standard Spanish name: lagartijas de lava de Slevin

Holotype. CAS 9428 , adult male from Gardner-near-Floreana islet, 1°19.9’S, 90°17.75’W, Galápagos Archipelago, collected by Joseph R. Slevin on 3 October 1905.

Paratypes (27). 10 females: CAS 9421 , 9424 , 9426 , 9429 , 9431 , 9432 , 9437 , 9439 , 9443 , 9446 ; 13 males: CAS 9422 , 9423 , 9425 , 9427 , 9428 , 9430 , 9433–9436 , 9438 , 9444 , 9445 ; and four juveniles: CAS 9440–9442 , 9447 . Same collection data as holotype; CAS 9443–9447 were collected by E. S. King.

Diagnosis. Microlophus slevini differs from all other species of Microlophus in the Galápagos, except M. grayii , in having conspicuous neck folds (rictal, longitudinal, gular, antegular, postauricular, oblique, and antehumeral); granular scales within folds; small, imbricate, and keeled scales on sides of neck (>4X smaller than dorsal neck scales), distinctive black spots on flanks, fore limbs, and hind limbs in males, less than 80 scales around midbody, and no more than 50 vertebral scales. The new species (N = 23) can be distinguished from M. grayii (N = 64, character states in parentheses) by having more gulars, 27–39, mean 31.86 ± 3.54 SD (23–30, mean 25.98 ± 1.74 SD; t-value = -7.316, p = 0.000); fewer loreals, 3–5, mean 4.18 ± 0.66 SD (2–10, mean 5.67 ± 1.56 SD, t-value = 6.172, p = 0.000); more lamellae on Finger IV, 19–21, mean 19.91 ± 0.51 SD (16–21, mean 17.86 ± 1.10 SD; t-value = -11.799, p = 0.000); more lamellae on Toe IV, 25–30, mean 27.74 ± 1.29 SD (22–27, mean 24.47 ± 0.99 SD; t-value = -12.504, p = 0.000); among other scutellational characters ( Table 2 ).

Description of the holotype ( Figs 3 , 4 ). SVL 86 mm; remaining tail length 101 mm, regenerated tail length 33 mm; head length 19.36 mm; head width 15.49 mm; head height 12.55 mm; interparietal width 4.84 mm, interparietal length 5.03 mm; distance between fore and hind limbs 39.24 mm; hind limb length 64.58 mm. Scales on frontonasal region juxtaposed, not imbricating posteriorly; conspicuous lenticulate organs on frontonasal and supraocular regions; rostral wider than high, 4.9 mm x 1.67 mm, highest medially, in contact with first supralabial, first lorilabial and three postrostrals; nasal single, slightly protruding, longitudinally elongated, in contact with postrostral anteriorly, first lorilabial and first loreal laterally, three tiny scales posteriorly and posteromedially, lateralmost internasal anteromedially, and postrostral anteriorly; nostril posteriorly located, about one half the size of nasal, posterolaterally oriented; five elongated supralabials followed posteriorly by four smaller scales up to rictus oris; supralabials not in contact with subocular; canthals two; four laminate supraciliaries anteriorly, in contact with a single supraciliary posteriorly; preocular single, keeled, in contact with canthal, three loreals and subocular; subocular single, elongate, with longitudinal keel dorsally, separated from supralabials by 5–6 lorilabials; palpebrals granular; medial row of supraoculars enlarged, the largest being more than half the width of the supraocular disk, in contact laterally with smaller scales more or less disposed in 2–3 longitudinal rows; three (two on left side) circumorbitals in contact with posteromedial margin of supraocular disk; interparietal enlarged, slightly longer than wide (5.03 mm x 4.84 mm), with concave lateral margins and convex anterior and posterior margins; parietal eye located slightly anterior to center of interparietal; temporals slightly keeled or multicarinate, smaller than lateral neck scales above folds; tympanum recessed; ear opening oval in shape, partially covered anteriorly by six (four on left side) projected smooth, lanceolate scales; mental slightly wider than high (2.81 mm x 2.22 mm), highest medially, in contact with first infralabials laterally and one pair of postmentals posteriorly; six (five on left side) elongate infralabials followed posteriorly by four (five on left side) smaller scales up to rictus oris; three pairs of postmentals, with only the anterior pair in contact medially; seven (eight on right side) elongate sublabials; gulars 32, smooth, imbricate, usually bearing one apical pit, decreasing in size laterally.

Vertebral crest prominent, with vertebrals on posterior half of body and anterior quarter of tail nearly twice as high as anterior vertebrals; dorsals strongly keeled and mucronate, gradually decreasing in size on flanks as they approach venter; dorsals on neck smaller than dorsals at midbody; lateral neck scales less than half the size of dorsals; ventral neck scales similar in size to dorsals, but smooth; rictal, longitudinal, gular, antegular, postauricular, oblique, and antehumeral neck folds present; scales within folds granular; keels on dorsal and caudal scales aligned to form anteroventrally oriented longitudinal ridges; posthumeral region with granular or small, flat, and smooth scales; ventrals smooth or slightly keeled, imbricate, non-mucronate, nearly half the size of dorsals; hands with smooth and imbricate scales dorsally, of which many bear an apical notch; palm scales and subdigital lamellae with 3–4 mucrons each; arm and forearm with keeled and imbricate scales dorsally (mucronate in arm), and smaller, smooth and imbricate scales ventrally; thighs with large, keeled, imbricate and mucronate scales dorsally, and smaller (less than half the size), smooth scales on posterior surface; scales on anterior and ventral aspects of thighs similar in size to dorsals, smooth and imbricate; shanks with keeled, imbricate and mucronate scales dorsally, and smooth and imbricate scales ventrally; most plantars and subdigital lamellae with three mucrons each, of which the medial one is more projected; dorsal foot scales and supradigitals imbricate, smooth or slightly keeled, most with apical notch; tail incomplete, slightly compressed, with conspicuous vertebral crest (verterbrals more than twice the size of adjacent dorsals) on anterior half; three scale whorls per autotomic segment; caudals keeled, mucronate, and imbricate; subcaudals smooth and imbricate.

Color in preservative of holotype. Dorsal aspect of head, body, limbs and tail light brown, or light gray on those scales that have lost their outer surface; dorsum, flanks and neck with a series of black dots (1–3 scales large) approximately arranged in transverse rows that meet medially along vertebral crest; dorsal surface of limbs, anterior end of tail (dorsally), chin, sides of head and pectoral region covered by smaller black or dark brown dots; conspicuous black gular patch extending laterally as far as longitudinal neck fold; chin and ventral surfaces of body, limbs and tail yellowish cream ( Figs 3 , 4 ).

Color in life. I was not able to examine live specimens of M. slevini . However, because there seem to be no differences in coloration between M. grayii from Floreana and M. slevini ( van Denburgh & Slevin 1913; Arteaga et al. 2019), I describe here the color in life of two specimens of M. grayii from Floreana that I photographed and examined in situ in 2010.

Adult female ( Fig. 5 ): Dorsal background of body, limbs and tail light brown with scattered dark brown spots, which are approximately arranged in transverse rows along body; thin, short, dark gray bar extending posterodorsally from anterior insertion of fore limb across scapular region; dorsal surface of head light brown with tiny, interspersed orange dots; bright orange face mark covering lateral aspect of both head and neck, as well as mental, postmentals, sublabials and a few adjacent gulars; gular region grayish cream, with irregular orange marks on most scales; ventral background of body, limbs and tail with grayish-cream tones; sides of venter between fore- and hind limbs with orange hue; pectoral region with a few faint, gray dots.

Adult male ( Fig. 5 ): Dorsal background of head, body, limbs and tail light brown with scattered dark brown to black spots (except on head), larger towards dorsal midline; sage dots scattered on hind limbs, posterior body and tail; vertebral crest with alternate smoky black and greyish green segments; ventral background of body, limbs and tail with yellowish-cream tones; sides of venter between fore- and hind limbs with brown hue; pectoral region with faint, black irregular marks; conspicuous black gular patch extending posterodorsally underneath antehumeral and oblique neck folds; ventral aspect of head anterior to gular patch cream with a few scattered black or dark brown spots.

Morphological variation. Measurements and scutellation of Microlophus slevini are presented in Table 2 . The vertebral crest is more pronounced in adult males. This is more evident on the anterior half of the tail and posterior part of the body, where vertebrals are at least more than twice the size of adjacent dorsals in males, but similar in size to adjacent dorsals in females. This species attains a maximum SVL of 86 mm in males and 77 mm in females. Although sample size of specimens with complete tails was small (N = 4 in females; N = 5 in males), tail length / SVL ratio was similar in both sexes (1.72–1.94, mean = 1.79 ± 0.10 SD in females; 1.73–1.90, mean = 1.80 ± 0.06 SD in males). Similarly, no sexual differences were found in head width (HW/HL 0.74–0.84, mean = 0.79 ± 0.03 SD in females; 0.76–0.81, mean = 0.79 ± 0.02 in males) or hind limb length (LL/SVL 0.70–0.90, mean = 0.80 ± 0.06 in females; 0.73–0.85, mean = 0.80 ± 0.04 in males). Sexual variation for additional mensural characters in M. slevini is presented in Table 3 .

Genetic variation. Uncorrected p genetic distances ( Table 4 ) between M. slevini and its sister species M. grayii range between 0.055 and 0.065 (mean 0.061 ± 0.000 SE) for the ND2 gene. Other species pairs (species name followed by island of occurrence; approximate shortest distance between island pairs in brackets) of lava lizards belonging to the western radiation with similar or lower mean distance values are M. pacificus Pinta / M. albemarlensis Isabela (0.024 –0.031, mean 0.027 ± 0.001 SE, [75.4 km]), M. duncanensis Pinzón / M. jacobii Santiago (0.056 –0.059, mean 0.058 ± 0.001 SE, [24.5 km]), and M. indefatigabilis Santa Cruz / M. jacobii (0.062 – 0.071, mean 0.065 ± 0.000 SE, [19.5 km]). The largest genetic distance in the western radiation is between M. slevini and M. delanonis Española (0.162 –0.173, mean 0.167 ± 0.001 SE, [60.7 km]).

Etymology. The specific epithet is a noun in the genitive singular case based on the unlatinized surname Slevin and is a patronym for American herpetologist Joseph R. Slevin (1881–1957), who during “a couple of hours” on October 3 rd 1905 collected most specimens of the new species reported in this paper as part of the famous 1905- 1906 Galápagos expedition by the California Academy of Sciences ( Fritts & Fritts 1982); the remaining type series was collected by his field assistant E. S. King. Remarkably, Slevin examined and recorded scale counts of 1,500 specimens included in van Denburgh & Slevin’s (1913) seminal work on lava lizards from the Galápagos.

Distribution. Microlophus slevini occurs in 0.8 km 2 Gardner islet, 8 km east of Floreana Island, southern Galápagos, Ecuador ( Fig. 6 ). Type specimens were collected from the coast to the top of the island at 227 m (field notes, October 3 rd, 1905, J. R. Slevin).

Natural History. The type specimens of Microlophus slevini were found active in the day (after 9:45 am) along a steep slope covered with lava fragments and cactus shrubs, from the NW coast to the top of Gardner (field notes, October 3, 1905, J. R. Slevin). The smallest female of Microlophus slevini with enlarged vitellogenic follicles had a SVL of 60 mm (CAS 9432). The smallest females of M. grayii with enlarged vitellogenic follicles from Floreana, Champion and Enderby had SVLs of 49 mm (CAS 11058), 47 mm (CAS 11056), and 52 mm (CAS 11628), respectively. Although no adult females of M. slevini with eggs were found, I examined females of M. grayii with two eggs from Floreana (CAS 104710, 58 mm SVL; MVZ 57557, 61 mm SVL), Champion (CAS 104702, 69 mm SVL), and Enderby (CAS 11624, 69 mm SVL). Juveniles of M. slevini , for which sex could not be determined, ranged between 38 mm (CAS 9442) and 41 mm (CAS 9441). Six of the 10 examined females and eight of 13 males had broken or regenerated tails, the latter representing 1–53% and 16–73% of the total tail length, respectively. This species is known to be one of the main prey items of the snake Pseudalsophis biserialis and the Floreana mockingbird Mimus trifasciatus ( Ortiz-Catedral et al. 2019; Wittmer-Naranjo et al. 2021).

Figures

FIGURE 3. Male holotype (CAS 9428; SVL = 86 mm) of Microlophus slevini sp. nov. in dorsal (top), lateral (middle) and ventral (bottom) views. Photographs by Erica Ely. Scale bar: 10 mm.

FIGURE 4. Head of the holotype (CAS 9428) of Microlophus slevini sp. nov. in dorsal (top), lateral (middle), and ventral (bottom) views. Photographs by Erica Ely. Scale bar: 5 mm.

FIGURE 5. Live adult female (A, B) and male (C, D) specimens of M. grayii from Floreana. Color in life between M. grayii and M. slevini sp. nov. is very similar. Photographs from Bioweb.bio.

FIGURE 6. Map of the Galápagos Archipelago with a close-up of Floreana Island and surrounding islets. Bathymetric contour lines delimit depths of 50 m (lighter blue), 100 m, 150 m, 200 m and>200m (darker blue). Microlophus slevini sp. nov. occurs on Gardner, whereas M. grayii is known from Floreana, Champion, Caldwell, and Enderby.