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doi: 10.7717/peerj.2955. eCollection 2017.

Off the scale: a new species of fish-scale gecko (Squamata: Gekkonidae:Geckolepis) with exceptionally large scales

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Off the scale: a new species of fish-scale gecko (Squamata: Gekkonidae:Geckolepis) with exceptionally large scales

Mark D Scherz et al. PeerJ..

Abstract

The gecko genusGeckolepis, endemic to Madagascar and the Comoro archipelago, is taxonomically challenging. One reason is its members ability to autotomize a large portion of their scales when grasped or touched, most likely to escape predation. Based on an integrative taxonomic approach including external morphology, morphometrics, genetics, pholidosis, and osteology, we here describe the first new species from this genus in 75 years:Geckolepis megalepissp. nov. from the limestone karst of Ankarana in northern Madagascar. The new species has the largest known body scales of any gecko (both relatively and absolutely), which come off with exceptional ease. We provide a detailed description of the skeleton of the genusGeckolepis based on micro-Computed Tomography (micro-CT) analysis of the new species, the holotype ofG. maculata, the recently resurrectedG. humbloti, and a specimen belonging to an operational taxonomic unit (OTU) recently suggested to representG. maculata.Geckolepis is characterized by highly mineralized, imbricated scales, paired frontals, and unfused subolfactory processes of the frontals, among other features. We identify diagnostic characters in the osteology of these geckos that help define our new species and show that the OTU assigned toG. maculata is probably not conspecific with it, leaving the taxonomic identity of this species unclear. We discuss possible reasons for the extremely enlarged scales ofG. megalepis in the context of an anti-predator defence mechanism, and the future ofGeckolepis taxonomy.

Keywords: Ankarana; Anti-predator defence; Geckolepis megalepis sp. nov.; Integrative taxonomy; Madagascar; Micro-Computed Tomography; Morphology; Osteology.

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Conflict of interest statement

The authors declare there are no competing interests.

Figures

Figure 1
Figure 1. Molecular phylogeny and distribution ofGeckolepis OTUs based mainly on Lemme et al. (2013).
Dotted lines in the phylogeny indicate uncertain placement. The phylogenetic position and distribution ofGeckolepis humbloti is inferred from Hawlitschek et al. (2016).
Figure 2
Figure 2. Schematic drawings exemplifying morphological measurements and scale counts, following the scheme of Hawlitschek et al. (2016) based on Köhler et al. (2009).
(A) Measurements and pholidosis of the head, drawn from the specimen in Fig. 3A (small scales around the eye and nostril not depicted); (B) body measurements; (C) postmental scale conditions, adapted from Lemme et al. (2013); (D) postnasal scale configuration types, adapted from Köhler et al. (2009). Scale counts in A: purple, canthal scales; blue, supralabials; red, infralabials. In C, cyan indicates mental scales and purple indicates postmental scales. For abbreviations and unillustrated characters, see Materials and Methods.
Figure 3
Figure 3. Specimens ofGeckolepis megalepis sp. nov. in life.
(A) A specimen observed by A. Anker (photograph used with permission); (B) a specimen observed by FG, and (C) a specimen photographed after scale loss, with inset indicating the transparent ‘tear zone’ at the base of a scale. None of the photographed animals were collected, but their attribution toG. megalepis is clear on the basis of the large size of their scales. Note that the tails of all three specimens are regenerated.
Figure 4
Figure 4. Specimens ofGeckolepis megalepis sp. nov. in preservative.
(A–C) The holotype, ZSM 2126/2007; (D–F) paratype ZSM 232/2016. Shown in dorsal (A, D) and ventral (C, F) view, with a close-up view of the postmental scales (B, E) coloured for reference to Fig. 1. Scale bars indicate 10 mm. Chin insets are not to scale.
Figure 5
Figure 5. Micro-CT images of mineralized scales ofGeckolepis specimens.
Shown in dorsal (A, D, F, H, J) and ventral (B, E, G, I, K) view, and coronal cut at the parietal level (C) ofGeckolepis megalepis (A–C, ZSM 2126/2007),Geckolepis OTU AB (D–E, ZSM 1520/2008),G. maculata (F–G, ZMB 9655), andG. humbloti (H–I, ZSM 80/2010; J–K, ZSM 81/2006). Note the high density of the scale covering in all the species, and the lack of mineralization in the postmental scales (compare with Figs. 2 and 3).
Figure 6
Figure 6. Micro-CT images of skull (cranium and jaw) of the holotype ofGeckolepis megalepis sp. nov. (ZSM 2126/2007).
(A) Dorsal, (B) ventral, (C) lateral, (D) labial, and (E) lingual view. Abbreviations:adf, anterior inferior dental foramen;amf, anterior mylohyoid foramen;ar, articular facet;asnp, ascending nasal process of premaxilla;bo, basioccipital;bp, basipterygoid process of parabasisphenoid;ch, choana;cob, compound bone;cor, coronoid;d, dentary;dpp, descending parietal process;ect, ectopterygoid;ept, epipterygoid;f, frontal;hscc, horizontal semi-circular canal;if, incisive foramen;j, jugal;larst, lateral aperture of the recessus scalae tympani;mdf, mandibular fossa;mf, mental foramen;mko, opening of the Meckelian canal,mx, maxilla;mx.ap, anterior process of maxilla;mx.fp, facial process of maxilla;mx.pp, posterior process of maxilla;mx.ps, palatal shelf of maxilla;n, nasal;occ, occipital condyle;oto, otooccipital;pal, palatine;pal.mp, maxillary process of palatine;pal.vf, vomerine flange of palatine;par, parietal;pbsh, parabasisphenoid;pmx, premaxilla;pmx.pps, premaxilla palatal shelf;pof, postorbitofrontal;pop, paroccipital process;ppp, posterolateral process of parietal;prf, prefrontal;pro, prootic;pro.ca, crista alaris of prootic;pro.cp, crista prootica of prootic;psaf, posterior surangular foramen;pscc, posterior semicircular canal;pt, pterygoid;pt.qp, quadrate process of pterygoid;q, quadrate;q.ch, conch of quadrate;rap, retroarticular process;s, stapes;saf, surangular foramen;scr, sclerotic ring;smx, septomaxilla;spl, splenial;sof, suborbital fenestra;sq, squamosal,so, supraoccipital;spht, sphenooccipital tubercle;tbr, trabeculae;v, vomer;v.lp, lateral process of vomer;v.mp, maxillary process of vomer. A rotational video of the skull is provided in Video S1.
Figure 7
Figure 7. Micro-CT images of spinal column ofGeckolepis, based onG. megalepis sp. nov. (ZSM 2126/2007).
(A) Lateral and (B) dorsal view. Abbreviations:lb, lumbar;sc, sacral. Regions are indicated by the posterodorsal-most point of the neural arches.
Figure 8
Figure 8. Micro-CT images of pectoral girdle ofGeckolepis, based onG. megalepis sp. nov. (ZSM 2126/2007).
(A) Ventral and (B) lateral view. Abbreviations:1cf, primary coracoid fenestra;2cf, secondary coracoid fenestra;acr, acromion process;cf, clavicular fenestra;cl, clavicle;cor, coracoid;ic, interclavicle;gf, glenoid fossa;hu, humerus;hu.c, humeral condyle;hu.dtp, deltopectoral crest of humerus;hu.ec, ectepicondylar crest of humerus;hu.hc, humeral crest of humerus;mc, metacarpal;ms, mesosternum;p, phalanges;ps, presternum;pu, patella ulnaris;r, radius;rl, radiale;s, scapula;sc.1c, primary coracoid ray of scapulocoracoid;sc.2c, secondary coracoid ray of scapulocoracoid;scf, scapulocoracoid fenestra;sf, scapular fenestra;ss, suprascapula;sc.sr, scapular ray of scapulocoracoid;sr, sternal ribs;sucf, supracoracoid foramen;u, ulna;ul, ulnare;xs, xiphisternum.
Figure 9
Figure 9. Micro-CT images of pelvic girdle ofGeckolepis, based onG. megalepis sp. nov. (ZSM 2126/2007).
(A) Dorsal and (B) lateral view. Abbreviations:ac, acetabulum;ag, astragalocalcaneum;ep, epipubis;f, femur;fb, fibula;f.it, internal trochanter;f.itf, intertrochanteric fossa;f.fc, femoral condyle;hyi, hypoischium;il, ilium;il.pap, preacetabular process of ilium;is, ischium;is.t, ischiadic tuberosity;ltp, lenticular tibial patella;mt, metatarsals;of, obturator foramen;p, phalanges;pic, proischiadic cartilage;pb, pubis;pb.pl, processus lateralis of pubis;pc, post-cloacal bone;pt, pubic tubercle;tb, tibia;tf, thyroid fenestra.
Figure 10
Figure 10. Comparative micro-CT images of the skull (cranium and jaw) of otherGeckolepis species.
Shown in dorsal (A, F, K, P), ventral (B, G, L, Q), lateral (C, H, M, R), labial (D, I, N, S), and lingual (E, J, O, T) view. DepictingGeckolepis OTU AB (A–E, ZSM 1520/2008), holotype ofG. maculata (F–J, ZMB 9655), andG. humbloti (K–O, ZSM 80/2010; P–T, ZSM 81/2006). From volume-rendering of micro-CT scans. Rotational videos of these skulls are provided in Videos S2–S5. For labels, see Fig. 6.
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