Isometrus amboli, Sulakhe & Dandekar & Padhye & Bastawade, 2020

Sulakhe, Shauri, Dandekar, Nikhil, Padhye, Anand & Bastawade, Deshabhushan, 2020, Two new cryptic species of Isometrus (Scorpiones Buthidae) from the northern Western Ghats India, Euscorpius 305, pp. 1-24 : 8-23

Isometrus amboli sp. n.

( Figures 17–31 , 37 , 41 , 47, 51, 55, 59 , Tables 1b, e, 2–6 ))

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TYPE LOCALITY AND TYPE REPOSITORY. India, Maharashtra State, Sindhudurg District, Amboli , 15.94°N 74.00°E, 872 m a. s. l.; BNHS.

TYPE MATERIAL. India, Maharashtra State, Sindhudurg District, Amboli , 15.94°N 74.00°E, 872 m a. s. l., 11 May 2019, 1♂ (holotype, BNHS SC 157 ) , 06 September 2017, ♂ (paratype, INHER-42), 11 May 2019, 1♀ (paratype, BNHS SC 158 ) , 5♂ (paratypes, INHER-110, 111, 112, 113, 114, 115), leg. S. Sulakhe.

ETYMOLOGY. The species epithet is a noun in apposition indicating the name of the Amboli Village located in Sindhudurg District, northern Western Ghats, where the type locality is situated. Suggested common name: Amboli Tree Scorpion.

DESCRIPTION. (♂ holotype, measurements in Table 1b) Coloration ( Figs. 17–18 , 24–25 ). Body and appendages dark brown and variegated with blackish brown stripes and spots; dark brownish last metasomal segment and pedipalp fingers. Ventral portion light yellowish except sternite VII with darker patches. Sternite V with pale yellowish color ( Fig. 18 ). Basal segments of chelicera dorsally yellowish with blackish reticulation ending anteriorly into brownish transverse patch; Chelicerae dark brownish on anterior portion of basal segments and fingers. Telson reddish brown in color.

Carapace ( Figs. 37 , 41 ). Surface densely and finely granular, almost entirely except very few areas without granules on the posterior median portion. Carapace without carinae, except for a pair of inconspicuous median supraocular carinae, with fine granular texture. A pair of median eyes situated anteriorly in the ratio 1:2.1 (ratio of median eyes to anterior margin and median eyes to posterior margin). Anterolateral ocular tubercle granular, provided with 5 pairs of lateral ocelli. Three pairs of sub-contiguous lateral ocelli and two micro-ocelli situated behind the lateral ocelli. Median longitudinal furrow throughout the length of carapace. Anterior margin with shallow emargination, finely granulated with conspicuous median notch. Lateral margins finely and densely crenulated below the lateral ocelli. Posterior margin finely crenulated.

Chelicerae. Characteristic of the family Buthidae with normal buthid dentation on both fingers. Basal segments and movable fingers with short and firm setae on the basal and ventral surfaces.

Pedipalp ( Figs. 27–31 ). Femur with 5 carinae (dorsal exterior, dorsal interior, exterior median, interior median, and exterior ventral). Exterior median carina with few granules more prominent, robust and triangularly tuberculate. All remaining carinae are evenly crenulated. Intercarinal space more granular on dorsal surface. Ventral surface almost smooth. Patella with 7 distinct carinae (dorsal median, dorsal interior, dorsal exterior, exterior median, ventral exterior, interior median and ventral interior). Dorsal median and dorsal interior carinae granular. Dorsal median present only on one-third distal portion. Dorsal exterior and exterior median almost smooth and obsolete. Intercarinal space weakly and sparsely granular. Interior median strongly tuberculated with few sub-denticulate granules. Both ventral carinae very weekly granular. Manus almost smooth, carinae weakly traceable. Fixed fingers with 2 smooth and obsolete carinae (dorsal exterior and dorsal interior). Dorsal exterior carina present all along the length. Fixed and movable finger armed with 5 rows of linear dentition Trichobothrial pattern typical for the genus.

Legs. Femur and patellae carinated. All carinae granular. Tibiae 3 and 4 without tibial spur. All legs with a pair of pedal spurs. Tarsomere covered with long delicate setae arranged in parallel rows on ventral side. Tarsomere I provided with tuft of short, stout blackish setae. Tarsomere II compressed laterally. Dorsal margin of each leg ending into a pointed projection and ventrally provided with paired row of short, pointed, anteriorly directed, closely placed setae. Tarsomere II armed with a pair of sharply pointed curved claws and a soft, triangular and blunt basal claw. Genital operculum ( Figs. 19 , 26 ). Wider than long, elliptical, separated with a pair of short male genital papillae, with a few reddish setae present on lateral posterior portion.

Pectines ( Figs. 19 , 26 ). Basal piece squarish, deeply notched on anterior median margin. Posterior margin of basal piece straight; smooth on surface with a parallel narrow sub-basal piece along the posterior margin. Surface provided with pairs of short, red setae. Pectine 4.6 times longer than its width, marginal lamella of 3 digits and median lamella of 6 digits, external margin armed with a row of stout short red setae and few setae on surface. Fulcra 16, roughly triangular each armed with few short red setae, placed in between adjacent pectinal teeth. Teeth 17, strong and stout.

Mesosoma ( Figs. 17–19 , 22–25 ). Tergites I–VI densely and finely granular, with a granular median carina. Posterior and lateral margins granular. Tergite VII narrowed posteriorly, granular, with 2 pairs of lateral granular carinae, inners up to pre-tergal portion while outer pair runs diverging laterally up to two-thirds portion and end abruptly. A broad median carina limited to anterior two-thirds of median portion. Sternites III– VI almost entirely smooth with a pair of spiracles. Margins smooth, each tergite with different numbers of setae on surface and posterior margins. Sternite V with extended, convex and exceptionally smooth posterior median margin. Sternite VII smooth on posterior margin while finely crenulated to serrated on lateral margins; with 2 pairs of granular carinae; median carinae restricted to posterior two-thirds portion; lateral carinae present in the middle portion.

Metasoma ( Figs. 17–18 , 22–25 ). All segments longer than wide; basal segment two times longer than wide. Segment I with 5 pairs of carinae (dorsals, dorsolaterals, laterals, ventrolaterals and ventrals) well developed and granular, ending posteriorly in a sub-triangular blunt and weakly pointed tubercle. Intercarinal space weakly and sparsely granular, anterior margin granular. Segments II and III with 4 pairs of carinae (dorsal, dorsolateral, ventrolaterals and ventrals). Laterals granular and marked on posterior one-third portion of II and III segments. Intercarinal portion weakly and finely granular, dorsolateral and dorsal carinae posteriorly ending in to subtringular tubercles. Segment IV with 4 pairs of granular carinae (dorsal, dorsolateral, ventrolaterals and ventrals). Dorsals ending into subtringular tubercles. Intercarinal space less irregularly granular. Segment V with 7 carinae (dorsal, dorsolateral and ventrolateral pairs and single ventral); dorsal carinae granular. Dorsolaterals present throughout. Laterals present on anterior one-fourth portion. Ventrolaterals and single ventral median carinae weakly granular and ending posteriorly into granular anal rim. Intercarinal space irregularly, weakly and finely granular than segments I to IV.

Telson ( Figs. 20–21 , 55 ) Vesicle elongated, less carinated; smooth and flat on dorsal surface. Lateral surface demarcated with granular ridge. Ventral median carina finely granular and ending posteriorly into triangular, subaculear tooth, on inner margin with minute denticle. Ventral portion with two pairs of sparsely and finely granular carinae. Intercarinal space weakly and finely granular. Aculeus with acute angle between subaculear nodule and base of aculeus. Subaculear tooth pointed and external margin along the ventral median carina angular with the vesicle.

SEXUAL DIMORPHISM. Male genital operculum partially exposed on posterior portion, from which a pair of small genital papillae is seen. In females, the genital operculum is separated with a median suture covering the female genital orifice ( Figs. 19 , 26 ).

AFFINITIES. Isometrus amboli sp. n. is distinguished from its congeners based on the following set of characters: 1) Surface of carapace densely and finely granular as opposed to densely and coarsely granular in I. tamhini sp. n., granular throughout but obsolete in I. maculatus , as opposed to sparsely granular with some areas without granules in I. thurstoni . ( Figs. 36–39 ). 2) External margin of subaculear tooth of telson along the ventral median carina, angular with the vesicle ( Fig. 20 ). 3) Pedipalp length less than or equal to 5 times the carapace length in males as opposed to more than 5 times in males of I. tamhini sp. n. ( Table 1e). 4) Anterior margin of carapace with shallow emargination as opposed to anterior margin of carapace with deep emargination in I. thurstoni ( Figs. 56–59 ). 5) Telson depth to telson length ratio is less than four times in males as opposed to more than four times in I. tamhini . ( Table 1). 6) Telson aculeus more elongated in males (telson length always less than 3 times telson aculeus length) as opposed to telson aculeus less elongated in males (telson length 3 times or more than 3 times telson aculeus length) in I. tamhini sp. n. ( Table 1e, Figs. 52, 53, 55 ). 7) Ventral median carina on vesicle strongly granular as opposed to very weakly granular in I. thurstoni ( Fig. 21 ). 8) Pectine length less than or equal to 5 times pectine width as opposed to pectine length greater than 5 times pectine width in I. maculatus in males and females ( Table 1e).

DISTRIBUTION, HABITAT AND ECOLOGY. The new species is currently known only from the type locality. In our primary surveys, it was found on tall trees in the semi-evergreen forests of Amboli. All specimens were found on the bark of trees with ridges, at a height from 2–4 meters. A few specimens were also collected from inside the tree holes ( Figs. 32–35 ).

Statistical Analysis

The first three PCA factors with eigenvalues more that 1.0 explained 99.17% of variation among the species (Table 2). The DFA using all the PCA factors as input resulted in 100% of individuals being classified into their respective species ( Table 3 ). The three discriminant functions with eigenvalues greater than 1.0 explained 100% of variation among these species ( Table 4 ), all the species formed distinct clusters on the factor plane using the first two DFA axes ( Fig. 60 ). Genetic Analysis The model selection suggested transition model with gamma distribution (HKY+I, lnL = -2272.654, df = 40, BIC = 4915.361) as the best nucleotide substitution model. Isometrus tamhini sp. n. and I. amboli sp. n. formed a monophyletic clade distinct from I. maculatus and I. thurstoni in maximum likelihood analysis ( Fig. 61 ). I. tamhini sp. n. differed from I. maculatus by a raw genetic distance of 13.5–13.7%, and from I. thurstoni by 11.6–12.4%. I. amboli sp. n. differed from I. maculatus by a raw genetic distance of 13.4 %, and from I. thurstoni by 13.0–13.2% ( Table 5 ). I. tamhini sp. n. and I. amboli sp. n. differ from each other by a raw genetic distance of 6.6–7.4% ( Table 5 ). Discussion The distribution records of the genus Isometrus from India (under I. maculatus and I. thurstoni ) were last listed by Kovařík (2003), based on older museum collections. Though Isometrus maculatus has been reported from the state of Maharashtra, none of our collected specimens from the northern Western Ghats matched I. maculatus morphologically and genetically. The COI gene sequence KY982207.1 ( Esposito et al., 2018) of I. maculatus from Wellawaya, Sri Lanka, used for comparison, is the only available DNA sequence of this species.

The species of the genus Isometrus are morphologically cryptic and the specimens that we collected and studied in the museum collections are difficult to distinguish based on morphology alone. In our DNA-based phylogeny, I. tamhini sp. n. and I. amboli sp. n. form a different clade and, among the Indian species, are closer to I. thurstoni than to I. maculatus .

Other sequences available in GenBank (MF422312.1 and MF422315.1) (Dahanukar & Suranase, unpublished) of unidentified Isometrus species from Ajara near Amboli are similar to the sequences of I. amboli sp. n. with a raw genetic distance of 2.3–2.5%; therefore we consider this population to belong to I. amboli sp. n. Also, a gene sequence MF422314.1 obtained by Dahanukar & Suranase (unpublished) of unidentified Isometrus species from Tamhini belongs to I. tamhini sp. n.

A type specimen of I. maculatus from DeGeer’s collection exists in the Swedish Royal Museum of Natural History, Stockholm (V. Fet, pers. comm); however, its type locality is undefined (it was originally listed as “ Suriname and Pennsylvania”!); this cosmopolitan species is assumed to have originated from South Asia (Fet & Lowe, 2000). Assignment of specimens collected worldwide to I. maculatus was made traditionally based on morphology. Considering the origin, presence and dispersal of I. maculatus around the world (Fet & Lowe, 2000; Lourenço & Huber, 2002; Kovařík & Ojanguren, 2013; Veronika et al., 2013; Kovařík et al., 2016), and the records of I. maculatus and I. thurstoni in more than five states in India ( Kovařík, 2003), it is imperative to follow integrated taxonomy to achieve clarity regarding distribution of these species. With our description of two new species from the northern Western Ghats, it is apparent that the genus Isometrus might have more undescribed species in India.

Considering the high faunal diversity in the Western Ghats biodiversity hotspot and the associated threats to the same, it is essential to understand the diversity through discovery of undescribed species as well as distribution pattern and delimitation of the species so as to set priorities and appropriate strategies for conservation.

Figures

Figure 60: Discriminant function analyses (DFA) projection on first two factor planes explaining 86.71% of variation among the four species.

Figure 61: Maximum likelihood (ML) phylogeny of the Indian Isometrus. Values along the nodes are % bootstraps for 1000 iterations.

Figures 17–21: Isometrus amboli sp. n., male holotype Figures 17–18. Dorsal (17) and ventral (18) views Figure 19. Sternopectinal area. Figures 20–21. Telson in lateral (20) and ventral (21) views.

Figures 22–26: Isometrus amboli sp. n. Figures 22–23. Male holotype in dorsal (22) and ventral (23) views, UV image. Figures 24–26. Female paratype, BNHS-SC-158, in dorsal (24) and ventral (25) views, and sternopectinal area (26).

Figures 27–32: Isometrus amboli sp. n. Figures 27–31. Male holotype, Pedipalp chela external (27), patella dorsal (28), and external (29), and femur in dorsal (30) and internal (31) view. Trichobothrial pattern indicated by yellow circles. Figure 32. Type locality of I. amboli sp. n., a dense semi–evergreen forest with tall trees.

Figures 36–39: Comparative surface granulation of carapace. Figure 36. Isometrus tamhini sp. n., male, holotype. Figure 37. I. amboli sp. n., male, holotype. Figure 38. I. thurstoni, male, INHER-SC-139. Figure 39. I. maculatus, male, CAS-66-486 (photo by Shruti Paripatyadar).

Figures 40–43: Comparative color pattern on carapace. Figure 40. Isometrus tamhini sp. n., male, holotype. Figure 41. I. amboli sp. n., male, holotype. Figure 42. I. thurstoni, male, INHER-SC-139. Figure 43. I. maculatus, male, Cuba (photo by Rolando Teruel)

Figures 44–59: Figures 44–47: Comparison of pedipalp femur, dorsalointerior view.Figures 48–51: Comparison of pedipalp patella, dorsalointerior view, Figures 52–55: Comparison of telson, lateral view. Figures 56–59: Comparison of anterior margins of carapace. Figures 44, 48, 52, 56. I. maculatus, male, CAS-66-486 (44, 48, photos byShruti Paripatyadar).and male from Cuba (52, 56 photosby Rolando Teruel).Figures 45, 49, 53, 57. I. thurstoni, male, INHER-SC-139. Figures 46, 50, 54, 58. I. tamhini sp. n., male, holotype. Figures 47, 51, 55, 59. I. amboli sp. n., male, holotype.