Scelimena gombakensis Muhammad, Tan & Skejo, 2018

Muhammad, Amira Aqilah, Deranja, Maks, Adzic, Karmela & Abdullah, Nurul Ashikin, 2023, Towards a better understanding of the genus Scelimena (Orthoptera, Tetrigidae, Scelimeninae): New insights and notes on the taxonomy, ecology, and physiology of the genus in Peninsular Malaysia, Journal of Orthoptera Research 32 (1), pp. 55-62 : 55

Scelimena gombakensis Muhammad, Tan & Skejo, 2018

Scelimena producta (Serville, 1838) - Mahmood et al. 2007: 1279; Storozhenko and Dawwrueng 2015: 543).

Scelimena gombakensis Muhammad, Tan & Skejo, 2018: 6, 46.

Examined material. -

Holotype: PENINSULAR MALAYSIA, Selangor • 1 ♂; Ulu Gombak Field Studies Centre; 24 Sept. 2017; Muhammad, A. A., Muhammad Hafiz Mohd Amin & Afyza Maisarah Azizan leg.; ZRC . Paratypes: PENINSULAR MALAYSIA, Selangor • 1 ♀; Ulu Gombak Field Study Centre ; 9 Mar. 2018; Muhammad, A. A. & Abdullah, N. A. leg.; ZRC • 1 ♂; same data as of preceding; FRIM • 1 ♀; same data as of preceding; FRIM • 2 ♂; same data as of preceding; MZUM • 1 ♀; Ulu Gombak Field Study Centre; 24 Sept. 2017; Muhammad, A. A., Muhammad Hafiz Mohd Amin & Afyza Maisarah Azizan leg.; FRIM • 1 ♀; same data as of preceding; MZUM .

Other material: PENINSULAR MALAYSIA, Selangor • 8 ♂; Ulu Gombak ; 7 Mar. 1964; AAM leg.; MZUM IOt 002350, 002351, 002355, 002361, 002362, 002366, 002367, 002369 • 3 ♀; same data as of preceding; MZUM IOt 002357, 002363, 002379 • 1 ♂; Ulu Gombak 16ms. [miles]; 27 May 1964; AAM leg.; MZUM IOt 002347 • 2 ♂; Ulu Gombak, 16ms. [miles]; 15 Apr. 1964; AAM leg.; MZUM IOt 002371, 002373 • 1 ♂; Ulu Gombak, 12ms; 15 Apr. 1964, AAM leg.; MZUM IOt 002372 • 3 ♂; Ulu Gombak, Bt [Batu] 16; 7 Mar. 1964; AAM leg.; MZUM IOt 002348, 002349, 002356 • 4 ♀; same data as of preceding; MZUM IOt 002358 to 002360, 002365 • 7 ♂; Ulu Langat; 16 Mar. 1964; AAM leg.; MZUM IOt 002333, 002334, 002340, 002342 to 002345 • 2 ♀; same data as of preceding; MZUM IOt 002339, 002341 • 1 ♀; Ulu Gombak; 15 Jul. 1969; JAB leg.; MZUM IOt 002428 • 1 ♂; Ulu Gombak; 15 Sept. 1974; Chua Eng Lok leg.; MZUM IOt 002407 • 1 ♂; same data as of preceding; L. Teo leg.; MZUM IOt 002408 • 1 ♂; same data as of preceding; B. H.Voon leg.; MZUM IOt 002415 • 1 ♀; same data as of preceding; Aru leg.; MZUM IOt 002413 • 1 ♀; same data as of preceding; K. C. Tung leg.; MZUM IOt 002414 • 1 ♀; Ulu Langat; 27 Oct. 1974; Wong Yow Sin leg.; MZUM IOt 002411, • 1 ♀; same data as of preceding; P. F. K. leg.; MZUM IOt 002412 • 1 ♀; Pansoon; 27 Oct. 1974; Heng. L. P. leg.; MZUM IOt 002409 • 1 ♀; same data as of preceding; Hoo Ah Teng leg.; MZUM IOt 002416 • 1 ♂; Sg. [Sungai] Tua; 27 July 1979; C. L. leg.; MZUM IOt 002406 • 1 ♀; Ulu Gombak; 1 Dec. 1982, Zuraidah Mian leg.; MZUM IOt 002388 • 1 ♀; Ulu Gombak; 21 Oct. 1984; Daiqah leg.; MZUM IOt 002410 • 1 ♀; Ulu Gombak; 18 Sept. 1995; Hasleyza leg.; MZUM IOt 002386 • 1 ♂; Ulu Gombak; 7 July 1997; Rosliza leg.; MZUM IOt 002430 • 1 ♂; Ulu Gombak; MZUM IOt 002391. Negeri Sembilan • 1 ♂; Ulu Bendul; 12 Aug. 1989; ZZ leg.; MZUM IOt 002427. Pahang • 1 ♂; Ketari; 7 June 1961; MZUM IOt 002385 • 1 ♀; same data as of preceding; MZUM IOt 002387 • 1 ♂; Nenasi; 17 Nov. 1974; W. C. Kang leg.; MZUM IOt 002404 • 1 ♀; Lentang; 2 Dec. 1995; Rohaya leg.; MZUM IOt 002426. Perak • 1 ♀; Grik; 17 Feb. 1991, McGyver leg.; MZUM IOt 002418 • 1 ♂; Perlok; 20 May 1997, Khaironizam Md. Zain leg.; MZUM IOt 002399. Johor • 1 ♂; B[atu] Pahat; 20 Nov. 1974; M. Ali-S leg.; MZUM IOt 002403 • 1 ♂; Duhsun; 17 Nov. 1974; Salleh leg.; MZUM IOt 002417. Terengganu • 1 ♂; Jerangau; 2 Mar. 1974; Baki leg.; MZUM IOt 002405. Kelantan • 1 ♂; Kg Senyul; 15 June 1962; KJK leg.; MZUM IOt 002375 • 1 ♀; same data as of preceding; MZUM IOt 002374 • 1 ♀; F[ort] Brooke; 15 Apr.1962; JAB leg.; MZUM IOt 002381 .

iNaturalist observation. -

PENINSULAR MALAYSIA, Perak • Hulu Perak; 5°30'10"N, 101°26'11"E; 4 July 2008; Fabio Cianferoni leg.; iNaturalist.org: https://www.inaturalist.org/observations/45968367. Selangor • Hulu Yam; 3°24'1"N, 101°41'4"E; 5 Dec. 2009; CheongWeei Gan leg.; iNaturalist.org: https://www.inaturalist.org/observations/127199050 • Hulu Yam; 3°19'55"N, 101°42'6"E; 5 Dec. 2009; CheongWeei Gan leg.; iNaturalist.org: https://www.inaturalist.org/observations/127199054 • Hulu Langat; 3°7'48"N, 101°53'17"E; 26 Aug. 2013; Phil Benstead leg.; iNaturalist.org: https://www.inaturalist.org/observations/71201238 • Gombak; 3°19'27"N, 101°44'54"E; 30 Aug. 2013; Erland Refling Nielsen leg.; iNaturalist.org: https://www.inaturalist.org/observations/63194111 • Hulu Langat; 3°12'37"N, 101°50'33"E; 11 Dec. 2021; Puteri Nuraida Syuhada Binti Abdullah leg.; iNaturalist.org: https://www.inaturalist.org/observations/102847175. Negeri Sembilan • Seremban; 2°47'55"N, 101°48'3"E; 29 Jan. 2019; Kees van Reenen leg.; iNaturalist.org: https://www.inaturalist.org/observations/35679667. Penang • Timur Laut; 5°26'2"N, 100°17'46"E; 23 Feb. 2019; Yiquan Chin leg.; iNaturalist.org: https://www.inaturalist.org/observations/20687721 • Timur Laut; 5°25'54"N, 100°17'55"E; 19 Dec. 2019; Alexius L.Z.L leg.; iNaturalist.org: https://www.inaturalist.org/observations/36773269 • Mukim 17; 5°21'35"N, 100°29'32"E; 11 Dec. 2021; Alexius L.Z.L leg.; iNaturalist.org: https://www.inaturalist.org/observations/102908617 • Tanjung Bungah; 5°27'54"N, 100°16'55"E; 1 Mar. 2022; Albert Kang leg.; iNaturalist.org: https://www.inaturalist.org/observations/107814195. Pahang • Genting Highlands; 3°24'40"N, 101°47'40"E; 14 Dec. 2021; Chloe Alison leg.; iNaturalist.org: https://www.inaturalist.org/observations/103086028. Kelantan • Pasir Puteh; 5°45'49"N, 102°24'32"E; 13 May 2022; Aiman Azmi leg.; iNaturalist.org: https://www.inaturalist.org/observations/116921973. THAILAND, Narathiwat • Waeng; 5°47'43"N, 101°49'42"E; June 2021; Vatcharavee Sriprasertsil leg.; iNaturalist.org: https://www.inaturalist.org/observations/84546541.

Examination of the specimens deposited at FRIM, MZUM, and ZRC revealed that the species was previously known from the region but was not recognized as a separate species. S. gombakensis had been wrongly identified by researchers as Scelimena producta (Serville, 1838) ( Mahmood et al. 2007, D.K. McE. Kevan’s notes on specimen labels in the UM collection). S. producta producta has been described from Java and has a similar body coloration to S. gombakensis (see specimen photographs available on OSF). However, it can be morphologically differentiated by two characteristics: pointed tubercles at humeral angles to the pronotum (rounded in S. gombakensis ) and numerous clearly visible teeth on the ventral side of its hind femora (while S. gombakensis has only two small teeth) ( Muhammad et al. 2018). Thus, we correct previous identifications and consider all listed specimens to belong to S. gombakensis , making these identifications new locality records for the species.

Variability. -

Thanks to the large number of specimens that we were able to examine, we found S. gombakensis to be a rather variable species, especially in terms of body size (♂: 18.0-24.0 mm; ♀: 24.0-31.0 mm). Nymphs do not differ much from adults, having similar coloration and general appearance, although they do have significantly shorter pronotum, making them easily distinguished from other Tetrigidae in Peninsular Malaysia. During the fieldwork, we observed one specimen belonging to S. gombakensis with unique coloration-the specimen’s general body coloration was brown (opposed to the common dark green coloration) with orange markings (opposed to yellow markings; Fig. 2E , indicated by an arrow). This coloration could be recessive given its rarity, or it could be caused by some kind of infection.

A change of coloration was also observed in pinned specimens (Fig. 2A-D ), which is a very interesting but rarely mentioned observation in Tetrigidae (an example of such observation was described by Mathieu et al. (2021)). In the MZUM collection, which holds a large number of S. gombakensis specimens, we observed color degradation in the older specimens. The colors of the older specimens were generally faded more than in recent ones, which gradually lost their dark green coloration with yellow markings and became generally brown in coloration. However, it is important to note that not all specimens had lost their color to the same extent, as some specimens from the 1960s are not as faded as the one represented in this paper (Fig. 2A ). Since all the specimens were collected around the same time and were all stored in the same box under the same conditions, it is possible that pre-pinning conditions play a vital role in coloration preservation in S. gombakensis specimens. Such factors might be influenced by the sampling and euthanization methods, duration of pinning of the specimens, preservation techniques, etc. Since we did not have information on the pre-pinning conditions older specimens were exposed to, this hypothesis requires consideration in the future.

Distribution of S. gombakensis .-

At first, it was hypothesized that this species would have general ecological traits similar to those of other Tetrigidae , including the fact that Tetrigidae are, in general, highly confined to water bodies, as they are often found in close proximity to fast-flowing rocky rivers ( Tan et al. 2017). Even so, we have also observed specimens flying long distances and maneuvering well during flight. It is likely that this species, like many other Tetrigidae , is tightly linked to large flowing bodies of water and disperses passively by water during diving as an escape behaviour.

With recently described species such as S. gombakensis , additional knowledge on species distribution, behavior, and other aspects of the species’ ecology are frequently understudied and incomplete. Revisiting old specimens deposited in museums or private collections is thus an important next step in understanding a species, as these repositories might hold historical specimens belonging to the species. Muhammad et al. (2018) stated that S. gombakensis is restricted to Sungai Gombak of the Gombak Catchment in Selangor, Peninsular Malaysia. Revision of specimens deposited in museum collections (UKM, UM, FRIM, and ZRC) and photos on online databases have shown that the species is, in fact, widely distributed across the country, especially along the West coast (Fig. 3 ). Social media observations on iNaturalist have greatly contributed to understanding species distribution (Table 1 ), once again demonstrating how useful citizen science can be (for other examples of the contributions of citizen science to the study of Tetrigidae , see Skejo et al. 2019, Kasalo et al. 2021, and Pavlović et al. 2022).

S. gombakensis is an example of a species that is easily recognized through photographs and highly unlikely to be misidentified in Peninsular Malaysia, making identification using iNaturalist very reliable. Additionally, thanks to iNaturalist, we were able to discover an observation of S. gombakensis in the Waeng district of Narathiwat, Thailand, very close to the border of Peninsular Malaysia; this represents the first official record of the species outside of Peninsular Malaysia, making this the first record for the country (Fig. 3 , Table 1 ). Further clarification of the species’ distribution is possible by comparing this species with Scelimena discalis Hancock, 1915 specimens from Thailand ( Storozhenko and Dawwrueng 2015), which may include some misidentified specimens. For now, we refrain from comparing S. gombakensis to S. discalis due to the inaccessibility of physical specimens and the lack of molecular and online data.

Ecology and habitat of Scelimena gombakensis .-

Muhammad et al. (2018) noted that S. gombakensis can be found perched on river rocks in lowland secondary rainforest where it is cool and very humid, especially in areas shadowed by tree canopies. Further field observation revealed that high moisture and indirect sunlight may be key to their survival, in tandem with the abundance of lichens and mosses that are their food source ( Zha et al. 2017). On the rocks, S. gombakensis tends to crowd near the water surface, where the high turbidity of the flowing stream creates a suitable humid biota. Juveniles are more likely to be observed close to the water surface than adults, as they are more susceptible to desiccation due to their immature exoskeletons. The juveniles are also less agile and unable to fly; hence, staying close to the water surface might increase their success rate when escaping from predators by diving underwater. Although individuals of various life stages can be found on the same rock, the place where S. gombakensis lays their eggs remains a mystery. For some Scelimena species, it is speculated that the eggs are laid elsewhere, such as in the sand along the riverbanks, and are perhaps well adapted to waterlogged conditions ( Zha et al. 2017).

Physiology of Scelimena gombakensis as key to adaptation to a semi-aquatic environment. -

Closer observation of the characteristics of the hind legs of S. gombakensis elucidates their swimming ability (Fig. 4 ). A close-up of the insect’s hind tibia and its first tarsal segment under a scanning electron microscope (SEM) reveals the following hydrodynamic characters: the first tarsal segment is laterally compressed along the whole length, and serration exists along the lateral edges of both the first tarsal segments and the hind tibiae (Fig. 4A, B, C ). The lateral compression provides a wider surface area for paddling underwater and likely aids in better propulsion during swimming. The serration along the lateral edges could serve multiple functions, but the tarsal serration most likely enhances the legs’ grip on wet and slippery rock surfaces since the arolium is absent underneath the claws (Fig. 4D ). Thus, the presence of microscopic serrations means porous rock surfaces offer more grip to the species’ limbs. Morphologically similar to riblet-like shark skin, another possible function of the serrations is to improve hydrodynamics by reducing the water drag acting upon its serrated tibiae when propelling underwater, reducing the formation of vortices and making swimming more energy efficient. The orientation of both microscopic structures is also parallel to the flow of water, hinting at functional homology ( Han et al. 2008, Zhang et al. 2011).

Our observations suggest that S. gombakensis utilizes both its hind legs and hindwings for navigation and survival, unlike Scelimena songkrana Zha & Wen, 2017 from Thailand, which seldom flies but often jumps, as described by Zha et al. (2017). On the other hand, Scelimena melli Günther, 1938 from China behaves similarly to S. gombakensis except for the fact that S. melli leaps further (for 10 meters or more). The mating behavior of S. gombakensis is consistent with that of other Scelimena ( Zha et al. 2017), in which the male securely positions itself on top of the female.

Figures

Fig. 2. Change of coloration in pinned specimens of Scelimena gombakensis Muhammad, Tan & Skejo, 2018 compared to the living specimen. A - C. Pinned S. gombakensis specimens; D. Living S. gombakensis specimens. E. Coloration variability and camouflage of three living S. gombakensis specimens; F. Natural habitat of S. gombakensis at the type locality Ulu Gombak, Selangor, Malaysia.

Fig. 3. Distribution map of species Scelimena gombakensis Muhammad, Tan & Skejo, 2018 based on museum collection and iNaturalist data.

Fig. 4. Scanning electron micrographs of the hind leg of S. gombakensis in ventral view. A. Hind tibia; B. First tarsal segment; C. Magnified view of the serration lining the edges of both tibia and tarsal segment; D. Tarsal claw. Scale bars: 100 μm (A, B); 50 μm (C, D).