Anderson’s Spiny Crocodile Newt
© 2015 Axel Hernandez (1 of 36)
Author: Axel Hernandez
Echinotriton andersoni (BOULENGER 1892)
Diagnosis and taxonomyThe holotype (BMNH 1918.104.22.168 RR 1822.214.171.124) was collected on “Okinawa, or Great Loo Choo Island” (=Okinawa-shima), Ryukyu Islands, Japan. Anderson’s spiny crocodile newt is a primitive species that has been endemic to the central Ryukyu Archipelago since the late Miocene (between 5 and 7 Mya) when the islands were cut off from the mainland (HONDA et al. 2012, HOU et al. 2014). It is a moderately stout and flattened newt with a broad and triangular head in which the females are larger and typically reach 16.5 cm in total length (TL) in the Okinawa group and generally 15-16.0 cm in the Amami group. In contrast, males have average lengths of 13.0 to 14.5 cm and appear “thin” by comparison, which a characteristic is found in many Tylototriton species. The females will have a distended abdomen when carrying eggs, though. The cloacal opening consists of a longitudinal slit in both sexes, but when slightly opened, that of the female will be smooth on the inside, whereas that of the male is more rugose. Sexual dimorphism is otherwise poorly pronounced (NUSSBAUM & BRODIE 1982). Echinotriton andersoni is characterized by a series of 12 to 15 conspicuous and prominent spiny warts. The 5th toe is developed rudimentary. It is uniformly dark brown or black on its dorsal and ventral faces, with only the underside of the tail, cloacal region, soles of the feet, and extremities of the costal warts (in some populations only) being yellow-orange. Its vomero-palatine teeth are arranged in V-shape in two longitudinal series that meet in the front (THORN 1969, RAFFAËLLI 2007, 2013, SPARREBOOM 2014). The tail is usually shorter than the snout-vent length.
Three types can be distinguished within this taxon, two of which are well separated genetically and morphologically. Molecular studies date their split back to some 7.9 Mya between Amami and Okinawa Islands, and 1.5 Mya between Amami- and Tokuno-shima, respectively (KURABAYASHI et al. 2012). They could in fact possibly be afforded at least subspecies status, but more detailed studies will need to be conducted first (HAYASHI et al. 1992, HONDA et al. 2012, HOU et al. 2014, HERNANDEZ 2016c,d).
• Echinotriton cf. andersoni “Amami group" This group is distributed on the three Japanese islands of Amami, Tokuno and Yoro. Its members are characterized by the ends of the vertebrae being furnished with brightly colored, anteriorly-directed projections, a series of 12 to 13 conspicuous and prominent yellowish to orange costal spiny warts, growing to an average length of 13.0 cm, having a dark brown or black dorsal and ventral ground color from which only the parotoids, underside of the tail, cloacal region, the soles of the feet stand out in yellow-orange, vomero-palatine teeth arranged in two series in V-shape, meeting in the front (THORN 1969, RAFFAËLLI 2013), and the tail usually being shorter than the snout-vent length (SVL). It can be distinguished from typical E. andersoni (from Okinawa that is) by the 12-13 dorsolateral spiny warts being more distinctly yellowish to orange, the larger parotoid glands with their yellow to orange coloration, and the broader and more distinctly triangular head. This type is in urgent need of taxonomic assessment and possibly formal description for conservation purposes (HOU et al. 2014, HERNANDEZ 2016a,c).
• Echinotriton andersoni "Okinawa group" This form occurs on three islands in the southern Ryukyu: Okinawa, Tokashiki and Sesoko. The population from Okinawa corresponds to the holotype and therefore to the true E. andersoni. Polymorphism is similar to that observed in sympatric Cynops ensicauda (RAFFAËLLI 2013). This form is characterized by its larger size yellow and its markings being indistinct. Juveniles are colored brown to reddish brown and will assume the black dress only when they turn adult. Within Okinawa, two types have been noted to occur, with one being more colorful and having more pronounced dorsolateral ridges and occurring in the south between Shinkawasaki and Osaki, and the other being darker and occurring in more northern regions at Yanbaru in the Kunigami District. Many instances of morphological and genetic variation have been observed within the Okinawa group in recent years, including a range of haplotypes, and southern populations (southern Okinawa; Tokashiki) were found to be genetically divergent from those in the north and center (KURABAYASHI et al. 2012, HONDA et al. 2012.) The author encountered a few yellowish to light brown adults with very pronounced dorsolateral ridges and prominent spiny warts in illegal imports from Hong Kong in 2013 and 2014. These specimens came from an undisclosed locality in the Ryukyu and might represent a cryptic form (HERNANDEZ 2016c,d).
• Echinotriton sp. "Taiwan" This form has remained a mystery. Its occurrence on Taiwan is based on three specimens (MCZ-22515-22517) that were collected between 1935 and 1937 on Mount Kwannon (=Kuanyinshan) in the north of the island and deposited in the Museum of Comparative Zoology in Cambridge, Massachusetts, USA. No additional specimens have since been found and the species’ occurrence on the island requires confirmation (ZHAO & ADLER 1993, ZHAO 1999, HERNANDEZ 2016a, c, d). ZHAO (1998) presumed it to be extinct in Taiwan, but then again, 121 years passed between the discovery of Echinotriton andersoni and that of E. maxiquadratus, which reopens the debate on the possible existence of this form here (HERNANDEZ 2016a,c,d). Moreover, our previous studies (HERNANDEZ 2016c,d, HERNANDEZ et al. in press) indicate that highly suitable habitats with primary forests at moderate elevations exist in large areas of central and eastern Taiwan, and these should be thoroughly surveyed for as yet unrecorded extant populations.
DistributionThe species is confirmed from six islands in the Japanese Ryukyu Archipelago: Okinawa, Amami, Tokun, Yorojima, Sesokojima and Tokashiki.
Habitat, ethology and ecologyEchinotriton andersoni is a lowland species (3−374 m a.s.l.) that inhabits a mosaic habitat composed of grasslands, sugarcane plantations, and forest (UTSUNOMIYA et al. 1978). The forested areas are dominated by itajii trees, Castanopsis sieboldii, Chinese guger trees Schima wallichii, and bamboo thickets (Phyllostachys spp.) (HERNANDEZ 2016c,d, HERNANDEZ et al. in press). On Okinawa Island, this species is scarce and lives near sugarcane fields in mountainous regions in the northern parts of the island, which used to be covered with humid subtropical forests until the mid-1960’ (UTSUNOMIYA et al. 1978). Today, all known populations occur in isolated places near patches of remnant forests (HAYASHI et al. 1992, KATO & OTA 1993). On Tokuno-shima, Echinotriton andersoni is found between 100 and 200 meters above sea level and seems to be more common to the east and southeast of the Minata Mountains, at Tanpatsu, Haku and Inutabu. It is usually encountered in remnants of mountain forests near sugarcane fields, finding shelter under rocks and in leaf litter near bodies of water. On Tokuno-shima, some larvae and adults were observed in rainy weather in August of 1978 at air temperatures of 25-28.0 °C whereas the species was observed at between 15.0 and 20.0 °C on Okinawa by MAX SPARREBOOM (RAFFAËLLI 2007, 2013). Some clutches of eggs were discovered under pine needles between February and June. The Ryukyu Archipelago is characterized by a warm and humid subtropical climate with high amounts of annual precipitation. Temperatures average between 15.0 and 20.0 °C throughout much of the year with maximum values of 28.0 °C being possible in summer (July and August). Echinotriton andersoni is terrestrial throughout its post-metamorphic life.
ReproductionThe breeding season begins in February and continues to the end of June, seemingly reaching its climax between mid-March and early April during the rainy season, but varying with the individual rainfall pattern of a year. Both mating and oviposition take place on land. The male will rub his head on the sides of the female while assuming a semicircular body posture and depositing a spermatophore if the female is found to be receptive. The female will then pick up the spermatophore with her cloaca for fertilizing her eggs. The eggs are larger in size (7.0 mm in diameter) than those of members of the genus Tylototriton. They are deposited one by one in one or two places under dead leaves and in humus in the immediate vicinity of ponds and small streams whose water temperature does not exceed 21.0 °C in March and April (HERNANDEZ 2016c,d). However, a water temperature of 27.8 °C was recorded in a pool containing eight well-developed larvae in August. The embryonic development takes two to three weeks (20 days on average) at >20.0 °C. The hatching larvae measure 17 mm in length, are yellowish green in color and turn black with age (SPARREBOOM 2014). According to ISIS (The International Species Information System), eleven zoos and aquariums were keeping the species as of 2015 (ten in the United States and one in Asia), but only one was successful propagating it (Cincinnati Zoo). CRAIG CAMERON (Ottawa, Canada) propagated this species and noted that it would take several weeks for a larva to form in its egg. It is necessary to collect the eggs after several weeks and place them on Sphagnum moss in a slightly inclined trough; the moss will keep itself wet by capillary action. Hatching larvae will then slip into the water below (RAFFAËLLI 2013). The larvae metamorphose after 4-6 weeks at 19.0 °C after which their black coloration will deepen. They are voracious and instances of cannibalism have been observed. Japanese scientists were able to raise 141 juveniles from 378 eggs originating from three different localities (Amami, Tokuno and Okinawa) at 20-22.0 °C in the laboratory during a period of five consecutive years (IGAWA et al. 2013). The adults were kept on natural soil in terraria outfitted with wall tiles that offered refuges in the spaces between them, and an aquatic section with a gently rising bank. The eggs were deposited separately on this wet slope. The larvae were raised at a temperature of 22.5 °C, fed with Tubifex, and kept separated to prevent cannibalism. The metamorphs were then kept in plastic containers laid out with a sponge material, maintained at 25.0 °C, and fed with micro-crickets, tropical woodlice (Trichorhina tomentosa), fruitflies, and springtails rich in calcium (HERNANDEZ 2016c,d).
Status, threats and conservationThis species is categorized as ‘Endangered’ (EN) class B1 in the IUCN Red List and as ‘Vulnerable’ (VU) on a national level (Environment Agency of Japan 2000, OTA 2000). It is also regionally protected by Okinawa prefectural legislation. The prefectures of Kagoshima and Okinawa have afforded this species the rank of ‘natural monument’. E. andersoni has undoubtedly become a rare species, with its populations declining year by year from illegal collection for export to Hong Kong, Europe and the United States, the invasion by a new predator in the shape of the Java mongoose, and the devastating deforestation mainly for creating space for sugarcane plantations and infrastructure that has been going on in the Ryukyu Archipelago since the 1960’, notably so on the islands of Okinawa and Tokuno. The newt seems to have adapted to live with these new plantations to some extent, though. On Okinawa, it seems to be more common in some national parks and the protected central northern parts of the island.
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Citation: AmphibiaWeb. 2019. <http://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 21 Oct 2019.
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