A new gecko emerges from Sri Lanka’s Nilgala savanna forest

The discovery of a new species of gecko in Sri Lanka has highlighted the island’s rich biodiversity as well as the perilous state of its unique and shrinking habitats.

The Nilgala day gecko (Cnemaspis nilgala) is named after the Nilgala savanna forest in Uva province where it’s found. It was described in a paper published in January in the journal Zootaxa, in which it’s identified as genetically distinct from another species, the Alwis’s day gecko (C. alwisi), for which it was previously confused.

The newly discovered geckos are diminutive, slender-bodied, and possess prominent forward and upward-directed eyes. Their coloration varies from light gray to brown, peppered with small black and white spots that provide them with efficient camouflage.

The discovery means Sri Lanka is home to 24 known species of Cnemaspis day geckos, so named because, unlike many other types of geckos, they’re active during the daytime. While the more than 140 species in Cnemaspis are geographically widespread, ranging from Africa to the Indian subcontinent to Southeast Asia, the two dozen found in Sri Lanka occur nowhere else.

“It is important to identify Sri Lanka not just as a biodiversity hotspot, in particular for lizards, but also for the much smaller geckos,” says lead author Suranjan Karunarathna, an expert committee member on herpetofauna in the National Red List Assessment.

This wealth of biodiversity stems from the rich range of habitat types in Sri Lanka, particularly attributable to the island’s geographic complexity, climatic variations and altitude-associated environmental gradients. These factors are believed to have given rise to biogeographic barriers, creating isolated enclaves in which species have evolved in unique ways over time, the paper says.

Karunarathna says the current diversity of Sri Lanka’s Cnemaspis geckos may be much higher than currently recognized, with new discoveries in the past decade highlighting the need for further taxonomic studies.

Habitat conservation

The new species is known only from the lowland savanna forest of Nilgala, and the number of individuals encountered in the study from the area was relatively small, according to the paper.

The Nilgala savanna forest spans just over 12,400 hectares (30,700 acres) in the lower plains of Sri Lanka’s southern Uva province. The forest experiences a mean annual rainfall between 1,500 and 2,000 millimeters (59 to 79 inches), received mainly during the October-January northeast monsoon. Much of the vegetation here is classified as dry monsoon grassland, although the area around Nilgala is mostly lowland tropical dry, mixed evergreen forest.

C. nilgala has so far been recorded only from rock outcrops with prehistoric granite caves of the type similar to those once occupied by prehistoric humans and now largely undisturbed. The paper suggests the gecko may also occur throughout the forest area and nearby habitats, though aggregated in the caves.

The new species faces immediate threats to its survival. These savanna and rock outcrop habitats have been heavily impacted  and modified by deforestation, man-made fires, invasive species, illegal forest encroachment, timber felling, unplanned farming activities such as rubber cultivation and slash-and-burn agriculture, use of broad-spectrum pesticides, granite quarrying, and road construction.

The paper says the mining of granite for highway construction has degraded habitat within the forest area, leading to both loss of effective habitat areas and fragmentation of already limited habitats for the geckos. “Such conditions will alter the micro-climate and micro-habitat conditions that are critical for life and natural histories of geckos in general,” the paper says.

These threats have serious implications for the area’s biodiversity. The Nilgala savanna forest is home to 17 species of geckos, including one listed as critically endangered, three as endangered and five as vulnerable, says Karunarathna, along with several undescribed species.

Overall, some 70 reptile species have already been recorded from this type of locality, marking out the forest area as a local hotspot of reptile diversity.

“This deserves special conservation,” says Anslem de Silva, a herpetologist and contributor to the study.

Critically endangered

According to the IUCN Red List criteria, C. nilgala would qualify as critically endangered for two reasons: the species is restricted to a small location at an elevation of about 500 meters (1,640 feet) in Uva province alone; and the characteristic habitat of the species, the monsoon-influenced savanna grasslands embedded with rock outcrops and granite rock caves, aren’t spatially extensive in the intermediate zone of Sri Lanka.

Though the Cnemaspis genus has received much attention in recent years, researchers call for extensive morphological and molecular data examination to understand the true diversity of Sri Lanka’s Cnemaspis species, highlighting the absence of extensive field surveys and ecological research, leaving conservation efforts weakened.

“There had been previous studies but the biodiversity and conservation requirements of day geckos still may be significantly underestimated,” Karunarathna says.

A number of Cnemaspis species dwell in constrained ranges and are highly localized, especially due to their low dispersal ability, a result of their small size and restrictive environmental niches.

The researchers call for additional surveys of the new species to be conducted in similar habitats to properly assess their possible distribution. “The present discovery highlights the need for dedicated herpetofaunal explorations in Sri Lanka,” the paper says, “especially in the intermediate bioclimatic zone and associated cave systems and rock outcrops.”

 

Citation:

Karunarathna, S., Bauer, A. M., Silva, A. D., Surasinghe, T., Somaratna, L., Madawala, M.,  Ukuwela, K. D. (2019). Description of a new species of the genus Cnemaspis Strauch, 1887 (Reptilia: Squamata: Gekkonidae) from the Nilgala Savannah forest, Uva Province of Sri Lanka. Zootaxa, 4545(3), 389. doi:10.11646/zootaxa.4545.3.4

 

Banner image of the Nilgala day gecko (Cnemaspis nilgala), a new species recorded from Sri Lanka’s Nilgala savanna forest. The gecko dwells in a unique habitat with rock outcrops and prehistoric granite caves. Image courtesy of Madhava Botejue.