- A new study shows how the endemic rough-nosed horned lizard (Ceratophora aspera) found in the lowland rainforests of southwestern Sri Lanka can be actually grouped into four genetically diverse populations.
- Researchers say these genetic differences are caused by the fragmentation of rainforests due to centuries of human activity.
- The study highlights the importance of factoring in such genetic variations into conservation efforts such as reintroductions or linking forest patches aimed at conserving forest specialist species like these horned lizards.
- In addition to the slow-moving lizard species, native plants in these fragmented forests may have also developed genetic differences due to prolonged isolation, researchers say.
COLOMBO — The leaf litter and other decaying plant matter that carpet Sri Lanka’s lowland rainforests are potential lurking points for numerous blood-sucking leeches and hideouts of some venomous snakes. And while stirring them up isn’t always a wise idea, it’s the only way to catch a glimpse of the endemic rough-nosed horned lizard (Ceratophora aspera) with its perfectly camouflaged slim body, long legs, and cryptic colorations.
“Sometimes we could see a stick running and it might be the lizard,” said Shanelle Wikramanayake, a graduate of the University of Washington who works with the university’s Burke Museum. Wikramayanake led a team that combed the forest floor from morning to dusk in search of this elusive lizard, to get samples for her research on genetic analysis of different individuals within the range of C. aspera.
Their findings, published in the journal Biotropica, highlight the genetic variations in C. aspera populations distributed across different parts of Sri Lanka’s southwestern lowland rainforests.
“We could identify four forest groups where individuals within a certain group are more genetically similar to each other than a member of another forest group,” Wikramanayake told Mongabay.
Four distinct groups
Ceratophora is a genus of agamid lizards found only in Sri Lanka. All six species in the genus have soft, fleshy, flexible horn-like structures called rostral appendages, made of modified scales, extending from the snout. Though confined to a single island, all six species have evolved in distinctive ways over millions of years of isolation caused by climatic and geographic barriers, such as mountains and river basins.
But even within a single species, variations exist, as the new study on C. aspera shows.
The lizard’s range spans swaths of lowland rainforest below elevations of 900 meters (3,000 feet) with similar climatic and biogeographic conditions.
But parts of these rainforests have been cleared due to agriculture, illegal logging and urban encroachment over the course of centuries, causing fragmentation. What the researchers concluded is that the genetic variations they found among the different forest groups of C. aspera are a result of this isolation due to forest fragmentation.
“We selected C. aspera for our research as it shows the widest distribution, which warrants us to study the impacts of fragmentation of southern lowland rainforests,” Wikramanayake said.
A key research outcome is their scientific preposition that genetic differences of these populations should inform conservation actions, such as linking forest patches or translocations of individuals.
“You do not want to introduce a species of too genetically differentiated individuals to other populations,” Wikramanayake said.
The research team collected 17 samples from eight forests representing different C. aspera populations. They measured the captured lizards, collected the tip of the tail, and released the lizards back into their habitats. From the samples, they analyzed mitochondrial DNA (mtDNA) and single nucleotide polymorphism (SNP) data to uncover the genetic diversity and population structure of C. aspera.
Wikramanayake, now pursuing a master’s degree at California State University, carried out this study as part of her undergraduate course. Her father, Eric Wikramanayake, a conservation biologist with WWF based in Hong Kong, supported the research and is credited as a co-author of the new paper.
In most places, forest conservation has now become an opportunistic enterprise because of the extent of loss and conversion, and the urgency to conserve whatever there is remaining. But forest conservation and restoration to increase ecological connectivity should be informed by genetic variability of these range-restricted species. the senior Wikramanayake said. It should also attempt to maximize the genetic variation by strategically selecting forest patches and connectivity in landscape design, he added.
Proper evaluation
As there can be populations with slight genetic variations shown by this study, Eric Wikramanayake called for proper evaluation when describing new species based on genetics.
“In Sri Lanka, there is now a trend for new species descriptions based on scant evidence. Some genetic differentiation occurring within a species among populations is to be expected, so we cannot keep pigeonholing populations with some genetic differentiation as new species,” he told Mongabay, adding that experts are beginning to question the validity of some research coming out of Sri Lanka due to this.
Researchers also recommend using DNA analysis methods to study the evolutionary development and diversification of other endemic species to create a suite of species with better representation in conservation planning in Sri Lanka. They also say this kind of model can be applied to other areas with an abundance of unique and endangered species, like Madagascar or the Amazon.
Nirmalie Pallewatta, a professor at the University of Colombo’s Department of Zoology and a co-author of the study, said forest fragmentation isn’t the only problem facing species like C. aspera. The degradation or loss of quality of forests is also a threat, especially for the range-restricted species. “Degradation can occur due to many reasons, such as spreading of invasive species, and it is difficult to measure its impacts,” Pallewatta said.
An entomologist by training, Pallewatta said she’s interested in studying how slow-moving butterflies could be impacted by forest fragmentation, following similar approaches of studying the genetic diversity of different populations. It would also be interesting to study the genetic diversity of plants, Pallewatta said.
Shanelle Wikramanayake said she wants to continue studying C. aspera with the aim of promoting it as a flagship species to conserve lowland rainforests. In Sri Lanka, the focus is mostly on the conservation of megafauna such as elephants and leopards. But while they also need to be conserved, it’s just as important to look at smaller, more threatened species.
“With its cryptic look, the rough-nosed horned lizard has some charisma,” she said, “which we can use to get the attention of the general public on the need of protecting Sri Lanka’s important lowland rainforests.”
Citation:
Wikramanayake, S. A, Wikramanayake, E. D, Pallewatta, N., & Leaché, A. D. (2021). Integration of genetic structure into conservation of an endangered, endemic lizard, Ceratophora aspera: A case study from Sri Lanka. Biotropica, 53(5), 1301-1315. doi:10.1111/btp.12970
Banner image of a rough-nosed horned lizard (Ceratophora aspera), found only in the lowland rainforests of Sri Lanka. Image courtesy of Shanelle Wikramanayake.