Amarasinghe Achchige Thasun successfully earned a doctorate in the Postgraduate Program in Biology from the Faculty of Mathematics and Natural Sciences, University of Indonesia (FMIPA UI). At the open doctoral promotion session held on Thursday, January 4, 2024, at the G.A. Siwabessy Hall, FMIPA UI, Depok, Thasun, as he is known, delivered a dissertation entitled “The Effect of Island Isolation on the Morphology, Evolution, and Biogeography of the Genus Bronchocela Kaup, 1827 (Reptilia: Agamidae) in Indonesia”. Isolation is a major factor in island biogeography. In his research, Dr. Thasun tries to understand this phenomenon.

Through his dissertation, he revealed the phylogeographic phenomenon of the chameleon group from the Agamidae family which is spread across Southeast Asia, namely the genus Bronchocela in the Indonesian Archipelago based on morphological data (skull size), molecular (mitochondrial and nuclear DNA), and evolutionary data.

This research on chameleons is the first research that is equipped with all aspects of external morphology, skull, molecular studies with many genes, and evolutionary and biogeographic analysis approaches that cover the entire Indonesian archipelago.

Bunglon genus Bronchocela It is known to have a wide distribution area, extending from the southern Greater Sunda Islands to Papua New Guinea. The complex morphological variation within this fragmented genus across the Indonesian archipelago makes it difficult to clearly define species boundaries.

“Therefore, based on molecular phylogenetics, we created potential biogeographic boundaries of this species composition. The phylogenetic tree reconstruction was performed based on two mitochondrial DNA genetic markers (16s rRNA and ND2), with intervening nuclear DNA loci (CMOS) indicating the presence of six evolutionary lineages. Bronchocela in Indonesia and in this study it is proven B. cristatella which is widespread as a species complex consisting of at least three different species,” said Dr. Thasun before the examiners.

He continued, estimates of population structure and gene flow across the Sunda region and the Greater Sunda Islands indicate total isolation unless there is a land bridge (land bridge) which connected the two regions during the maximum glacial period.

Genus Bronchocela Cosmopolitan, highly morphologically variable, distributed and isolated in fragmented forests across the Indonesian archipelago. Complex variation within this genus makes it difficult to clearly define species boundaries. Thasun revealed that 520 individual specimens from museum collections were examined to test the impact of geographical island isolation on population morphological structure. Statistical tests were performed using univariate and multivariate analyses.

“So far, only four species have been identified in Indonesia. After this research, at least six species have been identified,” he said.

The results of the BEAST analysis show that Bronchocela originated about 42 million years ago in mainland Asia and is a basal clade Bronchocela terdiri dari B. burmana whose ancestral taxa are largely restricted to the Malay Peninsula. The results of the maximum clade credibility (MCC) analysis indicate that the genus Bronchocela evolved in the early Miocene (~18.7 million years ago) and began rapid speciation in the late Miocene.

This research also shows that larger islands support the life of large-sized chameleons compared to smaller islands (island dwarfism phenomenon) and is in line with the theory of island isolation.

Thasun’s success in pursuing education and research in this Doctoral study program cannot be separated from the guidance of Prof. Jatna Supriatna, M.Sc., Ph.D. as promoter and Prof. Dr. Abinawanto, M.Si. and Dr. Noviar Andayani, M.Sc. as Co-promoters.

Prof. Jatna Supriatna, M.Sc., Ph.D., explained that Indonesia is a country with immense biodiversity, both on land and in the ocean. This is undoubtedly supported by Indonesia’s geographical location, which consists of islands with varied and unique characteristics.

This study, said Prof. Jatna, shows how island isolation affects a population’s external and internal morphology, genetic makeup, biogeographic adaptations such as body size variation, and ultimately evolution and diversity into separate species.

“Because this species is a habitat specialist, it is a highly potential bioindicator species for assessing forest quality. This research also shows that Pliocene climate change could have a significant impact on species diversification and the demography of forest species in the Indonesian archipelago,” said Prof. Jatna.

Also present at the open session of this doctoral promotion were the Sri Lankan Ambassador to Indonesia, Admiral Prof. Jayanath Colombage, Vice Dean for Education, Research, and Student Affairs of the Faculty of Mathematics and Natural Sciences, University of Indonesia, Prof. Dr. rer. nat. Budiawan, Vice Dean for Resources, Ventures, and General Administration of the Faculty of Mathematics and Natural Sciences, University of Indonesia, Dr. Tito Latif Indra, M.Si, and Director of Forest Prevention and Security of the Ministry of Environment and Forestry, Dr. Ir. Sustyo Iriyono, M.Si.

About Dr. Amarasinghe Achchige Thasun

Dr. Thasun was formerly a citizen of the Democratic Socialist Republic of Sri Lanka. He was born on November 22, 1984, in Colombo, Sri Lanka. He first came to Indonesia in 2010 to attend the ATBC symposium held by the University of Indonesia (UI) and the Indonesian Institute of Sciences (LIPI) in Bali. He then joined the 2010 ATBC field course program and began conducting research in Alaspurwo National Park, Baluran National Park, Rinjani National Park, and Bedugul Botanical Gardens.

During the event, Dr. Thasun first met Niki Kurniawati, another participant in the field course. Niki is a graduate of the Biology program at the Faculty of Mathematics and Natural Sciences, University of Indonesia. The two married in 2016. That same year, Dr. Thasun officially became an Indonesian citizen (WNI).

He chose to pursue a postgraduate degree in Biology at the Faculty of Mathematics and Natural Sciences, University of Indonesia, due to his strong motivation to gain a deeper understanding of the biogeography and evolution of animals in Indonesia. Furthermore, Dr. Thasun noted that Indonesia boasts a high level of biodiversity, comparable to the diversity of the Western Ghats hotspot in Sri Lanka.

He expressed his desire to disseminate his knowledge and research experience to the public, especially students.

“My deepest ambition is to be able to share my knowledge and experience with the next generation of students and prepare them to have skills that meet international standards,” said Dr. Thasun.

As an Indonesian citizen, he is committed to serving the Indonesian nation by continuing and developing research in his field, as a form of his contribution to preserving biodiversity in Indonesia.