Freshwater molluscs help clarify the boundaries of the regions of Southeast Asia

Freshwater molluscs help clarify the boundaries of the regions of Southeast Asia
Freshwater molluscs help clarify the boundaries of the regions of Southeast Asia

Researchers at the Federal Research Center for the Comprehensive Study of the Arctic of the Ural Branch of the Russian Academy of Sciences have summed up the results of six years of expeditions in Southeast Asia. During this time, scientists managed to discover 12 new species of freshwater mollusks, four of which were identified for the first time. The authors described their results in an article in Scientific Reports.

Southeast Asia is a region rich in endemic animal species. However, unlike other representatives of the fauna, local endemics are poorly studied. Until now, many undiscovered species and even genera of living beings remain in this area. To get rid of these "white spots", Russian researchers and colleagues from museums in Europe and the United States conducted a series of expeditions to Myanmar, Thailand and Northern Laos between 2012 and 2018. As a result, they discovered 12 species and four genera of freshwater molluscs previously unknown to science.

Most of the described species were found in hard-to-reach places. For example, the northern part of Rakhine State in Myanmar is closed to most foreigners. There is practically no population in this area, it is separated by mountain ranges from the main part of the country. It was there, in remote small rivers, that scientists were able to find a significant part of new species and genera that have a local distribution in Southeast Asia. Their discovery allowed scientists to expand their understanding of the taxonomy of the Unionidae family of freshwater molluscs.

As a result, the researchers were able to clarify the boundaries of the biogeographic regions of Southeast Asia. “The division into the Indian biogeographic subregion and the West Indochina subregion is accepted, but the boundaries between them were previously unclear. We used unionid mollusks to reconstruct ancient connections between freshwater basins throughout Asia, - says the lead author of the study, Corresponding Member of the Russian Academy of Sciences, Director of the FITSKIA UB RAS Ivan Bolotov. - We showed the role of the Kra Isthmus, which connects the Malacca Peninsula with the Asian continent. Millions of years ago, there was a sea strait here, dividing parts of the land. This strait played the role of a barrier for the exchange of species between the faunas of Western Indochina and Sundaland”.

Scientists have found that the freshwater molluscs of Southeast Asia developed mainly in three evolutionary foci - in Western Indochina, Sundaland and East Asia. Some of the species migrated from the Indian subcontinent several million years ago. Globally, Unionids are endangered species of fauna. The authors of the new work associate the extinction of freshwater molluscs with anthropogenic impact on their natural environment, the impact of industry on water bodies, as well as global climate change. In addition, according to scientists, alien species are also a danger to Unionidae.

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