Evolutionary origins of the endemic ichthyofauna in Inle Lake, an ancient lake in Myanmar

概要

Ancient lakes have been excellent sites for exploring speciation and community
assembly processes for their unique biota evolution. The theory of island biogeography
explains species diversity in isolated environments, such as islands and ancient lakes,
considering the dynamics of colonization from the species pool “continent” and
speciation and extinction within the “island.” According to this theory, species richness
increases through colonization and in situ speciation. On the other hand, the proportion
of endemic species increases through allopatric speciation under the limitation of gene
flow via immigration, and also through in situ radiation under further restricted
conditions. Empirical studies of community assembly in ancient lakes have mostly
focused on radiation from a small number of ancestors; but the development processes
of endemism under repeated colonizations are poorly understood.
Inle Lake, the only ancient lake in continental Southeast Asia (Shan Plateau,
Myanmar), is one of the biodiversity hotspots. The ichthyofauna of Inle Lake is
believed to have comprised widely distributed species that immigrated from the
surrounding areas and endemic species that differentiated via geographic isolation,
implying the assembly on a moderately isolated “island.” The aim of this thesis is to
clarify the biogeographic and ecological processes by which regional endemism is
formed under repeated colonizations from the surrounding areas, using the endemic
ichthyofauna of Inle Lake as a model system. In Chapters 2 and 3, I first tried to clarify
the origins of two endemic species with contrasting distribution patterns, i.e., an
endemic species with closely related species distributed over a wide area in Southeast
Asia and a species endemic to the Inle region (Inle Lake and the surrounding rivers in
the adjacent areas) at the genus level. ...