Title : When mainland meets islands: Unravelling the evolutionary legacy of Southeast Asian freshwater fishes in the Sundaland biodiversity hotspot
Abstract:
Sundaland represents one of the most dynamic biogeographic landscapes in Southeast Asia, where the mainland and islands have experienced recurrent shifts in connectivity driven by geological processes and Quaternary sea-level fluctuations. During periods of low sea level, exposure of the Sunda Shelf altered the configuration of freshwater habitats and established palaeodrainage networks that connected regions now separated by marine barriers. This history raises a fundamental question: to what extent does the evolutionary history of extant freshwater fishes retain signatures of past connections? The freshwater fishes provide an informative system for addressing this issue because their distributions are closely associated with drainage systems, while their limited ability to cross oceanic barriers can generate pronounced geographic genetic structure. Accordingly, this study examines the evolutionary legacy of ancient Sundaland by investigating how palaeogeographic history and environmental fragmentation may have shaped phylogeographic and evolutionary patterns in Southeast Asian freshwater fishes, with particular emphasis on genetic distinctiveness between mainland and island lineages. The mitogenomic evidence were used to resolve relationships among lineages and assess genetic divergence, which were subsequently contextualized in relation to geographic structure within a palaeolandscape framework. The findings suggest that evolutionary responses to palaeogeographic change vary among taxa, potentially reflecting differences in dispersal capacity and divergence times influenced by geological history. Overall, these observations highlight the importance of understanding Southeast Asian freshwater fish diversity within historical configurations of landscape connectivity rather than interpreting it solely through present-day biogeography. From this perspective, the mitogenomic approaches link contemporary genetic patterns to palaeogeographic scenarios connecting mainland and island regions of Southeast Asia, revealing insights into the persistence of the evolutionary legacy of ancient Sundaland in the genomes of extant freshwater fishes.
