In recent decades, a global acceleration of urbanization has been observed, leading to significant habitat loss and fragmentation. Economic development in eastern Thailand has been promoted, but this has often coincided with unsustainable exploitation of natural resources. The expansion of urban and industrial areas in the region puts many organisms at risk of extinction owing to habitat loss. Plakad-Pa Pak-Tawan-Ok (Betta siamorientalis) is an endemic species found only in the eastern Thailand. In this study, the genetic diversity and population structure of 17 B. siamorientalis populations were analyzed using microsatellite genotyping. High genetic variability was observed. The STRUCTURE plot reveals large, distinct gene pools in the lower Prachin River and Phra Prong River Part 2. Migration analyses showed that the estimated gene flow between populations aligned with the dominant water flow in the flooding direction toward the mouth of the Bang Pakong River on the western side of eastern Thailand. Thus, this area must be considered a vital genetic resource. The pairwise fixation index values were statistically significant for all populations, including those within the same sub-watershed, indicating genetic differentiation among populations. This suggests relatively low gene flow between ecologically divergent populations. Mean annual total precipitation was also significantly correlated with genetic diversity. We propose the need for careful consideration and awareness of the planning and implementation of industrial development within eastern Thailand. Resource allocation in management efforts may be most effective when directed toward the preservation of habitat suitability, specifically in relation to precipitation and water resources, rather than prioritizing enhancements in landscape connectivity for B. siamorientalis.
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