Abstract
Indochina is a biodiversity hot spot and harbors a high number of endemic species, most of which are poorly studied. This study explores the genetic structure and reproductive system of the threatened endemic timber species Dalbergia cochinchinensis and Dalbergia oliveri using microsatellite data from populations across Indochina and relates it to landscape characteristics and life‐history traits. We found that the major water bodies in the region, Mekong and Tonle Sap, represented barriers to gene flow and that higher levels of genetic diversity were found in populations in the center of the distribution area, particularly in Cambodia. We suggest that this pattern is ancient, reflecting the demographic history of the species and possible location of refugia during earlier time periods with limited forest cover, which was supported by signs of old genetic bottlenecks. The D. oliveri populations had generally high levels of genetic diversity (mean H e = 0.73), but also strong genetic differentiation among populations (global GST = 0.13), while D. cochinchinensis had a moderate level of genetic diversity (mean H e = 0.55), and an even stronger level of differentiation (global GST = 0.25). These differences in genetic structure can be accounted for by a higher level of gene flow in D. oliveri due to a higher dispersal capacity, but also by the broader distribution area for D. oliveri, and the pioneer characteristics of D. cochinchinensis. This study represents the first detailed analysis of landscape genetics for tree species in Indochina, and the found patterns might be common for other species with similar ecology.
Highlights
The region of Indochina, the mainland part of Southeast Asia, is recognized as part of one of the world’s biodiversity hot spots
We found that the major water bodies in the region, Mekong and Tonle Sap, represented barriers to gene flow and that higher levels of genetic diversity were found in populations in the center of the distribution area, in Cambodia
The present study represents the first assessment of region- scale patterns of genetic structure and diversity of populations of a tree species across central Indochina
Summary
The region of Indochina, the mainland part of Southeast Asia, is recognized as part of one of the world’s biodiversity hot spots. Assessment of the diversity and structure of intraspecific genetic variation as well as acquiring basic knowledge on traits such as reproduction and dispersal systems can contribute toward a more general understanding of how landscape and habitat changes affect species and populations Such knowledge is important in order to guide conservation and management of remaining populations of threatened species. Dalbergia cochinchinensis Pierre and Dalbergia oliveri Gamble ex Prain (Figure 1) are two of the most valuable timber species in Indochina and are highly sought after for their attractive wood, which is used especially for luxury furniture (CTSP 2004; GW 2015; Niyomdham, Hô, Dy Phon, & Vidal, 1997) Both species occur in Thailand, Laos, Cambodia, and Vietnam and are often found in the same localities, D. oliveri has a wider distribution area extending into Myanmar and occurs in a broader range of forest types. Our specific objectives are to 1) explore and describe the landscape genetic diversity patterns of the two species across the study area, 2) relate the patterns to current and ancient geographical characteristics of the Indochina landscape, 3) evaluate whether the recent deforestation and fragmentation levels have impacted the genetic diversity and inbreeding level of the two species, and 4) compare the genetic structure between the two species and relate it to differences in life-h istory traits
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