Abstract
Sturgeons (Order Acipenseriformes) represent an extremely valuable natural resource that is now facing depletion. In the current study we evaluate if the traditional classification in subspecies of Acipenser gueldenstaedtii, Acipenser stellatus and Huso huso, endemic to Ponto-Caspian region is sustained by molecular analysis and if these represent Evolutionary Significant Units (ESUs) that should be managed separately in conservation programs. To examine the classification of taxonomic entities we sequenced a fragment of the mitochondrial control region in case of three sturgeon species that inhabit the North-western of Black Sea and migrate for reproduction in the Lower Danube. Beside these sequences, we used previously published sequences from sturgeon individuals sampled in the Black Sea, Azov Sea and Caspian Sea. We determined the genetic diversity and genetic differentiation, conducted a Population Aggregation Analysis (PAA) and inferred an intraspecific molecular phylogeny and haplotype network. The results indicated a low level of genetic differentiation between the geographically designated subspecies and did not support a significant divergence or reciprocal monophyly between them. Our results confirm previous genetic studies with smaller samples sizes, but additional analyses including nuclear markers should be conducted for proper recommendations aiming at the development of conservation programs.
Highlights
Sturgeons represent an ancient group of fish with slow evolution, which maintained their morphological characteristics for more than 200 million years (Bemis and Kynard, 1997)
Among the sequences that we obtained for individual sturgeons sampled in the Lower Danube River we identified four distinct haplotypes in 28 specimens of A. gueldenstaedtii, seven haplotypes in 27 specimens of A. stellatus, and seven haplotypes in 23 specimens of H. huso
For the three Ponto-Caspian sturgeon species a taxonomic classification in subspecies based on morphological, meristic and ecological traits and related to the water body in which they are found was already proposed (Pirogovskii et al, 1989; Shubina et al, 1989; Vlasenko et al, 1989)
Summary
Sturgeons represent an ancient group of fish with slow evolution, which maintained their morphological characteristics for more than 200 million years (Bemis and Kynard, 1997). 27 species of sturgeon and paddlefishes (Order Acipenseriformes) are found on the IUCN Red List, the majority being classified as “Critically Endangered”, and four species are possibly extinct (http://www.iucn.org). In this situation it is crucially important to develop efficient programs aiming at conservation, repopulation of their original habitats and aquaculture, for supplying the request of the market for meat and caviar, and to raise appropriate reproducer sturgeons in the attempt of recover wild populations. One of the aims of endangered species conservation should be directed to the identification of ESUs, defined broadly as a subspecies, population or group of populations with a high genetic and ecological distinctiveness (Allendorf and Luikart, 2007) and characterized by reproductive isolation and adaptation (Waples, 1991); reciprocal monophyly at mtDNA loci (Moritz, 1994); the lack of “ecological exchangeability” (different life histories, morphology, quantitative trait locus variation, habitat, predators, etc.) and of “genetic exchangeability” (no recent gene flow, concordance between phylogenetic and geographic discontinuities) (Crandall et al, 2000)
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