Nonconcordant evolutionary history of maternal and paternal lineages in Adriatic sturgeon

Abstract

Although analyses of intraspecific variability are an important prerequisite for species identification assays, only a few studies have focused on population genetics and historical biogeography of sturgeon species. Here we present the first study on genetic variability of the last remaining Adriatic sturgeon, Acipenser naccarii, derived from mitochondrial and nuclear DNA. Our mitochondrial DNA analyses arranged individuals into three distinguished mitochondrial DNA haplogroups (Po1, Po2 and Buna). Two haplogroups (Po1 and Buna) were correlated to geographical distribution, whereas the third (Po2) was not. It was, however, very closely related to one lineage of its Ponto-Caspian sister species, A. gueldenstaedtii. The distribution of nuclear markers (microsatellites and amplified fragment length polymorphism) was strongly correlated to geographical distribution. An assignment test based on nuclear data placed no specimen of A. naccarii to A. gueldenstaedtii and vice versa. Therefore, the presence of gueldenstaedtii-like haplotypes within the Po population is either the result of a postglacial introgression or an ancestral polymorphism and does not indicate a hybrid population. The most valuable tool for forensic species identification purposes is one diagnostic deletion separating all A. naccarii from A. gueldenstaedtii. As both A. naccarii populations are genetically differentiated, stocking of sturgeon from the Po River in Italy into waters of the Buna River would jeopardize the genetic differences between both populations and should thus be avoided.

The biogeography of mitochondrial and nuclear discordance in animals

“…introgression of the Woodhouse toad's mtDNA, Bufo woodhousii, into the Arizona toad, B. microscaphus, which has a nested range within B. woodhousii; Malmos et al 2001) or differences in population sizes (e.g. the Russian sturgeon, Acipenser gueldenstaedtii, introgressing mtDNA into the critically endangered Adriatic sturgeon, A. naccarii; Ludwig et al 2003). In many cases, authors could neither confirm nor rule out demographic explanations for observed discordance, where mtDNA introgression occurred because of variation in range sizes or preceding a population bottleneck and range expansion; however, most offered more specific explanations, such as adaptive introgression or sex-biased asymmetries.…”

Multiple invasions of Europe by East Asian cobitid loaches (Teleostei: Cobitidae)

“…Therefore, we suspect that there has been an introgression of mtDNA from an Asian Cobitis by hybridization. There are many examples of introgression of mtDNA in vertebrates (Dowling & De Marais, 1993;Duvernell & Aspinwall, 1995;Rhymer & Simberloff, 1996;Avise et al, 1997;Dowling & Secor, 1997;Ludwig et al, 2003, Freyhof et al, 2005. Freyhof et al (2005) demonstrated that introgression of mtDNA is not even restricted to closely related species or genera in one group of cypriniform fishes.…”

First evidence of hybridization between endangered sterlets (Acipenser ruthenus) and exotic Siberian sturgeons (Acipenser baerii) in the Danube River

“…However, natural sturgeon hybrids are often rare (Ludwig et al 2002). Most times, backcrosses with native specimens resulted in a ''genetic cleaning'' of nuclear genotypes, so that evidence for ancestral hybridisation is often only detectable in mitochondrial DNA (Ludwig et al 2003;Birstein et al 2005).…”