Mitochondrial DNA Variation and Introgression in Siberian Taimen Hucho taimen

Evgeniy S Balakirev,Nikolai S Romanov,Pavel B Mikheev,Francisco J Ayala,William Barendse

doi:10.1371/journal.pone.0071147

Abstract

Siberian taimen Hucho taimen is the largest representative of the family Salmonidae inhabiting rivers of northern Eurasia. The species is under intensive aquaculture activity. To monitor natural taimen populations we have sequenced a portion (8,141 bp) of the mitochondrial (mt) genome in 28 specimens of H. taimen from six localities in the Amur River basin. Nucleotide variability is low (π = 0.0010), but structured in two divergent haplotype groups. A comparison of the data with the GenBank H. taimen mt genome (HQ897271) reveals significant differences between them in spite of the fact that the fish specimens come from neighboring geographical areas. The distribution of divergence is non-uniform with two highly pronounced divergent regions centered on two genes, ND3 and ND6. To clarify the pattern of divergence we sequenced the corresponding portion of the mt genome of lenok Brachymystax tumensis and analyzed the GenBank complete mt genomes of related species. We have found that the first and second divergent regions are identical between the GenBank H. taimen and two lenok subspecies, B. lenok and B. lenok tsinlingensis, respectively. Consequently, both divergent regions represent introgressed mtDNA resulting from intergeneric hybridization between the two lenok subspecies and H. taimen. Introgression is, however, not detected in our specimens. This plus the precise identity of the introgressed fragments between the donor and the recipient GenBank sequence suggests that the introgression is local and very recent, probably due to artificial manipulations involving taimen – lenok intergeneric hybridization. Human-mediated hybridization may become a major threat to aquatic biodiversity. Consequently we suggest that due attention needs to be given to this threat by means of responsible breeding program management, so as to prevent a potential spread of hybrid fishes that could jeopardize the resilience of locally adapted gene pools of the native H. taimen populations.

Highlights

Siberian taimen Hucho taimen (Pallas, 1773) is the world’s largest salmonid fish, reaching up to 2 m in length and 105 kg in weight [1,2,3]
Siberian taimen has significantly declined in abundance throughout their range in the large rivers of the Volga/Caspian, Arctic, and Pacific drainages of northern Eurasia and it is included as vulnerable species in the Mongolian, Russian, and Chinese red lists [5,6,7]
Intraspecific genetic variation in Siberian taimen has been investigated by means of chromosome analysis [8], allozymes [9], microsatellites [10,11,12,13], AFLP markers [14,15], and DNA sequences [16,17,18]

Summary

Introduction

Siberian taimen Hucho taimen (Pallas, 1773) is the world’s largest salmonid fish, reaching up to 2 m in length and 105 kg in weight [1,2,3]. Siberian taimen has significantly declined in abundance throughout their range in the large rivers of the Volga/Caspian, Arctic, and Pacific drainages of northern Eurasia and it is included as vulnerable species in the Mongolian, Russian, and Chinese red lists [5,6,7]. Significant genetic differentiation along with low nucleotide sequence diversity have been found in the European huchen, H. hucho (Linnaeus, 1758) [19,20]. This population structure might be explained by the relatively low dispersion capability of the fish and/or the homing like behavior suggested for H. hucho [1]. Anthropogenic factors may reduce gene flow between taimen populations [12], [15]

Methods

Results

Conclusion