Lenok

Abstract: DNA sequence data was collected for the C and D introns in the duplicate growth hormone loci (GH1 and GH2) from Brachmystax lenok, two subspecies of Hucho hucho, Hucho (Parahucho) perryi, Salmo salar, Salmo trutta, Acantholingua ohridana (Salmothymus), six species of Salvelinus, eight species of Oncorhynchus including O. masou, and three outgroups including Thymallus thymallus, Coregonus artedi, and Coregonus clupeaformis. Phylogenetic analyses were performed using maximum parsimony and maximum likelihood (PAUP, version 4.08beta) with gaps as missing data and as a fifth base. B. lenok was basal in all of the trees and all of the other genera were monophyletic with the exception that A. ohridana always placed within Salmo, and H. hucho sp. often placed with B. lenok. The GH1 introns supporteda sister relationship between Oncorhynchus and Salvelinus, while the combined GH2 introns were ambiguous at this node. This result contrasts with trees based on morphology and the ribosomal ITS1 sequences that support a sister relationship between Salmo and Oncorhynchus. The only estrogen response element (ERE) in the gene is found in the C intron and has mutated in GH2 in all of the species except B. lenok. The ERE element in GH1 has undergone another mutation in all of the species except for B. lenok, and members of the two genera Salvelinus and Oncorhynchus. Thus these latter two genera are the only ones with a difference in expression of GH1 and GH2 in the presence of estrogen. Differences in selective pressure on the introns in the duplicate genes in different taxa could account for the conflicting results obtained in the phylogenetic analysis.

Abstract: Broad-scale phylogeographic studies of freshwater organisms provide not only an invaluable framework for understanding the evolutionary history of species, but also a genetic imprint of the paleo-hydrological dynamics stemming from climatic change. Few such studies have been carried out in Siberia, a vast region over which the extent of Pleistocene glaciation is still disputed. Brachymystax lenok is a salmonid fish distributed throughout Siberia, exhibiting two forms hypothesized to have undergone extensive range expansion, genetic exchange, and multiple speciation. A comprehensive phylogeographic investigation should clarify these hypotheses as well as provide insights on Siberia's paleo-hydrological stability. Molecular-sequence (mtDNA) based phylogenetic and morphological analysis of Brachymystax throughout Siberia support that sharp- and blunt-snouted lenok are independent evolutionary lineages, with the majority of their variation distributed among major river basins. Their evolutionary independence was further supported through the analysis of 11 microsatellite loci in three areas of sympatry, which revealed little to no evidence of introgression. Phylogeographic structure reflects climatic limitations, especially for blunt-snouted lenok above 56° N during one or more glacial maxima. Presumed glacial refugia as well as interbasin exchange were not congruent for the two lineages, perhaps reflecting differing dispersal abilities and response to climatic change. Inferred demographic expansions were dated earlier than the Last Glacial Maximum (LGM). Evidence for repeated trans-basin exchange was especially clear between the Amur and Lena catchments. Divergence of sharp-snouted lenok in the Selenga-Baikal catchment may correspond to the isolation of Lake Baikal in the mid-Pleistocene, while older isolation events are apparent for blunt-snouted lenok in the extreme east and sharp-snouted lenok in the extreme west of their respective distributions. Sharp- and blunt-snouted lenok have apparently undergone a long, independent, and demographically dynamic evolutionary history in Siberia, supporting their recognition as two good biological species. Considering the timing and extent of expansions and trans-basin dispersal, it is doubtful that these historical dynamics could have been generated without major rearrangements in the paleo-hydrological network, stemming from the formation and melting of large-scale glacial complexes much older than the LGM.

Abstract: Brachymystax lenok tsinlingensis is an endangered teleost fish species that occurs in the Qinling Mountain region of China. It also happens to represent the southernmost distribution of an endemic Salmonid fish worldwide. Recently, the habitat of this species shifted towards a higher altitude presumably because of climate change, indicating that this species might be suffering from thermal stress. However, information on the thermal physiology of this species is extremely limited. Accordingly, we investigated the effects of acclimation temperature (6, 12, and 18 °C) on ecologically relevant end points such as critical thermal limits, swimming performance and metabolic rate. Our results showed that elevated acclimation temperatures resulted in increased thermal tolerance and decreased swimming efficiency. High temperature (i.e., 18 °C) did not have a marked effect on the critical swimming speed and the maximum metabolic rate but caused an increase in the energetic cost of transport compared with the results at 12 °C. Interestingly, we found that both the acclimation response ratio and the critical thermal maxima of B. lenok tsinlingensis were higher than that of many other Salmonidae fishes, suggesting that this species responds plastically to temperature changes and has a high thermal tolerance. These characteristics are hypothesized to be related to the southernmost distribution of this species.