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In fisheries, operational management units and biological data often do not coincide. In many cases, this is not even known due to the lack of information about a species' population structure or behaviour. This study focuses on two such species, the common ling Molva molva and the blue ling M. dypterygia , two Northeast Atlantic gadoids with overlapping geographical distribution, but different depth habitats. Heavily exploited throughout their ranges, with declining catches, little is known about their population structure. Genotyping-by-sequencing at thousands of genetic markers indicated that both species are separated into two major groups, one represented by samples from the coasts of western Scotland, Greenland, and the Bay of Biscay and the other off the coast of Norway. This signal is stronger for the deeper dwelling blue ling, even though adult dispersal was also identified for this species. Despite small sample sizes, fine-scale patterns of genetic structure were identified along Norway for common ling. Signatures of adaptation in blue ling consisted in signs of selections in genes involved in vision, growth, and adaptation to cold temperatures. [ABSTRACT FROM AUTHOR]

Studying the genetic basis of host-parasite interactions represents an outstanding opportunity to observe eco-evolutionary processes. Established candidates for such studies in vertebrates are immunogenes of the major histocompatibility complex ( MHC). The MHC has been reported to reach high intra- and interindividual diversity, and a diverse MHC might be advantageous when facing infections from multiple parasites. However, other studies indicated that individuals with an intermediate number of MHC alleles are less infected with parasites or have other fitness advantages. In this study, we assessed the optimal number of MHC alleles in the blunt-head cichlid Tropheus moorii from Lake Tanganyika. We investigated the influence of the interindividual variation in number of MHC length variants on parasite infection and body condition, measured by the amount of perivisceral fat reserves. Surprisingly, there was no correlation between parasite infection and number of MHC length variants or perivisceral fat deposits. However, the individual number of MHC length variants significantly correlated with the amount of perivisceral fat deposits in males, suggesting that male individuals with an intermediate number of alleles might be able to use their fat reserves more efficiently. [ABSTRACT FROM AUTHOR]

Phylogeographical patterns of the sand goby Poinatoschistus minutus (Gobiidae, Teleostei) were studied by means of sequence and single-stranded conformational polymorphism analysis of a 283-bp fragment of the cytochrome b locus of the mtDNA. A total of 228 individuals sampled at 13 sites throughout the species's distributional range revealed a moderate level of diversity and a low but significant level of overall genetic differentiation at all but one site. The goby sample from the Adriatic Sea differed in sequence by approximately 10% from the Atlantic P. minatas and is thought to belong to a cryptic species of the genus Poinatoschi stag. Limited genetic differentiation with a weak pattern of isolation-by-distance was recorded throughout the distributional range of the typical P. minutus. Phylogeographical analysis suggested a contiguous range expansion in the Atlantic and Baltic basins during the Eemian and evidence for a glacial refugium in the southern North Sea during the Weichselian. In P minutus from the western Mediterranean Sea a high number of endemic haplotypes as well as the most common Atlantic haplotype were recorded in appreciable frequencies. This might be explained by secondary contact between different mitochondrial lineages, which evolved in allopatry. [ABSTRACT FROM AUTHOR]

Abstract Pleistocene genetic structure of the bullhead, Cottus gobio, was evaluated across the western Palearctic using a 771-bp long fragment of the mitochondrial control region in 123 individuals collected at 35 sites (data set I). In total, 59 haplotypes that differed at 73 positions (9.3%) were detected. Data analysis also included sequences from Englbrecht et al . (2000 ), thus increasing the sampling to a more comprehensive data set of 529 fish and 63 control region sequences of 482 bp (data set II). A minimum spanning and phylogenetic tree identified a seventh clade (Brittany–Loire) in addition to the previously identified six clades. The geographical range of the North Sea and Lower Rhine clades was considerably larger than thought previously. Haplotype diversity was generally low, and the total fixation index high ( F ST = 0.49). Among-group differentiation accounted for 41.7% (data set I) of the variation. Contiguous range expansions and restricted gene flow combined with isolation by distance, interspersed with past fragmentation characterize bullhead across its range. New is the knowledge that dated interglacial periods correlated with population expansions; river captures, proglacial lake systems and sea level played a significant role in the dispersal and expansion either in northern or southern direction. Hence it became possible to identify and date the colonization routes and putative palaeorefugia, most of which were located in Central and North-west Europe. Glacial periods resulted in distinct fragmentation events and lineage sorting. [ABSTRACT FROM AUTHOR]