Northern areas as refugia for temperate species under current climate warming: Atlantic salmon (Salmo salar L.) as a model in Northern Europe

This is the author accepted manuscript. The final version is available from Wiley via the DOI in this recordIn this work, patterns of geographical genetic diversity in Atlantic salmon Salmo salar were studied across the whole Atlantic arc, as well as whether patterns (and thus genetic population structure) were affected by water temperatures. Salmo salar populations were here characterized using microsatellite loci and then analysed in the light of ocean surface temperature data from across the region. Analysis showed the presence of a latitudinal cline of genetic variability (higher in northern areas) and water temperatures (sea surface temperatures) determining genetic population structure (the latter in combination with genetic drift in southern populations). Under the current global change scenario, northern areas of Europe would constitute refuges for diversity in the future. This is effectively the inverse of what appears to have happened in glacial refugia during the last glacial maximum. From this perspective, the still abundant and large northern populations should be considered as precious as the small almost relict southern ones and perhaps protected. Careful management of the species, coordinated across countries and latitudes, is needed in order to avoid its extinction in Europe.J. L. Horreo was supported by a MINECO Spanish postdoctoral grant (“Juan de la CiervaIncorporación” (ref. IJCI-2015-23618). This work was funded by the European Union INTERREG IIIB programme (Atlantic Salmon Arc Project [ASAP], Project No. 040 and ASAP-2, Project No. 203). This study received additional funding from the Principality of Asturias Grants for Excellent Research (GRUPIN-2014-093) and the Contract CN-14-076

Introgressive hybridization in North American hakes after secondary contact

High levels of bidirectional introgressive hybridization were found between the two Atlantic North American hakes Merluccius albidus and M. bilinearis in their overlapping distribution area between the 34 and the 42°N parallels, employing mitochondrial and nuclear DNA markers. Absence of F1 hybrids, and varied levels of bidirectional introgression, indicate long-time hybridization and backcrossing. Based on the evolutionary history of the genus Merluccius, originated in this area from the ancestor of the present M. bilinearis by the rise of the Panama Isthmus, secondary contact between the two species has probably been promoted by northwards displacement of M. albidus. Higher introgression rates in southern areas of M. albidus could be explained by restricted gene flow in that area which may allow long-term accumulation of introgressed genes

Parallel evolution in Ugandan crater lakes: Repeated evolution of limnetic body shapes in haplochromine cichlid fish

BackgroundThe enormous diversity found in East African cichlid fishes in terms of morphology, coloration, and behavior have made them a model for the study of speciation and adaptive evolution. In particular, haplochromine cichlids, by far the most species-rich lineage of cichlids, are a well-known textbook example for parallel evolution. Southwestern Uganda is an area of high tectonic activity, and is home to numerous crater lakes. Many Ugandan crater lakes were colonized, apparently independently, by a single lineage of haplochromine cichlids. Thereby, this system could be considered a natural experiment in which one can study the interaction between geographical isolation and natural selection promoting phenotypic diversification.ResultsWe sampled 13 crater lakes and six potentially-ancestral older lakes and, using both mitochondrial and microsatellite markers, discovered strong genetic and morphological differentiation whereby (a) geographically close lakes tend to be genetically more similar and (b) three different geographic areas seem to have been colonized by three independent waves of colonization from the same source population. Using a geometric morphometric approach, we found that body shape elongation (i.e. a limnetic morphology) evolved repeatedly from the ancestral deeper-bodied benthic morphology in the clear and deep crater lake habitats.ConclusionsA pattern of strong genetic and morphological differentiation was observed in the Ugandan crater lakes. Our data suggest that body shape changes have repeatedly evolved into a more limnetic-like form in several Ugandan crater lakes after independent waves of colonization from the same source population. The observed morphological changes in crater lake cichlids are likely to result from a common selective regime

Genomics of adaptation to multiple concurrent stresses: insights from comparative transcriptomics of a Cichlid fish from one of earth’s most extreme environments, the Hypersaline Soda Lake Magadi in Kenya, East Africa

The Magadi tilapia (Alcolapia grahami) is a cichlid fish that inhabits one of the Earth's most extreme aquatic environments, with high pH (~10), salinity (~60% of seawater), high temperatures (~40 °C), and fluctuating oxygen regimes. The Magadi tilapia evolved several unique behavioral, physiological, and anatomical adaptations, some of which are constituent and thus retained in freshwater conditions. We conducted a transcriptomic analysis on A. grahami to study the evolutionary basis of tolerance to multiple stressors. To identify the adaptive regulatory changes associated with stress responses, we massively sequenced gill transcriptomes (RNAseq) from wild and freshwater-acclimated specimens of A. grahami. As a control, corresponding transcriptome data from Oreochromis leucostictus, a closely related freshwater species, were generated. We found expression differences in a large number of genes with known functions related to osmoregulation, energy metabolism, ion transport, and chemical detoxification. Over-representation of metabolism-related gene ontology terms in wild individuals compared to laboratory-acclimated specimens suggested that freshwater conditions greatly decrease the metabolic requirements of this species. Twenty-five genes with diverse physiological functions related to responses to water stress showed signs of divergent natural selection between the Magadi tilapia and its freshwater relative, which shared a most recent common ancestor only about four million years ago. The complete set of genes responsible for urea excretion was identified in the gill transcriptome of A. grahami, making it the only fish species to have a functional ornithine-urea cycle pathway in the gills--a major innovation for increasing nitrogenous waste efficiency

Differential predation on the two colour morphs of Nicaraguan Crater lake Midas cichlid fish: Implications for the maintenance of its gold-dark polymorphism

Predation can play an important role in the evolution and maintenance of prey colour polymorphisms. Several factors are known to affect predator choice, including the prey's relative abundance and conspicuousness. In polymorphic prey species, predators often target the most common or most visible morphs. To test if predator choice can explain why in Midas cichlid fish the more visible (gold) morph is also more rare than the inconspicuous dark morph, we conducted predation experiments using two differently coloured wax models in Nicaraguan crater lakes. Contrary to expectations, we observed an overall higher attack rate on the much more abundant, yet less conspicuous dark models, and propose frequency-dependent predation as a potential explanation for this result. Interestingly, the attack rate differed between different types of predators. While avian predators were biased towards the abundant and less colourful dark morphs, fish predators did not show a strong bias. However, the relative attack rate of fish predators seemed to vary with the clarity of the water, as attack rates on gold models went up as water clarity decreased. The relative differential predation rates on different morphs might impact the relative abundance of both colour morphs and thus explain the maintenance of the colour polymorphism