Temporal and spatial instability in neutral and adaptive (MHC) genetic variation in marginal salmon populations.

The role of marginal populations for the long-term maintenance of species' genetic diversity and evolutionary potential is particularly timely in view of the range shifts caused by climate change. The Centre-Periphery hypothesis predicts that marginal populations should bear reduced genetic diversity and have low evolutionary potential. We analysed temporal stability at neutral microsatellite and adaptive MHC genetic variation over five decades in four marginal Atlantic salmon populations located at the southern limit of the species' distribution with a complicated demographic history, which includes stocking with foreign and native salmon for at least 2 decades. We found a temporal increase in neutral genetic variation, as well as temporal instability in population structuring, highlighting the importance of temporal analyses in studies that examine the genetic diversity of peripheral populations at the margins of the species' range, particularly in face of climate change.

Population structure and phylogeography of the Gentoo Penguin (Pygoscelis papua) across the Scotia Arc.

Climate change, fisheries' pressure on penguin prey, and direct human disturbance of wildlife have all been implicated in causing large shifts in the abundance and distribution of penguins in the Southern Ocean. Without mark-recapture studies, understanding how colonies form and, by extension, how ranges shift is challenging. Genetic studies, particularly focused on newly established colonies, provide a snapshot of colonization and can reveal the extent to which shifts in abundance and occupancy result from changes in demographic rates (e.g., reproduction and survival) or migration among suitable patches of habitat. Here, we describe the population structure of a colonial seabird breeding across a large latitudinal range in the Southern Ocean. Using multilocus microsatellite genotype data from 510 Gentoo penguin (Pygoscelis papua) individuals from 14 colonies along the Scotia Arc and Antarctic Peninsula, together with mitochondrial DNA data, we find strong genetic differentiation between colonies north and south of the Polar Front, that coincides geographically with the taxonomic boundary separating the subspecies P. p. papua and P. p. ellsworthii. Using a discrete Bayesian phylogeographic approach, we show that southern Gentoos expanded from a possible glacial refuge in the center of their current range, colonizing regions to the north and south through rare, long-distance dispersal. Our findings show that this dispersal is important for new colony foundation and range expansion in a seabird species that ordinarily exhibits high levels of natal philopatry, though persistent oceanographic features serve as barriers to movement.

The genomes of two key bumblebee species with primitive eusocial organization.

BACKGROUND: The shift from solitary to social behavior is one of the major evolutionary transitions. Primitively eusocial bumblebees are uniquely placed to illuminate the evolution of highly eusocial insect societies. Bumblebees are also invaluable natural and agricultural pollinators, and there is widespread concern over recent population declines in some species. High-quality genomic data will inform key aspects of bumblebee biology, including susceptibility to implicated population viability threats. RESULTS: We report the high quality draft genome sequences of Bombus terrestris and Bombus impatiens, two ecologically dominant bumblebees and widely utilized study species. Comparing these new genomes to those of the highly eusocial honeybee Apis mellifera and other Hymenoptera, we identify deeply conserved similarities, as well as novelties key to the biology of these organisms. Some honeybee genome features thought to underpin advanced eusociality are also present in bumblebees, indicating an earlier evolution in the bee lineage. Xenobiotic detoxification and immune genes are similarly depauperate in bumblebees and honeybees, and multiple categories of genes linked to social organization, including development and behavior, show high conservation. Key differences identified include a bias in bumblebee chemoreception towards gustation from olfaction, and striking differences in microRNAs, potentially responsible for gene regulation underlying social and other traits. CONCLUSIONS: These two bumblebee genomes provide a foundation for post-genomic research on these key pollinators and insect societies. Overall, gene repertoires suggest that the route to advanced eusociality in bees was mediated by many small changes in many genes and processes, and not by notable expansion or depauperation.

Extensive local gene duplication and functional divergence among paralogs in Atlantic salmon.

Many organisms can generate alternative phenotypes from the same genome, enabling individuals to exploit diverse and variable environments. A prevailing hypothesis is that such adaptation has been favored by gene duplication events, which generate redundant genomic material that may evolve divergent functions. Vertebrate examples of recent whole-genome duplications are sparse although one example is the salmonids, which have undergone a whole-genome duplication event within the last 100 Myr. The life-cycle of the Atlantic salmon, Salmo salar, depends on the ability to produce alternating phenotypes from the same genome, to facilitate migration and maintain its anadromous life history. Here, we investigate the hypothesis that genome-wide and local gene duplication events have contributed to the salmonid adaptation. We used high-throughput sequencing to characterize the transcriptomes of three key organs involved in regulating migration in S. salar: Brain, pituitary, and olfactory epithelium. We identified over 10,000 undescribed S. salar sequences and designed an analytic workflow to distinguish between paralogs originating from local gene duplication events or from whole-genome duplication events. These data reveal that substantial local gene duplications took place shortly after the whole-genome duplication event. Many of the identified paralog pairs have either diverged in function or become noncoding. Future functional genomics studies will reveal to what extent this rich source of divergence in genetic sequence is likely to have facilitated the evolution of extreme phenotypic plasticity required for an anadromous life-cycle.

The need for transparency and good practices in the qPCR literature.

Two surveys of over 1,700 publications whose authors use quantitative real-time PCR (qPCR) reveal a lack of transparent and comprehensive reporting of essential technical information. Reporting standards are significantly improved in publications that cite the Minimum Information for Publication of Quantitative Real-Time PCR Experiments (MIQE) guidelines, although such publications are still vastly outnumbered by those that do not.

Genomic organization and evolution of the vomeronasal type 2 receptor-like (OlfC) gene clusters in Atlantic salmon, Salmo salar.

There are three major multigene superfamilies of olfactory receptors (OR, V1R, and V2R) in mammals. The ORs are expressed in the main olfactory organ, whereas the V1Rs and V2Rs are located in the vomeronasal organ. Fish only possess one olfactory organ in each nasal cavity, the olfactory rosette; therefore, it has been proposed that their V2R-like genes be classified as olfactory C family G protein-coupled receptors (OlfC). There are large variations in the sizes of OR gene repertoires. Previous studies have shown that fish have between 12 and 46 functional V2R-like genes, whereas humans have lost all functional V2Rs, and frog sp. have more than 240. Pseudogenization of V2R genes is a prevalent event across species. In the mouse and frog genomes, there are approximately double the number of pseudogenes compared with functional genes. An oligonucleotide probe was designed from a conserved sequence from four Atlantic salmon OlfC genes and used to screen the Atlantic salmon bacterial artificial chromosome (BAC) library. Hybridization-positive BACs were matched to fingerprint contigs, and representative BACs were shotgun cloned and sequenced. We identified 55 OlfC genes. Twenty-nine of the OlfC genes are classified as putatively functional genes and 26 as pseudogenes. The OlfC genes are found in two genomic clusters on chromosomes 9 and 20. Phylogenetic analysis revealed that the OlfC genes could be divided into 10 subfamilies, with nine of these subfamilies corresponding to subfamilies found in other teleosts and one being salmon specific. There is also a large expansion in the number of OlfC genes in one subfamily in Atlantic salmon. Subfamily gene expansions have been identified in other teleosts, and these differences in gene number reflect species-specific evolutionary requirements for olfaction. Total RNA was isolated from the olfactory epithelium and other tissues from a presmolt to examine the expression of the odorant genes. Several of the putative OlfC genes that we identified are expressed only in the olfactory epithelium, consistent with these genes encoding odorant receptors.

Rare and fleeting: an example of interspecific recombination in animal mitochondrial DNA.

Recombination is thought to occur only rarely in animal mitochondrial DNA (mtDNA). However, detection of mtDNA recombination requires that cells become heteroplasmic through mutation, intramolecular recombination or 'leakage' of paternal mtDNA. Interspecific hybridization increases the probability of detecting mtDNA recombinants due to higher levels of sequence divergence and potentially higher levels of paternal leakage. During a study of historical variation in Atlantic salmon (Salmo salar) mtDNA, an individual with a recombinant haplotype containing sequence from both Atlantic salmon and brown trout (Salmo trutta) was detected. The individual was not an F1 hybrid but it did have an unusual nuclear genotype which suggested that it was a later-generation backcross. No other similar recombinant haplotype was found from the same population or three neighbouring Atlantic salmon populations in 717 individuals collected during 1948-2002. Interspecific recombination may increase mtDNA variability within species and can have implications for phylogenetic studies.