Latitudinal Cline in Chromosome Numbers of Ice Cod A. glacialis (Gadidae) from Northeast Greenland

The ice cod Arctogadus glacialis (Peters, 1872) is one of the few fish species endemic to the Arctic. With a circumpolar distribution, the species is confined to the fjords and shelves of the Arctic seas. Biological information on A. glacialis is scarce, with genomic information restricted to microsatellites. Within the frame of the TUNU-Programme: Arctic Ocean Fishes—Diversity, Adaptation and Conservation, we studied A. glacialis at the chromosomal level to explore fish diversity and evolutionary aspects. The analysis of over 50 individuals from the Northeast Greenland fjords between latitudes 71°09′ N and 76°42′ N revealed a remarkable intraspecific diversity epitomized by chromosome numbers spanning from 28 to 33, the occurrence of putative B chromosomes, and diversified patterns of distribution of heterochromatin and rDNAs. The number of B chromosomes followed a latitudinal gradient from 0–2 in the north to 2–5 in the south. Considering the benthic and rather stationary life history of this species, the observed chromosomal differences might have arisen independently, possibly driven and/or fostered by the dynamics of repetitive sequences, and are being fixed in relatively isolated fjord populations. The resulting latitudinal cline we observe today might have repercussions on the fate of local populations facing the ongoing climate-driven environmental changes.

Florida Drosophila melanogaster genomes sampled 13 years apart show increases in warm-associated SNP alleles

ABSTRACTWe studied genetic change in Drosophila melanogaster using whole-genome SNP data from samples taken 13 years apart in Homestead, FL. This population is at the southern tip of a well-studied US latitudinal cline. On the non-inversion-carrying chromosome arms, 11-16% of SNPs show significant frequency changes. These are enriched for latitudinal clines and genic sites. For clinal SNPs each allele is either the northern- or southern-favored. Seventy-eight to 95 percent with significant frequency increase are southern-favored. Five to seven percent of SNPs also show significant seasonal change and involve increases in the northern-favored allele during the season. On the 2L and 3R chromosome arms there are significant seasonal shifts for common inversions. We identify regions and genes that are candidates for selection. These regions also show correspondence with those associated with soft sweeps in Raleigh, NC. This shift towards southern-favored alleles may be caused by climate shifts or increased African-European admixture.

Some like it hot: population-specific adaptations in venom production to abiotic stressors in a widely distributed cnidarian

Background In cnidarians, antagonistic interactions with predators and prey are mediated by their venom, whose synthesis may be metabolically expensive. The potentially high cost of venom production has been hypothesized to drive population-specific variation in venom expression due to differences in abiotic conditions. However, the effects of environmental factors on venom production have been rarely demonstrated in animals. Here, we explore the impact of specific abiotic stresses on venom production of distinct populations of the sea anemone Nematostella vectensis (Actiniaria, Cnidaria) inhabiting estuaries over a broad geographic range where environmental conditions such as temperatures and salinity vary widely. Results We challenged Nematostella polyps with heat, salinity, UV light stressors, and a combination of all three factors to determine how abiotic stressors impact toxin expression for individuals collected across this species’ range. Transcriptomics and proteomics revealed that the highly abundant toxin Nv1 was the most downregulated gene under heat stress conditions in multiple populations. Physiological measurements demonstrated that venom is metabolically costly to produce. Strikingly, under a range of abiotic stressors, individuals from different geographic locations along this latitudinal cline modulate differently their venom production levels. Conclusions We demonstrate that abiotic stress results in venom regulation in Nematostella. Together with anecdotal observations from other cnidarian species, our results suggest this might be a universal phenomenon in Cnidaria. The decrease in venom production under stress conditions across species coupled with the evidence for its high metabolic cost in Nematostella suggests downregulation of venom production under certain conditions may be highly advantageous and adaptive. Furthermore, our results point towards local adaptation of this mechanism in Nematostella populations along a latitudinal cline, possibly resulting from distinct genetics and significant environmental differences between their habitats.