Fish migrations are energetically costly, especially when moving between freshwater and saltwater, but are a viable strategy for Pacific salmon and trout (Oncorhynchus spp.) due to the advantageous resources available at various life stages. Anadromous steelhead (O. mykiss) migrate vast distances and exhibit variation for adult migration phenotypes that have a genetic basis at candidate genes known as greb1L and rock1. We examined the distribution of genetic variation at 13 candidate markers spanning greb1L, intergenic, and rock1 regions versus 226 neutral markers for 113 populations (n = 9,471) of steelhead from inland and coastal lineages in the Columbia River. Patterns of population structure with neutral markers reflected genetic similarity by geographic region as demonstrated in previous studies, but candidate markers clustered populations by genetic variation associated with adult migration timing. Mature alleles for late migration had the highest frequency overall in steelhead populations throughout the Columbia River, with only 9 of 113 populations that had a higher frequency of premature alleles for early migration. While a single haplotype block was evident for the coastal lineage, we identified multiple haplotype blocks for the inland lineage. The inland lineage had one haplotype block that corresponded to candidate markers within the greb1L gene and immediately upstream in the intergenic region, and the second block only contained candidate markers from the intergenic region. Haplotype frequencies had similar patterns of geographic distribution as single markers, but there were distinct differences in frequency between the two haplotype blocks for the inland lineage. This may represent multiple recombination events that differed between lineages where phenotypic differences exist between freshwater entry versus arrival timing as indicated by Micheletti et al. (2018a). Redundancy analyses were used to model environmental effects on allelic frequencies of candidate markers, and significant variables were migration distance, temperature, isothermality, and annual precipitation. This study improves our understanding of the spatial distribution of genetic variation underlying adult migration timing in steelhead as well as associated environmental factors and has direct conservation and management implications.

Within the Southern Ocean, the Antarctic Circumpolar Current is hypothesized to facilitate a circumpolar distribution for many taxa, even though some, such as pycnogonids, are assumed to have limited ability to disperse, based on brooding life histories and adult ambulatory capabilities. With a number of contradictions to circumpolarity reported in the literature for other pycnogonids, alternative hypotheses have been explored, particularly for Nymphon australe, the most common species of Pycnogonida (sea spider) in the Southern Ocean. Glacial events have been hypothesized to impact the capacity of organisms to colonize suitable areas without ice coverage as refuge and without the eurybathic capacity to colonize deeper areas. In this study, we examine populations of one presumed circumpolar species, the pycnogonid N. australe, from throughout the Western Antarctic, using a 2b-RAD approach to detect genetic variation with single-nucleotide polymorphisms. Using this approach, we found that N. australe included two distinct groups from within >5000-km sampling region. By using a discriminant analysis of principle components, sparse nonnegative matrix factorization, and admixture coefficient analysis, two distinctive populations were revealed in the Western Antarctic: one covered distances greater than 5000 km (Weddell, Western Antarctic Peninsula, and Ross Sea), and the other shared limited connectivity entrained within the Amundsen Sea. Under further scrutiny of the 3086 single-nucleotide polymorphisms in the data set, only 78 loci had alignment stacks between the two populations. We propose that the populations analyzed are divergent enough to constitute two different species from within this common Antarctic genus known for its phenotypic plasticity.

This a preprint and has not been peer reviewed. Data may be preliminary.

This a preprint and has not been peer reviewed. Data may be preliminary.

No abstract