No abstract

Newly formed hybrid populations provide an opportunity to examine the initial consequences of secondary contact between species and identify genetic patterns that may be important early in the evolution of hybrid inviability. Widespread introductions of rainbow trout (Oncorhynchus mykiss) into watersheds with native cutthroat trout (Oncorhynchus clarkii) have resulted in hybridization. These introductions have contributed to the decline of native cutthroat trout populations. Here, we examine the pattern of hybridization between introduced rainbow trout and 2 populations of cutthroat trout native to Colorado. For this study, we utilized 7 diagnostic, codominant nuclear markers and a diagnostic mitochondrial marker to investigate hybridization in a population of greenback cutthroat trout (Oncorhynchus clarkii stomias) and a population of Colorado River cutthroat trout (Oncorhynchus clarkii pleuriticus). We infer that cutthroat-rainbow trout hybrid swarms have formed in both populations. Although a mixture of hybrid genotypes was present, not all genotype combinations were detected at expected frequencies. We found evidence that mitochondrial DNA introgression in hybrids is asymmetric and more likely from rainbow trout than from cutthroat trout. A difference in spawning time of the 2 species or differences in the fitness between the reciprocal crosses may explain the asymmetry. Additionally, the presence of intraspecific cytonuclear associations found in both populations is concordant with current hypotheses regarding coevolution of mitochondrial and nuclear genomes.

Coastal seascapes can support high animal diversity and secondary productivity that attracts conservation interest and provides ecosystem services. Though the importance of spatial structure in marine habitats is well known, determining the dominant spatial scale for biodiversity patterns is an often‐overlooked dimension of the ecological and conservation value of seagrass meadows. We estimated biodiversity patterns at fine (0.28 m2), meadow and seascape scales to explore whether seagrass‐associated biodiversity patterns are consistent with spatial processes such as abiotic habitat filtering or metacommunity dynamics in a northeast Pacific seascape. In Barkley Sound, British Columbia, we quantified epifaunal biodiversity on eelgrass (Zostera marina) to test three hypotheses: Taxonomic diversity and composition (1) vary randomly within meadows but (2) vary systematically among meadows reflecting meadow location or environmental conditions, and (3) spatial patterns are stable over time. We sampled epifaunal invertebrates in a systematic spatial grid within nine eelgrass meadows. We found that epifaunal community composition varied as much over a few meters within the same meadow as among meadows separated by kilometers and of different sizes and wave exposures. In each meadow, we observed less than three‐quarters of the species in the regional species pool, and we observed non‐random spatial aggregation within many species. Even with spatial turnover, assemblages were more similar than predicted by null models based on random species distributions, suggesting that some species tend to co‐occur in high abundance. These spatial biodiversity patterns were not clearly explained by meadow location, area, or abiotic conditions, except that there were differences in clusters of meadows distinguished by their salinity (more marine vs. more fresh). Our results indicate that effective conservation and understanding of how seagrass can support high biodiversity and ecosystem function may require consideration of spatial connections among meadows, and not just the condition of the meadows themselves.

The boundaries between oceanographic domains often function as dispersal barriers for many temperate marine species with a dispersive pelagic larval phase. Yelloweye rockfish (Sebastes ruberrimus, YR) are widely distributed across the northeastern Pacific Ocean, inhabiting coastal rocky reefs from the Aleutian Islands in Alaska through southern California. This species exhibits an extended pelagic larval duration and has the capacity for long distance larval transport. We assayed 2,862 YR individuals from 13 general areas in the northeast Pacific Ocean for allelic variation at nine microsatellite loci. Bayesian model-based clustering analyses grouped individuals from the Strait of Georgia (SG) into a distinct genetic cluster, while individuals from outer coastal water locations (OCLs) were partitioned equally across two genetic clusters, including the cluster associated with the SG fish. Pairwise FST values were consistently an order of magnitude higher for comparisons between the SG and OCLs than they were for all OCL-OCL comparisons (∼0.016 vs. ∼0.001). This same pattern was observed across two time points when individuals were binned into an “old” and “young” group according to birth year (old: ∼0.020 vs. 0.0003; young: ∼0.020 vs. ∼0.004). Additionally, mean allelic richness was markedly lower within the SG compared to the OCLs (8.00 vs. 10.54–11.77). These results indicate that the Strait of Georgia “deep-basin” estuary oceanographic domain acts as a dispersal barrier from the outer coastal waters via the Juan de Fuca Strait. Alternatively, selection against maladapted dispersers across this oceanographic transition may underlie the observed genetic differentiation between the Georgia basin and the outer coastal waters, and further work is needed to confirm the SG-OCL divide acts as a barrier to larval dispersal.