The delineation of conservation units (CUs) is a challenging issue that has profound implications for minimizing the loss of biodiversity and ecosystem services. CU delineation typically seeks to prioritize evolutionary significance and genetic methods play a pivotal role in the delineation process by quantifying overall differentiation between populations. While CUs that primarily reflect overall genetic differentiation do protect adaptive differences between distant populations, they do not necessarily protect adaptive variation within highly connected populations. Advances in genomic methodology facilitate the characterization of adaptive genetic variation, but the potential utility of this information for CU delineation is unclear. Here we use genomic methods to investigate the evolutionary basis of premature migration in Pacific salmon, a complex behavioral and physiological adaptation that exists within highly-connected populations and has experienced severe declines. Strikingly, we find that premature migration is associated with the same single locus across multiple populations in each of two different species. Patterns of variation at this locus suggest that the premature migration alleles arose from a single evolutionary event within each species and were subsequently spread to distant populations through straying and positive selection. Our results reveal that complex adaptive variation can depend on rare mutational events at a single locus, demonstrate
In this paper, we test the hypothesis that male sand crickets, Gryllus firmus, experience a trade‐off between flight capability and reproductive potential expressed as reduced testis weight in flight‐capable morphs. We used a half‐sib design with 130 sires, three dams per sire and an average of 5.66 males per dam family, for a total of 2206 F1 offspring. Traits measured were head width, somatic dry weight, testis weight, wing morph (micropterous/macropterous), weight of the dorso‐longitudinal flight muscles (DLM) and the functional status of these muscles. Heritabilities of all traits were significant and ranged from 0.14 to 0.43. All traits were positively correlated with body size, but removal of this covariance revealed a highly significant trade‐off, both phenotypically and genetically, between testes size and flight capability as measured by wing morph, DLM size or DLM status. The possible implications of this for morph‐specific reproductive tactics are discussed.
The Devils Hole pupfish (Cyprinodon diabolis; DHP) is an icon of conservation biology. Isolated in a 50 m(2) pool (Devils Hole), DHP is one of the rarest vertebrate species known and an evolutionary anomaly, having survived in complete isolation for thousands of years. However, recent findings suggest DHP might be younger than commonly thought, potentially introduced to Devils Hole by humans in the past thousand years. As a result, the significance of DHP from an evolutionary and conservation perspective has been questioned. Here we present a high-resolution genomic analysis of DHP and two closely related species, with the goal of thoroughly examining the temporal divergence of DHP. To this end, we inferred the evolutionary history of DHP from multiple random genomic subsets and evaluated four historical scenarios using the multispecies coalescent. Our results provide substantial information regarding the evolutionary history of DHP. Genomic patterns of secondary contact present strong evidence that DHP were isolated in Devils Hole prior to 20-10 ka and the model best supported by geological history and known mutation rates predicts DHP diverged around 60 ka, approximately the same time Devils Hole opened to the surface. We make the novel prediction that DHP colonized and have survived in Devils Hole since the cavern opened, and the two events (colonization and collapse of the cavern's roof) were caused by a common geologic event. Our results emphasize the power of evolutionary theory as a predictive framework and reaffirm DHP as an important evolutionary novelty, worthy of continued conservation and exploration.
Two threatened osmerid species native to the San Francisco Estuary (SFE)-Delta Smelt (Hypomesus transpacificus) and Longfin Smelt (Spirinchus thaleichthys)-are subject to broad human influence, including significant habitat alteration and the presence of the introduced osmerid, Wakasagi (Hypomesus nipponensis). The identification of these closely related species and their hybrids is difficult in field collected specimens which are subject to damage through handling and may be difficult to identify morphologically, especially when young. In addition, it is known that these three species hybridize, but the extent and effect of hybridization is difficult to quantify and monitor. We developed assays for 24 species-specific single nucleotide polymorphisms (SNPs) that identify whether a sample is a pure species (Delta Smelt, Longfin Smelt, or Wakasagi), a first generation (F 1 ) hybrid, or a backcross. We used this SNP panel to genetically identify wild osmerids collected in Yolo Bypass from 2010 to 2016 and detected nine Delta Smelt × Wakasagi F 1 hybrids and two Wakasagi × (Delta Smelt × Wakasagi) backcross hybrids; all assayed hybrids had Wakasagi as the maternal parent. The backcrossing into Wakasagi suggests that hybridization may only occur in one direction and thus preclude introgression to Delta Smelt. We also found substantial morphological field misidentifications (32.7%) in the Yolo Bypass samples resulting in more Wakasagi and fewer Delta Smelt than previously recorded when based on morphology. The SNP panel described in this study constitutes a valuable resource for monitoring hybridization in the SFE and assigning species identifications with accuracy and efficiency.
Two primary patterns of body size variation have been recorded in ectotherms in relation to latitudinal/altitudinal shifts. In some, body size increases with increasing latitude/altitude whereas, in others, body size decreases with increasing latitude/altitude. This clinal variation is generally assumed to be caused by local adaptation to environmental conditions however the selective variable(s) (temperature, humidity, diet quality, etc.) is still heavily debated. Here we investigate geographic variation in body size of dark and pale color morphs of males of the bush-cricket Isophya rizeensis collected from 15 locations along an elevation gradient ranging from 350 to 2 500 m. Using an information theoretical approach we evaluate the relative support of four different hypotheses (the temperature size rule, the moisture gradient hypothesis, the seasonal constraint hypothesis, and the primary productivity hypothesis) explaining body size variation along the altitudinal gradient. Body size variation in pale color morphs showed a curvilinear relationship with altitude while dark color morphs showed no variation in body size. Body size variation in pale color morphs was highly correlated with precipitation and temperature seasonality values thus giving strong support for the moisture gradient and seasonal constraint hypothesis. Our results reinforce the importance of gradients in humidity and seasonality over temperature in the creation of altitudinal body size clines and the role of selection for resistance to stress factors in the establishment of these clines. Whether a body size cline is observed or not might also depend on the phenotypic properties of the individuals, like coloration.
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