International Journal of Molecular Ecology and Conservation 2024, Vol.14, No.5, 208-217 http://ecoevopublisher.com/index.php/ijmec 214 Figure 1 Fine-scale adaptive population genetic structure (Adopted from Dorant et al., 2022) Image caption: (Upper panels) RGB composite habitat layer for the (a) northern and (b) southern genetic clusters. The red, green and blue colour channels represent the intensities of the mean annual sea surface temperature (SST), sea surface chlorophyll concentration (SSC) and sea surface salinity (SSS) at each pixel, respectively. Environmental layers were normalized between 0 and 1 before RGB projection, and normalized layers were “contrast stretched” to enhance visual clarity (min quantile = 0.05 and max quantile = 0.95). For instance, a pixel coloured by magenta means that the intensity of SST and SSS are elevated and equivalent between the two variables. On the opposite, the intensity of SSC is very low or even zero (R = 0.99; G ~ 0, B = 0.99). Sampling sites are represented by circles coloured according to an RGB habitat value averaged over a buffer of two map units (2*5 arcmin; ~18.4 km radius). Black arrows represent major current circulation within the two regions. EMCC and WMCC indicate the “Eastern Maine Coastal Current ” and the “Western Maine Coastal Current”, respectively. (Middle panels) PCA biplot based on allele frequencies of candidate loci for sampling sites in the (c) northern (940 SNPs) and (d) southern (952) study regions, where each circle represents a sampling site coloured according to its RGB projection (a, b). (Lower panels) Regional distribution of environmental conditions among sampling sites in the (e) northern and (f) southern study regions. Vertical bars represent the absolute value of each environmental variable for a given site (y-axis) averaged over years 2000–2014 (biooracle marine database version 2.1) and coloured according to its RGB habitat projection above. Sampling sites are sorted according to their position along the PCA axis (Adopted from Dorant et al., 2022) 6.2 Phylogenetic approaches to understanding adaptive evolution Phylogenetic approaches provide a framework for understanding the evolutionary history and adaptive potential of crustaceans. Comparative genomics of krill species across various oceans has revealed phylogenetic interrelationships and genomic evidence of adaptive evolution. For example, Antarctic krill exhibit lower genetic variation and evolutionary rates compared to other species, suggesting a limited adaptive potential to rapid climate change (Choquet et al., 2023). This phylogenetic insight is crucial for predicting how different species might respond to environmental pressures.
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