Morphometric trait measurements of Arctic char in foothill lakes of arctic Alaska

Polymorphism facilitates coexistence of divergent morphs (e.g.,
phenotypes) of the same species by minimizing intraspecific competition,
especially when resources are limiting. Arctic char (Salvelinus sp.) are a
Holarctic fish often forming morphologically, and sometimes genetically,
divergent morphs. In this study, we assessed the morphological and genetic
diversity and divergence of 263 individuals from seven populations of
arctic char with varying length-frequency distributions across two
distinct groups of lakes in northern Alaska. Despite close geographic
proximity, each lake group occurs on landscapes with different glacial
ages and surface water connectivity, and thus were likely colonized by
fishes at different times. Across lakes, a continuum of physical (e.g.,
lake area, maximum depth) and biological characteristics (e.g., primary
productivity, fish density) exists, likely contributing to characteristics
of present-day char populations. Although some lakes exhibit bimodal size
distributions, using model-based clustering of morphometric traits
corrected for allometry, we did not detect morphological differences
within and across char populations. Genomic analyses using 15,934 SNPs
obtained from genotyping-by-sequencing demonstrated differences among lake
groups related to historical biogeography, but within lake groups and
within individual lakes, genetic differentiation was not related to total
body length. We used PERMANOVA to identify environmental and biological
factors related to observed char size structure. Significant predictors
included water transparency (i.e., a primary productivity proxy), char
density (fish·ha-1), and lake group. Larger char occurred in lakes with
greater primary production and lower char densities, suggesting less
intraspecific competition and resource limitation. Thus, char populations
in more productive and connected lakes may prove more stable to
environmental changes, relative to food-limited and closed lakes, if lake
productivity increases concomitantly. Our findings provide some of the
first descriptions of genomic characteristics of char populations in
arctic Alaska, and offer important consideration for the persistence of
these populations for subsistence and conservation.