One substance to rule them all and in the darkness bind them:
whole-genome sequencing illuminates multifaceted targets of humic
adaptation in Eurasian perch
Abstract
Extreme environments are inhospitable to the majority of species, but
some organisms are able to survive in such hostile conditions due to
evolutionary adaptations. For example, modern bony fishes have colonized
various aquatic environments, including perpetually dark, hypoxic,
hypersaline and toxic habitats. Eurasian perch (Perca fluviatilis) is
among the few fish species of northern latitudes that is able to live in
extremely acidic humic lakes. Such lakes represent almost “nocturnal”
environments; they contain high levels of dissolved organic matter,
which in addition to creating a challenging visual environment, also
affects a large number of other habitat parameters and biotic
interactions. To reveal the genomic targets of humic-associated
selection, we performed whole-genome sequencing of perch originating
from 16 humic and 16 clear-water lakes in northern Europe. We identified
over 800,000 SNPs, of which >10,000 were identified as
potential candidates under selection (associated with
>3,000 genes) using multiple outlier approaches. Our
findings suggest that adaptation to the humic environment involves
hundreds of regions scattered across the genome. Putative signals of
adaptation were detected in genes and gene families with diverse
functions, including organism development and ion transportation. The
observed excess of variants under selection in regulatory regions
highlights the importance of adaptive evolution via regulatory elements,
rather than via protein sequence modification. Our study demonstrates
the power of whole-genome analysis to illuminate multifaceted nature of
humic adaptation and highlights the next challenge moving from
high-throughput outlier identification towards functional validation of
causal mutations underlying phenotypic traits of ecological and
evolutionary importance.