Does genome size increase with water depth in marine fishes?

A growing body of research suggests that genome size in animals can be
affected by ecological factors. Half a century ago, Ebeling et al. (1971;
EEA71) proposed that genome size increases with depth in some teleost fish
groups and discussed a number of biological mechanisms that may explain
this pattern (e.g., passive accumulation, adaptive acclimation). Using
phylogenetic comparative approaches, we revisit this hypothesis based on
genome size and ecological data from up to 708 marine fish species in
combination with a set of large-scale phylogenies, including a newly
inferred tree. We also conduct modelling approaches of trait evolution and
implement a variety of regression analyses to assess the relationship
between genome size and depth. Our reanalysis of the EEA71 dataset shows a
weak association between these variables, but the overall pattern in their
data is driven by a single clade. While analyses based on the new dataset
resulted in positive correlations, providing some evidence that genome
size evolves adaptively as a function of depth, only a fraction of
individual subclade analyses yielded statistically significant results. By
contrast, negative correlations are rare and largely non-significant. All
in all, we find modest evidence for an increase in genome size along the
depth axis in marine fishes. We discuss some mechanistic explanations for
the observed trends.