Using replicated evolution in extremophile fish to understand diversification in elemental composition and nutrient excretion

Abstract

Summary Ecological sources of selection are key drivers of evolutionary change in populations. Information on the ecological relevance of such evolutionary shifts is comparatively sparse and has received renewed interest. The framework of ecological stoichiometry is useful to investigate the reciprocal effects between ecology and evolution, because data on somatic stoichiometry of ancestral and descendent populations can be used to predict ecological functions, such as nutrient recycling, using mass balance‐based models. Here, we investigated whether divergent populations of livebearing fishes (genus Poecilia) have diverged in elemental composition. We tested whether adaptation to local environmental conditions is manifested in changes of somatic stoichiometry by measuring carbon (C), nitrogen (N), phosphorus (P) and sulphur (S) contents of wild‐caught individuals inhabiting sulphidic (extreme) and non‐sulphidic (benign) habitats. We also attempted to isolate the sources (i.e. genetic, environmental and their interaction) of intraspecific variation in stoichiometry. Finally, we tested whether shifts in somatic stoichiometry impinge on the rates at which key nutrients (N and P) are excreted. We found significant differentiation in somatic stoichiometry between fish from the two different habitat types in two of three river drainages, with fish from sulphidic habitats having lower C but higher P and S contents. Even though there was evidence for temporal variation and plasticity in elemental composition, differences between sulphidic and non‐sulphidic populations in P and S contents were maintained in laboratory populations over multiple generations. Finally, some sulphidic and non‐sulphidic population pairs differed in the rates of N and P excretions, although excretion rates were not related to somatic stoichiometry. Together, these results show that the elemental composition of organisms appears to have the characteristics typically observed in the evolution of biochemical, physiological and morphological traits. Studying taxa that have undergone replicated evolution illuminate some of the evolutionary mechanisms that drive variation in somatic elemental composition. Applying stoichiometric principles to such variation, as we have performed here, is a useful, yet underutilised approach to understand the ecological relevance of evolutionary change.

Ecological Stoichiometry beyond Redfield: An Ionomic Perspective on Elemental Homeostasis

“…Genotype-specific effects common in ionomic studies discussed above are similar to discoveries about intraspecific variation in biomass C:N:P stoichiometries (e.g., Bertram et al, 2008; Goos et al, 2014; Downs et al, 2016) which are shaped by selection (e.g., El-Sabaawi et al, 2012; Tobler et al, 2016), and generate discernable patterns at higher levels of organization (e.g., Elser et al, 2000). While genetic recombination can produce endless varieties of biota, organismal evolution is bounded by principles of physics and chemistry (Williams and Frausto da Silva, 2006).…”

The effect of top‐predator presence and phenotype on aquatic microbial communities

“…It is possible that phenotypic effects on bacterial communities could be affected by diet‐induced differences in fish stoichiometry (Vrede et al., ), thereby affecting nutrient dynamics. Alternatively, variation due to an animal's elemental phenotype (Jeyasingh, Cothran, & Tobler, ) may differ between locally adapted populations (Sullam et al., ; Tobler, Alba, Arias‐Rodríguez, & Jeyasingh, ) and could influence nutrient recycling. Therefore, more work is warranted on the stoichiometry of lake and stream stickleback.…”

Ionome and elemental transport kinetics shaped by parallel evolution in threespine stickleback

“…; Tobler et al . ). Using only a few elements to describe an organism results in a limited view of phenotypic variation, potentially ignoring important interactions among elements that underlie traits (Salt et al .…”