Evol Ecol Res 20: 193-211 (2019)     Full PDF if your library subscribes.

The utility of stoichiometric and metabolic theory for understanding the foraging habitat and excretion of Threespine stickleback (Gasterosteus aculeatus)

Daniel J. Durston and Rana W. El-Sabaawi

Department of Biology, University of Victoria, Victoria, British Columbia, Canada

Correspondence: D.J. Durston, Department of Biology, University of Victoria, PO Box 1700 Station CSC, Victoria, BC V8W 2Y2, Canada. email: durston.dan@gmail.com

ABSTRACT

Background: Recent extensions to ecological stoichiometry theory propose that the evolution of an organism’s elemental content plays an important role in shaping the structure and function of ecosystems. Other work has shown that the elemental content of sticklebacks is meaningfully altered by genetic differences in armour.

Questions: Does genetic-based intraspecific variation in Threespine stickleback elemental content explain intraspecific variation in foraging habitat and elemental excretion rates? Are there theoretical effects of intraspecific variation in elemental demand on the community and ecosystem ecology of stickleback populations?

Hypotheses: High phosphorus (low N : P) sticklebacks containing phosphorus-rich traits and genetics will preferentially target phosphorus-rich prey types and exhibit lower rates of phosphorus excretion.

Methods: We studied ten wild populations of Threespine stickleback, including two focal populations naturally diverse in individual stoichiometry, related traits, and genetics. Individuals from these populations were captured, excreted, and sacrificed to assess morphology, stoichiometry, genetics, and foraging habitat (using δ¹³C stable isotopes).

Results: The N : P ratio of stickleback explained much of the intraspecific variation in δ¹³C isotopes within populations; high N : P individuals and Eda genotypes were associated with high N : P diet types. But elemental excretion rates and ratios were not correlated with stickleback N : P; instead, they varied in relation to metabolic factors and to reproductive investment. In particular, females investing in low phosphorus reproductive tissues showed high rates of phosphorus excretion.

Conclusions: Genetic-based differences in elemental demand can influence how individuals forage, and highlight the importance of considering sex and reproductive investment when evaluating the ecosystem effects of phenotypic variation. Overall, our results provide partial support for ecological stoichiometry theory as a useful framework for understanding the interplay between intraspecific variation and ecology, and we suggest that evolution can influence ecology through the evolution of elementally expensive traits.

Keywords: eco-evolutionary interactions, ecological stoichiometry, Ectodysplasin, elemental phenotype, intraspecific variation, metabolic theory of ecology, phosphorus, stable isotopes.

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