Testing the Shared-Pathway Hypothesis through experimentation on the mating behavior, carotenoid biosynthesis, and mitochondrial function of Tigriopus californicus

Abstract

For decades, scientists have noted connections between individual condition and carotenoid-based coloration in terrestrial and aquatic animals. Organisms that produce more vibrant carotenoid-based coloration tend to have better physiological performance and behavioral displays compared to less colorful members of the same species. Traditional explanations for this association between ornamental coloration and performance invoked the need for color displays to be costly, but evidence for such hypothesized costs is equivocal. An alternative explanation for the condition-dependence of carotenoid-based coloration, the Shared-Pathway Hypothesis, was developed in response. This hypothesis proposes that red ketocarotenoid-based coloration is tied to core cellular processes involving a shared pathway with mitochondrial energy metabolism, making the concentration of carotenoids an index of mitochondrial function. Since the presentation of this hypothesis, empirical tests of the mechanisms proposed therein have been conducted in many species. In this dissertation, I review the Shared-Pathway Hypothesis and the growing number of studies that have investigated a connection between carotenoid-based coloration and mitochondrial function. I then present experimental tests of the Shared-Pathway Hypothesis using the model organism, Tigriopus californicus. I also discuss future strategies for assessing the Shared-Pathway Hypothesis to more effectively disentangle evidence that may simultaneously support evidence of carotenoid-resource tradeoffs.