UC Davis

Color is a visible fingerprint of deep ecological relationships. Color traits are shaped by intraspecific, interspecific, abiotic, and/or physiological drivers across ontogenetic and evolutionary timescales. My dissertation is concerned with how organisms integrate multiple, often conflicting selection pressures on color, given these many functions. I specifically study how selection on color traits varies across development. How do individuals avoid predation despite temporal shifts in morphology, environmental conditions, and/or behavior? Further, are there general patterns in how organisms balance these constraints over time? To answer these questions, I combine theoretical work with field experiments using artificial caterpillars. In the first chapter of my dissertation, I review common sources of conflicting selection pressures on color strategies, and present a mechanistic framework for how organisms integrate these functions. I determine that color patterns can be intermediate, simultaneous, and/or plastic with respect to multiple pressures. These multivariate strategies encompass a wide range of defensive color phenotypes (from crypsis to aposematism) and provide avenues for future theoretical, meta-analytical, and empirical research on animal color. In my second and third chapters, I experimentally test how specific factors shape color plasticity in swallowtail caterpillars. Using artificial swallowtail-like prey exposed to natural predators in two separate field experiments, I find that size constrains the effectiveness of both feces masquerade and eyespots; background color does not significantly influence the effectiveness of either color pattern; and environmental modification (e.g., constructing leaf shelters) not only protects prey in general, but actively enhances the “startle” effect of eyespots. Overall, in these species, ontogenetic shifts in larval color are shaped by size and behavior. The study of animal coloration has a long history. My conceptual and experimental work builds on this history by (1) framing color patterns as functional strategies that extend beyond single-function phenotypes, (2) experimentally testing assumed constraints and functions of color, and (3) providing empirical evidence for the role of behavior in defensive color traits.