| Summary |
Studies of animal color patterns have provided important insights into the nature of evolution and adaptation. Coloration may be the target of multiple evolutionary processes, including natural selection, intersexual selection, and intrasexual selection, with adaptations to such pressures leading to both convergent and divergent evolution. However, the exact functions of such color patterns, as well as the molecular and cellular mechanisms that produce them, often remain elusive. I take functional and mechanistic approaches to examine multiple color traits within threespine stickleback (Gasterosteus aculeatus)- including pelvic spine and throat coloration- to understand how such traits may be produced and understand what role they play within behavioral and signaling ecology. I also take a synthetic approach to address the evolution of coloration broadly in stickleback, reviewing the genetic basis of adaptation and the role that distinct evolutionary influences play in the resultant color patterns. My results indicate that a color patch located along the pelvic spines is expressed mainly through pelvic spine erections and associated behaviors such as 'flees' and 'leads to nest', which are differentially utilized across the reproductive cycle and behavioral contexts. Further, some results raise the possibility of pelvic spine color functioning as a deimatic anti-predator trait, pointing to naturally selected functions. Next, my results point to carotenoids within the erythrophore layer of the dermal chromatophore as the primary pigment component of orange-red throat coloration in both male and female stickleback, with a limited role of melanin in darkening the tissue where orange-red color is not present. Unexpectedly, this work did not provide any evidence of iridophores, but found collagen fibrils to be an integral component of throat tissue surrounding the chromatophore components. Lastly, my review of the literature on stickleback color evolution reveals that orange-red coloration involves numerous candidate genes across many genomic regions, and that general as well as sex specific genetic mechanisms are involved. I found important ecological factors to influence coloration, including the aquatic photic environment. My review indicates substantial evidence that male nuptial color functions as an honest indicator, and a badge of dominance and aggressiveness within intrasexual competition. Taken together, I find that while much is known about the evolution and function of coloration in the threespine stickleback, more comprehensive analyses of complete color patterns are needed, and important questions remain to be addressed about orange-red color patches along the pelvic spine and female throats. |
