Crypsis can be an important mechanism of predator avoidance for organisms. However, many species exhibit sexual dichromatism, in which the males possess a suite of colorations in order to attract female attention. The resulting differences in crypsis between the males and females can provide insight into the relative strengths of the sexually and naturally selective forces shaping the coloration of the organism, as well as clues regarding potential sensory biases of the selecting sex. In this study, I examine variation in the coloration of four Pacific Northwest populations of the sexually dimorphic and dichromatic polygynous species of jumping spider Habronattus oregonensis and compare the coloration of different body regions of the spiders to their habitats. I also investigate differences in relative size of a male sexual ornament, the enlarged first leg tibia. Field work for this study was conducted in June and July of 2009. The three main foci of this study are 1) to compare the degree of color matching of females and their habitat to the degree of color matching of males and their habitat, evaluating whether sexual selection on males has reduced their degree of crypsis relative to that of females, 2) if there is indeed a difference in crypsis between the sexes, to gauge whether there are similar divergences from crypsis among the populations - both in the quantitative amount of divergences as well as the colorimetric direction of such divergences, and 3) whether there is any variation in sexual ornament size among populations. Male first leg tibia size is a sexual character that is presumably not influenced by habitat coloration; differences in male tibia allometry among populations would provide supporting evidence for the hypothesis that sexual selection is indeed maintaining phenotypic differences among the populations, regardless of habitat location and color. I found a high degree of conformity of hue and chroma between male and female spiders and their habitats, with three notable exceptions. The most extreme difference in coloration between spider and habitat was that of the Gorge and Siskiyou population male anteriors. The anteriors had proportionally less green and more ultraviolet reflectance than their habitat. Second, the Mt. Hood and Tillamook population male abdomens diverged from their habitat in a similar, although less pronounced manner to that of the Gorge and Siskiyou population male anteriors: they had proportionally less green and more UV reflectance. Third, female abdomens of all populations were highly variable in chroma, despite having hues that generally matched their habitat. Tibia area relative to body size of Gorge and Siskiyou population males was significantly smaller than that of Mt. Hood and Tillamook population males. The lower level of background hue matching among males compared to females implies that sexual selection has directly conflicted with natural selection, resulting in impaired crypsis. While the reduced crypsis of the Gorge and Siskiyou population males is centered on their anterior (the primary body region presented to the females during courtship), the deviations from crypsis in the Mt. Hood and Tillamook population males are highest on their abdomen, although the degree of contrast is lower than that of the Gorge and Siskiyou population anteriors. These differences in coloration between the Mt. Hood and Tillamook population male abdomens and their habitats are in the same colorimetric direction as those of the Gorge and Siskiyou population anteriors and their habitat; this may indicate a sensory bias of the females, conserved in all four populations, selecting for male reflectance with a higher UV to green ratio. The fact that Mt. Hood and Tillamook population male abdomens have a more modest reduction in background matching compared to Gorge and Siskiyou population male anteriors may be due to the search methods of flying predators (e.g., spider wasps); the dorsum would presumably be more conspicuous to predators than the anterior, and would thus be subject to more intense selection for crypsis despite sexual selection to the contrary. The variability of abdomen coloration of females of both morphs may indicate that selection for crypsis is less strong among females than among males. One possible reason for this would be if females spent less time in the exposed courtship habitat than males, a conclusion implied by a highly male-skewed sex ratio encountered during field collections. Like the differences in coloration between different males of different populations, the significant differences in male tibia size also imply variability in the intensity of sexual selection. Relative importance of male coloration and tibia size may be weighted differently among populations, operating under similar constraints on reductions in survival accrued by developing these characters. The high degree of variation found among the populations implies that there is a degree of reproductive isolation among the chromatically and morphologically dissimilar populations. However, the similarity of the environments in which the populations existed, the close geographic proximity of some of the dissimilar populations, and the lack of any substantial geographic boundaries between the populations imply that this isolation is not maintained through extrinsic factors. Rather, it would seem that the interpopulational diversity is maintained by sexual selection. However, evidence from morphology and coloration suggest that the generation of this diversity is not evolving exclusively under sexual selection pressure, but rather is constrained to a degree by natural selection.

abstract: Differences between males and females can evolve through a variety of mechanisms, including sexual and ecological selection. Because coloration is evolutionarily labile, sexually dichromatic species are good models for understanding the evolution of sex differences. While many jumping spiders exhibit diverse and brilliant coloration, they have been notably absent from such studies. In the genus Habronattus, females are drab and cryptic while males are brilliantly colored, displaying some of these colors to females during elaborate courtship dances. Here I test multiple hypotheses for the control and function of male color. In the field, I found that Habronattus males indiscriminately court any female they encounter (including other species), so I first examined the role that colors play in species recognition. I manipulated male colors in H. pyrrithrix and found that while they are not required for species recognition, the presence of red facial coloration improves courtship success, but only if males are courting in the sun. Because light environment affects transmission of color signals, the multi-colored displays of males may facilitate communication in variable and unpredictable environments. Because these colors can be costly to produce and maintain, they also have the potential to signal reliable information about male quality to potential female mates. I found that both red facial and green leg coloration is condition dependent in H. pyrrithrix and thus has the potential to signal quality. Yet, surprisingly, this variation in male color does not appear to be important to females. Males of many Habronattus species also exhibit conspicuous markings on the dorsal surface of their abdomens that are not present in females and are oriented away from females during courtship. In the field, I found that these markings are paired with increased leg-waving behavior in a way that resembles the pattern and behavior of wasps; this may provide protection by exploiting the aversions of predators. My data also suggest that different activity levels between the sexes have placed different selection pressures on their dorsal color patterns. Overall, these findings challenge some of the traditional ways that we think about color signaling and provide novel insights into the evolution of animal coloration. / Dissertation/Thesis / Ph.D. Biology 2012