Date of Award
Open Access Dissertation
Daniel I. Speiser
Variations in environmental factors such as temperature, precipitation, and day length during larval development are known to affect morphological traits in butterflies related to their visual ecology, including eye size and wing color. These vision-related traits are important for the ability of diurnal butterfly species to detect mates, especially at long distances. Thus, changes in environmental conditions may result in phenotypic modifications to butterflies which may alter their visual ecology and subsequently, their reproductive fitness. To study the interaction of phenotypic plasticity and visual ecology in the Mormon Fritillary, Speyeria mormonia, I set up a natural-laboratory experiment at the Rocky Mountain Biological Laboratory (RMBL) and collected butterflies from 5 different sites across an elevational gradient, spanning approximately 610 meters during two field seasons. I considered elevation to be a proxy for several shifting microclimate features, including temperature and precipitation. My first goal was to determine whether there was a relationship between elevation and natural variations in the dorsal wing chromaticity, eye surface area, or wing length (a proxy for body size) of male and female adult-stage S. mormonia from the study populations. In the case that I did find natural variations in wing chromaticity, my second goal was to use computational models to evaluate whether S. mormonia can discriminate between the different “oranges” (quantified using chromaticity values) displayed on the wings of their conspecifics. Across elevations, I found that females tended to be larger than males and that males tended to have larger eyes than females. I also found that butterflies from lower vi elevations had longer wings than individuals from higher elevations. Males had greater and more variable wing wear scores than females, and more perceivable variations in dorsal forewing and dorsal hindwing chromaticity, the values of which were linked to wing wear. The results also suggest that S. mormonia may have sex-dependent dynamics in the investment of nutrient resources. Females had longer wing lengths and more consistent wing wear scores than males across elevations. Longer wings are useful for female butterflies to maintain more efficient flight maneuverability while carrying heavy egg-loads during oviposition. Males, however, had larger eyes and more variable wing wear scores than females. Males may have larger eyes than females because vision is more important for mate location by males than it is for oviposition site location or materecognition by females. This may mean that while females are investing in producing larger bodies to optimize fecundity, males are investing nutritional resources into optimizing mate-seeking ability (i.e. patrolling) to maximize the number of copulations they can engage in. Finally, intersexual trends in wing wear scores suggest that there are different degrees of protandry occurring across the elevational gradient, likely because of sex-dependent reactions to shifts in local environmental factors.
Gonzalez, N.(2018). The Visual Ecology of Speyeria mormonia. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/5099