Degree

Doctor of Philosophy (PhD)

Department

Biological Sciences

Document Type

Dissertation

Abstract

Herein we explore the various forces that drive phenotypic variation in arthropods focusing on spatial and temporal differences as well as sexual dimorphism. We use both marine, Tigriopus californicus, and terrestrial, Melitaeini, organisms to investigate these forces.

Tigriopus californicus and Heat Hardening: The study explores how Tigriopus californicus, a copepod, adapts to thermal variation along the North American Pacific Coast. Researchers investigated intraspecific variation in heat hardening, measuring differences in upper lethal limits (ULLs) and potential fecundity costs across five populations. We found a cost of heat hardening: the size of the first brood produced after heat shock is proportional to the increase in ULLs. Northern populations showed significant ULL differences between control and heat-hardened individuals, whereas southern populations did not. Additionally, heat-hardened individuals reproduced earlier and had shorter intervals between broods, indicating a trade-off between reproduction timing and brood size. These results support the trade-off and environmental variability hypotheses for thermal plasticity, suggesting that populations in variable environments exhibit greater plasticity.

Chlosyne lacinia’s Natural History and Pupal Color Polymorphism: We reviewed the natural history of Chlosyne lacinia, a butterfly with high phenotypic variation, and the distribution of the morphs. C. lacinia shows significant color variation in larvae, pupae, and adults, with six distinct adult morphs across its range from Argentina to the midwestern and southwestern United States. Laboratory experiments designed to identify the proximal cue for pupal color variation included substrate color, shading, wounding, and temperature and density. We found that pupae on black backgrounds had higher melanization than pupae on white backgrounds, suggesting that crypsis may drive increased melanization.

Sexual Dimorphism in Checkerspot Butterflies: The study examined factors contributing to sexual dimorphism in checkerspot butterflies (Melitaeini: Nymphalidae), considering morphometric, behavioral, and ecological data from 33 species. We found perching species have greater thorax width dimorphism than patrolling species. Forest-dwelling species show pronounced hindwing angle dimorphism. Associations between host plant families and forewing curve dimorphism were also found. The study highlights the complex interplay of sexual selection and ecological factors in shaping wing morphology, suggesting adaptive radiation in hindwing angle dimorphism.

Overall, these investigations enhance understanding of thermal adaptation, phenotypic variation, and sexual dimorphism, emphasizing the need for further research on ecological and evolutionary drivers.

Date

7-18-2024

Committee Chair

Morgan W. Kelly

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