x, 36 p. : ill. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / Natural biological variation exists at different geographic scales. We compared phenotype distribution across latitude, region and habitat type in threespine stickleback (Gasterosteus aculeatus) to determine local adaptation. To quantify variation in photoperiodic response, the day length cue was used to time sexual maturation and morphological characters across these various scales. Using lab-reared lines, we developed an index of sexual maturation and experimentally determined critical photoperiod for Alaskan and Oregon populations. Results showed that photoperiodic response existed in Alaskan but not Oregon populations. We also collected morphological data and made comparisons between wild Alaskan and Oregon populations and found similarities within habitat type across latitude but differences across region and habitat type. These data support the hypothesis that local adaptation results in variation across geography and habitat and, in stickleback, parallel evolution of morphological phenotypes within similar but geographically distant habitats. / Committee in Charge: William E. Bradshaw, Chair; William A. Cresko; Christina M. Holzapfel