Abstract:
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.
