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Patterns of edaphic and phenotypic variation in the Lasthenia californica species complex (Asteraceae) Choe, Gina

Abstract

Members of the Lasthenia californica species complex show extensive ecological and phenotypic diversity. This thesis investigates patterns of edaphic, physiological, flavonoid, and morphological differentiation within the Lasthenia californica species complex in two distinct studies. In the first study, patterns of ecological and physiological variation along with flavonoid polymorphism and ITS1 species type distribution were characterized. The hypothesis of parallel evolution of edaphically differentiated flavonoid races across lineages of L. californica sensu lato was also examined in this study. We found evidence refuting the predictions of this hypothesis, particularly that flavonoid type and edaphic environments are correlated across the complex. However, when major axes of ecological and physiological variation were characterized within the complex, the greatest amount of edaphic/tissue variation occurred along lines of toxicity, reaffirming prior characterization. In the second study, the basis of the phenotypic differentiation observed between inland and coastal ecotypes of Lasthenia californica sensu stricto was investigated by growing populations of each ecotype in controlled conditions under varying levels of salinity (an important environmental factor differentiating ecotypic environments). Reaction norms of populations were compared under saline conditions to test for evidence of differential fitness between ecotypes (differential salt tolerance) and differences in intrinsic and induced levels of trait expression (e.g. sodium accumulation and succulence). The hypothesis of trade-offs between salt tolerance and growth potentials was also investigated. Under experimental conditions, coastal populations demonstrated uniformly greater salt tolerance than inland populations. We found that most traits showed both intrinsic differentiation and differential responses to salinity, where the extent and direction of trait responses were ecotype specific with little within ecotype differentiation. When comparing growth rate trends between salt tolerant and non-tolerant populations across salinity treatment levels, we found evidence of trade-offs between maximum intrinsic growth rates and investments in salt tolerance.

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