Evolutionary studies in Batrachoseps and other plethodontid salamanders: Correlated character evolution, molecular phylogenetics, and reaction norm evolution

I tested several hypotheses of correlated character evolution in the salamander family Plethodontidae. Using a phylogenetically-based comparative method, I confirmed that genome size is positively correlated with embryonic developmental time, an important life history trait. However, no relationship was found between egg size and developmental time.;I estimated phylogenetic relationships within Batrachoseps, a group of eight species distributed along the west coast of North America using DNA sequence data from a mitochondrial gene, cytochrome b. Taxonomy of the group has been difficult because of the high degree of morphological conservatism. Two of the three currently recognized widespread species are shown to contain deeply differentiated, distinct historical units. Relationships among these units are generally congruent with previous hypotheses of relationships inferred from allozyme data. Several cases of incongruence between allozyme and mtDNA data may reflect isolation followed by secondary contact. Taxonomic changes are recommended, resulting in the recognition of a minimum of 20 species.;Reaction norms depict the adult phenotype as a function of the environment in which development proceeds. I examined the evolution of a reaction norm, number of trunk vertebrae as a function of developmental temperature in Batrachoseps, using my phylogenetic hypothesis. Number of trunk vertebrae varies at many levels within Batrachoseps. Parallel clines in number of trunk vertebrae occur along an environmental gradient in three taxonomic units in the Coast Ranges of California. Because number of trunk vertebrae is affected by developmental temperature in other vertebrates, I hypothesized that the parallel clines resulted from a shared plastic response to environmental differences. I found extensive variation in reaction norms among population and species, but plasticity was not sufficient to account for the pattern of parallel clines. Plasticity may affect the evolution of traits in two conflicting ways, by facilitating or retarding it. I tested these hypotheses using data on plasticity in number of trunk vertebrae and change in number of trunk vertebrae in nine species of plethodontids. Changes in number of trunk vertebrae occurred more frequently than expected by chance in lineages in which it was plastic. This is consistent with the hypothesis that phenotypic plasticity facilitates evolutionary change.