PhD Program in Biology, The Graduate Center, City University of New York

Ecology, Evolutionary Biology and Behavior

Mike Friedman

City College

Dissertation advisor: Rob DeSalle

Topic: Co-evolution of members of the Batesian mimicry complex consisting of Lampropeltis triangulum (Serpentes: Colubridae), Cemophora coccinea (Serpentes: Colubridae) and Micrurus fulvius (Serpentes: Elapidae) in the Southeastern and South Central U.S.

Color pattern co-variation has long been noted between models and mimics among these snakes. Does this involve co-evolution, where speciation events are interactive? Does the evolution of the model induce co-evolution of the mimics? Theoretically, by conferring differential selective advantages on models and mimics, the mimetic association between coral snakes (Micrurus, Micruroides) and milksnakes (Lampropeltis triangulum) could lead to co-evolution between sympatric populations of the two groups. Co-evolution would be mediated by predator response to aposematic coloration. Phylogenetic inference provides a framework for assessing evolutionary history of species and of associations. This requires robust and resolved phylogenies for each of the associated taxa. Congruent model-mimic phylogenies and color pattern co-variation among sympatric populations would support a hypothesis of co-evolution driven by the mimetic association.

In the southeastern U.S., Micrurus fulvius fulvius and Lampropeltis triangulum elapsoides are the local components of this mimetic association. In order to assess co-evolution among these two groups it will first be necessary to test species boundaries and resolve phylogenetic relationships between designated populations of each group. Genetically distinct populations are hypothesized for the geographical areas east and west of Mobile Bay, north and south of the Savannah River and north and south of the Everglades. This study will shed light on evolutionary causality and has implications for conservation of genetically unique populations. Population Aggregation Analysis (PAA), which relies on population-unique and fixed characters and character combinations to define terminal taxa, will be employed to evaluate species boundaries. Phylogenetic inference will be carried out using a maximum parsimony approach. Model-mimic co-evolution will be assessed using Tree Reconciliation and Brooks Parsimony Analysis, while color pattern co-variation between sympatric populations will be investigated using a minimum evolution approach.

Initially, 75 specimens, principally from Florida and South Carolina, were obtained in the field and from institutional collections. DNA was extracted from these specimens and the ND4 gene was amplified and sequenced. In addition, a protocol for extraction and sequencing of DNA from formalin-fixed tissues was successfully assayed. This was attained with five specimens of Lampropeltis triangulum triangulum from the AMNH collection, ranging from over 100 years to less than 20 years of age. While L. t. triangulum is not included in this analysis, it is noteworthy that ND4 sequences from these specimens contained genetic markers, including an apparent frameshift mutation, that clearly distinguished them from L. t. elapsoides. A preliminary application of PAA, using the ND4 gene, revealed unique and fixed markers distinguishing South Carolina and Florida populations of L. t. elapsoides. Differentiation was lacking among M. f. fulvius from these regions. Phylogenetic inference for L. t. elapsoides, using the same molecular data, showed a derived South Carolina clade nested among Florida groups. Among M. f. fulvius, genetic variation was observed only for a single specimen from the southern tip of Florida. Further sampling is planned to encompass the geographically distinct regions previously mentioned, as well as intermediate zones. Additional DNA sequences, both mitochondrial and nuclear, will also be evaluated.

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