Current Research and Research Interests

M.S. Thesis:

The influence of colony architecture on morphological plasticity in the hydroid Podocoryne carnea

Phenotypic plasticity has been investigated in a variety of unitary (e.g., insects, fish, snails) and clonal organisms (e.g., plants, cnidarians, bryozoans) and differences in plasticity among genotypes is evidence of a genotype x environment interaction. In clonal taxa, it is often difficult to distinguish whether morphological plasticity is regulated more by genotype, or colony architecture. We investigated morphological plasticity in the colonial hydractiniid hydroid, Podocoryne carnea, to partition plasticity due to genotype, colony architecture and size. Podocoryne carnea exhibits a loose network of widely spaced polyps along long, sparsely branched stolonal connections allowing us to experimentally establish three different architectures (linear, loop and T shape) at two different colony sizes (1 polyp and 2 polyps). We hypothesized that the differing architectures and sizes would change patterns of gastrovascular circulation through stolons hence, a change in morphology. These data suggest that architecture and size affect branch number and length. Flow rate of fluid through stolons differed among genotypes, but not among architectures. We speculate that loop morphologies exhibit more branches due to their ability to continually pump nutrient rich fluid through stolons. Current investigations are focusing on distinguishing whether clonal differences in flow rate are a result of differing stolon diameters. If this is the case, these data would suggest that colony architecture is more important than genotype in regulating morphological plasticity.

Sedentary organisms are restricted to the environment they settle in; whether it is optimal or poor the organisms may exhibit plasticity to survive. Nonetheless, understanding an organism’s environment by quantifying abiotic factors can shed light on the daily stressors experienced by the individual. This study focused on quantifying the environment experienced by the colonial hydrozoan Hydractinia symbiolongicarpus, which lives on the back of hermit crab shells, by measuring the amount of dissolved oxygen (DO) at four sediment depths (surface, 1 cm, 3 cm & 5 cm) representative of those in which hermit crabs may be found buried and at two locations along the New England Coast (Barnstable Harbor, MA; Darling Marine Center, ME). In addition, we investigated where the hermit crabs were located during low tide and the sediment composition. DO significantly decreased with increasing sediment depth and was nearly anoxic at 5 cm. A majority of the total hermit crabs counted were found in normoxic pools compared to those buried in the sediment. The sediment at Barnstable Harbor had a higher sand composition compared to that of Maine suggesting a lack of organic material which may result in higher DO availability. This study indicates that H. symbiolongicarpus may experience near anoxic levels of DO during low tide due to their symbiosis with hermit crab shells. Current laboratory research on morphological plasticity exhibited by hydrozoans at variable oxygen concentrations may help us understand how hydroids are reacting to the abiotic stressor present in their natural habitat.