All ETDs from UAB

Advisory Committee Chair

Charles D Amsler

Advisory Committee Members

Bill J Baker

Stacy A Krueger-Hadfield

Juan Lopez-Bautista

James B McClintock

Document Type


Date of Award


Degree Name by School

Doctor of Philosophy (PhD) College of Arts and Sciences


Organisms produce chemical defenses to gain a competitive advantage, and to protect themselves from pathogens and predators. There is high inter- and, sometimes, intraspecific diversity in the types and quantities of defensive secondary metabolites. Yet, we do not know much about the mechanisms driving the diversity and its distribution. Macroalgae are important members of ecosystems since they provide living space and are primary producers. To prevent predation, macroalgae make structural or chemical defenses. Chemical defenses in the Antarctic red macroalga Plocamium sp. have extensively been studied. It is widespread along the western Antarctic Peninsula and abundant at sites where it is found. Plocamium sp. supports a high number of mesograzers which gain protection by associating with chemically-defended hosts. Thalli produce a variety of secondary metabolites and vary in the type and relative quantity of the metabolites. This “signature mixture” allows for the assignment of chemogroups of which we found 15 around our study sites near the U.S. Antarctic Program’s Palmer Station on Anvers Island (64° 46.5’ S, 64° 03.3’ W). These chemogroups protect Plocamium sp. from all known mesograzers except the amphipod Paradexamine fissicauda. It is beneficial for Plocamium sp. to produce some chemogroups over others since it is consumed at slower rates and its grazer produces less offspring when fed on certain chemogroups. We observed variation among individual amphipods which allows for selection and evolution in iv response to chemogroups. Sites differed significantly in their chemogroup assemblages and transects revealed within site differences among depths but not laterally. From reciprocal transplant experiments we concluded that the environment is not the main driver of the observed chemogroup distribution. In addition, life cycle stage does not influence chemogroup production either. Sequencing of a fragment of the cox1 gene revealed two main haplotypes which correlated with different chemogroups. To identify individuals, we developed ten microsatellite markers. Populations are mostly dominated by tetrasporophytes and we found evidence for intergametophytic selfing which may be inflated by substructuring within sites. This provides the foundation for future studies investigating how gene flow drives the distribution of genotypic diversity and therefore phenotypes in this ecologically important species.



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