Doctor of Philosophy (PhD)
Coral reefs are the most productive and species rich ecosystems in the ocean yet we lack knowledge about the distribution of genetic variation the within and among reef species, particularly for the sponges (Porifera). My dissertation describes how genetic variation at mitochondrial and nuclear genes is partitioned among and within species in the sponge genus Callyspongia. I compared patterns of genetic diversity and population subdivision in the mitochondrial and nuclear genomes of one species, C. vaginalis, in Florida (Chapter 2). Previous work revealed three divergent mitochondrial lineages, but nuclear alleles did not correspond to either mitochondrial clade or geography. Coalescent simulations showed mito-nuclear discordance was not the result of incomplete lineage sorting. Instead, patterns in mitochondrial and nuclear DNA were consistent with changes in population size and sperm-mediated gene flow. Across the Caribbean, I found subdivision in C. vaginalis for mitochondrial and nuclear DNA was concordant, suggesting geographic features and habitat discontinuity are important for structuring populations at large spatial scales (Chapter 3). Clustering analyses found C. vaginalis populations were divided west-east and model-based tests of species boundaries supported a cryptic lineage in Central America. Phylogeographic patterns for three invertebrate sponge commensals also showed a west-east split between Florida and the Bahamas. I tested for mismatches between morphological and molecular species boundaries for seven Caribbean Callyspongia species (Chapter 4). Genetic distances calculated within and among species support C. fallax, C. tenerrima, and C. plicifera as distinct species. However, C. armigera, C. longissima, C. ?eschrichtii and C. vaginalis shared alleles across loci and genetic distances among these taxa overlapped distances within them. Model-based species delimitation supported the hypothesis that these latter four taxa represent one evolutionarily significant unit. This dissertation demonstrates that in the common reef sponge Callyspongia vaginalis, demographic processes and geography influence population structure at small and large spatial scales, respectively, and genetic markers from different genomes can show contrasting patterns. My work also shows the relationship between morphology and evolutionary history is not straightforward in sponges and points to the importance of inter- and intraspecific genetic data for a thorough documentation of biodiversity in marine invertebrates.
Document Availability at the Time of Submission
Release the entire work immediately for access worldwide.
DeBiasse, Melissa Barrett, "Model-based Tests of Historical Demography and Species Delimitation in the Caribbean Coral Reef Sponge Callyspongia" (2014). LSU Doctoral Dissertations. 3540.