Molecular investigations of deep-sea black coral ecology
Open Access
- Author:
- RUIZ, DANNISE V
- Graduate Program:
- Biology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- July 22, 2014
- Committee Members:
- Iliana Brigitta Baums, Dissertation Advisor/Co-Advisor
Charles Raymond Fisher Jr., Committee Chair/Co-Chair
Claude Walker Depamphilis, Committee Member
Christopher Howard House, Special Member - Keywords:
- Population genetics
reproductive strategy
phenotypic plasticity
gene expression
black corals - Abstract:
- The black coral Leiopathes glaberrima is one of the most common species of Antipatharia (Cnidaria: Anthozoa) in the Gulf of Mexico. Dense aggregations of Leiopathes fulfill the role of a foundation species as their branching morphology and vertical growth provide substrate and refuge for a variety of deep-sea organisms. This thesis focused on the microsatellite content, spatial distribution, genetic differentiation and response to chemical stress of Leiopathes glaberrima in the Northern Gulf of Mexico. Microsatellite markers are useful in determining population genetic patterns and in detecting cryptic species yet they can be difficult to develop for Cnidaria. To elucidate the ancestral state of microsatellite dynamics in basal metazoans and develop molecular tools for L. glaberrima, abundance and type of microsatellite motifs were studied in eleven Cnidarian species representing two classes, three subclasses and eight orders within the phylum. Hierarchical clustering and log likelihood ratio tests revealed a weak relationship between phylogeny and microsatellite content. Further, comparisons between cnidaria harboring intracellular dinoflagellates and those that do not, show microsatellite coverage is higher in the latter group. The observed microsatellite patterns support previous studies that found tri- and tetranucleotides to be the most abundant motifs in invertebrates. Differences in microsatellite coverage and composition between symbiotic and non-symbiotic cnidaria suggest the presence/absence of dinoflagellates might place restrictions on the host genome. The microsatellite survey yielded 10 novel microsatellite markers for the study of L. glaberrima that were used to study gene flow and mating patterns of this species. L. glaberrima inhabits carbonate outcrops in the Northern Gulf of Mexico, where multiple color morphotypes grow in sympatry. Based on both phylogenetic analysis and colony morphology these color morphotypes constitute one species. However, gene flow was disrupted between and within two nearby hard ground sites (distance = 36.4 km). The lineages and color phenotypes occurred in different microhabitats and models of maximum entropy suggested that depth and slope might influence their distribution. Thus, L. glaberrima is one phenotypically plastic foundation species employing a mixed reproductive strategy in the Northern Gulf of Mexico. Utilizing a mixed mating strategy might enable this long-lived species to balance local recruitment with occasional long-distance dispersal to colonize new sites in an environment where habitat is limited. In the Gulf of Mexico, cold-water corals are mostly found on carbonate outcrops of authigenic origin, which occur in areas associated with hydrocarbon prospecting, drilling and fishing. The recent 2010 oil spill from the MC252 well site exemplified effects of these activities on the deep-sea fauna, and uncovered gaps in the baseline information on deep-sea ecosystems. Here, I used differential gene expression analyses to describe and quantify the physiological responses of deep-sea corals to a sudden increase in hydrocarbons, dispersant and hydrocarbon-dispersant mixtures. Fragments from the red and white morphotypes of L. glaberrima were exposed to different concentrations of oil, dispersant and oil-dispersant solutions. Dispersant and oil-dispersant treatments were more lethal to the colonies than oil alone, in agreement with previous studies on invertebrates. The use of dispersants might prevent the hazards associated with oil slicks, but might potentially increase the amount of oil compounds in the water column to the detriment of cold water corals. Interestingly, the red colonies of L. glaberrima had better survival rates than white colonies, and also showed more changes in gene expression in response to the experimental treatments. These results suggested physiological differences between the two main morphotypes of L. glaberrima, and might indicate that white Leiopathes colonies are more susceptible to stress than their red counterparts. This has implications for understanding how L. glaberrima populations might respond to oil spills and mitigation strategies.