Species distributions and population structure in cold seep vestimentiferan tubeworms of the genera Escarpia and Lamellibrachia (polychaeta, Siboglinidae)
Open Access
- Author:
- Cowart, Dominique Alexandria
- Graduate Program:
- Biology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 22, 2013
- Committee Members:
- Charles Raymond Fisher Jr., Dissertation Advisor/Co-Advisor
Stephen Wade Schaeffer, Dissertation Advisor/Co-Advisor
Kateryna Dmytrivna Makova, Committee Chair/Co-Chair
Christopher Howard House, Committee Member - Keywords:
- vestimentiferan tubeworm
hydrocarbon seep
microsatellite
siboglinid
population structure
deep sea - Abstract:
- Deep-sea cold seeps support diverse biological communities that rely on the seepage of hydrocarbon gases and fluids. Due to their dependence on irregularly occurring seepage, vestimentiferan tubeworms (Family: Siboglinidae) have patchy distributions on the seafloor. Tubeworms of the genera Escarpia and Lamellibrachia are important components of seep ecosystems, as they form long-lived aggregations that provide habitat for a variety of other deep-sea fauna. Three described species of Escarpia, E. spicata (Gulf of California), E. laminata (Gulf of Mexico) and E. southwardae (West African Cold Seeps), have been identified as one species through the use of mitochondrial markers Cytochrome Oxidase subunit 1 (mtCOI) and large ribosomal subunit rDNA, (mt16S), despite their geographic differences and dissimilar morphologies. Three morphologically distinct groups of Lamellibrachia are present over a bathymetric range of almost 3000m in the Gulf of Mexico; these include L. luymesi (<1000m) and two unnamed groups, L. sp. 1 and L. sp. 2 (>1000m). As with the Escarpia, mtCOI and mt16S identifies L. luymesi and L. sp. 1 as one species despite their differing depth ranges and dissimilar morphologies. This dissertation seeks to define the geographic and bathymetric ranges of Escarpia and Lamellibrachia by determining if geographically differentiated Escarpia and depth differentiated Lamellibrachia are genetically distinct within each respective group. For these investigations, we make use of molecular, morphological and environmental data, all of which are necessary to ascertain population boundaries and evolutionary processes occurring in the deep sea. Here we use Exon Priming Intron Crossing (EPIC) sequencing of a nuclear gene, and develop microsatellite markers with the aid of 454 and Illumina next generation sequencing to 1) determine if the described taxa are genetically differentiated and 2) identify possible population structure at the regional scale within the Gulf of Mexico and West Africa, respectively. To identify if the three Escarpia groups are genetically distinct, we have tested the mitochondrial gene Cytochrome B (CYTB) for its utility as a phylogenetically informative marker, as well as developed and analyzed the EPIC marker Hemoglobin subunit B2 intron (HbB2i) and 28 microsatellites in 229 Escarpia individuals collected from 12 seep sites around the world. Nine of the microsatellites were amplified across the three Escarpia taxa, and while CYTB identifies two groups rather than three, both HbB2i and the cross-amplified microsatellites support the occurrence of three genetically distinct groups of Escarpia based on geography. At the regional scale among eight sampling sites of E. laminata (n =129) and among three sampling sites of E. southwardae (n =80), no population structure was detected. To identify if the two Lamellibrachia groups are genetically distinct, we also tested CYTB, HbB2i and eight microsatellites in 76 Lamellibrachia individuals collected from 13 seep sites in the Gulf of Mexico. All eight of the microsatellites were amplified across 45 L. luymesi and L. sp.1, and while both CYTB and HbB2i identify L. luymesi and L. sp. 1 as a single group, the cross-amplified microsatellites support the occurrence of two genetically distinct groups. At the regional scale among eight sampling sites of L.sp.1 (n =24) and among six sampling sites of L. sp.2 (n =31), no population structure was detected. Findings in this dissertation illustrate that 1) nuclear markers support original morphological descriptions of Escarpia and Lamellibrachia, suggesting that each group is constrained to their respective geographic or bathymetric region, 2) despite the patchiness and isolation of seep habitats, connectivity is high on regional scales, 3) mitochondrial markers should be used with extreme caution when attempting to detect differentiation in seep vestimentiferan groups, and lastly 4) microsatellites may be another useful tool to determine genetic differentiation between described species when divergence is insufficient or too recent to be detected using gene sequences alone.