The Evolution and Ecology of Capitella (Annelida, Capitellidae) in the Gulf of Mexico

Members of genus Capitella (Annelida: Capitellidae) are often found in high abundance in areas of anthropogenic disturbance, such as fish farms and waste-water outflow sites and are frequently cited as ecological indicators of organic pollution. Understanding evolutionary relations and habitat preferences between Capitella species that can tolerate these, and other, harsh environments and those that cannot is important for their continued and improved use as indicators of pollution. Five previously undocumented species of Capitella and Capitella nonatoi, a species described from Brazil, were detected in the Gulf of Mexico (GoM) by DNA barcoding. Most of the new species were found in a single location, with one being distributed throughout the GoM. Two of the proposed species are supported by distinctive life history characteristics. These findings underscore the potential to uncover large amounts of biodiversity in the GoM, a region subject to many anthropogenic and natural disturbances. Additionally, support was found for a single evolutionary origin of acicular spines in Capitella, which seems to be a morphology unique to Western Atlantic estuarine waters. Comparing six species abundance modeling techniques using internal validation metrics with six capitellids in Tampa Bay, Florida indicated that none of the assessed models works best for all species. However, Hurdle and GAM-Tweedie models had good performance overall. This was attributed to how these models handle zero-inflation, which every species had. Species rarity was influential and required consideration. For example, Capitella aciculata was found to be a very rare species and this restricted model specification, resulting in the removal of one of the covariates. Assessment of environmental term importance indicated that depth and bay segment/region are important across all species, with higher abundance in shallow, near-shore regions of the bay. Investigation of the evolution of hypoxia inducible factor (HIF), a key transcription factor in the cellular oxygen-sensing pathway consisting of an alpha and beta subunit, revealed high diversity across Annelida. Some recognized groups of annelids were supported by both gene phylogenies. However, neither of the two genes mirrored current hypotheses of annelid phylogenetics but HIFβ reflected current annelid phylogeny hypotheses more closely, indicating stronger conservation of this gene. Additionally, the protein domains of the two genes were recovered with varying degrees of success. This was attributed to loss of low-quality data during transcriptome assembly and high divergence of the domains. These findings contribute to our understanding of Capitella species diversity, patterns of occurrence, and potential for low-oxygen tolerance. A key component to understanding how Capitella have come to occupy so many different marine habitats (e.g. sulfide vents, deep-sea wood falls, squid egg masses) lies in understanding their functional response to the low oxygen levels they encounter in some of these habitats. This will provide insights into the evolution of the HIF transcription factor across Annelida and its potential role in speciation across the phylum.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Marine Biology

Grantor

Texas A&M University

Year dc:date.issued

2020

Author dc:creator

• Hilliard, Justin Lee

Advisor dc:contributor.advisor

• Schulze, Anja

Committee members dc:contributor.committeemember

• Lawing, Anna M
• Alvarado-Bremer, Jaime R
• Highfield, Wesley

• Capitella
• Annelida
• Polychaete
• Cryptic Species
• Species Delimitation
• Ecology
• Machine Learning
• Generalized Additive Model
• Lorenz Curve
• Transcriptome
• Oxygen Sensing
• Evolution
• Hypoxia Inducible Factor

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/1969.1/191676

OAI record oai:identifier

https://oaktrust.library.tamu.edu/server/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Aoaktrust.library.tamu.edu%3A1969.1%2F191676