Defense Date

4-29-2022

Document Type

Thesis

Degree Type

Master of Science

Degree Name

Marine Science

First Advisor

Jose V. Lopez, Ph.D.

Second Advisor

Derek Burkholder, Ph.D.

Third Advisor

Rosanna Milligan, Ph.D.

Keywords

high throughput sequencing, hatching success, Caretta caretta, Chelonia mydas, beach sand, cloaca

Abstract

All seven extant species of sea turtles are classified as threatened or endangered due to natural and anthropogenic impacts. Sea turtle conservation efforts are largely dedicated to ensuring healthy nesting activity. Hatching success of sea turtle eggs can be affected by several factors including the proliferation of pathogenic microbes. However, it is unclear as to which microbes have the most impact on hatching success and how they are transmitted into the eggs. The primary aims of this study characterized and compared the bacterial communities (microbiomes) from the i) cloaca of nesting sea turtles; ii) sand within and surrounding the nests and iii) hatched and unhatched eggshells from two important species, the loggerhead (Caretta caretta) and green (Chelonia mydas) turtles. Samples were collected from nests in Fort Lauderdale and Hillsboro beaches in Broward County, Florida, where local nesting consisted of approximately 95% loggerhead, 5% green and 1% leatherback turtles (Dermochelys coriacea). Illumina MiSeq high throughput sequencing of 16S rRNA V3-V4 region amplicons was performed on 27 cloaca, 54 sand, and 162 egg samples. Significant differences were identified between hatched and unhatched egg microbiomes with the differences caused predominantly by the genus Pseudomonas, which was found in higher abundances in unhatched eggs (~11% relative abundance) than hatched eggs (~0.8% relative abundance). Although cloaca microbiomes were significantly different between turtle species, egg microbiomes were not found to be different between turtle species. Interestingly, significant differences were identified between beaches for both sand and egg microbiomes. Mixed mode transmission is hypothesized as the likely mode of pathogen transmission into sea turtle eggs since neither maternal nor environmental transmission alone were identified as the primary source. This study provides new insights into the bacterial communities associated with egg hatching failure in sea turtle nests and unveiled information about the impacts the environment has on bacterial introduction.

Comments

This research was approved under the Marine Turtle Permit #255 (MTP-20-255B & MTP-21-255) by the Florida Fish and Wildlife Conservation Commission (FWC).

Full data files (lists for potential pathogens, shared and unique ASVs, SIMPER analyses, Krona plots) can be found at https://github.com/colmcmaken/Turtle-Egg-Microbiome along with the R scripts used for this analysis.

Final sequence data were uploaded to NCBI’s Short Read Archive (BioProject accession: PRJNA804903).

ORCID ID

0000-0002-3561-8586

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