Evolutionary Comparisons of Chelonid Alphaherpesvirus 5 (ChHV5) Genomes from Fibropapillomatosis-Afflicted Green (Chelonia mydas), Olive Ridley (Lepidochelys olivacea) and Kemp's Ridley (Lepidochelys kempii) Sea Turtles

International overview of sea turtle fibropapillomatosis: a survey of expert opinions and trends

Introduction

Marine environments offer a wealth of opportunities to improve understanding and treatment options for cancers, through insights into a range of fields from drug discovery to mechanistic insights. By applying One Health principles the knowledge obtained can benefit both human and animal populations, including marine species suffering from cancer. One such species is green sea turtles (Chelonia mydas), which are under threat from fibropapillomatosis (FP), an epizootic tumor disease (animal epidemic) that continues to spread and increase in prevalence globally. In order to effectively address this epizootic, a more thorough understanding is required of the prevalence of the disease and the approaches to treating afflicted turtles.

Methods

To identify knowledge gaps and assess future needs, we conducted a survey of sea turtle FP experts. The survey consisted of 47 questions designed to assess general perceptions of FP, the areas where more information is needed, local FP trends, the disease status, and mitigation needs, and was voluntarily completed by 44 experts across a broad geographic range.

Results

Over 70% of respondents both recognized FP as a cancerous panzootic disease, and reported that FP is increasing in prevalence. They report several factors contributing to this increase. Nearly all of the respondents reported that FP research, patient treatment and rehabilitation required more funding in their area, and reported inadequate facilities and capacity for dealing with FP patients. Treatment approaches varied: just over 70% of the medical experts that responded surgically remove FP tumors, either using laser or scalpel. Just under half of respondents use anti-cancer drugs in their treatment of FP. Internal tumors were reported as justification for euthanasia by 61.5% of respondents, and 30.8% reported severe external tumors to be sufficient grounds for euthanasia. Most medical respondents (93.3%) routinely perform necropsy on deceased or euthanized FP-afflicted turtles. Over 80% of respondents considered large-scale multidisciplinary collaboration 'extremely important' for advancing the field of FP research.

Discussion

The survey responses provide a valuable insight into the current status of FP in sea turtles, FP treatment, rehabilitation and research, and help to identify critical FP-related areas most in need of attention.

Multicellular species environmental DNA (eDNA) research constrained by overfocus on mitochondrial DNA

Environmental DNA (eDNA) is becoming an established tool across the biological and medical sciences. Despite the evident successes and wide adoption of eDNA approaches, some fundamental questions remain. For instance, there is almost a dogma in the field around the superiority of mitochondrial DNA for use in eDNA studies, however robust comparison with nuclear eDNA is widely lacking. The dominance of mitochondrial-based eDNA for animal and plant studies appears to be largely settled, despite a widespread lack of rigorous nuclear eDNA testing. Outside of the source organism the protections conferred on eDNA by the cell, mitochondrial and nuclear membranes are poorly understood, including the contribution of each to eDNA persistence and degradation. Utilizing shotgun sequencing to unbiasedly assess the level of nuclear and mitochondrial eDNA across samples, we reveal stark differences in nuclear versus mitochondrial eDNA persistence and abundance. By focusing too heavily on mitochondrial DNA alone the field is underutilizing eDNA's full potential.

Microbial composition of carapace, feces, and water column in captive juvenile green sea turtles with carapacial ulcers

Introduction

Green sea turtles are endangered marine reptiles. Carapacial ulcers will develop on juvenile green sea turtles during artificial rescue, seriously affecting their health and potentially leading to death.

Methods

To determine the pathogens causing ulcerative carapacial disease, we performed 16S and ITS high-throughput sequencing, and microbial diversity analysis on samples from carapacial ulcers, healthy carapaces, feces, and seawater of juvenile green sea turtles.

Results

Our analysis showed that changes in microbial diversity of green sea turtle feces and seawater were not significantly associated with ulcerative carapacial disease.

Discussion

Psychrobacter sp. is the dominant species in the carapacial ulcers of green sea turtles. The bacterium is present in both healthy turtles and seawater where carapacial ulcers did not occur and decreasing seawater temperatures are likely responsible for the infection of juvenile green turtles with Psychrobacter sp. This is the first study on carapacial ulcers in captive juvenile green sea turtles. Our research provides theoretical guidance for the prevention and control of carapacial ulcers in captive juvenile green sea turtles.

Threats and Vulnerabilities for the Globally Distributed Olive Ridley (Lepidochelys olivacea) Sea Turtle: A Historical and Current Status Evaluation

The olive ridley (Lepidochelys olivacea) is the most abundant of all seven sea turtles, found across the tropical regions of the Atlantic, Pacific, and Indian Oceans in over 80 different countries all around the globe. Despite being the most common and widely distributed sea turtle, olive ridley populations have been declining substantially for decades. Worldwide, olive ridleys have experienced a 30–50% decline, putting their populations at risk and being considered an Endangered Species by the IUCN. Natural habitat degradation, pollution, bycatch, climate change, predation by humans and animals, infectious diseases and illegal trade are the most notorious threats to explain olive ridley populations rapidly decline. The present review assesses the numerous dangers that the olive ridley turtle has historically faced and currently faces. To preserve olive ridleys, stronger conservation initiatives and strategies must continue to be undertaken. Policies and law enforcement for the protection of natural environments and reduction in the effects of climate change should be implemented worldwide to protect this turtle species.

Occurrence of Fibropapillomatosis in Green Turtles (Chelonia mydas) in Relation to Environmental Changes in Coastal Ecosystems in Texas and Florida: A Retrospective Study

Fibropapillomatosis is a neoplastic disease of marine turtles, with green turtles (Chelonia mydas) being the most affected species. Fibropapillomatosis causes debilitating tumor growths on soft tissues and internal organs, often with lethal consequences. Disease incidence has been increasing in the last few decades and the reason is still uncertain. The potential viral infectious agent of Fibropapillomatosis, chelonid herpesvirus 5, has been co-evolving with its sea turtle host for millions of years and no major mutation linked with increased disease occurrence has been detected. Hence, frequent outbreaks in recent decades are likely attributable to external drivers such as large-scale anthropogenic changes in the green turtle coastal marine ecosystem. This study found that variations in sea surface temperature, salinity, and nutrient effluent discharge from nearby rivers were correlated with an increased incidence of the disease, substantiating that these may be among the significant environmental drivers impacting Fibropapillomatosis prevalence. This study offers data and insight on the need to establish a baseline of environmental factors which may drive Fibropapillomatosis and its clinical exacerbation. We highlight the multifactorial nature of this disease and support the inclusion of interdisciplinary work in future Fibropapillomatosis research efforts.

Detection and population genomics of sea turtle species via non-invasive environmental DNA analysis of nesting beach sand tracks and oceanic water

Elusive aquatic wildlife, such as endangered sea turtles, are difficult to monitor and conserve. As novel molecular and genetic technologies develop, it is possible to adapt and optimize them for wildlife conservation. One such technology is environmental (e)DNA - the detection of DNA shed from organisms into their surrounding environments. We developed species-specific green (Chelonia mydas) and loggerhead (Caretta caretta) sea turtle probe-based qPCR assays, which can detect and quantify sea turtle eDNA in controlled (captive tank water and sand samples) and free ranging (oceanic water samples and nesting beach sand) settings. eDNA detection complemented traditional in-water sea turtle monitoring by enabling detection even when turtles were not visually observed. Furthermore, we report that high throughput shotgun sequencing of eDNA sand samples enabled sea turtle population genetic studies and pathogen monitoring, demonstrating that non-invasive eDNA techniques are viable and efficient alternatives to biological sampling (e.g. biopsies and blood draws). Genetic information was obtained from sand many hours after nesting events, without having to observe or interact with the target individual. This greatly reduces the sampling stress experienced by nesting mothers and emerging hatchlings, and avoids sacrificing viable eggs for genetic analysis. The detection of pathogens from sand indicates significant potential for increased wildlife disease monitoring capacity and viral variant surveillance. Together, these results demonstrate the potential of eDNA approaches to ultimately help understand and conserve threatened species such as sea turtles.