Abstract
Wildlife diseases are an increasing concern for endangered species conservation, but their occurrence, causes, and human influences are often unknown. We analyzed 3,939 records of stranded Hawaiian green sea turtles (Chelonia mydas) over 28 years to understand fibropapillomatosis, a tumor-forming disease linked to a herpesvirus. Turtle size is a consistent risk factor and size-standardized models revealed considerable spatial and temporal variability. The disease peaked in some areas in the 1990s, in some regions rates remained constant, and elsewhere rates increased. Land use, onshore of where the turtles feed, may play a role. Elevated disease rates were clustered in watersheds with high nitrogen-footprints; an index of natural and anthropogenic factors that affect coastal eutrophication. Further analysis shows strong epidemiological links between disease rates, nitrogen-footprints, and invasive macroalgae and points to foraging ecology. These turtles now forage on invasive macroalgae, which can dominate nutrient rich waters and sequester environmental N in the amino acid arginine. Arginine is known to regulate immune activity, promote herpesviruses, and contribute to tumor formation. Our results have implications for understanding diseases in aquatic organisms, eutrophication, herpesviruses, and tumor formation.
Highlights
IntroductionHabitat loss, and climate change, emerging diseases pose major impacts to biodiversity worldwide [1,2]
Combined with overexploitation, habitat loss, and climate change, emerging diseases pose major impacts to biodiversity worldwide [1,2]
Bar plots show the demographic proportions through time fitted to a log-normal distribution, the highest-ranked model in all time steps
Summary
Habitat loss, and climate change, emerging diseases pose major impacts to biodiversity worldwide [1,2]. Marine turtles suffer numerous population threats [3] with green sea turtles (Chelonia mydas) afflicted by fibropapillomatosis (FP) a debilitating tumor-forming disease [4]. While surveys show key green turtle populations are steadily growing [5,6], FP remains widespread and its origins are unknown. We present a spatial epidemiology from 28 years of disease records from the Hawaiian population of green turtles. We construct time series of disease rates, address the spatial scale of variability, and examine the role of land use and invasive macroalgae. Hypotheses of causal factors of the disease examined vascular trematodes and toxins but results were inconclusive [7,8]. A viral origin for FP became apparent after experiments successfully transmitted the disease using cell-free tumor extracts [9]. Subsequent results showed sampled herpesviruses had low genetic variability [11,12] implying contact transmission, perhaps via ectoparasites [13]
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