Long-term survey of sea turtles (Caretta caretta) reveals correlations between parasite infection, feeding ecology, reproductive success and population dynamics

Emma C Lockley,João Pina Lomba,Albert Taxonera,Thomas Reischig,Liam N Nash,Leno Dos Passos,Herculano Dinis,Christophe Eizaguirre,Kirsten Fairweather,Silvana Monteiro Roque,Sahmorie J K Cameron,Leila Fouda,Sandra M Correia,Jandira Durão,Victor A Stiebens

doi:10.1038/s41598-020-75498-4

Abstract

Long-term monitoring of host-parasite interactions is important for understanding the consequences of infection on host fitness and population dynamics. In an eight-year survey of the loggerhead sea turtle (Caretta caretta) population nesting in Cabo Verde, we determined the spatiotemporal variation of Ozobranchus margoi, a sanguivorous leech best known as a vector for sea turtle fibropapilloma virus. We quantified O. margoi association with turtles’ δ15N and δ13C stable isotopes to identify where infection occurs. We then measured the influence of infection on reproduction and offspring fitness. We found that parasite prevalence has increased from 10% of the population in 2010, to 33% in 2017. Stable isotope analysis of host skin samples suggests transmission occurs within the host’s feeding grounds. Interestingly, we found a significant interaction between individual size and infection on the reproductive success of turtles. Specifically, small, infected females produced fewer offspring of poorer condition, while in contrast, large, infected turtles produced greater clutch sizes and larger offspring. We interpret this interaction as evidence, upon infection, for a size-dependent shift in reproductive strategy from bet hedging to terminal investment, altering population dynamics. This link between infection and reproduction underscores the importance of using long-term monitoring to quantify the impact of disease dynamics over time.

Highlights

Long-term monitoring of host-parasite interactions is important for understanding the consequences of infection on host fitness and population dynamics
We found evidence of within-year parasite dynamics, with infected turtles being significantly more likely to be encountered at the beginning of the nesting period than later in the season (Fig. 1E, Χ2 = 5.501, df = 1, p = 0.019; Model summaries in Supplementary Table S3)
We found a significant interaction of maternal carapace length (CCL) and infection on both clutch size (Fig. 3A, F1128 = 7.400, p = 0.007) and overall clutch mass (Fig. 3B, F1110 = 7.802, p = 0.006)

Summary

Introduction

Long-term monitoring of host-parasite interactions is important for understanding the consequences of infection on host fitness and population dynamics. Small, infected females produced fewer offspring of poorer condition, while in contrast, large, infected turtles produced greater clutch sizes and larger offspring We interpret this interaction as evidence, upon infection, for a size-dependent shift in reproductive strategy from bet hedging to terminal investment, altering population dynamics. Parasites and pathogens may prevent feeding of their host entirely, as in the case of sea turtle fibropapillomatosis, which leads to cutaneous lesions on soft tissues that impair vision, locomotion and eating capacity before death[19,20] In these cases, the impact of infection may be detected by a change in a host’s trophic niche as an early warning signal before severe symptoms appear[21,22]

Methods

Results

Conclusion