Harnessing the microbiome for turtle conservation: investigating the protective effects of the eggshell microbiome against the emerging fungal disease Fusariosis using the yellow-spotted Amazon river turtle as a model system

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The emergence of fungal pathogens threatening wildlife has increased exponentially, in part driven by emerging infectious diseases that are exacerbated by habitat degradation, pollution, and wildlife trade. Whilst catastrophic declines in amphibians and bats due to emerging fungal pathogens has been well documented, high mortality in sea turtles due to the emerging fungal disease Fusariosis has received less attention. This emerging disease is caused by the group of related pathogens in the Fusarium solani species complex (FSSC), involved in mass mortality of all seven sea turtle species by infecting turtle eggs during incubation and causing hatching failure. Alarmingly, this pathogen was recently detected in the Yellow-spotted Amazonian river turtle (Podocnemis unifilis) in the Ecuadorian Amazon, suggesting that this pathogen may also pose a threat to the 357 species of freshwater turtles and tortoises, many of which are already endangered. However, despite the imminent threat this emerging pathogen poses towards turtle biodiversity, we have very little understanding of this fungal disease, including its transmission dynamics, pathogenicity, and long-term fitness effects on turtle hosts. To address this gap, we propose to investigate Fusarium disease dynamics using P. unifilis as a model system. This species is part of a conservation program run by the Tipuni Biodiversity Station/Amazon since 2002, whereby eggs are collected at the point of laying and hatchlings are reared in captivity before being released, to avoid overharvesting of eggs for consumption and the illegal pet trade. Along this line, we will investigate the environmental and maternal sources of Fusarium infection at the point of laying and monitor eggs in captivity to characterise pathogenicity and infection development. Moreover, we will examine how habitat degradation due to palm oil agriculture alters Fusarium prevalence and pathogenicity. Lastly, we will test the role of the eggshell microbiome, which has recently been linked to Fusarium resistance, in mediating infection outcome and hatching success, with an aim of identifying eggshell microbes that can be harnessed for turtle conservation. Our knowledge about the development and assembly of the egg microbiome is limited to avian species and these mechanisms do not apply to turtles due to differences in parental care strategies between birds and turtles. Studies about the transmission and development of the egg bacterial and fungal microbiome in oviparous reptiles without parental care like turtles and their functional role in mediating pathogen resistance are missing. Together, these lines of research will considerably expand our understanding of Fusarium as an emerging infectious disease and the role of host-microbiome interactions for turtle health, thereby contributing to the development of effective turtle conservation strategies in the face of an emerging and potentially devastating threat.