Galapagos giant tortoises are among the most iconic reptile species on earth; however, an increase in anthropogenic activities has created new challenges for their health and well-being. The presence of whitish lesions on the carapace of Galapagos tortoises (Chelonoidis spp.) was previously described, potentially due to fungal growths, but its etiology
remained unexplored. Aiming to close this gap, we analyzed carapace scrapes from six different species of free-living giant tortoises of Santa Cruz, Isabela, San Cristobal, and Española islands. In total, we tested 145 fresh and frozen carapace scrapes from 145 individuals with carapace whitish lesions (W-L,
n = 80) and without them (W-O, n = 65), using panfungal endpoint PCRs for the ITS and D1-D2 regions. Aphanoascella galapagosensis was detected in W-L samples from all tortoise species and in none of the W-O samples. Four A. galapagosensis nucleotide sequence types (ST) obtained by using the D1-D2 protocol were identified in these tortoises; ST1 was detected on Santa Cruz, Isabela, and Española Islands whereas ST2 and ST3 were only detected on Isabela, and ST4 on San Cristobal. Neodevriesia spp. and Elsinoe spp. were the most common microorganisms found in W-O samples. These results suggest that A. galapagosensis is the etiological agent of whitish lesions in tortoise carapace contributing to baseline data on carapace fungi in giant Galapagos tortoises. Further research is needed to assess the prevalence and potential pathogenicity of A. galapagosensis and its impact for the conservation of these endangered species.

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