Comparative host-pathogen dynamics of Snake Fungal Disease in sympatric species of water snakes (Nerodia)

Abstract

The ascomycete fungus Ophidiomyces ophiodiicola (Oo) is the causative agent of ophidiomycosis (Snake Fungal Disease), which has been detected globally. However, surveillance efforts in the central U.S., specifically Texas, have been minimal. The threatened and rare Brazos water snake (Nerodia harteri harteri) is one of the most range restricted snakes in the U.S. and is sympatric with two wide-ranging congeners, N. erythrogaster transversa and N. rhombifer, in north central Texas; thus, providing an opportunity to test comparative host-pathogen dynamics in this system. To accomplish this, we surveyed a portion of the Brazos river drainage (~400 river km) over 29 months and tested 150 Nerodia spp. for the presence of Oo via quantitative PCR and recorded any potential signs of Oo infection. We found Oo was distributed across the entire range of N. h. harteri, Oo prevalence was 46 % overall, and there was a significant association between Oo occurrence and signs of infection in our sample. Models indicated adults had a higher probability of Oo infection than juveniles and subadults, and adult N. h. harteri had a higher probability of infection than adult N. rhombifer but not higher than adult N. e. transversa. High Oo prevalence estimates (94.4%) in adult N. h. harteri has implications for their conservation and management owing to their patchy distribution, comparatively low genetic diversity, and threats from anthropogenic habitat modification.

Parasite gene flow in riverine habitats: ascertaining the roles of stream drift, river bifurcations and host dispersal

“…Our results also have direct conservation implications within the Colorado and Concho Rivers. Snake fungal disease ( Ophidiomyces ophiodiicola ) has recently been reported infecting the watersnake community in the Brazos River, including the endemic Brazos watersnake ( Nerodia harteri harteri ), a close relative of the recently de-listed endemic Concho watersnake ( N. h. paucimaculata ) included in this study (Harding et al 2022). Both N. harteri subspecies are highly aquatic and rarely found more than a meter from water and exhibit short distance dispersal (Gibbons and Dorcus 2004; Janecka et al 2021).…”