Comparative host–pathogen associations 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, Nerodiaerythrogaster transversa and Nerodiarhombifer, in north central Texas; thus, providing an opportunity to test comparative host–pathogen associations 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 individuals 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.

Leveraging preserved specimens of Nerodia to infer the spatiotemporal dynamics of Ophidiomyces ophidiicola via quantitative polymerase chain reaction

“…In Texas, there is a paucity of data for Oo . Presently, six confirmed reports of Oo infections were made to Texas Parks and Wildlife (N. Rains & P. Crump, personal communications; see Harding et al, 2022 , Dryad repository: https://doi.org/10.5061/dryad.t76hdr83p ), one published study showed wide‐spread occurrence among contemporary populations of Nerodia in the upper Brazos River drainage (north central Texas) (Harding et al, 2022 ), and another estimated 15% prevalence among terrestrial and aquatic snakes via SYBR Green qPCR in northeast Texas (Lizarraga et al, 2023 ). Thus, there is a knowledge gap regarding Oo infection dynamics in this region, and it is unknown if Oo is naturally occurring and previously unrecognized, naturally occurring but emerging, or has recently spread into Texas (i.e., a novel pathogen).…”

“…We focused primarily on Nerodia spp. for three reasons: (1) the first confirmed report of Oo infection in Texas was from N. h. harteri , (2) the state contains several widespread species, and (3) to gain historical insight for Oo infection associations observed in contemporary Nerodia populations by Harding et al ( 2022 ).…”

“…To extract DNA from the swabs, we used the PrepMan Ultra Sample Preparation Reagent (Applied Biosystems) protocol followed by Harding et al ( 2022 ). Specifically, prior to DNA extraction, the screw‐cap tubes were opened and swabs were allowed to dry for 1 h to ensure that any residual ethanol evaporated.…”

“…In Texas, there is a paucity of data for Oo. Presently, six con- (Harding et al, 2022), and another estimated 15% prevalence among terrestrial and aquatic snakes via SYBR Green qPCR in northeast Texas (Lizarraga et al, 2023). Thus, there is a knowledge gap regarding Oo infection dynamics in this region, and it is unknown if Oo is naturally occurring and previously unrecognized, naturally occurring but emerging, or has recently spread into Texas (i.e., a novel pathogen).…”

Long‐term exposure to an invasive fungal pathogen decreases Eptesicus fuscus body mass with increasing latitude

“…Host species highly susceptible to infection with high mortality from infection receive the most research attention upon disease emergence (Altizer et al, 2004; Lorch et al, 2016; McGuire et al, 2017; Voyles et al, 2007). Hosts less susceptible to pathogen infections with low mortality from infection (relative to highly susceptible host species) also do receive research attention, but typically only within the context of highly susceptible hosts (Cheng et al, 2021; Dhondt et al, 2013; Fischer et al, 1997; Harding et al, 2022; Pannkuk et al, 2021; Poorten & Rosenblum, 2016). Consequently, we know less about responses of less susceptible hosts, although they are also at risk.…”