Mitochondrial sequence data reveal population structure within Pustulosa pustulosa.

Unionid mussels are among the most imperiled group of organisms in North America, and Pustulosa pustulosa is a freshwater species with a relatively wide latitudinal distribution that extends from southern Ontario, Canada, to Texas, USA. Considerable morphological and geographic variation in the genus Pustulosa (formerly Cyclonaias) has led to uncertainty over species boundaries, and recent studies have suggested revisions to species-level classifications by synonymizing C. aurea, C. houstonensis, C. mortoni, and C. refulgens with C. pustulosa (currently P. pustulosa). Owing to its wide range and shallow phylogenetic differentiation, we analyzed individuals of P. pustulosa using mitochondrial DNA sequence data under a population genetics framework. We included 496 individuals, which were comprised of 166 samples collected during this study and 330 additional sequences retrieved from GenBank. Pairwise ΦST measures based on ND1 data suggested there may be up to five major geographic groups present within P. pustulosa. Genetic differentiation between regions within Texas was higher compared to populations from the Mississippi and Great Lakes populations, which may reflect differences in historical connectivity. Mitochondrial sequence data also revealed varying demographic histories for each major group suggesting each geographic region has also experienced differential population dynamics in the past. Future surveys should consider exploring variation within species after phylogeographic delimitation has been performed. In this study, we begin to address this need for freshwater mussels via the P. pustulosa system.

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

Ophidiomyces ophidiicola (Oo) is a fungal pathogen and the causative agent of ophidiomycosis that has affected multiple snake taxa across the United States, Europe, and Asia. Ophidiomycosis has often been referred to as an emerging infectious disease (EID); however, its status as an EID has recently come under debate. Oo infections have been confirmed in wild snake populations in Texas; however, it is unknown if the pathogen is novel (i.e., invasive) or endemic to the state. To address this knowledge gap, we conducted surveys for Oo among preserved Nerodia deposited at three university museums in Texas. First, we visually assessed snakes for signs of infection (SOI), and if SOI were present, we sampled the affected area. We then used quantitative polymerase chain reaction to diagnose the presence of Oo DNA on areas with SOI and used these data to evaluate spatiotemporal patterns of Oo prevalence. We also tested for significant spatial clusters of Oo infenction using a Bernoulli probability model as implemented in the program SatScan. We found that the proportion of snakes exhibiting SOI was constant over time while the prevalence of Oo DNA among those SOI increased across space and time. Within these data, we detected an incidence pattern consistent with an introduction and then spread. We detected six spatial clusters of Oo infection, although only one was significant. Our results support the hypothesis that Oo is an emerging, novel pathogen to Texas snakes. These data narrow the knowledge gap regarding the history of Oo infections in Texas and establish a historical record of confirmed Oo detections in several counties across the state. Thus, our results will guide future research to those areas with evidence of past Oo infections but lacking confirmation in contemporary hosts.

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

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, Nerodia erythrogaster transversa and Nerodia rhombifer, 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.