The gill parasite Centrocestus formosanus (Trematoda: Heterophyidae) is an exotic parasite of concern in Texas because it has been shown to infect multiple threatened and endangered fish species. The purpose of this study was to determine if C. formosanus could present a threat to larval anurans, as well as threatened neotenic salamanders endemic to the spring-fed systems of Texas. We exposed adults of the San Marcos salamander Eurycea nana (Caudata: Plethodontidae) and tadpoles of the Rio Grande leopard frog Lithobates berlandieri (Anura: Ranidae) to the cercariae of C. formosanus . The San Marcos salamander showed no signs of metacercarial infection, suggesting that E. nana may be refractory to C. formosanus cercariae. Centrocestus formosanus readily infects the gills of leopard frog tadpoles, but the metacercariae apparently died prior to reaching maturity in our tadpoles.

Relatively few studies have focused on the evolution and development of divergent nervous systems. The salamander clade (Eurycea) from the karst regions of central Texas provide an ideal platform for comparing divergent nervous and sensory systems, since some species exhibit extreme phenotypes thought to be associated with inhabiting a subterranean environment, including highly reduced eyes. We describe ocular development and examine early ocular protein expression (Pax6 and Shh), comparing between two salamander species representing two phenotypes: the surface dwelling Barton Springs salamander (E. sosorum) and the obligate subterranean Texas blind salamander (E. rathbuni). Between the two species, similarities during the development of ocular tissue (e.g. optic cup and lens vesicle) were observed during embryogenesis. However, during late stage embryogenesis the two species display markedly different patterns of Pax6 localization, which parallel patterns previously reported in a cavefish. A lens vesicle was observed in E. rathbuniembryos at stage 40, yet the lens is absent in adults, suggesting the regression of the lens during ontogeny. We also include adult histology of the surface dwelling San Marcos salamander (E. nana) and note similarities to E. sosorum. Adult E. rathbunilack major histological features associated with vision; however, eye morphology did not differ significantly between E. rathbuniand E. sosorumin early developmental stages, suggesting a combination of underdevelopment and degeneration contribute to the reduced eyes of adult E. rathbuni.

The salamander clade Eurycea from the karst regions of central Texas provides an ideal platform for comparing divergent nervous and sensory systems since some species exhibit extreme phenotypes thought to be associated with inhabiting a subterranean environment, including highly reduced eyes, while others retain an ancestral ocular phenotype appropriate for life above ground. We describe ocular morphology, comparing three salamander species representing two phenotypes—the surface-dwelling Barton Springs salamander (E. sosorum) and San Marcos salamander (E. nana) and the obligate subterranean Texas blind salamander (E. rathbuni) - in terms of structure and size of their eyes. Eyes were examined using confocal microscopy and measurements were made using ImageJ. Statistical analysis of data was carried out using R. We also provide a developmental series and track eye development and immunolocalization of Pax6 in E. sosorum and E. rathbuni. Adult histology of the surface-dwelling San Marcos salamander (E. nana) shows similarities to E. sosorum. The eyes of adults of the epigean species E. nana and E. sosorum appear fully developed with all the histological features of a fully functional eye. In contrast, the eyes of E. rathbuni adults have fewer layers, lack lenses and other features associated with vision as has been reported previously. However, in early developmental stages eye morphology did not differ significantly between E. rathbuni and E. sosorum. Parallel development is observed between the two phenotypes in terms of morphology; however, Pax6 labeling seems to decrease in the latter stages of development in E.rathbuni. We test for immunolabeling of the visual pigment proteins opsin and rhodopsin and observe immunolocalization around photoreceptor disks in E. nana and E. sosorum, but not in the subterranean E. rathbuni. Our results from examining developing salamanders suggest a combination of underdevelopment and degeneration contribute to the reduced eyes of adult E. rathbuni.

Relatively few studies have focused on the evolution and development of divergent nervous systems. The salamander clade (Eurycea) from the karst regions of central Texas provide an ideal platform for comparing divergent nervous and sensory systems, since some species exhibit extreme phenotypes thought to be associated with inhabiting a subterranean environment, including highly reduced eyes. We describe ocular development and examine early ocular protein expression (Pax6 and Shh), comparing between two salamander species representing two phenotypes: the surface dwelling Barton Springs salamander (E. sosorum) and the obligate subterranean Texas blind salamander (E. rathbuni). Between the two species, similarities during the development of ocular tissue (e.g. optic cup and lens vesicle) were observed during embryogenesis. However, during late stage embryogenesis the two species display markedly different patterns of Pax6 localization, which parallel patterns previously reported in a cavefish. A lens vesicle was observed in E. rathbuniembryos at stage 40, yet the lens is absent in adults, suggesting the regression of the lens during ontogeny. We also include adult histology of the surface dwelling San Marcos salamander (E. nana) and note similarities to E. sosorum. Adult E. rathbunilack major histological features associated with vision; however, eye morphology did not differ significantly between E. rathbuniand E. sosorumin early developmental stages, suggesting a combination of underdevelopment and degeneration contribute to the reduced eyes of adult E. rathbuni.

Centrocestus formosanus is a digenetic trematode from Asia that parasitizes multiple hosts and is a concern in the Comal River, Texas, USA, because of its negative effects on the endangered fountain darter Etheostoma fonticola. To determine a practical sampling method to monitor C. formosanus in the Comal River, we evaluated three sampling methods using wild-caught fish, caged fish reared in the laboratory, and cercariometry. Cercariometry detected significant spatial and temporal patterns of cercarial density in river water that were similar with metacercarial intensity in caged fish, but inconsistent with metacercarial intensity in wild-caught fish. Our results also showed a positive correlation between cercarial density in river water and metacercarial intensity in caged fish. Conversely, the relationship was not significant between cercarial density and metacercarial intensity in wild-caught fish. Because cercariometry predicted similar trends with the caged fountain darter sampling method, cercariometry was useful in predicting C. formosanus gill infections, infection rate, and longevity in infected fountain darters. Although trends from cercariometry and caged fish sampling methods were similar, we recommend cercariometry because it was less expensive to use given the amount of sampling effort required and provides trends that can be used to make pro-active management decisions in C. formosanus-infested aquatic ecosystems.