Wood Frog Lithobates Sylvaticus Research Articles

Linking aquatic and terrestrial environments: can beaver canals serve as movement corridors for pond‐breeding amphibians?

AbstractBeaversCastor canadensisare well known as ecosystem engineers for creating ponds by damming streams. However, in wetlands with soft substrates and shallow banks, beavers often dig networks of foraging canals, the ecological effects of which have received little study. We examined how canals are used by pond‐breeding amphibians during dispersal and migration between aquatic and terrestrial habitat, focusing on the wood frogLithobates sylvaticus, inMiquelonLakeProvincialPark,Alberta,Canada. In late summer, the number of emigrating young‐of‐the‐year (YOY) wood frogs encountered at drift fences in riparian zones was highest at beaver canals and declined with distance from canal edges. On visual encounter surveys along the pond perimeter,YOYand adult wood frogs were up to nine times more abundant on beaver canals than along shorelines not modified by beavers. Beaver canals provided habitat for adult wood frogs and also functioned as movement corridors for emigratingYOYfrogs, with possible implications for survival to maturity, meta‐population dynamics and nutrient transfer between aquatic and terrestrial environments.

Fish Influences on Amphibian Presence and Abundance in Prairie and Parkland Landscapes of Minnesota, USA

Many amphibian populations are declining, and increased understanding of the drivers of amphibian presence and abundance will help in their conservation. In 2005 and 2006 we estimated relative abundance of larvae of two common amphibian taxa, Tiger Salamanders (Ambystoma tigrinum) and ranid tadpoles (Northern Leopard Frog Lithobates pipiens and Wood Frog Lithobates sylvaticus), in 75 shallow lakes in prairie and parkland areas in Minnesota. We used a two-step procedure in which we first modeled presence-absence with data from all lakes and then modeled abundance only in lakes where the amphibian taxa were present. For the two amphibian taxa, a generalized linear mixed effects model was used to examine the effects of dynamic factors like fish abundance and static (timeframe of study) variables like fish community type, depth, and adjacent land cover. Fish variables had the greatest influence but differed for the presence and abundance models. Salamander and tadpole presence was inversely correlated to the abundance of benthivorous fish, while salamander abundance was best explained by total fish abundance and tadpole abundance by fish community type. We did not detect influences of land cover types on the amphibian taxa we surveyed. Our findings are important because they complement previous studies documenting that negative correlations with fish extend beyond piscivores to include both planktivores and benthivores. Hydrological changes in our study landscape (e.g., installation of drainage networks, wetland consolidation) associated with agriculture and other land uses have likely increased the distribution and abundance of fish populations, thus dampening amphibian breeding success.

Host invasion by Batrachochytrium dendrobatidis: fungal and epidermal ultrastructure in model anurans

The chytridiomycete fungus Batrachochytrium dendrobatidis (Bd) colonizes mouthparts of amphibian larvae and superficial epidermis of post-metamorphic amphibians, causing the disease chytridiomycosis. Fungal growth within host cells has been documented by light and transmission electron microscopy; however, entry of the fungus into host cells has not. Our objective was to document how Bd enters host cells in the wood frog Lithobates sylvaticus, a species at high mortality risk for chytridiomycosis, and the bullfrog L. catesbeianus, a species at low mortality risk for chytridiomycosis. We inoculated frogs and documented infection with transmission electron microscopy. Zoospores encysted on the skin surface and produced morphologically similar germination tubes in both host species that penetrated host cell membranes and enabled transfer of zoospore contents into host cells. Documenting fungal and epidermal ultrastructure during host invasion furthers our understanding of Bd development and the pathogenesis of chytridiomycosis.