Columbia spotted frogs (Rana luteiventris) have characteristic skin microbiota that may be shaped by cutaneous skin peptides and the environment.

Global amphibian declines due to the fungal pathogen Batrachochytrium dendrobatidis (Bd) have led to questions about how amphibians defend themselves against skin diseases. A total of two amphibian defense mechanisms are antimicrobial peptides (AMPs), a component of amphibian innate immune defense and symbiotic skin bacteria, which can act in synergy. We characterized components of these factors in four populations of Columbia spotted frogs (Rana luteiventris) to investigate their role in disease defense. We surveyed the ability of their AMPs to inhibit Bd, skin bacterial community composition, skin metabolite profiles and presence and intensity of Bd infection. We found that AMPs from R. luteiventris inhibited Bd in bioassays, but inhibition did not correlate with Bd intensity on frogs. R. luteiventris had two prevalent and abundant core bacteria: Rhizobacter and Chryseobacterium. Rhizobacter relative abundance was negatively correlated with AMP's ability to inhibit Bd, but was not associated with Bd status itself. There was no relationship between metabolites and Bd. Bacterial communities and Bd differ by location, which suggests a strong environmental influence. R. luteiventris are dominated by consistent core bacteria, but also house transient bacteria that are site specific. Our emergent hypothesis is that host control and environmental factors shape the microbiota on R. luteiventris.

Gas exchange in the insect tracheal system.

The role of the insect tracheal system in gas exchange during cyclic ventilation is investigated using mathematical models. Three models are presented, one to describe the important elements of gas exchange during each of the three phases of cyclic ventilation. The effects of normobaric hypoxia on gas exchange are then examined, first assuming the initial parameter values set for the tracheal system and, second, assuming conditions of tracheal hypertrophy produced by an increase in the cross-sectional area of the tubes in the tracheal system. An increase in tracheal tube cross-sectional area is an important adaptation to normobaric hypoxia, but only if the tracheae themselves are the primary sites of resistance to gas exchange. Under conditions where the spiracles are the sites of resistance to gas exchange, volume expansion of the tracheae, not an increased cross-sectional area per se, is the important adaptation to normobaric hypoxia.