Epinephrine, norepinephrine and dopamine concentrations in amphibian brain

Tagging frogs with passive integrated transponders causes disruption of the cutaneous bacterial community and proliferation of opportunistic fungi

Symbiotic bacterial communities play a key role in protecting amphibians from infectious diseases including chytridiomycosis, caused by the pathogenic fungus Batrachochytrium dendrobatidis. Events that lead to the disruption of the bacterial community may have implications for the susceptibility of amphibians to such diseases. Amphibians are often marked both in the wild and in captivity for a variety of reasons, and although existing literature indicates that marking techniques have few negative effects, the response of cutaneous microbial communities has not yet been investigated. Here we determine the effects of passive integrated transponder (PIT) tagging on culturable cutaneous microbial communities of captive Morelet's tree frogs (Agalychnis moreletii) and assess the isolated bacterial strains for anti-B. dendrobatidis activity in vitro. We find that PIT tagging causes a major disruption to the bacterial community associated with the skin of frogs (∼12-fold increase in abundance), as well as a concurrent proliferation in resident fungi (up to ∼200-fold increase). Handling also caused a disruption the bacterial community, although to a lesser extent than PIT tagging. However, the effects of both tagging and handling were temporary, and after 2 weeks, the bacterial communities were similar to their original compositions. We also identify two bacterial strains that inhibit B. dendrobatidis, one of which increased in abundance on PIT-tagged frogs at 1 day postmarking, while the other was unaffected. These results show that PIT tagging has previously unobserved consequences for cutaneous microbial communities of frogs and may be particularly relevant for studies that intend to use PIT tagging to identify individuals involved in trials to develop probiotic treatments.

Social signals increase monoamine levels in the tegmentum of juvenile Mexican spadefoot toads (Spea multiplicata)

Monoamines are important neuromodulators that respond to social cues and that can, in turn, modify social responses. Yet we know very little about the ontogeny of monoaminergic systems and whether they contribute to the development of social behavior. Anurans are an excellent model for studying the development of social behavior because one of its primary components, phonotaxis, is expressed early in life. To examine the effect of social signals on monoamines early in ontogeny, we presented juvenile Mexican spadefoot toads (Spea multiplicata) with a male mating call or no sound and measured norepinephrine, epinephrine, dopamine, serotonin, and a serotonin metabolite, across the brain using high-pressure liquid chromatography. Our results demonstrate that adult-like monoaminergic systems are in place shortly after metamorphosis. Perhaps more interestingly, we found that mating calls increased the level of monoamines in the juvenile tegmentum, a midbrain region involved in sensory-motor integration and that contributes to brain arousal and attention. We saw no such increase in the auditory midbrain or in forebrain regions. We suggest that changes in monoamine levels in the juvenile tegmentum may reflect the effects of social signals on arousal state and could contribute to context-dependent modulation of social behavior.