Frogs and their friendly bacteria

This study evaluated factors that affect the symbiotic bacterial communities that develop on frogs' skin.

It is thought that these bacteria can offer the frog resistance to diseases and could potentially be used as a viable treatment for chytridiomycosis disease, which is partly responsible for widespread amphibian population declines in the wild. 

By looking at the diet, environment and housing of tree frogs at Chester Zoo, we found that specific husbandry practices (carotenoid availability) altered the symbiotic bacterial communities, whereas other husbandry practices do not (UV light and calcium). A second part of the study evaluated the effect of various tagging techniques used to identify individuals in the wild and in captivity. Implanting elastomer tags was found to be the method of least impact.

Project detail

This study aimed to assess the impact of current husbandry practices and marking techniques on the symbiotic bacteria found on frogs at Chester Zoo and the University of Manchester. 

Diseases such as chytridiomycosis are causing amphibian population declines in the wild and these symbiotic bacterial communities could potentially be used as a treatment against the fungal pathogen Batrachochytrium dendrobatidis that causes the disease. As using these frog skin bacteria as a probiotic action against chytrid could be heavily affected by factors such as diet, environment and housing, this research evaluated the impact of varying influences on these bacterial communities. 

Red-eyed and Black-eyed tree frogs were either fed a carotenoid-free diet or one high in carotenoids and had their bacterial colonies routinely measured from skin swabs. Growth, body condition, bacterial communities and fecundity were also monitored in 40 frogs exposed to two dietary treatments and varying UV light sources. 

In the second part of the study, two marking methods, routinely used in identifying both wild and zoo individuals were assessed for potential impact; implanted elastomer markers, which are visible beneath transparent or translucent skin, and passive integrated transponder (PIT) tagging, similar to microchipping. Faecal glucocorticoid concentrations, commonly used to assess adrenal activity, and microbial community abundance were measured before and after marking. 

We found that carotenoid availability in captivity affects the symbiotic bacterial communities. Therefore, by gut loading prey items, such as crickets, with carotenoids before feeding them to the frogs, we are encouraging a high abundance of these beneficial bacteria. Boosting baseline UV light provision had no impact on breeding success, growth or symbiotic bacteria, so this has been discontinued. 

When assessing the marking methods, injecting a visible implanted elastomer tag caused fewer changes in the frogs’ skin bacteria than the PIT tags. This is a new finding and further study into this area could discover whether the bacterial changes noted in this study increase the amphibian’s susceptibility to infectious disease.

Project team

Related publications

Antwis, R.E., Garcia, G., Fidgett, A.L., Preziosi, R.F. (2014). Passive integrated transponder (PIT) tagging frogs causes disruption to the cutaneous bacterial community and proliferation of opportunistic fungi. Applied and Environmental Microbiology, 80, 4779-4784.

Antwis, R.E., Haworth, R.L., Engelmoer, D.J.P., Ogilvy, V., Fidgett, A.L., Preziosi, R.F. (2014). Ex situ diet influences the bacterial community associated with the skin of red-eyed tree frogs (Agalychnis callidryas). PLoS ONE, 9.

Michaels, C.J.*, Antwis, R.E.*, Preziosi, R.F. (*joint first authors) (2014). Impact of plant cover on fitness and behavioural traits of captive red-eyed tree frogs (Agalychnis callidryas). PLoS ONE, 9.

Antwis, R.E., Purcell, R., Walker, S.L., Fidgett, A.L., Preziosi, R.F.. (2014) Effects of visible implanted elastomer marking on physiological traits of frogs. Conservation Physiology, 2.

Antwis, R.E., Preziosi, R.F., Fidgett, A.L. (2014). The effect of different UV and calcium provisioning on health and fitness traits of red-eyed tree frogs (Agalychnis callidryas). Journal of Zoo and Aquarium Research, 2, 69-76.

Michaels, C.J., Antwis, R.E., Preziosi, R.F. (2014). Manipulation of the calcium content of insectivore diets through supplementary dusting. Journal of Zoo and Aquarium Research, 2, 77-81.

Key Facts

Carotenoid availability alters the symbiotic bacterial communities on frogs' skin
UV and calcium availability have no effect on growth, breeding or symbiotic bacteria
Implanting elastomer tags impacts skin bacteria less than integrated transponders

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