Pseudophryne Toxins

Pseudophryne covacevichae

When most people think of poisonous frogs, images of brightly coloured frogs of the South American jungles spring to mind. Whilst these attractive frogs do take all the fame, Australia's Pseudophryne genus despite being less toxic, does contain equally charming and brightly coloured poisonous frogs.

Like the dart frogs of South America the many species in the Pseudophryne genus exhibit bright warning colours as a predator deterrent, a trait know as aposematism. In the case of these Toadlets (Pseudophryne genus) these colours alert the prey to the poisons excreted on the skin (Santos et al. 2003).

Two main toxins have been found on the skin of Pseudophyrne frogs. Pseudophrynamines (PSs) and Pumiliotoxins (PTX) (Smith et al. 2002). Pumiliotoxins are found on the skin of many frog around the world most notably the Phyllobates (South American Poison Dart Frogs) and the Mantilla genus of Madagascar (Santos et al. 2003). The toxin is obtained by the frogs by consuming specific invertebrates in particular beetles. Other animals including some birds have been known to also acquire this toxin from beetles (Daly et al. 2002).

Pseudophryne corroboree

The PSs are unique to the Pseudophryne genus. Studies comparing the toxins present on the skin of wild caught specimens and their captive bred young has shown that the toxin is biosynthesised by the frog instead of being sequestered. Captive animals had a controlled diet constraining any toxin excretions to those that are biosynthesised (Smith et al. 2002). PTXs are preferentially excreted by the frogs probably because sequestering the toxin may be metabolically less taxing, preventing the need to expend energy producing PSs toxin (Smith et al. 2002). 


Refernces

Daly, J.W., Kaneko, T., Wilham, J., Garraffo, H.M., Spande, T.F., Espinosa, A. and Donnelly, M.A. (2002). “Bioactive alkaloids of frog skin: combinatorial bioprospecting reveals that pumiliotoxins have an arthropod source.”, Proceedings of the National Academy of Sciences, Vol: 99, No: 22, pp: 13996-14001.

Santos, J. C., Coloma, L. A., & Cannatella, D. C. (2003). Multiple, recurring origins of aposematism and diet specialization in poison frogs. Proceedings of the National Academy of Sciences of the United States of America, Vol: 100, No: 22, pp: 12792–12797.

Smith, B.P., Tyler, M.J., Kaneko, T., Garraffo, H.M., Spande, T.F. and Daly, J.W.(2002). Evidence for biosynthesis of pseudophrynamine alkaloids by an Australian myobatrachid frog (Pseudophryne) and for sequestration of dietary pumiliotoxins.”, Journal of natural products, Vol: 65, No: 4, pp: 439-447.

Images

P.covacevichae by Nick Weigner

P.corroboree http://www.australiangeographic.com.au/blogs/australian-endangered-species/2014/05/endangered-southern-corroboree-frog ,22/3/16.