Fascinating toxic frogs

I'm moving away from my usual topic today by looking at a species that is neither British nor invertebrate - the green and black poison arrow frog Dendrobates auratus. Poison arrow/dart frogs (they have several non-scientific names) are familiar to many people because of their toxicity and bright colours, but what is actually known about them?

Dendrobates auratus showing green and black colouration.

Well, first of all, although there are around 175 species of arrow/dart frogs (all in the family Dendrobatidae), only 3 are known to be used to coat blowpipe darts with poison, and none of these are in the genus Dendrobates. So, we know that the common name is not an accurate description - good start! Now onto a little background info.

Found in humid lowland and submontane forest and secondary vegetation up to about 1,200m altitude, D. auratus is native to Central America (Costa Rica, Nicaragua & Panama) and NW Colombia and, although many dendrobatids (like many amphibians worldwide) are rare and/or decreasing, this species is not currently threatened in the wild, being rated as of 'Least Concern' by the IUCN. There are also some feral populations in Oahu, Hawaii following a release of around 200 frogs in 1932 as an attempt to control non-native insects - these bred successfully and their descendents persist in the island's mountains and valleys (McKeown 1996). It is a highly variable species with at least 15 distinct colour forms known in the wild - as well as the typical green shown above, there is yellow, largely black, largely brown and the rare blue which is known from the Pacific side of Panama, but threatened with extinction due to clearance for agriculture, which fragments the habitat, though the species as a whole can live around humans (e.g. in parks, gardens and rubbish dumps (Heselhaus 1992, Ostrowski 2009). Being small (c. 20-40mm depending on form) and brightly coloured, tt is a popular pet among keepers of exotic herpetofauna and over-collection may be an issue, although there is a thriving captive breeding trade supplying much of the demand.

It is a semi-arboreal species, conducting much of its activity in trees up to some tens of metres above the ground but descending to the ground to travel between trees as it can not jump between them. Climbing is aided by pads at the ends of its toes (visible in the photo above). Females lay clutches of 3-13 eggs on leaf-litter which the male guards (Heselhaus 1992); they hatch after about two weeks and the male carries tadpoles to stagnant water in a tree-hole, leaf axil of a bromeliad, or small ground-level pool (van Wijngaarden 1990). The tadpoles feed on protozoans and rotifers, metamorphosing after 39-89 days, with sexual maturity being reached in 6-15 months, and a life-span of at least 6 years in captivity (Zimmermann & Zimmermann 1994). Females compete for males, attempting to monopolise them and being known to destroy the eggs of rivals (Summers 1989). If you would like to hear a brief recording of their call, go here.

Although not the most poisonous of dendrobatids, it is toxic enough to make a human unwell with skin glands producing an alkaloid derived from the ants that form much of the wild diet (Caldwell 1996). This reduces the risk of being attacked by predators such as theraphosid spiders AKA tarantulas (Gray et al. 2010), although some of the development of toxicity (e.g. in different popualtions, and captive-bred individuals fed a wild diet) are not fully understood.

So, to finish, why did I decide to look at this species? Well, it is a charismatic species and makes a change from my long run of invertebrate posts. I am also a member of Hampshire Conservation Volunteers - our logo is a frog so we adopted a D. auratus (now named 'Den Bates') at Marwell Wildlife and I wanted to know more about it - if you like this idea, the yellow and black D. leucomelas is still available for adoption...

Mate-guarding in Dendrobates auratus

References

Caldwell, J.P. (1996). The evolution of myrmecophagy and its correlates in poison frogs (Family Dendrobatidae). Journal of Zoology (London) 240(1): 75-101.
Gray, H.M., Kaiser, H. & Green, D.M. (2010). Does alkaloid sequestration protect the green poison frog,
Dendrobates auratus, from predator attacks? Salamandra 46(4): 235–238.
Heselhaus, R. (1992). Poison-arrow Frogs: Their Natural History and Care in Captivity. Blandford, London.
McKeown, S. (1996). A Field Guide to Reptiles and Amphibians in the Hawaiian Islands. Diamond Head Publishing, Los Osos, California.
Ostrowski, T. (2009). Dendrobates auratus.  [accessed 13/08/2012].
Summers, K. (1989). Sexual selection and intra-female competition in the green poison-dart frog, Dendrobates auratus. Animal Behaviour 37(5): 797-805.
van Wijngaarden, R. (1990). Enkele klimaatgegevens en waarnemingen in de biotoop van de gifkikkers Phyllobates vittatus en Dendrobates auratus. Lacerta 48(5): 147-154.
Zimmermann, E. & Zimmermann, H. 1994. Reproductive strategies, breeding, and conservation of tropical frogs: dart-poison frogs and Malagasy poison frogs. In: J.B. Murphy, K. Adler and J.T. Collins (eds). Captive Management and Conservation of Amphibians and Reptiles. Society for the Study of Amphibians and Reptiles, Ithaca (New York). Contributions to Herpetology Volume 11, pp. 255-266.