The Bibron's toadlet or brown toadlet (Pseudophryne bibronii) is a species of Australian ground-dwelling frog that, although having declined over much of its range, is widespread through most of New South Wales, Victoria, south-eastern Queensland, and eastern South Australia, including Kangaroo Island. Bibron's toadlet settles in a wide variety of habitats within these region but they mainly reside in dry forests, woodland, shrubland, grassland, coastal swamps, heathland, and sub-alpine areas. They deposit their eggs in leaf litters during the flooding season, which is essential for the proper development of the egg. This species has high sexual dimorphism within the species and utilizes chemosignals to attract potential mates.
Taxonomy
The genus Pseudophryne encapsulates 14 different species of frogs localized to Australia. These frogs are morphologically similar to small bufonid frogs not localized to Australia. The first known nomenclature of the Pseudophryne genus dates back to 1835 with the characterization of the Bombinator australis. The types and localities of different Pseudophryne species has been debated, P. bibronni being localized to South Eastern Australia and other Pseudophryne localized to different regions in Australia.
Description
This species is variable and may represent more than one species. It grows to about 30mm in length and is brown, grey, or black above, often with scattered red spots. It is normally strongly marbled black and white on the ventral surface, however in some areas this marbling can be faint. There is always an orange, red or yellow patch in the armpits. This patch varies from yellow to orange between sites. At the Jervis Bay region this patch is always yellow, this may be a result of hybridization with the Dendy's toadlet (Pseudophryne dendyi) which has a strong yellow patch in the armpits. There is also a yellow/orange patch or raised bump on the back of the thigh. Its fingers and toes do not show any webbing nor do they contain any discs. The species has horizontal pupils and the iris displays a gold coloring.
The species shows high sexual dimorphism in terms of size. Females are 14% longer than male toadlets and 15% heavier than male toadlets. This is due to the hypothesized longer growing period of female members of the species compared to male members of the species. The cause of female longevity is unknown but it is speculated that it is due to decreased predation risk and increased lifetime expectancy.
Diet and predation
The diet of this species is very similar to the diet of another Australian toadlet, Pseudophryne coriacea. They primarily feed on small invertebrates present in leaf litter, such as small ants and greenflys. However, there seems to be no selection in the type of prey that this species will consume. They will consume any arthropod that becomes available to them in the leaf litter present in their habitat. Small black ants are the most common source of food for this species. This species also produces pumiliotoxins (PTXs) that deter predators through their diet. While the mechanism of this acquisition is unknown, consumption of certain alkaloids in their diet allows the toadlet to produce PTXs that deter predators like snakes. These toxins are similar to the compounds secreted by the Poison Dart frogs from South America.
Because of the toxic nature of PTXs, snake species avoid feeding on these frogs. The only real known predator of the P. Bibronii is Limnodynastes peronii, also known as the two striped grass frog. Bones of the Bibron's toadlet have been found in the gut content of two striped grass frogs in the Wallingat State Forest in New South Wales, Australia.
Behaviour
This species inhabits areas that are likely to be flooded after rain. This can be anything from coastal swamps, creeks, temporary ponds/roadside ditches in forest, cleared land, heathland and even sub-alpine areas. When threatened, the Bibron's toadlet will often lie on its back, unresponsive, pretending to be dead. This performance had been reported to last for up to an hour.
Reproduction
The males attract the females by making a grating "cre-eek" noise from a concealed area, in mud, under rocks, or within damp leaf litter. Breeding season begins after the heavy rains during the Australian autumn months of March, April, and May, and proceeds for four to five months after. Most breeding and mating occurs at night and can occur at cold temperatures.