Biology of Fijian ground frog (Platymantis vitianus): Breeding and Reproductive Endocrinology

A project undertaken at the Faculty of Science and Technology, Biology Division University of the South Pacific, Fiji, and implemented by Edward Narayan

Synopsis

Despite being listed as endangered on the IUCN (World Conservation Union) red list (Anon, 2006) and intense conservation efforts on its behalf, little is known about the reproductive biology of the Fijian ground frog (Platymantis vitianus). Breeding is important for species survival and hormones are the essence of reproduction. The certain aspects of captive breeding and reproductive endocrinology of P. vitianus is studied so that the basic reproductive patterns can be understood.

The breeding of P. vitianus is being studied in a purpose built outdoor enclosure based at the University of the South Pacific (USP), Fiji Islands as an insurance policy while invasive species eradication work is on-going on Viwa Island (one of the five remaining mongoose [Herpestes javanicus] free island habitats of P. vitianus). Primary focus of captive breeding is to establish an ex-situ captive management strategy, egg-embryo management and monitoring the health status of P. vitianus. Under the ex-situ captive management strategy, the ex-situ micro-environmental preferences and the association between the ex-situ climate and the activity (nocturnal behavior and movement) of P. vitianus are tested.

The reproductive endocrinology of P. vitianus is being studied in captivity at the USP and a sub-population of frogs present on Viwa Island. The reproductive (testosterone, progesterone and oestradiol) and stress (corticosterone) hormone metabolites present in the urine samples of P. vitianus will be assayed using enzyme immunoassay (EIA). The approach involves monitoring the reproductive and stress hormones in captive frogs through both breeding and non-breeding periods, comparing measures obtained with those from in situ populations and correlating findings with the observed reproductive status of individuals. Measures of hormone metabolites are made from voided urine, meaning that the technique has the advantage of being totally non-invasive. The knowledge gained would underpin improved captive management protocols that are likely to increase breeding success than what is currently achievable with the potential then of providing animals for re-establishing in the wild.

A captive management protocol for P. vitianus will be presented for zoological parks and specific individuals with aim to preserve P. vitianus in captivity as an insurance policy against a possible extinction crisis.

Background

Currently, Fijian ground frog Platymantis vitianus is listed as endangered (EN) under the Red List Category, EN B1 ab (v), because its extent of occurrence is less than 5,000 km2, its distribution is severely fragmented, and the frog numbers are considered to be declining in the wild. They have been extirpated from several Fijian Islands, e.g. Viti Levu.

Historical records of P. vitianus have been made from Viti Levu, Vanua Levu, Taveuni, Koro, Gau, Kadavu and Viwa but they are now only found on four mongoose-free islands (Taveuni, Gau, Viwa and Ovalau) and a remnant population in Vanua Levu. It has been suggested that cane toads Chaunus marinus (formerly Bufo marinus) and P. vitianus’s compete for food, which raises great concern regarding the long term population viability of this species.

On Viwa, work on distribution patterns and population studies of P. vitianus are continuing together with strategic eradication project to eradicate the Invasive Alien Species (IAS) off the natural habitats. Despite its dramatic decrease little data exist on P. vitianus including conservation and next to nothing is known about its ecology and effects of invasive species on its abundance and distribution. As a result, knowledge of the reproductive biology of P. vitianus is limited.

The establishment of a captive population of P. vitianus in captivity can be viewed as an insurance policy while invasive species eradication work is on-going on Viwa Island (one of the five remaining mongoose [Herpestes javanicus] free island habitats of P. vitianus). Furthermore, reproductive hormone monitoring would significantly improve understanding of the endocrinology and reproductive physiology of P. vitianus.

References

Narayan, E., K. Christi and C. Morley (2008). Ecology and reproduction of the endangered Fijian Ground Frog
Platymantis vitianus - Fiji Islands. The South Pacific Journal of Natural Science, 26, 28-32.

Narayan, E, K. Christi and C. Morley (2007a). Captive management of newly hatched Fijian ground frog Platymantis vitianus froglets: lessons learnt from an unanticipated invertebrate predator invasion, Suva, Fiji. Conservation Evidence, 4, 58-60.

Narayan, E, K. Christi and C. Morley (2007b). Improvement in ex-situ egg hatchability of Fijian ground from Platymantis vitianus by laboratory incubation of egg masses, University of the South Pacific, Suva, Fiji. Conservation Evidence, 4, 25-27.

Narayan, E, K. Christi and C. Morley (2007c). Provision of egg-laying sites for captive breeding of the endangered Fijian ground frog Platymantis vitianus, University of the South Pacific, Suva, Fiji. Conservation Evidence, 4, 61-65.

 

Figure 1. The outdoor enclosure constructed at the USP for captive breeding of the Fijian ground frog.

Figure 2. A female (svl= 75mm) Fijian ground frog sitting within natural refugia in the outdoor enclosure.

 

Figure 3. Newly hatched froglet (svl= 8.5mm) of Fijian ground frog placed on FJ 5 cents coin.

 

Figure 4. Fijian ground frog nest with fertile eggs (n=50) discovered in captivity. Number of eggs per clutch = 50. Average diameter of each egg = 9.5 mm.

 

Figure 5. Edward Narayan working on EIAs at the Landcare Research Lab, Auckland NZ