Torrent Tree Frog

Population and Distribution Litoria nannotis was found throughout the Wet Tropics Bioregion, North Qld, from Paluma to Cooktown (Hero & Fickling 1994) at altitudes between 180 and 1300 m (McDonald 1992). The area of occurrence of the species is approximately 9000 km2 (M. Cunningham pers. comm.). Litoria nannotis includes three deeply divergent mitochondrial DNA lineages, distributed from Paluma to Tully R., Tully R. to Lamb Range and Mt. Lewis to Big Tableland (Schneider et al. 1998). Litoria nannotis was first noted to have declined in 1990 (Richards et al. 1993). The species had apparently disappeared from most upland sites south of the Daintree R.. The species occurred at all lowland sites, and at upland sites north of the Daintree R. during summer surveys of 1991-1992. In 1994 it was sighted at several locations over 600m on Mt Father Clancy in February 1998 (Hero et al. in press). Lowland populations surveyed in Tully Gorge appeared to be relatively stable between 1995 and 1998 (Hero et al. in press). At the southern end of its range it was last observed in Mt Spec SF in 1991 (Richards et al. 1993) however adults occurred at a lower-elevation site in a different creek system (Crystal Creek Stone Bridge, 300m) from Jan. 1994 to Sep. 1995 (Hero unpublished data). This species is currently known to have stable populations at lowland sites (Hero et al. 1998, in press; McDonald & Alford 1999).Litoria nannotis is known from Cape Tribulation, Cedar Bay, Crater, Crater Lakes, Daintree, Lumholtz, Millstream, Paluma Range and Wooroonooran NP, Kirrama Range, Lamb Range, Maalan, Mt Baldy, Mt Lewis, Mt Spec, Tully and Windsor Tableland SF, Daintree Timber Reserve (165 Monkhouse) (Tyler 1997), Elizabeth Grant Falls, Millstream Falls, Mt Lee, Seaview Range NP (Wallaman Falls, Sword Ck., Garrawalt Falls), Cardwell Range, Ravenshoe SF (M. Cunningham pers. comm.).Habitat Litoria nannotis is a habitat specialist endemic to the W.T. Bioregion (Williams & Hero 1998; 2001), a stream dwelling/breeding species (Hodgkison and Hero 2001). Litoria nannotis is restricted to rocky stream habitats in rainforest or wet sclerophyll forest where there is fast flowing water, waterfalls and cascades (Liem 1974; McDonald 1992). Unlike most stream-breeding frog species that live in the adjacent forest and use the stream habitat for breeding, the stream is the primary habitat for both male and females throughout the year (Hodgkison & Hero 2001; in press). On several occasions the adults and juveniles were noted to form small aggregations (4 � 6 individuals) amongst large boulders behind waterfalls (Liem 1974; J-M. Hero pers. obs.). Tadpoles are predominantly found in fast flowing sections of stream, in riffles or torrents, adhering to rocks (Richards 1992).

ReproductionGravid females and males with nuptial pads are encountered all year round (Martin & McDonald 1995). Unpigmented eggs 136-216 (1.98-3.4 mm diameter) are laid in gelatinous egg masses under rocks in water (Liem 1974; Hero & Fickling 1996). Liem (1974) described the tadpole and noted that it is one of the few species of tadpole known to exhibit adaptations to torrent environments of Australia, such as a streamlined body shape, large suctorial mouthparts and a muscular tail. Richards (1992) also provided information on the tadpoles of the L. nannotis group.FeedingAdults feed indiscriminately on both aquatic and terrestrial invertebrates (Hodgkinson and Hero in press). Their principal diet includes: Dipteran and Odonate (adults and larvae), Coleoptera, Hemiptera, Blattodea, Hymenoptera and Diplopoda (Hodgkinson and Hero in review).Invasive speciesFeral pigs are a potential cause of riparian habitat damage and adult frog mortality (Richards et al. 1993). The activity of feral pigs has been recorded to have increased over the period 1989-1992 in an area previously inhabited by L. nannotis (Richards et al. 1993). There is very little research, however, into the impact of feral pigs on native frog populations (Richards et al. 1993).MovementsLiem (1974) observed large numbers of females residing near a stream and considered Litoria nannotis to be a true stream-dwelling anuran, unlikely to venture far from the stream. Hodgkison and Hero (2001) found that the species displayed distinctly different nocturnal and diurnal behaviour. During the day, nearly all frogs were restricted to the stream environment where they sheltered in small refuges behind waterfalls or wedged between rocks in the stream. On a small number of occasions individuals were located basking in splash zones beside waterfalls. At night frog activity increased substantially and frogs were located in exposed positions within the stream and some ventured away from the stream, amongst stream side vegetation. Frogs did not venture further than 15m from the stream and always returned before dawn.

Reason for decline unknown. Richards et al. (1993) reject drought, floods, habitat destruction or pollution by pesticides, inorganic ions or heavy metals. The habitat of the species in the Wet Tropics has been protected since 1988, therefore habitat destruction is no longer a threat (McDonald & Alford 1999). Current research is examining the possibility that disease, such as a viral infection or chytrid fungus, may have contributed to the decline of this species (Berger et al. 1999).

Unusually for frogs, the torrent tree frog is active during the day as well as at night. It does, however, remain close to the protective shelter of the stream during the day, only venturing into more exposed positions in the surrounding vegetation at night (8). In contrast to most stream-breeding frog species that live in adjacent forests, the stream is the primary habitat for both males and females throughout the year, with adults and juveniles noted on several occasions to form small aggregations (four to six individuals) amongst large boulders. Gravid females and males with nuptial pads are found all year round, and it is thought that breeding is possible at any time of the year. Un-pigmented eggs are laid in gelatinous egg masses under rocks in water (1). Adult torrent tree frogs are opportunists with a generalist diet, feeding on both aquatic and terrestrial invertebrates (8).

A recovery plan for this species has been developed (10). As the cause of its decline is uncertain the recovery plan focuses on protection of remaining populations and their habitat, population monitoring, and research into its ecology and the disease. Indeed, unless the determinants of this decline are accurately identified and appropriately dealt with, the future of this species cannot be safeguarded.

The torrent tree frog is a moderately large, robust species of Australian frog, which at first glance possesses only the typical olive-green skin characteristic of many frog species. On closer inspection, however, it can be distinguished by the extensive dark mottling found across the back and an attractive metallic blue sheen spanning the sides of the body. Additionally, the underbelly is white or cream, the armpits and the groin flesh coloured, and the throat brown. The skin on the back and underbelly has a granular surface; certain individuals possessing small warts scattered across their back. Finger and toe discs are large, with fully webbed toes but only basal webbing on the fingers (4). Males have well developed nuptial pads with small spines on their thumbs and chests so they can cling to females during breeding and avoid being swept off by the turbulent waters of their habitat. Males lack a vocal sac, and the mating call has been described as a slow growl-like sound that is difficult to hear above the sound of flowing water (5).

The torrent tree frog is a stream dwelling species, inhabiting areas of rainforest where there is fast-flowing water, cascades and waterfalls at altitudes of between 180 – 1,300 m above sea level (6). Normally found on boulders near waterfalls, the torrent tree frog is occasionally seen amongst vegetation next to streams (7).

Litoria nannotis was formerly found throughout the Wet Tropics Bioregion of north Queensland, from Paluma to Cooktown, but is now absent from most upland sites (4).

Classified as Endangered (EN A2ae) on the IUCN Red List 2004 (1), and as Endangered on both the Queensland Nature Conservation Act 1992 and the Commonwealth Endangered Species Protection Act 1992 (3).

The reason for the decline of this frog is most likely due to the disease caused by the amphibian chytrid fungus (Batrachochytrium dendrobatidis) (9). Habitat destruction poses no threat, as the Wet Tropics Heritage Area of Queensland that the torrent tree frog inhabits has been protected and undisturbed since 1988 (1) (7). The effects of drought, floods, and pollution have also been ruled out as contributors to the decline (1).

The Australian waterfall frog or torrent treefrog (Ranoidea nannotis) is a species of tree frog native to Far North Queensland, Australia. The common name "waterfall frog" is indicative of its habitat of moist, rocky streams, and is often found along waterfalls within its range.