Assa wollumbin Mahony, Hines, Mahony, Moses, Catalano, Myers & Donnellan, 2021
Mount Wollumbin Hip-pocket Frog
|Species Description: Mahony MJ, Hines HB, Mahony SV, Moses B, Catalano SR, Myers S, & Donnellan SC. (2021). A new hip-pocket frog from mid-eastern Australia (Anura: Myobatrachidae: Assa). Zootaxa, 5057(4), 451–486.
With the exception that Assa wollumbin females are smaller than their sister taxon, A. darlingtoni, the two species are morphologically indistinguishable. However, they can be distinguished based on their range with the former only being found on Wollumbin (Mount Warning), New South Wales, Australia and the latter found on the surrounding Tweed caldera region and in four other localities ranging from the Conondale range in Queensland to the Dorrigo Plateau in New South Wales. It is possible their ranges overlap in the Tweed Volcanic region, however, if they do, those populations have not been identified as of 2023. Unambiguous differentiation requires molecular analysis (Mahony et al. 2021).
In life, Assa wollumbin individuals have highly variable dorsal and ventral coloration and patterning. Variation in the base color of the dorsal surface of the head, body, and limbs include light cream with an orange tinge, reddish brown, darker brown, and brown-black. Many individuals with lighter coloration also feature distinct darker brown to black markings, which often occur as two anterior direct v-shaped darker chevrons on the upper and lower dorsum. Other individuals have a broad, darker, mid-dorsal stripe with distinct broad lighter cream and black margins. Most individuals also have a faint interorbital bar that does not extend up onto the orbit. The face may be the same color as the flanks, or a darker hue, and may be immaculate or have ill-defined black mottling. Some individuals have a darker marking on the canthus rostralis between the anterior margins of the eye to the nare. Most individuals have a dark vertical bar beneath the eye to the maxilla, occasionally with a cream lined edge; this may be obscured in darker individuals. Most individuals have a distinct delineation across the dorsal-lateral margin with a ridge featuring highly contrasting coloration between the dorsum and flanks. There is often a thin, lighter colored line on the ventral side of the ridge. The upper lateral surface is dark brown to black, diffusing into a lighter brown towards the ventral surface. The ventral surface including the groin, limbs, hands and feet, posterior surface of the thigh, and chin are all the same color within an individual, but the color varies significantly across individuals. Some examples are darker brown-black with small lighter colored granules that are prominent on the edges of the mandibles, and light burnt-yellow with darker flecks (Mahony et al. 2021).
Females are slightly larger than males, however, the most distinctive form of sexual dimorphism is the occurrence of hip-pockets in the male, one on each side. The lateral pouch opening is up to 3 mm long and inclined posteriorly at a slight angle on the upper dorso-lateral margin. It is continuous with the dermis and extends forward into the lymph sac beneath the lateral and ventral surfaces. The pouches on each side are independent and do not join (Mahony et al. 2021).
Distribution and Habitat
Life History, Abundance, Activity, and Special Behaviors
Males call by expanding the skin below their chin, but their vocal sacs are not loose. Their advertisement calls have a duration of about 1.2 s, and is comprised of a series of fully modulated repeated notes of the same duration separated by slightly longer inter-note intervals. The number of notes range from 5 to 14. The first few notes are very slightly lower in amplitude than the subsequent notes. The call is broadband with a relatively high dominant frequency ranging from 3593 to 3992 Hz; there is no frequency modulation across the call or within notes. Call duration, inter-call duration, and note repetition rate are significantly negatively correlated with temperature; the number of notes in the call is positively correlated with temperature. Synchronous calling among males has been observed (Mahony et al. 2021).
The courtship call is made by the male when a female approaches closely, during amplexus, and sometimes when males are in very close proximity. It is often produced independently, but it may also precede the advertisement call by a short time interval less than 0.2 s. The courtship call has a short duration and is produced at the same dominant frequency as the advertisement call. The courtship call’s individual pulses cannot be distinguished. There is amplitude modulation with a rapid rise to a plateau prior to a rapid decay, and no frequency modulation (Mahony et al. 2021).
Males establish a calling position, often in secluded areas beneath dense leaf litter, and females are attracted to the male who does not move away from the calling position. After a female has been attracted, the male quickly moves to an inguinal amplexus embrace. The female then moves, with the male attached, to the oviposition site which is up to 20 cm from the male’s calling position — this represents the preferred oviposition site and indicates that the male was not calling from a microhabitat that the female preferred. Oviposition often occurs beneath leaf litter, in a location that is moist but not in standing water. A small clutch of large eggs is placed closely together; there is adherence between the eggs and usually at least two layers of eggs. Eggs have a thick and transparent jelly coat, and embryonic development proceeds for at least seven days (Mahony et al. 2021).
The male displays interesting parental care behavior. The male stays close to the egg clutch during embryonic development, about two or three body lengths away, under the leaf litter in a position where the clutch is in view. Sometimes, the male moves to the clutch and over it. At hatching, the male moves over the clutch, and the eggs’ jelly coat liquifies. The embryos wriggle vigorously during hatching with their head arched downward. The male slowly rotates within the clutch, opening a crevice between his flanks and legs by holding his legs slightly away from the body. The newly hatched tadpoles wriggle up the crevice into the male’s hip pouches. The male does not assist tadpoles into the pouch other than displaying this rotating behavior. There are usually an equal number of tadpoles that end up in the left and right pouch. While carrying tadpoles, males have a rounded and robust body habitus, but their pouch openings are not more distinct than in non-carrying males. Metamorphosis occurs in the pouches, and the young emerge without any prompting or assistance by the male. Males can be found carrying two groups of tadpoles at different developmental stages, showing that males can incorporate separate clutches that were fertilized at different times. During mating, females do not inspect males to see if he is already holding tadpoles in his pouches, and males carrying young can mate a second time during one breeding season (Mahony et al. 2021).
Trends and Threats
Laboratory observations have shown that Assa are highly susceptible to chytridiomycosis, but there are no reports of declines in Assa populations consistent with this threat. One possible explanation is that since Assa inhabit terrestrial leaf litter, they do not use shared bodies of water with other frogs and the likelihood of chytrid spore transmission is low (Mahony et al. 2021).
Land clearing is not a likely threat to A. wollumbin; there is good evidence that they are dependent on native forests, but all of their habitat (Wollumbin) is located within Wollumbin National Park, which is a protected area (Mahony et al. 2021).
Climate change is the most significant threat to Assa, since it is restricted to cool, moist montane forest areas that are predicted to warm in the coming decades. Model investigations with projected climate change predict that the species will remain stable until around 2040 - 2050, after which declines are expected at different rates based on different model scenarios. The most severe projection predicts Assa will become extinct in the wild by 2095 (Mahony et al. 2021).
The recommended conservation status for A. wollumbinby the authors of its description is “Critically Endangered” following IUCN Red List criteria (Mahony et al. 2021).
Possible reasons for amphibian decline
Climate change, increased UVB or increased sensitivity to it, etc.
PHYLOGENETIC RELATIONSHIPS:Assa wollumbin was split from A. darlingtonia in 2021 after a population genetics study showed significant genetic structure. The analyses included Bayesian Inference and Maximum likelihood analyses on ND2 Mitochondrial DNA, and principal coordinates analysis, Bayesian clustering, and Maximum likelihood analysis of single nucleotide polymorphisms. These analyses showed, with strong support, that two main clades are apparent: A. wollumbin and its sister taxon A. darlingtonia (Mahony et al. 2021).
The species epithet, “wollumbin” refers to the distribution of the frog. Given by the First Nation Traditional Custodians for the Tweed, Wollumbin (also known as Mount Warning) is the name of the mountain that is the central volcanic cone of the Tweed volcano region, and the only place where A. wollumbin is known to be found (Mahony et al. 2021).
OTHER INTERESTING INFORMATION:
Molecular data indicates that there has likely been long-term reproductive isolation between A. wollumbin and A. darlingtoni, with the former found in the central Wollumbin volcanic cone and the latter found on the surrounding caldera and slopes. The caldera is about 32 km in diameter with Wollumbin in the center. The natural barrier to gene flow between the two species is unknown and it is possible they may come in contact in areas that have yet to be sampled (Mahony et al. 2021).
Originally submitted by: Justin Lee (2023-06-06)
Description by: Justin Lee (updated 2023-06-06)
Distribution by: Justin Lee (updated 2023-06-06)
Life history by: Justin Lee (updated 2023-06-06)
Larva by: Justin Lee (updated 2023-06-06)
Trends and threats by: Justin Lee (updated 2023-06-06)
Comments by: Justin Lee (updated 2023-06-06)
Edited by: Ann T. Chang (2023-06-06)
Species Account Citation: AmphibiaWeb 2023 Assa wollumbin: Mount Wollumbin Hip-pocket Frog <https://amphibiaweb.org/species/9452> University of California, Berkeley, CA, USA. Accessed Feb 22, 2024.
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Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 22 Feb 2024.
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