Malabar Tree Toad

Pedostibes tuberculosus is a narrow and slender-bodied toad with an adult snout-to-vent length ranging from 35.0 - 47.2 millimeters. It has a flat head with no cephalic ridges and a short and pointed snout. Its eyes are large relative to the size of its head with horizontally-compressed, diamond shaped pupils. The tympanum is very small, but externally visible. Also visible are its short, rounded parotoid glands. As one of its common names suggests, P. tuberculosus has a warty skin texture, but the warts are more distinct on its dorsum. Eight presacral vertebrae are present in addition to dorsolateral folds and a bony sternum. Pedostibes tuberculosus has short and broadly expanded sacral diapophyses, characteristic of its arboreal lifestyle. Its limbs are relatively slender with distinctive digit webbing (partial webbing of fingers and complete webbing of toes). The tips of the digits are widely expanded to spatulate discs with squared anterior ends (also characteristic of its arboreal lifestyle). Tarsal folds are absent. The relative length for the fingers and toes are as follows: 3 > 4 > 2 > 1 and 4 > 5 > 3 > 2 > 1, respectively (Chandramouli and Amarasinghe 2016).Pedostibes tuberculosus tadpoles of Gosner stage 21 have dorsolaterally compressed, transparent bodies with a narrow head and distinct oral disc. The eyes are miniscule in size and the yolk sac in the abdomen is large. Tail musculature and vent tube are distinctly visible within the transparent tail fin. By stage 27, the body of the tadpole becomes dorsoventrally compressed. The eyes migrate anteriorly on the body and its sucker becomes more ventral in position. The ventral side of the body remains transparent and distinct limb buds can be seen at the junction of the body. The tail fin is still present. At stage 41, the body of the tadpole reverts to being dorsolaterally compressed with enlarged eyes. The length and width of the tail become reduced while the mouth region becomes rounded and the hindlimbs finally emerge out of the body. By stage 42, the eyes grow larger and round, the mouth becomes more circular with a dorsolaterally positioned oral disc and the forelimbs are finally visible within the skin sac while the hindlimbs are almost completely grown. The tail becomes rounded and tapered. At stage 43 the beginnings of a snout and canthus rostralis become apparent, while the forelimbs and hindlimbs are completely formed with distinct fingers and toes. By stage 44, the snout and canthus rostralis become distinct, and the tail is further reduced. Finally, by stage 46 the tail of the tadpole is completely resorbed into the body and metamorphosis is complete (Dinesh and Radhakrishnan 2013).While there is not a single common divide among P. tuberculosus and similar species, it may be distinguished from similar species such as Bufoides kempi (previously known as Pedostibes kempi) in having a visible tympanum (as opposed to concealed) and from both Rentapia hosii (previously known as Pedostibes hosii) and Rentapia rugosa by the absence of a tarsal fold (instead of the presence of a well-defined tarsal fold). Additionally, P. tuberculosus and R. hosii have eight presacral vertebrae while other similar species such as Bufoides meghalayanus only have seven. Other osteological differences between P. tuberculosus and R. hosii and B. meghalayanus include the presence of a bony sternum (as opposed to cartilaginous) as well as the presence of long and narrow frontoparietal skull elements in P. tuberculosus versus a broader posterior end in Rentapia and B. meghalayanus. Lastly, the terminal phalanges in both the front and hind digits are widely expanded to truncate discs in P. tuberculosus, yet they are relatively narrower in R. hosii, and with basal expansions in B. meghalayanus (Chandramouli and Amarasinghe 2016).Live adult specimens tend to be brownish gray in color, with darker flanks and white coloration underneath complete with black spotting. Live individuals also have a white band that runs from below the eye to the front armpit as well as a second white band in the lumbar region. Preserved adult specimens vary slightly in that they appear to have a pale brown dorsum with dark and white marbling on the sides as well as marbling on ventral surfaces (Chandramouli and Amarasinghe 2016). At stage 21, live P. tuberculosus tadpoles are transparent and lack any color apart from the visible, yellow yolk sac and the dark eyes. At stage 27 the dorsum transitions to a brownish color, but the tadpoles remain predominantly transparent up to stage 41 when their dorsum is entirely a brownish color. At stage 42, the entire body is brownish and the eyes are black. By stage 43, the tadpoles still appear brownish, but also appear to have two lateral silvery yellow stripes on their dorsum. At stage 44 the stripes expand to the head. At stage 45, the tadpoles retain their brownish color with the silvery-yellow edges of their dorsum, but also display blackish-brown coloration on their sides (Dinesh and Radhakrishnan 2013).The species authority is: Günther, A. (1875). "The Secretary on Additions to the Menagerie." Proceedings of the Zoological Society of London 43(1): 565-633. The genus, Pedostibes, is part of the family Bufonidae, and was previously believed contains six species: P. everetti, P. hosii, P. kempi, P. maculatus, P. rugosus, and P. tuberculosus. However, Pedostibes, was found to be a largely polyphyletic clade due to genetic and/or morphological differences in several related tree toads in Southeast Asia. Because of this, it was proposed in 2016 that P. tuberculosus become a sole species in a monophyletic clade, and that three tree toads found in Southeast Asia (P. rugosus, P. hosii, and P. everetti) be categorized into a new genus, Rentapia while P. kempi be moved to the genus Bufoides (Chandramouli and Amarasinghe 2016, Chen et al. 2016).Based on Bayesian inference and Maximum Likelihood analyses of 3,375 bases pairs combined from the mitochondrial gene 16S and nuclear genes CXCR4 and NCX1, P. tuberculosus was determined to be a monophyletic clade sister to a clade formed by species in the genera Adenomus, Xanthophyrne, and Duttaphyrnus. The species, rugosus and hosii, formerly in the genus Pedostibes were revealed to be more distantly related and thus placed in the genus Rentapia (Chen et al. 2016). Two more species formerly in Pedostibes (kempi and evertti) were determined based on morphology to belong to the genus Bufoides and Rentapia respectively (Chandramouli and Amarasinghe 2016). The etymology of the species epithet “tuberculosus” can be split into “tubercle,” the English word for a small rounded projection, and “-osis” denoting a condition. This name is in reference to the warty skin texture of the species. The common name “Malabar tree toad” came from the Old-World term for the northern part of Kerala India and was coined by Dr. Albert Günther (Biju et al. 2004).

Pedostibes tuberculosus is endemic to fragmented parts of western India. According to the IUCN, there are only four known extant distributions, located in either forests or inland wetlands in India’s Western Ghats. The fragmented distribution of the species, which is no larger than 5,200 square kilometers of India, has prompted the IUCN to list the species as "Endangered" (Biju et al. 2004).The lowest distributions of the species are in the Neyyar Wildlife Refuge, which overlaps the Kerala and Tamil Nadou border of southern India. The second largest fragment of the species occurs in Val Parai’s surrounding areas, in the Parambikulam Tiger Reserve as well as parts of Manoboly and Indira Gandhi National Park. A small southern distribution is located in Karuvarakundu, adjacent to Silent Valley National Park. Two western distributions occur in the Cotigo Wildlife Sanctuary in Goa, as well as the Chanduli Wildlife Sanctuary near the Konya River and Shivaji Sadar Lake (Biju et al. 2004).Suitable habitats for P. tuberculosus are subtropical lowlands, montanes, and any permanent natural freshwater waterways (i.e. streams, creeks, rivers) including waterfalls. Since the species can be found in either lowland or moist montane ecosystems, the elevational range of this tree toad is between 300 meters to 1,800 meters (Biju et al. 2004). They are considered to be semi-arboreal because their habitats consist of freshwater systems and many evergreen forests (Biju et al. 2004). Using the observations of a close relative in southern India, Adenomus kelaartii (Kelaart’s Dwarf Toad), it is assumed that P. tuberculosus also commonly dwells in leaf litter along stream banks and trees (Chan et al. 2016).

Little is known about the natural history of P. tuberculosus except for its distribution and mating calls in India. After its discovery by Günther in 1875, the species was not examined and studied again until the late 20th century. The population sizes of P. tuberculosus are still unknown. However, the species is considered rare and endangered, due to its fragmented populations (Biju et al. 2004).Parts of the reproductive mode for P. tuberculosus are still unknown. Herpetologists K.P. Dinesh and C. Radhakrishnan (2013) discovered that males participate in typical mating calls, usually before the monsoon season in early summer. Males gather near bodies of freshwater and advertise calls to females. Advertisement calls last from 3 – 7 seconds and contain 14 – 37 pulse groups at an average dominant frequency of 3782 +/- 30.58 Hz that sound like “Shchirrrrrr shirrrr shirrr shirr…” The calls were described as “single and chorus, and antiphonal”, with the choral calls being “synchronous and initiated by the individual.” Pulse groups contained 3 – 11 pulses but usually consisted of 4 – 8 pulses. The first two pulse groups tended to be longer, 145.63 +/- 21.72 ms, with longer inter-pulse intervals at 117.69 +/- 22.09 ms. The pulse frequency ranged from 12.87 – 44.67 Hz and pulse groups lasted from 61 – 134 ms (Gururaja et al. 2006).Amplecting pairs were not observed during breeding (Dinesh and Radhakrishna 2013), but since P. tuberculosus is part of the larger order, Bufonidae (true toads), which are New World Frogs (Neobatrachia), they are assumed to partake in more derived characteristics of amplexus, most likely axillary (Chan et al. 2016). The complex life cycle of P. tuberculosus begins in the streams and rivers of western India, where adults breed and deposit their eggs in stagnant water. According to Chan et al. (2016), adults lay about 1,100 translucent eggs per clutch, which are then suspended just beneath the surface of the water. Each egg is about 1.1 mm in diameter. Pedostibes tuberculosus larvae indirectly develop, spending most of their larval stages in aquatic environments until they metamorphose into terrestrial adults (Biju et al. 2004). While developing underwater, the tadpoles feed mainly through their sucker on the bottom of rivers and streams (Dinesh and Radhakrishna 2013). The diet of the tadpole has yet to be observed and recorded, so it is assumed to be herbivorous, a general anuran trait in tadpoles. After becoming fully fledged terrestrial adults, the species spends much of their lives in the forest, where their cryptic morphology blends in with the surrounding leaf litter (Dinesh and Radhakrishna 2013). Other characteristics of their reproductive mode such as egg-laying, hatch time, or parental care have yet to be discovered.

According to the IUCN, the general population trend of P. tuberculosus is “declining” due to the species’ extensive fragmentation in India. However, P. tuberculosus is currently protected in the following areas in India: Neyyar Wildlife Refuge, Parambikulam Tiger Reserve, Indira Gandhi National Park, Silent Valley National Park, Cotigo Wildlife Sanctuary, and Chandoli Wildlife Sanctuary. It has an IUCN Red List status of "Endangered" (Biju et al. 2004).

The Malabar tree toad (Pedostibes tuberculosus), or warty Asian tree toad, is a species of toad found in forests along the Western Ghats of great Karnataka or Deccan. It is a small species and is found in wet tree hollows or leaf bases containing water. It is the only species in the monotypic genus Pedostibes, also known as Asian tree toads.