Description
Gracixalus lumarius is a rhacophorid of medium size with a robust body. Snout vent lengths in one the one available adult female specimen are 36.3 millimeters and adult male ranges are 38.9 - 41.6 millimeters. Its head is wider than long and when viewed dorsally its snout is rounded. When observed from the side its snout gradually shortens with a slight under-bite. The canthus rostralis is subtle and round, while the loreal region is straight, and the interorbital region is convex. Gracixalus lumarius’ oval-shaped nostrils somewhat protrude and lack a lateral flap of skin. Nostrils are marginally closer to the tip of the snout than the eye. Its pupils are horizontal and oval. The tympanum of G. lumarius is about one third of the diameter of its eyes and is rather inconspicuous. It lacks a pineal ocellus, and its skin and forehead are not co-ossified. Its supratympanic fold is not distinct. Its barely discernible rictal gland is connected to its mouth. Males have a vocal sac, two definite oval openings at the base of its jaw, and a baggy gular region (Rowley et al. 2014).

The forelimbs of G. lumarius are relatively robust. Its four fingers vary visibly in length; relative finger lengths are I < II < IV < III. It has relatively wide, well-developed disks with circummarginal grooves at the tip of each finger. The disks are very wide compared to the fingers; the third disk is about 204% the finger width. The fingers have modest dermal fringes, and there is distinct basal webbing between the each forefinger. The subarticular tubercles are round and prominent. The inner metatarsal tubercle is noticeable, while the outer metatarsal tubercle and supernumary tubercles are absent. Males have a prepollex, which may have a distinct nuptial pad on the inner side when males are in breeding condition. Its relative toe lengths are I < II < V < III < IV with conspicuous webbing and dermal fringes between toes (Rowley et al. 2014).

The dorsal surface of its hindlimbs is smooth, but its thighs are coarsely granular. Densely distributed conical tubercles cover the entire dorsum region of the head such as the snout, eyelids, tympanum, and back. Tubercles are more scattered on the dorsum surface of the arms. The fore and hind-limb dorsum surfaces are smooth. The surface of the ventral thighs and abdomen are granular and coarse, while the throat is more finely granular. The limbs lack dermal fringes, tibiotarsal projection, and supracloacal glands (Rowley et al. 2014).

Gracixalus lumarius is distinct from other Southeast Asian rhacophorids due its medium body size, diurnally brown and nocturnally yellow dorsum, pink venter, indistinct tympanum and supratympanic folds, dark gold with reticulating black irises, white conical tubercles present on adult males, and behavior of depositing eggs onto the walls of phytotelm (water bodies within terrestrial plants). In addition, the species displays a daily change in dorsum coloration that is an uncommon characteristic in amphibians (Rowley et al. 2014).

Within the genus Gracixalus, Gracixalus lumarius is distinct from the clade including G. supercornutus and G. quangi based on G. lumarius’ dorsum differs from the typical greenish dorsum and white or yellow venter of other species in its clade. Additionally, the tympanum and supratympanic fold of closely related species in the clade is much more distinct. Its irises are distinct from the clade’s typical irises of bright copper or olive-gold irises with non-uniform black reticulations. Its conical asperities are markedly different from other species’ mostly smooth or only somewhat tuberculate male dorsum. The body size of G. lumarius is typically larger than those of related species. Behavioral variances include depositing eggs on the wall of a phytotelm instead of in a foam nest, typical in Gracixalus (Rowley et al. 2014).

Although Gracixalus lumarius is very similar to Kurixalus ananjevae, both morphologically and (probably) molecularly, K. ananjevae’s smaller body size (32.4 millimeters), grayish white venter, distinct tympanum and supratympanic fold, and male dorsum with irregularly distributed, small tubercles differentiates it from G. lumarius (Rowley et al. 2014).

Gracixalus lumarius also differs from all other Southeast Asian rhacophorids of medium size (34 - 45 millimeter adult snout - vent - length). For example, Kurixalus banaensis has a white venter, distinct tympanum and supratympanic fold, granular dorsum in males, and distinct fringing along forearms and tarsus. Kurixalus odontotarsus’ white venter with black or gray marbling, distinct tympanum and supratympanic fold, present vomerine teeth, and rugose dorsum in males differentiates it from G. lumarius. Gracixalus lumarius differs from both Polypedates leucomystax and P. megacephalus because both those species have white venters, distinct tympanum and supratympanic folds, present vomerine teeth, bright gold irises without black reticulations, smooth dorsum in males, and lay eggs in a foam nest. Rhacophorus bipunctatus is distinct from G. lumarius because it has a yellow venter, distinct supratympanic fold, present vomerine teeth, bright gold irises with limited, non-uniform black reticulations, smooth dorsum in males, and lays eggs in a foam nest. Rhachophorus calcaneus differs because it has green or deep reddish-brown dorsum, yellow venter, distinct tympanum and supratympanic fold, present vomerine teeth, irises with bright red periphery, and smooth dorsum in males. Rhacophorus orlovi differs by having a reddish brown dorsum with dark brown markings, a white to light brown venter, distinct tympanum and supratympanic fold, present vomerine teeth, bright gold irises with limited, non-uniform black reticulations, smooth dorsum in males, and lays eggs in a foam nest. Rhacophorus rhodopus differs because it has a yellowish venter, distinct tympanum and supratympanic folds, present vomerine teeth, bright gold irises with limited, non-uniform black reticulations, smooth dorsum in males, and lays eggs in a foam nest. Rhacophorus spelaeus is distinct due to its light gray venter covered by dark specks, distinct tympanum and supratympanic folds, present vomerine teeth, bright gold or yellowish cream irises with limited, non-uniform black reticulations, and smooth dorsum in males. Rhacophorus robertingeri varies from G. lumarius because of the former’s white, grey or cream venter, distinct tympanum, present vomerine teeth, bright gold or yellowish cream irises with limited, non-uniform black reticulations, smooth dorsum in males, and behavior of laying of eggs in a foam nest. Finally, Theloderma ryabovi differs by having a dorsum with light beige with lilac patterns and black spots, dark a dark gray venter, dark brown irises, and small dorsal asperities in males (Rowley et al. 2014).

In life, the dorsal surface of Gracixalus lumarius is yellowish brown with a dark brown inter-orbital crossbar and a cross-mark on the back that starts between the eyes and continues down the back. Diurnally, its dorsum is brown, while nocturnally it is yellow. This daily color change is an uncommon trait in amphibians. The webbing and toe tips are a pinkish gray. Gracixalus lumarius lacks loreal and tympanic markings. Its flanks are vibrant yellow with some dorsal pink mottling with yellow mottling interspersed ventrally. The throat, chest, belly, and ventral surfaces of the limbs are pink and somewhat paler pink on the chest. Around the vent, its small glands are a creamy white. Its irises are dark gold with evenly distributed thin black reticulations. The periphery of the iris is black and the periphery of the eye is gray. The brightness of dorsal coloration varies over its lifetime (Rowley et al. 2014).

In preservative, the dorsal surface is similar to in life, but the conical tubercles appear more distinct, as they become paler and whiter. The bright pink and yellow colorations fade with the chest and belly becoming pinkish white and the margins of the throat, ventral surfaces of the limbs, hands, and feet (including webbing) becoming a pale brown (Rowley et al. 2014).

Coloration does not dramatically vary in paratypes. In preservative, some specimens were somewhat darker than others. In addition, some had more distinct patterning. All adult males have distinctive, white conical asperites on their dorsum. These asperites, however, vary significantly between individuals. Females and juveniles lack asperites and instead have raised tubercles. Juveniles often lack dorsal markings and bars on limbs and are a uniform, pale tan with a slightly darker canthal stripe (Rowley et al. 2014).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Viet Nam

View distribution map in BerkeleyMapper.

Currently, G. lumarius is only known to reside in montane bamboo and evergreen forests on Mount Ngoc Linh at elevations of more than 1800 meters. When found, the holotype was in a water-filled tree-hole near conspecific eggs along the phyptotelm wall. Scientists found all other specimens away from streams or ponds on arboreal vegetation like montane evergreens or bamboo forests. The distance between the farthest localities, is less than 20 kilometers. Although the species’ distribution is presently unknown, they likely strictly inhabit the high-elevation forests of Mount Ngoc Linh and nearby peaks (Rowley et al. 2014).

Mount Ngoc Linh and its surrounding peaks are characterized by highly endemic fauna. Gracixalus lumraius is one of several frog species found at high elevations (greater than 1700 meters) in this area. Other species found in the area include Leptobrachium ngoclinhense and Theloderma nebulosum; these species appear to be endemic to Ngoc Linh and surrounding peaks as well. This may be due to the peaks’ isolation from other high-elevation forests (Rowley et al. 2014).

Life History, Abundance, Activity, and Special Behaviors
Gracixalus lumarius lays about 130 eggs, usually tightly deposited in the wall of a phytotelm above water. Eggs have two jelly layers and in preservative are a creamy gray and measure about 1.3 millimeters in diameter. In life, their coloration is bluish gray. Gracixalus lumarius’ advertisement call and larvae are unknown (Rowley et al. 2014).

Only approximately 2% of species in the anuran taxa breed in phytotelma. At least nine species in the family Rhacophoridae are obligate phytotelm breeders with free living larvae. These species are currently categorized under the genera Chiromantis, Kurixalus, Nyctixalus, and Theloderma. Although its tadpoles weren’t observed, judging by Gracixalus lumarius’ oviposition over water and relatively small, pigmented ova, it is almost definitely an obligate phytotelm breeder with free-living tadpoles. Phyptotelm breeding behavior is generally thought to have evolved to avoid, predation, competition, or unfavorable abiotic conditions of ancestral waters. However, the limited availability of streams or pools and the high abundance of water-filled tree-holes at elevations about 1800 meters suggest that G. lumarius is simply taking advantage of the most available water source (Rowley et al. 2014).

The distinctive, dorsal white conical asperities of G. lumarius are unique in the family Rhacophoridae. However, similar noticeable asperities appear on the dorsum of males in some species of Afrixalus (Hyperoliidae), Boophis (Mantellidae), and Osteocephalus (Hylidae). Scientists hypothesize that these sexually dimorphic asperities facilitate sex recognition in frogs. Specifically, in Osteocephalus, male display of tuberculate dorsal skin with keratinized spicules occurs only during breeding season. Females on the other hand consistently have clear, smooth skin. Based on this, it appears that the size of the asperities of G. lumarius may be directly correlated with breeding readiness. A male holotype collected in the dry season (April) with distinct nuptial pads and conspecific eggs had the most distinctive asperities, while a male collected during the wet season (July) had no distinct nuptial pads and less conspicuous asperities. Therefore, the asperities are present but less noticeable in the non-breeding season (Rowley et al. 2014).

Trends and Threats
Currently unknown.

Comments
Preliminary analysis of molecular data supports categorization of Gracixalus lumarius in the genus Gracixalus. Gracixalus lumarius forms a clade with G. gracilipes as well as G. quyeti, G. supercornutus, and G. quangi. Gracixalus lumarius has a high molecular differentiation from all other Gracixalus species, with 13.3 - 15.91% uncorrected sequence divergence at the 16S rRNA gene fragment analyzed. This amount of pairwise divergence at the 16S rRNA gene in frogs strongly indicates differentiation at the species level (Rowley et al. 2014).

The scientific name for Gracixalus lumarius is derived from the Latin word, lumarius, meaning of thorns. This refers to the multitude of conical tubercles on the species’ dorsal surface. Gracixalus lumarius’ suggested common name is thorny tree frog, a direct translation of the Vietnamese common name, Êch cây gai (Rowley et al. 2014).

References

Rowley, J. L., Le, D. T. T., Dau, V. Q., Hoang, H. D., Cao, T.T. (2014). ''A striking new species of phytotelm-breeding tree from (Anura: Rhacophoridae) from central Vietnam.'' Zootaxa, 3785(1), 025-037.

Species Account Citation: AmphibiaWeb 2022 Gracixalus lumarius: Thorny Tree Frog <https://amphibiaweb.org/species/8151> University of California, Berkeley, CA, USA. Accessed Dec 28, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 28 Dec 2024.

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