Description
Myersiohyla chamaeleo is a medium-sized robust treefrog, with males reaching a snout-vent length of 44.6 - 49.6 mm, and females 46.0 - 56.9 mm. The head is slightly depressed dorsally and almost as wide as it is long, corresponding to about a third of the total body length. The snout is rounded in dorsal view and truncated in lateral view, with a rounded canthus rostralis and a concave loreal region. The lip is straight and the nostrils are slightly protuberant, directed dorsolaterally and located posteriorly to the anterior margin of the lower jaw. The eyes are large, and the distance between the orbits is shorter than the eyelid. The tympanum is rounded, with a diameter approximately equal to half of the eye diameter. A thin supratympanic fold is present, from the posterior margin of the eye to the posterior margin of the arm insertion. Males have a single evident vocal sac below the throat, as well as an evident gland in the mental area. The cloacal opening is positioned at the upper level of the thighs and directed posteroventrally, surrounded by some whitish tubercles. The skin on the dorsal surfaces is smooth, while in the ventral surfaces is granular (Faivovich et al. 2013).

The arms are robust, well-developed, and lacking a row of tubercles on the ventrolateral edge of the forearm. Fingers are long and slender, with relative lengths of 1 < 2 < 4 < 3 and prominent ovoid apical disks. Webbing is poorly developed on the fingers and exclusive to the outer ones, with a formula of II 2⅓–3½ III 3–3 IV. Subarticular tubercles are prominent and mostly rounded, except for the distal tubercle of finger IV, which is ovoid. Tubercles on the palm of the hand are large, and variable in shape on the base of fingers III, IV, and V. On the metacarpus, the outer tubercle is round and bifid but small and barely visible, while the inner tubercle is large and elliptical. An enlarged and semicircular prepollex is present at the base of the Finger I. In males, this prepollex is covered by two nuptial pads, composed of dark epidermal projections (Faivovich et al. 2013).

The hind limbs are slender, with the length of the tibia being approximately half of the snout-vent length, and the length of the foot about a third of the snout-vent length. There are no calcar projections or tarsal folds. Along the tarsus, there is a subtle dermal ridge. The toes are relatively short, with a relative length of 1 < 2 < 3 ≈ 5 < 4, and also with apical disks (smaller than those of the fingers). Subarticular tubercles are large and rounded. On the sole of the foot, the inner metatarsal tubercle is large and elliptical, while the outer one is rounded. Webbing is extensive between the toes, with a formula of I 2–2+ II 1+–2½ III 1+–2½ IV 2–1+ V (Faivovich et al. 2013).

DIAGNOSIS:

Considering the external morphology of adult individuals, Myersiohyla chamaeleo differs from its closest relatives mainly by its unique coloration pattern in life (dorsum varying in shades of light brown to greenish and punctuated by many irregularly distributed stellated melanophores, and orangish flanks). Such a pattern distinguish this species from Myersiohyla aromatica, Myersiohyla inparquesi, Myersiohyla loveridgei, Myersiohyla neblinaria and Nesorohyla kanaima (a former member of the genus Myersiohyla), which have a dorsum uniformly brown colored or marbled in shades of cooper and darker brown, often with a dark dorsal line, dark brown transversal bars on limbs, and flanks mottled or covered with whitish dots; as well as from Myersiohyla liliae, which also has a greenish dorsum but with fewer and more homogeneously distributed stellated melanophores. The presence of two nuptial pads in males and the absence of a row of tubercles on the ventrolateral edge of the forearms also distinguish Myersiohyla chamaeleo from Myersiohyla inparquesi, Myersiohyla loveridgei, Myersiohyla liliae and Myersiohyla neblinaria, which possesses a single nuptial pad and such tubercles. Other characteristics of Myersiohyla chamaeleo such as the robust body, a prominent prepollex, and males with a minimum snout-vent length of 44.6 mm also distinguish it from Nesorohyla kanaima, which has a slender body, a reduced prepollex, and smaller males (with a maximum of 37.8 mm of snout-vent length). Considering these species, Myersiohyla neblinaria is the only species known to co-occur with Myersiohyla chamaeleo (Faivovich et al. 2013, Pinheiro et al. 2019).

COLORATION:

Dorsal surfaces of living individuals when active (during the night) are punctuated by many contrasting and irregularly distributed stellated melanophores over a background varying among individuals in shades of reddish and greenish brown, olive or tan. Flanks and the dorsal and ventral surfaces of the thighs are orange colored. Ventrally, the throat is pale green, while the arms, chest, and abdomen are translucent. The upper eyelid is outlined by a light yellow line. The iris has a black ground color and is covered by an intricate metallic copper reticulum. When the species is inactive, during the day, the background color of the dorsum and flanks changes dramatically to light green, tan, or yellow, and the iris becomes bright coppery, golden, or pale bronze (Faivovich et al. 2013).

In preservative, the dorsal background acquires a light cream to tan coloration, uniformly covered by a variable number of two types of chromatophores, the larger ones brown are stellate with a creamy center, and the small ones are round and glossy. In some cases, these chromatophores cover the dorsal surface to the extent that specimens appear brown, or are sparser on limbs, which acquires a more uniform creamy coloration. Ventral surfaces are immaculate and paler than the dorsum (Faivovich et al. 2013).

VARIATION:

Apart from the most notable variation in coloration patterns and sexual dimorphism in body size stated above, the macroscopic evidence of mental glands can vary among individuals, and the two nuptial pads can be either separate or medially coalescent. Additionally, the subarticular tubercle of finger IV may have a median notch, and there is variation in the webbing formula in the foot, which is I (1½–2)–(2–2+) II (1+–1½)–(2+–3-) III (1–1½)–(2–2½) IV (2–2½)–(1+–1½) V (Faivovich et al. 2013).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Venezuela

View distribution map in BerkeleyMapper.

Myersiohyla chamaeleo is only known from the highlands of the Neblina Mountain Range, on the border between southern Venezuela (Amazonas state) and northwestern Brazil (Amazonas state). Although it has been formally reported only on the Venezuelan side of this mountain range, its occurrence on the Brazilian side is highly anticipated. It occurs throughout the mosaic of typical montane environments, including open seasonally flooded savannas, rocky outcrops, and forestal formations. Individuals have been recorded from 1450 to 2100 m above sea level (Faivovich et al. 2013).

Life History, Abundance, Activity, and Special Behaviors
Due to its remote and inaccessible montane habitat, much of the natural history of Myersiohyla chamaeleo remains poorly known and limited to the information provided in its original description. According to available information, this nocturnal species can be recorded perched on vegetation or rocks along stream margins during its active period. During the day, it rests hidden among leaves of plants that form rosettes, such as bromeliads (Faivovich et al. 2013). Males are known to call at night while perched along streams, and a chorus of three males was also observed around a deep pool. The species' call is characterized by short "beep"-like single notes, which vary in duration between 20 – 50 milliseconds. These notes can be pulsated or non-pulsated. The calls are emitted at a consistent rate of 1 to 2 notes per second, and they have a fundamental frequency ranging from 950 to 1100 Hz. All specimens used for the species description, which were collected in February, were found in breeding condition. This was evident from the well-developed nuptial pads observed in males and the gravid females (Faivovich et al. 2013).

Larva
At Gosner stage 25, tadpoles of Myersiohyla chamaeleo have a remarkable wide range in total length (from 23 to 80 mm), suggesting that they have a long lifespan. They have a globular body with a rounded snout dorsally and sloping laterally. The oval-shaped nostrils have a small fleshy projection. The eyes are positioned dorsolaterally and are not visible in ventral view. The spiracle is positioned on the left of the body, fused with it in its medial portion. The vent tube is on the right of the body and longer than wide. The fin starts at the body-tail junction and tapers posteriorly, ending in a pointed and transparent tip. The oral disc is ventral and not emarginated, although it has a posterior fold. This disc consists of a single row of marginal papillae and tooth rows formula varying among individuals from 4/7 to 6/11, with short gaps (~0.1 mm). The jaw sheaths are pigmented, with the upper one narrow and M-shaped, and the lower one V-shaped and with larger pointed serrations (Faivovich et al. 2013).

Considering the larvae of closely related species, Myersiohyla chamaeleo can be distinguished by possessing a reduced labial tooth row formula (maximum of 6/11) when compared to Myersiohyla aromatica and Myersiohyla neblinaria (minimum of 9/10). On the other hand, the labial tooth row formula of Myersiohyla chamaeleo is larger when compared to Nesorohyla kanaima (maximum of 2/4). Compared to Myersiohyla inparquesi, Myersiohyla chamaeleo differs by having a longer fin and a single row of marginal papillae on the oral disc (fin not reaching the base of the tail and three rows of marginal papillae) (Faivovich et al., 2013).

In life, tadpoles exhibit a uniform dark brown body coloration, with lighter shades present on the snout, oral region, and spiracle. Additionally, there are distinct lighter marks visible on the dorsum. Some rows of whitish neuromasts of variable length are present below and posterior to the eyes, on the head, and dorsolaterally on the body. The tail can display two different color patterns: it may be bicolored, with a dark brown medial portion and lighter brown outer portions, or it can be uniformly dark brown (Faivovich et al. 2013).

These tadpoles are typically found swimming in black water streams and their associated pools. The observed color variation among individuals is attributed to adaptations to their distinct habitats. Bicolored tadpoles are often recorded in fast-flowing streams located in gallery forests, while uniformly colored tadpoles are more commonly found in exposed lentic pools. The coloration of the tail also changes throughout the ontogenetic stages, with younger tadpoles exhibiting lighter tails (Faivovich et al. 2013).

Trends and Threats
Despite limited data on population sizes and temporal trends of Myersiohyla chamaeleo, and the species being highly constrained to a single montane region (Faivovich et al. 2013), its occurrence in a remote and inaccessible area currently encompassed by protected areas on both the Venezuelan and Brazilian sides limits many of the direct threats to its survival and viability. The increasing impacts of climate change on species typical of colder montane environments, along with the emergence of globally impactful pathogens, are considered current threats to the species (Señaris and Rojas-Runjaic, 2022).

Possible reasons for amphibian decline

Subtle changes to necessary specialized habitat
Disease
Climate change, increased UVB or increased sensitivity to it, etc.

Comments

PHYLOGENETIC RELATIONSHIPS:

As of 2023, only three out of the six known species of Myersiohyla have been included in a broader phylogenetic context, which greatly hinders our understanding of the species' relationships within this genus. Maximum Parsimony, Bayesian Inference and Maximum Likelihood analyses based on the information of mitochondrial and nuclear DNA have consistently shown the genus Myersiohyla as one of the earliest diverging lineages within the treefrog Cophomantini tribe radiation, and the sister taxa of the monotypic genus Nesorohyla. Within the genus, Myersiohyla chamaeleo is found to be sister taxa of Myersiohyla liliae, and these two species are sisters to Myersiohyla neblinaria (Faivovich et al. 2013, Pinheiro et al. 2019).

ETYMOLOGY:

The remarkable ability of Myersiohyla chamaeleo to change its color across the day inspired its naming. The species epithet, “chamaeleo,” is derived from the Latin word “chamaeleon” and the Greek word “chamaileōn,” which also inspired the naming of the chameleon genus, a group of lizards widely known for their ability to undergo rapid and drastic changes in coloration (Faivovich et al. 2013).

OTHER INTERESTING INFORMATION:

Specimens of Myersiohyla chamaeleo were initially collected from its remote habitat between 1984 - 1985. However, it took several years of investigation and analysis from various data sources before the species was formally described in 2013 (Faivovich et al. 2013). This significant time lapse highlights the value and relevance of information sheltered within scientific collections over time.

References
Faivovich J, McDiarmid RW, and Myers CW. (2013). Two new species of Myersiohyla (Anura: Hylidae) from Cerro de la Neblina, Venezuela, with comments on other species of the genus. American Museum Novitates 3792, 1–63 [link].

Pinheiro PD, Kok PJR, Noonan BP, Means B, Haddad CFB, and Faivovich J. (2019). A new genus of Cophomantini, with comments on the taxonomic status of Boana liliae (Anura: Hylidae). Zoological Journal of the Linnean Society 185, 226–245 [link].

Señaris JC and Rojas-Runjaic FJM. 2022. Myersiohyla neblinaria (amended version of 2020 assessment). The IUCN Red List of Threatened Species 2022: e.T87735921A198667433. https://dx.doi.org/10.2305/IUCN.UK.2022-1.RLTS.T87735921A198667433.en. Accessed in June 2023

Species Account Citation: AmphibiaWeb 2023 Myersiohyla chamaeleo <https://amphibiaweb.org/species/8109> University of California, Berkeley, CA, USA. Accessed Dec 3, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 3 Dec 2024.

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