Guatemala Spikethumb frog
© 2013 Néstor Ruballo (1 of 7)
Plectrohyla guatemalensis has a moderately robust body, with thick skin on the dorsum that is covered with numerous, closely-packed round tubercles. The skin is smooth on the ventral surfaces of forelimbs, thighs and shanks, but granular on the throat, belly, posterior, and posteroventral surfaces of thighs. The vent is bordered on the sides with vertical dermal folds, located at the mid-level of the thighs, and directed posteroventally (Duellman and Campbell 1992).
The upper arms and forearms are robust in males, but slender in females. There is no axillary membranes, but both males and females have a row of small tubercles on the ventrolateral surface of the forearm. The hands are large with a low, flat, and bifud palmar tubercle. The fingers are slender with narrow dermal fringes and large round discs. The disc on the third finger is larger than the diameter of the eye. The moderately large subarticular tubercles are subconical, and the large supernumerary tubercles are around, but only found on the proximal segments. The relative length of the fingers is 1 < 2 < 4 < 3 and the webbing formula for the outer fingers is II2 – 3 ½ III3 - 2-IV. The males of this species lack nuptial pads, but have massive bifid prepollices, which are extra rudimentary digits on preaxial side of thumb, with a cleft dividing it in two. There is no webbing between the first and second finger, but the outer fingers are about one-fourth webbed (Duellman and Campbell 1992)
The hind limbs are moderately short and robust. The tibia is about about 50% of the snout vent length and slightly longer than the foot. The distal three-fourths of the tarsus has an inner fold, but no outer fold is present. There is no outer metatarsal tubercle but the inner metatarsal tubercle is flat, elliptical, and visible from the dorsal view. The toes end in discs that are slightly smaller than the fingers. There are dermal fringes from the inner metatarsal tubercle to the discs of the first toe. The relative length of the toes is 1 < 2 < 3 < 4 < 5. The toes are all about four-fifths webbed with a formula of I1 - 2II1 - 2III1 - 2IV2 - 1V. The moderately large subarticular tubercles are round and the small supernumerary tubercles are only found on the proximal segments (Duellman and Campbell 1992). These frogs are not fossorial, so they have no specialized digits for burrowing (Oliveira et al. 2017).
Three tadpoles of P. guatemalensis at developmental stages 29, 30, and 33, had body lengths of 17.9 mm, 17.2 mm, and 18.0 mm, and total lengths of 44.5 mm, 45.1 mm, and 48.8 mm, respectively. Tadpoles have slightly depressed bodies that are as wide as they are deep. In the dorsal and profile view, the snout of the tadpole is bluntly rounded. The nostrils are pointed dorsolaterally, about halfway between the eye and the tip of the snout. Plectrohyla guatemalensis tadpoles have small, widely separated eyes, which are pointed dorsolaterally. The oral disc is large and ventral without any lateral folds. The disc is completely bordered by a single row of small papillae, and a second row of papillae is present midventrally. Another row of large, discrete papillae is present, medially to the fringe-like papillae on the upper and lower lips. There are also large papillae on the lateral side of the disc. The jaw sheaths of tadpoles are fairly robust, and have short, blunt serrations. The broadly arched upper beak has short lateral line processes, while the lower beak is broadly V-shaped. There are two upper rows of labial teeth and three lower rows, all of about equal lengths, and the ridges which support the second upper row of teeth are discontinuous and are adjoined at the center of the roof the mouth. The spiracle is sinistral, directed posterodorsally, and located around the midway point of the body on the midline. The anal tube is dextral and short. In the dorsal view, the posterior edge of the body is gradually rounded. The caudal musculature is robust and tapers gradually to a point just before the tip of the acutely rounded tail. The dorsal fin does not extend onto the body, and at the mid-tail is the same depth as the tail musculature. The ventral fin depth is shallower than the dorsal fin (Duellman and Campbell 1992).
The bifid prepollical spine distinguishes this genus of frog from others. In general, P. guatemalensis can be differentiated from other members of the genus by having closely-packed dorsal tubercles (Duellman and Campbell 1992). More specifically, P. acanthodes, P. exquisita, P. hartwegi, and P. teuchestes are larger than P. guatemalensis, and do not have red-brown markings on the dorsum; all have a green or gray dorsums (Duellman 2001). Plectrohyla acanthodes also has scattered conical tubercles (Duellman and Campbell 1992), P. hartwegi has vertical, cream-colored bars on the anterior and posterior of the thighs, P. exquisita has yellow coloring in the axilla and groin areas, and P. teuchestes has a smooth dorsum. Plectrohyla pokomchi is of a similar size to P. guatemalensis, but P. pokomchi has a bright green dorsum with dark green tubercles and red webbing, distinguishing it from P. guatemalensis (Duellman 2001). Plectrohyla guatemalensis is very similar to P. calvata, which was split from P. guatemalensis in 2017, but can be distinguished by the latter having a dark dorsum that lacks distinct markings with few tubercles in females and a generally smoother surface in males. Male P. calvata also have somewhat smaller prepollical process (McCrain 2017).
Tadpoles of P. guatemalensis can be distinguished based on mouth parts and nostril position. More specifically, having two rows of small fringing papillae on the lips and approximately equal length labial rows differentiates P. guatemalensis from P. dasypus, P. avia, P. acanthodes, P. quecchi, P. sagorum, P. tecunumani, and P. glandulosa. From P. hartwegi and P. teuchestes the focal species differs in having a smaller oral disc that lacks suction structures. From P. matudia and P. ixil, the focal species can be identified by having an upper jaw sheath with blunt or approximately equal serrations. And lastly, from P. pokomchi, P. guatemalensis differs because its nostrils are halfway between the eyes and the snout (Duellman and Campbell 1992). The nostril placement also differentiates P. guatemalensis from P. chryses, which has nostrils that are closer to the snout tip than eyes (Kaplan et al. 2016)
The dorsum of P. guatemalensis, in life, is dark green in coloration and can include reddish brown spots. On the thighs and webbing, the posterior surfaces are tan to dull gray with the ventral surfaces being white. The iris is deep bronze. In preservative, dorsal surfaces are a duller, darker or paler brown with uneven and unpredictable dark brown spots. The ventral surface is cream and the posterior sides and flanks of the thighs range from brown to grey (Duellman and Campbell 1992).
In preservative, the larvae of P. guatemalensis appear brown on the dorsum and grey on the ventrum. The caudal musculature appears brown with pale flecks, and the fins are transparent (Duellman and Campbell 1992).
The coloration and texture of the dorsum varies considerably in life. It can appear with or without spots or flecks on its dorsum, and the spots can vary from reddish brown to brown (Duellman and Campbell 1992).
Distribution and Habitat
Country distribution from AmphibiaWeb's database: El Salvador, Guatemala, Honduras, Mexico
Life History, Abundance, Activity, and Special Behaviors
Although male P. guatemalensis do not have vocal slits or sac, males of the species do call from concealed places such as between rocks, arboreal bromeliads, and underground root systems near streams. The single low-pitched call is described as sounding like a grunt and is one low-pitched note that is repeated in two-minute intervals. These calls can be heard from distances of 5 meters in smaller, quiet, montane streams, but are unlikely to be heard in large, fast moving streams. Several males can call from the same location at a time (McCranie et al. 1987).
Amplexus is axillary with the male’s arms almost completely encircling the female’s body. The male presses his swollen upper lip on the top of the female and may rub his teeth on her head. The purpose of male swollen lips has not been tested, but the rubbing on the female head appears similar to the use of mental gland by salamanders to initiate ovulation (Duellman and Campbell 1992).
Plectrohyla guatemalensis is oviparous and it is believed eggs are laid at the bottom of shallow streams, in the roots of shrubs and trees. A clutch of presumably P. guatemalensis eggs was found that contained 240 eggs and with each egg measuring 3.4 mm in diameter (Duellman and Campbell 1992, McCranie et al. 1987).
Plectrohyla guatemalensis tadpoles slowly develop in cold mountain streams (Duellman and Campbell 1992).
Plectrohyla guatemalensis can be found in sympatry with Plectrohyla euthysanotu (Duellman and Campbell 1992).
Trends and Threats
They are currently protected in El Salvador within Montecristo National Park (Greenbaum and Komar 2005) and their range includes in protected parks or forests in Honduras, Guatemala, and Mexico. However, because of the threat of chytridiomycosis a captive-breeding program may be needed for the species survival (Santos-Barrera and Canseco-Márquez 2010).
Possible reasons for amphibian decline
General habitat alteration and loss
Although, genetic analysis of the species has been limited by tissue sample availability, studies have compared genetic sequences of P. guatemalensis to P. chrysopleura, P. grlandulosa, and P. matudai (by Duellman et al. 2016) and to P. arborescandens, P. bistincta, P. calfhula, P. chryses, P. cyclada, P. grandulosa, P. matudai, P. mykter, and P. aff. thorectes (by Kaplan et al. 2016). These studies were consistent in the results of P. guatemalensis being is sister to Plectrohyla matudai.
Plectrohyla guatemalensis was long thought to be a composite species and several species, including P. calvata, P. pokomchi and P. tecunumani, have all been split from it (Duellman and Campbell 1992, McCraine 2017).
Plectrohyla guatemalensis gets its genus name from the Greek words “plektron”, which means “spur”, and “Hylas”, a character from Greek mythology (Duellman et al. 2016)
The species epithet, “guatemalensis” comes from the country it was originally found in, Guatemala (Brocchi 1887).
Plectrohyla guatemalensis was initially placed in the genus as Plectrohyla but later the same year assigned to a new genus, Cauphias to accommodate a species thought to be closely related. Plectrohyla guatemalensis was assigned to Hyla guatemalensis by Boulenger in 1882. However in 1941, Hartweg argued that it should be placed in Plectrohyla guatemalensis because the terminal phalanges were not truly T-shaped terminal phalanges (Hartweg 1941).
Boulenger, G.A. (1882). Catalogue of the Batrachia Salientia s. Ecaudata in the Collection of the British Museum, Ed. 2. Taylor and Francis, London.
Brocchi, P. (1877). ''Description d’un nouveau genre de phaneroglosse hylaeforme (Plectrohyla guatemalensis).'' Bulletin de la Société Philomathique de Paris, 7(1), 92–93.
Duellman, W. E. (1964). A review of the frogs of the Hyla bistincta group. University of Kansas, Lawrence, Kansas.
Duellman, W. E. (2001). The Hylid Frogs of Middle America. Society for the Study of Amphibians and Reptiles, Ithaca, New York.
Duellman, W. E., Campbell, J.A. (1992). ''Hylid frogs of the genus Plectrohyla: systematics and phylogenetic relationships.'' Miscellaneous Publications, Museum of Zoology, University of Michigan, 181, 1-32.
Duellman, W. E., Marion, A. B., Hedges, S. B. (2016). ''Phylogenetics, classification, and biogeography of the treefrogs (Amphibia: Anura: Arboranae).'' Zootaxa , 4104, 1 - 109.
Greenbaum, E. Komar, O. (2005). ''Threat assessment and conservation prioritization of the herpetofauna of El Salvador.'' Biodiversity and Conservation, 14, 2377-2395.
Hartweg, N. (1941). ''Notes on the genus Plectrohyla, with descriptions of new species.'' Occas. Papers Mus. Zool. Univ. Michigan, 437, 1-10.
Kellogg, R. (1932). ''Mexican tailless amphibians in the United States National Museum.'' Bulletin of the United States National Museum, 160, 1–224.
McCranie, J. R. (2017). ''Specific status of the Montana de Celaque Honduran frogs previously referred to as Plectrohyla guatemalensis (Anura: Hylidae: Hylinae).'' Mesoamerican Herpetology, 4, 393-398.
McCranie, J. R., Wilson, L. D., Williams, K. L. (1987). ''Plectrohyla guatemalensis reproduction.'' Herpetological Review, 18, 72.
Oliveira, B. F., São-Pedro, V. A., Santos-Barrera, G., Penone, C., Costa, G. C. (2017). ''AmphiBIO, a global database for amphibian ecological traits.'' Sci. Data., 4, 170123.
Santos-Barrera, G., Canseco-Márquez, L. (2010). ''Plectrohyla guatemalensis''. The IUCN Red List of Threatened Species 2010: e.T55876A11367513. http://dx.doi.org/10.2305/IUCN.UK.2010-2.RLTS.T55876A11367513.en.
Written by Joshua Curtis, Mia Guarnieri, and Danielle Myers (jmcurtis AT ucdavis.edu,mguarnieri AT ucdavis.edu, dmmyers AT ucdavis.edu), University of California, Davis
First submitted 2019-04-30
Edited by Ann T. Chang (2019-05-02)
Species Account Citation: AmphibiaWeb 2019 Plectrohyla guatemalensis: Guatemala Spikethumb frog <http://amphibiaweb.org/species/1040> University of California, Berkeley, CA, USA. Accessed Aug 22, 2019.
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Citation: AmphibiaWeb. 2019. <http://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 22 Aug 2019.
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