Hourglass Treefrog

The size of the Dendropsophus ebraccatus varies between regional populations. The average snout-vent length of an adult male ranges from 23.63 - 26.75 mm (Ohmer et. al 2009), while females are slightly larger, reaching 36.5 mm (Duellman 1970). The species has a short, truncated snout, and its head is flat and wider than its body (Duellman 1970). The eyes are large compared to the head, and the pupil is horizontal (Leenders 2016). Adults have vomerine teeth (Rivera-Correa and Orrico 2013). There is a thin dermal fold that extends from the back edge of the eye to near the arm. This fold covers the upper edge of the tympanum, which is roughly one-fourth the size of the eye (Savage 2002) and has a distinct ridge on the front edge (Duellman 1970). Adult males have paired vocal slits and a single extensible vocal sac. The skin on the dorsum is smooth, while the skin on the ventrum is granular (Savage 2002).The limbs are relatively short. The front limbs have an extensive axillary membrane and are slightly more robust than the hind limbs. The tips of all the digits have discs, with the discs being larger on the hands than the feet (Duellman 1970). The disc on the third digit of the front limb is larger than the tympanum (Savage 2002). The front foot has webbing covering roughly half the length of the digits. The webbing between the first and second digit is vestigial, and extends from the middle of the penultimate phalanx on the second digit to the base of the penultimate phalanges on the third and fourth digits. The webbing on the hind foot is more extensive, covering roughly three-quarters of the length of the digits. The webbing starts at the base of the toe disc on the first digit, continues to the distal end of the penultimate phalanx on the second digit, then connects to the base of the penultimate phalanx on the third digit. The webbing then connects from the base of the toe disc on the third digit to the distal end of the antepenultimate digit on the fourth digit, and terminates at the toe disc on the fifth digit. The hind foot also has a thin tarsal fold that runs the full length of the tarsus (Duellman 1970).Hatchling tadpoles can range from 6.72 to 7.47 mm long in total length (Gonzalez et al. 2011). Tadpoles at developmental stage 36 average 29 mm in total length (Savage 2002). The tadpoles have a blunt snout, small dorsolateral nostrils, and laterally directed eyes (Duellman 1970). The body is violin-shaped (Rivera-Correa and Orrico 2013) or ovoid with a sinistral spiracle. The small mouth is terminal (Duellman 1970) and has finely serrated upper and lower beaks, though no denticles (Savage 2002). The tail is long with a thin flagellum at the end (Savage 2002) and high fins (Duellman 1970). Dendropsophus ebraccatus is one of at least 97 species in the genus Dendropsophus and is placed within the group of leaf-gluing frogs that includes at least eight other species. Dendropsophus ebraccatus is the only species of the nine that is trans-Andean; the other eight species are cis-Andean. Dendropsophus ebraccatus can be differentiated from similar species by the bands that are usually on the upper side of its dorsum. Dendropsophus ebraccatus has abnormal bands that are disrupted by brown smudges, while its close relatives D. manonergra and D. triangulum have a more consistent pattern. Dendropsophus manonergra does not have disruptions within its bands while D. triangulum has a consistent disruption, if present. Dendropsophus manonergra, D. roassalleni, and D. sarayacuensis have triangle shaped blotches between both of their eyes (Rivera-Correa and Orrico 2013). Dendropsophus ebraccatus is also commonly confused with D. phlebodes and D. microcephala. Both of the latter species lack the hourglass pattern on the dorsum, allowing for easy differentiation when the D. ebraccatus individual has this distinctive pattern. When the hourglass pattern is absent on an individual, D. ebraccatus can be distinguished from both D. microcephala and D. phlebodes by its dark eye mask and pale lip stripe (Leenders 2016), as well as its finger webbing, which is more extensive than the other two species (Savage 2002). Dendropsophus phlebodes also has a grey tint to its dorsum coloration, whereas D. ebraccatus is brightly colored (Guyer and Donnelly 2005). Dendropsophus ebraccatus can be further differentiated from D. microcephala and D. phlebodes by its long primary calling notes. These three species have different pulse rates in their callings, with D. ebraccatus having the slowest pulse rate (Savage 2002). In addition, D. microcephala callings are much higher in frequency than D. ebraccatus (Wilczynski et al. 1993). In life, D. ebraccatus usually has a yellow dorsum with golden-brown blotches forming the shape of an hourglass, giving it the common name “hourglass treefrog.” The dark blotches are sometimes bordered by lighter colors, such as bright yellow, cream, or white (Guyer and Donnelly 2005). While the hourglass pattern is most common, there are 10 different pattern variants that range in the extent of the dark blotches, from completely tan-yellow with no blotches to the actual hourglass-shaped pigmentation (Ohmer et al. 2009). Dendropsophus ebraccatus also has a dark brown eye mask extending as a stripe past the eye and covering the tympanum. Beneath this dark eye mask they often have a pale lip stripe that expands below the eye to form a light spot (Leenders 2016). Dendropsophus ebraccatus generally have banded limbs, with the same coloring as their dorsum (Leenders 2001). The thighs are uniformly bright yellow or orange on both the dorsal and ventral sides (Leenders 2016). The fingers generally have no color (Cope 1874). The iris varies in color from a pale yellow or tan to a dark brownish-red (Guyer and Donnelly 2005). In life, tadpoles have a brown to black dorsum with brightly colored blotches, and a pale ventrum (Savage 2002). The blotches are red, gold, white, or any combination of the three colors (Guyer and Donnelly 2005). The tail is primarily gold with black barring, and the fins are generally red with black barring (Savage 2002). There is a pigmented spot on the tail that varies in color and size depending on the predators in their environment (Touchon and Warkentin 2008 Oikos). The iris is red and bronze (Savage 2002). Dendropsophus ebraccatus lives in a range of elevations. One study shows that D. ebraccatus’ body size throughout all stages of growth correlates with the elevation a population is living at, with populations living at higher elevations (greater than 300 m) in Pacific versant populations being larger than those at lower elevations. The same study also showed that populations on the Pacific side of the Cordillera de Talamanca mountain range have larger body sizes. In addition, there are roughly ten different color variations (Ohmer et al. 2009). The patterning on the dorsum ranges from a clear hourglass shape with or without additional spots surrounding it to a solid yellow dorsum with no blotches, and spans all coloring in between (Savage 2002). Dendropsophus ebraccatus females are slightly larger than males, and males have an easily discernible vocal patch (Guyer and Donnelly 2005).The species authority is: Cope, E. D. (1874). “Description of some species of reptiles obtained by Dr. John F. Bransford, Assistant Surgeon United States Navy, while attached to the Nicaraguan Surveying Expedition in 1873”. Proceedings of the Academy of Natural Sciences of Philadelphia 26: 64–72. Dendropsophus ebraccatus is a frog in the family Hylidae. In 2005, D. ebraccatus was moved from the genus Hyla to the genus Dendropsophus in accordance with its molecular evidence. The genus Dendropsophus was resurrected to encompass many species that were moved from Hyla due to shared characteristics of mitochondrial evidence and pectoral glands in males and females (Faivovich et al. 2005). Dendropsophus ebraccatus is part of the D. leucophyllatus species group. Based on Maximum Parsimony analysis of 12S rRNA, 16S rRNA, and tRNA Valine genes, D. ebraccatus is sister to the clade composed of D. bifurcus, D. leucophyllatus, D. manoegra, D. saryacuensis, and D. triangulum (Rivera-Correa and Orrico 2013). This analysis supports an earlier Baysian and Maximum Likelihood analysis of 808 base pairs of 12S and 16S rRNA, which had lower confidence scores (Fouquet et al. 2011). Both studies indicate that the clade including D. ebraccatus is sister to a clade including D. salli and D. elegans but disagree on the placement of D. miyatai in relation to D. ebraccatus (Fouquet et al. 2011, Rivera-Correa and Orrico 2013).The species epithet, ebraccatus is latin for “without trousers” (Smithsonian Tropical Institute: Amphibians of Panama, accessed 2018); the name is thought to reference the lack of patterning on the species’ thighs (Leenders 2001). Dendropsophus ebraccatus was first named Hyla ebraccata in 1874 (Cope 1874). In 1954, its name was changed to Hyla weyerae. In 2005, the species was changed from the genus Hyla to the genus Dendropsophus, which gave rise to the scientific name used today, Dendropsophus ebraccatus (Faivovich et al. 2005). Dendropsophus ebraccata has 30 diploid chromosomes, or a karyotype of 2n = 30 (Savage 2002).

Dendropsophus ebraccatus lives in Central America from southern Mexico to Ecuador (Karl-Heinz et al. 2010) at elevational ranges of 0 - 1600 m. Populations are isolated in some areas by the mountain range, Cordillera de Talamanca (Ohmer et al. 2009), and are not as prevalent in Ecuador (Karl-Heinz et al. 2010). Dendropsophus ebraccatus is most commonly found in humid lowland forests (Leenders 2016), but they have also been found in habitat edges, orchards, pastures, and secondary vegetation indicating a tolerance of human disturbances. Dendropsophus ebraccatus is typically found on vegetation that hangs above both permanent and temporary pools of water (Matias and Escalante 2015).

Dendropsophus ebraccatus is a nocturnal, arboreal frog that is abundant throughout its range (Gonzalez et al 2011). Dendropsophus ebraccatus has been found to cohabitate with closely related frogs that utilize the same spatial and food resources. The species preys on terrestrial invertebrates and has been found to have little to no competition with its close relative D. phlebodes, the San Carlos treefrog. Due to D. ebraccatus’ larger size, it eats larger prey animals while D. phlebodes eats smaller invertebrates. Regardless of the predation distribution, empty frog stomachs in the field provide evidence that the majority of their time is allocated to calling. These males have overlapping breeding grounds that are utilized to find mates. It is believed that these frogs can coexist due to the heterogeneity in the environment; they have been found to use various types of foliage with differing heights to call for females, which allows for perch height segregation (Jiménez and Bolainos 2012).Dendropsophus ebraccatus mate from May to November, when its surrounding environment is at its wettest (Ohmer et al. 2009). Hoping to attract a female, males call from 15 cm to 2 m (Miyamoto and Cane 1980 Copiea) above ponds created during the rainy season (Ohmer et al. 2009). Males produce multiple types of calls including defensive and aggressive calls, which they use to compete with males of their own species and neighboring heterospecifics, as well as advertisement calls (Savage 2002). The different types of calls have different pitches. High pitch calls are used for intrasexual competition. However, females show preference for low pitches over high pitches (Reichert 2011). Advertisement calls are composed of buzz-like introductory notes that may be followed a click-like secondary notes or aggressive calls depending on if they are calling alone or in response to other males. Lone males often only call with the first note. The duration of advertisement calls is between 96 – 240 ms, with a pulse rate of 85 - 110 pulses per second and with 54 – 92% of the call spent rising in amplitued. The dominate frequency is around 3 kHz (Wells and Schwartz 1984). Females prefer a swifter call rate that includes multiple notes, rather than a single note (Vitt and Caldwell 2009).Aggressive calls are more variable but are generally longer (120 – 664 ms) than adveritsement calls, have a higher pulse repetition rate (157 – 461 pulses per second) and may include secondary click notes. The proportion of call time spent rising in amplitued also has a greater variation of 11 – 93%. The dominate frequency, like the advertisement call, is around 3 kHz (Wells and Schwartz 1984). Males increase the aggressiveness in their calls when other males are nearby (Reichert 2011). When males are further from each other they have shorter introductory notes which increase in length as distance between males decreases. Additionally, pulse rate is positively correlated to an aggressive response from other males and rising time appears to be an important feature when pulse rates were high (Wells and Schwartz 1984). Males call throughout the night while staying in a vegetative pond area (Touchon and Worley 2015). Non-calling, sneaker, males are also present and position themselves in the space between the calling males and the females. From this position, the silent males remain still so when an allured female makes her way to the calling male he can attempt to mate with her (Miyamoto and Cane 1980 Biotropica).Advertising males call faster as females approach them until the female rotates her body toward the male, at which point he stops calling (Savage 2002). Males position themselves on the females via axillary amplexus (Miyamoto and Cane 1980 Copiea). After external fertilization, a female can lay around 180 to 300 eggs in one night (Touchon and Worley 2015). Females are capable of ovipositing on both land and water. The terrestrial eggs are commonly placed above the water on a plant to allow the tadpoles to fall into the water after hatching, while aquatic eggs are place beneath the surface on vegetation. Their decision of placement depends on environmental cues rather than genetics. For example, less shaded regions would influence the female to oviposit aquatically rather than terrestrially to decrease chances of desiccation (Touchon and Warkentin 2008 PNAS). If aquatic predators are present, D. ebraccatus will lay eggs in overlying vegetation and risk desiccation. Eggs oviposited in the water are able to hatch after forty hours ; the developmental rate for terrestrial eggs is much slower (Touchon and Worley 2015). In order for the species to oviposit on both land and water, the eggs must be able to withstand the either environment. While most amphibians begin releasing a hatching enzyme right before they hatch,D. ebraccatus gradually releases the enzyme as the embryo develops and the vitelline membrane slowly degrades. This process accelerates hatching, enables the tadpole to avoid threats such as predation or desiccation, and allows offspring to take the best course of action for survival (Cohen et al. 2018). Tadpoles graze the shallow waters for algae (Gonzalez et al. 2011), generally hiding in clumps of vegetation (Leenders 2001). One study showed how the presence of dragonflies causes tadpoles to develop a redder pigment on their tail and a larger tail in comparison to the presence of fish, which causes tadpoles to grow smaller tails. These different responses in tail morphology may be evolutionary adaptations to avoid predators. The red spot and large tails on tadpoles subjected to dragonflies may be deterring dragonflies from eating them while the small tails may help propel tadpoles away from fish (Touchon and Warkentin 2008 Oikos). The tadpoles metamorphose into frogs four to six weeks after hatching (Savage 2002).Adult variation in dorsal patterning is explained by both regional genetic drift and environmental pressures. The purpose for the bright coloration in D. ebraccatus is unknown; it is possible the color and patterns are a form of aposematism or a form of crypsis. The toxicity of the poison glands are unknown, and due to the broad range of endemicity, it is difficult to determine the selection pressures acting on the coloration of the species. There is some indication that the variation and frequency in coloration is not due to sexual selection, but rather natural selection (Ohmer et al. 2009). Dendropsophus ebraccatus is highly susceptible to predation and parasitism (Touchon and Warkertin 2008 PNAS). In one study, individuals were found to host the nematode parasite Cosmocerca parva. However, there is no indication that this parasite has a major effect on the species population (Bursey and Brooks 2010). In addition to parasites, large aquatic invertebrates-such as dragonfly larvae and water bugs- and fish have been seen to regularly prey on D. ebraccatus eggs (Touchon and Warketin 2008 PNAS). When aquatic predators are abundant, D. ebraccatus may lay eggs terrestrially to increase the chances of egg survival (Cohen et al. 2018). Terrestrially lain eggs are subject to predation by spiders, wasps, and ants (Touchon and Warketin 2008 PNAS).

Dendropsophus ebraccatus’ population trend is stable, and is listed as “Least Concern” on the IUCN Red List. The hourglass treefrog is an adaptable species that has thus far not been impacted by human disturbances (Karl-Heinz et al. 2010). The ability of females to oviposit on both land and water allows reproduction to be flexible. However, changes in the amount of rainfall due to climate change could make terrestrial egg deposits more susceptible to desiccation (Touchon and Worley 2015). While the environment could lead to egg desiccation, deforestation and contamination from pesticides associated with farming could affect adults because the species is primarily forest dwellers. However, the flexibility of D. ebraccatus' life history allows some populations to live in unforested areas (Karl-Heinz et al. 2010), including parks and agricultural lands (Leenders 2016). However, it was found that the mean size and age was decreased in areas of high human disturbance. It is possible that the difference in size is due to lowered life expectancy; no limb asymmetry was found. (Matias and Escalante 2015).The presence of chytridiomycosis in D. ebraccatus is low. When scientists examined if the root of the low frequency could be due to differences in the environment or differences in their microbiota, it was found that the microbiota of Panamanian treefrogs is in fact different from other frogs, but no conclusive evidence linked the differing microflora to the low rates of chytridiomycosis (Belden et al. 2015).

Dendropsophus ebraccatus is used for research purposes with special interest surrounding its rapid hatch rate and its ability to oviposit both terrestrially and aquatically, which is found only in a few species. In addition to the research interest, these animals are kept as pets (Karl-Heinz et al. 2010) and used as attractions for ecotourism sites in Central America (Spangler 2015).