Dendropsophus ebraccatus, also known as the hourglass treefrog, referring to the golden-brown hourglass shape seen surrounded by skin yellow on its back. Their underbellies are yellow. Their arms and lower legs usually display bold patterns while their upper legs or thighs are light yellow giving them the appearance of wearing no pants. The species name "ebraccata" translates to "without trousers" in Latin.
The hourglass treefrog is throughout Mexico from southern Veracruz and northern Oaxaca, slightly more southern in Chiapas, Tabasco, and the Yucatán Peninsula. The hourglass treefrog also presides south of Mexico in the northern Guatemala and Belize areas. The range of the hourglass treefrog becomes more scarce in Honduras and a few more known locations in Nicaragua, but then has been commonly reported again in Central America spanning from Costa Rica to Panama even venturing into Colombia and northwestern Ecuador.
Taxonomy
Dendropsophus ebraccatus is a member of the wide-ranging tree frog family Hylidae and the genus Dendropsophus. Dendropsophus is a group of small, primarily yellow tree frogs found throughout Central and South America. A unique feature of the genus is that all individuals within the genus have 30 chromosomes. After a large revision to the family Hylidae in 2005, D. ebraccatus was moved from the Hyla genus to the Dendropsophus genus within the Hylidae family. The D. ebraccatus can be distinguished from similar species by identifying its the D. ebraccatus dominant dorsal pattern, the hourglass, since it can be confused with close relatives D. manonergra and D. triangulum.
Description
D. ebraccatus are smooth, small treefrogs exhibiting sexual dimorphism, with males being significantly smaller than females. Their dorsal coloration consists of blotches and spots that vary in its exact color from yellow, gold, or brown. These blotches can look like an hourglass while the rest of their skin provides a bright yellow background the darker patterned blotches. The dorsal color pattern of D. ebraccatus can be characterized as hourglass with spots, hourglass without spots, spots, and plain; however, the hourglass pattern is dominant in most populations. They are also called "pantless frogs" because when their hind legs are extended, their dark patterned blotches do not continue on their thighs and instead display pale-yellow skin on their thighs. This gives them the appearance of having no pants. The hourglass tree frog has relatively large forelimbs compared to the proportion of its body. It also has well developed toe discs for tree climbing. Their toe pads adhere via deformation of the soft epithelial cells. They also have long hind limbs for jumping from tree to tree. As compared to most Anura, most gas exchange occurs through their nostrils but actually release most carbon dioxide through their permeable skin.
Distribution
The hourglass tree frog is native to Mexico in specific areas of Mexico: southern Veracruz, northern Oaxaca, Chiapas, Tabasco, and the Yucatán Peninsula. D. ebraccatus have been commonly seen throughout more southern countries including Guatemala, Belize, Costa Rica, and Panama. There are only a few known populations of D. ebraccatus in Nicaragua and Honduras. They are even seen more frequently throughout the northern Colombia and northwestern Ecuador.
Reproduction
Hourglass tree frogs migrate to freshwater pools in vegetated areas to breed during the rainy seasons of Central and South America, between May and November. Once aggregated around freshwater pools, they utilize chorus as strategies to select mates. Males hide behind foliage around edges of marshes and ponds during the night and produce long mating calls to attract potential female mates. Once a male is selected by a female, he will climb onto her back and release his sperm into her cloaca.
Females reproduce multiple times within the breeding season, with gaps between reproductive spells as short as 10 days. Females will lay between 180 and 300 eggs, separated between up to eight different masses within a single night. Egg clutches are laid either in single layers on the upper surface of leaves overhanging freshwater or in clusters connected to floating vegetation within the water itself. Hourglass tree frogs are unique in their reproductive plasticity, allowing them to produce both aquatic and arboreal eggs. Arboreal eggs are deposited on the upper surfaces of leaves overhanging water, so the tadpoles can roll into the water once hatched, and aquatic eggs are attached to floating vegetation within the water to keep the eggs from sinking.
Mating
Mate Searching Behavior Research on anuran communication reveals that groups of male frog chorus to attract female frogs to mate. The relative success of these male frogs at attracting females depends on how their advertisement call is able to lead females to their calling space. As male density increases, a male's advertisement call is confused with the other calls. This confusion leads to females' inability to find which calling space the advertisement call originated from. The lowest intensity of a neighbor's call that a male frog is tolerant of is known as the aggressive threshold. When this threshold is reached, a male frog will use a different call known as an aggressive call to initiate male-male conflict or intolerance. Advertisement and aggressive calls both consist of an introductory note ending with a wide range of a number of clicks, and multiple notes and patterns.
Opposed to advertisement calls, aggression calls are characterized by a higher rate of repetition and longer timed calls.
Male/male Interactions In opposition to most frog chorus species, D. ebraccatus chorus groups produce far-range aggressive calls more frequently than close-range. The higher proportion and number of far-range aggression calls causes D. ebraccatus males to be influenced by various surrounding calls in chorus groups instead of just calls from individual frogs. This influence from other males forces these male frogs to constantly adjust their calls accordingly. Generally, male frogs will respond to 2–4 Hz calls with synchronous advertisement calls. On the flip side, males will produce alternating advertisement calls or an initial delayed aggressive call when responding to a call that is 100 dB or more.
For aggressive calls, long calls are utilized for close interactions and physical altercations. During close interactions in which a male frog attacks another, they tussle with each other while still exchanging long duration calls. These physical alterations usually only last one minute unless they remain in close contact and will sometimes continue. On the other hand, short calls are utilized during far-range interactions.
Female/Male Interactions
Mate Choice Call timing plays a significant role in female D. ebraccatus mating choice. Simultaneous male advertisement calling produces less reproductive success for males in close proximity. A male that starts its calls later is the preferred mating choice because females seem to prefer calls that end last. Click notes at the end of the late advertisement call may be one reason why females prefer the late call since the clicking of the lead call is blocked by the late call.
The timing of male calls only depends on the call they produce and not the ones they hear. D. ebraccatus males show more synchrony, or overlapping calls, when producing advertisement calls and prefer to alternate with other calls when they produce aggressive calls. Calls with 150 to 200 millisecond introductory note durations produced synchronous response calls the most efficiently. Although females generally prefer the late call, they are more attracted to the late call with the general timing of an advertising call being produced first and last. In cases where the lead male switches to aggressive calling (which is introduced in the courting section), the increased overlap between the lead aggressive call and the late advertisement call can cause females to not prefer the late advertisement call anymore.
Another aspect of male calls that influences mating choice is the number of notes. Many times, a responding advertisement call is synchronized to the first advertisement call as explained before but is also multi-noted. The advertisement calls are only 1-noted if in very dense choruses.
Courting D. ebraccatus males produce calls in order to attract and court females leading to mating. There are two types of timed calls males produce: lead calls, which start first, and late or lagging calls, which start in the middle of the lead call. The timing of late calling males forces their male competitors to finish calling in the middle of their own advertisement call. This means the late caller finishes the call with its competitor calls being heard at the same time. In response to late male callers, the leading male callers adapted a strategy using aggressive calling. Since aggressive calling is longer than advertisement calling, the lead male switches to an aggressive call while the lagging male uses an advertisement call, which allows the lead male to finish last in more cases and increase their reproductive success. This strategy is an explanation for why D. ebraccatus have high levels of aggressive calls that would be costly for any other species of chorus frog mentioned in the male/male interactions subsection.
Despite this, the late call males cannot lengthen their time delay to decrease overlap and ensure that they finish last. The response time from one male call to another remains around 210 milliseconds no matter what call type they are producing or responding to besides the break increasing when male frogs switch to aggressive calling. There is also evidence that male frogs make many errors in aggressive call detection leading to decreased response time of a threat and decreased attraction by females since the call timing is off. Because females are more attracted to low aggression calls and advertisement calls, this could explain why male frogs are more likely to coordinate their levels of aggression to other calls. This is opposed to simply increasing the intensity of aggression in their call in response to other aggression calls.
The multi-noted synchronized call has two advantages: multiple notes can hide click notes in the leading call and synchronizing decreases the chance of the leader producing a call response. The decreased chance of a call response happens since many frogs will not answer if a call is produced less than 210 milliseconds after their first call has started. The only time a synchronous advertisement call is not multi-noted is in very dense choruses where advertisement calls are only 1-noted.
Diet
While tadpoles are macrophagous herbivores, they may display cannibalistic behavior in the presence of dead tadpoles. Lepidoptera, Diptera larva, and Araneae are the most important aspects of the adult D. ebraccatus diet when this prey is abundant in the surrounding area. The prey of D. phlebodes and D. ebraccatus diet are the same and are only different in that the D. ebraccatus consumes larger prey.
Parental Care
Oviposition Undisturbed aquatic eggs develop at a slightly faster rate than arboreal eggs with an average hatch time of 3.5 days after placement. Both egg groups can alter their rate of development in the presence of unfavorable conditions such as weather or predation. Rates of development and hatching time can be altered from 67% faster to 600% slower than undisturbed hatch times. The rate of development is partially controlled by the rate of enzyme secretion by the hatching gland within the egg. The enzymes secreted by the hatching gland control the rate at which the eggs gel membrane is degradation.