Dendropsophus ebraccatus

Description

Dendropsophus ebraccatus, also known as the hourglass treefrog or pantless treefrog, is a Neotropical treefrog, found scattered from through Central and South America from southern Mexico to northern Ecuador [5]. The common names of D. ebraccatus come from the dark hourglass shaped pattern found in the centre of the back and the distinct smooth yellow thighs that contrast the rest of the brazenly patterned body. The contrasting of the smooth yellow thighs from the rest of the bodies pattern provide the illusion that D. ebraccatus is not wearing pants. The name ebraccata in Latin means "without trousers". D. ebraccatus has a number of unique reproductive features such as the ability to alter rates of hatching shared in a number of Anura families. D. ebraccatus is also extremely unique in its ability to alter its mode of reproduction as it is the only known vertebrate to be able to do so [5]. Taxonomy D. 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 in dense jungles throughout Central and South America. A unique feature of the genus is that all individuals within the genus have 30 chromosomes [5]. After a large revision to the family Hylidae following Faivovich et al. (2005) the genus Dendropsophus was revived and separated from Hyla.[5] Distribution and Habitat The hourglass tree frog is native to southern Mexico, Belize, Colombia, Costa Rica, Ecuador, Guatemala, Honduras, Nicaragua, Panama, western Colombia and northwestern Ecuador. They can be found in terrestrial and freshwater habitats usually under the canopy of tropical rainforests and prefer temperature ranges of 74-76oF with moderately high humidity between 60-70%. It has an upper elevation limit of 1600 metres (Pough 2004). Physiology These are smooth, small treefrogs exhibiting sexual dimorphism. Males are significantly smaller than females. Their dorsal coloration consists of an hourglass pattern on their backs with gold spots in this pattern. This pattern varies from bright yellow-green to pale yellow or cream. They are also called “pantless frogs”. When you extend their hind legs you can see that only on their thighs they do not have the pattern continued but rather just a pale yellow color (Cope 1874) [4]. The hourglass tree frog has relatively large forelimbs in comparison to the proportion of its body. It 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 (Touchon and Warkentin 2008) [10]. As compared to most Anura they are capable of gas exchange through their permeable skin (Pough 2004). The frog family Hylidae has the unique adaptation of forming cocoons (by shedding the outer skin layer of the stratum corneum) or refuge in tree holes to protect themselves from desiccation during unfavorable conditions (Pough 2004). They also wipe themselves with waxy lipid secretions from their lipid glands in the dorsal skin to reduce water loss (Castanho 2001)[1]. They also secrete a watery mucus to aid in evaporative cooling. Their granular glands contain a wide range of bioactive molecules for defense. Compounds such as alkaloids, quinones, steroids, biogenic amines and a diversity of biologically active peptides can be found across the family Hylidae (Konig 2012) [7]. Adults are nocturnal creatures, their diet consists of small arthropods. While tadpoles are macrophagous herbivores or cannobols as they feed on dead tadpoles (Cope 1874)[4]. They can make loud calls due to the elasticity of their throats (Pough 2004). Their call is a prolonged “creek” followed by several higher pitched “eeks”. They emit rain calls in the daytime before or during a rain shower (Pough 2004). 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 [13]. Once aggregated around freshwater pools they utilize chorus and mate finding 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 300 and 180 eggs separated between up to eight different masses within a single night [13]. Egg masses 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, depending on various environmental factors. 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. If there is a risk of egg desiccation, eggs will be placed in the hydrating water but if there is a risk of egg predation from fish in freshwater pools, eggs will be placed on leaves [13]. The threat of aquatic predation has been shown to outway the risk of desiccation. 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 unfavourable 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 [13]. 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 [8]. Once eggs hatch, tadpoles either emerge in the water or roll of leaves into the pond below. Tadpoles are brown and gold with black eye bands and develop bright red tail colours in the presence of predators. Tadpoles feed on micro fauna and scavenge what they can in the water until they mature after 6–8 weeks. Young frogs live near pools of water and only make their way back to the forest canopy when nearing adulthood. Conservation The IUCN Red List of Threatened Species listed the Hourglass Tree Frog as a species of least concern (LC) in 2010 due to wide distribution, stable, large population, and high tolerance to adapt to habitat modifications. This species population is in many protected areas throughout the range. Although it is very adaptable it still faces many threats such as deforestation, agriculture and aquaculture (livestock farming and ranching, annual and perennial non-timber crops), logging, residential and commercial development, the pet industry, and pollution. Research The skin of the family Hylidae is vastly studied due to its rich sources of bioactive peptides, which has spiked the interest for drug development (Conlon 2014) [2]. Hylids use the peptides in defense against bacteria, fungi, protozoans, viruses, and desiccation (Conlon 2014) [2]. These peptides are of interest to scientist due to their anti-infective and therapeutic potential. Peptides have been found to stimulate insulin release for Type 2 diabetes mellitus therapy (Conlon 2014) [2]. They are also used for their ability to be the precursor for encoding cDNAs (Konig 2012) [6]. Pathogenic bacteria and fungi antibiotic resistance constitutes a serious threat to public health worldwide, scientists are looking to frogs skin secretions for further drug advancements (Conlon 2014) [2]