Agalychnis callidryas

Though the main coloring of Agalychnis callidryas is consistent, there are some variations in morphs across the geographical range of the species. Red-eyed tree frogs have variation in the color of their side stripes, which in Costa Rica and Panama specifically includes blue, blue/red, orange and purple.[9] There are several hypotheses for the reason behind the existence of these color morphs. One strong hypothesis is that the existence of orange and purple morphs in Costa Rica are caused by isolation by distance, because the orange and purple morphs were not genetically distinct groups. It is possible that color patterns have been affected by different selective pressures, and that the existence of some morphs are due to genetic drift.[10]

As a species of tree frog, Agalychnis callidryas has a claw shaped terminal phalanx.[11] Other synapomorphies of this genus include the presence of a red hue on the iris and a golden reticulated palpebral membrane.

Tree Fogs lay eggs on plants so that the eggs can hatch, this is called Commensalism

[12]

Adult red-eyed tree frogs are primarily carnivores, eating crickets, moths, grasshoppers, flies, mosquitoes, and other insects.[16] Occasionally, they also eat smaller amphibians. Tadpoles eat plants, algae, plankton, bacteria, carrion, and their fellow tadpoles.[16][17] After metamorphosis, froglets begin consuming small insects like fruit flies and pinhead crickets.[18] A study on carotenoids consumption has shown they play an important role in development, phenotype, and fecundity. [19] There is a critical window after metamorphosis where carotenoids improve female growth rate and fecundity, and lead to a redder skin in both sexes. Carotenoids are important nutrients for wild red-eyed tree frogs and especially for captive red-eyed tree frogs, who sometimes suffer skin pigmentation degradation due to an inadequate diet.

Red-eyed tree frogs in axillary amplexus

Red-eyed tree frogs mate seasonally, specifically in the rainy season during the months of October to March.[20] Males attract females by croaking and wrestle with each other in male-male competition in order to gain access to females for reproduction.[21] Females latch on to the underside of a leaf using the suction cup like structures on their webbed feet, and the female must hold on to the leaf while males compete and wrestle nearby. The winning male and female will then participate in amplexus, and the female will lay eggs on the underside of the leaf as they are fertilized by the male.[22] The eggs typically hatch within 6 to 7 days if left undisturbed.[23] This process occurs above or very close to a body of water, because tadpoles which hatch from the eggs will drop into water from the leaf. Eggs will hatch early if their survival is threatened, in a process called phenotypic plasticity. The female chooses a leaf above a pond or large puddle on which to lay her clutch of roughly 40 eggs. Since oviposition generally occurs on both sides of a leaf, red-eyed tree frogs may fold the leaf to hide the eggs from predators. They also produce sticky jelly to glue the eggs together; this may protect the eggs from splitting and dehydration.[24]

Following fertilization, females lay clutches of about 40 eggs, and can lay multiple clutches in a single night. Since the eggs are often adhered to a leaf above water, tadpoles fall into the water below as soon as they hatch. Eggs will usually hatch 6-8 days after they have been laid, with some variation depending on geography and risk assessment through vibration.[25] Depending on environmental conditions, the tadpoles will then stay in the water for a few weeks or months. They will change to adult colors following metamorphosis, and live for about five years in the wild.[26]

Red-eyed tree frog embryos use natural day and night light cycles as a signal for when to hatch, and tend to hatch just after nightfall.[27] Red-eyed tree frog eggs may hatch early (exhibiting phenotypic plasticity) when a change in the environment signals a danger to their survival.[28] Dragonflies, fish, and water beetles prey on the tadpoles. The tadpoles remain in the water from three weeks to several months, until they metamorphose into frogs. The time of metamorphosis depends on duration of larval stage, which varies depending on environment. After metamorphosis, the color of tadpoles' torsos changes from green to brown, and their eyes, which are initially yellow, turn into deep red without much side patterning. These changes mark maturity. The lifespan of red-eyed tree frogs is about five years.[29]

Red-eyed tree frogs females are typically choosy about which males they mate with. Females will choose mates based on visual and auditory clues, mainly the male frogs’ croaking calls as well as their size and flank stripe. Females are likely to choose males with “local” flank stripes and call patterns, meaning that male frogs from nearby areas are selected for in mating.[30] Call and stripe patterns are considered simultaneously by females in this situation. Size plays a role in mate choice for red-eyed tree frogs as well. Often larger males are more successful in amplexus compared to smaller males. However, size-assortative mating also plays a role and larger females are more likely to pair with proportionally large males and vice versa for small females and males.[31] This is so the male can successfully fertilize the female’s eggs during amplexus.

During the mating season, the male frogs shake the branches where they are sitting to improve their chances of finding a mate by keeping rivals at bay. This is the first evidence that tree-dwelling vertebrates use vibration to communicate.[32] When rainfall is at its highest, a male red-eyed tree frog calls "chack" to get the attention of the female. Females use the call, as well as color (specifically, the stripped sides) of the male frog, in order to find a possible mate.[33] Both the call and color of the male frog show territorial display, and anti-predatory behavior. During amplexus, the female carries the male on her back for several hours during the oviposition process. Because of external egg fertilization, there is still risk of competition even after a female has selected a mate. There is not sperm priority in Agalychnis callidryas, and so a single clutch of eggs may have been fertilized by multiple males.[34]

Red-eyed tree frogs' embryos exhibit phenotypic plasticity, hatching early in response to disturbance to protect themselves. Though embryos are bred synchronously, they normally hatch after 6 to 10 days from oviposition without disturbance.[24] However, a simultaneously early hatching in entire clutches is triggered when embryos are exposed to their predators or threatening environmental changes such as rainstorm and flood.[24][35] Early hatching has also been linked with egg dehydration, hatching earlier in dry egg clutches than in wet ones.[36]

Hatching early is an important defense to predators, but is also a risky strategy for embryos because early hatching increases predation risk in water.[37] Therefore, to maximize the benefits of this strategy embryos must only hatch when they are truly at risk by a predator. Studies show that this strategy is multifaceted and a specific combination of vibrational pulse duration and inter-pulse intervals is needed in order for embryos to exhibit this response.[38] This combination of pulse duration and inter-pulse intervals is thought to be specific to the embryo predators, thus ensuring the response only occurs when absolutely necessary to ensure survival.

Predators are the major cause of this response. Since these frogs usually lay eggs on both the upper and the undersides of leaves above ponds, clutches need to protect themselves against arboreal, aerial and aquatic predators, such as snakes, dragonflies, fish, monkeys, and pathogenic fungi.[39] When predators are close enough to produce detectable vibration, the embryos assess disturbance. After a few seconds, embryos vigorously hatch out into tadpoles and spread out to escape.[24][40] Since eggs are usually laid above ponds, the response improves survival because tadpoles often fall into water on hatching. Hatching direction also has implications on embryo survival. Embryos often hatch and fall into the water, but hatching direction may also be influenced by light. A study found that A. callidryas embryos hatch towards light, suggesting they use light and dark as directional cues to determine hatching direction.[41]