The grey foam-nest tree frog (Chiromantis xerampelina), or southern foam-nest tree frog, is a species of frog in the family Rhacophoridae. They are found in southern Africa. Its natural habitats are subtropical or tropical dry forest, dry savanna, moist savanna, subtropical or tropical dry shrubland, subtropical or tropical seasonally wet or flooded lowland grassland, intermittent freshwater marshes, arable land, pastureland, rural gardens, urban areas, heavily degraded former forests, ponds, and canals and ditches. Grey foam-nest tree frogs are known for simultaneous polyandry, where female frogs have multiple mates on separate territories that guard the eggs and care for young. This behavior is owed to their external fertilization mechanism. During the mating process, the female frog produces a foam nest, typically on branches that hang above bodies of water, in order to keep her eggs moist as they develop. This practice is what gives the grey foam-nest tree frogs their name.
Description Grey foam-nest tree frogs are arboreal. Like other species in the genus Chiromantis, they have discs on their toes, and their outer two fingers are widely spaced and nearly at a right angle to their inner two fingers on each hand. The grey foam-nest tree frog typically has a snout length of 50–80 mm. Males have a snout-vent length of 43–75 mm, while females have a 60–90 mm snout-vent length. They have relatively impermeable skin, which allows them to survive dry spells under tree detritus. Their skin is slightly bumpy and dry. Their coloration ranges between white and brown and changes in response to temperature (see adaptations below). They tend to turn white when they die. The grey foam-nest tree frog typically has a snout length of 50–80 mm. Males have a snout-vent length of 43–75 mm, while females have a 60–90 mm snout-vent length.
Distribution and habitat Grey foam-nest tree frogs usually reside in varying habitats, such as savannah, shrubland, forests, pastureland, and urban areas. There have been mentions of these frogs living in Australia in addition to their native range in southern Africa. They are considered habitat specialists, which refers to a species known to only breed in unsettled environments and unperturbed areas. Grey foam-nest tree frogs dislike arid conditions and need humidity to survive; however, they can still be found in dry environments such as: dry forests, miombo, mopane, savannah, and cultivated areas in low altitudes. They are able to survive dry seasons under loose bark, hence why they are referred to as tree frogs. Large rainstorms stimulate an increase in breeding from these frogs, because high humidity decreases egg mortality and improves survival across multiple stages of life. Habitat destruction and disturbance impacts breeding abilities of these frogs.
Ecology and behaviour
Reproduction Mating activity of grey foam-nest tree frogs typically occurs at night from October to February in south-eastern Africa's wet summer months. These frogs choose to mate in arboreal settings, as they create their foam nests in tree branches overhanging bodies of water. Female mate choice is often limited due to males forcing copulations. Mating primarily occurs on the branches of trees, making females very visible to males. Unpaired males may also intercept females by waiting at the base of a tree. Matings from male interception are often from genetically undesirable males. Over 90% of females mate with ten or more males in the production of a single clutch. The female grey foam-nest tree frog begins the process of reproduction by producing a thick mucus-like fluid from its cloaca (a cavity at the end of the digestive tract in amphibians). During this process, the frog uses its hind legs to whip the mucus into elastic froth that will eventually serve as physical protection for the developing eggs. The female will leave temporarily to rehydrate before returning to the nest. Nest construction can take around five to six hours. Males then incorporate their sperm into the recently laid foam, fertilizing them. The next day, the female will return to its egg-laying site and add a layer of foam to protect the eggs from drying out.
Foam-nest building behaviors and patterns have evolved several times. The foam nest made by the female provides different functions for aquatic and terrestrial breeding alike. Some grey foam-nest tree frogs breed exclusively in water. In these water-breeders, foam nests allow the eggs to be suspended in oxygenated water. Grey foam-nest tree frogs that reproduce on land create these nests to minimize drying out, temperature changes, and predation. Polyandry, an important characteristic of the grey foam nest tree frog, has proven to substantially increase offspring survival. Polyandrous matings may provide eggs with additional nutrients via the seminal fluid from multiple males. These nutrients increase yolk availability for post-hatching development and increases survival of tadpoles. Sperm competition may also allow for increased egg interaction with steroids in seminal fluids, which may accelerate yolk metabolism and increase growth rate of tadpoles. Offspring as a result of polyandry are more likely to survive than offspring of monogamous matings.
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