Hyperolius viridiflavus

Hyperolius viridiflavus, or African reed frogs, are a widespread species that occupy most suitable habitats (ponds and lakes) throughout northwestern Ethiopia, through Southern Sudan to western Kenya, Rwanda, Uganda, Burundi, northwestern Tanzania, northeastern Democratic Republic of Congo, and most likely eastern Central African Republic. (Schiøtz, et al., 2004)

Hyperolius viridiflavus lives in the tropical African savanna. It is associated with emerging vegetation in savanna, grasslands, and at the margins of forests, lakes, rivers, and swamps, where these frogs may live in high densities. Hyperolius viridiflavus also lives in areas associated with humans, like cultivated land and gardens. This species breeds in a variety of aquatic habitats from very small to large ponds that may be permanent but are usually temporary. It ranges from low altitudes to 2,400 m in Ethiopia. (Schiøtz, et al., 2004; Schiøtz, 1999)

Hyperolius viridiflavus is a highly variable species that exhibits considerable polymorphism in color pattern. Some populations contain distinct morphs while in others there is gradation among extremes. It is widely regarded as a superspecies with more than fifty subspecies recognized. The subspecies are divided into two subgroups, parallelus and viridiflavus, based on variation in geographic range and coloration. There is some controversy about the taxonomy of H. viridiflavus that is discussed further in the other comments section.

Hyperolius viridiflavus is a small to medium sized frog species with an average mass of 2 g and body length of 15 to 30 mm, depending on the subspecies.

This species exhibits sexual dimorphism with males slightly smaller than females. Females are more colorful than males; their adult pattern is referred to as Phase F which is highly variable and contains several distinct morphs. Mature males frequently remain in the juvenile phase (Phase J), which ranges from brownish to green with paired light dorsolateral lines.

Members of this species have horizontal pupils, extensive webbing of the feet, a brief snout, and a very large, shagreened, gular flap. They lack an external metatarsal tubercle. Males have a large dilatable vocal sac. Females have a tranverse gular flap All subspecies have a subdermal dark bluish lateral streak caused by black pigmentation of the musculus obliquus abdominal muscle. This band is sometimes difficult to see if the sides of the frog are heavily pigmented. The band differs in placement between the sexes.

The subspecies have different coloration ranging from solid light green in the H. viridiflavus mwanzae to light brown in H. viridiflavus pantherinus to very brightly spotted and striped in H. viridiflavus tauniatus. The feet are frequently brightly colored. (Grafe, et al., 1992; Schiøtz, et al., 2004; Schiøtz, 1999)

Hyperolius viridiflavus eggs hatch into tadpoles two to five days after laying, depending on the temperature of the water. Tadpoles take eight weeks to metamorphose into juveniles. Juveniles mature sexually in three to twelve months depending on the climate. Juvenile H. viridiflavus have a different coloration than adults, referred to as Phase J, which is light brown to green in color. Sexually mature males frequently maintain the juvenile coloration throughout adulthood. Phase F, the adult phase, is a highly variable color pattern with distinct morphs. (Bubac, 2009; Grafe and Lisenmair, 1989; Schiøtz, 1999)

Hyperolius viridiflavus breeds during the wet season. The length of the breeding activity varies among subspecies but typically lasts several months. This species is polygynandrous. At the beginning of the breeding season, males migrate to bodies of water such as shallow ponds and form calling choruses to attract mates. Males maintain an individual calling space through combat. Males typically call at dusk and expend considerable energy trying to attract a mate. Females H. viridiflavus may select larger males as mates. Females approach males and initiate amplexus. Amplexus is axillary (the male holds the female around the armpits). The eggs are laid on vegetation under the water in ponds, lakes, and slow-moving streams. Female H. viridiflavus produce multiple clutches during the breeding season. (Bubac, 2009; Grafe and Lisenmair, 1989; Grafe, et al., 1992)

Hyperolius viridiflavus breeds during the wet season. The length of the breeding activity varies among subspecies but typically lasts several months. Females have multiple clutches over the course of the breeding season. The average size of a clutch is 330 eggs. Eggs hatch after 2 to 5 days, and have metamorphosed into juveniles by 8 weeks of age. Juveniles of both sexes become sexually mature at 4 to 12 months old.

Hyperolius viridiflavus has been shown to experience protogyny, or female to male sex change, in the laboratory. The new males were able to fertilize the eggs of females. This likely occurs when the sex ratio within a population is heavily weighted towards males.

Hyperolius viridiflavus is semelparous, but may breed multiple times in its one breeding season. This reproductive strategy is largely due to climatic factors, as no adults have been documented surviving the annual, harsh dry season. Even in laboratory settings, individuals will senesce shortly after the breeding season. (Grafe and Lisenmair, 1989)

Hyperolius viridiflavus provides no parental investment other than yolk and sperm for the eggs. (Bubac, 2009)

Hyperolius viridiflavus lives in an environment with widely fluctuating weather conditions. Shortly after the breeding season, these frogs face a severe dry season when they must rely on stored water. Adults do not handle this water shortage as well as juveniles. Adults do not generally survive the dry season, and in areas with prolonged dry seasons adults are probably annual. Linsenmair has never found an adult H. viridiflavus nitidulus that has survived the dry season in West Africa. Even under laboratory conditions, adult H. viridiflavus senesce quickly after the end of breeding activity. Males also experience high mortality because they are highly vocal and are therefore more susceptible to predation by acoustically-hunting predators. (Geise and Linsenmair, 1988; Grafe and Lisenmair, 1989)

These frogs utilize exposed calling sites and males exhibit territorial behavior during the breeding season at these sites. In order to maintain an individual calling site, males engage in intense and prolonged combat. During the dry season, H. viridiflavus aestivates. Juveniles estivate on dry vegetation in exposed positions, instead of burrowing in the ground. This behavior is unique among frogs. Only juveniles are able to survive the dry season; they do so by reducing metabolism and adjusting water economy. Adults are not able to make these changes and generally do not survive the dry season. Juveniles do not move, eat, urinate, or defecate during the dry season. Juveniles must rely on stored water for several months during the dry season so they must minimize evaporative water loss. The dorsal and ventral skin of H. viridiflavus is differentiated in order to maximize water conservation and uptake. During the dry season the skin turns white because of built-up purine crystals in the skin. (Geise and Linsenmair, 1988; Grafe and Lisenmair, 1989)

There is no information on home range for this species.

Hyperolius viridiflavus has a melodic call like a xylophone that is more tonal than that of other species in this genus. Their calls are a characteristic part of the African night sounds. Males have an exposed calling site and form choruses in order to attract mates.

Hyperolius viridiflavus nitidulus males have two distinct calls, a mating call and a territorial call. The territorial call is longer and deeper than the mating call, and lasts from 0.28 to 0.36 seconds and has a frequency of 0.98 to 2.6 kHz. The mating call is a short metallic click that lasts between 0.10 to 0.24 s and has a frequency of 2.04 to 3.43 kHz, depending on the size of the frog. Female H. viridiflavus cannot make sounds.

Members of this species use keen visual perception in order to capture insects. They have bulging eyes and horizontal pupils. (Bubac, 2009; Grafe and Lisenmair, 1989; Schiøtz, et al., 2004; Schiøtz, 1999)

Hyperolius viridiflavus are insectivores that feed on many different types of insects including flies in the genera Drosophila, Musca, Phormia, Lucilia, and Calliphora. The free-living tadpoles of Hyperolius viridiflavus nitidulus eat algae. (Bubac, 2009)

Hyperolius viridiflavus has a bright warning coloration that wards off predators. Dragonfly larvae, beetle larvae, turtles, ray-finned fish and water snakes eat the tadpoles of H. viridiflavus. (Bubac, 2009)

Hyperolius viridiflavus is a predator of insects in the African savanna. It is also the prey of several species of animals. (Grafe and Lisenmair, 1989)

This species is a part of the international pet trade although not at high levels. (Schiøtz, et al., 2004)

There are no known adverse effects of Hyperolius viridiflavus on humans. However, the Masai of East Africa have a superstition that their cattle will die if they eat these frogs because of their bright warning coloration. (Schiøtz, 1999)

Hyperolius viridiflavus is listed as least concern by the International Union for Conservation of Nature because of its very wide distribution and tolerance of a broad range of habitats. It also likely has a large population size with no significant threats. This species is occasionally found in the international pet trade, but not at a high enough level to pose a threat to it. (Schiøtz, et al., 2004)

The taxonomy of Hyperolius viridiflavus is complex and has been the subject of much debate. Much of the difficulty has come from the dependence on dorsal color patterns as taxonomic characters. Schiøtz argues that H. viridiflavus is a superspecies with many subspecies that can be divided into two subgroups, parallelus and viridiflavus based on coloration and geographic range. Wieczorek has broken up the various subspecies of H. viridiflavus into ten full species based on mitochondrial DNA. Adult H. viridiflavus are unique because they can regenerate fully functional digits after amputation. (Richards, et al., 1975; Schiøtz, 1975; Wieczorek, et al., 2001)