Common Reed Frog

AmphibianAfrica

Jul 29

Hyperolius viridiflavus

The common reed frog exhibits extreme variation in colour patterns — with some 50 recognised subspecies. Additionally, this frog changes the colour of its skin according to weather and temperature, turning pure white in the heat of the dry season.

Going on a Frog Hunt

Say that you were sent to find and document frogs throughout the countries of Central-East Africa. You'd trek through the humid rainforests of the Democratic Republic of Congo and the Central African Republic, following winding streams and rivers. You'd journey across the drier savannahs of Tanzania, Kenya, and Uganda, tracing the shores of the giant Lake Victoria. You might ask to search through a few fields of rice or sugarcane and gardens, to flip some leaves and check some puddles. You search by night, sweeping your flashlight over waters echoing with nocturnal anuran choruses. This is just a hypothetical adventure, of course, but what would you find?

Clockwise from top left; shovel-nosed frog (*Hemisus marmoratus*), giant African bullfrog (*Pyxicephalus adspersus*), red-banded rubber frog (*Phrynomantis bifasciatus*), natal puddle frog (*Phrynobatrachus natalensis*), and African clawed frogs (*Xenopus laevis*).

If you dug around in the mud for a bit, you might come face to pointy snout with the shovelnose frog. This rotund frog with a small head and upturned nose is subterranean — true to its name, it digs its burrow head first, using its nose. The African bullfrog is hard to miss, as it is diurnal and one of the largest frogs in the world, almost reaching lengths of 25 cm (10 in). Its massive body is wide and flat, and handling one feels like holding an oversized slimy hamburger in your hands. You'll want to avoid touching the banded rubber frog, however, which you might encounter in cultivated fields, wet savannahs, or even hidden under some rocks miles from the nearest water. Its skin is rubber-like and dark, banded and spotted with bright orange markings — an aposematic signal to not touch(!) because it's toxic to most living things, including humans. The natal dwarf puddle frog may not be toxic — and it may have a cute name — but you'd likely not touch it if you saw it, given the copious wart-like bumps that cover its body. In contrast, the African clawed frog is slick and smooth, but even less friendly looking. Found in many rivers and ponds, it floats ominously, displaying its characteristic trait: its unnerving Freddy Krueger claws. To its aquatic neighbours, it truly is a nightmare, for it uses its claws to tear up its victims and eat anything that fits in its mouth.

However, most frequently — especially on tropical savannahs and along forest margins — you'll encounter a lot of lithe-looking tree frogs, that measure about 15 to 30 mm (0.6 - 1.2 in) long, with blunt snouts and extensively webbed feet. Almost anywhere you go in Central-East Africa, you find these little frogs crawling among the reeds in marshes and ponds, pasturelands and ditches; they gather in large groups, inflating their voluminous vocal sacs to croak to the night, like a choir of chiming xylophone bars.

Endless Forms

In each new local you travel to, you notice that these little frogs look strikingly different. Some are a single solid colour — an almost uniform light green or brown. Some are speckled with many dots as if an artist flicked a paintbrush at them. Many have colourful feet and bellies as if they waded across the artist's palette. Some just look like they were dropped in ink. There are those that mimic their African neighbours — exhibiting the spots of a leopard or stripes of a zebra — and those mimicking our domestic breeds, blotched black and white like a Dalmatian or cow. The most striking appear like glistening green jewels or deliberate works of art, decorated in colourful whorls and smears, or psychedelic patterns — like hopping optical illusions. To be so varied in colour and pattern, they must be different species, right?

All of these frogs — with their plain green-brown bodies, leopard spots, and kaleidoscopic patterns; living in savannahs, forests, gardens, and ditches — are all considered a single species: the common reed frog (Hyperolius viridiflavus) — its specific name combines "viridis" (green) +‎ "flāvus" (yellow), despite the frog itself displaying many more colours. There are, however, more than 50 recognised subspecies. ¹

Pale Frogs

As you travel Central-East Africa in your search for frogs, you'll notice a change as the dry season, beginning in late June and ending around September, bakes the landscape and parches the vegetation — and not just a change in weather, but a change in the frogs. As temperatures soar, unrelieved by rainfall, and the mercury hits 35°C (95°F), you notice that the once colourful reed frogs are turning a dull whitish-brown or grey colour. At 40°C (104°F), the air is like a massive heated blanket forcibly draped over you, smothering you, while the ground radiates heat like a stovetop, and the once lush plants appear wilted and fatigued. And all the reed frogs have turned a brilliant pure white.

The common reed frog’s skin becomes a bright white to survive the dry season.

This rapid colour change isn't for courtship or camouflage — for, in the dry season, no predator is as dangerous to a frog as the sun is. Frogs are amphibians and, more than any other terrestrial animals, they need moisture to survive. A frog's skin isn't just a protective cover for its insides — although it is that too, covered in substances with antibacterial and antifungal properties — but perhaps its most important organ. While a frog does have lungs, a large portion of its breathing is done through its skin; absorbing oxygen from the skin's surface and directly into its bloodstream to be circulated around its body. But to "skin-breathe" in this manner (technically called "cutaneous respiration") the frog's skin must be moist. And so, most frogs never stray far from a source of water, be it a lake or a puddle, and while they're able to secrete a mucous that keeps their skin moist, it is a flimsy protection against parched air and searing heat — for a frog, temperatures above 30°C (86°F) can mean dehydration, desiccation, suffocation, and death.

Our human skin is much thicker, and less permeable than that of frogs. Although we can scarcely breathe through our skin, it does serve to regulate temperature and fluids, so perhaps "skin-breathing" isn't so hard a concept to grasp. However, what happens in/to the skin of a common reed frog, is a little more complicated — brace yourself for some skin-related vocabulary.

As the hottest parts of its range reach 40°C (104°F), the common reed frog rearranges its chromatophores — cells found in the dermis, or middle skin layer, that provide pigment to its skin. Usually, during the wet season, the reed frog's iridophores — a type of chromatophore that reflects light from stacks of platelets called purine crystals — are distributed irregularly throughout its skin cells. But, as the dry season sets in, the amount of iridophores on its back and stomach increase by 4 - 6 times and arrange themselves parallel to the surface. The platelets of purine crystals inside the iridophores, multiplied and arranged in such a manner, act to reflect a large amount of energy from the sun and make most of the frog's skin much less permeable, thereby reducing water loss through evaporation. It also has the effect of turning the frog's skin white.

Man-children & Annual Adults

A common reed frog calling for a mate out in the open.

Common reed frogs court and breed during the wet season; when moisture is plentiful and the sun isn't trying to kill them. As the season begins, males migrate to shallow bodies of water and display themselves proudly and flagrantly as they sing their courting songs at dusk — perhaps a bit too flagrantly. Sitting out in the open while calling loudly attracts turtles and water snakes, and significantly increases the mortality rate of male reed frogs. Meanwhile, the male frogs are busy competing amongst themselves in drawn-out battles for the best calling sites. A lucky male — which has won a good spot and has avoided being eaten — is approached by a larger female, whom he mounts in axillary amplexus (which simply means that he grabs her from behind, under the armpits), and they copulate. She then retreats below the water, typically under some vegetation, to lay her clutch of 330 or so eggs.

The eggs hatch quickly, after only 2 to 5 days, and metamorphose from algae-eating tadpoles into insectivorous juveniles by 8 weeks of age. Young reed frogs go through two phases — or sometimes only one, if they are male. Phase J is the juvenile phase, when the frogs look plain brownish to green with a few light stripes. Phase F is the adult phase, when the frogs diversify into their highly varied patterns and colours. Some males, however, never undergo a change to Phase F and remain in their juvenile phase for life — like adult men who refuse to stop wearing their clothes from high school.

A juvenile, or Phase J, common reed frog.

But before these frogs get a chance to grow out of their youthful phase, they must survive the heat of the dry season. It is juveniles that perform the complex physiological magic; turning their skin a reflective white and sealing in their moisture, lest it be stolen by the hot dry air. They lie dormant, estivating, on wilting grass and leaves. Light red skin around their pelvic regions and inner limbs becomes specialized for taking in any meagre moisture available — drawing from sources as scant as an evaporating dew drop. The adult frogs do not handle the heat well. In the driest and hottest parts of the common reed frog's range, no adult was ever found to have survived the dry season — the lives of these "annual adults" are restricted to a single year by extreme forces of weather.

¹ Unsurprisingly, there is some debate among taxonomists as to the proper categorization of the common reed frog. There are those who argue that the common reed frog is a single united superspecies, divided into two subgroups — parallelus and viridiflavus — based on geography and morphology, with over 50 subspecies. Other taxonomists, positing mitochondrial DNA as their evidence, have suggested splitting this taxonomic headache of a frog into ten fully different species.

**Where Does It Live?**

⛰️ Occupy most most suitable habitats (ponds and lakes) in savannah, grasslands, and at the margins of forests, lakes, rivers, and swamps, cultivated land and gardens.
📍 Central-eastern Africa.

‘Least Concern’ as of 05 April, 2017.

IUCN

Size // Small
Length // 15 - 30 mm (0.6 - 1.2 in)
Weight // 2 grams
Activity: Nocturnal 🌙
Lifestyle: Solitary 👤
Lifespan: Typically 1 year in the wild
Diet: Carnivore (Insectivore)
Favorite Food: Insects, such as flies 🦗
Class: Amphibia
Order: Anura
Family: Hyperoliidae
Genus: Hyperolius
Species: H. viridiflavus

A few of the common reed frog's forms include; solid green or brown, flecked with many dark spots, white skin smeared in black like a cow or striped monochrome like a zebra, shining in multiple hues and patterns of green, and psychedelic patterns that appear like optical illusions.

Some parts of this frog's range reach temperatures of 40°C (104°F). The structure of its skin changes to more effectively reflect sunlight, turning white as a consequence. The skin around pelvic regions and inner limbs typically becomes a light red and is specialised for absorbing what moisture is available.

They breed during the wet season. Males sit out in the open and croak their xylophone-like calls into the night.

A female common reed frog can lay as many as 330 in a clutch, which hatch in only 2 to 5 days.

Young reed frogs go through two phases — or sometimes only one, if they are male. Phase J is the juvenile phase, when they look fairly plain. Phase F is the adult phase, when the frogs diversify into their highly varied patterns and colours. Some males never undergo a transition into their adult forms.

Adults do not fare well in the heat, so it is typically the juveniles that survive the dry season in the hottest parts of this frog's range. As a result, many of these frogs live for only a year.

In the lab, these frogs have been shown to undergo protogyny; a female-to-male sex change. These new males were capable of successfully fertilizing the eggs of females.

Some argue that the common reed frog is a single united superspecies, divided into two subgroups — parallelus and viridiflavus — based on geography and morphology, with over 50 subspecies. Other taxonomists, positing mitochondrial DNA as their evidence, have suggested splitting this taxonomic headache of a frog into ten, fully different species.