Amphibians
Gardiner's Seychelles Frog
Sechellophryne gardineri · also called gardiners seychelles frog, Gardiner's frog
Gardiner’s Seychelles frog is small enough to perch on a fingernail — one of the tiniest frogs alive. It also has no eardrum and no middle ear at all, and yet it clearly hears its own species calling, apparently by routing the sound through its own mouth.
Overview
Gardiner’s Seychelles frog lives only in the mist forests of two Seychelles islands in the Indian Ocean, in damp leaf litter and moss. Adults are just 8–11 mm long and brown, feeding on mites, springtails, and tiny insects.
Hearing without an eardrum
It lacks the tympanic middle ear most land animals use for airborne sound, yet responds to recorded calls — research suggests sound enters its large mouth cavity and passes to the inner ear through unusually thin bone.
No tadpole, no pond
It lays eggs in moist leaf litter that hatch directly into froglets, freeing it from any need for standing water.
Status
Gardiner’s Seychelles frog is Vulnerable, locally common but confined to a tiny area of mist forest sensitive to invasive species and climate change.
Gardiner's Seychelles Frog: common questions
How small is Gardiner's Seychelles frog?
Adults measure only about 8 to 11 millimetres from snout to vent, small enough to sit on a human fingernail with room to spare, which places the species among the smallest frogs and smallest four-limbed animals in the world, in the same size range as the tiny New Guinea and Brazilian frogs that hold the overall record. At this size the frog has to contend with challenges of physics that larger animals do not, such as an extreme risk of drying out because of its high surface-area-to-volume ratio, which is one reason it is confined to consistently damp, misty forest.
How can a frog hear if it has no eardrum?
Most frogs, like most land vertebrates, hear by way of a tympanic middle ear, in which an eardrum on the side of the head picks up airborne sound and passes the vibrations through a small bone to the fluid-filled inner ear. Gardiner's Seychelles frog has no eardrum and no middle ear at all, which for a long time raised the question of whether it could hear its own calls or was effectively deaf. Playback experiments showed that males do respond to recorded calls, and X-ray and computer modelling studies concluded that sound enters the frog's disproportionately large mouth cavity, which acts as a resonating chamber, and is then transmitted to the inner ear through a region where the bone is unusually thin and there is very little tissue in the way, allowing enough sound energy through for the frog to hear.
Why does Gardiner's Seychelles frog matter for understanding evolution?
The Seychelles are fragments of ancient continental crust that separated from other land masses tens of millions of years ago, and they carry a distinctive, relict fauna that has been evolving in isolation ever since, including several unique frogs and caecilians. Gardiner's Seychelles frog belongs to this old lineage, and its eardrum-free hearing is of particular interest because it demonstrates an alternative solution to a problem, detecting airborne sound, that vertebrates usually solve with a middle ear. Studying it helps researchers understand both the deep history of amphibians in the Indian Ocean region and the range of ways that hearing can work.
Is Gardiner's Seychelles frog endangered?
It is currently classified as Vulnerable rather than Endangered, because although it can be locally abundant in the right habitat, its entire world range consists of small patches of high-elevation mist forest on just two Seychelles islands, so the total area it occupies is very small. Within that range it faces threats from introduced species, degradation of forest, and the prospect of climate change altering the cool, humid, misty conditions it depends on, since a frog this small has very little tolerance for drying out. Much of its remaining habitat lies within protected areas, which is an important factor in its favour.