During a targeted survey among the boulder clusters of Dauan Island – a granite island just 275 meters above sea level in the Torres Strait Islands, between Australia and Papua New Guinea – researchers from James Cook University have discovered not one, but many three new species of vertebrates: a gecko and two frogs. Nactus simakalit’s a gecko with an elongated body and raised scales while Callulops gobakula And Choerophryne koeypad, two frogs with the unmistakable croaking of the Microhylidae family. All species live hidden between the cracks of the boulders, in an environment so particular that they have them isolated for millennia from the rest of the world. Dauan Island is located just 11 km off the coast of New Guinea, but belongs politically to Australia. It’s one small island-mountainthe last emerged strip of the Australian continental basement. During the last ice age, when the sea lowered more than 100 meters, the lands of the Torres Strait formed a bridge between the two continents. With the rising waters, the species trapped on the islands have disappeared evolved in isolationas in tiny natural laboratories.
What is the new rock gecko: the Nactus simakal
The new gecko, baptized Nactus simakalwas collected in January 2021 at 50 meters above sea level. AND slender and slimbetween 44.4 mm and 53.6 mm long from the snout to the cloaca, with a even longer tail: up to 63 mm, i.e. 139% of the body length. The gecko’s skin is covered with small scales. Those on the belly have a light central ridge – like a tiny “thorn” – while those under the tail have a more obvious one, like small raised gills. This detail, which may seem minimal, is actually what makes it distinguishes from other similar geckos.
Adult males also have nine tiny pores arranged in a “V” shape in front of the cloacal opening (the part of the body through which digestive and reproductive functions pass): they are glands that produce odorous substancesuseful for marking the territory or attracting females.
On the back the gecko presents 12–14 rows of tiny growthscalled tubercles, and another 30–35 along a central line of the body. The head is narrow and slightly flattened, with big eyes (they occupy about 6% of the total length) and a nose that curves slightly upwards, giving it a curious and somewhat “beaked” appearance.
Analyzing the Mitochondrial DNA – a part of the genetic heritage that is passed from mother to child – researchers have discovered that this species is different by more than 20% compared to more similar geckos, such as Nactus eboracensis And Nactus alotau. Such a large difference means that it is not just one variant, but one completely distinct evolutionary lineseparated from the others for a long time.
This species lives exclusively among granite rocks of Mount Cornwallislocally called Simikal Pad, from which it takes its scientific name. Analyzes suggest that its population occupies a very small area, which needs to be urgently protected.
The two frogs croaking at the stones
A few meters lower, in the same rock maze where the new gecko lives, the researchers also discovered two tiny tropical frogs never seen before, both exclusive to Dauan Island. The first, Callulops gobakulait is about big 5 centimetershas a stocky body and uniform brown skin; the second, Choerophryne koeypadAnd just 2 centimeters large and has tiny adhesive discs on its fingers that allow it to climb between damp stones.
To recognize them as new species, scientists measured with extreme precision 22 body characteristicsusing an electronic caliper with a margin of error of one tenth of a millimeter. In males Callulops gobakula the length of the tibia is equal to 40% of the body, in Choerophryne koeypad slightly less, and their mitochondrial DNA also showed clear differences: 2.5% different from the best known Callulops omnistriatus And 3% as compared to Choerophryne exclamitans – values which, in frogs of this family, are sufficient to define a distinct species.
But the real confirmation came from the voice. In fact, each frog has a unique recall like a fingerprint: Callulops gobakula produces 9–12 hoarse sounds similar to small “rarks”, emitted at a rate of approx 4 notes per secondthey last 2.5 seconds and are followed by long pauses of silence, even of 30–40 seconds. The lower case Choerophryne koeypadhowever, sings higher and faster: 10–19 notes in secondswith tones reaching i 3,000 Hz and a pace beyond 6 notes per second. Two very different voices, born to resonate among the stones, which tell the hidden and surprising life of a tiny island on the border between two worlds.
Both species live in the boulder-fieldsdeep masses of rocks that maintain aConstant humidity even during dry periods. The name gobakula (“boulders”) e koeypad (“rocky mountain”) refer precisely to these environments in the local language (Kalaw Kawaw Ya). It is believed that precisely these microclimates have allowed the survival of genetic lines once widespread between northern Australia and New Guinea, which then retreated due to increasing aridity.
Today, Callulops gobakula And Choerophryne koeypad they are the first microilides – family of amphibians widespread in the southern hemisphere – never recorded in Torres Strait and they represent abiogeographical exception: Their closest relatives live over 200–280 km away, in the mountains of Papua New Guinea.
