Genes and mating calls set Lantau's endangered horned toads apart in a 19-animal Lingnan study

Nine animals carry the Lantau side of the comparison ^[6]. The other ten samples came from Hong Kong Island and Kowloon ^[15]. The genetic analysis also set Lantau apart from Shenzhen toads ^[7]. None of the 19 listed samples came from Shenzhen, though, or from the New Territories, where the species also lives in mountain streams ^[16][5].

The design used three kinds of evidence. The team examined genetic and morphological traits in the samples ^[6] and recorded males calling on Lantau, Hong Kong Island and Kowloon ^[8]. Two of the three separated Lantau. Its toads form their own genetic group, which the team takes as a sign that the population has been apart for a considerable period ^[7]. Lantau males call faster, with shorter notes, and the researchers describe the difference as significant ^[8]. The published summary does not give the number of recordings, the size of the call differences or the genetic markers used.

The third line came back flat. In appearance, the Lantau toads showed no marked differences from the others ^[9]. Jonathan Fong, the corresponding author, said that is why the team combined methods. "Many amphibians look very similar, making evolutionary differences difficult to detect through traditional methods that examine morphology alone. By integrating genetic and acoustic data, we found that frogs on Lantau Island have a distinct genetic makeup and male toads have different mating calls. This suggests that the Lantau population is following a distinct evolutionary trajectory," he said ^[10].

On cause, the account is measured. Sung Yik-hei, the first author, said Lantau was cut off from the mainland about 10,000 years ago, and that the isolation likely reduced gene flow between populations ^[11]. The team offers geographic isolation as the likely contributor to the island's distinct traits ^[3]. That fits the genetic pattern. As reported, it is an explanation for the divergence and has not been shown to cause it.

Sung was also plain about how far the speciation reading goes. "The results suggest that the short-legged horned toad population on Lantau Island may represent an early stage of speciation, although current evidence is insufficient to determine whether the Lantau population constitutes a distinct species," he said ^[12].

So the management proposal does not depend on a new species name. It rests on the argument that the Lantau toads cannot be replaced. If the Lantau population declines or dies out, Sung said, "its unique genetic traits could be lost and could not be replaced by populations from other areas" ^[13]. "We therefore propose that conservation management recognize the Lantau population as an independent conservation unit, giving due consideration to its specific conservation needs to ensure the survival of this unique native population," he said ^[14].

I think the case for treating Lantau separately is reasonable on this evidence. Two independent kinds of data point the same way: DNA, and a behaviour that matters for mating. The condition is the sample. Nine Lantau animals is a small base. I would want the split to hold with more island animals, and with the unsampled New Territories populations, before calling it settled.

The species is endangered on the IUCN Red List and is the only known small frog in Hong Kong in the genus Boulenophrys ^[1]. The authors say the work suggests the territory may hold biodiversity not yet described ^[17]. The paper appears in Current Herpetology ^[4].