Taiwan: How an earthquake wiped out a butterfly species

An earthquake in 1999 may have wiped out the Taiwanese swallowtail subspecies Papilio machaon sylvina forever. According to a recent study in the journal PLOS, this may be the first documented case in which an earthquake caused the extinction of a butterfly.

The Old World swallowtail (Papilio machaon), one of Europe’s largest and most impressive butterflies, is widespread across the Palearctic and occurs in numerous subspecies. In Taiwan, two known subspecies existed: P. m. schantungensis, which lives on the Matsu Islands near the Chinese coast, and P. m. sylvina, which was restricted to the main island of Taiwan.

The subspecies endemic to Taiwan, first described in 1930 by Japanese lepidopterists, developed unique genetic and ecological characteristics. Its home was in the middle to high elevations of the central mountain range, at altitudes of 1,000 to 2,500 meters. The butterfly larvae fed on the host plant Peucedanum formosanum and produced at least three generations per year. But its specialization to these elevations and this plant also made it vulnerable to sudden environmental changes.

The Jiji earthquake and its consequences

On September 21, 1999, an earthquake known as the “Jiji earthquake” with a magnitude of 7.7 shook central Taiwan. It was one of the most severe earthquakes in the island’s history and had devastating consequences: more than 2,400 people lost their lives, more than 11,000 were injured and about 100,000 buildings were destroyed.

In addition, the earthquake caused massive landslides that blocked rivers and formed dams. Large parts of the landscape were permanently altered by mud and debris; the mountain regions in particular were severely damaged. Numerous animal and plant species thus lost their natural habitat, including the butterfly P. m. sylvina.

At the time of the earthquake, the butterflies were in the pupal stage, with the pupae attached to the host plants, which were completely buried under mudslides. Since then, the Taiwanese swallowtail subspecies has not been seen again despite intensive searches, even though the host plant still exists in the affected areas. The researchers therefore assume that the subspecies is extinct.

A genetically unique lineage

To ensure that P. m. sylvina is in fact a distinct subspecies, the Canadian entomologist Vazrick Nazari and his team carried out a genetic analysis. They used the COI barcode sequence of a specimen raised in 1995 to compare its genetic features with other populations of the Old World swallowtail. The results clearly showed that the swallowtail subspecies on Taiwan’s main island forms an independent genetic lineage.

Surprisingly, the Taiwanese subspecies proved to be genetically closer to populations from northern Eurasia, such as the Russian Republic of Buryatia and the Kamchatka Peninsula, than to populations from the Chinese mainland. This genetic isolation shows that P. m. sylvina was on an independent evolutionary path before it was presumably wiped out by the Jiji earthquake. Its adaptation to the special conditions of Taiwan’s mountains made it unique, but also especially vulnerable.

How did the butterfly subspecies arise?

The evolution of the swallowtail subspecies Papilio machaon sylvina is closely linked to Taiwan’s geological history. Around four to five million years ago, the island was formed by the subduction of the Philippine Sea Plate beneath the Eurasian Plate. About 1.55 million years ago, Taiwan finally separated from the Asian mainland—a decisive moment for the subspecies’ evolution.

The study shows that the last common ancestor of P. m. sylvina and the continental populations of the Old World swallowtail lived around 1.4 million years ago. Through isolation in Taiwan’s high elevations, an independent evolutionary development began. This gave rise to a subspecies that adapted perfectly to the special conditions of Taiwan’s mountains—and thereby differed significantly from its mainland relatives.

Hope dies last

Whether the earthquake alone was responsible for the disappearance or whether other factors such as climate change, pesticides or commercial collecting had already weakened the population beforehand cannot be fully ruled out by the scientists. But the host plant Peucedanum formosanum still grows in the former habitats.

Although the butterfly has not been seen or collected since 1999, there remains hope that it still exists in remote mountain regions of Taiwan’s highlands and may one day be rediscovered. Nature has delivered surprises before: for example, the Mesilau toad in Malaysia, considered extinct after an earthquake in 2015, was rediscovered in 2023.

The fate of P. m. sylvina is not an isolated case. Natural disasters have also contributed to species extinctions in the past. For example, the Swan Island hutia and the Guadeloupe ameiva, two animal species, lost their habitat after devastating hurricanes and disappeared forever. These examples show how strongly extreme environmental events can endanger the survival of specialized species.

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Source

• Nazari V., Yen, S. H., Hsu, Y. F., Shapoval, G., Shapoval, N., et al. (2024). Wiped out by an earthquake? The ‘extinct’ Taiwanese swallowtail butterfly (Lepidoptera, Papilionidae) was morphologically and genetically distinct. PLOS ONE 19(11). e0310318. https://doi.org/10.1371/journal.pone.0310318