Jurassic viral gene may have helped apple snails start laying eggs on land

Pomacea canaliculata, or the 'apple snail.' Credit: Lingnan University

Pomacea canaliculata, commonly known as the apple snail, is a pest commonly found in Hong Kong's wetlands and farmlands. It feeds on aquatic plants and produces toxic pink egg masses resembling miniature grapes that adhere to plants or stone bunds. It is listed by the International Union for Conservation of Nature (IUCN) among 100 of the World's Worst Invasive Alien Species.

The Division of Science at Lingnan University and its collaborative research team analyzed the genomes of Pomacea canaliculata and its close relatives and discovered that, despite being aquatic animals, they possess the trait of terrestrial reproduction. Their egg masses also exhibit desiccation resistance, UV screening and predator deterrence. This capability may have originated from a viral infection during the Jurassic period, when their ancestors integrated the viral gene into their own genome.

Scholars say this could not only provide foundational insight into how land invasion occurred, but also suggest potential avenues for developing inhibitors to eradicate the snail pest at its source. These research findings were recently published in Advanced Science .

Tracing an ancient adaptation

The research team was led by corresponding author Prof. Jack Ip Chi-Ho, assistant professor (Presidential Early Career Scholar) in the Division of Science (DoS) at Lingnan University, in close collaboration with Prof. Jian-Wen Qiu (Hong Kong Baptist University) and Prof. Jin Sun (Ocean University of China), together with international malacological experts.

The team said that after the ancient continent split around 128 million years ago, the ancestors of Pomacea canaliculata living in freshwater environments parted ways and evolved independently across Asia, Africa and the Americas. Interestingly, a similar land-laying reproductive trait evolved independently in two apple snail lineages that diverged more than 100 million years ago—one in Asia and Africa (Pila) and one in the Americas (Pomacea).

The team deduced that the ancestors of the apple snail were infected by a virus before the split, as early as 145 million years ago during the Jurassic period. By integrating the viral gene into their own genome, they drove the evolution of the reproductive trait of laying eggs on land, thereby reducing the threat to the egg masses from aquatic predators such as fish.

The Pomacea canaliculata is a common agricultural pest in Hong Kong. It produces toxic pink egg masses resembling miniature grapes adhered to plants or stone bunds, and is listed by the International Union for Conservation of Nature (IUCN) among the 100 of the World's Worst Invasive Alien Species. Credit: Lingnan University

How the eggs stay protected

Using comparative genomics, the team analyzed the genomes of six apple snail species from Asia, Africa and the Americas, and conducted a genome-wide comparison with their close relatives, including the family Viviparidae (river snails) and other mollusks. The results revealed that in the terrestrial egg-laying species of the Old World genus Pila and the New World genus Pomacea, the egg fluid contains more than 80% of the protein PV1, which helps enhance resistance to desiccation and ultraviolet rays.

Further analysis indicated that within the New World genus Pomacea, including Pomacea canaliculata and Pomacea maculata, there is also a neurotoxic protein called PV2, which provides additional toxic defense to deter predators. Together, these key egg-fluid proteins exhibit unique neurotoxic and physical protective characteristics, which may have helped drive the apple snail to enhance its reproductive capacity—producing red-pink, toxic egg masses resembling miniature grapes that deter terrestrial predators such as birds and insects while allowing the egg masses to maintain water balance in the air and resist desiccation and ultraviolet rays.

The threat and possible control

Prof. Ip explained that Pomacea, originally native to the Amazon River basin in South America, was introduced to Asia for food, but because it harbors parasites that can cause severe diseases in humans, it ultimately became an invasive species in freshwater ecosystems worldwide, including Hong Kong. Each apple snail can produce up to 500 eggs in a single week and eats aquatic plants such as water spinach and watercress, affecting crop growth. Its astonishing reproductive capacity allows it to compete with native freshwater snails for living space, disrupting the ecological balance of wetlands, affecting the habitats of birds and amphibians, and causing severe environmental damage.

Prof. Ip said, "In the past, controlling the snail pest in Hong Kong relied mainly on manual removal of egg masses and the application of chemical pesticides, which yielded limited efficacy. The use of chemical agents could also cause pollution to wetland ecosystems and crops. Pomacea is not the only aquatic animal to ha…