Why are there so few insects in the ocean?

Tokyo, Japan –The scientists from Tokyo Metropolitan University have come up with a possible explanation for why insects are not commonly found in marine environments. They have previously discovered that insects have a special chemical mechanism that helps harden their shells, which uses an enzyme called multicopper oxidase-2 (MCO2) and molecular oxygen. The scientists believe that this mechanism is not advantageous for insects in the sea, but it does help them survive on land.

Based on this, the scientists propose that MCO2 plays a central role in the ecological and evolutionary development of insects. Insects that have evolved to use this mechanism are well-suited for life on land, but it puts them at a disadvantage in marine environments. This hypothesis sheds light on the unique adaptations and challenges faced by different species in different environments.

Insects are incredibly successful and important organisms, with a significant impact on the global ecosystem. They are the most abundant and diverse group of animals on land, making up the majority of terrestrial biomass. However, despite their biological ancestors originating from the sea, insects are very rare in marine environments. This is a puzzle that scientists have been trying to solve for many years, as it is not clear why insects have been so successful on land but not in the sea. This mystery highlights the unique adaptations and challenges faced by different species in different environments.

A team of researchers from Tokyo Metropolitan University led by Assistant Professor Tsunaki Asano has proposed an explanation for why insects are rare in marine environments. They have used evolutionary genetics to show that both crustaceans and insects are part of the same family, Pancrustacea, and that insects were a branch that adapted to the land. The researchers have found that insects evolved a unique gene that creates an enzyme called multicopper oxidase-2 (MCO2) to harden their cuticles using oxygen when they moved to terrestrial environments. In contrast, crustaceans harden their cuticles using calcium from seawater. The researchers believe that the abundance of oxygen on land makes it more suitable for insects, while the lack of oxygen and competition from better-adapted organisms make the sea a harsh environment for them. This suggests that the evolution of MCO2 is a key factor in the success of insects on land and their rarity in the sea.

In addition to the lack of oxygen in the sea, the hardening process used by insects to protect their cuticles may have also contributed to their rarity in marine environments. The process not only creates a protective layer but also makes the cuticle lightweight, enabling insects to climb, glide, and eventually fly, giving them the ability to migrate and occupy new niches in the ecosystem. This allowed insects to thrive and become the most abundant terrestrial animals. Crustaceans, on the other hand, have denser shells due to their use of calcium for hardening.

Although insects are not the only arthropods to have adapted to the land, it is clear that the presence of MCO2 is not a strict requirement for success in terrestrial niches. Nonetheless, the structure of insect cuticles is indicative of their achievements in the terrestrial environment. The team believes that MCO2 could be a defining characteristic of insects, with no MCO2 leading to no insects. Their research offers a fresh perspective on the significance of cuticle hardening in insect evolution and terrestrialization.