Marine insects, there are, there are, we can say paraphrasing the well-known Galician saying ("Meigas habelas, hainas"), although they are certainly very few and barely known. The alkaline fly or brine fly (Ephydra hians) is one of the examples that are mentioned when asking about insects capable of living in salty waters such as those of the Dead Sea (Israel, the West Bank and Jordan) or Mono Lake (California, USA.).
The scientific community has so far described approximately one million different species of insects and it is speculated that, in reality, there are more than six million taxa of these arthropods on our planet, generally endowed with one pair of antennae, two pairs of wings, and three pairs of insects. pairs of legs Insects are the most diverse animals on Earth, never better said, because practically all of them live on land, if the expression is allowed for some bugs that on many occasions are characterized by their flying ability.
Some hundreds of species of aquatic insects are known, but almost all of them live totally or partially in fresh water (rivers, lakes...) so, we repeat, Ephydra hians is an exception in every rule. Although not the only one, so are the three species of the genus Halobates: Halobates micans, Halobates sericeus and Halobates flaviventris (stilts that live on the surface of the Pacific and Indian oceans).
A group of scientists from Tokyo Metropolitan University (Japan) has now proposed a hypothesis to explain why insects are so rare in marine or saltwater environments.
As the first step in their research, the team led by Tsunaki Asano believes that insects have developed a unique chemical mechanism to harden their shells, a process in which these animals use molecular oxygen and an enzyme called multicopper oxidase-2 (MCO2).
The authors of this research affirm that this process is very effective in the terrestrial environment (in the presence of air) but practically impossible if you live permanently in salt water, which leaves insects at a disadvantage in this environment.
The same is not true of crustaceans, which live and reproduce very effectively in the marine environment thanks to the fact that they grow their shells in a very different way than insects.
The comparison is not free because, although sitting at the table we prefer the former, both crustaceans and insects belong to the same phylum as arthropods.
What's more, the authors of this new study, whose results have been published in the journal Physiological Entomology, recall that crustaceans and insects are part of the same family, Pancrustacea (with an exoskeleton consisting of a layer of wax and a hard cuticle). , and that insects originate from a variety of this family (phylogenetically speaking) that came out of the sea and adapted to land.
Asano's team explained in a previous study that as insects adapted to terrestrial environments, they evolved a unique gene that creates MCO2, which helps them toughen their cuticles using oxygen.
MCO2 mediates a reaction in which molecular oxygen oxidizes compounds called catecholamines in the cuticle, turning them into surface-hardening and binding agents.
This process is completely different from that of crustaceans, which harden their cuticles using calcium from seawater.
Consequently, the authors of the study affirm that the process mediated by the MCO2 of the insects determines that they are basically terrestrial animals, where it is easier to use oxygen for their skeletal formation.
The sea is now an inhospitable environment for insects due to the lack of oxygen and the abundance of better adapted organisms. In addition, they point out, the hardening and drying of the cuticle through the MCO2 pathway leads to a biomaterial that is poorly protective and lightweight.
Insects are not the only arthropods that have adapted to land and MCO2 is presumably not strictly necessary for the proliferation of these animals with hard exoskeleton. However, the nature of insect cuticles speaks volumes about their success in the terrestrial environment. In fact, the team believes that MCO2 could be a defining characteristic of insects: "without MCO2, there are no insects," Tokyo Metropolitan University notes in a release note of its researchers' results.