Insects are said to be the most prosperous organisms on earth, adapting to any environment on land and boasting a diversity of more than one million species.Curiously, however, very few species are adapted to marine environments.
Why are there no insects in the sea?In response to this question, various hypotheses have been proposed, such as ``inability to adapt to seawater (osmotic pressure, salinity)'', ``water pressure destroys the trachea'', and ``high predation pressure (existence of fish?)''. Although it cannot be said to be persuasive from the point of view of insect physiology, active debate continues.
This time, a research group from Tokyo Metropolitan University and Kyorin University presented a new hypothesis about why insects are not found in the sea, focusing on the "exoskeleton", which is an important body structure for insects, which are arthropods.This is because some crustaceans, which originally lived in the sea, migrated to the land environment and eventually evolved into insects. It is related to the theory of this group that it has come to perform skeletal hardening.The trait of insects that uses oxygen to harden their exoskeleton was advantageous in the process of adapting to an oxygen-rich terrestrial environment, but it contains only 2/2th of the oxygen on land (air). It is said that it may be one of the obstacles when re-entering the water.
In contrast, crustaceans, arthropods that are closely related to insects and are thought to compete for the same habitat, use calcium, which is abundant in seawater, to stiffen their exoskeletons. .Crustaceans, which have a strong exoskeleton made of calcium, are dominant in seawater, and it is thought that insects that cannot harden their exoskeleton efficiently in seawater are difficult to re-enter the sea. .
This research, which attempts to explain why there are few insects in the sea by relating it to the mechanism that hardens the exoskeleton, has uniqueness not seen in past research and hypotheses, based on considerations that incorporate genomic information and molecular evolutionary knowledge. As a new hypothesis with a high degree of safety, it has received positive feedback from marine entomologists.
Paper information:[Physiological Entomology] Eco-evolutionary implication for a possible contribution of cuticle hardening system in insect evolution and terrestrialisation
