The results of this study * , which will be published in an upcoming issue of the Journal of Biogeography, suggest that snails adapting to life in the deep sea follow similar evolutionary trends as species adapting to life on isolated islands. In other words the so-called “ island rule”, describing the evolution of body-size under specific constraints, may have more applications than previously thought, although classical factors such as reduced habitat, predation and competition may not apply in the deep sea.

There, food seems to be the limiting factor; less food is available, and at greater distances. The authors hypothesize that in the deep sea large gastropods became smaller because of a lack of food, while small ones became larger because this enabled them to expand their operating radius on the see floor and to store food surplus when available. The body size of deep-sea species would converge towards an optimal size related to their particular ecological strategy and habitat.

To test the new hypothesis on the rule’s applicability and its possible causes in marine systems, it will be necessary to extend such studies to other marine animals, including bivalves (such as clams) and cephalopods (such as squids).

A crustacean, the isopod Bathynomus giganteus, is supporting the hypothesis. Found in many gardens as a tiny “pill bug”, its marine relative at the sea floor is a “monstrous” animal. And who knows what else we can find in the still poorly explored abyssal world ** …