The island rule and the evolution of body size in the deep sea

Abstract

Aim: Our goal is to test the generality of the island rule - a graded trend from gigantism in small-bodied species to dwarfism in large-bodied species - in the deep sea, a non-insular but potentially analogous system. Location: Shallow-water and deep-sea benthic habitats in the western Atlantic Ocean from the North to South Poles. Methods: We conducted regression analyses of body size of deep-sea gastropods species relative to their shallow-water congeners using measurements from the Malacolog ver. 3.3.3 database. Results: Our results indicate that, consistent with the island rule, gastropod genera with small-bodied, shallow-water species have significantly larger deep-sea representatives, while the opposite is true for genera that are large-bodied in shallow water. Bathymetric body size clines within the deep sea are also consistent with predictions based on the island rule. Main conclusions: Like islands, the deep sea is characterized by low absolute food availability, leading us to hypothesize that the island rule is a result of selection on body size in a resource-constrained environment. The body size of deep-sea species tends to converge on an optimal size for their particular ecological strategy and habitat. © 2006 The Authors.