A Description and Experimental Analysis of Batesian Mimicry between a Marine Gastropod and an Amphipod

Abstract

An apparent case of Batesian mimicry is described between three co-occurring species of the marine gastropod Lacuna (the model) and an amphipod mimic (Stenopleustes). Similar characteristics include size, color pattern, and locomotory behavior on eelgrass blades. Both animals inhabit subtidal eelgrass beds, but the mimic is only 1.0-4.2 percent as common as the model. Predatory fish (Cottidae, Pholidae) from the eelgrass habitat rarely eat Lacuna or Stenopleustes (shown by fecal analysis) but will readily eat Stenopleustes if the mimic betrays its snail disguise by swimming. Only 8.8 percent of the Stenopleustes (which walks along eelgrass blades and seldom swims) were eaten, compared to 62.5-percent predation of a co-occurring nonmimetic gammarid amphipod (which often swims), in laboratory predator-prey experiments. These data suggest that the amphipod, by resembling a conspicuous and relatively inedible snail, enjoys a protective advantage from predation by fish in the eelgrass habitat.