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CONVERGENT EVOLUTION BETWEEN PHYLA: A TEST CASE OF MIMICRY BETWEEN CADDISFLY LARVAE ( HELICOPSYCHE BOREALIS ) AND AQUATIC SNAILS ( PHYSA INTEGRA )
Author(s) -
Berger Joel,
Kaster Jerry
Publication year - 1979
Publication title -
evolution
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.84
H-Index - 199
eISSN - 1558-5646
pISSN - 0014-3820
DOI - 10.1111/j.1558-5646.1979.tb04703.x
Subject(s) - mimicry , caddisfly , population , biology , test (biology) , ecology , larva , archaeology , zoology , history , sociology , demography
Many cases of potential mimicry are reported simply because the species in question are quite similar in external appearance. However, neither data nor testable hypotheses are advanced to determine if mimicry actually exists (e.g., Eaton, 1976; Gingerich, 1975). We have observed morphological similarity in the structure of the protective body cases of caddisfly larvae (Helicopsyche borealis: Insecta; Trichoptera) and aquatic snails (Physa integra: Gastropoda). The resemblance of body coverings between larvae and snails appears analogous to Batesian mimicry (see Wickler, 1968), whereby the apparent model (i.e., the snail) might be undesirable, but because of a protective body covering rather than a noxious taste. A possible mimic (i.e., the caddisfly larvae) could then enhance its survival probability, if less predation resulted (because of its resemblance to the model) and if a predator could not discriminate between the two species. The protective cases of caddisfly larvae and aquatic snails are similar in coloration and characterized by a prominent whorl (Fig. 1B, C). Originally, H. borealis was described as a snail based on the case only (Lea, 1834); and, although early taxonomists placed them in the same family (Denning, pers. comm.), fundamental differences exist in shell construction. The cases of caddisfly larvae are formed by cementing sand grains together with excretions from silk glands. In contrast, the shells of aquatic snails are formed by calcium carbonate excretions from the mantle. Since these species occur in sympatry (Pennak, 1953; Cummins, pers. comm.), we tentatively hypothesized that caddisfly larvae mimic the external morphology of aquatic snails. In nature, fishes are a known predator of caddisfly larvae (Pennak, 1953). However, further systematic study of the specific circumstances regarding their predation is necessary. If our tentative hypothesis were correct, the fol