L Journal of Experimental Marine Biology and Ecology 243 (2000) 295–304 www.elsevier.nl / locate / jembe The different morphs of Chthamalus anisopoma :a phenotypic response? Direct molecular evidence a, b b b * O. Mokady , L. Mizrahi , R. Perl-Treves , Y. Achituv a Institute for Nature Conservation Research, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel b The Faculty of Life Sciences, Bar Ilan University, Ramat Gan 52900, Israel Received 7 July 1999; accepted 13 August 1999 Abstract Chthamalus anisopoma is a rock-inhabiting barnacle which appears in two radically different morphs: the shell may be either conical or bent at a right angle. Based on field experiments, it was previously concluded that the two morphs are phenotypic variants, with the bent morph being induced by the presence of a predator gastropod. In the present study we used molecular data in order to examine directly the degree of genetic similarity between the two morphs. We compared the sequences of two mitochondrial DNA segments previously shown to exhibit substantial inter- and intra-specific variability in barnacles: the 12S mt rDNA and the cytochrome C oxidase subunit 1 (CO1). The sequences obtained for the different C. anisopoma morphs showed complete identity (12S rDNA) or very high similarity ( . 99.5%, CO1). We thus provide direct genetic evidence indicating that barnacles of the different morphs originate from a common gene pool. This supports previous conclusions that predation in this case is an inductive factor rather than selective.  2000 Elsevier Science B.V. All rights reserved. Keywords: Cirripedia; mt DNA; Phenotypic induction; Selection 1. Introduction Within-species morphological variability exhibited by different organisms may reflect different levels of genetic differences, such as those arising between isolated populations along the process of speciation. On the other hand, the same variability may be the result of environmental factors, such as differences between or within the habitat. Shell *Corresponding author: Tel.: 1 972-3-640-6358; fax: 1 972-3-640-7304. E-mail address: mokady@post.tau.ac.il (O. Mokady) 0022-0981 / 00 / $ – see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S0022-0981(99)00124-0