Reference: Biol. Bull. 201: 143-203. (October 2001 1 Molecular Phylogeny of the Model Annelid Ophryotrocha THOMAS G. DAHLGREN 1 2 *, BERTIL AKESSON 2 . CHRISTOFFER SCHANDER 2 ' 3 , KENNETH M. HALANYCH 1 , AND PER SUNDBERG 2 ' Woods Hole Oceano graphic Institution, Biologv Department, MS 33, Woods Hole, Massachusetts 02543, USA; Goteborg Universitv, Department of Zoology, Box 463, 405 90 Goteborg, Sweden; and ^University of Copenhagen, Arctic Station, Box 504, DK-3953 Qec/ertarsuaq, Greenland Abstract. Annelids of the genus Ophryotrocha are small opportunistic worms commonly found in polluted and nutrient-rich habitats such as harbors. Within this small group of about 40 described taxa a large variety of reproductive strategies are found, ranging from gonochoristic broadcast spawners to se-quential hermaphroditic brooders. Many of the species have a short generation time and are easily maintained as laboratory cultures. Thus they have become a popular system for explor-ing a variety of biological questions including developmental genetics, ethology, and sexual selection. Despite considerable behavioral, reproductive, and karyological studies, a phyloge-netic framework is lacking because most taxa are morpholog-ically similar. In this study we use 16S mitochondrial gene sequence data to infer the phytogeny of Ophryotrocha strains commonly used in the laboratory. The resulting mtDNA to-pologies are generally well resolved and support a genetic split between hermaphroditic and gonochoristic species. Although the ancestral state could not be unambiguously identified, a change in reproductive strategy (i.e.. hermaphroditism and gonochorism ) occurred once within Ophryotrocha. Addition-ally, we show that sequential hermaphroditism evolved from a simultaneous hermaphroditic ancestor, and that characters pre-viously used in phylogenetic reconstruction (i.e.. jaw morphol-ogy and shape of egg mass) are homoplasic within the group. Introduction Marine annelids belonging to the group Ophryotrocha have been used as a laboratory system for much of this century (e.g.. Bergh, 1895: Bergmann. 1903: Meek. Received 15 December 2000; accepted 11 June 20111 *To whom correspondence should be addressed. E-mail: tdahlgren whoi.edu 1912; Huth, 1933; Hartmann and Lewinski, 1940; Bacci and La Greca. 1953; Bacci, 1965; Akesson. 1972; Sella, 1988; Vitturi et ai. 2000), not least because they are easy to maintain in cultures and have short generation times. Oplirvotroclni has traditionally been treated as a genus within the eunicimorph family Dorvilleidae (e.g., Fau-chald, 1977; Eibye-Jacobson and Kristensen, 1994), but inclusion within the Dorvilleidae has been challenged (Orensanz, 1990). Many ecological (e.g., Akesson, 1977; Berglund. 1991; Cassai and Prevedelli, 1999), ethologi-cal (e.g., Sella, 1991), developmental (e.g., Akesson, 1967. 1973; Zavarzina and Tzetlin, 1991 ), and toxicolog-ical (e.g., Akesson, 1970, 1975) studies have been con-ducted on these worms. Charnov ( 1982) and Gambi et al. (1997) among others, argue that Ophryotrocha is a near ideal group for studies of the evolution of sex strategies, since all known forms (gonochorism, sequential and si-multaneous hermaphroditism) are represented within a few closely related species. Since Oplin'otrocha was first described (Claparede and Mecznikow, 1869), more than 40 species have been added to the group, most of which are reported from shallow, nutrient-rich waters such as harbors (e.g.. La Greca and Bacci, 1962; Akesson, 1976; Paavo et al.. 2000). Recent contributions have also shown a consider-able diversity in the deep sea (Jumars, 1974; Blake, 1985; Hilbig and Blake. 1991: Lu and Fauchald. 2000). To the best of our knowledge, the Appendix lists all the de-scribed species of Ophryotrocha with their type locality. Only species from shallow, temperate or tropical waters, however, have been successfully cultured in the labora-tory (at present 20 distinct forms). Among the cultured forms, some of which are yet to be formally described. 193
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