Very Low Mitochondrial Diversity and Genetic Homogeneity in the Starfish Echinaster sepositus Along the Tunisian Coast

Phylogeographic structure in marine organisms is ascribed to contemporary and/or historical barriers to dispersal (Benzie and Williams 1997; Waters and Roy 2003). In addition, life history mode can exert a strong influence on the genetic structure of populations (Hart et al. 1997; Riginos and Victor 2001), as illustrated by the consequences of the extreme heterogeneity of dispersal capability on geographic distribution of genetic polymorphism (Kinlan and Gaines 2003). For instance, some species with long-lived planktotrophic larvae show vast geographic distributions and limited genetic structure (Booth and Ovenden 2000; Colgan et al. 2005). Conversely, taxa with brief larval stages or direct development often show marked phylogeographic structure (Collin 2001; Planes et al. 2001; Riginos and Victor 2001). Mitochondrial DNA is commonly used as a genetic marker to infer phylogeographic relationships in most marine organisms (Avise 2000). The gene coding for cytochrome c oxidase subunit I (COI) is among the most frequently used markers because of its high degree of variability (e.g., Avise 2000; Duran et al. 2004a; Lee 2000). Among marine invertebrates, few examples of almost negligible levels of intraspecific variation in COI have been reported for basal phyla such as porifera and anthozoa (Duran et al. 2004b; France and Hoover 2002; Shearer et al. 2002). In asteroids, the COI gene has proven to be highly polymorphic (Flowers and Foltz 2001; Waters et al. 2004).