“…Although producing toxins is useful to prevent grazing by zooplankton filter feeders and large animals (Alonso-Andicoberry et al, 2002;López-Rodas et al, 2008;De Mott et al, 1991;Kinder, 1995;Rohrlack et al, 1999;Trubetskova & Haney, 2000;Vanderploeg et al, 2001;Frances, 1878;López-Rodas & Costas, 1999), it is also costly in terms of fitness, whereby the toxin-producing m+genotypes showed diminished fitness with respect to non-producing mgenotypes in the absence of grazers (Carrillo et al, 2003;López-Rodas et al, 2006). Our results also show significant negative regression between fitness and toxin production.…”