MCGOVERN, TM: Sex ratio bias in the clonal brittle star Ophiactis savignyi

Despite the prevalence of clonal organisms in many communities, few investigators have explicitly related clonal and sexual modes of reproduction. Clonal reproduction is likely to affect sexual reproduction in a variety of ways, including the alteration of operational sex ratios. Sex ratios in natural populations of the clonal brittle star Ophiactis savignyi are consistently and significantly male-biased. To explore the impact of clonal reproduction on sex ratios in this species, I examined patterns of clonal structure and conducted field experiments to determine gender-specific rates of clonal reproduction. Using RAPD patterns to demarcate clones, I have shown that male clones typically had more clonemates than female clones. The greater number of individuals in male clones can explain the bias toward male individuals in natural populations. In a field experiment in which I followed the fates of individuals of known gender, I demonstrated that males are more likely to divide than females. This bias in division rates is likely responsible for the greater number of clonemates in male clones. Differences between the genders in allocation to sexual reproduction and the cost to sexual reproduction associated with cloning may underlie the differences in rates of clonal division. These findings demonstrate that differences between the genders in rates of clonal division and the subsequent effects on clonal structure have the potential to influence sexual reproduction on a population level by generating a bias in the operational sex ratio.