p aland Keywords: Complex life cycle

igen rate edi the second intermediate host is relatively immobile and cercarial dispersal is the sole mechanism that ites w s obse Natural selection may have favoured and maintained complex life cycles in trematodes because they confer advantages, including greater channelling toward the definitive host and enhanced growth and fecundity in the latter (Choisy et al., 2003; Poulin, 2007). Trophic transmission has also been suggested as a way to ensure that parasites can find conspecifics and cross-fertilise (Brown et al., 2001). The predator host can concentrate many resulting in the accumulation of a variety of clones (Rauch et al., 2005). This was echoed by the findings of Keeney et al. (2007a) who quantified the clonal diversity of Maritrema novaezealandensis in its first intermediate host, the snail Zeacumantus subcarinatus, and one of its second intermediate hosts, the crab Macrophthalmus hirtipes. They found that while the snail can harbour up to five trematode genotypes, only about half of the snails were actually infected by multiple clonal lineages. Meanwhile, the genetic diver-sity in individual crabs was markedly higher, with all metacerca-riae sampled in a crab representing different genotypes in th