Behavioural plasticity of social trematodes depends upon social context

Abstract

Members of some social insects adjust their behaviours depending upon social context. Such plasticity allows colonies to sustain efficiency of the whole without the cost of additional production of individuals or delayed responses to perturbations. Using the recently discovered social clonal stage of trematode parasites, we investigated whether members of the reproductive caste adjust their defensive behaviour according to the local availability of non-reproductive defensive specialists, and if so whether the plasticity affects the short-term reproductive success of reproductive morphs. In vitro experiments demonstrated plasticity in competitive interactions of the reproductive morphs depending on the number of non-reproductive defensive specialists present nearby, which lead to differences in reproductive output at the individual level. This study provides support for the benefit of maintaining non-reproductive morphs in competitive situations, arising through socially mediated behavioural plasticity.

Figure 1.

Proportion of reproductive morphs of Philophthalmus sp. seen in contact with the competing Maritrema novaezealandensis over 14 days as a function of differing numbers of non-reproductives in the culture. Sample sizes are shown. The variation in sample sizes occurred owing to contamination of one culture.

Figure 2.

Number of encysted cercariae over 7 days from individual Philophthalmus sp. reproductive rediae, regressed against the proportion of time spent in contact with the competing Maritrema novaezealandensis. Twelve reproductives each from 10 colonies were involved (r² = 6.7%).