Barnacle settlement behaviour in response to con- and allo-specific cues

Abstract

The project aimed to investigate the utility of selected temperate barnacles as a model species for recently-developed laboratory assays, and to progress the understanding of barnacle con- and allo-specific settlement behaviour through laboratory and field experiments, and the partial characterisation of the adult cue. Elminius modestus larval settlement assays using a 24-well plate assay indicated a preferred settlement temperature of 22±1°C, and gregarious settlement was demonstrated significantly at a Settlement Factor (SF) concentration of 10 μg ml"1. Experiments on the effects of ageing revealed a pattern to settlement not previously observed in the larval community, with high settlement when cyprids were young, reduced when mid-aged, and then increasing with increasing age with an accompanying loss of discrimination to settlement cues. It was questioned whether this may be due to the species physiology, or the presence of different phenotypes. Similar experiments with Semibalanus balanoides wild cyprids were far from conclusive, though the preferred settlement temperature was 19±1°C. Further laboratory experiments using S. balanoides cyprids were not pursued The active adult protein, known as settlement-inducing protein complex (SIPC), was isolated from E. modestus. One subunit was selected for amino acid sequencing, and subsequent gene isolation by molecular methods. Two short amino acid sequences were isolated from the protein; 1) ATPSLPDNI and 2) QYTYEYEAK. Laboratory experiments investigating settlement behaviour of Emodestus and Balanus amphitrite larvae to SF, from six species including the conspecific, showed that settlement by each species was significantly different to different concentrations of each SF tested. However, comparisons between different SFs of the same concentration were not significantly different. Results of choice assays, using several species' SFs in a single experiment, again indicated that there was no significant difference in settlement between different species. In field experiments S. balanoides settlement preferences were defined as: - S. balanoides > E. modestus > (B. improvisus = B. crenatus = C. montagui) (where '>' indicates a significant preference and `=' indicates no significant difference), while settlement by E. modestus cyprids was the same to all SFs.