Repeatability of nest size choice and nest building in sand gobies

To be useful as mate choice cues, behavioural traits have to be performed consistently within individuals. This may also be true for nest construction, which, in addition to influencing offspring survival, can also function as an extended phenotype of the builder. We tested whether choice of a nesting resource and subsequent nest-building performance are repeatable traits in the sand goby, Pomatoschistus minutus, a small marine fish with paternal egg care and female mating preferences that are influenced by male nest-building behaviour. When given a choice between three different-sized nesting resources (flowerpots), males, on average, preferred medium-sized nesting resources, with larger males preferring larger nests than smaller individuals. At the individual level, the choice of nesting resources was so variable between consecutive trials that choice behaviour was not repeatable. Furthermore, nest building, measured as the amount of sand piled on top of the nesting resource, was highly repeatable when males were free to choose their nest, but had only a low repeatability when males had just a single option. In neither case was the size of the nest entrance repeatable between consecutive rounds of nest building. These results highlight the context-dependent signal value of extended phenotypes. In particular, reliability of nest-building behaviour as a signal seems to be influenced by the maleʹs opportunity to choose the object it uses for nesting.