Nests as ornaments: revealing construction by male sticklebacks

Nests are built by animals from a variety of taxa, and serve as receptacles for eggs and developing offspring. Where nests are built solely or mainly by one sex, they also have the potential to serve as extended ornaments, because aspects of construction potentially reveal or amplify characteristics of the builder to prospective mates. Here, we develop novel indices to quantify nest structure and examine variation in temporal and structural aspects of nest construction in relation to morphological, immunological, and physiological traits in male three-spined sticklebacks, Gasterosteus aculeatus. Wild-caught male sticklebacks that began construction within 3 days of being transferred to the laboratory built “neater” nests than fish that took longer to start, and we present alternative testable hypotheses that could explain this pattern. Various characteristics of nest-building males correlated with nest structure. The relative weight of the building male's kidney—which secretes a glue-like protein used in nest building and whose development is androgen-dependent—correlated positively with nest “ neatness.” We also found males with enlarged spleens (an indicator of immune stress) to construct less “compact” nests. The structure of a nest may therefore be important not only in determining its functional capacity, but may also act as a quality-revealing ornament. We suggest that females may gain valuable information regarding male health status and androgen levels from nest inspection.