Effect of egg predator on nest choice and nest construction in sand gobies

Nest defence is a particularly costly component of parental care. The costs of nest-related behaviours are affected by the nest's location, size and architecture; yet surprisingly little is known about how choice of a nesting site or nest characteristics are adjusted as a response to the threat of future nest predation. To address this topic, we investigated whether egg predation threat influenced nest choice and nest construction in the sand goby, Pomatoschistus minutus, a small marine fish with exclusive paternal egg care. We found that exposure to sand shrimp, Crangon crangon, a predator of sand goby eggs, did not affect male preferences for large nesting resources or the onset of nest-building activity. Small and large males did, however, respond differently to the presence of shrimp during the nest-building phase. In particular, large males used more sand to cover their nests in the shrimps' presence. By contrast, neither the presence of egg predators nor male size class affected the size of the nest entrance. Together, our results show that while the risk of future egg predation may not necessarily influence a male's decision to nest, during the nest construction phase it can nevertheless induce responses that strongly depend on builder phenotype.