Hypoxia increases the risk of egg predation in a nest-guarding fish.

Karin H Olsson,Maria Norevik Andrén,Charlotta Kvarnemo,Therése Larsson

doi:10.1098/rsos.160326

Abstract

For fish with parental care, a nest should meet both the oxygenation needs of the eggs and help protect them against predators. While a small nest opening facilitates the latter, it impedes the former and vice versa. We investigated how the presence of potential egg predators in the form of shore crabs Carcinus maenas affects nest building, egg fanning, defensive displays and filial cannibalism of egg-guarding male sand gobies Pomatoschistus minutus under two levels of dissolved oxygen. In the high oxygen treatment, males retained their nest opening size in the presence of crabs, while males in low oxygen built large nest openings both in the absence and presence of crabs, despite the fact that crabs were more likely to successfully intrude into nests with large entrances. Males in low oxygen also fanned more. In the presence of crabs males increased their defensive displays, but while males in high oxygen reduced fanning, males in low oxygen did not. Filial cannibalism was unaffected by treatment. Sand gobies thus prioritize egg ventilation over the protection afforded by small nest openings under hypoxia and adopt defensive behaviour to avert predator attention, even though this does not fully offset the threat from the egg predators.

Highlights

Many species construct nests that shelter eggs and young, allowing parents to control the microclimate and optimize the developmental conditions of the offspring [1,2,3]
After 24 h, the nest opening size was significantly larger in the low oxygen treatment than in the high oxygen treatment, while there was no effect of predator presence
In the high oxygen treatment, it was significantly lower in the presence compared with the absence of an egg predator (Welch’s ANOVA: F1,15.82 = 9.41, p = 0.0075) while in the low oxygen treatment the rate remained high in the presence of an egg predator (Welch’s ANOVA: F1,9.62 = 1.07, p = 0.33; figure 2b)

Summary

Introduction

Many species construct nests that shelter eggs and young, allowing parents to control the microclimate and optimize the developmental conditions of the offspring [1,2,3]. Have focused on birds, but the importance of nest attributes to the breeding success of species of fish, 2 insects and spiders is becoming increasingly better understood. Nest defence strategies can be either stealthy, seeking to avoid the attention of predators through camouflage and the adoption of inconspicuous behaviour, or active in the form of mobbing, distracting or outright attacks for the purpose of deterring or misleading the potential predator. Guarding parents may calibrate the intensity of their defence, for instance by escalating from warnings to outright attacks, depending on the type of predator and its proximity to the nest, presumably reflecting the likelihood that the exact location of the nest has been discovered [20,21,22]

Methods

Results

Conclusion