Effects of a low oxygen environment on parental effort and filial cannibalism in the male sand goby, Pomatoschistus minutus

In fish, brood cycling parental males sometimes eat some or all of their eggs, a behavior termed filial cannibalism. We tested predictions of filial cannibalism models related to the cost of parental care in the male sand goby, Pomatoschistus minutus, by increasing the parental effort (fanning expenditure) through reduced levels of dissolved oxygen to 39% in an experimental group, whereas a control group had fully saturated water. Males showed both full-clutch cannibalism and partial-clutch cannibalism in both treatments. Giving the males one to three females to spawn with, we found that small clutches were completely eaten more often than were larger ones, whereas partial-clutch cannibalism was not affected by clutch size. Although treatment did not affect filial cannibalism, it did affect a male’s energy state such that males in the low oxygen treatment lost more body fat, indicating a greater fanning effort. This shows that males in the low oxygen treatment allocated more energy to the present brood, potentially at the expense of future reproductive success. Our study strongly suggests that filial cannibalism in male sand gobies represents a strategic life-history decision as an investment in future reproductive success, and is not triggered by a proximate need for food necessary for the male’s own survival. Furthermore, males in the low oxygen treatment built nests with larger entrances, and were less likely to rebuild their nests after destruction. Presumably, this makes fanning easier but the nest more vulnerable to predators, suggesting a trade-off between fanning and nest defense.