The Bold and the Variable: Fish with High Heterozygosity Act Recklessly in the Vicinity of Predators

Variation in the innate behavioral response to predation threat is often assumed to reflect genetic differences among the prey individuals. To date, no published results, however, exist that would offer explanation for the origin of this behavioral variation within populations. Using microsatellites as markers, we estimated the genetic variability of juvenile brown trout (Salmo trutta) individuals whose behavior had been individually recorded in a trade‐off situation where both predator chemical cues and food were present. Mean overall heterozygosity and the internal relatedness of fish associated significantly with their activity and foraging, so that the genetically more variable individuals showed more risk‐prone behavior under predation risk. No association between genetic variability and behavior was found in trials where predator odors were not present. These results were consistent over the three study populations of brown trout with different backgrounds, suggesting that the phenomenon is of general nature in this species. Of the possible mechanisms suggested to enable the existence of the positive association between neutral microsatellite variation and fitness‐related trait, the local effect hypothesis gained more support from our data than the general effect hypothesis.