Testing for a transgenerational, behaviorally mediated trophic cascade

Recent studies suggest that prey behavior in response to perceived risk of predation, and not just consumption by predators, contributes significantly to creating trophic cascades. Here, we suggest a mechanism that generates a trophic cascade and that works across generations. In rock pools in the Middle East, a tritrophic system often consists of the predatory backswimmer, Notonecta maculata, a periphyton-grazing mosquito, Culiseta longiareolata, and periphyton. In outdoor artificial pools, Culiseta females, in response to perceived risk of predation to their progeny, strongly avoided ovipositing in pools containing Notonecta regardless of whether the predators were caged or free. Consequently, Culiseta larval densities were highest in pools without predators, considerably lower in caged Notonecta pools (due to oviposition avoidance of Notonecta) and virtually absent in free-ranging Notonecta pools (due to a combination of larval prey consumption and oviposition avoidance of Notonecta). The number reaching the pupal stage per egg raft deposited was reduced in non-predator pools suggesting strong food limitation. Diatom densities were statistically significantly lower in non-Notonecta pools compared to free Notonecta pools, demonstrating an overall trophic cascade. Intermediate diatom densities were found in caged Notonecta pools supporting the existence of a weak transgenerational behaviorally mediated trophic cascade, though the difference between free and caged predator pools was not statistically significant. This appears to be due to strong intraspecific competition among mosquito larvae resulting in strong depressions of diatom densities at the low to moderate larval densities found in the caged Notonecta pools. We argue that stronger transgenerational behaviorally mediated trophic cascades will occur under condition of higher nutrient concentrations.