Notonecta

Abstract: I conducted a series of laboratory experiments to contrast the responses of two species of mosquito larvae to a common predator, the freshwater bug Notonecta undulata. One prey species, Culex pipiens, commonly co-occurs with Notonecta, whereas the other, Aedes aegypti, shares no evolutionary history with this predator. I tested the evolution-based prediction that Culex should be killed at a lower rate due to stronger and more precise antipredator responses. I then studied the types of cues used by these prey to gauge predation risk by examining prey responses to simple disturbances and to potential chemical cues associated with predation. The results were that (1) both mosquito species responded to Notonecta by moving less and by shifting their microhabitat use; (2) Culex was indeed killed at a lower rate; (3) Culex showed far stronger responses to notonectids; (4) the response of Culex was correlated with actual predation risk even after encounter rate with predators was accounted for; and (5) Culex, but not Aedes, responded to water in which conspecifics had been preyed upon by Notonecta. The differences in the responses of the two species can be explained by a fun- damental difference in the way in which they estimate predation risk. Whereas the behavior of Aedes can be understood as a response to disturbance per se, Culex behavior is also mediated by chemical cues associated with the actual predation act. Since more predation on Culex should produce more alarm chemical, this cue is probably responsible for the observed "precise" (i.e., correlated with risk) responses.

Abstract: Eight different clones (seven species) of Daphnia had behavioral responses to fish and invertebrate predators. The behavioral response was measured in the laboratory as a change in the average population depth, relative to controls, when exposed to a predator. Behavior for each clone was tested with three common predators: Chaoborus, Lepomis, and Notonecta. Each Daphnia clone responded to at least one predator. Some clones responded to all three predators. The responses are both predator and. prey-specific. The stimulus produced by the predator is a water-soluble chemical that persists for up to 7 h in the laboratory. The number of predator species to which a clone responds shows a positive correlation with average body size of the Daphnia. Number of responses per clone is independent of lake size, although there was a tendency (not statistically significant) for the number of responses to decrease with lake size. Behavioral responses may be components of diel vertical migration and horizontal distribution patterns seen in nature.

Abstract: Natural selection should favor females that avoid ovipositing where risk of predation is high for their progeny. Despite the large consequences of such oviposition behavior for individual fitness, population dynamics, and community structure, relatively few studies have tested for this behavior. Moreover, these studies have rarely assessed the mode of detection of predators, compared responses in prey species that vary in vulnerability to predators, or tested for the behavior in natural habitats. In an outdoor artificial pool experiment, we tested the oviposition responses of two dipteran species, Culiseta longiareolata (mosquito) and Chironomus riparius (midge), to the hemipteran predator, Notonecta maculata. Both dipteran species have similar life history characteristics, but Culiseta longiareolata larvae are highly vulnerable to predation by Notonecta, while Chironomus riparius larvae are not. As their vulnerabilities would suggest, Culiseta longiareolata, but not Chironomus riparius, strongly avoided ovipositing in pools containing Notonecta. An experiment in natural rock pools assessing oviposition by Culiseta longiareolata in response to Notonecta maculata yielded an oviposition pattern highly consistent with that of the artificial pool experiment. We also demonstrated that the cue for oviposition avoidance by Culiseta longiareolata was a predator-released chemical: Notonecta water (without Notonecta replenishment) repelled oviposition for 8 days. Oviposition avoidance and mode of detection of the predator have important implications for how to assess the true impact of predators and for the use of commercially produced kairomones for mosquito control.

Abstract: Numerous adaptive predator-induced responses occurred when eight clones representing seven Daphnia (Crustacea: Cladocera) species were tested against three common predators: fourth instar larval phantom midge Chaoborus americanus, adult backswimmer Notonecta undulata, and small sunfish Lepomis macrochirus. The predators were confined within small mesh bags, suggesting that the signal for induction is chemical. The induced responses included longer tail spines, longer heads, smaller bodies, increased egg clutches, and decreased lipid reserves. Each Daphnia species responded to each of the three predators in a unique manner. Induced responses in the above characters showed no significant association. The induced morphological changes are generally consistent with current theories of what is an adaptive response for the various sizes of Daphnia exposed to tactile and visual predators. The abundance of induced responses in these experiments suggests that predator-induced responses are a widespread and ecologically important phenomenon of the freshwater zooplankton.