Abstract
BackgroundHabituation, a form of non-associative learning, has several well-defined characteristics that apply to a wide range of physiological and behavioral responses in many organisms. In classic patch time allocation models, habituation is considered to be a major mechanistic component of parasitoid behavioral strategies. However, parasitoid behavioral responses to host cues have not previously been tested for the known, specific characteristics of habituation.MethodsIn the laboratory, we tested whether the foraging behavior of the egg parasitoid Trissolcus basalis shows specific characteristics of habituation in response to consecutive encounters with patches of host (Nezara viridula) chemical contact cues (footprints), in particular: (i) a training interval-dependent decline in response intensity, and (ii) a training interval-dependent recovery of the response.ResultsAs would be expected of a habituated response, wasps trained at higher frequencies decreased their behavioral response to host footprints more quickly and to a greater degree than those trained at low frequencies, and subsequently showed a more rapid, although partial, recovery of their behavioral response to host footprints. This putative habituation learning could not be blocked by cold anesthesia, ingestion of an ATPase inhibitor, or ingestion of a protein synthesis inhibitor.DiscussionOur study provides support for the assumption that diminishing responses of parasitoids to chemical indicators of host presence constitutes habituation as opposed to sensory fatigue, and provides a preliminary basis for exploring the underlying mechanisms.
Highlights
As animals experience repeated environmental stimuli that become irrelevant or unreliable, they often show less intense behavioral responses as a result (Thompson & Spencer, 1966; Pinsker et al, 1970; Carew, Pinsker & Kandel, 1972)
These characteristics include decreasing response intensity following repeated experiences with a given cue, and a ‘‘spontaneous recovery’’ of the response over time after stimulation ceases. Both the decline and the recovery of habituated responses tend to be more rapid and more pronounced when habituation training takes place at shorter intervals. These defining characteristics are useful for distinguishing habituation from sensory fatigue—wherein sensory structures become saturated by chemical, visual, or acoustic stimuli as well as motor fatigue (Rankin et al, 2009)
Residence times declined with each subsequent training session for all three training interval treatments, but to different degrees: residence times were similar among training interval treatments for the first training session, and were significantly lower for shorter training intervals during the second through fourth training sessions (Fig. 1A)
Summary
As animals experience repeated environmental stimuli that become irrelevant or unreliable, they often show less intense behavioral responses as a result (Thompson & Spencer, 1966; Pinsker et al, 1970; Carew, Pinsker & Kandel, 1972). Habituation shows a well-defined set of characteristics that apply to many different physiological and behavioral responses (reviewed by Thompson & Spencer, 1966; Rankin et al, 2009) These characteristics include decreasing response intensity following repeated experiences with a given cue, and a ‘‘spontaneous recovery’’ of the response over time after stimulation ceases. Both the decline and the recovery of habituated responses tend to be more rapid and more pronounced when habituation training takes place at shorter intervals. Our study provides support for the assumption that diminishing responses of parasitoids to chemical indicators of host presence constitutes habituation as opposed to sensory fatigue, and provides a preliminary basis for exploring the underlying mechanisms
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