Importance of olfaction to suppression of attack response through conditioned taste aversion in the grasshopper mouse

Clair CC, Tobajas J. Conditioned Taste Aversion as a Tool for Mitigating Human-Wildlife Conflicts

Modern wildlife management has dual mandates to reduce human-wildlife conflict (HWC) for burgeoning populations of people while supporting conservation of biodiversity and the ecosystem functions it affords. These opposing goals can sometimes be achieved with non-lethal intervention tools that promote coexistence between people and wildlife. One such tool is conditioned taste aversion (CTA), the application of an evolutionary relevant learning paradigm in which an animal associates a transitory illness to the taste, odor or other characteristic of a particular food item, resulting in a long-term change in its perception of palatability. Despite extensive support for the power of CTA in laboratory studies, field studies have exhibited mixed results, which erodes manager confidence in using this tool. Here we review the literature on CTA in the context of wildlife conservation and management and discuss how success could be increased with more use of learning theory related to CTA, particularly selective association, stimulus salience, stimulus generalization, and extinction of behavior. We apply learning theory to the chronological stages of CTA application in the field and illustrate them by synthesizing and reviewing past applications of CTA in HWC situations. Specifically, we discuss (1) when CTA is suitable, (2) how aversion can be most effectively (and safely) established, (3) how generalization of aversion from treated to untreated food can be stimulated and (4) how extinction of aversion can be avoided. For each question, we offer specific implementation suggestions and methods for achieving them, which we summarize in a decision-support table that might be used by managers to guide their use of CTA across a range of contexts. Additionally, we highlight promising ideas that may further improve the effectiveness of CTA field applications in the future. With this review, we aspire to demonstrate the diverse past applications of CTA as a non-lethal tool in wildlife management and conservation and facilitate greater application and efficacy in the future.

Olfactorily mediated attack suppression in the southern grasshopper mouse toward an unpalatable prey

Predatory behavior toward an unpalatable sympatric prey was examined in the southern grasshopper mouse, Onychomy torridus (Coues). Mice preferred the palatable grasshopper Brachystola magna over the unpalatable secretion-producing grasshopper Taeniopoda eques. Consumption of T. eques decreased 35% while consumption of B. magna remained stable during three nights of testing. Olfactorily mediated attack suppression was demonstrated when O. torridus rejected palatable B. magna which had been coated with 5 ul of T. eques defense secretion. These results show that O. torridus discriminates and is capable of rejecting prey at any point in the prey capture sequence. These are adaptive attributes for a predator like O. torridus, which commonly attacks well-defended or dangerous prey.

Grasshopper mouse's use of visual cues during a predatory attack

This study examined the grasshopper mouse's use of visual cues to recognize a potential prey. The mouse's latency of attack was measured in response to models presented in five experiments. The mice responded to the contrast, movement and relative size of a visual stimulus, but did not respond to different orientations or shapes. Furthermore, the mice did not learn to recognize a particular prey by its shape or by a combination of visual cues. Essentially, the mice used vision primarily to detect and follow a potential prey rather than to recognize a particular species. The significance of the mouse's use of visual cues compared with olfactory and auditory cues was discussed.

Aversiveness of denatonium saccharide and quinine in grasshopper mice Onychomys leukogaster

The responses toward denatonium saccharide and quinine by three rodent species differ from those exhibited by humans. This study measured the relative aversiveness of these two compounds in grasshopper mice (Onychomys leucogaster) to determine if this species responded similarly to or differently from these other rodents. In a choice test, the mice clearly preferred quinine over denatonium saccharide at concentrations of 1/10,000 and 1/50,000, but only marginally preferred quinine at a concentration of 1/1000. When denatonium or quinine was paired with toxicosis, both suppressed drinking at concentrations from 1/10,000 to 1/50,000, but only denatonium suppressed drinking at 1/100,000. Neither compound suppressed drinking at 1 part in million. Grasshopper mice perceived denatonium saccharide as more aversive than quinine in both experiments. Such a response resembled the behavior of humans more than that of the other three rodents previously tested.

Importance of tactile and olfactory cues to the inhibition of the grasshopper mouse's attack through toxicosis

This study examined the effect that toxicosis paired with the presence of a distinctive texture had on the inhibition of the grasshopper mouse's predatory attack. The first experiment measured the context in which tactile cues would be most effective by presenting prey with various combinations of added stimuli. The combination of distinctive tactile, olfactory, and gustatory cues produced the longest lasting inhibition. Because certain manipulations also had an unintended weak odor associated with them, the second experiment measured the importance of a weak or strong odor to inhibition of a mouse's attack. A combination of strong odor and distinctive texture paired with toxicosis inhibited an attack more effectively than a weak odor and a similar texture. In a third experiment, toxicosis was paired with an acraea moth caterpillar which has a highly distinctive texture. This produced the longest lasting inhibition of mouse's attack observed thus far. The ecological significance of a combination of a distinctive texture and odor to the inhibition of the grasshopper mouse's attack is discussed.