Date of this Version
A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Biological Sciences, Under the Supervision of Professor Alan C. Kamil. Lincoln, Nebraska: April, 2008
I examined a variety of factors hypothesized to be important in the evolution and maintenance of aposematism. Aposematism occurs when prey individuals advertise their toxic or otherwise aversive nature to potential predators via evolved conspicuous signals. I conducted three experiments in which blue jays (Cyanocitta cristata) were allowed to search a printed grayscale pixilated background for grayscale pixilated moths in an open room. I manipulated moth appearance and food reward, and recorded jay predation on the varying moth stimuli. In my first experiment, I repeated Alatalo & Mappes’ (1996) study examining the effects of prey gregariousness, or grouping, on predation rates of cryptic (difficult to detect) palatable, cryptic unpalatable, and conspicuous (easy to detect) unpalatable (aposematic) artificial prey. I found that gregariousness does not provide a benefit to prey, suggesting gregariousness did not facilitate the initial evolution of aposematism, in contrast to Alatalo & Mappes (1996). My second study investigated why predation on aposematic prey was continually low in experiment 1. I found that the moth stimuli used in experiment 1 were truly cryptic and conspicuous, so the low predation on conspicuous unpalatable (aposematic) moths in experiment 1 was likely due to very rapid learned avoidance of aposematic prey. Finally, in experiment 3, I asked whether jays from experiment 1 and 2 would attack novel cryptic and conspicuous moths differently based on their prior experience: experience with unpalatable food (experiment 1), or no experience with unpalatable food (experiment 2). Jays that had experienced unpalatable moths previously attacked significantly more novel cryptic moths than novel conspicuous moths, both overall and in the first attack of the first trial. In contrast, jays that had not experienced unpalatable moths previously attacked significantly more novel conspicuous moths than novel cryptic moths. This may suggest a conspicuousness-dependent generalization threshold for food aversions.