Date of Award

8-30-2022

Document Type

Campus Access Thesis

Degree Name

Master of Science (MS)

Department

Biology

First Advisor

Robert Stevenson

Second Advisor

Mayra C. Vidal

Third Advisor

Luis DeLeón

Abstract

To avoid predation by visual predators, caterpillars can be cryptic to decrease detectability or aposematic to warn predators of potential unpalatability. However, for some species, it is not clear if the patterns are selected to avoid predation. For example, Pandora sphinx (Eumorpha pandorus) caterpillars are assumed to be palatable and have both cryptic (green, brown) and conspicuous (orange, red) color morphs. Five lateral, off-white splotches on either side may serve as a warning for predators or to draw attention away from the caterpillar’s form and function as distractive marks. We conducted a field study in three temperate fragmented forests in Massachusetts to investigate the potential utility of E. pandorus coloration and splotch markings. The four plasticine caterpillar model treatments, green and red with and without lateral splotches, were placed on host plants in 14 patches at three sites repeatedly over six, week-long, trials spanning from July through October. We tested the effects of color, splotch patterning and seasonality on predation rates. We found 43% of the models (n = 964) had bite marks by an array of predators including arthropods (67.5%), birds (18.2%), rodents (11.5%), and large mammals (2.8%). Arthropods as dominant predators align with conclusions from previous studies of models placed near ground level. Attack rates peaked for arthropods in late August and early September but were more constant across trials for vertebrates. Arthropods, a heterogeneous group, as indicated by the variety of bite marks, showed only a marginal preference for green colored and splotch-less models, whereas vertebrates, more visually-oriented predators, had significantly higher predation on red colored models and a marginal preference toward splotched models. Thus, our results did not suggest that splotch patterning reduced predation and therefore, we did not find support for the distractive mark hypothesis. Further, our study shows clear contrasting interpretations by different predators regarding visual defensive strategies.

Comments

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