Year of Publication

2002

Document Type

Dissertation

College

Arts and Sciences

Department

Biology

First Advisor

Andrew Sih

Abstract

My research explores the complex strategies animals adapt to cope with multiple selection pressures. I studied the behavioral and color response of two salamander sister species, Ambystoma barbouri and A. texanum, to temperature, predation risk and ultraviolet radiation (UVR, 280-320 nm). Ambystoma barbouri undergo development in streams, while A. texanum larvae inhabit ponds. Thus, A. barbouri are exposed to increased habitat ephemerality, enhanced predation risk, and UVR exposure. I show how A. barbouri have evolved alternate coping mechanisms in response to these environmental factors, relative to A. texanum. In this comparison study, I've quantified the affects of these selection pressures on larval color change, refuge use and depth choice.I found Ambystoma barbouri to have a significantly darker mean color than A. texanum. Additionally, both species significantly change color to match their background and in response to temperature. When exposed to warm temperatures, early-stage larvae of both species became lighter. Both species also changed color over ontogeny, with larvae becoming significantly lighter over development. Remarkably, A. texanum larvae mediated risk from predatory fish chemical cues by visually assessing the degree to which they cryptically match their background. If cryptic, A. texanum larvae remained on that background color rather than in refuge. A. barbouri larvae preferred to hide in refuge or on dark backgrounds regardless of crypticity, butquickly change color to match their new background. I found that both species darken in response to UVR. When given the choice of refuge, both species spent significantly more time in hiding when UVR was present. When given a choice of water depth, larvae preferred deep water in the presence of UVR radiation.Adapting multiple color and behavioral responses to individual selection pressures help organisms mediate conflicting demands from multiple selection pressures. For example, when predatory fish are present, larvae should move to shallow water to avoid predation. In the presence of UVR, however, larvae should prefer deeper water. I found A. barbouri larvae choose deep water to avoid high UVR exposure despite the risk of predation. Evolving multiple behavioral strategies allows A. barbouri larvae to avoid UVR damage and mediate predation risk.

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