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| 文件类型： | 文章 |
|---|---|
| 所有的著者/提供者： | Michael F Benard; James A Fordyce |
| ISSN: | 0012-9658 |
| OCLC号码： | 480419352 |
| 语言注释： | English |
| 注意： | Fig. 1. Flow chart illustrating the experimental procedure of predator and control treatments for western toad (Bufo boreas) larvae. Table 1. MANOVA for the effects of treatment (predator vs. control) on tail height, tail length, tail muscle height, body length, and mass of western toads (Bufo boreas) at the time of the mid-larval assay (Gosner Stage 31). Fig. 2. Survival plot for Bufo boreas larvae in each arena in the mid-larval bioassay. (A) Aeshna (dragonfly nymphs) consumed B. boreas at the same rate irrespective of treatment (Mantel-Cox, χ<sup>2</sup>=0.434, df = 1, P = 0.51). (B) Dytiscus (predaceous diving beetle larvae) consumed B. boreas from predator treatments significantly faster than they consumed B. boreas from control treatments (Mantel-Cox, χ<sup>2</sup>=4.524, df = 1, P = 0.033). Table 2. MANOVA for the effects of treatment (predator vs. control) on tail height, tail length, tail muscle height, body length, and mass of western toads at the time of the late-larval assay (Gosner Stage 35). Fig. 3. Survival plot for B. boreas larvae in each arena in the late-larval bioassay. (A) Aeshna (dragonfly nymphs) consumed B. boreas from predator treatments significantly faster than they consumed B. boreas from control treatments (Mantel-Cox, χ<sup>2</sup>=3.928, df = 1, P = 0.048). (B) Abedus indentatus (giant water bugs) consumed B. boreas at the same rate, irrespective of treatment (Mantel-Cox, χ<sup>2</sup>=0.800, df = 1, P = 0.371). Fig. 4. Effect of consuming B. boreas from the two treatments on Ambystoma tigrinum. Values are mean ± 1 SE. (A) A. tigrinum took significantly longer to consume B. boreas from control treatments than from predator treatments. (B) A. tigrinum that had eaten B. boreas from the predator cue treatment did not take a significantly different amount of time to first strike at a cricket than did A. tigrinum that had eaten B. boreas from the control treatment. (C) Ambystoma tigrinum that ate a B. boreas from the control treatments took significantly longer to catch a cricket than did A. tigrinum that had eaten a B. boreas from the predator treatment. Asterisks indicate a significant difference between treatments at P < 0.01. Table 3. ANCOVA for the effects of larval treatment on the time that it took for each adult salamander to consume a western toad, once captured. Table 4. ANCOVA of the effects of larval treatment on the time that it took each adult salamander to first strike at a cricket placed into its cage, one hour after it swallowed a toad. Table 5. ANCOVA of the effects of larval treatment on the time that it took for each adult salamander to catch a cricket placed in its cage, one hour after it swallowed a toad. Fig. 5. Total amount (mean ± 1 SE) of bufadienolide in postmetamorphic B. boreas from the predator treatment vs. the control; the former had significantly higher amounts of bufadienolides (P < 0.05). |
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摘要：
Induced defenses are widespread in nature, and in amphibian larvae they are often expressed as altered behavior and changes in tail shape, color, and size. Theory predicts that induced defenses should be costly in the absence of a predator threat. No costs have been found for these defenses after metamorphosis. In this study, we tested for induced defenses in western toads, Bufo boreas, and measured larval and postmetamorphic consequences of these responses. Larvae were raised in either the presence or absence of nonlethal predator cues. Defense responses to these larval treatments were measured during the larval stage and shortly after metamorphosis using both predator bioassays and quantification of the putative chemical defense common in toads, bufadienolides. We found no differences in larval morphology, growth rate, or development rate between the predator and control treatments. In the larval bioassays, some types of invertebrate predators consumed significantly fewer of the B. boreas larvae that were reared with predator cues compared to the control treatments. Bufadienolides were not present in B. boreas larvae. In the postmetamorphic bioassays, tiger salamanders (Ambystoma tigrinum) had longer handling times when consuming B. boreas that had developed in larval environments without predator cues compared to predator-treatment B. boreas. However, postmetamorphic B. boreas from predator cue larval environments had significantly higher concentrations of bufadienolides than did those from larval environments without predators, suggesting that these defenses are ineffective against tiger salamanders. Our results demonstrate that there is plasticity in the chemical defenses of toads and suggest that induced larval defenses may incur costs that are only apparent after metamorphosis.