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| Ecologists have long sought to understand the plasticity of organisms in environments that vary widely among years, seasons, and even hours of the day. Though environmental change is ubiquitous, relatively few empirical studies have considered the consequences of diel temperature variation on developing organisms, instead comparing phenotypes among un-natural stable conditions. Our research aims are examine the effects of daily fluctuating environments on the growth and development of larval amphibians and determine whether we can predict their final phenotype when they develop in complex fluctuating environments. Anurans represent an ideal system for examining ontogenetic changes in the relationship between morphology and performance because they undergo dramatic phenotypic changes throughout ontogeny. This enables an examination of the effects of the environment and morphology on performances at multiple stages. |
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| Here Amanda is testing the influence of a stable thermal environment (flowing creek) on the behavioural response of lab mascot Lupa Niehaus. |
| In one experiment, we determined whether reaction norms based on stable environments (18, 22, 26, 30 and 34°C) could be used to predict hatchling, larval and metamorphic phenotypes of anurans in variable environments (18°-28°C and 18°-34°C). We used existing theory to evaluate how acclimation might result in poor predictability. Our empirical models did not accurately predict anuran phenotypes in fluctuating temperatures, suggesting that extrapolation from studies conducted under unrealistic, stable conditions may lead to erroneous conclusions. Overall, development was generally faster than expected in variable environments, but the predictability of growth differed widely among treatments and stages of development. The inaccuracy of our predictions was not always in the direction expected if optimal acclimation occurred in the stable conditions. |
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| Striped marsh frog tadpoles growing up in an unstable home |
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We also conducted a comprehensive phenotypic analysis of ontogenetic shifts in both performance and the relationship between morphology and performance in the striped marsh frog (Limnodynastes peronii). Our aims were to determine (i) whether performance or morphology were more closely related among larval stages than they were between larval and metamorphic stages and (ii) how developmental temperature(s), larval or metamorphic morphology, and larval performance interacted to produce variation in metamorphic performance.
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We raised embryos and larvae of striped marsh frogs in stable and fluctuating environments, encompassing the range of temperatures encountered in nature. Body size, relative tail or leg length, and swimming or jumping performance were recorded for individuals at two larval stages and at metamorphosis (N = 125-150 at each stage). Among stable thermal environments, we found that metamorphic performance depended directly on temperature, but was also indirectly related to temperature via metamorphic size, with larger frogs jumping farther.
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| A Striped marsh frog tadpole measures up |
| As expected, morphology and performance were related between larval stages, but not between larval and metamorphic stages. In contrast, thermal variance only indirectly affected locomotor performance of metamorphic frogs, via changes in morphology during larval and metamorphic stages. Relationships among the environment, morphology, and performance depended on whether temperature remained stable or fluctuated during development, signifying the importance of including realistic thermal variation in studies of developmental plasticity. Furthermore, relationships differed among developmental stages, demonstrating that ontogeny plays an important role in establishing the link between morphology and performance. |
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