Dissertation Research: Evolution and Development of Alternative Amphibian Morphologies

论文研究：替代两栖动物形态的进化和发展

• 批准号: 8800986
• 负责人: Mark Kirkpatrick
• 金额: $ 0.55万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1988
• 资助国家: 美国
• 起止时间: 1988-06-15 至 1990-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=8800986&HistoricalAwards=false
• 关键词: Dissertation; Research; Evolution; Development; Alternative

Under the concept of natural selection, individuals should respond to their environment in such a way as to increase their genetic fitness. Individuals in a population may respond differently, however, to identical environmental conditions; there are often alternative, equally adaptive responses to selection pressure. The proposed research will study spadefoot tadpoles which occur as two discrete phenotypes: a large, rapidly developing carnivore morph and a smaller, slower developing omnivore morph. This system provides a unique opportunity to examine how an animal's ecology can profoundly affect its development. The system poses interesting problems on the population level as well. The first goal of this study will be to ascertain how the dimorphism is maintained evolutionarily. Carnivores appear to do better in highly ephemeral pools (because of their more rapid development), but omnivores may do better in more permanent ponds (because of their greater postmetamorphic survivorship and reduced susceptibility to carnivore predation). The hypothesis that these fitness trade-offs balance will be tested by examining whether survivorship (both pre- and postmetamorphic) of the two morphs is equal within a given pond. If this experiment shows that the two morphs do equally well, this would provide the opportunity to analyze the strategies of development. The second goal is to explain what factors favor the spread of this and other similar dimorphisms. Research will be done on the extent to which this variability represents genetic adaptation to different environmental conditions at opposite ends of the species' range as opposed to environmentally induced phenotypic variation. The third goal is to explain the physiological basis of morph determination. Whether the ingestion of naturally occurring thyroxine (the endocrine "trigger" of amphibian differentiation at metamorphosis) causes young tadpoles to develop into carnivores will be examined. If thyroxine is the trigger of morph differentiation, the underlying physiological mechanisms will be studied. This study will provide much needed information, at both the proximate and ultimate levels, concerning how alternative strategies of development can persist in a population. Scaphiopus with its dimorphic tadpole is an excellent model animal for studying the evolution of developmental plasticity. The results of this study may have potential applications. Tadpoles have long been used in the study of animal development and spadefoots may provide developmental biologists with a unique opportunity to study large scale facultative shifts in development in a vertebrate. Finally, the carnivore's ability to switch to omnivory has already interested a German scientist attempting to increase yields in commercial fish hatcheries, where fish are typically fed a more expensive carnivorous diet.

在自然选择的概念下，个体应该以这样一种方式对环境做出反应，以增加其遗传适合度。然而，同一种群中的个体对相同的环境条件可能有不同的反应；面对选择压力，通常会有不同的、同样适应性的反应。拟议的研究将研究两种不同表型的掌足蝌蚪：一种是大的、快速发育的食肉蝌蚪，另一种是小的、发育较慢的杂食蝌蚪。这个系统提供了一个独特的机会来研究动物的生态如何深刻地影响它的发育。这个系统在人口层面上也带来了有趣的问题。本研究的第一个目标将是确定二态性是如何在进化上维持的。食肉动物似乎在高度短暂的池塘中表现得更好（因为它们的发育速度更快），但杂食动物可能在更永久的池塘中表现得更好（因为它们的变质后存活率更高，对食肉动物捕食的敏感性降低）。通过检查在给定的池塘中两种变体的存活率（包括前变质和后变质）是否相等，将检验这些适应性权衡平衡的假设。如果这个实验表明这两种变体表现得同样好，这将为分析发展策略提供机会。第二个目标是解释什么因素有利于这种和其他类似的二态性的传播。将研究这种变异在多大程度上代表了物种范围两端对不同环境条件的遗传适应，而不是环境诱导的表型变异。第三个目标是解释形态决定的生理基础。摄入自然产生的甲状腺素（两栖动物变态分化的内分泌“触发器”）是否会导致小蝌蚪发育成食肉动物将被研究。如果甲状腺素是形态分化的触发因素，那么潜在的生理机制将被研究。这项研究将在近期和最终两级提供非常需要的资料，说明备选的发展战略如何能够在人口中持续下去。具有二形蝌蚪的爪蟾是研究发育可塑性进化的良好模式动物。本研究结果可能具有潜在的应用价值。长期以来，蝌蚪一直被用于动物发育的研究，而大脚可能为发育生物学家提供了一个独特的机会来研究脊椎动物发育中的大规模兼性变化。最后，食肉动物转变为杂食动物的能力已经引起了一位德国科学家的兴趣，他试图提高商业鱼类孵化场的产量，在那里，鱼通常被喂食更昂贵的食肉食物。