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首页> 外文学位 >Adaptation of reproductive strategies: Endocrine and ecological factors associated with the evolution of terrestrial breeding in amphibians.
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Adaptation of reproductive strategies: Endocrine and ecological factors associated with the evolution of terrestrial breeding in amphibians.

机译：生殖策略的适应：与两栖动物陆地繁殖进化有关的内分泌和生态因素。

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The goal of this study was to identify the endocrine and ecological factors associated with the evolution of terrestrial breeding in amphibians. I focused on the redbacked salamander, Plethodon cinereus, a woodland species that has a reproductive strategy typical of terrestrial salamanders, involving direct development, small clutches of large eggs, terrestrial oviposition, and obligate maternal care. This strategy differs from the more ancestral, aquatic breeding amphibians that have a biphasic life cycle, oviposit large clutches of small eggs in ponds, and do not exhibit parental care.; Two physiological adaptations associated with terrestrial breeding were suggested from experiments. First, clutch size is determined at the earliest stages of ovarian development (one year prior to the time of oviposition), as supplemental feeding treatments throughout the foraging period did not increase the numbers of developing oocytes. Second, injections of follicle stimulating hormone (FSH) and luteinizing hormone (LH) were associated with separate effects on oocyte development: FSH controlled oocyte recruitment and caused moderate oocyte growth, and LH primarily controlled oocyte growth and restricted oocyte recruitment. This is the first study to show different roles of FSH and LH in amphibian oocyte development, as both FSH and LH affect oocyte recruitment and growth in aquatic-breeding amphibians.; Ecological experiments using hormone treatments to increase the range of oviposition dates conducted in 1999 and 2000 demonstrated that stabilizing selection might have acted to produce the oviposition times observed in natural populations. In both years, females ovipositing during intermediate times (June) were least likely to abandon their clutches and had the highest fecundity. Body size, egg number, egg size, and oviposition date were shown to affect offspring size at hatching. The specific relationships between these maternal traits and offspring size differed in magnitude and direction between years, probably due to the differences in the environmental conditions. A cross-fostering experiment showed that size-mediated behaviors of mothers during brooding had a greater effect on offspring size than pre-ovipositional maternal traits, such as egg size or yolk quality. These results suggest that maternal phenotypic effects on offspring are complex and are important factors in the ecology and evolution of terrestrial amphibians.
机译：这项研究的目的是确定与两栖动物陆地繁殖进化有关的内分泌和生态因素。我专注于红背sal，Plethodon cinereus，这是一种林地物种，具有典型的陆生strategy繁殖策略，包括直接发育，大卵小的抓取，陆生产卵和专职的产妇护理。这种策略不同于具有双相生命周期的祖先水生两栖动物，在池塘中排卵着大的小卵卵，并且没有父母的照料。实验提出了与陆地育种有关的两种生理适应性。首先，离合器的大小是在卵巢发育的最早阶段（在排卵前一年）确定的，因为整个觅食期的补充喂养处理并未增加发育中的卵母细胞的数量。其次，注射卵泡刺激素（FSH）和促黄体生成素（LH）分别对卵母细胞发育有影响：FSH控制卵母细胞募集并引起中等卵母细胞生长，而LH主要控制卵母细胞生长和限制卵母细胞募集。这是第一个显示FSH和LH在两栖卵母细胞发育中不同作用的研究，因为FSH和LH都影响水生两栖动物的卵母细胞募集和生长。在1999年和2000年使用激素处理来增加产卵日期的生态实验表明，稳定的选择可能会产生自然种群中产卵时间。在这两年中，在中间时间（6月）产卵的雌性都最不可能放弃离合器，并且产卵量最高。孵化时的体形，卵数，卵大小和产卵日期会影响后代的大小。这些母体特征与后代大小之间的具体关系在年份之间的大小和方向上有所不同，这可能是由于环境条件的差异所致。一项交叉寄养实验表明，与产卵前产妇性状（如卵大小或蛋黄质量）相比，育雏期间母亲通过大小介导的行为对后代大小的影响更大。这些结果表明，母亲对后代的表型效应是复杂的，并且是陆地两栖动物的生态学和进化的重要因素。

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