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Reproductive Timing in a Changing World: Understanding Mechanisms and Costs Associated with Reproductive Timing Decisions

机译：瞬息万变的世界中的生殖时机：了解与生殖时机决策相关的机制和成本

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摘要

Organisms in temperate zones time reproduction to occur when conditions are optimal for raising offspring. However, individuals of many taxa vary in precise timing of breeding. The mechanisms underlying the existing variation are not well understood, particularly in females. I hypothesized that individual variation in daily (i.e., circadian) rhythms, which are highly conserved across taxa, are related to variation in reproductive timing. By measuring activity onset in two species of songbirds, we found that females beginning their day earlier also breed earlier. I further asked if sex-steroid hormones were related to onset of daily activity in free-living individuals. My results show that maximal levels of estradiol are correlated with onset of activity in free-living females. This suggests that circadian rhythms may influence much of the variation seen in timing of breeding and individual physiology influences circadian behavior. In addition to mechanisms underlying reproductive timing, I also investigated potential selective pressures that could act on timing decisions. Early breeding females often produce more and larger offspring, however, most of the population breeds later than this optimum, suggesting there are costs associated with early reproduction. To determine if early breeding females are better able to handle an additional energetic challenge, I injected incubating females with a mild antigen and monitored nest survival in early and late breeders. The immune challenge caused a significant increase in nest failure compared to controls and success did not differ between early and late breeders. Next, using a long-term dataset I asked whether females who breed early experience accelerated rates of aging via telomere loss. I found that early breeding females experience higher telomere attrition compared to females breeding later. Annual change in telomere length was not related to reproductive output, but females experiencing cooler temperatures during egg laying and incubation (i.e., laying earlier in the season) had higher telomere attrition. With telomere loss and length being important determinants of lifespan and longevity, higher telomere attrition in early breeders may be linked with reduced overwinter survival. A better understanding of mechanisms and costs will help determine how populations will adjust to, or suffer from, a changing climate.
机译：温带地区的有机体在繁殖后代的最佳条件下会繁殖时间。但是，许多类群的个体在精确的配种时间上会有所不同。尚不清楚现有变异的潜在机制，尤其是在女性中。我假设日常（即昼夜节律）的个体差异在整个分类群中是高度保守的，与生殖时间的变化有关。通过测量两种鸣禽的活动开始，我们发现雌鸟早起的日子也早于繁殖。我进一步问，性固醇激素是否与自由生活者的日常活动有关。我的结果表明，雌二醇的最高水平与自由生活女性的活动开始有关。这表明，昼夜节律可能会影响繁殖时机中出现的许多变异，而个体生理也会影响昼夜节律。除了生殖时机的机制外，我还研究了可能影响时机决策的潜在选择压力。早期繁殖的雌性通常会繁殖出更多，更大的后代，但是，大多数种群的繁殖都比这个最佳时期晚，这表明早期繁殖需要付出一定的代价。为了确定早期繁殖的雌性是否能够更好地应对其他精力充沛的挑战，我向温育的雌性中注入了温和的抗原，并监测了早期和晚期育种者的巢生存。与对照组相比，免疫挑战导致巢的失败率显着增加，早期和晚期繁殖者的成功率没有差异。接下来，我使用一个长期数据集，我问早育的雌性是否通过端粒丢失而加速了衰老速度。我发现与早期繁殖的雌性相比，早期繁殖的雌性的端粒损耗更高。端粒长度的年度变化与生殖产量无关，但是在产卵和孵化过程中温度较低（即在产蛋季节较早）的雌性端粒损耗较高。端粒的丢失和长度是寿命和寿命的重要决定因素，早期种鸡的端粒损耗增加可能与越冬存活率降低有关。对机制和成本的更好理解将有助于确定人们如何适应或适应气候变化。

著录项

  • 作者

    Graham, Jessica Lynn.;

  • 作者单位

    North Dakota State University.;

  • 授予单位 North Dakota State University.;
  • 学科 Biology.;Conservation biology.
  • 学位 Ph.D.
  • 年度 2018
  • 页码 107 p.
  • 总页数 107
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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