DISSERTATION RESEARCH: Sperm Competition and the Evolution of Alternative Reproductive Strategies

进化生物学中的一个基本问题是生物多样性是如何进化和维持的。在许多物种中，雄性在解剖、生理和行为特征上存在显著差异，这些特征构成了获取配偶的不同选择策略。一种拟议的维持这种变异的机制是频率依赖性，即如果给定的雄性策略变得罕见，它在生殖竞争中的成功将比其他策略更多，从而防止其灭绝。在黑剑鱼中，有两种策略与雄性体型相关，一种是通过强迫交配来先发制人的小型运动鞋雄性，另一种是体型较大的雄性，它们会产生雌性认为有吸引力的行为表现。为了验证频率依赖性假说，在半自然圈养环境中，偷偷摸摸和求偶的雄性黑线姬蜂将以不同的频率分布，并用遗传标记来衡量它们的繁殖成功率。自然界中策略的成功程度也将通过比较成年种群中的策略频率与从怀孕雌性动物中收集的后代样本中的策略频率来衡量。此外，这项研究还将考察频率依赖对雌性所产个体内的遗传多样性的影响。运动鞋雄性X.nigrensis会产生射精，其中包含更高比例的活精子和更长寿命的精子，因此，预计不同策略之间精子质量的差异将影响多重父子的比率。这项研究将扩大我们对频率依赖如何影响种群水平和后代之间的遗传变异模式的理解。该项目的更广泛影响包括对研究生的培训、对本科生的指导和对小学生的宣传。

A fundamental question in evolutionary biology is how biodiversity evolves and is maintained. In many species, males vary markedly in anatomical, physiological, and behavioral traits that constitute discrete alternative strategies for obtaining mates. A proposed mechanism for the maintenance of such variation is frequency dependence, which states that if a given male strategy becomes rare its success in reproductive competition will increase relative to the other strategies therefore preventing its extinction. In the fish Xiphophorus nigrensis, there are two strategies that are correlated with male body size, small 'sneaker' males that pre-empt female choice by forcing copulations and larger 'courting' males that produce behavioral displays females find attractive. To test the frequency dependence hypothesis, sneaking and courting male X. nigrensis will be distributed at different frequencies in semi-natural enclosures and their reproductive success measured using genetic markers. The success of the strategies in nature will also be measured by comparing strategy frequency in the adult population to strategy frequency in a sample of offspring collected from pregnant females. In addition, this study will examine the effects of frequency dependence on the genetic diversity within individual broods produced by females. Sneaker male X. nigrensis produce ejaculates that contain both a higher proportion of living sperm and sperm that is longer lived, and as a result it is expected that variation in the quality of sperm between strategies will influence the rates of multiple paternity. This research will broaden our understanding of how frequency dependence affects patterns of genetic variation both at the population level and among offspring within broods. The broader impacts of this project involve training of a graduate student, mentorship of undergraduates and outreach to elementary school children.