The evolutionary significance of the extreme sexual size dimorphism in orb-web spiders

球网蜘蛛极端性体型二态性的进化意义

• 批准号: 329184-2006
• 负责人: Foellmer, Matthias
• 金额: $ 1.54万
• 依托单位: Trent University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2008
• 资助国家: 加拿大
• 起止时间: 2008-01-01 至 2009-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=398106
• 关键词: evolutionary; significance; extreme; sexual; size

In many animals males and females differ in characteristics such as size, weaponry, or colouration. In some groups, notably the orb-web spiders, females can weigh more than one hundred times as much as males. The reasons for such extreme size differences are not well understood. Identifying the processes that underlie the evolution of extreme body size differences between the sexes are important to understand how natural selection and the genetic architecture of organisms interact to result in observed patterns of morphological and behavioural diversity. This research project examines factors that contribute to the evolution of extreme sexual size dimorphism in the orb-web spider Argiope aurantia, a large and conspicuous spider common to Eastern North America. I address the consequences of the adult size differences for the early juvenile stages. Juvenile males and females have to pursue different foraging strategies: females have to catch more prey, but may as a result engage in risky behaviours, exposing themselves to predators. Males of all web-building spiders have to leave their webs to search for females. I examine how habitat structure effects male movement through the vegetation and if males of different sizes are more efficient at moving through particular habitat types. Large females are commonly hypothesized to have the advantage to be able to lay more eggs and to have outgrown relevant predators. Large females may however have the disadvantage of taking more time to grow to maturity so that less time to mate and to lay clutches is available. I investigate reproductive success of females in detail to evaluate the various hypotheses. Furthermore, I estimate the variability in male mating success and compare this to the obtained estimate for female reproductive success, which is the number of offspring produced. I test the hypothesis that, unlike in the majority of species, the variability is greater in females than in males, leading to stronger selection on females and thus enabling the evolution of giant size in the female sex.

在许多动物中，雄性和雌性的特征不同，如大小，武器或颜色。在某些群体中，特别是圆网蜘蛛，雌性蜘蛛的体重可以是雄性蜘蛛的一百倍以上。这种极端大小差异的原因还不清楚。确定两性之间极端体型差异的演变过程对于理解自然选择和生物体的遗传结构如何相互作用以产生观察到的形态和行为多样性模式至关重要。本研究项目探讨了导致圆网蜘蛛Argiope aurantia（一种常见于北美东部的大型引人注目的蜘蛛）极端性别大小二型性进化的因素。我解决的后果成人大小差异的早期少年阶段。幼年的雄性和雌性不得不采取不同的觅食策略：雌性不得不捕捉更多的猎物，但可能因此而从事危险的行为，将自己暴露在捕食者面前。所有结网蜘蛛的雄性都不得不离开它们的网去寻找雌性。我研究栖息地结构如何影响男性运动通过植被，如果男性不同大小的移动通过特定的栖息地类型更有效。大型雌性通常被假设为具有优势，能够产更多的蛋，并已超过相关的捕食者。然而，大雌性可能有缺点，需要更多的时间来成长到成熟，以便更少的时间来交配和产卵。我调查繁殖成功的女性详细评估各种假设。此外，我估计男性交配成功的变异性，并将其与女性生殖成功的估计值进行比较，这是产生后代的数量。我测试的假设，不像大多数物种，变异性是在女性比男性更大，导致更强的选择对女性，从而使女性的巨大尺寸的进化。