Department of Mathematics and Statistics, University of Melbourne, Parkville, VIC 3010, Australia.
J Theor Biol. 2011 Apr 21;275(1):1-11. doi: 10.1016/j.jtbi.2010.12.040. Epub 2010 Dec 30.
Natural parasitoid systems exhibit considerable variation in their life history properties yet little is known about the effects of development time on parasitoid fitness or of the conditions that might select for rapid development at the expense of reduced parasitoid growth. In this study the techniques of adaptive dynamics are applied to a discrete time host-parasitoid model to examine the evolution of parasitoid life history strategies. In particular, we explore the conditions that select for variation in parasitoid traits, such as, the timing of parasitoid attack and emergence from the host. The process of evolutionary branching, leading to dimorphism, can occur when the benefits to reproduction of early parasitoid attack are bought at a cost in terms of mortality of late parasitoid emergence from the host. We also find that trends in parasitoid life history traits depend critically on the nature of the underlying population dynamics. Increases in the strength of host density-dependence acts to select for shorter parasitoid development time and lower searching efficiency when the underlying population dynamics are at equilibrium. This trend is reversed when the underlying population dynamics exhibit fluctuations. Here, fluctuations in host density driven by parasitism become more extreme as the strength of host density-dependence decreases and so the parasitoid selects early emergence to avoid the mortality experienced at outbreak host densities. Our results are consistent with the general principle that parasitoids facing high mortality risk favour short development times over size and high searching efficiency, whereas species facing low mortality risks favour size at the cost of increased development time.
自然寄生系统在其生活史特性上表现出相当大的变化，但人们对发育时间对寄生适应性或可能选择以牺牲寄生生长为代价快速发育的条件对寄生适应性的影响知之甚少。在这项研究中，适应性动态的技术被应用于离散时间的宿主-寄生模型，以研究寄生生活史策略的进化。特别是，我们探讨了选择寄生特征变化的条件，例如寄生攻击和从宿主中出现的时间。当早期寄生攻击的繁殖收益以从宿主中晚期寄生出现的死亡率为代价时，导致二态性的进化分支过程就会发生。我们还发现，寄生生活史特征的趋势取决于潜在种群动态的性质。当潜在种群动态处于平衡时，宿主密度依赖性的增强会选择更短的寄生发育时间和更低的搜索效率。当潜在的种群动态表现出波动时，这种趋势就会逆转。在这里，由于宿主密度依赖性的减弱，寄生驱动的宿主密度波动变得更加极端，因此寄生选择早期出现以避免在爆发宿主密度下经历的死亡率。我们的结果与一般原则一致，即面临高死亡率风险的寄生生物更喜欢短的发育时间而不是体型和高搜索效率，而面临低死亡率风险的物种则以增加发育时间为代价来偏爱体型。
