Kelley Scott T, Farrell Brian D
Department of Environmental, Population and Organismic Biology, University of Colorado, Boulder, Colorado, 80309-0334.
Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts, 02138.
Evolution. 1998 Dec;52(6):1731-1743. doi: 10.1111/j.1558-5646.1998.tb02253.x.
Ecological explanations for the prevalence of resource specialists are abundant, whereas phylogenetic evidence on their origins is scarce. In this paper, we provide a molecular phylogenetic study of the 19 specialist or generalist species in the bark beetle genus Dendroctonus, which collectively attack species in four different genera in the conifer family Pinaceae. Given substantial variation in diet breadth, we asked two general questions concerning the evolution of resource use in this group. How conservative is the evolution of host use in these insects? Does specialization tend to be derived (i.e., a "dead end")? To answer these questions, we estimated the phylogeny of Dendroctonus using mitochondrial DNA sequences and mapped transitions in resource use on the resulting phylogeny estimate. The evolution of affiliations with Pinus and Picea hosts in Dendroctonus was conservative among beetle species (PTP test; P < 0.012), but there was no significant correspondence between the phylogeny of these beetles and the phylogeny among their Pinaceae hosts (among genera, P = 0.28; among Pinus species, P = 0.82). Degree of specialization, as measured in the proportion of hosts used, was bimodally distributed with "generalist" species utilizing < 60% of the congeneric hosts within their range and six specialist species utilizing < 40% of the available hosts. Among the generalists, we found a strong correlation between the number of hosts encountered and the number of hosts utilized (R = 0.97, P < 0.0001), whereas there was no significant correlation among the specialists (R = 0.27, P = 0.59). The evolution of specialization in Dendroctonus proved highly labile-specialists arose from generalists at least six separate times (without reversal) all in derived positions, and closer examination of some specialists revealed instances where they appear to have lost particular host species from their diet. However, evidence from the ecological literature also suggests that several Dendroctonus generalists may have increased their range of host genera within the Pinaceae.
关于资源 specialists 盛行的生态学解释有很多，而关于它们起源的系统发育证据却很少。在本文中，我们对树皮甲虫属 Dendroctonus 中的 19 种 specialist 或 generalist 物种进行了分子系统发育研究，这些物种共同攻击松科四个不同属的物种。鉴于食性广度存在很大差异，我们提出了两个关于该类群资源利用进化的一般性问题。这些昆虫宿主利用的进化有多保守？专业化是否倾向于衍生而来（即“死胡同”）？为了回答这些问题，我们使用线粒体 DNA 序列估计了 Dendroctonus 的系统发育，并将资源利用的转变映射到由此产生的系统发育估计上。Dendroctonus 与松属和云杉属宿主的关联进化在甲虫物种中是保守的（PTP 检验；P < 0.012），但这些甲虫的系统发育与其松科宿主的系统发育之间没有显著对应关系（属间，P = 0.28；松属物种间，P = 0.
