Futuyma Douglas J, Keese Mark C, Scheffer Sonja J
Department of Ecology and Evolution, State University of New York, Stony Brook, Stony Brook, New York, 11794.
Evolution. 1993 Jun;47(3):888-905. doi: 10.1111/j.1558-5646.1993.tb01242.x.
We ask whether patterns of genetic variation in a phytophagous insect's responses to potential host plants shed light on the phylogenetic history of host association. Ophraella communa feeds chiefly, and in eastern North America exclusively, on Ambrosia (Asteraceae: Ambrosiinae). Using mostly half-sib breeding designs, we screened for genetic variation in feeding responses to and larval survival on its own host and on seven other plants that are hosts (or, on one case, closely related to the host) of other species of Ophraella. We found evidence for genetic variation in feeding responses to five of the seven test plants, other than the natural host. We found no evidence of genetic variation in feeding responses to two plant species, nor in capacity for larval survival on six. These results imply constraints on the availability of genetic variation; however, little evidence for constraints in the form of negative genetic correlations was found. These results are interpreted in the context of a provisional phylogeny of, and a history of host shifts within, the genus. Ophraella communa does not present evidence of genetic variation in its ability to feed and/or survive on Solidago, even though it is probably descended from a lineage that fed on Solidago or related plants, possibly as recently as 1.9 million years ago. Genetic variation in performance on this plant may have been lost. Based on evidence for genetic variation and on mean performance, by far the greatest potentiality for adaptation to a congener's host was evinced in responses to Iva frutescens, which not only is related and chemically similar to Ambrosia, but also is the host of a closely related species of Ophraella that may have been derived from an Ambrosia-associated ancestor. Genetic variation in O. communa's capacity to feed and/or survive on its congeners' hosts is less evident for plants that do not represent historically realized host shifts (with one exception) than for those that may (but see Note Added in Proof). The results offer some support for the hypothesis that the evolution of host shifts has been guided in part by constrained genetic variation.
我们探究植食性昆虫对潜在寄主植物的反应中的遗传变异模式是否能揭示寄主关联的系统发育历史。北美东部的黄斑直缘跳甲主要以豚草（菊科：豚草亚科）为食，且仅以豚草为食。我们主要采用半同胞育种设计，筛选了黄斑直缘跳甲对自身寄主以及七种其他植物（这些植物是其他黄斑直缘跳甲物种的寄主，或在一种情况下与寄主密切相关）的取食反应和幼虫存活的遗传变异。我们发现，除自然寄主外，在对七种测试植物中的五种的取食反应中存在遗传变异的证据。我们没有发现对两种植物的取食反应存在遗传变异的证据，也没有发现幼虫在六种植物上存活能力存在遗传变异的证据。这些结果意味着遗传变异的可用性存在限制；然而，几乎没有发现以负遗传相关性形式存在的限制证据。这些结果是在该属的临时系统发育和寄主转移历史的背景下进行解释的。黄斑直缘跳甲在一枝黄花上取食和/或存活的能力没有遗传变异的证据，尽管它可能起源于一个以一枝黄花或相关植物为食的谱系，可能距今仅190万年。这种植物上表现的遗传变异可能已经丧失。基于遗传变异的证据和平均表现，到目前为止，对弗吉尼亚盐角草的反应表现出对同属寄主最大的适应潜力，弗吉尼亚盐角草不仅与豚草相关且化学性质相似，而且是一种与黄斑直缘跳甲密切相关的物种的寄主，该物种可能起源于与豚草相关的祖先。对于那些并非历史上实际发生寄主转移的植物（有一个例外），黄斑直缘跳甲在同属寄主上取食和/或存活的能力的遗传变异，不如那些可能发生（但见校样补充说明）寄主转移的植物明显。这些结果为寄主转移的进化部分受遗传变异限制这一假说提供了一些支持。
