McCauley David E
Department of Biology, Vanderbilt University, Nashville, TN, 37235, USA.
Evolution. 1991 Nov;45(7):1675-1684. doi: 10.1111/j.1558-5646.1991.tb02672.x.
The patchy local distribution of the common milkweed, Asclepias syriaca, organizes populations of a beetle that feeds on it, Tetraopes tetraophthalmus, into numerous local demes. Genetic and ecological characteristics of demes of adult milkweed beetles occupying two naturally occurring size classes of patches, defined as large and small, were studied in order to describe the effect of patch size variation on local population structure. Allele frequency variance in two of three protein polymorphisms was significantly greater in collections of beetles from an array of 13 small patches when compared to collections from an array of 11 large populations. A multivariate measure of variance using information from all 3 genetic markers confirmed that the small patches displayed greater overall genetic differentiation. This was further quantified by computing an F value, combined across loci, of 0.018 for the small patches and 0.004 for the large patches. No significant difference between patch size classes in mean allele frequency was detected. Mark and recapture studies of the adults found in five small and four large patches showed the residence times of adults in small patches to be less than half of those found in large patches. This was interpreted as resulting from higher emigration rates from small patches. It is proposed that greater genetic differentiation is found among demes from smaller patches because smaller patches support smaller population sizes and further because smaller patches act as net exporters of migrants while larger patches act as net migrant importers.
普通马利筋（Asclepias syriaca）的斑块状局部分布，将以其为食的一种甲虫——四眼斑叶甲（Tetraopes tetraophthalmus）的种群组织成了许多局部种群。为了描述斑块大小变化对局部种群结构的影响，研究了占据两种自然存在大小类别的斑块（定义为大斑块和小斑块）的成年马利筋甲虫局部种群的遗传和生态特征。与从11个大种群阵列收集的甲虫相比，在来自13个小斑块阵列的甲虫收集中，三种蛋白质多态性中的两种的等位基因频率方差显著更大。使用来自所有3个遗传标记的信息进行的多变量方差测量证实，小斑块显示出更大的总体遗传分化。通过计算合并位点的F值进一步量化，小斑块为0.018，大斑块为0.004。未检测到斑块大小类别之间在平均等位基因频率上的显著差异。对在五个小斑块和四个大斑块中发现的成年甲虫进行的标记重捕研究表明，成年甲虫在小斑块中的停留时间不到在大斑块中发现的停留时间的一半。这被解释为是由于从小斑块中迁出的比率更高。有人提出，在较小斑块的局部种群之间发现更大的遗传分化，是因为较小的斑块支持较小的种群规模，还因为较小的斑块是移民的净输出者，而较大的斑块是移民的净输入者。
