Graham John H, McArthur E Durant, Freeman D Carl
Department of Biology, Berry College, 30149-0446, P.O. Box 490446, Mount Berry, GA, USA.
USDA Forest Service, Shrub Sciences Laboratory, 84606, Provo, UT, USA.
Oecologia. 2001 Jan;126(2):239-246. doi: 10.1007/s004420000520. Epub 2001 Jan 1.
Several species of gall-forming insects specialize on big sagebrush (Artemisia tridentata), a species that shows much clinal and subspecific variation throughout its geographic range. Two of those subspecies, basin big sagebrush (A. t. ssp. tridentata) and mountain big sagebrush (A. t. ssp. vaseyana), form a narrow hybrid zone at Salt Creek, Utah. Reciprocal transplant experiments have shown that the hybrid big sagebrush at Salt Creek are more fit than either parental subspecies, but only in the hybrid zone. Do genotype and environment influence the density and distribution of galls on big sagebrush? We counted galls on parental and hybrid big sagebrush in three reciprocal transplant gardens at Salt Creek. Gardens were in each of the two parental zones and in the hybrid zone. Transplanted seedlings came from five source populations: two parental and three hybrid populations. We identified seven kinds of gall-forming flies (Rhopalomyia midges and Eutreta fruitflies) that produced identifiable galls. Densities of galls varied among the three gardens and five source populations, and there was also a significant garden by source interaction in gall density. In general, variation in gall density among gardens (i.e., environments) was much greater than the variation among source populations (i.e., genotypes). Nevertheless, significant genotype-environment interactions were observed for five of the seven kinds of galls. Overall density of galls, mostly due to Rhopalomyia ampullaria, was greatest in the high-elevation (mountain) garden and least in the low-elevation (basin) garden. To the best of our knowledge, this is the first reciprocal transplant experiment addressing herbivore richness in a hybrid zone.
几种形成虫瘿的昆虫专门寄生于三齿蒿（Artemisia tridentata），该物种在其整个地理分布范围内表现出许多渐变群和亚种变异。其中两个亚种，即盆地三齿蒿（A. t. ssp. tridentata）和山地三齿蒿（A. t. ssp. vaseyana），在犹他州的盐溪形成了一个狭窄的杂交带。互交移植实验表明，盐溪的杂交三齿蒿比任何一个亲本亚种都更具适应性，但仅在杂交带内如此。基因型和环境会影响三齿蒿上虫瘿的密度和分布吗？我们在盐溪的三个互交移植园中统计了亲本和杂交三齿蒿上的虫瘿数量。这些园分别位于两个亲本区域和杂交带内。移植的幼苗来自五个来源种群：两个亲本种群和三个杂交种群。我们鉴定出七种形成虫瘿的蝇类（Rhopalomyia 蠓和 Eutreta 果蝇），它们产生可识别的虫瘿。虫瘿密度在三个园和五个来源种群之间存在差异，并且在虫瘿密度方面还存在显著的园与来源的交互作用。一般来说，园（即环境）之间虫瘿密度的变化远大于来源种群（即基因型）之间的变化。然而，在七种虫瘿中的五种上观察到了显著的基因型 - 环境交互作用。虫瘿的总体密度，主要由壶腹形三齿蒿瘿蚊（Rhopalomyia ampullaria）导致，在高海拔（山地）园最高，在低海拔（盆地）园最低。据我们所知，这是首次在杂交带中针对食草动物丰富度进行的互交移植实验。
