Mason Paul, Rothstein Stephen I
Department of Biological Sciences, University of California, Santa Barbara, CA, 93106.
Evolution. 1986 Nov;40(6):1207-1214. doi: 10.1111/j.1558-5646.1986.tb05745.x.
The Rufous Hornero (Furnarius rufus) is an important host of the brood parasitic Shiny Cowbird (Molothrus bonariensis) in Uruguay, but not in nearby Buenos Aires Province, Argentina. Eggs of the Shiny Cowbird are extremely variable in size, and horneros eject cowbird eggs with widths less than about 88% of the widths of their own eggs. Uruguayan cowbird eggs are, on average, 12% larger than those from Buenos Aires, a geographic pattern in egg size that corresponds to the pattern of successful host use. Uruguayan cowbird eggs are also wider per unit volume than eggs from Buenos Aires. Allometric analyses of egg width and volume indicate that this shape change is apparently an evolutionary response to selection exerted by the hornero. Such a response is absent in Buenos Aires because interactions between the cowbird and the hornero are probably of recent origin there.
棕灶鸟（Furnarius rufus）在乌拉圭是巢寄生辉拟鹂（Molothrus bonariensis）的重要宿主，但在附近的阿根廷布宜诺斯艾利斯省则不是。辉拟鹂的卵大小差异极大，而灶鸟会将宽度小于其自身卵宽度约88%的拟鹂卵逐出。乌拉圭拟鹂卵的平均大小比布宜诺斯艾利斯的拟鹂卵大12%，这种卵大小的地理分布模式与成功的宿主利用模式相符。乌拉圭拟鹂卵每单位体积的宽度也比布宜诺斯艾利斯的卵宽。对卵宽度和体积的异速生长分析表明，这种形状变化显然是对灶鸟施加的选择的一种进化反应。在布宜诺斯艾利斯不存在这种反应，因为拟鹂和灶鸟之间的相互作用在那里可能是最近才出现的。
