Predator–prey interactions play a key role in the evolution of species traits through antagonistic coevolutionary arms races. The evolution of beak morphology in the Darwin's finches in response to competition for seed resources is a classic example of evolution by natural selection. The seeds of Tribulus cistoides are an important food source for the largest ground finch species (Geospiza fortis, G. magnirostris, and G. conirostris) in dry months, and the hard spiny morphology of the fruits is a potent agent of selection that drives contemporary evolutionary change in finch beak morphology. Although the effects of these interactions on finches are well known, how seed predation affects the ecology and evolution of the plants is poorly understood. Here we examine whether seed predation by Darwin's finches affects the ecology and evolution of T. cistoides. We ask whether the intensity of seed predation and the strength of natural selection by finches on fruit defense traits vary among populations, islands, years, or with varying finch community composition (i.e., the presence/absence of the largest beaked species, which feed on T. cistoides most easily). We then further test whether T. cistoides fruit defenses have diverged among islands in response to spatial variation in finch communities. We addressed these questions by examining seed predation by finches in 30 populations of T. cistoides over 3 yr. Our study reveals three key results. First, Darwin's finches strongly influence T. cistoides seed survival, whereby seed predation varies with differences in finch community composition among islands and in response to interannual fluctuations in precipitation. Second, finches impose phenotypic selection on T. cistoides fruit morphology, whereby smaller and harder fruits with longer or more spines exhibited higher seed survival. Variation in finch community composition and precipitation also explains variation in phenotypic selection on fruit defense traits. Third, variation in the number of spines on fruits among islands is consistent with divergent phenotypic selection imposed by variation in finch community composition among islands. These results suggest that Darwin's finches and T. cistoides are experiencing an ongoing coevolutionary arms race, and that the strength of this coevolution varies in space and time.

中文翻译：

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加拉帕戈斯群岛上Dar藜Tri虫的达尔文雀科捕食者的生态学和进化

捕食者与猎物的相互作用通过对抗性的协同进化军备竞赛在物种性状的进化中起着关键作用。达尔文雀雀对种子资源的竞争而产生的喙形态演变是自然选择进化的一个典型例子。的种子大花蒺藜是最大的地雀物种的重要食物来源（Geospiza富通，G.巨嘴龙属，和G. conirostris），在干旱的月份，果实的硬多刺的形态是选择的有力媒介，可推动当代雀科喙形态的进化变化。尽管这些相互作用对雀科的影响是众所周知的，但种子捕食如何影响植物的生态和进化却知之甚少。在这里，我们研究了达尔文雀科的种子捕食是否会影响顺丁香锥虫的生态和进化。我们问种子捕食的强度和雀科对水果防御性状的自然选择的强度在种群，岛屿，年份之间还是在雀科群落组成不同的情况下（即以最大的喙类物种的存在/不存在为食）是否有所不同。T. cistoides最容易）。然后，我们进一步测试是否有T. cistoides由于雀科群落的空间变化，各岛之间的水果防御措施也有所不同。我们通过在30人口由雀检查种子捕食解决这些问题T. cistoides超过3年。我们的研究揭示了三个关键结果。首先，达尔文的雀科强烈影响顺式梭菌的种子生存，从而使种子捕食随岛屿之间雀科群落组成的不同以及对降水年际波动的响应而变化。其次，雀将表型选择强加于顺丁螺果实形态，具有更长或更多刺的较小和较硬的果实表现出较高的种子存活率。雀科群落组成和降水的变化也解释了水果防御性状在表型选择上的变化。第三，岛上果实上的刺数变化与岛上雀科群落组成的变化所造成的表型选择不同是一致的。这些结果表明，达尔文的雀科和T. cistoides正在经历一场持续不断的军备竞赛，而且这种共同进化的力量在时空上也有所不同。