McCall Claire, Mitchell-Olds Thomas, Waller Donald M
Department of Botany, University of Wisconsin, Madison, WI, 53706.
Evolution. 1989 Aug;43(5):1075-1084. doi: 10.1111/j.1558-5646.1989.tb02552.x.
Using field and greenhouse experiments, we tested two hypotheses that could account for the maintenance of outcrossing in Impatiens capensis. Seedlings derived from cleistogamous (CL) and chasmogamous (CH) flowers were grown under competitive conditions while flanked by neighbors that were either related or unrelated. In both experiments, CH progeny sometimes expressed more phenotypic variability than CL progeny. In the greenhouse experiment, CH progeny attained the same weight as CL progeny, and the relatedness of neighboring plants did not affect the growth of either type. In the field experiment, CL and CH progeny performed similarly when grown with related competitors. However, CH progeny were somewhat larger when planted with nonsibs, while CL progeny were somewhat smaller under those conditions. Thus, there is no evidence that either frequency-dependent selection or the avoidance of competition among siblings favors the maintenance of outcrossing in this species. We also modeled the relative variability of selfed and outcrossed progeny under several reproductive systems. When females mate with one male (progeny are full sibs), selfed progeny are often more variable than outcrossed progeny. When females engage in both selfing and outcrossing, variation among progeny is frequently maximized at an intermediate selfing rate. The sib-competition mechanism, under a range of genetic models, is not apt to promote outcrossing, since selfed progeny are commonly more variable than outcrossed progeny.
通过田间试验和温室试验，我们检验了两种可以解释北美凤仙花异交维持机制的假说。将闭花受精（CL）花和开花受精（CH）花产生的幼苗种植在竞争环境中，其两侧的邻居既有亲缘关系的，也有非亲缘关系的。在这两个试验中，CH后代有时比CL后代表现出更多的表型变异性。在温室试验中，CH后代与CL后代达到相同的重量，相邻植物的亲缘关系不影响任何一种类型的生长。在田间试验中，CL和CH后代与亲缘关系相近的竞争者一起生长时表现相似。然而，当与非同胞种植在一起时，CH后代稍大一些，而CL后代在这些条件下稍小一些。因此，没有证据表明频率依赖选择或同胞间竞争的避免有利于该物种异交的维持。我们还模拟了几种生殖系统下自交和异交后代的相对变异性。当雌性与一个雄性交配时（后代为全同胞），自交后代通常比异交后代更具变异性。当雌性既进行自交又进行异交时，后代的变异性通常在中等自交率时达到最大。在一系列遗传模型下，同胞竞争机制不太可能促进异交，因为自交后代通常比异交后代更具变异性。
