Departamento de Ecología Evolutiva, Instituto de Ecología, UNAM A.P. 70-275, Mexico D.F. 04510, Mexico.
Am J Bot. 2005 Jan;92(1):116-22. doi: 10.3732/ajb.92.1.116.
The evolution of male-sterile individuals in hermaphroditic species represents the first step in the evolution of sex specialization. For male-sterile individuals to persist they must have some fitness advantage that compensates for their loss of the male function. Female fecundity also depends on environmental factors as those determining the likelihood of pollination and fertilization. Here we assessed the effects of both male sterility and reproductive synchrony (an environmentally affected trait) on the magnitude of female compensation of Erythroxylum havanense, a distylous shrub with morph-biased male sterility. In vitro measurements of pollen germination showed that thrums were more male sterile than pins. The compensatory advantage of thrums changed by a factor of five depending on flowering synchrony. Flowering in synchrony with the population increased fruit production in both morphs. However, because pins that flowered out of synchrony produced almost no fruits, the reproductive compensation of thrums was higher in these circumstances. Because the magnitude of compensation is frequently considered as a key factor in the evolution of sex specialization, the environmentally induced variation in the magnitude of the reproductive compensation of thrum plants may have profound effects on the evolutionary dynamics of the reproductive system of E. havanense.
雌雄同体物种中性不育个体的进化代表了性特化进化的第一步。为了使性不育个体得以持续存在，它们必须具有某种适应度优势，以弥补雄性功能的丧失。雌性繁殖力也取决于环境因素，如那些决定授粉和受精可能性的因素。在这里，我们评估了雄性不育和生殖同步（受环境影响的特征）对具有偏态雄性不育的二型性灌木 Erythroxylum havanense 雌性补偿程度的影响。花粉萌发的离体测量表明，雄蕊比雌蕊的雄性不育程度更高。雄蕊的补偿优势根据开花同步性变化了五倍。与种群同步开花增加了两种形态的果实产量。然而，由于不同步开花的雌蕊几乎没有产生果实，因此在这种情况下，雄蕊的生殖补偿更高。因为补偿的程度通常被认为是性特化进化的关键因素之一，所以受环境影响的雄蕊植物生殖补偿程度的变化可能对 E. havanense 生殖系统的进化动态产生深远影响。
