Centre d'Ecologie Fonctionnelle et Evolutive (CNRS), 1919 Route de Mende, F-34293 Montpellier, France.
Am J Bot. 2001 Aug;88(8):1424-9.
Inbreeding depression is a major selective factor acting to maintain outcrossing in hermaphroditic plants. Recently it has been shown that environmental conditions may greatly affect the levels of inbreeding depression. In this study, the effects of intraspecific competition, from either crossed or inbred progeny, and plant density on the expression of inbreeding depression were estimated for the allogamous colonizing plant Crepis sancta (Asteraceae). The population used in this experiment showed a very high outcrossing rate (t = 0.99). Inbreeding depression was measured for germination, survival to reproduction, number of capitula, and a multiplicative fitness estimate. We found that inbreeding depression on survival, the number of capitula, and total fitness was the greatest when inbred plants compete with outbred plants. The effect of density on inbreeding depression was less evident. The major implication of our study is that the relative fitness of selfed progeny is strongly influenced by the type of competitors (outbred or inbred). These results support the hypothesis that inbreeding depression varies according to the density and frequency of outbred plants and suggest that it could be considered as a density- and frequency-dependent phenomenon.
自交衰退是作用于维持雌雄同体植物异交的主要选择因素。最近的研究表明，环境条件可能会极大地影响自交衰退的程度。在这项研究中，我们估计了种内竞争（来自杂交或自交后代）和植物密度对异交植物 Crepis sancta（菊科）自交衰退表达的影响。本实验中使用的种群具有非常高的异交率（t = 0.99）。我们测量了自交衰退对萌发、繁殖存活率、头状花序数和乘法适合度估计的影响。结果发现，当自交植物与异交植物竞争时，自交衰退对存活率、头状花序数和总适合度的影响最大。密度对自交衰退的影响则不那么明显。我们研究的主要意义在于，自交后代的相对适合度受到竞争类型（异交或自交）的强烈影响。这些结果支持了这样一种假说，即自交衰退会根据异交植物的密度和频率而变化，并表明它可以被视为一种密度和频率依赖性现象。
