Hestmark Geir
Division of Botany, Department of Biology, University of Oslo, P. b. 1045, N-0316, Oslo 3, Norway.
Oecologia. 1992 Dec;92(3):305-312. doi: 10.1007/BF00317455.
The lichen Lasallia pustulata has a mixed strategy of asexual and sexual reproduction. Close-dispersed, asexual, symbiotic isidia are produced early, when the thalli are small. The asexual propagules are subsequently supplemented by far-dispersed, sexually generated ascospores when the thalli grow larger. This observation is consistent with evolutionary stable strategy (ESS) models of dispersal allocations in heterocarpic plants accordin to which the production of far-dispersed propagules should increase as clutch size and sibcompetition in the local habitat increases. The observation is also consistent with the "tangled bank" or "elbow room" hypothesis for the maintenance of sexuality, according to which sex, by generating genetic variation, represents an escape from competition in biologically saturated environments. Thus the advantage of sex is density dependent. L. pustulata grows in densely packed populations where intraspecific competition results in self-thining and the development of distinct sizehierarchies.
地衣脓疱状茶渍采用无性繁殖和有性繁殖的混合策略。当叶状体较小时，会早期产生紧密分布的无性共生粉芽。随后，当叶状体长大时，远距离传播的有性产生的子囊孢子会补充无性繁殖体。这一观察结果与异果植物扩散分配的进化稳定策略（ESS）模型一致，根据该模型，随着当地栖息地的集群大小和同胞竞争增加，远距离传播繁殖体的产生应该增加。这一观察结果也与维持有性生殖的“纠结河岸”或“生存空间”假说一致，根据该假说，有性生殖通过产生遗传变异，代表了在生物饱和环境中从竞争中逃脱。因此，有性生殖的优势是密度依赖性的。脓疱状茶渍生长在密集的种群中，种内竞争导致自我疏伐和明显的大小等级发展。
