Apomictic Parthenogenesis and the Pattern of the Environment

Advantages of obligatory apomixis are modeled, and curculionid weevils are used as examples. It is suggested that the alleged twofold number of female offspring in relation to sexual parentals should not be exaggerated. Instead, specific circumstances facilitating the origin of especially heterotic genotypes capable of apomixis should be sought; crosses between differentiated (long-isolated) populations (preferably followed by a population flush) seem promising. Optimal strategies in temporally heterogeneous environments are studied, and situations favoringsexual reproduction both in fine-grained and coarse-gained environments seem common (apomicts are capable only for individual adaptability, but sexual populations may track even one-generation changes by evolving). In apomicts, diapause determination and other seasonal constraints need specific attention, as they may interfere with geographical dispersal, and only life-cycles of one or more years seem possible. In rich biotic communities, which evolve continuously, evolutionary rigidity of apomicts may lead to their extinction. This shows that the dichotomy between immediate and long-term advantages of apomixis needs revision; if the number of generations needed for competitive exclusion between asexual and sexual organisms is relatively high, the greater evolutionary potential of sexual populations must be considered (there are directional changes both in the physical and biotic environments). Apomixis then seems most advantageous in low-competitive, early succession habitats which are recurrent and change relatively slowly (increased colonization ability of apomicts is here advantageous). Also, apomixis may succeed in spatially coarse-grained environment in stable patches small enough to exclude high-competitive community at the site. Then reduced vagility (loss of flight) may facilitate the origin of apomixi