Narrow roads to Fern Land: revisiting and re-analysing the paradox of sexual reproduction

Some major thought on the evolutionary maintenance of sexual reproduction is revisited. This leads to a new perspective about the role of complex life cycles for the maintenance of sex. And it leads to a new comparison of organisms with different life cycles. Organisms like strawberries propagate contrary to what would be adaptive under red-queen selection from micro-parasites. Their recombinant offspring disperses, and their clonal offspring stays close to the parent. In organisms like ferns fertilisation and meiosis occur in different generations. Their zygotes grow on the spot of their maternal gametophyte and are recombinant through syngamy. The resulting sporophytes produce dispersing spores, which are also recombinant through meiosis. This should better adapt ferns to red-queen selection than strawberries or corals. Hence, ferns are a good reference group to strawberry like organisms. We tested fungal parasite richness of ferns against that of strawberry like plants, (strawberries & cinquefoils). The occurrence and number of fungi was significantly higher in the strawberry-like plants. This refutes the hypothesis that organisms like strawberries falsify the red-queen model. They would do better with recombinant offspring that stays, and clonal offspring that disperses. Yet, this would amount to sexually producing runners, tubers, polyps, etc. This may well-nigh be an evolutionary impossibility. Theoretically, life cycles with recombinant offspring that stay and clonal offspring that disperse should be best adapted against red-queen selection from micro-parasites. The rarity of this “red-queen life cycle” among multicellular species remains perplexing.