The evolutionary advantage of different sexual systems in multicellular eukaryotes is still not well understood, because the differentiation into male and female individuals halves offspring production compared with asexuality. Here we propose that various physiological adaptations to oxidative stress could have forged sessility versus motility, and consequently the evolution of sexual systems in multicellular animals, plants, and fungi. Photosynthesis causes substantial amounts of oxidative stress in photoautotrophic plants and, likewise, oxidative chemistry of polymer breakdown, cellulose and lignin, for saprotrophic fungi. In both cases, its extent precludes motility, an additional source of oxidative stress. Sessile life form and the lack of neuronal systems, however, limit options for mate recognition and adult sexual selection, resulting in inefficient mate-searching systems. Hence, sessility requires that all individuals can produce offspring, which is achieved by hermaphroditism in plants and/or by multiple mating types in fungi. In animals, motility requires neuronal systems, and muscle activity, both of which are highly sensitive to oxidative damage. As a consequence, motility has evolved in animals as heterotrophic organisms that (1) are not photosynthetically active, and (2) are not primary decomposers. Adaptations to motility provide prerequisites for an active mating behavior and efficient mate-searching systems. These benefits compensate for the “cost of males”, and may explain the early evolution of sex chromosomes in metazoans. We conclude that different sexual systems evolved under the indirect physiological constraints of lifestyles.

中文翻译：

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多细胞真核生物中的氧气、生命形式和性别进化


多细胞真核生物中不同性别系统的进化优势仍不清楚，因为与无性生殖相比，分化为雄性和雌性个体的后代产量减少了一半。在这里，我们提出，对氧化应激的各种生理适应可能形成了固着性与运动性，从而形成了多细胞动物、植物和真菌的性系统的进化。光合作用在光自养植物中引起大量的氧化应激，同样，对于腐生真菌来说，聚合物分解、纤维素和木质素的氧化化学也引起这种情况。在这两种情况下，其程度都会妨碍运动，这是氧化应激的另一个来源。然而，固着生命形式和神经系统的缺乏限制了配偶识别和成年性选择的选择，导致寻找配偶的系统效率低下。因此，无蒂性要求所有个体都能产生后代，这是通过植物中的雌雄同体和/或真菌中的多种交配类型来实现的。在动物中，运动需要神经系统和肌肉活动，这两者都对氧化损伤高度敏感。因此，动物的运动能力已进化为异养生物，这些生物（1）不具有光合作用活性，（2）不是初级分解者。对运动性的适应为积极的交配行为和高效的择偶系统提供了先决条件。这些好处补偿了“雄性的成本”，并可能解释后生动物性染色体的早期进化。我们得出的结论是，不同的性系统是在生活方式的间接生理限制下进化的。