Department of Ecology and Evolution, Biophore Building, University of Lausanne, Lausanne, Switzerland.
J Evol Biol. 2021 Feb;34(2):416-422. doi: 10.1111/jeb.13720. Epub 2020 Nov 9.
In dioecious plants, males and females frequently show 'leaky' sex expression, with individuals occasionally producing flowers of the opposite sex. This leaky sex expression may have enabled the colonization of oceanic islands by dioecious plant species, and it is likely to represent the sort of variation upon which selection acts to bring about evolutionary transitions from dioecy to hermaphroditism. Although leakiness is commonly reported for dioecious species, it is not known whether it has plastic component. The question is interesting because males or females with an ability to enhance their leakiness plastically in the absence of mates would have an advantage of being able to produce progeny by self-fertilization. Here, we demonstrate that leaky sex expression in the wind-pollinated dioecious herb Mercurialis annua is plastically responsive to its mating context. We compared experimental populations of females growing either with or without males. Females growing in the absence of males were leakier in their sex expression than controls growing with males, producing more than twice as many male flowers. Our results thus provide a striking instance of plasticity in the reproductive behaviour of plants that is likely adaptive. We consider how females might sense their mating environment as a function of pollen availability, and we discuss possible constraints on the evolution of plasticity in sex expression when the environmental signals that individuals receive are unreliable.
在雌雄异株的植物中，雄性和雌性经常表现出“渗漏”的性别表达，偶尔会有个体产生异性的花。这种渗漏的性别表达可能使雌雄异株的植物物种能够在海洋岛屿上殖民，并且很可能代表了选择作用于从雌雄异株到雌雄同体进化转变的那种变异。尽管雌雄异株物种的渗漏现象很常见，但它是否具有可塑性成分尚不清楚。这个问题很有趣，因为在没有配偶的情况下能够增强其可塑性渗漏的雄性或雌性将具有通过自交产生后代的优势。在这里，我们证明了风媒雌雄异株草本植物 Mercurialis annua 的渗漏性别表达对其交配环境具有可塑性反应。我们比较了在有或没有雄性的情况下生长的雌性实验种群。与与雄性一起生长的对照相比，在没有雄性的情况下生长的雌性在性别表达上更加渗漏，产生的雄性花超过两倍。因此，我们的结果提供了植物生殖行为可塑性的一个显著实例，这可能是适应性的。我们考虑了雌性如何感知其交配环境作为花粉可用性的函数，并且我们讨论了当个体接收到的环境信号不可靠时，性别表达可塑性进化的可能限制。
