Self-incompatibility limits sexual reproduction rather than environmental conditions in an invasive aquatic plant

Abstract

SummaryFruitfulness and fertility are important components of sexual reproductive success in plants, and often depends on environmental conditions and reproductive systems. For invasive plants, fruitfulness and fertility control their ecological success and adaptation in invaded ecosystems. We studied which factors bring about fruitfulness and fertility in invasive populations of the aquatic plant Ludwigia grandiflora subsp. hexapetala.We analysed fruitfulness and fertility of 37 populations growing under variable climatic conditions in Western Europe, and sub-sampled fruitful and fruitless populations grown in common controlled conditions. We carried out self- and cross-pollinations and measured their floral biometrics.Environmental conditions, and temperature in particular, did not affect fruitfulness and fertility in-situ or in common controlled environments. Hand-pollinations resulted in fruit production by individuals sampled from fruitless populations when pollen came from fruitful populations, and by individuals sampled from fruitful populations whatever the origin of pollen. Floral biometrics evidenced the existence of two floral morphs that overlapped with fruitfulness, and individual incompatibility.Our results rebutted the hypothesis that environmental conditions control fruitfulness and fertility in these invasive populations. We instead found that fruit and seed production were controlled by a reproductive system involving a self-incompatible approach herkogamous morph and a self-compatible reverse herkogamous morph. We assessed the floral morphs distribution worldwide of fruitless and fruitful native and invasive populations that matched our results at larger scale. Our results may constitute the first evidence of a possible heteromorphic self-incompatible system in Ludwigia populations and in Onagraceae phylogeny. It calls for further investigations on reproductive systems in this plant family. Finally, the observation that the self-incompatible morph seemed to be the world most invasive morph in this species tackles our understanding of biological and ecological conditions for invasiveness.Synthesis. Our study showed that fruitfulness and fertility in the aquatic invasive plant, Ludwigia grandiflora subsp. hexapetala depend on a self-incompatibility system coinciding with two floral morphs, rather than environmental conditions and limitations. These new explanations on the sexual success of Ludwigia invasive populations will help defining new predictions about its worldwide spreads and ecological success, and will help reappraising future management plans.