Abstract
Fruit-set and seed-set depend on environmental conditions and reproductive systems. They are important components of sexual reproductive success in plants. They also control the ecological success and adaptation of invasive plants within their non-native ecosystems. We studied which factors bring about fruit-set and seed-set in invasive populations of the aquatic plant Ludwigia grandiflora subsp. hexapetala. We analyzed fruit set and seed set in 37 populations growing under variable climatic conditions in Western Europe. Sub-samples of seven fruitful and fruitless populations were grown in common controlled conditions. We carried out self- and cross-pollinations, and measured the floral morphometry. Environmental conditions did not affect fruit-set and seed-set in-situ and in common controlled environments. Hand-pollinations showed that individuals from fruitful populations exhibited fruit and seed production whatever the pollen donor, whereas individuals from fruitless populations only did so when pollen came from fruitful populations. Floral morphometry evidenced the existence of two floral morphs that fully overlapped with fruitfulness, and individual incompatibility. Our results rebutted the hypothesis that environmental variations control fruit set and seed set in these invasive populations. We instead showed that fruit set and seed set were controlled by a heteromorphic reproductive system involving a self-incompatible and inter-morph compatible morph (long-styled morph), and a self- and inter-morph compatible reverse morph (short-styled morph). We collected morphs and fruit set records of this species worldwide and found the same relationship: fruitless populations were all composed only of individuals with long-styled floral morph. Our study constitutes the first evidence of a heteromorphic self-incompatible system in Ludwigia genus and Onagraceae family.
Highlights
Reproductive success is a central biological feature key to understanding the ecology and evolution of populations and species, and for managing endangered, invasive, cultivated, or unwanted populations (Barrett et al, 2008)
Our results argued that the geographical distribution of a self- incompatible morph, rather than biotic or abiotic environmental conditions, explained the success of the sexual reproduction of invasive populations of Lgh in Western Europe
Our results argued for the first evidence of a self-incompatibility system coinciding with two different floral morphs, with this worldwide invasive species having one short-styled morph and one long-styled morph
Summary
Reproductive success is a central biological feature key to understanding the ecology and evolution of populations and species, and for managing endangered, invasive, cultivated, or unwanted populations (Barrett et al, 2008). Fruit and seed-sets are known to be affected by abiotic environmental factors, such as sunshine, temperature and hygrometry, and biotic factors, including abundance of pollinators for entomophilous plants, flower grazers, and seed diseases (Giles et al, 2006; Grass et al, 2018; Harder & Aizen, 2010; McCall & Irwin, 2006; Sun et al, 2018; Sutherland, 1986) These environmental factors are key to understanding the sexual reproduction of plants invading new areas, especially in the context of global changes. On the Atlantic side of Europe, Lgh populations produced fruits and viable seeds while in the Mediterranean zone, all Lgh populations remained fruitless (Dandelot, 2004) All those European populations massively bloomed with the presence of a multitude of insect foraging their flowers. Our results i/ contributed to qualify and understand the mating system of Ludwigia genus, ii/ revealed a new type of mating system not yet described in the Onagraceae family, and iii/ contributed to show that we should not rely on natural environmental variations to limit the invasibility of this species worldwide as previously assumed
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