There is nothing permanent except change: Assessing reproductive shifts in the invasive Bermuda buttercup



Biological invasions pose a major threat to biodiversity, having ecological and evolutionary consequences both for species and communities being invaded and for invasive species themselves. Understanding invasive plants colonization strategies enable to develop habitat restoration actions more efficiently and contribute to the conservation of threatened plant species. The Bermuda buttercup (Oxalis pes-caprae L.) is a tristylous polyploid plant native to South Africa, having become invasive in Mediterranean regions globally. In its native habitat, populations are isoplethic having three flower morphs and sexual reproduction, while in most invaded areas, populations are dominated by the pentaploid short-styled morph that reproduce asexually. Nevertheless, new forms have been discovered in western Mediterranean basin, introducing new reproductive strategies and, consequently, new invasion contexts.

We aimed at understand the current distribution of floral morphs and cytotypes within the wider region of the Mediterranean Basin, as well as patterns and changes in sexual fitness and possible breakdowns in the heterostylous syndrome.

For that, within the COST Action ConservePlants we have gathered the 'Finding Bermuda buttercup' team that sampled floral morph composition, fresh leaves and fitness variables in invasive populations across the Mediterranean basin. Ploidy was determined using flow cytometry on fresh leaves, and floral morphometric analyses and quantification of pollen loads were analysed in ethanol presenved flowers. This large-scale sampling provides novel insights into the distribution of ploidy and floral morphs and reveals two distinct reproductive strategies, one through uniparental reproduction and the other throught the re-establishment of sexuality. Our finding highlight the dynamic nature of invasion processes, emphasizing that ecological and genetic constraints inherent in the invasion process can lead to unique reproductive strategies, ultimately influencing the probability of invasion success.


Finding Bermuda buttercup

In 2023 we gathered a network of researchers from the Mediterranean Basin collaborating to a common experimental protocol to comprehensively study sexual reproductive strategies of the invasive Bermuda buttercup (Oxalis pes-caprae L.) in this region. Bermuda buttercup is native to the western part of South Africa and has been introduced to all areas with Mediterranean climate of the world, where it became and invasive species. This plant has a complex flower biology consisting of three floral morphs (tristily) – short- (SS), mid- (MS) and long-styled (LS) morph (Figure 1) – and different ploidy levels (di-, tetra- and pentaploid). It has been considered that invasive populations are largely composed solely of pentaploid short-styled morph (SS). Consequently, the species has completely switched to asexual reproduction via the production of bulbils due to a self- and morph-incompatibility system. However, other floral morphs (MS and LS) were recently detected in western Mediterranean Basin, along with the production of fruits and seeds. This opens the possibility for broad-scale changes in sexual ability with consequences for heterostyly maintenance during invasion.

Download  the protocol here

Download the power point explaining the protocol here

Download the poster here.