Abstract
BackgroundThe wild radishes, Raphanus raphanistrum and R. pugioniformis (Brassicaceae) are native to the East Mediterranean region. However, whereas R. raphanistrum is widely distributed worldwide, the endemic R. pugioniformis is limited to specific habitats. In R. raphanistrum the diaspores of the indehiscent fruits comprise glabrous, light, single-seeded segments, whereas the intact fruits of R. pugioniformis are heavy and covered with spiny backward-pointing trichomes. We aimed to investigate whether the structure of the diaspores was directly associated with long- and short-range dispersal in R. raphanistrum and R. pugioniformis, respectively. We further surveyed within-population spatial distributions, to test the hypothesis that short- and long-range dispersal contribute to a patchy vs. uniform distribution patterns of R. pugioniformis and R. raphanistrum, respectively.ResultsThe results indicated that dispersal by wind and run-off water was substantially lower for diaspores of R. pugioniformis than for those of R. raphanistrum diaspores. Supporting the hypothesis that backward-pointing trichomes promote adherence to soil particles, the displacement on soil surface of R. pugioniformis fruits depended on their orientation relative to wind direction. Furthermore, trichome removal from fruits of R. pugioniformis significantly reduced wind velocity needed to remove fruits that were placed on soils typical of the species’ natural habitats. The spatial-distribution survey results indicated a patchy distribution of R. pugioniformis populations as compared with the more uniform arrangement in the studied populations of R. raphanistrum; consistent with the unidirectional vs. homogeneous wind dispersal of the respective diaspores, with respect to wind direction. In addition, R. pugioniformis population sizes changed less between years than those of R. raphanistrum.ConclusionsOverall, our results indicate that fruit structure is strongly linked to dispersal ability and spatial distribution of the two closely related wild radish species. Whereas R. raphanistrum inhabits homogenous sandy soil habitats, the distribution range of R. pugioniformis includes heterogeneous environments in which growth niches are scarcer. We suggest that the different modes of dispersal have evolved as adaptive traits appropriate to the species’ specific habitats.
Highlights
The wild radishes, Raphanus raphanistrum and R. pugioniformis (Brassicaceae) are native to the East Mediterranean region
Preliminary experiments indicated that single-seeded segments of R. raphanistrum detached from the substrate at a wind speed below 1.5 m s−1, which was substantially lower than that recorded for removal of intact fruits of R
Raphanistrum and R. pugioniformis (Fig. 3). In light of their low threshold of wind-velocity for removal (WVR), single-seeded segments of R. raphanistrum were not included in the subsequent wind-dispersal analysis, and we focused on intact fruits
Summary
The wild radishes, Raphanus raphanistrum and R. pugioniformis (Brassicaceae) are native to the East Mediterranean region. We aimed to investigate whether the structure of the diaspores was directly associated with longand short-range dispersal in R. raphanistrum and R. pugioniformis, respectively. We further surveyed within-population spatial distributions, to test the hypothesis that short- and long-range dispersal contribute to a patchy vs uniform distribution patterns of R. pugioniformis and R. raphanistrum, respectively. The mode of seed dispersal (short- vs long-range), which is influenced by seed and fruit traits, is generally associated. In the Brassicaceae, differing dispersal mechanisms characterize dehiscent fruits, from which seeds are freely released to the environment, and indehiscent ones whose dispersal segments contain one or few seeds. In fruits of Cakile for example, traits of the indehiscent dispersal segment promote long-range seed dispersal [13, 14]. It seems likely that there is a trade-off between the relatively heavy weight of the indehiscent dispersal units and long-range dispersal [15, 16]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
