Seed Size, Not Dispersal Syndrome, Determines Potential for Spread of Ricefield Weeds by Gulls

• Published in: Plants
• Main Author: Peralta Sánchez, Juan Manuel
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI 2023
• Subjects: Endozoochory; Lesser black-backed gull; Larus fuscus; Dry-fruited seeds; Fleshy-fruited seeds; Dispersal syndromes
• Online Access: https://hdl.handle.net/10481/82041; https://doi.org/10.3390/plants12071470

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/plants12071470/s1 This research was funded by the Spanish Ministry of Science and Innovation (project Refs CGL2016-76067-P and PID2020-112774GB- I00/AEI/10.13039/501100011033). S.R. was supported by a research contract in the framework of the project CGL2016-76067-P (AEI/FEDER, EU) and by the European Social Fund and Junta de Andalucía (Talento Doctores DOC_01221). Recent field data suggest that migratory gulls disperse many rice field weeds by gut passage (endozoochory), most of which are dry fruited and widely assumed to have no long-distance dispersal mechanisms, except via human activity. We investigated this mechanism with a feeding experiment, in which seeds of five common rice field weeds (in order of increasing seed size: Juncus bufonius, Cyperus difformis, Polypogon monspeliensis, Amaranthus retroflexus, and the fleshy-fruited Solanum nigrum) were fed to seven individuals of lesser black-backed gulls Larus fuscus held in captivity. We quantified seed survival after collecting faeces at intervals for 33 h after ingestion, then extracting intact seeds and running germination tests, which were also conducted for control seeds. All five species showed high seed survival after gut passage, of >70%. Gut retention times averaged 2–4 h, but maxima exceeded 23 h for all species. Germinability after gut passage was 16–54%, and gut passage accelerated germination in J. bufonius and S. nigrum, but slowed it down in the other species. All species had lower germinability after gut passage compared to control seeds (likely due to stratification prior to the experiment), but the loss of germinability was higher in smaller seeds. There was no evidence that the different dispersal syndromes assigned to the five species (endozoochory, epizoochory or barochory) had any influence on our results. In contrast, mean gut retention time was strongly and positively related to seed size, likely because small seeds pass more ...