Pollen flowers face a trade-off (pollen dilemma) between rewarding pollinators with pollen and retaining sufficient pollen content. The division of labour between feeding and pollinating stamens mitigates this dilemma; however, whether it occurs in small flowers with closely positioned stamens remains unclear. We investigated the pollination ecology of Bredia hirsuta (Melastomataceae) through behavioral observations, fluorescent powder experiments, and emasculation experiments. Of the two buzz-pollinating bees observed, Amegilla dulcifera showed a consistent visitation posture and stable stigma contact, whereas Lasioglossum sp. mainly acted as a pollen thief and stigma-pollen remover. The Amegilla bee gripped the short stamens ventrally, whereas the long-stamen anther tips and the stigma were positioned dorsally on the abdomen. Fluorescent powder experiments confirmed the spatial separation between stigma-contact and gripping sites on the bee's body, suggesting that short stamens function as feeding stamens and long stamens as pollinating stamens. The emasculation experiments revealed that dimorphic stamens also provide mechanical support that stabilizes pollinator posture. These results suggest that dimorphic stamen differentiation can occur in small flowers through consistent pollinator behavior and physical stamen support.
This study aimed to evaluate the competitive effects of invasive grasses on the growth, physiology, and nutrient utilization of Khaya ivorensis. The treatments consisted of one K. ivorensis plant positioned at the center of each pot and one grass individual, in addition to a control treatment containing only one K. ivorensis seedling. The study compared the cultivation of K. ivorensis without competition and in coexistence with Urochloa decumbens, Megathyrsus maximus, Sorghum arundinaceum, Digitaria insularis, and Cynodon dactylon. Plants of K. ivorensis grown in association with U. decumbens, M. maximus, and S. arundinaceum showed lower increases in height and stem diameter. Evaluations included height and diameter increments, specific leaf area, shoot and root dry mass, chlorophyll a and b indices, photosynthetic rate, water use efficiency, transpiration, stomatal conductance, nutrient content, biological utilization coefficient (BUC), and nutrient absorption efficiency. The presence of the competitors M. maximus and S. arundinaceum reduced the leaf area of K. ivorensis. Plants grown in coexistence with U. decumbens, M. maximus, and S. arundinaceum also exhibited lower chlorophyll a and b indices, reduced photosynthetic rate, lower water use efficiency, and decreased relative content and concentration of macronutrients. Coexistence with grasses altered the BUC by weed species, notably increasing the nitrogen BUC under competition with M. maximus, while generally decreasing the macronutrient absorption efficiency of K. ivorensis. Invasive grasses negatively affect the growth, physiological performance, and macronutrient utilization of K. ivorensis, with Megathyrsus maximus being the most detrimental weed species to the growth and physiology of the tree species.
Large-scale anthropogenic disturbances, including deforestation and fragmentation, are increasing worldwide. Lianas often proliferate after such events, yet the mechanisms underlying these increases-particularly their demographic sources-remain unclear. We quantified the extent to which clonal expansion, rather than seed recruitment, accounts for post-disturbance proliferation of Wisteria floribunda (Fabaceae), the dominant liana in a 21.6-ha fragmented forest landscape in Japan. We divided the study area into 20 & times; 20 m grid cells, randomly sampled up to one W. floribunda ramet per cell, and genotyped 273 ramets at 10 microsatellite loci to assign ramets to genets and quantify genet areas and their spatial distribution. Genotyping revealed a substantial contribution of extensive clonal reproduction: 83% of ramets were clonal, resolving into 47 genets. These genets collectively occupied 58% of the 21.6-ha study area, and expansion produced extensive genets-the largest covered 9.5 ha. Several genets spanned multiple forest patches; three multi-patch genets accounted for 43% of all ramets, including one spanning seven patches. Multi-patch genets were concentrated within areas covered by forests prior to disturbance (odds ratio = 6.83; p < 0.001). Clonal expansion thus accounts for most post-disturbance proliferation, while seed recruitment likely contributes to establishment in newly formed forest patches. Some genets attain broad spatial coverage in a fragmented forest, and part of this dominance reflects legacy effects of genets established prior to disturbance. Explicitly accounting for clonal contributions and genet spatial scale is critical for accuratly predicting disturbance-driven liana dynamics.
Seabirds are thought to be involved in long-distance dispersal of plant seeds. However, the seed adhesion process in seabirds remains unclear. Nests are likely an important link between seabirds and plant seeds, because seabirds use plant tissues as nest materials. We analyzed 90 seabird nests collected from the Ogasawara Islands, Japan, and identified seeds with the potential to adhere to the seabirds. 24 seed species were found in the seabird nests, at least 16 of which could potentially adhere to seabirds. This is the first study to reveal the seed floras of pelagic seabird nests. Nests likely provide opportunities for various seeds to adhere to seabirds and may mediate adhesive seed dispersal by seabirds.
Duckweed is a floating aquatic plant that inhabits freshwater ecosystems and has attracted attention for its potential applications in animal feed and biofuel production. To facilitate such practical applications, an efficient and cost-effective cultivation system is required. Duckweed weevils are among the most common and widely distributed insect herbivores that feed on duckweed. In this study, we investigated the duckweed weevils (Tanysphyrus brevipennis) behaviors and feeding preferences for three common duckweed species: Spirodela polyrhiza (Sp), Landoltia punctata (Lp), and Lemna aequinoctialis (La). Fasted duckweed weevils were placed with individual duckweed species, and the Lp consumed significantly smaller areas than Sp and La because of fewer duckweed weevil feeding events and less damage per feeding bout. In the mixed-species settings, duckweed weevils showed a clear feeding preference for Sp and La over Lp; the preference in descending order was Sp, La, and Lp. We further examined the effect of anthocyanins on preference using stress-induced anthocyanin accumulation in Sp. Plants with anthocyanins had smaller areas of consumption than those without anthocyanins, suggesting that anthocyanins serve as a deterrent to duckweed weevil feeding. In conclusion, our findings regarding the feeding preferences of duckweed weevils and the defensive role of anthocyanins provide valuable insights for the dynamics of the community composition of coexisting duckweed species, contributing to more robust and efficient duckweed cultivation systems.
