Biology subjects

Hirayama, G. S.

Publications and source records attributed to Hirayama, G. S..

4 recordsLinked to original sources

bioRxiv2025

Nectar Sugar Enhancement in Response to Bee Buzzing in Rhododendron x pulchrum: Sound-sensing Organs and Sensitivity Range

Plants can perceive and respond to airborne sounds, but our current understandings of this phenomenon remain limited. Flowers are known to exhibit increased nectar sugar concentration in response to pollinator sounds; however, there has been only a single report from Oenothera drummondii. To test the generality of pollinator-sound-induced nectar enrichment in bee-pollinated plants, we examined nectar responses to airborne sounds, particularly those produced by bee buzzing, in Rhododendron x pulchrum and Lamium amplexicaule. We exposed the flowers to playback sounds of bee buzzing, a similar synthetic sounds signal (200 Hz) and those with higher frequency (5000 Hz) and compared nectar sugar concentrations among these sound-treated and silent control flowers. We found an approximately 10% increase in nectar sugar concentration in response to playback sounds of bee buzzing and synthetic sounds signals at bee-like frequency (200 Hz), while no such response was observed under higher-frequency stimuli or silent condition in R. x pulchrum. A similar response to bee sounds was also observed in L. amplexicaule. Furthermore, these responses were observed at a sound pressure level of 65 or 100 dB, but not at 50 dB in R. x pulchrum, indicating a sound sensitivity threshold. We experimentally removed petals, stamens, or pistils (alone or in combination) from flowers and exposed them to 200 Hz sounds and silent treatments and found that both petals and stamens were necessary for such sound responses, suggesting that these floral organs are involved in acoustic sensing. Our findings provide new insights into floral sound sensing and suggest that acoustic responses to pollinator visitations may be more widespread among bee-pollinated flowering plants.

plant biology↗

bioRxiv2025

Generalist flowers recover rapidly in grassland restoration: The importance of floral traits in community reassembly

Community assembly process, through biotic and abiotic filtering of species traits, is crucial for understanding the recovery of biodiversity and ecosystem function in restored ecosystems. While previous studies have highlighted very slow recovery of pollination networks in ecological restoration, the reassembly process of plant communities focusing on floral traits that influence pollination networks remains underexplored. We hypothesised that plant species with flowers that allow visits by various pollinators (generalist flowers) would recover more easily than those with flowers which limit pollinators (specialist flowers) during grassland restoration. We investigated floral trait assemblages, interaction patterns with pollinators, and pollination success for each floral trait (floral tube and colour) across 28 pollination networks. We examined their temporal change patterns within restored grasslands (2-75 years old) and compared them with reference old grasslands (>165 years old). Our results revealed that generalist (open/shallow and white/yellow) flowers have recovered rapidly, interacting with many pollinator species with similar traits in the early stages of restoration. In contrast, specialist (long-tubed and blue/purple) flowers exhibited more delayed recovery due to low pollination success, taking approximately 75 years for the recovery to the levels of reference old grasslands. Importantly, we found that functional specialisation was crucial for the recovery of these specialist flowers. Corresponding to temporal changes in floral trait assemblages, pollinator composition has shifted from dipteran dominance to a greater abundance of long-tongued bees, with interaction patterns of each trait group approaching those of old grasslands. Our findings underscore the pivotal role of floral trait reassembly in influencing temporal changes in pollinator community, network structure, and pollination function during grassland restoration. By integrating trait-based framework, this study provides novel insights into the co-reassembly process of plants and pollinators in restored ecosystems.

ecology↗

bioRxiv2024

Long-lasting negative effects of past forestation on grassland pollination networks and their function

O_LIGrasslands are facing a rapid decline worldwide. Among the primary threats to these ecosystems are changes in land use, such as land abandonment and forestation, which promote forest vegetation in detriment of grassland plant diversity. To support the conservation and restoration of grasslands, it is key to understand what ecological processes limit the recovery of their biodiversity and functions after perturbations. However, we still know little about the legacy effects of forestation on the ecological mechanisms involved in the recovery of grasslands, especially concerning long-lasting impacts on plant-pollinator interaction networks and plant reproduction. C_LIO_LIHere, we aim to fill this gap of knowledge by comparing the plant and pollinator diversity, the degree of network generalization, the pollination success and pollen limitation of native plant species in 30 plant-pollinator networks of old-growth and restored grasslands of different ages since recovery (from 2 to 84 years). We hypothesized that past forestation would exert long-lasting legacy negative effects on plant richness and plant-pollinator networks, increasing pollen limitation for native plants, thereby delaying community recovery in restored grasslands. C_LIO_LIResults showed that restored grasslands exhibited significantly lower plant richness, less specialized (more generalized) interaction networks, lower pollination success and pollen-limited seed reproduction of native plants compared to old-growth grasslands. Meanwhile, the degree of network specialization and pollination success gradually increased with time after grassland restoration initiated. Overall, network generalization, which was caused by low plant richness, reduced pollination and reproduction success in native grassland plants, and degraded pollination networks and functions could recover in restored grasslands with continuous management. These findings imply that plant diversity restoration was slow because of the negative feedbacks associated with low plant richness and consequently, generalized plant-pollinator interaction networks, which diminished native plant reproduction in restored grasslands. C_LIO_LISynthesis and applications Our findings suggest that the recovery of specialized plant-pollinator networks by enhancing plant diversity is essential for restoring pollination function. For quicker grassland restoration, it may be effective to facilitate the establishment of highly specialized pollination networks by seeding or planting diverse native plants collected from neighbouring areas while avoiding genetic contamination. C_LI

ecology↗

bioRxiv2022

Habitat preference influences response to changing agricultural landscapes in two long-horned bees.

Agricultural intensification and urban development have drastically influenced pollinators living in semi-natural grasslands. Pollinators are likely to have different responses to these land-use changes; some decline rapidly while others maintain or increase their populations. We predicted differences in interspecific response to land-use changes are partly attributed to differences in habitat preference. We examined the distribution and flower use patterns of two closely related Eucera species with different habitat preferences. Study sites were meadows surrounding traditional, intensified, and urbanised agricultural lands in the Osaka-Kobe metropolitan area, Japan. Forest-associated Eucera nipponensis were significantly fewer in consolidated and urbanised meadows than traditional meadows, whereas open land-associated E. spurcatipes exhibited the opposite. A significant negative relationship between their abundances was also found. Both species foraged on legume flowers most frequently (83.5%), but floral use pattern was significantly different in traditional and consolidated meadows. Bee species preferring stable habitats were vulnerable to land consolidation and urbanisation, while species associated with disturbed habitats maintained or increased population size in meadows with the land-use changes. Thus, recent land uses may have different impacts on species with different habitat preferences.

ecology↗