Biology subjects

Shagawa, T.

Publications and source records attributed to Shagawa, T..

2 recordsLinked to original sources

bioRxiv2026

Evolutionary origin of prolonged delayed fertilization in the Fagaceae

The temporal organization of flowering, fertilization, and fruiting is a fundamental axis of life-history evolution in angiosperms. While most species complete fruit development within a single growing season ("1-year fruiting"), many Fagaceae species delay fertilization and fruit maturation until the year following flowering ("2-year fruiting"). Despite its ecological prevalence, the evolutionary origins of this strategy and its coordination with other functional traits remain poorly understood. In this study, we investigated the evolutionary origins of the two-year fruiting strategy by reconstructing ancestral states on a phylogeny comprising 88 species that represent all eight genera of Fagaceae. We further employed phylogenetic comparative analyses to test whether the fruiting trait is evolutionarily constrained by pollination mode (animal versus wind-pollinated) or leaf habit (evergreen versus deciduous). Our results support a single origin of 2-year fruiting in the common ancestor of the major clade excluding Fagus and Trigonobalanus, followed by multiple independent reversions to 1-year fruiting in lineages including Castanea, Quercus, and Castanopsis. Ancestral-state reconstructions of pollination mode and leaf habit strongly support entomophily and an evergreen leaf habit as ancestral traits of Quercoideae, predating the emergence of the 2-year fruiting strategy. Although entomophily and evergreen habit were ancestral in Quercoideae, our correlation analyses indicate that transitions in fruiting strategy did not depend on changes in these traits. These results provide macroevolutionary evidence that extreme extensions of the interval between pollination and fertilization can be evolutionarily stable yet rarely re-evolve once lost over long evolutionary timescales.

ecology↗

bioRxiv2024

Male and female gametophytes meet after winter: Testing the overwintering hypothesis for delayed fertilization in Japanese stone oak

PremiseFertilization delays of nearly a year have been observed in many acorn-producing Fagaceae trees. Despite this long-standing recognition, the underlying mechanisms and adaptive significance of delayed fertilization remain largely unexplored. It has been hypothesized that these prolonged delays may serve as an adaptive strategy, allowing ovules to be fertilized and seeds to develop during more favorable seasons, thereby avoiding the adverse conditions of winter. However, empirical evidence to support this hypothesis is still lacking. MethodsTo test the overwintering hypothesis, we observed the seasonal progression of pollen tube growth and ovule development in Lithocarpus edulis, a species exhibiting two flowering seasons, spring and autumn. We conducted monthly observations of pollen tube growth and ovule development in both spring and autumn flower samples. We employed microtome techniques and scanning confocal microscopy to closely examine the seasonal progression of pollen tube growth and ovule development. ResultsWe found that pollen tubes were arrested at the style-joining site, and ovules remained immature in both spring and autumn samples prior to winter. Following winter, pollen tube regrowth and ovule maturation were synchronized in the subsequent spring in both spring and autumn samples. ConclusionsOur results support the overwintering hypothesis, suggesting that delayed fertilization may serve as an adaptive strategy to ensure fertilization in spring, overcoming the reproductive challenges posed by cold winter conditions. Our study introduces a new avenue for studying the temporal organization of plant reproductive phenology, specifically the alignment of flowering, pollination, fertilization, and fruiting in seasonal environments.

plant biology↗