From bud to fruit: How flowering time and insect activity interact to influence plant reproduction

Abstract

The Arctic is warming faster than any other biome on Earth, leading to changes in vegetation patterns, including the advancement of overall flowering. However, the implications of these changes for plant reproduction are not yet fully understood. Additionally, the phenology of pollinating insects is expected to change as it gets warmer, although exactly how they will change remains uncertain. Given that many plants rely on insects for pollination, ensuring synchronization between their flowering and insect activity is crucial for successful reproduction. There is a risk for phenological mismatch between plants and insects if they differ substantially in their responses to warming. To investigate the impact of shifts in flowering time on reproduction, we selected Silene acaulis as model species. Typically blooming shortly after snowmelt, S. acaulis exhibits diverse flowering times across topographically varied landscapes. We tracked the flowering of around 300 S. acaulis plants with diverse flowering times and assessed their reproductive success. We additionally used pan traps to monitor insect activity and compare insect dynamics with S. acaulis flowering. A unimodal relationship between flowering time and per-flower seed set was observed, with peak per-flower seed set occurring on July 8th. Flowering time, together with insect activity, explained approximately 9.8% of the variation in seed set per flower, with flowering time alone accounting for 3.6% of this variation. However, 47% of the variation in seed set per individual was explained by individual flower count. Interestingly, early-flowering individuals had a higher flower count compared to those flowering later, resulting in higher total seed set in early-flowering individuals. Early-flowering individuals may benefit from longer snow-free periods, allowing greater energy accumulation for reproduction and higher flower counts. Our study highlights the complexity of the relationship between flowering time and reproduction: mid-season offers better pollination, while early season provides more resources for reproduction.