Sex-Specific Floral Phenology in Plants: What Does and Does NOT Explain the Production of More Male Flowers

Flowering plants display remarkable diversity in their reproductive strategies, including when and how many male or female flowers they produce. Within a single flowering season, it is common to observe plants producing more male flowers, a pattern often linked to flower longevity and the seasonal timing of flowering. Understanding the ecological and evolutionary factors behind this sex-specific floral phenology is crucial for both basic science and applied conservation. This article examines the arguments that support—and do not support—this phenomenon, focusing on the interplay between resource limitation, climate, pollinator dynamics, and sexual selection.

The Phenomenon: More Male Flowers in Flowering Seasons

Many flowering plants exhibit plasticity in their sex expression, sometimes producing more male flowers than female flowers during certain periods of the flowering season. This pattern can be influenced by a range of factors, including resource availability, climatic conditions, and the reproductive strategies of the plant. The production of more male flowers can be adaptive, helping to maximize reproductive success in variable environments.

Arguments Supporting Sex-Specific Floral Phenology

Let’s review the arguments that support the observed pattern:

(1) Females are often resource limited and therefore pollination levels will be increased by producing more male flowers.

When resources are limited, plants may allocate more energy to producing male flowers, which are generally less costly than female flowers (which must support fruit and seed development). By producing more male flowers, plants can increase their chances of pollen transfer and reproductive success, even if the environment is not ideal for fruit set2. This adaptive strategy is well-documented in many plant species.

(2) Fluctuations in the rainfall pattern can influence pollinator service due to altered physiology of the plant during its reproduction, leading to a shift in flowering phenology of both sexes.

Climate variability, such as changes in rainfall or temperature, can significantly affect plant physiology and pollinator activity. For example, drought or heavy rain can alter the timing and abundance of flowers, as well as the availability of pollinators. Plants may shift their flowering phenology in response to these changes, sometimes producing more male flowers if conditions are unfavorable for female investment12. This plasticity is a key adaptation to environmental uncertainty.

(4) Male competition will favour floral features that improve pollinator visits and therefore more male flowers.

Sexual selection, particularly male-male competition for pollinator visits, can drive the evolution of floral traits that attract more pollinators. In some cases, this leads to the production of more male flowers or the enhancement of male floral displays, increasing the plant’s chances of successful pollen transfer9. This mechanism is supported by studies of floral evolution and pollinator behavior.

The Argument That Does NOT Support Sex-Specific Floral Phenology

(3) Plasticity in sex and their flowering phenology is determined neither by resource status of a taxa nor by fluctuations in climatic factors.

This argument is not supported by current ecological and evolutionary evidence. Research consistently shows that resource status (such as nutrient availability, light, and water) and climatic factors (such as rainfall, temperature, and seasonality) are primary drivers of plasticity in sex expression and flowering phenology in plants128. Plants adjust their reproductive strategies in response to these environmental cues, often favoring male function when conditions are less favorable for female investment.

Why Is This Important?

Understanding the factors that influence sex-specific floral phenology is essential for predicting how plants will respond to environmental change, such as climate variability or habitat alteration. It also informs conservation strategies for plant populations that may be vulnerable to shifts in resource availability or pollinator communities.

Summary Table

Conclusion

The production of more male flowers during certain periods of the flowering season is a well-documented phenomenon in many plant species. This pattern is supported by arguments related to resource limitation, climate variability, and sexual selection. However, the argument that plasticity in sex and flowering phenology is determined neither by resource status nor by fluctuations in climatic factors does NOT support the observed sex-specific floral phenology. Current research clearly demonstrates that both resource availability and climatic conditions are fundamental drivers of reproductive plasticity in plants