Just add water: Rainfall-induced anther closure and color change in Ripariosida hermaphrodita (Malvaceae)

Abstract

Anther opening has commonly been thought of as unidirectional, but reports of anthers closing in response to rainfall show this is not the case. In some species, anther closure can protect pollen from degrading or washing away, thus possibly enhancing male fitness. Similarly, although floral color is often presumed to be static, numerous floral parts may change color during blooming. These color changes primarily occur in response to pollination or aging, thus potentially increasing pollination efficiency by directing floral visitors to recently opened, unpollinated flowers. Daily observations of 364 Ripariosida hermaphrodita flowers from seven individuals showed that anthers that were purple, open, and shedding pollen became beige colored and tightly closed after rainfall. These findings were further supported by observations of plants exposed to simulated rainfall in a greenhouse and time-lapse photography of flowers misted with water. To our knowledge, our work represents the first report of anther closure in response to rain in Malvaceae and the first report of floral color change induced by rainfall.

Keywords: Malvaceae; anther closure; floral color change; pollination; rainfall.

FIGURE 1

(a) Whole plant image of Ripariosida hermaphrodita in the wild. (b) Inflorescence of R. hermaphrodita. Images by C. Skema.

FIGURE 2

(a) Floral morphology of Ripariosida hermaphrodita. (b) The open, purple anthers of flower #360 on August 21, 2022. There was no rain during the week before this date. (c) The closed, beige anthers of flower #360 on August 22, 2022, after a rain event. a, anthers; p, petals; sc, staminal column; st, style lobes. Images by Emily A. Humphreys.

FIGURE 3

Changes in anther position (top row) and color (bottom row) away from open/purple and towards closed/beige in Ripariosida hermaphrodita corresponded to rainfall events (middle row). Each line connects points from an individual flower and is 90% transparent. As such, more opaque lines indicate a greater number of flowers on the same trajectory. Circled Xs indicate rain events with no corresponding response in >50% of flowers. Blue arrows indicate transitions in anthers in >88% of flowers.

FIGURE 4

Simulated rainfall induces anther closure and color change in Ripariosida hermaphrodita. (a) Anther position and (b) color before and after simulated rainfall treatment. The differences between the experimental (14 flowers) and control (18 flowers) groups for both anther position and anther color were shown to be statistically significant. Asterisks indicate a p‐value of <.01.