Absence of Sex Differential Plasticity to Light Availability during Seed Maturation in Geranium sylvaticum

Abstract

Sex-differential plasticity (SDP) hypothesis suggests that since hermaphrodites gain fitness through both pollen and seed production they may have evolved a higher degree of plasticity in their reproductive strategy compared to females which achieve fitness only through seed production. SDP may explain the difference in seed production observed between sexes in gynodioecious species in response to resource (nutrients or water) availability. In harsh environments, hermaphrodites decrease seed production whereas females keep it relatively similar regardless of the environmental conditions. Light availability can be also a limiting resource and thus could theoretically affect differently female and hermaphrodite seed output even though this ecological factor has been largely overlooked. We tested whether the two sexes in the gynodioecious species Geranium sylvaticum differ in their tolerance to light limitation during seed maturation in the field. We used a fully factorial block experiment exposing female and hermaphrodite plants to two different light environments (control and shade) after their peak flowering period. Specifically, we measured fruit and seed production in response to decreased light availability and compared it between the sexes. Shading reduced the number of fruits and seeds produced, but the decrease was similar between the sexes. Furthermore, shading delayed seed production by three days in both sexes, but did not affect seed mass, seed P content, or the probability of re-flowering the following year. Our results give no evidence for reproductive SDP in response to light during seed maturation.

Light availability affects sex lability in a gynodioecious plant

“…Environment induced plasticity in reproductive output in response to light has been previously investigated in the greenhouse using the close species G. maculatum (Van Etten et al, 2008) and in the field during seed maturation in G. sylvaticum (Varga et al, 2015). In both studies, seed production was limited by light availability and both sexes showed a similar reduction.…”

Prolonged stigma and flower lifespan in females of the gynodioecious plant Geranium sylvaticum

“…1B) the stigma generally opens during or shortly after flower opening. Nectar is produced at the base of the flower (Varga et al, 2015). Flower visitors and potential pollinators include bumblebees and other hymenopterans, syrphid flies and other diptera, and a pre-dispersal seed predator specialist weevil Zacladus geranii (Varga and Kytöviita, 2010;Varga, 2014).…”

Sexes in gynodioecious Geranium sylvaticum do not differ in their isotopic signature or photosynthetic capacity

“…Overall, and corroborating previous findings (Varga et al . ; Varga & Kytöviita ), light was an important factor limiting seed production but did so similarly in both genders. Females and hermaphrodites both achieved higher photosynthesis rates, transpiration, stomatal conductance and WUE when grown under High light.…”

“…We have previously shown that the sexes do not differ in their tolerance to light limitation during seed maturation, a period when plants may receive less light due to the natural closing of the canopy or as a result of self‐shading (Varga et al . ). In the present case, both genders decreased seed production similarly in response to shade, suggesting that light limitation is not an important factor determining female maintenance in this gynodioecious species.…”

“…In G. sylvaticum , light levels have been shown to limit seed production similarly in both sexes (Varga et al . ; Varga & Kytöviita ). Therefore the specific research questions were: (i) do the sexes differ in their reproductive output; (ii) do the sexes show sexual dimorphism in physiology and/or isotopic signatures; and (iii) how does light availability determine these responses?…”