Characteristics and ecological significance of natural foliar variegation from Begonia formosana
Begonia species commonly have variegated leaves, often caused by intercellular space above the first layer of chlorechyma, which scatters light, creating light areas. This is a structural mechanism of variegation and need not be associated with loss of photosynthetic ability. Many studies have suggested that foliar variegation can inhibit herbivory. For example, it has been suggested ovipositing insects will avoid leaves that have egg-mimicking patterns. Another possible advantage of foliar variegation may be scattering of strong light providing photoprotection from sunflects. However, there has been little study beyond speculation. To investigate these issues, we took advantage of a natural population of Begonia formosana containing a mixture of variegated and nonvariegated individuals in northern Taiwan (Wulai, Neidong). We studied the variation in population composition along a transect in six repeat surveys over two years, and recorded intensity of the variegation pattern as a function of leaf height, photosynthetic performance, chlorophyll content, photoprotection, and damage from herbivores on eight, 2 m x 1 m plots with abundant Begonia formosana along the 1.8 km transect.
The average ratio of variegated to nonvariegated plants over the six surveys was 20.72% to 79.28%. Five of the eight plots changed in composition several times between dimorphic (variegated and nonvariegated plants) and monomorphic (nonvariegated plants). Photosynthetic rate, and chlorophyll content did not differ significantly between variegated and nonvariegated leaves, consistent with previous findings for structural foliar variegation. However, variegation patterns were strikingly and statistically significantly stronger at low leaf height deeply shaded by other leaves. These striking variegation patterns are on the early leaves of a plant, and it is unclear whether the effect is strictly developmental or induced by low light. Chlorophyll fluorescence measurements gave lower value of non-photochemical quenching (NPQ), photochemical quenching (qP) and electron transfer rate (ETR) for variegated compared with nonvariegated leaves. These results do not support the hypothesis of the photoprotective function of variegation in the leaves in B. formosana. Although herbivore damage was lower on variegated leaves, this difference was not statistically significant. High variability in the herbivory data may have resulted from the presence of herbivores that do not use visual cues to select leaves, which will be tested in future studies.