Red galls: the different stories of two gall types on the same host

Abstract

Several studies have suggested reasons why galls have conspicuous colours, but none of the ideas have been confirmed. However, what if the vibrant colours of some galls are explained simply by the effect of light exposure? This may lead to anthocyanin accumulation, functioning as a defence mechanism against the effects of high light. We studied the globoid galls induced by Cecidomyiidae (Diptera) on Qualea parviflora (Vochysiaceae), relating anthocyanin accumulation and chlorophyll fluorescence parameters to light incidence in abaxial and adaxial galls. We also tested if the anthocyanin accumulation patterns apply to another Cecidomyiidae‐induced gall morphotype (intralaminar) within the same plant. Adaxial galls are exposed to higher incident light, with more anthocyanin accumulation and therefore red coloration. In galls from angled leaves, the greater the angle of the leaf, the higher the difference between anthocyanins on the sun and shade sides of galls. Photosynthetic pigment concentrations did not differ between abaxial and adaxial galls. However, we found higher (Fm′ − F′)/Fm′ and Fv/Fm in the abaxial galls. Conversely, NPQ and Rfd were higher in adaxial galls. Finally, the pattern of anthocyanin accumulation was not found in the intralaminar gall. Anthocyanin accumulation in galls functions as a photoprotective strategy, maintaining tissue vitality in regions exposed to high light conditions. However, this mechanism may vary even among galls within the same host, indicating idiosyncrasy when it comes to coloration in galls. To date, this is the first study to demonstrate quantitatively why the galls of a specific species may be coloured: the variation in light regimes creates differential anthocyanin accumulation, influencing coloration.

A novel family of secreted insect proteins linked to plant gall development

“…Red pigmented galls could result from production of carotenoids, 41 anthocyanins, 42,43 or betacyanins. However, in red galls induced by H. cornu, the seven most strongly upregulated plant genes are all homologous to genes annotated as enzymes of the anthocyanin biosynthetic pathway (Figure 4C).…”

Gall-Colonizing Ants and Their Role as Plant Defenders: From ‘Bad Job’ to ‘Useful Service’

“…Galls are neoformed structures on host plant tissues caused by the parasitic action of insects or other organisms [1,2,3,4,5]. In the 19th century, many biologists assumed that plants controlled the formation of galls [6].…”

“…The global richness of gall-inducer insects is estimated at about 133,000 species [4,8,9]. In particular, gall wasps (Hymenoptera: Cynipidae) constitute a relevant group of gall-inducing organisms, with roughly 1400 described species [6].…”

A novel family of secreted insect proteins linked to plant gall development

“…Red pigmented galls could result from production of carotenoids (Smits and Peterson, 1942), anthocyanins (Blunden and Challen, 1965; Bomfim et al, 2019), or betacyanins. However, in red galls induced by H.cornu , the seven most strongly downregulated plant genes are all homologous to genes annotated as enzymes of the anthocyanin biosynthetic pathway (Fig.…”