Ovule-gall stimulating a large fake fruit onMiconia chamissoisNaudin (Melastomataceae): a structural overview

Abstract

The developmental processes of galls are better known when induced on vegetative organs, while they have hardly ever been described for reproductive ones. Herein, galls induced by Allorhogas uberlandiensis (Hymenoptera) on ovules of Miconia chamissois (Melastomataceae) were analyzed in terms of morphological, anatomical, histochemical and cytological characteristics. Galls are induced on the ovules before fertilization, acting as a physiological seed. Therefore, the ovary grows and develops into a fruit-like gall. The ovule-galls are on average 20 times larger than the seeds, and fruit-like gall volume is on average 5.4 times larger than that of mature fruits. These are related to cell hypertrophy and tissue hyperplasia in the host organ. There is a typical nutritive tissue formation in the ovule-gall with lipid, protein and pectin storage, as well as a storage tissue close to the epidermis. This nutritive tissue shows a smooth endoplasmic reticulum, multivesicular bodies and mitochondria-rich cells. After gall induction, all the ovules degenerate and ovary and hypanthium hypertrophy to form the fruit-like gall. The fruit-like galls form a physical barrier blocking the anthesis, preventing fertilization and keeping only ovule-galls. Our study shows that the A. uberlandensis galling insect may reduce the reproductive success of Miconia chamissois, thus acting as a biological control agent for this host plant population.