Galls on Smilax campestris Griseb. (Smilacaceae) protect the insects against restinga constraints, but do not provide enriched nutrition

Smilax campestris Griseb. (Smilacaceae) is a superhost of galling insects, adapted to xeric environments such as those of the restingas of the Parque Estadual do Acarai, Santa Catarina, Brazil. Currently, we evaluate the structural and histochemical changes induced by a Cecidomyiidae on S. campestris leaves, originating globoid midrib galls. We hypothesized that the macroenvironmental constraints of the restingas should reflect in gall developmental sites, resulting in enhanced xeromorphic anatomical features. The mesophyll of S. campestris nongalled leaves is dorsiventral, hypostomatic, with an adaxial homogeneous parenchyma, some cells with invagination in the walls, and an abaxial ordinary spongy parenchyma. In galls, the cells of leaf mesophyll redifferentiate into a homogenous parenchyma, with polygonal cells and straight cell walls. Few intercellular spaces are observed. Galls have uniseriate epidermis, without stomata, an outer parenchymatic cortex, a mechanical layer, and a nutritive tissue, limiting a diminutive central larval chamber. The histochemical profile reveals an increment in lignified cell walls, and accumulation of polyphenols, tannins, and alkaloids from non-galled leaves toward the galls. The absence of any special type of reserve in nutritive cells, and the occurrence of secondary metabolites in outer cortical layers, indicate reduction or absence of photosynthesis in gall tissues. Gall structure is redirected to a protective shelter against UV and oxidative damages imposed by the excessive light and water deficiency of the restingas, but do not provide enriched nutrition to the gall inducer. Current results contrast with common observations in insect-induced galls and reveal an alternative adaptive morphogenetic pathway for xeric environments induced on Smilax campestris by the gall inducer.