Extrafloral nectaries in the Leguminosae: Insights into the evolutionary history of a hyperdiverse character.

BRIGITTE MARAZZI; ALFONSO DELGADO-SALINAS; MELISSA A. LUCKOW

Boise, Idaho

Conferencia; Botany 2014; 2014

Extrafloral nectaries (EFNs) are secretory structures that often mediate ecologically important protection mutualisms with ants and other arthropods. They occur in over one hundred plant families and are most common in legumes (family Leguminosae). Legumes form the third largest angiosperm family, are dominant in many ecosystems, and have highly diverse interactions with ants. In spite of the importance of ant-legume EFN mutualisms, the diversity of EFNs is still sparsely documented in the family. Our study investigates structural diversity of EFNs in legumes (location on the plant, kinds of morphologies, and variation within individual morphologies) and examines their complex evolutionary history in a phylogenetic framework. We compiled from published reports and herbarium, greenhouse, and field observations a list of 126 genera with EFNs. Fifty-five genera belong to the subfamily Mimosoideae, 49 to the Papilionioideae, and 22 to the caesalpinioid grade. Genera of papilionoids and caesalpinioids with EFNs represent only 10% and 13% of all genera in their respective subfamilies, whereas 61% of mimosoid genera possess EFNs. Most EFN genera - and probably also most EFN species ?are concentrated in the sister clade to the Papilionoideae, which includes many caesalpinioid lineages and the Mimosoideae. EFNs can be found on eleven different locations of a plant (with up to six different locations within a genus), the most common of which are leaves (71%), followed by stipules (24%) and bracts (12%). EFN morphology ranges from glandular trichomes or a few cryptic secretory cells to modified pre-existing organs and specialized gland-like EFNs. They also vary in shape, size, and color. This broad diversity makes EFNs an outstanding example of a ?hyperdiverse? plant character. Our parsimony reconstructions of the presence of EFNs mapped onto a mega-phylogeny of the legume family agree with previous work, suggesting the general pattern that EFNs originated multiple times in the Caesalpinioideae grade and Papilionoideae, but only once in Mimosoideae. We also coded EFNs using different assumptions, either as homologous structures or functional suites of characters. Because these character codings reflect different assumptions about homology, they can lead to an incomplete or one-sided interpretation of the evolutionary history of EFNs, no matter which reconstruction method is used. Therefore, only by disentangling the hyperdiversity of EFNs and considering its many evolutionary scenarios can we fully appreciate the complex evolutionary history of legume EFNs.