Relationship between elaiosome and EFN gland size in castor bean (Ricinus communis L.), an exotic mymercophyte in Southern California

Abstract

Castor bean (Ricinus communis L.) relies on seed dispersal by attracting ants with elaiosomes; lipid rich seed appendages, which serve as a source of food for ant larvae. Additionally, castor bean petioles and inflorescences have extra floral nectary (EFN) glands that secrete sugars that also attract ants, which in return, defend against herbivores. We propose that in order to attract ants, castor bean would have to balance allocation of energy toward plant defense and seed dispersal per the Principle of Allocation. Specifically, we hypothesized that in castor bean, an increase in elaiosome size would correspond to result in a decrease in EFN gland size. We examined proportion of elaiosome:seed (by weight) investment relative to the EFN gland size on a given castor bean plant. We found that elaiosome weight was not correlated with EFN gland area (p = 0.1542), and report a one to five fold range in elaiosome investment across 34 plants. We present a range of environmental factors contributing to the observed variation in elaiosome investment.