Background/Question/Methods Plants possess a finite amount of resources that must be allocated into different life history processes, including maintenance, growth, defense, and reproduction. Within reproduction, resources must then be allocated into seed production and seed dispersal. Elasiosomes (nutrient-rich fat bodies) act to entice and reward seed-dispersing ants and have evolved independently over 80 times. Resource investment into these ecologically critical structures is essentially unknown. To address this gap, two sympatric species of Datura (Solanaceae), the perennial D. wrightii and the annual D. discolor, both of which reward seed-dispersing ants with elaiosomes, were grown under nutrient-rich and nutrient-poor conditions. Flowers were self- or cross-pollinated by hand or allowed to produce seeds autogamously. The average mass per seed and per elaiosome were measured on ten haphazardly chosen seeds from each matured fruit. The caloric content of the elaiosomes was also quantified using bomb calorimetry. Ants generally prefer seeds with larger elaiosomes, so we hypothesized that when plants were grown in high resource environments, they would invest more into seed dispersal and produce larger elaiosomes with higher caloric content. Results/Conclusions Nutrient availability had no effect on the mass or caloric content of elaiosomes in either species, failing to support the hypothesis that when plants have more resources they will produce larger, more calorie-rich elaiosomes. This indicates that resource investment into elaiosome production is not resource limited and implies that an increase in either of those traits may not benefit the plant. Although Datura wrightii produced heavier elaiosomes than Datura discolor, the ratio of elaiosome mass to seed mass was larger in D. discolor than in D. wrightii. This suggests that investment into elaiosomes and seed dispersal may be more important to the annual D. discolor. Pollination treatment did affect elaiosome mass and caloric content: seeds from selfed flowers had larger elaiosomes with more calories than seeds from outcrossed flowers in both species. Future studies will examine preferences of local seed-dispersing ant to determine the ultimate effect of resource availability on investment into elaiosomes and seed dispersal and whether selfed seeds with larger elaiosomes are more likely to be dispersed by ants.
