PARENT SESSION
Oral Session #79: Mutualism / Parasitism.
Presiding: J. Bronstein
Thursday, August 8. 9:00 AM to 11:30 AM. Cochise Meeting Room, TCC.

Exploring the nature of the relationship between Datura seeds and Pogonomyrmex californicus ants.

Marussich, Wendy^*,1, ¹ Arizona State University, Tempe, AZ

ABSTRACT- Interspecific interactions are often assumed to be mutualistic because one species appears to benefit. However, most studies do not test whether both participants benefit. Myrmecochory is characterized by a lipid-rich appendage, or elaiosome, on a seed. Typically, ants gather the seeds, carry them to the nest, consume the elaiosome, and discard the seed unharmed either in the nest or refuse pile. The benefit to the ants is presumably the nutritional content of the elaiosome, while benefits to the plant include dispersal from the parent plant, protection from seed predators, reduced seedling competition, protection from fire, or transportation to nutrient-rich microsites. I tested whether Pogonomyrmex californicus benefits from consuming Datura wrightii and D. discolor elaiosomes by raising queens on different diets and measuring survival and brood production. A diet of Datura alone was sufficient for queen survival, but brood production was reduced relative to a standard diet. Adding Datura to a standard diet did not increase queen survival or reproduction. As ants do not appear to eat the seeds, I tested the hypothesis that myrmecochorous plants use physical or chemical defenses to prevent seed consumption by ants. I raised queens on Datura seeds that were 1) whole with elaiosomes intact, 2) whole with elaiosomes removed, 3) cut with elaiosomes removed, and 4) elaiosomes only. Queen survival and reproduction was highest for diet 3 and lowest for diet 2. These results suggest that ants do not benefit from interacting with Datura, and that Datura is using chemical cues to deceive ants into dispersing its seeds.

KEY WORDS: ants, Datura, mutualism, seed dispersal