PARENT SESSION
Oral Session 67: Mutualism - Parasitism III: Ants.
Presiding: K Mooney
Wednesday, August 4, 8:00 AM to 11:30 AM, Meeting Room D 135.
The 'long arm' of protective mutualisms.
Leigh, Michael*,1, 3, Inouye, David2, 3, 1 University of Maryland, College Park, MD, USA3 Rocky Mountain Biological Laboratory, Crested Butte, CO, 812242 University of Maryland, College Park, MD, 81224
ABSTRACT- Ants in protective ant-plant mutualisms often chase away enemies of the plant, rather than killing them. In so doing, ant mutualists may cause some of those enemies to move onto neighboring plants. This may handicap nearby, potentially-competitive plants, and provide plant mutualists with benefits beyond just protection. Results from a 2003 study reveal just such an effect in two species of sunflower native to the Colorado Rocky Mountains, Helianthella quinquenervis (H) and Wyethia sp. (W). At the study sites near the Rocky Mountain Biological Laboratory, ants are rarely found on W plants; however, ants are frequently found on H plants, where they collect extrafloral nectar and chase away flies that would otherwise lay eggs in the flowerheads. These flies use the buds of H and W plants as the primary hosts for their larvae, and the larvae can cause considerable damage to developing seeds. Four treatments were established, each consisting of pairs of plants: H + H ; H + W with ants ; H + W without ants ; and W + W. The phenology of each flowerhead was tracked to enable comparisons between similarly-developing flowerheads and, at the end of the flowering season, the flowerheads were collected and inventoried for fly infestation and seed survivorship. Consistent with the mutualistic nature of the ant-H relationship, H flowerheads contained significantly fewer fly larvae when ants were present than when ants were absent (p<0.01). At the same time, W flowerheads growing next to ant-tended H plants had significantly more fly larvae than those growing next to H plants without ants (p<0.05), implying that ant attendance on H plants harmed W plants. These results confirm tentative results from previous studies by the author, and suggest that the protective mutualism between ants and Helianthella quinquenervis plants causes harm to neighboring Wyethia sp. plants.
Key words: predispersal seed predation, Tephritidae, ant-plant mutualism, Asteraceae