PARENT SESSION
Oral Session #45: Herbivory: Effects on Plants. Presiding: T. Craig.
Wednesday, August 8, 2001. 8:00 AM to 12:00 PM. Hall of Ideas H.
Violating the sexual taboos of plants: The effects of inbreeding on plant-insect interactions.
Hull-Sanders, Helen1, Eubanks, Micky 1, 1
ABSTRACT- When insect pollinators are limited in nature, plants are forced to self-pollinate or inbreed. Offspring produced by these incestuous matings typically suffer reduced fitness as a consequence. Adverse effects include reduced germination of seed, reduced growth, and reduced flower production. Although self-pollination is relatively common in the plant world, few studies have focused on how inbreeding affects interactions with insect herbivores. This study examines the effects of self-pollination on the resistance to insect herbivores in the entire leaf morning-glory, Ipomoea hederacea. We found that only 24% of the seed produced by inbred I. hederaceae plants germinated, whereas 55% of the seed produced by outbred parents germinated. In addition, inbred plants were 52% smaller than outbred plants and, most importantly, they produced 76% fewer flowers than their outbred counterparts. These results suggest that I. hederacea suffers significantly reduced fitness as a result of self-pollination. Inbreeding, however, may benefit the plant under some conditions. We found that tortoise beetles (the primary insect herbivore of morning glories) reared on inbred plants were significantly smaller than those reared on outbred plants. Inbreeding, therefore, actually increases I. hederacea's resistance to tortoise beetles and inbred plants may suffer reduced herbivory as a result of this increase in resistance. Under conditions of heavy herbivore pressure in the field, the loss of plant fitness due to inbreeding may be counter-balanced by the subsequent increase in resistance to insect herbivores.
KEY WORDS: Ipomoea hederacea, tortoise beetles, inbreeding depression, herbivory