Family matters: variation in defensive chemistry in the pipevine swallowtail

DIMARCO ROMINA D.; NICE CHRIS C.; FORDYCE JAMES A.

Congreso; Southeastern Population Ecology and Evolutionary Genetics 2008; 2008

Pipevine swallowtails (Battus philenor) sequester toxic alkaloids called aristolochic acids from their Aristolochia host plants, rendering larvae and adults unpalatable to a broad range of predators. Plants that invest in toxic chemical defenses are confronted with a paradox because the plant is providing defensive chemicals to their herbivore, which in turn defend the herbivore against predators. Previous work has shown that the amount of aristolochic acid sequestered by caterpillars of the pipevine swallowtail is positively correlated with caterpillar survivorship under natural field conditions, and sequestration ability is heritable. It has been proposed that genetic variation for sequestration ability is "invisible to natural selection" because intra- and interindividual variation in host plant chemistry will largely eliminate a role for genetic variation in determining caterpillar chemical defense. We examined intra- and inter-plant variation in aristolochic acid chemistry and assessed the relative importance of plant chemical variation on sequestration. Here we ask: 1. Is there intra-and inter plant variation in aristolochic acid content and/ or plant toughness? 2. Does caterpillar performance vary depending on the position on the plant where feeding occurs? If so, is this related to AA content OR leaf toughness? 3. Does caterpillar family or host plant chemistry best explain AA content of caterpillars?