Ecological and evolutionary consequences of variation in aristolochic acids, a chemical resource, for sequestering specialist Troidini butterflies

Plant-insect interactions provide an opportunity to examine fundamental ecological and evolutionary processes, including mechanisms of species cooccurrence and adaptations to herbivory and predation. An example is the interaction between butterflies in the Troidini tribe (Papilionidae), a group that sequesters chemical defenses from its host plants in the genus Aristolochia (Aristolochiaceae).

In this dissertation, I examined the ecological and evolutionary consequences of variation in aristolochic acids, the chemical compounds sequestered by Troidini from it host plants, through a combination of observational, experimental and laboratory studies. I conducted studies at several sites throughout the Americas where different levels of knowledge about this interaction are available. These differences allowed me to ask specific questions in areas where there is ample background information (i.e. North America) and to ask more general, but fundamental questions in areas where little is known (i.e. South America).

In North America, I showed for a Troidini species, Battus philenor, that larvae preferentially fed on less tough, younger leaves, and found no evidence that aristolochic acid content influenced larval foraging. For these herbivores, mechanical resistance might be a more important determinant of larval foraging behavior and development compared to plant chemical defenses. In another study in North America, with data from three consecutive seasons, I found that larger egg clutches of B. philenor suffer less predation compared to small clutches. This study suggests that, for eggs protected with toxic chemicals, there is a clear benefit in laying eggs in large clusters in areas with high levels of predator threat.

In Iguazú National Park, Argentina, little is known about Troidini- Aristolochia interaction; therefore I studied general and specific aspects of this interaction. Our main finding, in contrast to what has been reported in North America, is that many Aristolochia and Troidini are not defended with aristolochic acids, contrary to the currently accepted paradigm that all Troidines are toxic. Studying these species in areas where they are understudied and reach higher diversity gives a more complete picture of this plant-butterfly interaction. My results contribute to furthering our understanding of the role of chemical ecology in shaping evolutionary dynamics and ecological processes.