Ecology and evolution go hand-in-hand, and perhaps nowhere is the link between these two fields clearer than in the study of plant defenses: the conspicuous prickles, toxic chemicals, and defensive mutualisms that have long fascinated plant ecologists are all the result of evolutionary arms races between plants and herbivores that have played out over millennia. The combination of comparative phylogenetic and classic field ecology methods is a powerful approach to understanding ecological and evolutionary patterns, whether across generations or genera. Below, I highlight some of my recent work in the area of plant defense evolution.
Induced defenses (those produced only after herbivore attack) are commonly considered a cost-saving strategy: plants produce defenses when they need them, and don't invest in them when they don't. Less well understood is why all plants don't rely on induced defenses; one explanation for this observation is that the ability to induce defenses may itself be costly. Consistent with this notion, I have shown that induction is lost in plants that experience little herbivory. More recently, I showed this same pattern in several genotypes of horsenettle (Solanum carolinense) that differed in their previous exposure to insecticide: offspring of plants that had not been sprayed responded to jasmonic acid by increasing investment in defense, whereas the offspring of plants that had historically been sprayed with insecticide (and thus did not experience herbivory) did not respond to the same treatment. This result points to potentially unexpected microevolutionary consequences of pesticide use in crops, which may result in less resistant genotypes following insect attack.
Solanum is a hyper-diverse genus of plants that include well-known species like tomato, potato, tobacco, and deadly nightshade. Many Solanum species--including several at my field site in Kenya--produce physical defenses (e.g., thorns and prickles) as an anti-herbivore deterrent. Comparatively little is understood about the evolution of physical defenses; by comparing the repeated evolution of physical defenses across the genus, I hope to better understand the fundamental selective pressures that have driven the diversity of physical defenses in this clade. Of particular interest to me are the repeated colonizations of continents by prickly and non-prickly Solanum species, as well as the potential for correlated evolution between physical defenses and other leaf traits. Results from several projects in this area are coming soon!