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Systematics, Plant-herbivore defense, and Macroevolution
It has long been known that species interactions are critical to diversification. Herbivory can generate selective pressure on plants to become less palatable to herbivores and has led to the evolution of plant defenses through various morphological and chemical mechanisms. Leaves host numerous herbivorous interactions, while balancing beneficial interactions with those of natural enemies. The two main plant defenses are direct and indirect defenses, where direct defenses are plant characteristics that interact directly by prohibiting the herbivore’s ability to uses its host. Indirect plant defenses attract natural enemies of herbivores. Leaf morphology can protect against herbivores with both direct defenses (e.g. leaf thickness, hairs, trichomes, colleters, secondary metabolites, prickles), and indirect defenses (e.g. foliar domatia, extrafloral nectaries, or volatile organic compounds).
I am specifically interested in the indirect defense, foliar domatia in the Rubiaceae family. Foliar domatia (or acarodomatia) are characterized by the presence of a depression, cavity, or hairs that occur on the abaxial side of leaves usually shelter beneficial mites that are either predacious or fungivorous. Rubiaceae, a primarily tropical family, are known for species that contain various defense strategies against herbivores. Secondary metabolites, such as, alkaloids (e.g. caffiene), iridoids (sub-family, Ixoroideae) have been reported in Rubiaceae, along with many instances protective associations with other organisms, in the case of bacterial nodules (e.g. Pyschotria, Pavetta, Sericanthe), acarodomatia (e.g. Tricalysia, Plectroniella), and ant mutualisms (e.g. Anthorrhiza, Hydnophytum, Mymecodia, Mymephytum, and Squamellaria).
To understand if foliar domatia affects rates of diversifcation, I am currently in the process of creating a nuclear phylogeny of Tricalysia using the Angiosperm-353 target capture kit.
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