Plant exudate defense

Many plants secrete a variety of compounds onto their surfaces. These compounds serve both physiological, for example UV protection, and defensive functions. These chemicals act as effective first lines of defense against herbivores, pathogens and competitors. As they lie on the outside of the plant, they are liable to removal due to environmental forces including rainfall and chemical reactions with atmospheric chemicals. I am working on exudates in a few systems including Trichostema (a mint), Madia (an aster), various Chenopodium species (goosefoots) and others. 

Direct and indirect defenses of sticky plants
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A great diversity of plants have independently evolved stickiness, which may be a direct and indirect defense. Entrapped insects die and this carrion provides predators with a food source; these same predators reduce the herbivore load on a plant by consumption or interference. Sticky plants in California are marked by a very consistent predator community, which are ecologically not phylogenetically host specific. The interactions between these predators, as well as between predators and herbivores, have interesting and important effects on the plant. 

Additionally, a subset of sticky plants are 'psammophorous' ('sand-carrying') and are naturally coated in a layer of substrate, generally sand. We've found that this covering - entrapped by the same sticky trichomes as insects are - protects the plant against herbivory, but it doesn't seem to be a camouflage, as might be expected. It acts directly, by wearing down mouthparts and slowing growth of the herbivores. 

Ecology of the Chenopodiaceae

The chenopods (goosefoots) are widely distributed mostly herbaceous annual weeds. They are tolerant of many extreme environmental conditions, including saline soils, drought, heavy metals and more. One interesting clade of the chenopods has evolved modified trichomes - salt bladders - which help osmotic regulation as well as serve as herbivore deterrents, probably both chemically and physically. I published a paper in Oecologia about the defensive nature of these bladder trichomes, both in field and lab. In this system, my main questions are: how does the plant balance the physiological and defensive functions of this system? Do these functions interact synergistically or antagonistically? I have a variety of projects in this system, both in field and lab, mostly with the really cool genera Chenopodium and Atriplex. I am working on integrating an evolutionary aspect to this research, both on a species-level (local adaptation in Chenopodium album) and on a genus level within Chenopodium. 
Additionally, I have been working on the strange species Chenopodium vulvaria, which sequesters large amounts of trimethylamine in its salt bladders. Trimethylamine gives rotten fish its odor and has various functions across most of organismal diversity: it is in coyote scent marks, bacteria degrade other molecules to trimethylamine, seabirds cue in on it, plankton use it as a migration cue and some fungi produce it in copious quantities. Its function in this particular plant is unknown. I have been testing it as a volatile defense, a direct defense and as a plant signal and hope to have more data this winter. 

Variation in birds' egg shapes

I spent a couple years working on bird nesting and the variation I noticed in egg shape, even within a clutch of eggs from the same female, was striking. Using equations for egg shape from theoretical papers (figure to the right adapted from Barta and Szekely 1997), I am working with a couple stellar undergrads on two small projects. 

1) How variation of egg shape is partioned among females within a population, among populations (across environmental gradients) and among species?

2) Do brood parasites (cowbirds) match their egg shape to their hosts?
Functional floral variation in Trichostema laxum

Trichostema laxum, a small annual serpentine mint, is a really cool plant in a number of ways (including copious exudates!); most strikingly it shows a huge amount of floral variation. The overall color varies from white to pink to purple, the amount of nectar guide patterning varies, the height, width and corolla length vary 2- to 3-fold across plants, the pollen color is polymorphic and lastly, the separation between stigma and anthers is either nonexistant, or widely separated. This last trait is reproductively important: in the lab, the latter do not produce any seed without pollination, while the former do. Currently, Jenny Van Wyk and I are crossing and growing out a large set in the lab to ascertain whether variation in these traits is heritable (it is for at least flower color and size). Field experiments in the summer of 2016 are planned. 
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