Seed Mucilage and Seed Ecology
External seed mucilage, which causes the seed to swell up in a sticky goop when wetted, is an extremely common trait across plants. It has evolved at least 100 times independently, interestingly, often in xeric habitats or in aquatic plants - that dichotomy certainly suggestive of multiple functions!
​
Seed mucilage is an economically-important trait, for instance, the mucilaginous seed husks of Plantago ovata make Metamucil/Psyllium supplements, chia seeds, a highly mucilaginous Salvia species, are used for their mucilage in baking, cooking, and breakfast foods, and flax seeds (Linum) are used in many breakfast cereals and granolas because the mucilage is a good binder.
Ecologically, not a whole lot is known about the roles of seed mucilage. Lab studies have shown that it can both inhibit and promote germination, itmay be useful in both epizoochorous and endozoochorous dispersal, it may lubricate the radicle during germination and establishment, and it surely changes the microbial community around the seed. Our work has focused on the defensive aspects of mucilage, once wetted and dried, it either binds sand and substrate tightly to the seed or strongly cements the seed to the ground. Both of these aspects reduce seed predation!
A thousand interesting ecological and evolutionary projects could be done to look at the functional importance of seed mucilage in nature. If this is of interest to you, let me know: the lab would love to have smaller undergraduate projects, larger grad student projects, and even postdoctoral projects focusing on seed mucilage.
Pollination Ecology
Pollination is an amazing process - plants are able to move a substance far smaller than a grain of sand some distance - short or long - away from the plant and onto a small surface that will cause fertilization of an embryo. You can think of it like shooting a basket from 10 miles away! Of course, most plants enlist helpers - teammates in this basketball analogy - to move the ball upcourt. We study the plants and the insects and birds that are part of this intricate and fascinating series of interactions.
​
The pollination ecology projects done in the lab have varied widely - changes in pollinator communities and pollinator effectiveness after wildfire, morphology of hummingbird-pollinated flowers, contributions of diurnal and nocturnal pollinators, effect of pigment concentrations on pollination, etc. We are interested in many aspects of pollinator ecology and looking forward to developing local SC systems and questions on which to work.
​
​
Sticky Plant Ecology
​
If a sticky plant grows in an area with unstable or wind-blown substrate, it becomes covered in that substrate. This is most commonly sand, as many coastal and desert dune plants are sticky. This may serve a wide variety of functions; Norbert Jurgens laid out a number of hpotheses in a nice paper on this phenomenon/trait, which he terms "psammophory" (i.e. sand carrying). I have been studying the defensive functions. In both inland and coastal sticky plants in California, sand coatings reduced herbivory. When caterpillars were forced to feed on sandy plants, they wore down their mandibles, grew more slowly, and pupated at smaller sizes. Future work will look at trade-offs between this sand defense and other functions, as well as the function of sand defense against diverse herbivore guilds. See LoPresti and Karban 2016 Ecology and LoPresti et al 2018 Ecological Entomology for more information.
Sand Verbena Evolution and Ecology
​
The sand verbenas - Abronia and Tripterocalyx (Nyctaginaceae) - are a fascinating radiation of plants in Western North America. Most live in sand dunes, but others grow other equally difficult substrates such as gypsum. They range from sea level on beaches to near the alpine zone in the Sierra, Rockies, and Basin Ranges. Many are exceedingly rare; a few species have < 5 populations in currently extant.
​
There is a rich tradition of growing and studying a few coastal species of Abronia - Darwin and Asa Gray corresponded about them and far more recently, the Eckert Lab has done excellent work on A. umbellata, and Tom Kaye has done very successful restoration work on the same species. However, most of the diversity occurs in the Great Basin and southwestern deserts and these species are almost completely unstudied.
​
With the help of a fantastic group of collaborators and an NSF PRFB fellowship, I have been studying various aspects of the ecology and evolution of this group. These collaborators include Marjorie Weber (Michigan State), Norm Douglas (Florida), Caroline Edwards (Indiana), Matt Johnson and Sherese Price (Texas Tech), Michael Moore (Oberlin), Sonia Nosritinia (Berkeley), Micah Freedman (Chicago), and Rick Karban (Davis). So far, we have published two papers about a novel defensive strategy (sand entrapment) in this group; many more studies are forethcoming!
​
Defense against herbivores: The majority of species are sticky and entrap sand, which defends them against most herbivores. Herbivores feeding on sandy Abronia foliage suffer worn mandibles, reduced growth rate, and longer development times; unsurprisingly, when given the choice, they prefer not to feed on sandy foliage. (Read more in LoPresti and Karban 2016, Ecology, and LoPresti et al. 2018 Ecological Entomology.) Our current work on defense focuses on evolution of defensive strategies and trade-offs between physical and chemical defenses.
Conservation: An alarmingly high proportion of the ~27 species are rare, Ruth Wilson in 1972 presciently noted in a section called "disappearing species" that "Perhaps [Abronia species] will vanish completely from the major portions of their ranges because of housing and industrial projects, recreation facilities, agriculture, or grazing". Three decades later, one species is on the endangered species list, two are confined to one or few scattered populations along single water bodies, and at least six species are state-listed in one or more states. I am working on collecting and maintaining living collections of these rare species to learn more about their ecology and husbandry requirements as well as to generate a stock of seed.
Pollination: Most species of sand verbena are self-incompatible, and thus, are obligate outcrossers. However, degrees of autogamy have evolved several times within the clade. A very interesting paper by Laura Doubleday (Doubleday et al 2013, American Journal of Botany) showed that selfing populations of Abronia umbellata had smaller flowers and reduced volatile emissions compared to outcrossing populations. Micah Freedman (UC-Davis), an accomplished chemist, Caroline Edwards (Oberlin/MSU), Michael Moore (Oberlin), Marjorie Weber (MSU) and I took volatile profiles of most species, and coupled with ongoing phylogenetic and morphological data, we will examine these evolutionary changes across the several evolutionary origins of self-compatibility in the genus.
Dispersal: Sand verbena achenes are wind-dispersed via rolling, however, wings are very variable both within and among species (in fact, one species is heterocarpic - producing winged and nonwinged achenes within an infructescence!!!). Using field collected fruit, I performed laboratory dispersal assays, with the help of a large fan, to get a relative dispersal kernel for each species. I also have quantified dispersal across transects in a couple species and will gather more data to put into an evolutionary context.
​
Horticulture: Abronia were a common garden plant from the late 1700's to the early 1900's... and then they just disappeared from seed catalogs and gardens! Given these are beautiful, drought tolerant, pollinator-attracting plants, we'd love to do some projects on developing varieties for use in gardens today!
​
If you are interested in studying Abronia, I would love to hear from you - I have openings in my lab for graduate students (masters or phd level), with many projects possible in this system, and would love new collaborators on many aspects of Abronia ecology and evolution; the more people with diverse interests and skills studying them, the richer all of our understanding will be!
​
A short video about Abronia, featuring Sierra and me, from OK Gardening.
