Monday, April 25, 2016

Sandy plants: a paper, an update, some wacky plant photos.

A little while back, I published a paper that Rick and I had been working on for awhile. In short, there are quite a number of plants which entrap substrate - sand, dirt, etc. - on their surfaces with sticky trichomes. These species occur worldwide in dunes, beaches and deserts. Quite a number of people, dating back to the late 1800's, had hypothesized that this "sand armor" must protect the plant, but nobody had actually gone out and tested it. So we tested both the hypothesis that it is physically defensive (who wants to chew on sand?) and that it is a form of camouflage (since of course, it makes the plant look like the background).

Abronia pogonantha, one of the sandiest plants I've seen. Photo: EL.

We found support for the physical defense hypothesis (in two tests) and did not find any evidence that the camouflage protects the plant. You can read (Inkfish - one of the best science blogs) or hear (Quirks and Quarks) more about this project.

The best part of publishing this was hearing from a prominent researcher (who had noticed this phenomenon), that he tells his students: "if you don't believe that sand is defensive for the plant - try sandpaper instead of toilet paper!" Since publishing this, I've been able to continue this research and observe quite a few more cool sandy plants - some of which were new to me and some of which I had only heard of.

The best sandy plant in the world. The common names for Pholisma arenarium include "scaly-stemmed sand plant", which is my personal favorite plant name ever. About an inch tall. Near Morro Bay, CA. Photo: EL
In that paper, there is a list of sand-entrapping plants. Many of these I had seen and noticed. Others were from published literature. I surveyed a bunch of really good naturalists and they suggested many others (their list was the longest). That is how I happened upon Pholisma, pictured above. This odd plant is a borage (the family includes some wellish-known plants including borage, heliotrope, fiddleneck, baby blue eyes, phacelia, etc.). Looking like a lump - maybe a mushroom? - it is completely chlorophyll-free, instead sucking nutrients from nearby plants (it is an obligate parasite, like Indian pipe, Monotropa, in the east). And the coolest part, of course, is how much sand it catches - it is nearly completely covered! It is very possible that plants which coat themselves in sand suffer a photosynthetic cost because less light reaches them. For Pholisma, that doesn't matter at all!

LOOK AT ALL THAT SAND! (I am pretty sure those purple things are flower buds - I didn't unfortunately get to see a flowering individual).
Pholisma was, since I learned about it last year, the top of my list of must-see plants and seeing it was one of my spring highlights so far. I happened upon it accidentally while looking at another sand-entrapping plant, Abronia umbellata (I used Abronia latifolia in my experiments).

Abronia umbellata is not as sandy as some congeners, but it is pinker than most! (there is also a really, really, cool paper on floral evolution in this species - check it out). Photo: EL.
The central coast of California has three species of Abronia which grow in close proximity on coastal dunes. Abronia maritima is generally on the beach while latifolia and umbellata are a little farther up (and occasionally grow over each other). They each catch sand to some extent.

Abronia maritima. The yellow anthers are positioned right above the stigma and seem to drop pollen onto it (from my couple flower dissections). It has far smaller flowers than the other species. I'd bet quite a bit that it is selfing. Photo: EL. 
Abronia latifolia, the common sand verbena for most of the California coast. Common doesn't mean boring though, its quite awesome. Photo: EL
My labmate/collaborator, Patrick, found this bizarre plant. My best guess - and it was pre-fruiting, so I can't be sure - is that its an umbella x latifolia hybrid. It had leaves reminiscent of latifolia (large, broad, very fleshy but held upright like umbellata and somewhat in between the two in glandularity) and stems which were stickier than umbellata, but very red like umbellata. The flowers were too long for an abberant maritima (and leaf structure wrong), but seemed fine for either latifolia or umbellata (though with aberrant coloration). Jury is out. Thoughts? Photo: EL
Abronia are awesome (everyone knows that already) but there are some smaller, more inconspicuous plants that are also really good at sand-catching.

This is Tiquilia plicata. It mostly grows as a little roadside weed in the Mojave. It catches lots of sand on the margins of its leaves (!) and stems. Margins of leaves are usually where caterpillars and other chewing insects begin feeding... (hand-wavy adaptationist explanation over). Like Pholisma, it is also in the borage family. Photo: EL 

Tiquilia has nice flowers, but you have to look really hard to find them (they are tiny). This was a tall individual growing in a less-sandy spot (hence the lack of sand on the leaves and stems in the photo - the bottom still had lots). Photo: EL. 
Another new favorite plant was Centrostegia thurberi. A tiny, cherry red, spiny bizarre thing, it is mildly sticky and has bracts encircling its stems which catch lots of sand - seemingly with stickiness and also just being shaped like a bowl. This was another favorite. 

Centrostegia thurberi. Photo: EL.

It catches a lot of sand on its stems, but... (photo: EL)

It also does this! Dipsacus - teasel - often has these sorts of bracts that fill with water and mosquito larvae and stuff. I've never seen bracts full of sand before (and every plant had them!). Photo: EL. 
And lest I turn completely into a botanist, there were some insects, too. Importantly, there was one caterpillar - Hyles lineata - that was really common in a bunch of spots on Abronia. This species, the white-lined sphinx moth, is common over much of North America some years and absent others. Fortunately for me and unfortunately for many herbaceous plants, it is having a good year in southern California (especially near Anza Borrego).

This Abronia villosa is not as happy as I am about this big (3"+) final-instar caterpillar. Photo: EL. 
While Hyles likes to eat Abronia (I've found them on pogonantha, latifolia, umbellata and villosa this year), they not like to eat sand at all. While it doesn't have a good mechanism for taking it off, it seems to concentrate on nonsandy plants first and then on nonsandy parts of the plant, but it always ends up eating the sandy parts of the plant eventually.

A green-morph H. lineata on pogonantha. They come in lots of colors - black, green, yellow and all manner of in-betweens. They all seem to turn into identical moths. Photo: EL
Unsurprisingly as they don't like it, sand on plants is damaging to them. A normal Hyles mandible at pupation looks like this:

An SEM micrograph of the right mandible of a Hyles lineata fed on nonsandy Abronia latifolia. Those "teeth" are for grinding up the plant before it enters the body. Photo: EL
But if they eat sandy plants, they get pretty rough:

Look at the "teeth" - or lack thereof - on this right mandible, from a caterpillar feeding on sandy A. latifolia. Photo: EL

That's it for today: a description of a study, some weird sandy plants, and a teaser of a future paper...

The woolly bear presidential election outlook, 2016

In the age of cell phones, accurate polling of the electorate has become difficult. In a world where a disproportionate percentage of people answering landlines for pollsters is white and over 50, we desperately need a new method of predicting elections. As the 2016 presidential election looms, a crack team of UC Davis innovators has a promising new source of information, woolly bear caterpillars (Platyprepia virginalis).

A woolly bear contemplates the madness of the 2016 election cycle while resting on its preferred host plant, a coastal lupine. Photo: Eric LoPresti
Rick Karban, a UC Davis professor of entomology, has tracked woolly bear caterpillar abundance since the early 1980’s at Bodega Bay, California. Each March, Karban censuses the same patches of lupine that he has for over 30 years. The study asks a vexing question: Why are there are so many caterpillars in some years and so few in others? Many insects, including pests cycle like this, therefore it is of keen interest to many. Dozens of papers later, Karban, his students, and his collaborators have answered a great many questions, including how caterpillars deal with parasites, whether population cycles are influenced by rain, whether caterpillars enjoy eating plant hairs, and how caterpillars avoid their predators.

The population highs and lows seem random at a first pass, a jagged line moving up and down each year. 

The collected data, 1983-2015, full data available here

What separates high years from low years? These motivated researchers have found a striking pattern in this data. This data set includes eight presidential election years, with four Democrat and four Republican victories. Plotted with colors corresponding to the party association of the winner, the pattern becomes obvious.

Red corresponds to Republican presidential victories and blue to Democrats. To reiterate: this is actual data!
Woolly bears have years of high abundance when Democrats win and low when Republicans win. The average woolly bear abundance was 0.21 (+ 0.07 se) woolly bears per lupine in Republican years and 1.96 (+0.27 se) in Democratic years.  This data shows that woolly bear abundance in March is a good predictor of presidential victories in the general election.

It is tempting to assume that woolly bears are Democrats (and were particularly thrilled by second-term Bill Clinton), but we cannot exclude the possibility that their abundance is a protest gesture. 

Note that 2016 is not included on the preceding two graphs. For about a year, news sources have made predictions about the primary race and have even speculated about the general election. Given their wildly erroneous predictions thus far for both primaries, trusting their predictions for the general election seems ill-advised. The woolly bears, on the other hand, have a 100% accurate prediction record over the past 30 years. In years of low abundance, a Republican is elected, and in years of high abundance, a Democrat. 

Therefore, we are pleased to announce the woolly bears’ prediction. In mid-March of this year, Karban censused the woolly bears for their opinion on this volatile election year where no subject seems out of bounds and the populist wings of each party have come out like no election in recent memory. Even the woolly bears seem hesitant this year. 

Full data, including this year's census (conducted in March).
A superficial examination suggests that 2016 will be a Republican year – woolly bear abundance is not particularly high. However, looking a little closer, it may not be. The number of woolly bears per lupine bush in 2016 (0.53) is higher than the average Republican year by 152% and is 36% above the highest Republican year ever recorded (1988). However, it is only 27% of an average Democratic year and still only 36% of the lowest Democratic year (2008). This result is without presidential precedent in the last 30 years.

We suspect that the Republicans have the edge. However, a valid hypothesis would be a third-party winner, such as a right-leaning independent (a logical placeholder in between Democrats and Republicans). Perhaps Donald Trump will take particular interest in our data. Alternately, a contested Republican convention could produce a fractured party and the old Republican woolly bear average would not accurately represent the mean caterpillar abundances seen by this new party.

The mainstream media have been shockingly inaccurate in their predictions so far, even despite complex and supposedly accurate statistical models. We need a new strategy to predict key events such as the 2016 presidential election. Rather than trust the opinion of a few people with a pulpit, the historically robust predictions of this population of caterpillars may serve as a better guide.

A congregation of woolly bears meets on a lupine flower spike, presumably to discuss politics. Photo: Eric LoPresti

(This research has been in progress and was presented at ESA 2014)

This post was written by Eric LoPresti, Mikaela Huntzinger, Patrick Grof-Tisza, Ian Pearse, and, of course, Rick Karban (who we suspect is not fooling these infallible caterpillars with his Bernie Sanders impersonation). 

Rick Karban/Bernie Sanders. Who is who? Photo on left stolen from, right: Mikaela Huntzinger.

Monday, April 11, 2016

Data I'll never publish: Antirrhinum herbivory

Inspired by this post, I'm going to try to put the results of small (but interesting) experiments up here every once and awhile. In the summer of 2014, I spent a lot of time washing plants. I was - and still am - curious of the function(s) of plant exudates. I primarily did this with Trichostema laxum and Atriplex rosea (in 2013), but I also did it with Mimulus layneae and Antirrhinum cornutum (California snapdragon). The snapdragon gave me interesting results.

(this post should also be regarded as potential project for someone else: I started it in May - there is plenty of time to get up to McLaughlin and do it again this year).

One of the experimental A. cornutum, showing leaf damage. 
This snapdragon, while not as heavily glandular as Trichostema or that Mimulus, is fairly glandular-sticky, even entrapping a small number of minute insects (see the table/supplementary material). Under the microscope, you can see the fairly dense short glandular trichomes (the longer trichomes are mostly nonglandular) on the stalk and flower bud.

Stem of A cornutum with an entrapped insect.
Flower bud showing short glandular and long nonglandular trichomes.
Wondering whether the glandular exudate is defensive, I did an experiment where I removed it with water. Most glandular exudates in CA summer annuals seem water soluble, so a spray bottle rainfall takes off much of the exudate (observationally verified in situ with a 20x loupe - plus whatever was in this exudate made suds on the plant!). This manipulation was my first treatment group. Of course, adding water to a plant has an effect of its own, so I also had a water control group, where I added the same amount of water below the plant's leaves, as to not wash off any exudates. Finally, I had a true control group, which received no water whatsoever. I instituted these treatments on the 30th of May and reapplied them on the 17th of June. Each time, I recorded the number of leaves, flowers, fruit, and plant height, as well as any damage. I also checked the plants, but did not reapply treatments on the 2nd and 19th of July (the last check all were senescent).

During the experiment, plants suffered two main forms of herbivory. The first type, which was most common and most destructive, was that the stems were entirely clipped off. I'm nearly positive this was by jackrabbits (indicated by a single flat cut diagonally across the stem) and it usually killed the plant. The photos below shows what remained.

A killed experimental A. cornutum plant. See it?!? Its the little stem to the bottom left of the flag. Also notice a nice healthy Lessingia in the background. They, too, are extremely glandular and sticky.  
A survivor of mammalian herbivory. If the meristem was not completely destroyed, they often came back and branched like this. Like the classic overcompensation "herbivore-plant mutualisms", the resulting plants were often bigger than the others, with more reproductive structures, but unlike this "mutualism", it was too late in the season and they had low fitness, as they could not mature these structures. 
The mammalian herbivory was not random. Of the 25 plants per treatment, 11 in the control group, 13 in the rainfall simulation (exudate removal) and a whopping 20 in the water control group were eaten by mammals (this is nonlethal, lethally was 10, 12, 18). With a simple chi-squared test, we can demonstrate that this was likely nonrandom (X2 = 7.3688, df =2, p = 0.025) (for lethal, X2 = 5.5714, df=2, p = 0.062). Why were the mammals targetting the water control plants so heavily?

Were they bigger and thus easier to find or just more profitable to eat? They were not significantly different in height, fruit or flower numbers from the other two groups during any check. I don't have data on plant quality (perhaps the less water-limited plants were more nutritious or something?).

The other type of damage was equally-interesting. Heliothis phloxiphaga is a generalist caterpillar on glandular plants. It was the primary herbivore on my columbines, as well as a common herbivore on Trichostema laxum and other sticky plants. Like most heliothiine noctuids, it feeds primarily (but not exclusively) on reproductive structures. I only observed it once on Antirrhinum (eating a fruit), but all the fruit damage I found was consistent with it (and that's one more time than I saw a jackrabbit eat it!).

The other type of damage: caterpillar fruit predation. 
I had hypothesized, that if the exudate were defensive, the washed plants would be most heavily eaten. This hypothesis was supported with the fruit damage. Rainfall plants received far more damage than the other groups. (note: I didn't actually analyze this with zero-inflated binomial, as it should be. There is a problem, in that only 7/25 of the water control plants had any fruit at all because of the rabbits.)

A crumby excel graph of proportion fruits damaged.
What does this all mean? Obviously, it means that mammalian and insect herbivores are responding to different plant traits. What they are exactly, I'm not sure (especially for mammals). If anyone (nudge, nudge, wink, wink) were to repeat this experiment, with a larger sample size, and maybe some other mechanistic experiments (perhaps cage controls and lots more trait data to see what is different in the water control and rainfall manip groups), I think its a pretty good system that someone could get a paper - if not a few - out of.