Saturday, December 24, 2016

Data I'll never publish II: Salinity and herbivory

I spent a lot of my second year of grad school thinking about salinity and insect herbivory. Generally, insects don't like very much salt (i.e. how many marine insects have you seen?). Salt is a fairly effective herbivore deterrent - an observation seemingly first made in 1980 by D. Newbery in an Oecologia paper on mangrove herbivory. I made the same observation, and tested it experimentally, in chenopods in a 2014 paper (also in Oecologia - they've seemingly cornered the salinity/insect herbivory market).

Coconut palms might be the most widespread and useful (to human) halophytic plant. They were useful for that hammock, at least.  Abaco Island, Bahamas, 2011. 

Plants are also affected by salt and have myriad ways to deal with it, basically all variations on either excluding it, sequestering it, or excreting it. Obviously some plants are much better at dealing with salt than others (see mangroves, Zostera, etc.) - we call plants that are adapted to saline environments "halophytes" (i.e. salt plant in Greek). I happened upon a little, weedy, nonnative, and pretty much unremarkable chenopod - Oxybasis glauca - growing at the edge of a building in Davis and somehow I decided it was a pretty cool plant. Given all the other cool halophytes available, I'm not sure why I chose this plant to do a bunch of experiments on, but I did.

This is Oxybasis glauca growing in volcanic sand on the edge of Mono Lake, Mono, CA. I was with a group of about 30 people when I found this and was very excited. I couldn't really even articulate a single cool thing about the plant - it is salt tolerant, but every plant in that area is salt tolerant. Maybe the coolest thing is that Oxybasis species have really small seeds compared to Chenopodium or Atriplex... maybe there is nothing special about it?
Like most Atriplex and Chenopodium (the genus which Oxybasis was split from) species, Oxybasis glauca has salt bladders - little bubble like trichomes which the plant shunts salt to and then they burst, an odd but effective form of salt excretion. This leaves a layer of salt on the outside of the plant. This protects the plant from herbivory somewhat.


Pre- (above) and post- (below) bladder burst O. glauca leaves (lab-grown). 

Because O. glauca is salinity-tolerant and the primary herbivore of most weedy chenopods in the valley, the spotted cucumber beetle (Diabrotica undecimpunctata), doesn't like salt (see my 2014 paper), I wondered if there might be a refuge from herbivory effect at higher salinities and maybe there would be an intermediate salinity where the plant would still grow well, but herbivores would be deterred. So I did an experiment - I grew plants in three salinities* and then exposed half of them to a week* of cucumber beetle herbivory. I expected herbivore pressure would be most intense at low salinities, but also growth would be retarded at higher salinities. 

So the hypothesis looks something like this - if plant "performance" is on the y-axis and the green line is effect of herbivory and grey the effect with solely salinity, if there is some overlap, the plant might do best at that overlap point (or it might not). (note: this is not a particularly good graphical representation for a number of reasons). 


What did I find?

Plant response to salinity (w/o herbivores):
Salinity increasing left-right. Standard deviation plotted.

Plants did worse as salinity increased (as expected). 

Herbivory:

Salinities increasing in treatments 1-4. Standard deviation plotted.
Total leaves damaged by the herbivores decreased with increasing salinity (as expected, as they are less palatable), but because the plants had fewer leaves, the proportion damaged increased. 

THE INTERACTION


Biomass of plants. Dark green: with herbivores, light green: without herbivores. Salinity increasing left to right. Standard deviation plotted. 

Sadly, there wasn't. Beetles didn't really have an effect on biomass (or any other metric). Maybe I didn't have them in there for long enough? Maybe they really don't have a fitness effect (I can certainly believe this). 

Maybe this data will be useful to someone. Email me for the sheets. 


*Note: the exact procedures are in one of about 40 notebooks in my office, so I don't actually know exactly the salinities or number of days right now. If anyone is interested for any reason, I can easily dig this up.    

Monday, September 26, 2016

Musings on pollinators and sticky plants

Having spent much of the last four years seeking out sticky plants, I'll admit to mostly having thought about their herbivores and general insect communities on the plant surfaces, without too much thought to pollination. A labmate's question about columbine (Aquilegia eximia) pollination - "Do they have any adaptations to prevent bees?" got me thinking about this. A. eximia is hummingbird-pollinated and is extremely sticky (see here). I've spent enough time looking at, and photographing, over a hundred species of sticky plants that I was able to dredge up some pertinent observations (some from field notebooks) and I'll reference a few papers that have mentioned this.

A honeybee entrapped on the sticky flower/pedicel of serpentine columbine (Ranunculaceae: Aquilegia eximia). Note the robbing hole present on the front (out of focus) and left spur. These were made by carpenter bees (Xylocopa californica). Honeybees and other bees visit as secondary robbers, though they do not regularly visit unrobbed flowers. The primary pollinator of A. eximia here is Anna's Hummingbird (Calypte anna).  McLaughlin Reserve, Lake County, CA. 
The general explanation for sticky plants is that it prevents herbivory directly (by slowing or entrapping herbivores). This is generally an insufficient explanation, as pointed out by Tom Eisner and colleagues (here) who found that ladybugs were slowed or entrapped, allowing a specialist aphid to feed on Mentzelia pumila (Loasaceae - a painful plant family). Eisner's explanation, however, also seems simplistic and incomplete - it turns out that a suite of specialist predators are good at moving on sticky plants and do effectively prevent herbivory (here, herehere, more coming!). Whether these are exceptions or the rule, I suspect this defense is fairly common. While I think Eisner et al. missed the boat on trophic relations in Mentzelia (this is not a completely baseless accusation; I have some data to back my case up), they do make an astute observation on a cost of being sticky: "among the insects we found dead on M. pumila there were several individuals of an andrenid bee, Perdita sp., ... a genus known to include pollinators of Mentzelia. Evidently the trichomes can be a hazard to [pollinators] ".

People have long thought about adaptations both for a specific pollinator and against others that are not as effective. Is stickiness a problem for pollination or could it be a benefit in some cases?

Entrapped Lycaenid butterfly (I think it is Plebejus acmon) on Mentzelia micrantha. It seems likely this butterfly was entrapped while visiting a flower, as it is entrapped on a flowerhead (it is on a bract surrounding a fruit, but it probably had been there since there was a flower). Napa County, CA.
First, we should ask: do sticky plants actually entrap their pollinators commonly? Unlike the smaller-flowered Mentzelia (like micrantha pictured above), which are likely self-pollinating, the larger-flowered species, including Eisner's pumila (and the widespread and stunning laevicaulis) have large flowers separated from the very sticky (like velcro) leaves. Carnivorous plants, including the sticky sundews, often have widely separated flowers and traps. Yet, a nice study by Jurgens et al (here) found that the separation in one sundew is simply because taller flowers attract more pollinators (and the sundew's sticky leaves remain near the ground). They found that the color differences between the flower and trap were more important in keeping pollinators on the flower and off the leaves. Complementing this, a more recent study showed that color is important, but odor might also be important, especially in sundew species without much physical separation (here). A strange paper (see footnote) on a South American aster showed practically no overlap between pollinators and entrapped insects (here). The sticky columbines - eximia, shockleyi, and some populations of formosa - are all hummingbird-pollinated, as is the sticky monkeyflower, Mimulus cardinalis; the chance a hummingbird becomes entrapped is virtually zero. 

The first thing to note is that none of these papers have actually examined whether there is a pollination cost to being sticky. Of course, a past cost may shape evolution, but not be obvious now. While these examples make the case for putative adaptations to not entrap pollinators, none except El-Sayed's paper have any sort of comparative aspect. Therefore, we can't be sure that these are actually adaptations. This isn't to belittle the research, of course, as the experimental studies are very nice and convincing that these factors underly the non-trapping of pollinators.

A small bee of some sort entrapped on a serpentine columbine bud. Two Tupiocoris californicus, one of the mutualistic predators, are pictured on the right of the bud. McLaughlin Reserve, Lake County, CA. 

I wonder, if perhaps in addition to these chemical and visual cues keeping pollinators away, if another way to avoid entrapping pollinators is to utilize pollinators which are too large to be entrapped? Could it then be used to exclude suboptimal pollinators? Might stickiness might be easier to evolve in plants with larger pollinators or sticky plants be selected on to have larger pollinators? This chicken-or-egg situation need not be resolved; it would be interesting enough to find out whether there is a correlation. One could go about testing this by looking at insect-entrapping plants and comparing them to their close relatives and asking (quantitatively), is the pollinator of this sticky plant larger than expected given the pollinators of its closest relatives? Our paper on columbines includes a genus-level list of insect entrapping plants, this would be a good place to start when looking for possible comparisons (at whatever level you choose, you'd need to have both sticky and non-sticky members of each taxa). Off the top of my head - Aquilegia, Mimulus,  Salvia, Calceolaria, Ribes, Nicotiana seem like genera with both sticky and nonsticky members and pollinator variation and would be a good place to start (surely I am missing some).

A small solitary bee (I'm not good on bee genera) on Mimulus bolanderi. Among Mimulus that I've investigated, bolanderi entraps the most insects. There is little information on this strange, fire-following species, and I have only seen one pollinator visit (this one!), but I was mostly looking for predators. Another insect-entrapping Mimulus is hummingbird-pollinated (cardinalis). Some populations of common monkeyflower (M. guttatus) are sticky, others are not - all are bumblebee pollinated, I believe.
In conclusion:

1) Sticky plants occasionally entrap potential pollinators, though we don't know yet whether there is a realized cost to this, indeed it could be a benefit and may keep less-effective pollinators away.

2) Several experiments have demonstrated that features of some sticky plants prevent pollinators from being entrapped.

3) I hypothesize that sticky plants may have larger pollinators, as it would reduce chance of a cost (but I am agnostic about which might evolve first) and might even have a benefit (as an adaptation to exclude some pollinators).

I'd love other people's thoughts or other references (I haven't really dipped my toes into the literature on keeping less effective pollinators out of flowers).




Footnote:
I hope this group follows up on this system, as cool questions could be asked, but this paper is confusing (and if they read this post, they should read Patricia Thomas's 1988 dissertation at U. Illinois, which looks at a similar system in a thistle - I have a pdf). They looked at Haplopappus flowers, which have sticky bracts (like Grindelia and some Cirsium) and recorded flower visitors and entrapped insects to see whether there was overlap. This, in and of itself, is a good exercise. However, the paper is lacking in much pertinent information and clear discussion of what they found, What stuck out to me most was that they found that the tephritid fruit fly, Dioxyna chilensis, (which is an herbivore of this plant) was a common flower visitor and commonly entrapped, thus the stickiness may be a direct defense. Somehow this and really any herbivory isn't mentioned - despite "herbivores" being mentioned in the title - herbivores weren't really discussed in the paper. Also, they discuss pollinators, but not really any functional explanations of why some insects might end up on bracts and others on flowers (for instance, they found ants and a family of beetles were the most commonly entrapped insects - yet they don't discuss that both primarily walk, whereas the non-entrapped taxa fly). Their conclusions are technically right, but rather incomplete: "Thus, comparing all arthropod genera found, it seems that bracteal resin selectively traps insect genera with lesser pollen transfer potential." Hopefully more work will come out, as it seems Villagra's lab is working more on the system. 

Monday, August 29, 2016

An unexpected herbivore

Columbines are toxic! Like larkspurs, columbines are supposedly toxic to most livestock and humans. So say the books. This rabbit doesn't listen to the books. (The internet, in its infinite wisdom, says that the eastern species has edible - to human - flowers, so maybe the rabbit is just rather tech-savvy)


I actually suspect that the roots and leaves may be somewhat toxic but the reproductive parts, including the flowers and pedicels (which the same rabbit eats in the next video!), are not. Deer also eat them, especially in one particular population, which I've mostly stopped using for experiments because of it. Wild speculation aside, just thought I'd share the video as I got a kick out of it.

Also, a question - is this a brush rabbit (Sylvilagus bachmani), a European rabbit (Oryctolagus cuniculus) or a black-tailed jackrabbit (Lepus californicus)? . A terrible still of the tail from the video is below. I feel a bit silly that I can't even conclusively get it to genus. I'd be kicking myself pretty seriously if I couldn't get a dragonfly, bird, wildflowers, or butterfly to genus and really this should be far easier!


Friday, August 12, 2016

Another sticky columbine with dead bugs and predators!

A few weeks back, Rick Karban and I headed to the east side of the Sierras and the White Mountains to look for some Abronia and Nicotiana species for continuing projects. I also took a wish list of species (with herbarium GPS coordinates) that seemed worth checking out. We were able to easily find Abronia nana (not really sand-catching), Abronia turbinata (somewhat sand-catching), Nicotiana attenuata (bug-catching), and Alliciella monoensis (sand-catching). I also had a record of Aquilegia shockleyi, the desert columbine. After spending so many hours over a few years looking at eximia (here, here), I've spent more time looking at other columbines. The sierra species, formosa, is fairly boring from an insect-plant perspective, being nonsticky, largely devoid of predatory bugs and often covered in aphids.

This Aquilegia formosa was growing along Mormon Emigrant Trail (El Dorado county), seen on the way to the east side. Compared to my eximia, it has tiny flowers (probably 2/3 the size of eximia). With only anecdotal evidence to support this, I suspect that this is because Calliope Hummingbirds, the smallest one around, are a common visitor (though others are, too) and would be unlikely to successfully access the nectar in a much bigger flower.  
Aphid exuviae on a bud of A. formosa.
The Jepson said that shockleyi hybridizes with formosa in desert mountains, so I was expecting it to be fairly similar - nonsticky and not that interesting from my plant-insect perspective. Fortunately, I was wrong.

Aquilegia shockleyi, White Mountains, CA.
In a really pretty little desert oasis, we found a nice population of shockleyi growing in a flowing spring with my favorite thistle, Cirsium douglasii, an associate of A. eximia at my field site. This species is every bit as sticky as eximia, every stem had dozens to hundreds of entrapped insects.

A typical shockleyi stem - dead beetles, flies, wasps - tasty morsels for the right predator!
Another, for good measure.
Of course, my first thought was - is a carrion-mediated defense system happening in this species, too? That requires that there are scavenging predators and herbivores that the predators can eat (often they eat just the herbivore eggs). Sure enough, in just a few stems, I quickly found both.

The herbivore was, predictably, Heliothis phloxiphaga - a really common and destructive caterpillar that is common on most glandular plants in California and is multivoltine (has several generations per year). It is extremely bad for plants as, unlike many caterpillars, it largely eschews leaves in favor of buds, flowers and fruit (it is part of the aptly named group, the budworms). This is the same species that eats eximia and is controlled by the sticky plant predators at McLaughlin, where they consume its eggs and small caterpillars. 

A late-instar caterpillar on shockleyi. They have no trouble at all moving on the sticky stems of any plant, though I don't know exactly how they do it.

Typical Heliothis damage to a shockleyi fruit. It has consumed 3 of the carpels (the seed pods) completely and consumed all the immature seeds from the two remaining ones seen in the picture.
Predators were present as well. They were not in abundance, but were around. The most common was Hoplinus eschinatus - usually the most common on eximia, as well as tarweeds, sticky Mimulus, sticky tobaccos, etc. They are great egg predators and are just great insects in general. I got only crummy pictures that are not worth sharing here. The other interesting predator present was Oecantha - tree crickets. I only saw two really tiny nymphs (pictured below), but they are also on eximia in low numbers. Unlike most Orthoptera (the grasshopper/cricket/katydid order), they are really omnivorous, feeding on dead insects, live insects, as well as the plant in small quantities. On tarweeds, especially Madia, where they are common, they have benefits and costs the plants - they are predators and remove some herbivores, but they also chew leaves and oviposit into the stem, leaving big scars. I've never seen these scars or any evidence of them chewing on columbines (which are notoriously toxic to many animals), so I suspect that is less of a problem, but I really don't know. I've only seen them three or four times in three years of working on eximia, so I'd bet they are too rare to really have a huge impact - and these two were the only which I saw on shockleyi

Two tree cricket nymphs. 
There was one interesting contrast to the eximia system. A seed bug of some sort (I didn't collect it) was present and feeding on the seeds. I've noticed occasional clutches of eggs on eximia, but the nymphs either disperse or perish in the stickiness; I've never seen one actively feeding. This bug moved with seeming ease and was common. I'd bet that Hoplinus and other sticky plant predators would be effective at controlling it; the egg masses are present on the plant and the nymphs likely stick around on the same plant (somewhat important for the carrion-provisioning system to work). 

Unknown bug feeding on shockleyi seeds in a ripe fruit.

Just hatched nymphs of the unknown bug on a ripe shockleyi fruit.

In conclusion, this was a really cool plant, and it is a strong, strong, candidate for the carrion-provisioning system which I described in eximia. Someone should study it. A simple carrion-removal experiment, checked weekly through the growing season would be an easy project (for an undergrad, perhaps?) and would give us new insights (how do these sticky plant predators control seed bugs?) and would be really fun. There is nothing as much fun as being in a wet place in the desert or coast range, with hummingbirds visiting the columbines around you and other birds, mammals and insects abundant in the little watery oasis. 


Another picture of dead stuff on shockleyi stems. Please study it.

Saturday, July 2, 2016

A natural history idea for ecologists: the natural history supplement

At risk of rehashing what is in this very short paper (open access pdf here), a few colleagues and I have a simple idea for how to encourage natural history in current ecology and evolution. A whole bunch of notable folks, including Harry Greene, Josh Tewksbury, Paul Dayton and more have noted the decline in traditional natural history - the taking of observations, collecting specimens, and classes in zoology and botany - among academics over the last half decade or so. Their papers all deserve a read as they point out very real problems and quantify these declines.

Though these papers draw attention to the issue and make a very convincing case that it is an issue, they don't offer realistic solutions. I'll not overstate our case; our small idea won't bring back botany classes where they once were taught or inspire people to create an insect collection at a college without one. However, we have an idea that may incentivize natural history study, at least a small bit. We propose that ecologists and evolutionary biologists create a natural history supplement with their paper to highlight potentially interesting observations and important natural history data.

An example of character displacement? A somewhat disjunct population of Abronia pogonantha in the coast range (left) is deep pink-purple, where populations I've looked at in the Mojave which grow near Abronia villosa (a deep pink purple species) are whitish or very light pink (right). I'm not going to investigate it, but I'll include it in a natural history supplement so someone else might and I took specimens of these plants and sent them to an herbarium.  
Anything of potential interest could go into this supplement (though it should not be used as support for the main assertions of a paper - any natural history of that sort still belongs IN the paper). This needn't only apply to field studies, either - researchers working in greenhouses or in laboratories with colonies of microorganisms make important natural history observations, too - they are just as intimately familiar with their study systems as a field biologist.

We think that there are a few reasons why this small addition would be particularly important and useful. First and most obviously, these observations WILL be useful to someone down the line, somewhere, sometime. Even if it takes 50 years for someone to investigate a particular plant or insect, these observations of behavior, population size, flowering time, etc. in 2016 are an invaluable snapshot of what you saw when. Richard Primack and co.'s wonderful reanalysis of flowering time data which Thoreau gathered in the 1800's are a perfect example of this type of use. Secondly, meta-analyses and comparative studies are commonplace and particularly informative and could use those life history data included in these supplement that wouldn't make it into a paper on another aspect, but are likely data that many folks take instinctively.

Since we have the internet, archiving these sorts of things has never been easier. Many papers have a great deal of supplementary information (especially in short-form journals) and publishers have ways to archive it. While it doesn't need to be done immediately, if this practice is adopted, a database of these natural history supplements could be compiled at any time.

This caterpillar, Sympisits [Lepipolysperscripta, is having a good year on both Antirrhinum vexillo-calyculatum (pictured) and A. cornutum. However, it is far more abundant on v-c. even when cornutum is the more abundant food. I'll likely never write a paper on snapdragons, but if I did, this would be a perfect type of observation for the natural history supplement. 
Lastly, it incentivizes natural history observations and data. The "currency", if you will, of academia is papers and citations. While including a natural history appendix doesn't boost the first aspect, if the additional information in that supplement is of use to others, it can only boost your citation count and make your work more widely read.

If those sound like good or bad arguments, read the full paper (again, here), there is a good bit more in it. I'll conclude by saying that I've written two of these, both for papers in Ecology (here and here) and they have been easy and enjoyable to write. Has anyone actually read them? I'm not sure (do tell if you have!). Maybe not, but that doesn't seem particularly troubling to me - even if one person reads them and gets inspiration for a study or uses some data in an analysis decades after I'm gone, I'll be happy. Plus, they were more fun to write than the main text of these papers. I focused both of these by describing briefly a great deal of natural history, hoping that someone studying one of these systems (especially the well-known ones, like Mimulus or Petunia or Nicotiana) would think about insect- or sand-entrapment.

On another level completely, I'm sure Ecology wouldn't have let me use the fantastic quote “[Pholisma feels like] a squishy gummy bear covered in fuzzy sand covered hairs” in the main article :) .

This stilt bug, Jalysus wickhami, moves easily on the sticky surfaces of many plants, including this weird, sticky fire-following monkeyflower, Mimulus bolanderi, by grabbing the glandular trichomes below their sticky heads. However, when I perturbed it for this photo, it got a bit of the sticky stuff on its front legs (visible in photo) and was visibly disoriented and had to groom it off with its other legs. Some cool papers have focused on movement on sticky plants, so the trichome grabbing behavior is well-known, but I might still include this in a supplement (with proper citations to those papers, of course). 

Thursday, May 5, 2016

Variation in phenotype (mutants!)

Obviously, variation in traits is present in all populations and all species, but its quite easy to forget that - a mallard looks like a mallard, right? Evolution acts upon this variation, be it timing of flowering, anti-predator behavior or body size, constantly. I find variation in "characteristic" traits very interesting (and by "characteristic", I mean how a naturalist would recognize a species, for instance in plants this might be color, growth form, leaf shape, etc.). I've been noting these for quite awhile and keeping a photo log - mostly of flower color, which is especially interesting to me - here's a selection.

This isn't meant as a real ecology post, just an appreciation for the natural world, but do bear in mind the little tidbits of science thrown in - they'll only make it more interesting. As Huxley famously said, "To the person uninstructed in natural history, his country or sea-side stroll is a walk through a gallery filled with wonderful works of art, nine-tenths of which have their faces turned to the wall."

I'll mostly put a "normal" picture first and then the mutant. Here's a normal Mimulus guttatus, the common yellow monkeyflower - a widespread, common and lovely species.

McLaughlin Reserve, Lake County, CA. 
And a weird red mutant:

McLaughlin Reserve, Lake County, CA
A normal Tritelia laxa.

Berryessa-Knoxville Rd., Napa County, CA
And a white one:

Berryessa-Knoxville Rd., Napa County, CA
A normal blue-eyed "grass" (really an iris), Sisyrinchium bellum:

McLaughlin Reserve, Lake County, CA

and a white one:
McLaughlin Reserve, Lake County, CA
Normal Mimulus nudatus, a cool serpentine endemic in the northern coast range.

McLaughlin Reserve, Lake County, CA
And a weird beige morph:

McLaughlin Reserve, Lake County, CA
And both normal and white morphs of Collinsia sparsiflora:

McLaughlin Reserve, Napa County, CA
Normal and white morphs of Mimulus layneae. Interestingly, the two white individuals in this population had flatter flowers as well.

McLaughlin Reserve, Lake County, CA
Why are white flowers so common in plants? Purple or reddish colors are caused by a group of chemicals called anthocyanins. These are synthesized in a pretty complex pathway that involves a bunch of steps, all mediated by proteins. If a mutation (or developmental issue), interrupts the function of any of these steps, you get a loss of function, which in this case becomes a white flower.

In some species, there is simply a polymorphism - its not rare to have differently-colored flowers (or -colored seed, or -shaped fruit, etc.). This Leptosiphon sp. has both pink and white flowers in roughly equal proportions in a population I looked at.

McLaughlin Reserve, Lake County, CA

Like Leptosiphon, many other members of the Polemoniaceae have white/colored polymorphisms within populations. Navarretia mellita (often a sandy plant!), is one:

McLaughlin Reserve, Lake County, CA

McLaughlin Reserve, Lake County, CA

Of course, color polymorphisms aren't restricted to flowers, or even plants. A cool hypothesis to explain the existance of color polymorphisms in many species of raptors is that it is harder for prey to figure out what is a predator if they all look different. To the best of my knowledge, that hypothesis is still up for debate, but its clever and seems logical. Here is a pair of Variable Hawks, Buteo polyosoma:

Bosque del Pomac, Lambayeque, Peru
And another morph, of the same species!

A juvenile, I think. Bosque del Pomac, Lambayeque, Peru
I don't know any hypotheses for the maintenance of color polymorphisms in caterpillars, but some have them. Hyles lineata feeding on Abronia villosa:

San Diego Co., CA

San Diego Co., CA

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...