Thursday, November 20, 2014

Germination of Abronia, a new trick

Abronia, sand verbena, is a cool genus of an odd plant family - the Nytaginaceae "four o'clock family" - that has a number of members in coastal and desert western North America. Growing it is a pain; I've talked to now about a half dozen people who've said they gave up.

Pretty flowers reminiscent of garden Lantana, but not closely related!

Rick Karban and I are doing a project at Bodega on Abronia latifolia and I thought it'd be nice to have some in the lab for a future experiment. I poked about and found that others had some success using various methods: cold stratification, scarification with sandpaper, a ripe apple as a source of ethylene. Others just expressed frustration. I tried the apple, sandpaper and cold stratification without any success.

The cool, weird mine of Lithariapteryx abroniaeella, a mining caterpillar common on A. latifolia at Bodega.
Fortunately, I found a trick that's given me greater than >75% germination. Unfortunately, it is not possible on a large scale (i.e. a couple dozen plants are fine, a couple hundred would be maddening). Abronia seeds come wrapped in an anthocarp. Remove that - most will be empty, but 25-50% will have a seed. Take the seeds and soak them in DI water for a few hours - I generally do this from the morning to the afternoon, so about 4 hours, but I forgot about one batch and left them in for 24 and they were fine. Now the tricky part. Take a pair of fine tipped forceps and carefully remove the entire seed coat. In soaked seeds it will just come off. Be very careful not to damage the seed. Don't worry though, you'll get the hang of it after a few. Then place on wetted blotting paper under a light - don't allow it to dry out. In three or four days, the leaves will be green and roots will have started forming and you can transplant into well-drained soil.

A sand-verbena living up to its name. 
They grow slowly, but seem hearty (n.b. I've only had them alive for a month or so). I don't have seeds of any species besides A. latifolia, so I can't say it works for them, but I'd bet it does (and if anyone does have any, I'd love to get ahold of some). Do let me know if you try!

Saturday, September 27, 2014

Cutting up an old friend: the life and times of a suburban tree.

I'm back in the northeast for a bit. My parents had to have an old white oak (Quercus alba) removed from our yard, as it hung over the driveway and the house and dropped a big branch on my dad's car last year. The two trunks stood less than a meter from the driveway and it was shaded on one side by tall white pines (Pinus strobus), the other side by the house and sheltered an understory of pokeweed and poison ivy. Notably, in the mid-90's, I spent considerable time in a rickety treehouse between the two trunks. More recently, I'd watch migrant warblers in the spring and fall and chickadees, nuthatches and creepers in the fall on it - for awhile a suet feeder hung which we watched from the kitchen windows.

The author in the tree "house", 1993. The author is 5, the tree ~ 90.
I only know the history of the tree since ~1991 (and those early years, I don't actually remember). But the removal of the tree offered the opportunity to see its history. What had it seen? How old is it? Did the building of a house/driveway next to it cause it any harm? It was obvious from the start that this "tree" started as two individual oaks, which then joined (inosculated is apparently the correct term for this - see some striking examples here)

Days before its demise. 2014. 
Chainsaw marks had made reading the rings difficult, so I sanded a line on each side of the stump and tried to make out the rings.

In progress. The far right side of this photo actually is asphalt, though hidden under debris - the tree was only 

What I found, indicated that I needed to do more work. A set of really thin lines occurred in the early 1970's on one trunk and late 1970's on the other. So clearly I couldn't delineate them accurately. What caused those really lean years, I figured initially must have been the construction of the house and the building of the asphalt driveway practically on the tree.

Something is wrong here! Blow this up to see better. 
Therefore, my dad and I planed the whole stump (until the planer broke, ~50% done). This allowed us to also see clearly the junction of the two trees.

So what caused that big set of lean years, now correctly dated as 1976-1982? The house was built in 1982... the driveway a few years later - that certainly didn't cause the lean years as I had initially hypothesized. So what happened?

Now, a couple hours later, they line up!

Let's construct the history of the tree. Because the planer broke before I could get to the very center, I actually don't have good resolution the first couple years. The left trunk (father from the driveway), looks to have put down its first ring in ~1900, the other a few years later, ~1904. What was happening in Wrentham at that time? In 1870, Wrentham had 2202 people, 1900 - 2720 and 1910 - only 1748 people. I suspect that loss of populations corresponded with the degradation of farmland, and increased exports of agriculture from the great plains (at least this is what I remember from a New England environmental history course in college). A large dairy farm up the road - Birchwold Farm, now a great conservation area (best place to find black racers around Wrentham) - folded at about the same time.

Had the tree been paying attention to world events, it might have noticed these (a smattering of things I could think of
no rhyme or reason to them). 
So these trees took root - not a meter apart, in the first decade of the century or slightly before on what was likely fallow farmland reverting to mixed deciduous forest - what most of New England has gone through at one point or another. They then grew steadily through the next few decades until 1944-1946, when growth slowed to an inchworm's pace for both stems. Many factors could slow a tree's growth in this way including drought, this hurricane, an abnormally short growing season, an ice storm (leading to loss of healthy limbs), or insect outbreaks, to name but a few. Which ones contributed to this, I don't know, nor can I find any information on anything abnormal happening in that period (but do let me know if you do!).

The next big hit the trees took was in the late 1970's - 1980's. At first glance, the cause is obvious: the two trees hit. When this happened, they seem to have put much effort into wood building at the junction - perhaps as a form of competition - as the lines are quite wide at the junction, but get infinitesimally small around the other 3/4 of the trunk. This period is why I didn't get equal counts from the two trees. Even with a hand lens, I couldn't make out the lines accurately on the first area I sanded. In the center of the junction a crack is visible - this is where vascular tissue never grew, I suspect the soft material in the center is old, compacted outer layers of bark which had nowhere to go when the fusion happened around them.

A branch with some sort of rot - I presume fungal
But I suspect that is not the whole story. 1981 was the worst year for both trees - they put on pretty negligible growth even in the usually fat junction area. I suspect this was due to the worst ever infestation of gypsy moths, an invasive caterpillar which defoliated almost 13 million acres of oak and other deciduous trees in this area that year. Because these caterpillars can almost entirely defoliate a tree, that tree won't have much photosynthetic tissue that season and will suffer reduced growth, and if this repeats, as another invasive, the winter moth, often does, it can kill trees.

Since that time, the trees had been growing steadily... gaining a tree "house" in 1993 and losing a limb here or there in a storm, possibly pre-weakened branches because of fungal infection or physical injury.

Two days of this before the fun (the tree rings and research) began.
Now that my parent's house has a wood-burning stove, a tree will have to be taken out every year or so. Will that upset the ecology of the area? It probably won't have a huge effect, but it may midly benefit it by creating a rare microhabitat in the area. Because our neighborhood is suburban, most snags (dead trees) are removed quickly and probably not left on the ground. The stumps and leftover wood which could not be split and used as firewood will lie around, food for insects (perhaps horntails!) or fungi, which will of course attract other insects or birds and continue on up. And for curiousity's sake, the next tree will give us a better idea of what happened in 1944-1946 and the 1970's and 1980's. If we see that the 70's and 80's cruised by without a single hitch, the reduced growth in these trees is probably competitively-caused. If 1981 was a bad year for the new tree - gypsy moths are the likely culprit. If the whole period is bad for the other tree as well, then the microclimate may have been unfavorable. Perhaps before the house was built construction or other land use change occurred, which was unfavorable to the trees.

While it is a little sad to see an old friend go, it was necessary for safety of the house, cars and inhabitants, useful for heating, and the history was exciting and informative. Next time you see a tree down, check it out - much can be learned from it!

Friday, August 8, 2014

ESA2014 preview: External chemical defenses in plants

I'll be presenting this at 1:30 PM on Wednesday in the Plant-Insect Interactions II session in the Compagno room. Fellow GGE student and collaborator Billy Krimmel will follow soon after with an interesting talk on tarweeds. 

I've been studying chenopods and their salt bladder system - which is important both physiologically and defensively for the plant - for awhile and with some gentle nudging from my committee, I've been trying to place the chenopod system into a broader context. Namely, what ecologically and evolutionarily differs between a plant which sequesters its chemical defenses (alkaloids, tannins, etc.) in its tissues and one which secretes them onto plant surfaces?

Glandular trichomes (secretory and non-secretory) cover the surfaces of Trichostema laxum.
Coming from New England, where plants with copious exudates are less common, the summer in California is a bonanza of sticky, oily, slimy (!) and otherwise exudate-covered plants. Is this pattern driven by rainfall? Many of these species have congeners elsewhere without copious exudates (e.g. Trichostema, Lessingia, etc.), which begs the question: are exudates effective defenses only in arid environments? Are the defenses liable to environmental removal?

I therefore set up a series of experiments examining these questions. In one, I simulated rain on individuals in a population of Atriplex rosea - a chenopod with defensive exudates - while holding other individuals as controls and rainfall controls (which received water at the base, not on the leaves) and assessed herbivory at the end of the season. Perhaps unsurprisingly, I found a significant increase in herbivory in the group which received rainfall, suggesting that instead of helping these arid, water-starved plants, the rainfall and subsequent removal of exudates (which are entirely water-soluble in A. rosea) actually increased its susceptibility to herbivores.

Chenopods with external defenses (Atriplex prostrata and rosea) and without (Chenopodiastrum murale) at my field site.
Come to my talk to hear more!

Saturday, June 28, 2014

Polymorphic flowers - cool natural history observations

I've been spending as much time in the field (at McLaughlin reserve, which I can't say enough good stuff about) as I can manage lately - trying to complete all the projects I've begun. A quick update on some interesting stuff.

This guy greeted me yesterday morning. Western rattlesnake, Crotalus viridis.
Not sure about the bunny - but maybe a juvenile jackrabbit?

The exudates of Trichostema laxum - also known as turpentineweed or bluecurls - are rather strange smelling (like herbaceous vinegar) and seem to be very deterrent to herbivorous insects in lab trials. So I have a large scale exudate removal experiment going, that while taking up a huge amount of time, seems to be going really well.

Trichostema laxum. You can even see the exudates shining on the leaves!
I am seeing an increase in herbivory (haven't crunched the numbers, but it is noticeable) in the exudate-removed plants, and hopefully, I'll be able to show a fitness effect. However, I wanted to be able to say that any fitness effect was due to herbivory, not differential pollination. So I've been spending 6 or so hours a day watching pollinators visit these plants. Which is also going well, but sitting for that long in the heat is driving me crazy. So I've been taking breaks and visiting other populations of T. laxum to look for herbivory.

All populations suffer some herbivory, but one population is getting annihilated by this leafhopper and
some noctuid caterpillar!
While scouting populations, I've come across some flower polymorphisms that apparently haven't been described for the species. They occur in low frequency (1:1,000-100,000 depending on the population), but occur nonetheless, and therefore, are interesting. Are they selected against heavily? Or with big populations, are they just swamped out as neutral?

The top left is the "normal" morph - a purple flower which varies a small amount in shade, but not too much. The pink morph is in at least two populations in low frequency and probably exhibits a different molecular structure of anthocyanin - the pigment that gives most plants a reddish or pinkish color. The bottom right plant lacks anthocyanin entirely, it has no reddish parts, including the stem that is reddish in all other individuals of the species. The bottom left has anthocyanin - probably the same form as the normal, and has dark reddish stems - but lacks it on the flowers except on the lower lip.

I'm not sure what to make of these, but I've been gathering fitness data (the anthocyanin-less morph seems to be sterile) and pollination data and I'll hopefully collect seed and do some breeding experiments.

Otherwise, life has been good!

Ctenucha sp. (rubroscapus/multifaria group, I do believe) which is all over the Stachys flowers here.