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.

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!

 

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.