Thursday, 20 November 2014

Venom, vidi, Vikki

When people ask me if trapdoor spiders are poisonous, I usually say "yes" just to simplify things. But really, they are probably not poisonous, and very few spiders are. Poisonous animals are those which will make you sick if you eat them, whereas venomous animals deliver a bite or sting which causes anything from slight pain up to death.

 Trapdoor spiders are most definitely venomous; they rely on venom to subdue their larger prey items. I've always been quite interested in poisons and venoms, their evolution and effects on prey. However, most studies into venom seem fixated on its medical significance. This doesn't really interest me much, but it interests one of my colleagues, so we have a deal - I will do the spider squeezing and some of the analysis, and he will do the other magic that has to happen that I don't know about.

We've put together a few ideas towards a venom project which, if it doesn't work, won't take much time out of my study - but if it does work, it will be a good additional chapter in my thesis (and could perhaps take me further than that, but who knows?). Analysing venom seems pretty straightforward, as it is just a set of proteins (though it still presents a few healthy challenges), but getting the venom in the first place is the trickiest, and most important, part.

How you collect venom differs depending on the spider species. The Sydney funnelweb (Atrax robustus) is probably the easiest to collect from - if you annoy one (which isn't difficult, by all accounts), it rears up and exposes fangs that drip with venom. You can then just collect the venom from those droplets. Venom collection from other spiders involves knocking them out and then electrocuting them. Unfortunately they tend to vomit, so your samples can become contaminated very easily and you need to suck up the vomit as soon as it appears. A third method is similar to that used to milk snakes for their venom: getting the spider to bite through parafilm (thin plastic film) and deposit their venom in a tube. For that, you need an annoyed spider with big fangs. Luckily, all of the Cantuaria have fangs big enough to punch through parafilm.

It's annoying them that can be the problem. Large female spiders tend to be extremely volatile, and rear up into a threat stance as soon as you lift the lid of their container. However, smaller species, and males, tend to keep running away, and won't inject venom even if you hold them down and manually poke their fangs into the tube.

To start with, I annoyed the spiders by poking a parafilm-covered tube at them until they bit into it. However, they would often get a bit over-zealous and drive their fangs into the sides of the tube rather than through the top. It's amazing how far in front of their bodies they can bite. So instead, I now grab them with the tweezers and hold them above the tube, annoying them with it until they finally go postal. That method seems to work pretty well.

Another method I tried was to get the spider to bite a cotton bud and then wash the venom off into a container, but that diluted the venom too much.

A Bradford assay done on one of the venom samples from a particularly aggressive female has shown that the venom is concentrated, so we have enough to work on. I just have to get it from other spiders and see if there is much difference between the proteins. There are a few other things to work on too, but that will do for now.

In other news, it looks like I may have finished the first round of optimising PCR - yay! I have three working genes with which to construct a phylogeny. There are some stubborn samples which refuse to be sequenced, but I'll deal with those when I've exhausted the ones that work. I may not need them anyway.

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