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Natasha Mhatre
We published a preprint on black widow spiders and their mechanosensory system a little while ago. I'm going to do a little try and put the work in context! Better late than never!
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Natasha Mhatre 17. pro 2018.
Odgovor korisniku/ci @NatashaMhatre
Black widows are interesting for many different reasons. One of them is their webs, which are called 'cobwebs'. We're used to seeing the nice planar orb webs, which tend to have a fairly stereotypical structure and so nice tractable mechanics.
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Natasha Mhatre 17. pro 2018.
Odgovor korisniku/ci @NatashaMhatre
Black widow webs are bit different as you can see! It's challenging even to capture their structure! Markus Beuhler's group has just gotten an interesting method going to do just that.
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Natasha Mhatre 17. pro 2018.
Odgovor korisniku/ci @NatashaMhatre
Another interesting difference is that the spiders hang upside down on this web! Which means their mechanics is going to be quite different as well.
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Natasha Mhatre 17. pro 2018.
Odgovor korisniku/ci @NatashaMhatre
Add to this the fact that the females (who are much larger than the males) can vary a lot in size. And can even double their body weight after feeding, things start to get quite interesting mechanically.
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Natasha Mhatre 17. pro 2018.
Odgovor korisniku/ci @NatashaMhatre
People have been thinking about how vibrations transmit through the web and generally spider silk is a pretty huge area of research.
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Natasha Mhatre 17. pro 2018.
Odgovor korisniku/ci @NatashaMhatre
Very few people have thought about the body itself though. How it's mechanics, structure, posture and weight distribution will affect what gets to mechanosensors. So we decided to do just that. To think about the body...
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Natasha Mhatre 17. pro 2018.
Odgovor korisniku/ci @NatashaMhatre
I'll do two tweet threads. This one will deal in with what we did, what the results were and what they might mean for the female spider. And in a separate thread I'll deal with the broader philosophical issues in embodied cognition that our work touches on.
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Natasha Mhatre 17. pro 2018.
Odgovor korisniku/ci @NatashaMhatre
So let's get started with what did we do...We let females build themselves webs on square frames. And once they'd done that, we let them position themselves on the web pretty much as they wanted and stuck the whole thing 'under' the vibrometer.
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Natasha Mhatre 17. pro 2018.
Odgovor korisniku/ci @NatashaMhatre
We also stuck a small neodymium magnet on the web (about the same weight as a male) and made it move using a electromagnet that didn't touch the web. A seperate vibrometer monitored the motion of this magnet and...
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Natasha Mhatre 17. pro 2018.
Odgovor korisniku/ci @NatashaMhatre
a separate scanning vibrometer measured the motion of the entire spider body on the web. I feel deep gratitude to the females who cooperated during the experiments. They were free to go anywhere, do anything.
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Natasha Mhatre 17. pro 2018.
Odgovor korisniku/ci @NatashaMhatre
And while they did occasionally move, by and large they stayed still and we had a really high rate of success in measuring full body scans! Thank you ladies, you were marvellous!
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Natasha Mhatre 17. pro 2018.
Odgovor korisniku/ci @NatashaMhatre
From the data we got, we looked at how vibrations transmitted through the body and wanted to understand how much and at which frequencies the different joints were being bent.
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Natasha Mhatre 17. pro 2018.
Odgovor korisniku/ci @NatashaMhatre
Spiders perceive vibrations via these beautiful organs, which are activated when their joints are bent. So we wanted to know how much the joints were bending.
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Natasha Mhatre 17. pro 2018.
Odgovor korisniku/ci @NatashaMhatre
This is possible to get from this data but it's messy. We took a different more flexible route. We used the data to make models, which we fitted to this data and then checked against other data in a few different ways. And from these we could get joint bending directly
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Natasha Mhatre 17. pro 2018.
Odgovor korisniku/ci @NatashaMhatre
So what did we learn? A few salient points: High frequencies didn't really travel far into the body and were dissipated in more peripheral joints. Lower frequencies travelled further.
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Natasha Mhatre 17. pro 2018.
Odgovor korisniku/ci @NatashaMhatre
But many joints were actually tuned to vibrations of certain frequencies. This wasn't apparent from previous measurements in which the weight of the animals was supported and the joints mechanically 'isolated'
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Natasha Mhatre 17. pro 2018.
Odgovor korisniku/ci @NatashaMhatre
So basically while the sensors themselves aren't particularly tuned, the body gives the joints tuning. Tuning arises from the body's mass and mechanics rather than from sensor characteristics.
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Natasha Mhatre 17. pro 2018.
Odgovor korisniku/ci @NatashaMhatre
Which would mean that as the spider changed the body, its weight, its posture, its position on the web it could change its own mechanosensory tuning!
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Natasha Mhatre 17. pro 2018.
Odgovor korisniku/ci @NatashaMhatre
So we tested this. What happens when the spider puts on weight? After eating? Or becoming gravid?
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Natasha Mhatre 17. pro 2018.
Odgovor korisniku/ci @NatashaMhatre
Turns out almost nothing happens to the tuning!!! Joint tuning is super-robust to body weight changes, so a hungry and a full spider can sense that courting male just as well as each other.
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Natasha Mhatre 17. pro 2018.
Odgovor korisniku/ci @NatashaMhatre
And if they decide to eat him, that's a decision they made and likely not a sensory mistake!
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Natasha Mhatre 17. pro 2018.
Odgovor korisniku/ci @NatashaMhatre
But posture, on the other hand, changes everything! Tuning at all the joints changes! Here's an example below...what happens in the crouching posture is tuning shifts up in frequency...
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Natasha Mhatre 17. pro 2018.
Odgovor korisniku/ci @NatashaMhatre
This shift may allow female to ignore low frequency vibrations, typically found in male courtship and in large prey items and to concentrate on smaller prey items. So basically females may be deployin this posture when they're hungry.
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Natasha Mhatre 17. pro 2018.
Odgovor korisniku/ci @NatashaMhatre
Paying more 'attention' to small prey on the web! Or perhaps when winds blow and the whole web shakes. They may use this posture to prevent their mechanosensory system from being desensitized by overstimulation!
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Natasha Mhatre 17. pro 2018.
Odgovor korisniku/ci @NatashaMhatre
So essentially we show that female black widow spiders can use posture to change the tuning of their mechanosensory system and can use it to direct attention to different signal components!
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