Social Spiders: Brainy Stuff

A few weeks ago, I introduced you to a project I’m working on in my lab with social spiders in this post here. In that post, I talked about overarching differences between solitary, subsocial, and social spiders that will factor into my research question about spider brains – we’ll get to the question in a few posts.

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This is incorrect. The legs come off the first section – the ‘head’ of the spider.

I thought I’d move in this post to discussing the spider brain, which resides in the cephalothorax – or the first section (not the silk spinning abdomen) of the spider. When I started this project, I thought a spider looked like my drawing to the right – and many of our popular representations of the spider incorrectly show the legs coming off the abdomen (think Halloween decorations). It’s important to remember that the legs actually come out of the first section, the ‘head’ of the spider; it plays into the really cool layout of the brain/central nervous system.

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Photo credit: Meghan Barrett and the O’Donnell lab at Drexel University.

To the left is a picture of the ‘ventral’ portion of the spider nervous system – called the subesophageal ganglion – the V shaped bit in the center of the picture, in lighter blue (the darker blue is muscle – wow, these spiders are strong!). It sits really close to the belly of the spider, because this portion of the CNS is responsible for movement in the spider and thus needs to be close to the legs. It takes up most of the head, with several discrete sections, radiating out from a central body. The two sections at the top of the photo innervate the pedipalps – sensory organs near the mouth in spiders. The other eight sections each innervate one of the spider’s legs, and the very bottom of the photo is where the nerves go to the abdomen.

These structures are made of motoneurons (neurons that control movement) that go out, into their respective organs/legs and sensory neurons that come in – giving chemical and mechanical information from hairs that cover the body and legs. In the smallest of spiders, these regions can extend pretty significantly into the legs as the spider has a limit to how small its brain can be and still function.

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Photo credit: Meghan Barrett and the O’Donnell lab at Drexel University

The subesophageal ganglion is really large, compared to the ‘brain’ portion of the central nervous system – called the supraesophageal ganglion (so named because the esophagus runs between the sub and supra sections of the spider CNS). The supraesophageal ganglion is pictured to the right and is about a third the size of the subesophageal ganglion; you can see the central body, the strip at the bottom, and the main mass of the brain in front of it. This is the part of the brain responsible for receiving input from the eyes, learning, memory, and other pre-programmed behavior (more classic ‘brain’ activities). It is dorsal to the subesophageal ganglion, meaning it sits (unsurprisingly) closer to the eyes while the sub is closer to the legs.

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Photo/data credit to Meghan Barrett and the ODonnell lab at Drexel University.

Below and to the left are some photos of my 3D reconstruction of an Anelosimus guacomayos brain – enjoy! You can really see the difference in size between the supra and sub, and the large space above the sub where the stomach of the spider sits. In my next post I’ll talk about some of the incredible behaviors this tiny CNS is capable of – more than you’d think! Does the spider brain look like you expected? Cool – or creepy? Share your thoughts with me in the comments below!

Photo/data credit to Meghan Barrett and the ODonnell lab at Drexel University.

 

 

 

Sources: Check out the paper linked below for more great views of spider brains, and a good diagram showing the sub/supra divide at the esophagus. 

Park Y, Moon M (2013). Microstructural Organization of the Central Nervous System in the Orb-Web Spider Araneus ventricosus Araneae: Araneidae). Applied Microscopy, 43, 65-74.

Many thanks to Leticia Aviles for the specimen. 

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An Introduction to the Social Spider Project

I’m about to begin a series of posts on social spiders – yes, those creepy crawly arthropods we all despise – to give some background information on a research project that my PI and I have been developing for a while (now in pre-proposal stage). My hope is that this series of bite-sized bits of my project, the theory behind it, and the journey of the research itself will be interesting enough to turn some of the fear we have into curiosity. As a child I was terrified of spiders, and made my father ‘take care of’ any of the unfortunate few that wandered into my room; but through all this research, I’ve actually developed a (very small) fondness for the little guys, and I hope I can share that fondness with you.

We’ll start this introduction by discussing the study organism itself – the spider. In this study, we’ll be looking at closely related spider species that differ dramatically in one major type of behavior – sociality. There are three ‘types’ of this behavior – solitary, subsocial, and social.

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Found on the @ApprenticeRPG twitter

Solitary spiders are the ones most of us are probably familiar with – you know, the spider that chills out on its own web or wanders around on the ground by itself. It meets with other spiders for mating, but that’s the extent of its desire to socially interact.

Subsocial spiders are those that engage in some social behaviors – perhaps they live together or engage in cooperative prey capture maneuvers, but they also have some kind of obligate solitary phase. This could be a particular season of the year or a particular age that they spend alone, or they could even have communal webs but with marked, individual territories. The behaviors here are really diverse.

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Photo Credit: Donna Garde, Texas Parks & Wildlife, link through photo.

Lastly, you have the social spiders. For people with arachnophobia this is probably the WORST thing ever because if you find one spider, you know there are bound to be many more nearby. Social spiders engage in cooperative maternal care, nest maintenance, and prey capture behaviors and live together pretty much 24/7 – except during dispersal, when young spiders leave the nest to venture out into the world alone.

Social spiders come in various shapes and sizes just like the more familiar solitary spiders; you have larger huntsman in Australia that can have up to 300 spiders in a colony and the smaller Anelosimus (the spiders I’ll be working with, known as cobweb spiders) found throughout the Americas – Anelosimus eximus, a species I’ll be working with frequently, can have tens of thousands of spiders in a web (found as far north as Panama, though there are other Anelosimus in the US). There are other social spiders found throughout the world, in varying colors, numbers, sizes, and with varying behaviors.

That’s it for today’s introduction to the project – be sure to check back for future installments on spider brains, brain resource allocation theory, social spider behavior, and more!

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