Worker-caste Differences in Army Ant Brains: Soldier Specialization

In my most recent publication with Drs. Sean O’Donnell, Susan J Bulova, and Christoph von Beeren entitled ‘Brain investment under colony-level selection: soldier specialization in Eciton army ants (Formicidae: Dorylinae)’, we discuss the differences in the brains of task-specialized workers in multiple species of army ants. 

Worker army ants come in a variety of shapes and sizes that generally correspond to the task that worker performs (form meets function). In the case of the Eciton burchellii cupiens to the left (a), the grey arrow points to a small ‘foraging’ worker ant who cares for brood, assembles the nest, forages for food, and cares for queen and soldier ants. The white arrow points to a larger ‘soldier’ worker ant in charge of colony defense (the mouth parts are so large that this ant can’t even feed itself!). Neither of these belongs to the reproductive caste, like queens, yet they look very, very different and complete very different tasks too!

Different tasks impose cognitive loads on the different regions of the brain that help the organism complete them (for example, flight requires an organism to bring in a lot of visual information quickly so it imposes a large load on the visual processing region of the brain called the optic lobes). Since brain tissue is expensive to produce and maintain, evolutionarily-successful organisms will invest more in the parts of the brain that help them deal with the cognitive load of their behaviors (and will not invest in more brain tissue than strictly necessary, to conserve those resources for other tissues like reproductive organs or muscle).

At the colony level, there may be selection across different worker types so that workers, like soldiers, with reduced sets of behavior have smaller brains than other workers, like foragers. In b, above, we see a foraging worker (A) has a much larger brain relative to body size than the soldier (B) – and a similar size brain, even regardless of the differences in body size!

Looking across eight species of army ants, we assessed the volumes of the total brain, mushroom bodies (centers of learning, memory, and sensory integration), optic lobes (visual information processing) and antennal lobes (olfactory information processing) in forager and soldier workers. We found:

  1. As body size (measured by head capsule volume) increases, the ratio of brain:body increases sharply in support of Haller’s Rule (the idea that there is a minimum size the brain can be and still allow the organism to function as that type of organism). In Fig 2a to the right, we see that as body size gets very, very small, brains take up significantly more space in the head because we are approaching the minimum brain size it takes to function as an ant of any kind!
  2. Soldiers, despite being significantly larger (open symbols in 2b) do not have significantly larger brains than workers of the same species that have a smaller body size (closed symbols) and their ratio of brain size relative to their body size was significantly smaller. Soldiers – larger bodies but relatively smaller brains (Figure 1b illustrates this well).
  3. Not all regions of the brain are equally affected (Figure 3; not shown but can be found here) by this forager-soldier difference. The relative volumes of the mushroom bodies and antennal lobes compared to the rest of the brain volume was smaller in soldiers of all eight species (meaning they de-prioritize sending their already limited resources to these regions).

In total, these results suggest that there can be consistent, colony-level selection on the brains of workers in army ants and that specialized soldiers have reduced investment in their brains (particularly in the mushroom bodies and antennal lobes) to correspond with their reduced set of behaviors.

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The Third Quarter: Checking In

Me, in the field having a successful bee-catching day.

If I thought the second quarter of this year went fast, quarter three has gone even faster. I’m writing this a tad early – I’m currently (as of this post) in Cuba, so I had to write this post in advance since my internet access is spotty depending on my day’s activities.

The big thing I want to emphasize about this last quarter: I passed my candidacy! Indeed, I am now a PhD candidate – and coming off the back of a pretty successful field season, this feels especially good. I am excited to get the chance to settle down and work on my own thesis specimen this fall.

I met 3 of 4 goals (as expected!) for last quarter – Candidacy Boss Battle, Part 2; The Pallid Bee; and at least started Carpenter Contemplation (an ongoing meditation on America’s hardest-working bees). What’s on the docket for July-September?

  1. Carpenter Contemplation, part 2 – Returning to New York to see how my nest boxes are doing and potentially gather some genetic and cognitive data!
  2. Colliding Conferences – Conferences here, conferences there, oh my! I’m currently organizing two conferences – the Evolution in Philadelphia Conference and also, hopefully, the NE regions Social Insect conference.
  3. Termite Trials – To increase the sample size of one of our soon-to-be-papers, we need to run a few more termites through our histology mill. Sit tight…
  4. Pest Mess (please!) – This is the one I just can’t seem knock off my to-do list – third time’s the charm? Hopefully, the Tetramorium will be plentiful outside upon my return from Cuba and ripe for experimental tests!

I’ll admit that my to-do list has really gotten to be extensive – I am hoping after my field season is over I might have the chance to calm down a bit. Here’s to a happy, and productive, summer!

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The First Field Season

Me and a male Centris cockerelli friend; Tucson, AZ.

I arrived back from my first field season in Arizona on May 5th, and have been running around like mad ever since – trying to process specimen, taking my qualifying exam, and prepare for my next two field seasons this year (to New York, starting tonight, and Cuba, in June). But I felt I should take some time to reflect on the five biggest lessons I learned from this first foray into fieldwork.

  1. Me, in the Papaj lab, using Steve Buchmann’s net to collect bees from trees.

    Never underestimate the generosity of your peers – the number of people it took to make this season ‘go’ is astounding. From my ‘funders’ (fiance, Alex, and grant giver, B Cavello), to those that gave me lab space or let me borrow/taught me how to use equipment (literally a dozen people and counting), to those that let me stay with them (the amazing Kathryn Busby) which really made the trip affordable and fun, there are so many people who believed in me and supported me throughout this field season. The first big lesson I learned was to not be afraid to ask for help or support; the scientific community has a ton of wonderful people in it who want to help make science happen, and this field season I have countless people to thank for their generosity.

  2. Nothing will go according to plan – part of the reason it took so many people to make the season happen is because nothing went according to plan! The bees showed up 3 hours away from where I was staying, so suddenly new lab space and housing had to be found closer to where they were. Equipment suddenly became inaccessible, requiring me to find new people to borrow it from. At every turn, it felt like my carefully constructed plan (that I had made in January, because I am a planner at heart!) was breaking apart. And yet, somehow, thanks to all the people who came together to help me out, everything came back together again at the end of the season and I got to test out my equipment and collect a lot of specimen. I think being flexible is the key to field work – have plans for if you don’t get your equipment running the way you would like, or if your organism appears elsewhere than expected (or later than expected…).  Having a flexible mindset in how and where you gather data, and what data you gather, will help your season be more productive.

    On my cactus tour, avoiding the spines while practicing plant ID.
  3. Attitude is half the battle – Reader, when I did not find my bees for the first three weeks of the season I was DESPONDENT. But honestly, that’s just fieldwork for you and each day you need to get up and at ’em again. In the meantime, keep your eyes and ears peeled for other interesting phenomenon and do whatever you can to keep your spirits high; getting down on yourself will only make things even harder. Sometimes this may mean taking a break when things aren’t going well – a good taco, mountain view, cactus tour, fun reading day, etc, can do wonders to restore your spirit.
  4. Bring more vials – I ran out of vials about eight times in five weeks, it was incredible. I had no idea one could possibly use so many vials. How??? This isn’t just for vials, its for all supplies – bring more than you need. Things will break, get lost, evaporate if you don’t seal your EtOH container tightly enough (*sigh*) etc – having lots more than you thought you needed will help you survive these curve balls.
  5. No, these are not mini-pineapples. This is a cactus, with fruit.

    Fieldwork is fun! – There is nothing more enjoyable than being out in nature, intentionally observing things, day in and day out and getting to call it ‘work’. Particularly, being in an area that is so different from where I grew up and that has such great diversity was an amazing experience. Each day was a revelation, watching cacti grow flowers and bees emerge from the ground, seeing spiders and lizards catch prey, following flower-petal trails to seed-harvesting ant nests… it was all tremendously enjoyable, and I can’t wait to do it again.

Ant nest surrounded by palo verde flower petals.

I’d like to thank everyone on below for their help – accessing lab space or supplies, providing me with a couch or guest room to sleep on/in, teaching me how to use new equipment, checking different field sites for me, providing endless encouragement, and even financial support. I could not have done this without all of you believing in me, and with that belief supporting me in so many ways.

Thanks to my Drexel support: Dr. Sean O’Donnell, Katie Fiocca, Dr. Jacob Russell, Dr. Jennifer Stanford, and Dr. Michael O’Connor; to my lodging/funding support: Sarah Cook, Ellen and Adam Lowry, Kathryn Busby and Logan Schoolcraft, Alexander Glica, and B Cavello (Women’s Mini-Grant); to my University of Arizona support: Dr. Stephen Buchmann, Dr. Dan Papaj, Dr. Wulfila Gronenbergm Dr. Goggy Davidowitz, Dr. Judie Bronstein, Noah Giebink, and Bruce D Taubert; to my Arizona State University support: Dr. Jon Harrison, Dr. Kaitlyn Baudier, Dr. Jennifer Fewell, Dr. Rebecca Clark, and Megan Duwel.

And, always, a thank you to Anne Zimmer and Richard Barrett – for believing in me.

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Grant Writing: Are You Listening?

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Photo by Fredrik Rubensson entitled ‘diary writing’ (Creative Commons Attribution-ShareAlike 2.0 Generic), link through photo

Grant writing is a new thing for me, so you should take all my advice with a grain of salt – but this is one piece I think might be worth considering. Grant writing isn’t really a big, scary exercise in writing and self-promotion (well, I mean, it is that too) but more importantly it’s an exercise in listening.

But who are we listening to? To answer this, we must think about who are we in conversation with as we write our grants. There can be several answers to this question – and several audiences for you to consider.

  1. The Grant Reviewers – Imagine you have to sit down and look over hundreds of applications from, mostly, similarly qualified candidates. What would make some stand out? It isn’t likely to be that one extra paper you published – it’s more likely to be that your application was enjoyable and easy to read. When the pages fly by and your story is interesting, you’ll leave the reviewers with a far more positive impression of you, and your science. So spend lots of time perfecting the readability of your writing – the reviewers will thank you.
  2. The Grant-granting Agency – I work as an assistant poetry editor for a literary magazine – in some ways we are a ‘granting agency’ in that we grant author’s work publication in our journal. Nothing is more irritating than reading work that doesn’t fit the stated goals of our magazine! Granting agencies likely feel the same way – if your work doesn’t fit the criteria, or address the points in the application instructions clearly, it doesn’t matter how amazing you are, you simply haven’t demonstrated you deserve this grant. Pay close attention to the wording used in the application for who they are looking to give this money to – and then use that same language to describe yourself and your work, so it’s easy to spot how you fit the bill.
  3. Your Critics – Another creative writing tidbit is the idea of workshops; you bring in a piece of writing and distribute it to your peers, who read it and comment on it – telling you what worked and what didn’t. You usually end up with 15 copies of your work that all say slightly different things… but have some common underlying thread. Apply the same principles to your grant – send it to lots of people, those with and without experience in your field or with you/your projects, etc. The suggestions they send back will vary and you absolutely should not take every suggestion, but look for the underlying themes. Are certain sections unclear? Do you need to reorganize so your question is broader and has more impact on your field? Is the tone bogging the piece down? Listen to what your critics are saying underneath their suggestions to get to some of the real issues with the piece.
  4. Your Cheerleader – Grant writing, maybe because it’s new or maybe because I have some serious impostor syndrome, is some hard stuff. I have to catch myself from making all kinds of qualifying, humbling statements like ‘this was a pretty big paper’ (since grant writing is all about acknowledging your accomplishments). So make sure you have a cheerleader – preferably somebody in your field but not your adviser who can tell you that you are GRRRRRREAT. It could be your mom, but would you really believe her? Find that one professional who can make you feel like others in your field recognize how awesome you are – and then read their email while listening to that ‘New Avengers’ song from ‘Avengers: Age of Ultron’. I promise, you’ll feel ten feet tall after and swagger like you’re Iron Man.
  5. Yourself – If you can’t represent yourself in the grant application, you don’t deserve to get it – whoever you represented does. No matter everyone else’s suggestions, edits, comments, and concerns, make sure before you submit that the grant still sounds like you. No one knows your smarts, skills, achievements, creativity, humor, etc like you do – so always read that last draft with yourself in mind.

Listening is hard and takes practice – pulling out the ‘underlying concerns’ in a critic’s piece or identifying what to do to make your narrative read more easily can be difficult. Not receiving a grant isn’t actually always about you and your qualifications – there are so many nuanced reasons, especially when there’s so little money to give out and such competitive pools of applicants (that you’re a part of!). Put your best application forward, then back away from the result – and be prepared to try again.

Each day, a new day.

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Caste Differences in Wasp Brains

Brain section within this photo credit to the O'Donnell lab and Drexel University.
Brain section within this photo credit to the O’Donnell lab and Drexel University.

My first co-author published paper came out this summer in Behavioral Ecology and Sociobiology, and I’m (no surprise) very excited. The paper, the foundation for the kind of work I want to do in my PhD, is titled: Caste Differences in the Mushroom Bodies of Swarm-Founding Paper Wasps: Implications for Brain Plasticity and Brain Evolution (Vespidae, Epiponini), authored by Sean O’Donnell, Susan J Bulova, Sara De Leon, Meghan Barrett, and Katherine Fiocca. If you haven’t left me after the long title, that’s a good sign – let’s take a quick jog back to our eusocial basics!

A eusocial colony has several different types of individuals (called castes) which perform different tasks in the colony. In the most advanced colonies, reproducing Queens complete few tasks besides laying eggs; they rarely leave their nests, have extensive social contact with workers, and do not gather food. In contrast, female Workers don’t reproduce, complete a variety of tasks inside and outside of the nest (gathering food, feeding larvae, maintaining the nest, defense), and often act alone. It would be hard for these two groups to act more differently!

In theory, we could see how some of these tasks could differ in the demands they place on the animal’s brain. For example, flying outside and searching for food while avoiding predators might require larger regions of the brain in charge of processing visual information (called optic lobes) when compared to sitting in a dark nest all day, laying eggs.

And this is where a key ecological theory comes in – called Neuroecology Theory. This theory predicts that, because brain tissue (like all tissue) is costly to produce and maintain, evolutionarily successful organisms won’t invest willy-nilly in brain tissue they don’t need since those resources can be spent elsewhere. Instead they will invest more in regions of the brain that help them deal with the cognitive demands their environment presents – for the flying wasp, this is the optic lobes.

Imagine we are building a two story house in a flood plain. Sure, we could invest in fire-resistant materials, nuclear-grade shutters, and the kinds of steel they use to make sky-scrapers sway just right in the wind. But if we have a limited amount of money, or resources, we know we will be most successful if we address the most pressing demand of our environment and build a house on stilts, to withstand floods.

The ‘mushroom bodies’ are one area of a wasp brain, involved in learning, memory, and integrating information from the various senses. Previous to our study, scientists have shown that the relative size of the mushroom bodies (mushroom body volume as compared to total brain volume) increases with foraging behavior, the job of the workers. But scientists had also shown that maintaining social dominance via aggressive social interactions can have positive relative mushroom body size effects. This leaves us in a bit of a pickle:

Do queens, with their limited task repertoire but high social dominance, or workers, with their many tasks but decreased social demand, have larger relative mushroom bodies?

Histological section and photo credit to the O'Donnell lab and Drexel University.
Histological section and photo credit to the O’Donnell lab and Drexel University.

To answer this, we sliced wasp brains at a thickness of 14 microns – or 1/7 the thickness of a sheet of paper (see left). After setting the slices on glass slides, we stained the brain tissue a deep blue and photographed each slice – allowing us to measure the area of each region of the brain every 14 microns. By stacking all the slices on top of one another, we get a complete 3D image of the brain – and thus the volume of each of the pieces, since we know the thickness of our slices! Then, we could compare the relative volumes of our mushroom bodies in queens and workers of several different eusocial wasp species. You can see a 3D brain below.

Brain reconstruction credited to the O'Donnell lab and Drexel University.
Brain reconstruction credited to the O’Donnell lab and Drexel University.

 

Figure credit to the O'Donnell lab and Drexel University.
Figure credit to the O’Donnell lab and Drexel University.

So what did we find? In a nutshell:

  1. for 13/16 species, Queens had greater relative mushroom body sizes than their workers
  2. species with larger colony sizes saw larger differences in the relative mushroom body sizes of their queens and workers

These results are consistent with the idea that maintaining social dominance increases relative mushroom body investment – and adds the additional caveat that it seems to increase investment more than foraging.

 

The fact that larger colonies saw larger queen-worker differences in mushroom body investment may be a result of increasing ‘caste specialization’ – this is the idea that, as colonies get larger, the gap in work performed by the queen and the workers gets larger as well.

This is just one kind of question we can answer using histological techniques – we can also look at the effects of light, sociality and other behaviors, disease, body size, etc. on animal brains. All of this gives us a better understanding of how evolution works, and how different brain region sizes are selected for – or against – in different conditions.

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The Pesticide (maybe) in Your Coffee

Insecticides are a huge industry in the United States – whether we’re talking the small-scale can of Raid for your kitchen counter ants or the much larger scale agricultural market. But what if there was something already on your kitchen counter that might take care of those ants for you?

Erythritol is the main compound found in Truvia, a common artificial sweetener that many people use for baking or their morning Cup o’ Joe. Erythritol is a non-nutritive sugar alcohol – so while it sweetens your food, it can’t be digested by your body. The fact that it is sweet (like sucrose or other sugars) makes it attractive to insects such as Drosophila melanogaster, one species of small fruit fly that is a very common organism for scientific study. In this case, attractive can also mean deadly.

Figure 1. Drosophila melanogaster raised on food containing Truvia show decreased longevity. Truvia is red, Purevia is green, control nutritive sugars are dark blue, and other non-nutritive sugars are light blue. Graph shows percentage of living adult flies raised on food containing different nutritive and non-nutritive sweeteners over time. Note significant decrease in longevity of adult flies raised on food containing Truvia compared to other food.
Figure 1. Drosophila melanogaster raised on food containing Truvia show decreased longevity. Truvia is red, Purevia is green, control nutritive sugars are dark blue, and other non-nutritive sugars are light blue. Graph shows percentage of living adult flies raised on food containing different nutritive and non-nutritive sweeteners over time. Note significant decrease in longevity of adult flies raised on food containing Truvia compared to other food.

My lab published its first ground-breaking (what, can’t a girl brag?) paper on erythritol in PLoS One, entitled “Erythritol, a Non-Nutritive Sugar Alcohol Sweetener and the Main Component of Truvia, is a Palatable Ingested Insecticide” (Baudier et al 2014, before I arrived). As you can see on the graph to the left, flies that ate Truvia had significantly decreased longevity as compared to flies fed PureVia, Sweet ‘N Low, Sucrose, Equal, Splenda, or Corn Syrup. It’s a pretty drastic split. They also ran an experiment confirming which compound in Truvia was the killer compound (spoilers above: it’s erythritol).

Figure 6. CAFE experiments show Drosophila melanogaster actively consume erythritol over time. Upper graph shows prandial behavior of 10 individually housed flies fed 5% erythritol (red columns) and 10 individually housed flies fed 5% sucrose (blue columns) over a 6 hour period. Average intake per fly per hour is graphed for each treatment and separated by sex. Lower graph shows prandial behavior of 10 individually house flies when presented with a choice between 5% erythritol (red columns) and 5% sucrose (blue columns). Average intake per fly per hour is graphed for each treatment and is separated by sex. Note the significant increase in erythritol intake compared to sucrose intake for both sexes.
Figure 6. CAFE experiments show Drosophila melanogaster actively consume erythritol over time. Upper graph shows prandial behavior of 10 individually housed flies fed 5% erythritol (red columns) and 10 individually housed flies fed 5% sucrose (blue columns) over a 6 hour period. Average intake per fly per hour is graphed for each treatment and separated by sex. Lower graph shows prandial behavior of 10 individually house flies when presented with a choice between 5% erythritol (red columns) and 5% sucrose (blue columns). Average intake per fly per hour is graphed for each treatment and is separated by sex. Note the significant increase in erythritol intake compared to sucrose intake for both sexes.

 

 

 

But it doesn’t matter if erythritol kills the flies if they won’t choose to eat it! So Baudier et al. ran several CAFE experiments; one gave the flies access to both sucrose and erythritol of the same concentration and measured how much of each solution the flies ate over time (bottom graph of the figure to the right). As you can see, the red bars are much higher than the blue for both sexes – the flies, when presented with a choice, ate more erythritol than sucrose. If that trend were to hold in the wild, that would be very good news – the flies would self-select to eat the pesticide over other available foods containing non-lethal sucrose!

 

 

 

 

 

 

 

 

While this paper looked at a few more things, the last piece of the puzzle I want to talk about here is the effects of higher or lower doses of erythritol on fly longevity. The graph below shows that flies fed two molar erythritol all died within 48 hours! That’s incredibly fast-acting for a pretty tame pesticide.

Figure 4. Increasing concentrations of erythritol show decreased longevity in Drosophila melanogaster. Graph shows percentage of living adult flies raised on food containing different concentrations of erythritol. Control food is 0.5 M sucrose (blue line), 2 M erythritol (red line), 1 M erythritol (orange line), 0.5 M erythritol (green line), and 0.1 M erythritol (black line) were used. Note significant decrease in longevity of adult flies as concentration of erythritol is increased.
Figure 4. Increasing concentrations of erythritol show decreased longevity in Drosophila melanogaster. Graph shows percentage of living adult flies raised on food containing different concentrations of erythritol. Control food is 0.5 M sucrose (blue line), 2 M erythritol (red line), 1 M erythritol (orange line), 0.5 M erythritol (green line), and 0.1 M erythritol (black line) were used. Note significant decrease in longevity of adult flies as concentration of erythritol is increased.

I hear you saying: “Okay, Meghan, but this is all about flies. Didn’t you promise me that I could take out ants with this stuff?” A recent study by another lab has shown that erythritol works against Solenopsis invicta – the red imported fire ant that causes so much trouble in the United States and abroad. While that probably isn’t the species of ant you have on your counter, it is a promising sign that this stuff may just work on many different groups of insects – from flies to ants, perhaps beyond.

And because erythritol is found in a sweetener meant for human consumption it has been rigorously tested by the FDA and is known to be human-safe (though if you eat a lot, and I mean a lot, of it all at once it may have a laxative effect). In other words, you can feel better about spraying this stuff onto your countertops than Raid. Compared to neurotoxins and other nasty chemical pesticides, erythritol is also thought to be more environmentally friendly too!

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What I’m Working On

The last ‘What I’m Working On’ was all the way back in September 2016, and a lot has happened since then – so you probably deserve an update!

Research/Science Projects:

I’m still working on gathering data for the Eciton ant brain project (the only thing which did stay consistent between my last post and this one). It turns out that this project is going to be a really, really long one… we’ve got about 12 heads left to embed and slice and somewhere around 45 left to photograph and quantify. If you imagine that it takes a week to embed, 1.5 hours to slice each head, 6 hours to stain them all, 3 hours to coverslip them all, 1.5 hours each for photographs, and 2 hours each to quantify… basically, see you never! In addition to the Eciton spp project, we’re doing something similar with termites – I’m helping Susie finish up the tail ends of that project by taking photographs and embedding for her so she can be the master quantifier. Termite brains are funny (though not as funny as the spiders!).

While we’re waiting to hear back from the NSF on social spider brains, I’ve been doing some work for Sean on our super-secret pesticide project. Unfortunately, this is one I really can’t talk much about given that there’s patents and all kinds of legalese involved. Basically, I’m learning lots of things about lots of different arthropods and pesticides and animal husbandry it’s been really absorbing lots of my time in a (mostly) good way.

Photo by Arizona Board of Regents/ASU Ask A Biologist entitled ‘digging male’ (Attribution-ShareAlike 3.0 Unported), link through photo

I have a few other project ideas brewing as I begin thinking more about my thesis – some involving Centris pallida, a beautiful species of desert bee with really dimorphic male mating behaviors. I also have some developing interest in the brains of myrmecophilous beetles – parasitic beetles that live in ant colonies and utilize their resources. Hopefully, these more collaborative projects will start to develop soon, since I’m not currently in the position to collect these insects myself!

Writing Projects:

As my last post stated, I recently embarked on my Camp NaNoWriMo journey for April of 2017 and managed to write about 20,000 words of my novel-in-progress that I didn’t actually even conceptualize until April 2nd! April was a whirlwind month, but I feel pretty good about this story, and am excited to continue it when my life gets a bit more under control. The story features a journalist in England in the early 1800s, and her investigation into the Foreign Office and a prolific English assassin. I’ve had a lot of fun researching who the assassin kills, and making sure the timeline and locations fit – overall, this story is a set up for another that I’ve been working on for a long time and filling in all the background is really rewarding and intriguing.

I also managed to participate in the Creative Writing Collaboration since my last September post – but pretty much everything else has been at a standstill with graduate school at the forefront of my mind.

And that’s what you missed on… Glee?

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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.

LEAD Technologies Inc. V1.01
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.

spider
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.

ssd
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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New Years Goals: 2017

With the New Year comes new year’s resolutions – which are typically a bit of a mess, in my opinion. Oft hyped but rarely completed, resolutions are something you find on a scrap piece of paper three years later and realize you (maybe) achieved one of the eight things on your list.

Nevertheless, as an eternal optimist, I make resolutions every year without fail and, usually, one or two of them happen. As I get older, my resolutions have gotten more tailored to my actual desires (no ‘run a marathon’) and less numerous – I think, more reasonable overall.

So here are my, hopefully modest, new year goals, not resolutions. Next year, I’ll hopefully be able to reflect back on these and feel like I achieved something significant – just like in my 2016 Wrap Up post.

  1. Finish gathering data for the Eciton army ant project
  2. Maintain an active blog presence here, with at least one post a week
  3. Develop my board game idea into a reality
  4. Publish three more poems
  5. Have my committee and thesis ideas outlined for my PhD

What’s on your list for 2017? How do you feel about New Years Resolutions/goals? Let me know in the comments and thanks, as always, for reading.

 

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