Effects of mannitol ingestion on adult fruit flies

My very first, first-author publication (coauthored with the incredible Katherine Fiocca) came out last month in PLoS One (an open access journal, which means anyone can view the article for free, found here). The article is titled “Mannitol ingestion causes concentration-dependent, sex-biased mortality in adults of the fruit fly (Drosophila melanogaster)”; I’m excited to have the opportunity to share some of the main findings of this work with all of you! But first – what even is mannitol?

Image result for mannitolMannitol is a “sugar alcohol” (don’t worry, it won’t get you drunk). It’s found naturally in fruits and fermented products and (like erythritol and other sugar alcohols) is often used as a low-calorie sweetener. Basically, it tastes sweet to your tongue without increasing your blood sugar levels dramatically. #lifehacks Mannitol is also cool because it’s used medically to reduce pressure around the brain following traumatic injury.

It turns out that when you feed mannitol to different groups of insects you get vastly different responses. This is particularly interesting because mannitol is naturally occurring in some of the stuff these organisms might regularly eat (especially flies that eat a lot of rotting fruits). In some insects, eating mannitol is lethal – in others, mannitol is a carbohydrate they can break down and use for nutrients! Crazy.

Madboy74 CC0 (Wikipedia)

In fact, even within a species mannitol seems to have varying effects. We were interested in following up on a previous study from our lab that showed, at one concentration, that mannitol is more lethal to female than male fruit flies. We aimed to replicate this sex-biased mortality effect, and see if it would be consistent across concentrations (dose-dependence provides strength to a cause-and-effect relationship). We also noted in the previous data set that flies housed in vials with the opposite sex might have been dying more than flies housed in single-sex vials and wanted to follow up on this observation more carefully. Finally, we wondered if this sex-biased effect was consistent at the larval (developmental) stage – or only adults.

Ultimately, we wondered – why is mannitol sex-biased? Is this effect consistent across concentrations? Across life stages? Is it consistent across culturing (single vs. mixed sex conditions) and mating conditions? Understanding the answers to these questions can begin to help scientists understand the mechanisms behind mannitol’s lethality – and perhaps why it affects different insects in different ways – providing us with a tool for studying the biological pathways that underpin insect development, reproduction, and nutrition.

Result 1: Concentration-Dependent, Sex-Biased Adult Mortality

Figure 2 in the paper; stars indicate a difference in survival between males and females.

Mannitol’s lethality was found to be concentration-dependent for both adult males and females (i.e. the more they eat, the faster they die); but females died at lower concentrations and faster than males. However, this was not true in larvae – male and female larvae saw equally reduced survival on mannitol foods! This indicates that the cause of mannitol’s sex-biased lethality is not genetic (i.e. it’s not inherently to do with being a female fruit fly). Instead, it’s something about being an ADULT female fruit fly – perhaps, something to do with the demands of reproduction.

Adult female fruit flies can lay 60 eggs a day after only mating once. Producing all those eggs requires a lot of protein – much more than it takes for male fruit flies to make sperm. To get all this protein, adult females are constantly eating, and when there’s mannitol in the food, this increased food consumption could lead to increased self-dosing with mannitol and thus increased mortality. To support this hypothesis that increased eating might underlie increased female fly mortality, we tested two things:

  1. Do female flies actually eat more than male flies?
  2. If female flies are not mated (and thus lay fewer eggs and have lower reproductive demands), does that increase their survival compared to mated female fruit flies?

Result 2: Differences in Food Consumption between Male and Female Flies

To measure how much flies eat, we put liquid food in a tube and (over five hours) measured the change in volume of liquid food per tube (compared to evaporation controls with no flies). Vials of male flies ate significantly less mannitol food than vials of female flies, showing that female flies do eat more food per hour than males.

Result 3: Mortality Depends on Mating Status and Culturing Condition

Fig 5 in the paper; letters that are different from one another indicate a significant difference in survival. Longevity is just another way of viewing survival (instead of average # dead, it’s average # of days survived).

Is female fly survival in mixed-sex vials lower than female fly survival in single-sex vials because the females in these vials are mated – or because male flies are present? To answer this, we tracked survival in vials of unmated females housed only with other females, vials of females that mated once but were then housed only with other females, and vials of mated females and males together. For female flies, mating with males once reduced longevity on mannitol foods, even if they were housed with only other females after mating – indicating that the increased demands of reproduction (leading to increased food consumption) may be responsible for reductions in female survival.

What it means?

Overall, we found that mannitol’s sex-biased effects on fruit flies are not genetically-based (no larval stage sex-biased mortality). Instead, like most other drugs, lethality is concentration-dependent and based on the ‘dose’ the individuals take. In the case of female flies, eating more food to meet the protein demands of egg laying means they dose more, and die more, than males. Preventing them from mating increases their survival, by reducing the nutritional demand of laying eggs. Understanding this mechanism of sex-biased mortality may help us figure out why different species, and different individuals within each species, are differently impacted by mannitol.

Next steps?

More follow-up work on larvae (which had delayed development on mannitol foods) would be a great future direction (and stay tuned…). Additionally, while we know what’s causing the sex-bias in mortality, we still don’t understand the cause of mortality itself. There’s some evidence that polyols cause flies to regurgitate to a lethal extent and dehydrate, which fits with our observation of mannitol encrusted on dead fly mouths. Mannitol could also be accumulating in the body cavity if it cannot be broken down, starving the flies by taking up all the available space for nutritive food. More work needs to be done to understand how mannitol acts as a lethal agent to adults, which will lead to a better understanding of how mannitol affects different insects SO differently!

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2019: Quarter Two

Amazing undergraduates at ESA EB 2019

In my Oct-Dec update in 2018, I suggested that winter coming might be ‘restful’. As anyone who has done a PhD should know, and as I am beginning to learn, there is no time in an academic’s life that could be considered restful.

Still, my Oct-March went really well for being such a whirlwind. As far as some research updates, I have three first author papers current in prep (one in review), another three papers on which I am an author in prep (one in review), and several presentations under my belt – including an invited talk at Penn State Schuylkill as a part of their faculty research seminar. My Entomological Digest talk at the ESA Eastern Branch meeting won second place (!) and three of my undergraduate students gave posters/presentations, one of whom came in second in the BS/MS poster competition. The Social Insects in the North East Regions conference that I organized went off without a hitch – and it was so exciting to get to catch up with old and new science friends. I also got the first of my thesis data, which was relatively encouraging, and applied for four grants to help fund the research (I’ll hopefully be hearing back soon).

In addition, I’ve made some real strides in my ‘service’ world as Biology Graduate Student Association President – which is why this blog and some of my science communication has taken a small backseat. I’ve begun the process of organizing my department’s first scientific retreat (as a collaborative initiative with faculty) since I started my PhD. I’ve cleaned up and organized our student community spaces, including getting a lending library running, and pushed the Graduate Student Association at our school to set up an infrastructure grant program where graduate student organizations can apply for funds to improve their spaces and purchase equipment (microwaves, furniture, etc). We’ve started a website for our organization, and are putting together a welcome package with information for newly accepted students.

We also worked with our Graduate Program Committee, Department Chair, and Graduate College Dean to get a vacation policy in place for graduate students in our department. Finally, I feel I’ve made some strides establishing open lines of communication between some of the faculty and students in our department – and between students in different labs and cohorts. While these are not accomplishments that will show on my CV, being in a more collaborative and happier department matters to my personal sense of morality – I like to leave every community healthier than when I found it.

So what about moving forward? My big goals for this coming quarter (April to June) are to:

  1. Finish the review process for my two first-author papers on mannitol and D. melanogaster
  2. Finish gathering and writing up my erythritol data on ants
  3. Finish gathering and analyzing data on Centris pallida neuroanatomy
  4. Generate new materials for Bio 208 course revisions with Dr. Gurney
  5. Gather data on Centris pallida thermal tolerance
Me, in the field having a successful bee-catching day.

I’m really excited to be heading out to Arizona for my field season on April 3rd, which will give me some excellent time to catch up on reading and writing, while also getting some wonderful thermal data on my lovely Centris pallida bees!

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The Fourth Quarter: Checking In

I’m excited for quarter four because it’s going to be comparatively restful – winter hits the northeast and so I get a bit of a break from fieldwork and time to process my specimen! To me, quarter four looks like the time to wrap up a lot of loose ends.

EPiC 2018 organizing committee and plenary speakers, left to right: Meghan Barrett, Alexandra Brown, Rob Kulathinal, speaker Paul Turner, speaker Jason Weckstein, Nate Shoobs, and Rohini Singh.

Before I move on to the ‘big goals’ I have for quarter four, let’s celebrate what happened in quarter three. First, the EPiC conference (Evolution in Philadelphia) was a huge success with 108 attendees from 24 different university and 62% of the attendees being early career researchers. 29 presentations, 2 plenaries, and 25 posters later, we learned a lot about the amazing evolutionary science going on in and around Philly!

In June, I was able to travel to Cienfuegos, Cuba for a month with four amazing undergraduate students and Dr. Dane Ward to study Melipona beecheii stingless bees as part of my Eva Crane Trust grant (Dr. Ward is my Co-PI). We presented our findings in four posters at Drexel’s Students Tackling Advanced Research showcase in August and are hoping to flesh out at least one of those into a publication and a return trip. I was able to present my publication on wasp brains at the International Union for the Study of Social Insects Conference in Guaruja, Brazil in August which was an absolute blast. I also worked at my field site in NY at the Huyck Preserve and at SUNY Geneseo, studying the grass-carrying wasps that moved in to my bee nests (nope, no bees. It’s cool, nature). I was able to do some outreach – including some podcasts (PhDrinking, School of Batman), a Scientist Saturday at the Academy of Natural Sciences, and public and high school lectures at the Huyck Preserve. All in all, it was a busy quarter and there was a lot to celebrate!

For this final quarter, my goals:

  1. Publication Proliferation – Finish writing the first drafts of my first two first-author publications – this will be a big challenge, since I’ve never written my own paper before!
  2. Quality before quantity – Quality control my data on Centris bee ovaries and Melipona morphology and send it off to my co-authors to get their thoughts.
  3. Conference Coasting – Plan the Social Insects in the North-East Regions Conference for December 2018.
  4. Classroom Antics – I’ll be taking a class for my Masters on Theories of Individual Cognition in STEM Education and an online Morphology Course.
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Drexel Profile on Research and Teaching

Practice Teaching!

My university just published a profile on my teaching/mentorship style and research over the past two years! You can find this fun, informative piece here:

https://drexel.edu/now/archive/2018/September/PhD-Candidate-Finds-Place-for-Entomological-Research-Teaching-Goals-to-Grow-at-Drexel/

Enjoy!

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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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