This is a relatively older publication (2018) that I co-authored with my adviser, Dr. Sean O’Donnell, and lab members Dr. Susan Bulova and Katherine Fiocca, titled “Size constraints and sensory adaptations affect mosaic brain evolution in paper wasps (Vespidae: Epiponini)”. By looking across paper wasp species, we can see really big and really small wasps – in fact, the biggest species in our study was 25 times the size of the smallest!
Does getting so tiny have an impact on brain size – or do brains just scale 1:1 with the wasp’s body size? Do different regions of the brain stay relatively larger as body size shrinks – perhaps because they’re more important? These are the questions we set out to address in our study.
We looked at several different regions of the brain, represented in this 3D reconstruction to the left. In light blue are the optic lobes which bring in visual information from the eyes. In dark green are the antennal lobes which bring in chemical and other sensory information from the antennae (think of antennae like a wasp’s nose and fingertips rolled into one). We also looked at the mushroom bodies (light green and dark blue) which integrate sensory information and are centers of learning and memory. Everything else we’ll just call ‘rest of brain’ (ROB). If you add all those pieces together you get total brain volume.
The first thing we found was expected – if you have a larger body (here, measured by head volume) then you have larger total brain volumes (top graph). But, we saw a different pattern when we looked at relative brain:head volume (bottom graph). Basically, however much space your brain takes up inside your head gets increasingly larger as your head gets smaller – so, smaller wasps have bigger relative brains!
This relationship is seen all over the animal world and is known as Haller’s rule; within a group of related organisms, smaller-bodied species have relatively bigger brains in their heads. This could be because you still need a certain number of neurons (and thus a certain size brain) to be able to behave like an organism of that ‘type’.
The coolest thing, however, is that not all regions of the brain change at the same rate. As head size got smaller, the relative proportion of brain volume spent on both antennal lobes and mushroom bodies sharply decreased – but this was not the case for optic lobes. This suggests that wasps may be prioritizing bringing in visual information over other processes/cognitive needs as body size decreases and brain space gets limited. We did find a cool outlier to this pattern, however, in the nocturnal wasp Apoica pallens.
Apoica wasps are nocturnal – so they do a lot of their flying at night, in a really low-light environment. These wasps had very small relative optic lobes for their size – but a relatively larger area of the mushroom body dedicated to processing and integrating visual information. This ‘break’ of the trend suggests that environment can have a big impact on brain resource allocation patterns. In addition, it suggests functional differences for these two pieces of the brain in how they help wasps deal with visual information; the optic lobe may not need to be as large as for day-time wasps because there’s less ‘light’ information to bring in… but processing that information is demanding because its low-light and so the mushroom body collar region is relatively larger than in day-time flying wasps.
Time flies when you’re having fun, and this April-June was no exception. Between heading to the field in AZ for a month to work on my C. pallida thesis work and my trips to NY to check in on my Isodontia wasp project, the months absolutely breezed by me. Particularly incredible was the graduation of my first five undergraduates from the lab; we held a small going away party for them and the two students who worked with my partner in PhD, Katie Fiocca. I can’t wait to see all the amazing things they go on to achieve!
For some quick updates on last quarter’s goals:
Finish the review process for my two first-author papers on mannitol and D. melanogaster: paper one is published and paper two is in review!!
Finish gathering and writing up my erythritol data on ants – While the paper is nearly finished being written up, we are waiting on a few more choice bits of data to come in. Winter extended later than I expected and we didn’t really start finding bigger colonies to test until the end of May.
Finish gathering and analyzing data on Centris pallida neuroanatomy – I did finish and analyzing all the data I intended to collect when I wrote this goal… but the analysis pointed to some additional interesting data I could collect so… here we go with that!
Generate new materials for Bio 208 course revisions with Dr. Gurney – finished! I am now in the midst of trying out these new materials in the classroom and writing a short paper up on a teaching tool we generated for the class.
Gather data on Centris pallida thermal tolerance – Done!
Overall, not a bad term. This summer, I’m implementing new course material for Applications in Biology II and also teaching a new class: Cell, Molecular, and Developmental Biology II. Because of this, my research goals are a bit less lofty:
Finish the histological sectioning of my new C. pal work
Finish making the aperatures for my C. pallida trip to IL
Finish the erythritol-ant draft and get it submitted
And let’s not forget the other ‘biggie’ coming up – my wedding! Coming to PA in October of 2019. Weddings are a tremendous amount of planning, and I anticipate the months right before will be even more harried.
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?
Mannitol 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.
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
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:
Do female flies actually eat more than male flies?
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
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.
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!
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:
Finish the review process for my two first-author papers on mannitol and D. melanogaster
Finish gathering and writing up my erythritol data on ants
Finish gathering and analyzing data on Centris pallida neuroanatomy
Generate new materials for Bio 208 course revisions with Dr. Gurney
Gather data on Centris pallida thermal tolerance
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!
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.
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:
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!
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.
Conference Coasting – Plan the Social Insects in the North-East Regions Conference for December 2018.
Classroom Antics – I’ll be taking a class for my Masters on Theories of Individual Cognition in STEM Education and an online Morphology Course.
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:
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!
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 smallerbrains (Figure 1b illustrates this well).
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.
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?
Carpenter Contemplation, part 2 – Returning to New York to see how my nest boxes are doing and potentially gather some genetic and cognitive data!
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.
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…
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!
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.
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.
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.
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.
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.
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.
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.
Centris pallida are known for their vibrant, yellow-green eyes and pale fuzz as they buzz around desert palo verde – females are also known for the lovable ‘chaps’ on their rear legs which help them gather pollen.
C. pallida are some of the best bees at maintaining a stable body temperature; they are often found within 2 degrees Celsius of lethal overheating!
C. pallida females dig long tunnels to lay a single egg in a wax-lined cell, 8-10 cm under the dirt. These cells are provisioned with a soupy, orange-colored bread made of pollen and nectar. After sealing the cell, the mother fills in the whole tunnel with dirt and starts over for her next egg. Females often aggregate in the same area, collectively laying hundred of eggs in a relatively small area.
In early spring, the next generation of adults emerge and aggregate by the thousands to mate. Males emerge first, and begin searching the ground for females. Large males can smell females underground as they start to dig themselves out of their cells and will fight with one another to help dig her out and mate with her. Small males can’t afford to brawl so they employ a sneakier strategy! Hovering on the outside of the aggregation, they wait for escaped females to mate with instead.
Sources and Further Reading:
A friendly webpage written by C. pallida expert, John Alcock that summarizes his papers listed below.
Alcock J, Jones E, Buchmann S (1976). The Nesting Behavior of Three Species of Centris Bees (Hymenoptera: Anthrophoridae). Journal of the Kansas Entomological Society, 49: 469-474.
Alcock J, Jones E, Buchmann S (1976). Location before emergence of the female bee, Centris pallida, by its male (Hymenoptera: Anthrophoridae). Journal of Zoology, 179: 189-99.
Alcock J, Buchmann S (1985). The significance of post-insemination display by male Centris pallida (Hymenoptera: Anthophoridae). Z. Tierpsychol.,68: 231-43.
Alcock J (1976). The social organization of male populations of Centris pallida (Hymenoptera, Anthophoridae). Psyche, 83: 121-31.
Alcock J, Jones C, Buchmann S (1977). Male mating strategies in the bee Centris pallida Fox (Anthophoridae: Hymenoptera). The American Naturalist, 111: 145-55.
Chappell M (1984). Temperature regulation and energetics of the solitary bee Centris pallida during Foraging and intermale mate competition. Physiological Zoology, 57: 215-25.
Gilliam M, Buchmann S, Lorenz B (1984). Microbial flora of the larval provisions of the solitary bees, Centris pallida and Anthophora sp. Apidologie, 15: 1-10.
Roberts S, Harrison J, Hadley N (1998). Mechanisms of thermal balance in flying Centris pallida (Hymenoptera: Anthophoridae). Journal of Experimental Biology, 201: 2321-31.
Roberts S (2005). Effects of flight behavior on body temperature and kinematics during inter-mate male competition in the solitary desert bee Centris pallida. Physiological Entomology, 30: 151-7.