Friday, March 3, 2017

Secret Science Club Post-Lecture Recap:Formidable Formicidae

Last night, I headed down to the beautiful Bell House, in the Gowanus section of Brooklyn, for this month's Secret Science Club lecture featuring myrmecologist (how I love that word), evolutionary biologist, and adventurer Dr Corrie Moreau of Chicago's Field Museum of Natural History.

Dr Moreau (could there be a more perfect name for a biologist?) began her lecture with a note of gratitude toward her subjects, noting that ants have taken her around the world, and that tropical fieldwork is tough, fun, and rewarding. She learned how to do rainforest 'canopy work' in French Guiana, and her travels sometimes involved unintended consequences, such as dealing with tropical illnesses. While her collecting of specimens was typically above-board, involving extensive dealings with customs agents, she once smuggled a tick out of Uganda... in her nose (this seems to be a trend). She underscored the importance of documenting biodiversity by noting that habitat degradation is affecting many ecosystems. Dr Moreau chose to study ants because they are beautiful and diverse, with approximately thirteen-thousand species known to science, with estimates of unidentified species being twice that number. Notable ant varieties include the fungus-growinng ants, the army ants, which can be used as emergency sutures in the field, and the honeypot ants, which include two convergently-evolved lineages, one in Mesoamerica, one in Australia. Dr Moreau noted that the honeypot ants live in environments which have boom-or-bust resource cycles, so 'repletes' store liquid resources until they are needed. She offered this piece of advice- eat the golden repletes, which are filled with nectar... the dark ones are often filled with the remains of rotting carcasses. Dr Moreau then covered the Dracula ants, which feed prey items to their larvae, then poke holes in them in order to drink their hemolymph, resulting in heavily-scarred larvae.

After this introduction to some of the more outré ants, Dr Moreau then discussed the processes that generate biodiversity. Some branches of the ants' evolutionary tree have more species than others, and some regions of the globe harbor more species of ants than others. Some traits have evolved numerous times in different ant lineages. Speciation can occur due to geographic separation of populations. Determining the pace of evolution, whether fast or slow, depends on studying the fossil record. One crucial factor in evolution is symbiosis- organisms evolve together. Dr Moreau quoted her doctoral advisor, E.O. Wilson, who characterized ants and other invertebrates as "The little things that run the world." Then she amended this observation by noting that microbes are the little things which run the little things which run the world.

Dr Moreau then covered variety of symbiotic relationships which ants have with other organisms. There are ants which 'farm' scale insects for the honeydew they secrete. Other ants have a mutualistic relationship with acacia trees- the trees provide food and shelter for the ants, which defend the trees from herbivores. Also, there are ants which have symbiotic relationships with fungi, both beneficial and horrifically deleterious. Ants don't exist in isolation, when studying them, researchers need to think about other organisms as well.

Ant evolution and the evolution of the flowering plants are inextricably linked- although ants aren't pollinators, some groups of ants exploded evolutionarily with the spread of the angiosperms. Many ants shifted from predation to plant-based diets. Ants play an important role in seed distribution, with certain plants having evolved structures called elaiosomes, protein-rich and fatty tissues which are attractive to ants. After eating the elaiosomes, the ants discard the rest of the seeds in their nitrogen-rich middens, far from the mother plant.

With thirteen thousand ant species known to science, a phylogeny of ants is needed to understand evolutionary relationships and dispersal. Fossil ants are not uncommon- ant fossils are typically of insects trapped in amber and insects being compressed in fine sediment. To form a decent paleontological record, at least forty-three fossils are needed for minimum calibration points. The are extant ant fossils from one-hundred million years ago on, but there seems to be an explosive radiation of ant genera in a narrow window, about thirty million years ago- this ant invasion explosion occurred when the ants rode the wave of flowering plants.

There is a latitudinal gradient in ant species richness, with the tropics harboring more species than colder regions. Dr Moreau indicated that there are two models to explain the biodiversity of the tropics- the cradle model and the museum model. The cradle model posits that evolution occurs more quickly in the tropics, that new species evolve in the tropics more frequently than in higher latitudes. The museum model posits that older evolutionary lineages tend to survive better in the tropics, that ancient forms persist. Put succinctly, in the cradle model, the tropics are species pumps, in the museum model, they are stable places in which species can hold out for a long time. The first ants evolved about one-hundred and forty million years ago. The configuration of Earth's continents was different then- subsequent plate tectonics affected the distribution of ants. The greatest diversity among the ants, the most endemic genera and the most species, is in the Neotropics. With evidence of the survival of older forms and the diversity of novel forms, it would be safe to characterize the tropics as both cradle and museum.

Ants are efficient at exploiting novel ecological niches. With the evolution and spread of flowering trees, ants were able to spread into the forest canopy (conifers aren't a rich source of exploitable resources). The evolution of herbivory among the ants coincided with the co-evolution of ants and endosymbiotic bacteria. Ants provide an excellent opportunity to study the diversity, distribution, and influence of gut bacteria. While ants harbor diverse bacterial communities, the nitrogen-fixing Rhizobiales are common among plant-eating ants, which feed at low trophic levels. The highly predatory army ants do not need nitrogen-fixing symbionts. Herbivory necessitated bacterial symbionts, which are not distributed equally throughout the ants' evolutionary tree. In the co-evolutionary process, more closely related ants have more closely related bacterial symbionts.

Dr Moreau then gave us an overview of the gastrointestinal anatomy of an ant, with an emphasis on the locations in which bacterial symbionts are found. Dissections of ants were conducted, and the bacteria in the mouth, the crop (from which ants can regurgitate liquid for other ants), the midgut, and the hindgut (the leg was also sampled as a 'control'). All of the dissected individuals had similar bacterial flora in their midguts and hindguts. The bacterial communities of the ants were dictated by what the ants ate. The herbivorous turtle ants have co-evolved with their gut bacteria for over forty-five million years. The bacterial communities of various ants- the herbivorous ants, the highly predatory army ants, the not-entirely predatory bullet ants- have to be compared and contrasted. In one particular project, Costa Rican bullet ants were collected, and their gut bacteria were studied.

After this fantastic overview of ants and their bacterial symbionts, Dr Moreau shifted the topic of the talk to the importance of science outreach, and the diverse tools needed to share scientific knowledge. Commitment to science necessitates outreach and popularization. Scientists have to convey to people how important science is to their lives. In order to combat the stereotypical view people have of scientists, scientists have to meet with people. Dr Moreau put together an exhibit called The Romance of Ants to chronicle her life and career in graphic novel form. The theme of the exhibit is that everyone is a scientist at heart.

The lecture was followed by a Q&A session. The first question involved the evolution of eusociality in the hymenoptera- eusociality evolved several times among the different branches of the hymenoptera- there are non-eusocial bees and wasps as well as eusocial ones. Here's an overview of eusociality and genetics (ants, bees, and wasps are haplodiploid- males are born from unfertilized eggs, so sisters are more closely related to each other than they are to the mothers or to any potential offspring). Some bastard in the audience asked about the antibiotic properties of ants- ants have a metaplueral gland which produces an antibiotic fluid which protects against bacterial or fungal pathogens- ants have a lot of associated bacteria and fungi. Dr Moreau then pointed out that the bastard had attended all-but-one of the Secret Science Club lectures, which caused said bastard to blush in a most incandescent fashion, luckily the beacon-like effect wasn't so apparent in the darkened Bell House. The bastard then asked Dr Moreau a hypothetical about using ants to treat a cut in the field- while ant, uh, antibiotics aren't a panacea, the use of army ant heads as sutures would definitely be in the tropical pharmacopeia. Another attendee asked about the ant population of New York- after a joke about hipster ants in Brooklyn, Dr Moreau noted that fungus-growing ants survive on Long Island, tending to build their colonies under power lines. Another question concerned invasive ants- out of the one-hundred worst invasive species worldwide(PDF), five are ants. Invasive ant species can devastate ecosystems and outcompete native species. They thrive in locations disturbed by humans. Ants have many characteristics which make them good invaders, such as the ability to exploit novel ecological niches. In the case of the Argentine ant, the insects form mega-colonies which do not compete- offspring of different queens will interact cooperatively, probably due to the ants passing through a narrow genetic bottleneck, so all of them are closely related. Another questioner asked when eusociality first appeared in the Tree of Life- the termites, which can be likened to eusocial cockroaches, were the first eusocial insects to evolve and there are even fungus-farming termites. How do ants communicate? Ants communicate through scent- they have glands which produce pheromones, which are chemical signals to other ants. How do researchers determine fossil ant affinities? Some fossil ants have unique morphologies, but many fossil ants are similar to modern genera- younger specimens look more similar to modern ants than older ones. Regarding behavior, every ant colony acts as an individual, each worker ant can be likened to a cell in a multicellular animal. This breaks down in the case of the invasive Argentine ant supercolonies, in which neighboring colonies are not recognized as different from each other. Regarding dissection, ant specimens are handled with jewelers' forceps, though Dr Moreau joked that a common refrain in the lab is, "Don't talk to me on dissection day!" Dr Moreau noted that there is ant-specific citizen-science- volunteers can catch ants in their backyards and send them to the lab. Dr Moreau then discussed the various body forms among ant species, and while most ants produce small workers and big soldiers, there are about ten species which produce super-soldiers, and that the 'super-soldier' gene can be switched on in individuals to produce these oversized soldiers... super-soldiers can be produced in the lab. Regarding the acquisition of gut bacteria, every time an insect sheds its exoskeleton, it sheds its respiratory and digestive invaginations, and loses gut bacteria. New bacteria are obtained from other ants through oral/anal trophallaxis.

Dr Moreau ended her lecture by stating that she is unwilling to let go of field research... She is a typical field biologist, she likes looking at live things as much as studying dead ones. She joked that some of her keenest observations were picked up lying on the ground picking up chiggers and ticks while studying her subjects.

As an individual who tends to prefer biology to the other sciences, I have to say that Dr Moreau really hit a grand slam with this lecture. She imparted important knowledge about some of our most interesting fellow denizens of Earth with passion, she outlined a model for communicating scientific knowledge to the general public, and she was very entertaining. I like to talk about the 'Secret Science Sweet Spot'- that combination of hard-science lecture, adventure narrative, and advocacy that characterize the best of the lectures, and this lecture hit on all of those cylinders. Also, Dr Moreau was in town for a conference, and all-around good-guy Dr Simon Garnier was the person who told her about the SSC, inspiring her to lecture in Gowanus. Dr Garnier attended with a bunch of students from his lab, and there were a gaggle of entomologists hanging out in the beautiful Bell House. In an informal discussion over beers, I had a talk with a young entmologist about haplodiploploidy and eusociality, and he mentioned that the thrips, which are haplodiploid, also have some eusocial species. Surrounded by entomologists, I made a joke about these entomologists forming a 'hymenoptera gang' and zooming along the highways and byways on Vespas. Good times, nerding out with great people!

Kudos to Dr Moreau, Dorian and Margaret, and the staff of the beautiful Bell House. Also, high fives to all of the assorted biologists in attendance, you are all doing great work.

Here's a short video of Dr Moreau lecturing on the evolution of ant gut bacteria:

Here's a longer video featuring Dr Moreau lecturing on biodiversity and the evolution of ants:

Dr Moreau also has several videos on the Field Museum's Brain Scoop YouTube channel. If you are going to get stuck in a time-sink, I can think of few better ones than the Brain Scoop.

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