Bill and TED's malarial adventure

It's rather old news by now, but I wanted to bring your attention to the events at last week's TED conference. Bill Gates gave a talk that centered largely on education and socioeconomic patterns in the United States. He said plenty about teaching excellence and the impact of talented teachers on their students. He drew a number of conclusions, some I agree with, and some I would argue about. It's a rich subject, with a great deal of controversy, and high very high stakes. However, the headline-stealing event happened early in the talk when he was discussing malaria. As he opened a jar of mosquitoes in the auditorium, he said "there's no reason only poor people should have the experience." In the very next moment he assured the audience that those mosquitoes were not infected with malaria, and no one seemed panicked about contracting a dreaded disease. The only discomfort in the room seemed to stem from the knowledge that the attendees of the conference were part of a privileged society that spent more money on research and medicine for baldness than for malaria. It often seems to me that people who are out "raising awareness" might spend their time more productively "raising money." But Bill Gates has done that and through the Bill and Melinda Gates foundation continues to support work on a range of neglected diseases, including malaria. So I applaud the mosquito stunt. I wish there were an analogous act that could drive home that shameful fact mentioned by Gates in his talk that a poor person in the U.S. is more likely to go to prison than to earn a college degree.

snail tentacles

As I mentioned in a recent post, ants that are infected with the trematode, Dicrocoelium, are compelled by the presence of the parasite in their brains to march to the top of a blade of grass, bite down, and hang on. This behavior would seem to make it more likely that the fluke will be eaten by a grazing mammal like a cow or sheep, which needs to happen if the parasite is to complete its life cycle. It looks like a fascinating adaptation on the part of the parasite to modify the behavior of its host allowing the parasite to be transmitted more readily to the next host. Ideally, there would be data to document that the parasitized ants are eaten at higher rates than are uninfected ants. But this is not the ideal system in which to gather that kind of data. In fact, even though the manipulation of host behavior by parasites is not considered to be a controversial phenomenon, rigorous studies that are well supported by behavioral data are not as common as you might think. One of the best is Janice Moore's work on birds, pill bugs, and their acanthocephalan parasites, a system I also mentioned earlier. Moore discusses several other examples in her book, Parasites and the Behavior of Animals.
One of the earliest suggestions that parasites might modify the behavior or appearance of their host came from Wesenberg-Lund in 1931. He was studying another trematode, Leucochloridium. In typical trematode fashion, a snail serves as the initial host and a vertebrate, in this case a bird, serves as a final host. There is no arthropod (no insect or crustacean) anywhere in the life cycle, which is a challenge for the parasite, as the bird prefers insect prey and doesn't typically eat snails. To get itself from the snail into the bird, so the story goes, the fluke moves into the snail's tentacles, making them look like colorful, wiggly, and oh-so-tasty caterpillars, which the bird happily gobbles up, thus infecting itself. Alas, experimental confirmation of this tale is lacking. There haven't even been any reports of natural occurrence of predation by birds of these parasitized snails in the wild. But the behavior is pretty cool anyway, and you can be the judge regarding its adaptive significance and consider what sort of evidence would convince you that the parasite is modifying the snail host so that transmission to the bird is improved. As my father, my initial teacher in skeptical thinking, would say, "interesting if true."

California dreaming

I was supposed to fly out to visit family in California for the holidays, but the nor-easter that blew through Sunday has adjusted our schedule rather dramatically. Our flight's been postponed 5 days. On the bright side, I love the white Christmas in Maine. It's also Nina's birthday, and Isaac Newton's, too, so there's much to celebrate. Unfortunately, my husband traveled a few days earlier to spend extra time with his mom and to work on a paper with a colleague in San Diego, so he's already been out there for some time. I keep reminding myself that we spent the first year of our marriage on separate coasts, while I was finishing grad school and he was starting up at COA. This helps put one Christmas 22 years later into perspective.

ant brains

Winter break and holiday plans aside, I'm already thinking about the parasites tutorial I'll be teaching next term. Carl Zimmer's book, Parasite Rex, makes the case very persuasively: parasites are so much more than grotesque little footnotes in life's pageant. They are major players in the ecology and evolution of many species. Of course, in addition to their ecological and evolutionary heft, many of them exhibit some really weird and creepy lifestyles. One of the most disturbing tricks that some parasites have developed is that of mind control. An infected host's behavior is altered by the parasite in a way that increases the ability of the parasite to complete its lifecycle. In many cases, parasites gain access to the final host, where reproduction occurs, by first infecting an intermediate host that is later eaten by the final host. Any behavior by the intermediate host that makes it more likely to be eaten benefits the parasite (but not the intermediate host, of course). Some parasites are able to manipulate theirs hosts, actually causing them to engage in reckless behavior. Pill bugs harboring acanthocephalan parasites may spend more time in dryer places and even prefer walking around on whiter surfaces.  This may not sound like especially exciting risky behavior, but compared to the safety of  the dark, moist leaf litter, where healthy pill bugs prefer to be, the infected pill bugs are more easily seen by birds, which gobble up the pill bugs and serve as the final host of their parasites.
Mind control of ants by liver fluke parasites has been colorfully presented in this video.

Endangered Marine Invertebrate

A physicist friend recently sent me a link to 20 strange and exotic endangered species, saying that the list was "sufficiently yucky and biological" to appeal to me, and it got me thinking about endangered marine invertebrates. The white abalone is the only marine invertebrate that's been listed as endangered under the Endangered Species Act. "Only one? Those marine inverts must be in pretty good shape," you might be tempted to surmise. But you're more sophisticated than that, so you probably wouldn't. There is a long list of assaults on marine invertebrate species: habitat loss, overharvesting, invasive species, disease outbreaks, pollution, global climate change, and more. Most marine invertebrates just haven't been studied in sufficient depth to be listed as endangered, and there are only a handful that are considered to be "threatened" or "species of concern," which are lesser categories than "endangered." To read more about threatened and endangered marine species, you can find plenty here.
White abalone have suffered dramatically from overharvesting. Here's the somewhat oversimplified ecological tale: Usually as population size goes down, individuals enjoy enhanced rates of growth and reproduction, because competition between individuals decreases as populations shrink. But there's a limit. When populations get extremely small (and what's extreme will vary with the ecology of each species), individuals may suffer reduced rates of growth and reproduction. If you do better with some neighbors around, the benefits of reduced competition that come with a shrinking population ultimately lead to other challenges, the most obvious being finding a mate. The general phenomenon of individuals doing worse as population size gets even smaller is called the Allee effect. This is what happened to white abalones. Mating in abalones is not a particularly touchy-feely process. Males and females shed gametes directly into the ocean where fertilization and subsequent embryonic and larval development occur. Fertilization cannot happen if spawning partners are too far away from each other; even a few meters can result dilution of gametes that is severe enough to eliminate the possibility of fertilization. Moving adult abalone closer to each other in the field, as well as spawning them in the lab to produce offspring are management measures that are being taken to rescue this species from the threat of extinction. There's plenty to read about regarding sustainable seafood (white abalone clearly not included) at this month's Carnival of the Blue.

hermit crab home improvement

Among the favorite characters in the touch-tank in the museum at College of the Atlantic are the Acadian hermit crabs. Hermit crabs typically live in empty snail shells, which offer protection for their soft, slightly curved abdomens. There are some exceptions to this pattern: a few hermit crabs have straight abdomens and live in worm tubes; others, like the giant coconut crabs, don't use extra coverings at all during adulthood, relying solely on their chitinous exoskeleton for protection. The large Acadian hermit crabs we see here usually inhabit the old shells of moon snails (Lunatia heros) or ten-ridged whelks (Neptunea decemcostata). An odd thing about these shells is that they are often missing chunks along the margin of the shell opening. Odder still, the hermit crabs hack away these chunks themselves, once they've taken up residence in the shell. Diver Ed has captured this behavior on film, and he has routinely seen them doing it during his tens of thousands of hours underwater. Maybe they're getting the size of their shell JUST right. If they left it any bigger, a larger hermit crab might want it and could easily wrestle it away from the smaller resident. Hermit crabs are certainly known to compete for shells. But if customizing the shell is a way to limit competition from larger hermit crabs, why do we see this phenomenon only among the largest individuals? Do bigger hermit crabs have disproportionately larger and stronger claws, capable of pinching off pieces of shell margin, or do the largest snails have disproportionately thinner shells, making modification possible only for the hermit crabs that inhabit the largest shells? I suspect some size-related pattern, but of course I would suspect that. I'm rather obsessed with size-related patterns; my favorite mathematical expression is the allometric equation.

growing clams

Here is some additional information about Sarah D's clam monitoring project, that the invertebrate zoology class helped out with last month. The main part of her project involves measuring recruitment rates for soft-shelled clams (Mya arenaria, also known as "steamers" on local menus) as well as understanding what kinds of factors may enhance recruitment. A definition is probably needed here: when a larval clam, which has spent a couple weeks swimming and feeding in the plankton, encounters a suitable site, it will metamorphose from a larva into a juvenile clam, burrow into the sediment and take up residence, thus recruiting into the local population. Clearly, the larval supply will affect recruitment rate, but larval choice also plays a role, and marked preferences for a variety of factors including substrate texture, flow regime, presence of conspecifics, presence of prey, and absence of competitors or predators, have been demonstrated among a wide range of larvae of marine invertebrates. They may be tiny, but those larvae can exercise some sophisticated decision-making. For one of Sarah's treatments, she added adult clams to her site to measure the effects of adult conspecifics on recruitment rate. These adults were not enhancing the local supply of larvae; any offspring they produced would be widely dispersed during their weeks-long larval life in the plankton. But the adults do provide settling larvae with the information that the site can support clams from settlement to adulthood, and might be a good choice. As long as Sarah and her project supervisor, Chris Petersen, were moving clams (they added hundreds of clams to several large treatment plots), they decided to also measure growth rates of the clams. They marked the outer margin of the shell with permanent marker in the spring, when they added the clams to their site, with the help of students from MDI High School. Then, this month, they measured the marked clams that they found while they were monitoring clam density and recruitment rate. I was surprised that the marks persisted for 6 months, even though the method was suggested by Brian Beal, from U Maine Machias, who definitely knows his way around clam flat research. The marking technique works, and growth rates were quite variable, even among clams in the same plot, with some showing obvious, substantial shell growth, and others not changing size at all since spring. There are clearly plenty of future projects there waiting on the clam flat for some curious and energetic students. Climbing into a pair of waders and splooshing around on the mudflat offers its own unique rewards: fingers numbed from sorting through samples in November, the aroma of anaerobic sediment (think rotten eggs), gooey mud covering everything from tools to clothes to data sheets. What's not to love?