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A blog written for those whose interests more or less match mine.

The Woman Who Stared at Wasps

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Evolution has shaped baroque solutions in creating networks of benefits and trade-offs in various lifeforms. Take, for example, wasps…  Veronique Greenwood interviews Joan Strassmann in Quanta:

As an undergraduate in the 1970s, Joan Strassmann split her time between writing short stories and laying siege to the office of her mentor, the sociobiologist Dick Alexander. For two years, she insisted on meeting with him every Friday to discuss research, a schedule that she now thinks was probably quite an imposition. “He would give me so much reading,” she recalled, “it would take me forever. I would work night and day to finish it, and maybe this was his strategy — maybe he was hoping I’d cancel or something.” But that intense focus became one of the hallmarks of her pioneering research on social insects. link

In graduate school at the University of Texas, Austin, Strassmann began to study wasps that live in hierarchical colonies, starting with a nest that was thriving in a tractor shed near the main campus. “I was really planning to work on something else, some other social organism, like ground squirrels,” said Strassmann, now at Washington University in St. Louis. “Everyone knew that I was actually terrified of wasps.” But on a dare, she and a friend ventured into the shed and painted each wasp with a different identifying dot of paint, the standard preparation for studying the social dynamics of an insect colony. Then she just started watching them. And watching them.

She was in good company. Insects that live incooperative colonies — ants, termites, and some wasps and bees — have fascinated scientists for more than a century because they pose an evolutionary conundrum. Darwin himself saw their way of life as a challenge to his ideas. The theory of evolution seems to predict that each individual will fight to pass on its traits, but in a colony, only a very small number of insects actually get to reproduce: the queens and their mates. The rest give up their chance to contribute to the gene pool, caring for the offspring of others instead. How could this lifestyle, known as eusociality, have evolved? How could it make sense for the ancestors of modern worker bees or wasps to give up their autonomy? It seems biologically implausible.

Right around the time Strassmann was in college, however, biologists began to understand how social insects could fit into the framework of evolutionary theory. In aseminal paper, W.D. Hamilton proposed that cooperation might make sense in closely related individuals that share enough genes. If a bee with a maiden-aunt helper produces twice as many offspring as it might have otherwise, that arrangement makes evolutionary sense for the non-reproducing assistant, which is indirectly passing on its genes. But that benefit is reduced as relatedness declines, so eusociality would only arise among close relatives.

Strassmann found clear evidence of Hamilton’s idea in her tractor-shed wasps. When a nest is destroyed, its members will disperse to sister nests in a pattern that reflects their level of relationship to the queens. Each wasp serves only the leaders it is most closely related to. Strassmann continued to study wasps over the next 20 years with her husband and collaborator, David Queller, and the two have uncovered many other details of how relatedness shapes the behavior of social insects, including how colonies keep relatedness high when multiple queens reign, and what it takes to turn a worker into a queen.

About 17 years ago, however, the pair began to shift to a new model organism, the amoeba Dictyostelium discoideum. They suspected that this unusual creature could offer new insights into the dynamics of cooperation. In moments of starvation, these soil-dwelling amoebas crowd together and build a tower rising above the ground from which they disperse their spores to other, more hospitable places. Some 20 percent of the group will sacrifice themselves to build the tower with their bodies, while the rest take advantage of it to spread their genes.

Quanta Magazine spoke with Strassmann about the evolution of social insects, the secret lives of queen wasps, and what she’s learned about cooperation from a single-celled creature. An edited and condensed version of the interview follows.

QUANTA MAGAZINE: You began to study social wasps just as scientists were debating the origins of eusociality. What was that like?

JOAN STRASSMANN: It was a really exciting time. W.D. Hamilton’s paper came out in 1964, but it wasn’t really appreciated until the early ’70s, when I was in college. He outlined the framework of something called inclusive fitness, which is the sum of the effects of an individual’s actions on its own and others’ reproduction. Ultimately, it is the measure of an individual’s actions on the representation of its genes in the next generation.

You would help relatives, because they share genes with you. But it’s not quite as simple as that. People often act like you’ll always help a sibling more than a cousin, and so on, but the costs and benefits are really crucial. For example, you wouldn’t help sisters who share half your genes unless they would have at least double the number of progeny as a result of of your help.

Relatedness is easy to assess with molecular techniques. Assessing the costs and benefits, though, requires that you really understand the biology of the individuals in their natural habitat. Dave and I have a paper laying out two major benefits social insects gain from joining forces: fortress defense, where two of you can guard better than one, especially if you live in a nest with a tiny opening; and life insurance, where if one of you dies, the other ensures the survival of your babies. Fortress defense and life insurance are the two main reasons that cooperating could be beneficial in social insects.

Are there behaviors or traits that make it easier to become eusocial?

Yes — they’re actually very well known. The ancestors of social insects are parasitic wasps. As a parasite, you don’t want to make your host sick until you’re going to kill it, so these wasps don’t really poop as larvae. They just sort of hold it in. The same goes with social insects — you really don’t want to poop in the nest. How you control the poop in social organisms is a really important question.

Then there is maternal care. . .

Continue reading.

Do read the whole thing. It becomes more and more interesting.

Written by LeisureGuy

5 November 2015 at 4:52 pm

Posted in Evolution, Science

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