Symbiosis II: Dr. Steven A. Frank's lecture at STRI

Steven A. Frank, a professor in the University of California-Irvine Department of Ecology and Evolutionary Biology, expresses a research interest that flies over the heads of many people outside his field. “I develop mathematical, computational, and conceptual models to study complex phenotypes,” he says on his website.

Ah, but what IS his field?

Broadly speaking, we can identify Dr. Frank as a biologist. Early in his career, well before computerized genetic sequencing and many other modern research techniques, he studied the ways that evolution and genetics shape reproductive traits and behavior.

(Genetics shaping behavior? Now THAT’S a political minefield, in its human implications encompassing the search for a “gay gene,” Nazi eugenics and other theories about the relative intelligence of different races, Richard Nixon’s idea of screening male kindergarten students for the XYY chromosome trait that’s associated with aggressive behavior and so on. But the protesters generally won’t come to close down a scientist’s lab if the work is about how genes determine the behavior of birds, bugs or bacilli.)

In recent years, however, Frank says that biology has advanced to the point that researchers can “see below the surface of complex phenotypes to the biochemical and genetical mechanisms.” Now biologists can go farther than looking at microbes under a microscope and separating those with one appearance into one category and those with a different characteristic into another, and look at genetic evidence to get past the superficial and reach a better understanding of ancestral relationships and evolutionary trends.

Thus he has attempted to merge mechanistic and evolutionary points of view in his book “Immunology and Evolution of Infectious Disease” and related studies of parasites and their hosts, and is currently looking into cancer from the evolutionary point of view of the process of normal cell replacement changing into the creation of tumors.

At the Smithsonian Tropical Research Institute’s science lecture series, however, Frank did not emphasize his cutting edge new work. Instead he highlighted work done in the 1950s and 1960s by German biologist Paul Buchner, who studied the symbiotic relationships between blood-sucking insect pests and the bacteria that live in their guts.

(Eeeeew --- gross! you might naturally say, because bedbugs and lice are parasites to us. But like the critters that send people to the pharmacy in search of Pyrinate A-200, we human beings also have symbiont microbes in our gastro-intestinal tracts. Just as lice can’t digest our blood without the help of their symbiotic bacteria, we can’t process the food we eat without maintaining similar relationships.)

But what about the evolution of such microbes?

There can be vertical transmission, wherein the mother passes some of her symbionts to the child, in the case of insects, through her eggs. But what if the female has 100,000 symbionts of a number of lineages in her body, but can only pass on a few hundred in her eggs, and many of the microbes that get into her eggs die? What are the evolutionary implications for her microbe lineages? How can she make sure that her offspring get the germs they need to do the job?

There might be a competition among the microbes for inclusion in the eggs, but this may not be in the host insect’s interests.

Or else the host organism might control the reproduction of various lineages in her gut by denying some of them access to her eggs.

“Repression of competition is a powerful force” in the evolution of such symbionts, Frank pointed out.

How powerful? Dr. Frank points to a 1950s work by Dr. Buchner, which was updated in 1965, “Endosymbiosis of Animals with Plant Microorganisms.”

Buchner, working before the days of DNA analysis, found that in sucking lice certain cells contain large concentrations of bacterial symbionts. He also noticed in his research that some insects have evolved special organs to manage symbionts, as in temporary holding cells that confine microbes until the time of reproduction, when the cells break down and allow the microbes to migrate to the ovaries; or in organs that collect bacteria and move them around the body. Frank noted that Buchner found a great deal of variation in the mechanisms by which symbionts are moved around the hosts’ bodies and are transmitted from one host generation to another, something that Frank finds very interesting.

For example, do males also transmit lineages? It would seem, from Buchner’s studies of bedbugs, that they do. But then, Frank pointed out, that would imply a mixing of lineages and consequently increased symbiont competition.

In the question-and-answer period following Frank’s main presentation, the audience heard “I don’t know” much more than is usually the case at the Smithsonian’s Tuesday lectures.

Bedbug behavior? Genetic variation of symbionts within a single host? Horizontal transmission of gut bacteria? The proportion of symbiont lineages that get excluded from the host’s eggs? Specifically how are certain symbionts excluded?

Steven Frank had few answers to these questions, but maybe somebody in the audience now has a topic for his or her next research project.

To Frank the issue is not an understanding of abstruse processes taking place within pests that are to be killed and not seen. It’s about building “a framework to organize biology.”

“With our modern understanding of symbiosis,” he said, “we can go back and take a new view.”

Also in this section:
Symbiosis I: Cats and people
Polio back in Africa?
Symbiosis II: Looking back at old science, knowing what we know
Smithsonian's photo chief talks digital history, future

science

Looking back at old research, knowing what we now know

Looking back at old research,
knowing what we now know