Science Friday – A Selection from Natural Selection

A significant debate is currently underway in the scientific community over the evolution of the Great White shark, and Chuck Ciampaglio, Ph.D., an assistant professor of geology at the Wright State University Lake Campus, is right in the middle of it.

The issue is if the Great White, one of the most feared predators of the sea, evolved from the huge prehistoric megalodon shark or if its ancestry rests with the mako shark.

“Most scientists would probably say the Great Whites evolved from the megalodon line, which existed from two million to twenty million years ago. They were huge sharks, approximately the length of a Greyhound bus and possessing teeth that were up to six inches long,” explains Ciampaglio. “However, our research, which is based on analyzing fossils of several hundred shark teeth, shows that the Great White shares more similarities with the mako shark.” He added that because sharks regularly replace their teeth, it is relatively easy to obtain tooth samples through fossil field work along the Atlantic seaboard.

A paper published in Nature on May 12th (1) provides new data that resolves a long-standing scientific controversy. In the 1960s, Nobel Prize winning zoologist, Karl von Frisch, proposed that honeybees use dance (the”waggle dance”) as a coded message to guide other bees to new food sources. However, some scientists did not accept von Frisch’s theory. Using harmonic radar, scientists, funded in part by the UK’s Biotechnology and Biological Sciences Research Council (BBSRC) have now tracked the flight of bees that had attended a “waggle dance” and found that they flew straight to the vicinity of the feeding site, as predicted by von Frisch. The tracks allowed the scientists to determine how accurately bees translate the dance code into successful navigation, and showed that they correct for wind drift even when en route to destinations they have never visited before.

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In another set of experiments, bee recruits leaving the hive were taken to release sites up to 250m away. These bees flew, not to the feeding site, but in the direction that would have taken them to the feeding site had they not been displaced from the hive. This result adds weight to von Frisch’s original theory and allows alternative hypotheses about bee behaviour to be firmly discounted.

Bacteria acquired up to 90 percent of their genetic material from distantly related bacteria species, according to new research from The University of Arizona in Tucson.

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“To maintain effective treatments and develop new antibiotics, it’s important to monitor the rates and patterns of lateral gene transfer,” said team member Howard Ochman, a UA professor of biochemistry and molecular biophysics and a member of UA’s BIO5 Institute.

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 The research also solves a long-standing evolutionary puzzle. Many scientists have argued that drawing traditional family trees does not make sense for bacteria, because their genomes represent a mix of genetic material from their parental cells and from other species of bacteria.

Ochman and his colleagues’ work shows that bacterial lineages can still be traced by considering only the “traditional” forms of genetic inheritance. The widespread exchange of genes does not blur the line of descent because the acquired genes get lost from the genome at a later point or, if they do persist, the bacteria then transmit them to their offspring.

Being able to classify bacteria is crucial for medicine, Ochman said. “If you go to the doctor with strep throat he can be pretty certain that it’s the result of an infection with a species of Streptococcus and can therefore prescribe an appropriate antibiotic. If you couldn’t classify bacteria because they have genes from all over, doctors wouldn’t be able to do this.”

A biologist at Washington University in St. Louis has shown that for some fish species, females prefer males with larger sexual organs, and actually choose them for mating. That does not exclude males with an average-sized sex organ, called a gonopodium. These fish out-compete the larger-endowed males in a predator-laden environment because they have a faster burst speed than the males with larger genitalia, who lose out because the size of their organ slows them down, making them ripe for capture by larger fish.

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 Brian Langerhans, Washington University biology graduate student in Arts & Sciences, has performed studies on mosquitofish (guppy-like fish, about an inch long) and found that female mosquitofish spend 80 percent more time with males who have a large gonopodium.

“A male with a larger gonopodium has a higher chance of mating, but in a predator environment he has a higher probability of dying,” Langerhans said. “That’s the cost, the tradeoff. On the other hand, we found that in predator-free environments gonopodia size was larger, as there is minimal cost for large genitalia in that environment. Bigger is better for mating, but smaller is better for avoiding predation.”

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Researchers have thought for about 20 years that the striking diversity of genital form results from post-mating sexual selection, such as sperm competition or cryptic female choice. That is, most evolutionists have believed that for animals with internal fertilization — like the livebearing fish Langerhans studies which don’t lay eggs– selection acting within the female’s body that biases fertilization toward males with a particular genital morphology has been largely responsible for the generation of genital diversity. Langerhans’s finding, however, contradicts that theory: he has shown that female mosquitofish make their choice before mating, and overwhelmingly that choice is made with size being the prize.