A Window into the Origin of Species
Erik Dopman, PhD, joined the Department of Biology in 2009. He uses his expertise in evolutionary biology (PhD, Cornell University) and genomics and bioinformatics (postdoctoral research, Harvard University) to explore how species originate. “The critical features that generate new species are called isolating barriers, which are traits that prevent the exchange of genetic information between organisms,” says Dopman. “The organism we study is called the European corn borer [the moth Ostrinia nubilalis], which is a major economic pest of corn and many other crops. We study it because many isolating barriers have evolved between two lineages, which are in the process of becoming new species.”
Dopman and his research group identified seven isolating barriers that limit gene flow between strains of the European corn borer (ECB). “None of these traits is sufficient to completely eliminate gene flow, but when you add them all together, about 90% of gene flow is eliminated,” Dopman says. Theoretical work suggests that about 95% of gene flow must be eliminated before two strains diverge into two separate species. Dopman and his group are studying two reproductive isolating barriers in two ECB strains, the “E” strain and the “Z” strain: (1) temporal isolation due to different timing of strain maturation, and (2) behavioral isolation due to different sex pheromones. They have determined that the temporal isolating barrier eliminates about 60% of gene flow; they are currently working on quantifying the effects of the behavioral isolating barrier. “Ultimately what we’d like to be able to do is understand how the genes have evolved to create these isolating barriers, because these are genes that are responsible for the speciation process—for explaining diversity, the 10,000,000 species in nature—and our hope is that by understanding these genes we can come to appreciate how other organisms have diversified,” says Dopman.
Another application of this work centers on the ECB as an agricultural pest that costs about a billion dollars each year to manage. “If we can identify the genetic basis for differences in development time, we can accurately predict when the insects are going to be present over the course of the season, which is very powerful because it gives farmers information that can be used to help manage this pest species,” says Dopman. “We are also looking at where resistance to insecticides evolves in the ECB genome.”
Dopman breeds the E and Z strains of the ECB in his lab in Barnum Hall. The E strain develops earlier in the year than the Z strain, so E-strain moths have been termed “fast” and Z-strain moths have been termed “slow.” Dopman’s research group makes crosses between fast and slow individual moths and looks at the reproductive isolation traits displayed by the offspring. “We’re looking for regions of the ECB genome that show perfect correspondence with fast or slow development,” Dopman says. “We’re actually using recombination to sort of remove the chaff—we’re winnowing away the pieces of the genome that are not contributing to the trait—and looking across thousands of offspring at the pieces of the genome that are always associated with fast and slow development. We send the DNA to the Tufts high-throughput sequencing facility, and they send us back the sequencing data that we manipulate and use. We take these base pair sequences and match them up, and eventually we’ll identify all of the chromosomes. It’s a huge jigsaw puzzle; right now we’ve sequenced about 5 to 10% of the genome.”
For collaboration, Dopman offers his expertise in genomics and bioinformatics and in using new sequencing technologies. He would like to find collaborators with expertise in transgenic techniques and RNA interference (RNAi). “To prove that a gene is responsible for a trait, it would be useful to genetically manipulate the gene product by RNAi,” says Dopman. “So if we take an individual with long development time, if we apply RNAi to this candidate gene, can we turn it into a short-development-time individual?” While RNAi is a fairly common technique, aspects of RNAi machinery might be organism specific. “It’s unclear why the same technique works in some organisms but not in others,” says Dopman. “Similarly, it’s unclear why some genes within the same organism can be knocked down effectively whereas other genes cannot. So while it is routine, the ability to apply the technique across organisms and across genes is more of a challenge.”
For more information, please go to http://ase.tufts.edu/biology/labs/dopman.