July 1, 2003 CHICAGO -- When conservation biologists decide how to protect an endangered animal or reintroduce one to an area from which it has disappeared, they consider many factors, such as how many genetically distinct populations are involved, where they came from, and who their ancestors were.
But the very problem such scientists are trying to address – the animal's disappearance – makes it hard to answer these questions. Examining the DNA of museum specimens, however, can fill information gaps caused by the lack of living animals in key locations. This is what two scientists have done to help guide the reintroduction of the Northeastern Beach Tiger Beetle into areas from which it has been wiped out by human activity.
"We have aimed the 21st century technology of DNA sequencing at museum specimens from the 19th and 20th centuries to address current conservation issues," said Paul Goldstein, PhD, an insect curator at the Field Museum.
Dr. Goldstein and co-author Rob DeSalle, PhD, of the American Museum of Natural History discuss their work in a paper published in next month's issue (July) of Molecular Ecology.
The tiger beetle, Cicindela d. dorsalis, has undergone a precipitous decline in the last 100 years. Once commonly found along sandy beaches from Massachusetts to the Chesapeake Bay, only one viable population remains north of the Chesapeake Bay on the island of Martha's Vineyard. As a result of their limited dispersal and declining numbers, the tiger beetle was listed under the federal Endangered Species Act in 1991.
The researchers surveyed museum specimens collected from 21 towns up and down the Northeast Coast between 1885 and 1971. They examined the specimens for the presence of a small-scale DNA shuffle (called a single nucleotide polymorphism, or SNP) to help understand the current genetic variation that exists between the New England population and the Chesapeake Bay populations.
They discovered considerably more variation at this genetic site across the historical range of the specimens analyzed than occurs among the remaining populations. This suggests that the human impacts leading to the fragmentation of these tiger beetle populations resulted in the genetic "fixation" of the single-letter DNA shuffle that became a permanent feature of the tiger beetles' genomes in these increasingly isolated populations.
They discovered considerably more variation at this genetic site across the historical range of the specimens analyzed, suggesting that human impacts led to the fragmentation of these tiger beetle populations and the concomitant single-letter DNA shuffle that became permanent features of the tiger beetles' genomes in these increasingly isolated populations.
"Essentially, we used museum specimens to fill gaps in the story of species formation that could not be sampled because the tiger beetles no longer exist at certain locations," Dr. Goldstein said.
This finding has implications for the conservation management of these tiger beetles and other threatened species. In this case, the authors advocate independent management of the New England and the Chesapeake Bay tiger beetle populations, despite the fact that the genetic distinctness between the two populations arose only recently.
"The molecular genetic data and the ecological-behavioral data corroborate one another in the current strategy to restore C. d. dorsalis to as much of its historical New England range as possible using the northernmost extant populations," Dr. DeSalle said.
The authors also discuss the use of the "phylogenetic species criterion" to distinguish species, especially when such decisions are based on a single letter shift in a species' genome. Coming up with criteria for distinguishing species is a longstanding intellectual challenge for the fields of taxonomy and phylogenetic systematics. Although their findings corroborate decisions to manage northern and southern populations of this threatened species independently, the authors recommend against making major conservation decisions on the sole basis of SNPs.
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