Locust (36 page)

 

On our final day of the expedition, we packed early because the horses were supposed to show up by mid-morning to take us back out. The wrangler, stringing only four horses, appeared in camp just after lunch. He muttered an excuse for his tardiness but offered no explanation for why there was only a single riding horse other than his. We loaded the three packhorses, gave Charlie the remaining mount, and resigned ourselves to making the twenty-five-mile hike. The last few miles were traversed in moonlight. Gary and Sue offered
us profuse apologies for the wrangler’s lack of planning. Although it was nearly midnight by the time we’d unpacked, Sue prepared a meal featuring melt-in-your-mouth sirloin steaks and butter-slathered baked potatoes crowned with dollops of sour cream. After days of eating rehydrated macaroni and semicrunchy rice dishes (at 12,000 feet water boils at 190 degrees, which made it difficult to fully cook food), the dinner transformed annoyance into deep satisfaction. We bid our hosts farewell, and looked forward to working with them again the following year.

The next year’s expedition featured a cruel ice storm that generated a couple of tense hours during which hypothermia became a real possibility. The rest of the trip went well, with many more whole bodies recovered from the ice. It would be our last collecting trip to the Wind River Glaciers.
⁶
Funding sources tightened their belts and presumably found projects that kept species alive to be more important than supporting grave robbers.

 

The grasshoppers that we brought back to the laboratory from Knife Point Glacier provided valuable material for more refined analyses than had been previously possible. As fate and fortune would have it, we had discovered neither fool’s gold nor twenty-four-carat gold nuggets. Perhaps the best metaphor would be a treasure map, hinting at a solution to our mystery but not quite being the answer itself.

Although the proteins in the bodies were too degraded for comparative studies, other molecular features were remarkably well preserved.
And Dick was the ideal collaborator on the analysis, being as skilled in the laboratory as he was in the field. Dick was still working for the USDA’s research laboratory on campus, and he’d taken personal leave to join the second expedition to Knife Point Glacier. His administration was not fond of his open-ended curiosity and scientific meanderings outside the laboratory’s circumscribed boundaries of vector biology. Unlike many government scientists, Dick had a hard time being a good “company man.” He was a harsh critic of bureaucratic bungling and self-aggrandizing scientists; he did not suffer fools gladly, and he found no shortage of buffoons within the agency.

Dick began working for the USDA when they maintained a honey-bee laboratory in Laramie, and he’d switched to studies of biting gnats when the feds reorganized and created the Arthropod-Borne Animal Diseases Research Laboratory. In his initial research on bees, he’d used the chemical profiles of the waxes that coat the bodies of insects as a means of distinguishing between the gentle European honeybees and the homicidal Africanized honeybees. Being small, insects are highly prone to desiccation, and they protect themselves from water loss with a veneer of wax, not unlike our use of paraffin as a means of sealing jars of jelly to prevent them from drying out and to keep molds from getting in. Dick had worked closely with Dave Carlson—a USDA colleague and the pioneer of this analytical method. Dave had discovered that there are hundreds of different lipid molecules that insects mix together to create their wax layer, and the particular blend forms a chemical fingerprint for each species. During Gurney’s work on the taxonomic status of the Rocky Mountain locust, this diagnostic feature was not known, and in any case, the sophisticated analytical instruments necessary to separate and identify the lipid cocktails were not readily available to entomologists at that time. So in an effort to close the book on the identity question, Dick, Dave, and I collaborated on a project to determine whether
spretus
and
sanguinipes
had different types of waxes.

We dribbled a few drops of a solvent down the legs of museum specimens of
spretus
to extract the surface waxes. The same procedure provided wax samples from museum specimens of
sanguinipes
along with locust remains from our first Grasshopper Glacier expedition and from Knife Point Glacier. The
spretus
and
sanguinipes
samples provided distinctly different blends of lipids, each having more than a hundred different hydrocarbons. The extracts from Grasshopper Glacier were frustratingly ambiguous, lying somewhere between our two known blends. The recession of the glacier and the consequent exposure of the insect remains probably led to the slow deterioration of the surface waxes, much as one might expect from an 800-year-old candle. To our delight, however, the samples from Knife Point Glacier, having been entombed deep within the ice, provided a much higher-quality chemical fingerprint. There could be no doubt that these specimens matched those of
spretus
. But the search for DNA—the ultimate chemical evidence to establish both the taxonomic standing of
spretus
and the identity of the glacial remains—would not be so simple.

Bill Chapco is a bespectacled, always-happy-to-see-you professor from the University of Regina in Saskatchewan. This warm and authentic fellow is also the world’s foremost grasshopper geneticist. For years he has worked on methods for extracting and analyzing the DNA from grasshoppers, which, as it turns out, is no mean trick. In 1993, I sent him some of my treasured locust mummies from Knife Point Glacier, knowing that if anyone could eventually tease the genetic code out of these creatures it would be Bill. And I was right, although I had to wait nearly a decade for his deliberate and systematic efforts to bear fruit. In reality, he had developed effective methods some time earlier, but knowing the rarity of
spretus
specimens, Bill wanted to be absolutely certain of his technique before applying it to the Rocky Mountain locust.

In November 2002, Bill presented his first findings on the genetics of the Rocky Mountain locust at the national meeting of the Entomological Society of America. Somewhere around 3,000 entomologists converge each winter to share their findings on every imaginable—and a few unimaginable—aspects of insects. Using museum specimens representing a wide range of species, along with the material from the glacier, Bill showed that the standing of
spretus
as a valid species was fully supported by key regions of their DNA. Much to everyone’s surprise,
neither
sanguinipes
nor even
femurrubrum
shared the greatest genetic similarity to the Rocky Mountain locust. Rather, the nearest living relative was
Melanoplus bruneri,
a species with a catholic diet and a propensity for irregular outbreaks in the mountain meadows of the United States and Canada. Bill’s work also left no doubt that the museum and glacial specimens of locusts were the same species. Indeed, much to my delight, the genetic material from the glacial specimens had suffered substantially less degradation than that obtained from the dried museum specimens.

Molecular analysis can also shed light on the events leading up to extinction. If there was a detectable loss of genetic variation in the Rocky Mountain locust—a genetic bottleneck—this change would indicate if and when the species began a gradual decline leading to its final extinction. Such a narrowing of genetic diversity occurs when a species engages in a high degree of inbreeding in fragmented or reduced populations. We all have a small proportion of abnormal and adverse genes acquired from one of our parents, but the corresponding traits are often not expressed because the alternative, healthy form of the gene from our other parent masks or dominates the deleterious form. So there’s a good reason why we frown on brothers marrying their sisters—and, perhaps, why evolution has predisposed us to find our siblings lacking in sexual desirability. The children of such matings are much more likely to receive a double dose of these rare, harmful genes and to manifest the associated deformities and illnesses. All of this genetic change would have made for an exciting discovery, except the molecular analysis provided no evidence of a bottleneck in the museum specimens from the turn of the last century relative to the older, glacial specimens.

While Bill had been working on his molecular methods, we had been taking meticulous measurements of glacial and museum specimens looking for evidence of a genetic bottleneck through a trait called
bilateral asymmetry
. Most animals exhibit bilateral symmetry, meaning that if we were to slice them in half longitudinally the two pieces would be near-mirror images of one another. Of course, this pattern is not found in creatures such as sea stars, which have radial symmetry. Even in bilaterally symmetrical animals, like humans and
grasshoppers, the two halves are not perfectly identical. However, in genetically healthy organisms, the degree of symmetry is much greater than in organisms arising from inbreeding. Our measurements of tibial lengths and counts of tibial spines from the right and left hind legs consistently failed to show any differences between Rocky Mountain locusts before and during their decline to extinction. The locust’s breeding pattern during the last few years of its existence was not unusual; no evidence indicated that there were several generations of abnormally diminished or exceptionally isolated populations leading to inbreeding. Our findings agreed with Bill’s—these insects had not been in a prolonged decline.

The late 1800s were not the last gasp of a dying species. Rather, it seemed that the extinction happened suddenly and without warning to a normal, healthy species. It appeared that the Rocky Mountain locust had been decimated throughout its range within a matter of a few years in an entomological Armageddon. But what sort of force could act in such a manner without leaving evidence of its presence spread across the West?

T
HE FIRST COURSE THAT I TAUGHT AT THE UNIVERSITY of Wyoming was in the fall of 1986. During the summer, I prepared intensively for my first solo venture into academia, amassing a file drawer of journal articles, reviewing texts, and compiling more than 200 pages of lecture notes. On the first day, I was ready to plunge into the wonderful world of “Insect Population Biology” with a class of graduate students from entomology and zoology and a smattering of senior-level biology students. I had prepared like a football team readies for the Super Bowl, but the students were in preseason form. The experience was traumatic for all concerned.

I had assumed a far greater grasp of mathematics than the students possessed, so that my early lectures were a source of confusion, fear, and borderline outrage—rather than joyful enlightenment—for my students. Eventually, we reached an academic truce that had the hall-mark of a classic compromise—nobody was entirely happy. They
stretched beyond their comfort zone, and I backed-off from my expectations. Having survived my first teaching experience, I set about revamping the course to make the cabalistic field of population biology compelling to the students.

The virtue of teaching for a professor heavily engaged in research is that being effective in the classroom requires one to take a far more comprehensive view of a subject than might be normally the case for a research scientist. Preparation for a course requires a substantial expansion of one’s reading into areas that are tangential, even seemingly unrelated, to the central focus of a typical research program. But in my experience, there is a great chance of happening upon a new perspective, concept, or method that is applicable to one’s research. And although I manage to work my various research projects into my lectures whenever possible, I have gleaned more exciting and creative ideas from teaching for use in my research than vice versa.

Over the years, I have found a number of fascinating examples of changes in insect populations that served as relevant starting points for the more detailed and abstract principles that formed the infrastructure of my course. Perhaps the best-known and most dramatic display of insect population dynamics in North America is the migration of the monarch butterfly across the continent. Not only would the ecology of this butterfly turn out to serve as a case study for my students, but the life history of this creature also would provide the clue that allowed me to break the case of the Rocky Mountain locust’s mysterious disappearance.

 

Each spring, monarch butterflies move northward from their overwintering grounds in Mexico. In late March they appear in the southernmost parts of the United States, extending into the central region of the country by the end of April. The children of the Mexican population of butterflies pass through the larval stage in about two weeks—longer if the weather is cool. Then the larvae attach themselves to plants and enter the pupal stage. Upon emerging as adults, this generation continues the northward journey into much of eastern North America.