Synopsis
The book begins with the discovery of a large number of deformed frogs by schoolteacher Cindy Reinitz and her students in August 1995. They were on a field trip to a farm owned by Donald Ney near the town of Henderson, Minnesota. As the students approached the rain-fed pond, they noticed that a large number of the northern leopard frogs (rana pipiens) had deformities, such as missing legs, extra legs, and other disfigurements. Concerned about the possibility that the deformities occurred because of a contaminant in the water, Ms. Reinitz contacted the Minnesota Pollution Control Agency (MPCA). As the MPCA did not have an amphibian specialist at the time, Reinitz was referred to the MPCA's invertebrate researcher, Dr. Judy Helgen. At the time Ms. Helgen was studying frogs as part of an effort to develop a bio-index for measuring the overall health of a pond or wetland. As Helgen was busy at the time, she sent an intern, Joel Chirhart, to investigate the pond. Chirhart is alarmed by the widespread nature of the deformities - present in over 1/3 of frogs collected.
Later that year, Ms. Helgen called Robert McKinnell, a biologist at the University of Minnesota. Mr. McKinnell is considered the authority on frogs in Minnesota, having specialized in herpetology for over 50 years. While initially the two thought that the deformities were an isolated occurrence that would disappear like an earlier outbreak at Granite Falls, the persistence of leg deformities into late summer and the discovery of other outbreaks, elsewhere around Henderson and elsewhere around the state, such as at Litchfield, quickly disabused of that notion.
In that same month (August 1995), Dennis and Rhonda Bock found many deformed frogs near their lake in Brainerd, Minnesota. At first they were unconcerned, thinking the appearance of these frogs was a freak, but natural occurrence. However, as more reports of frog deformities came from the rest of the state, they grew concerned and called the Minnesota Department of Natural Resources (DNR). While the DNR could not do anything about the frogs, they sent the information on to David Hoppe, a herpetologist at the University of Minnesota Morris campus. Hoppe was unable to come to the Bock's lake until October, because of previous commitments. When he did manage to go to the Bock property, Hoppe was very surprised, as the Bocks lived on a relatively large natural lake, rather than on the small farm ponds where others had reported deformed frogs. The presence of these deformities in both natural and man-made bodies of water cast doubt on the theory of chemical contamination, as the larger, natural lakes should not have been as susceptible to harboring high concentration of pollutants as smaller, man-made agricultural ponds.
The next year Hoppe, Helgen and McKinnell obtained a $150,000 grant from the state to study the frog deformities. Even more sightings of deformed frogs were reported that year. Short on funds, the MPCA managed to successfully confirm 21 sites with deformed animals. Of the 3000 deformed frogs collected, just under 12 percent had deformities. However, there was a considerable variance in the incidence of deformities between sites and between collection intervals at the same site. As deformed frogs were more systematically collected and dissected, there was considerable evidence of internal abnormality. Digestive systems and reproductive systems were especially hard hit, with some frogs "starving to death, despite being stuffed to bursting with food". As the summer of 1996 progressed, Hoppe paid more attention to the Bock lake. Although the frogs at the lake seemed normal at the beginning of the summer, the number and variety of deformities rose dramatically as the season progressed.
As alarming as the findings at the various sites were, there was very little published material on the subject of frog deformities. Therefore, the researchers could not conclude that there was anything out of the ordinary, simply because they didn't know what the baseline rate of these deformities were. A review of existing literature on the subject showed that although deformities were a known phenomenon, there was no precedent for the variety or the rate of deformity that was being observed.
As the mystery deepened, internal tensions within the investigative team mounted. David Hoppe became increasing concerned with protecting the integrity of sites from outside interference. He was especially concerned about the Bock's lake, labeled CWB ("Crow Wing county - Bock"), as it was one of the few natural bodies of water that had been affected by the deformities. While Helgen was also concerned about the integrity of sites, Hoppe felt that the MPCA, as a public agency was not well equipped to ensure site integrity.
The story then takes a detour and discusses the findings of Martin Ouellet, a French-Canadian biologist who was studying the effect of agricultural chemicals on frogs in the St. Lawrence river valley. Ouellet found that the frogs in agricultural ponds developed deformities at a significantly higher rate than frogs in natural control environments. He had seen and noted the same abnormalities that were being discovered in Minnesota. He became convinced that the deformities were being caused by agricultural chemicals.
After introducing Ouellet, the book moves on to a discussion of possible causes of frog deformities. There are two main theories: parasites, and agricultural chemicals. The parasite theory, advocated by Stan Sessions stated that parasitic cysts from flatworms blocked limb buds, forcing the tadpoles to try to adjust their limb development around the invaders. The pollutant theory, pushed by McKinnell, stated that there were pollutants that were having teratogenic effects on the frogs. The unknown pollutant or pollutants were theorized to be mimics of retinoic acid. Retinoic acid is a hormone that signals limb development in metamorphosing frogs. The pollutant theory stated that these pollutants were disrupting retinoic acid levels in tadpoles, leading to missing or misplaced limbs, in addition to internal developmental abnormalities.
The rest of the book revolves around the interplay between advocates of these two theories. As both sides move to gather evidence to support their theory (retinoic acid disruption vs. parasites) conflicts inevitably develop. The book covers the emergence and development of those conflicts, especially between Sessions and Ouellet.
The book equivocates on the actual cause of the deformities. It states that both parasites and deformities can be traced back to environmental changes caused by humans. Parasite ranges are altered by global warming. Modern farming techniques rely on a large variety of chemicals, whose breakdown and interaction in the environment is still virtually unknown. These changes create, as McKinnell puts it, a "quality of life" issue for ambphibians. The deformities in the frog population are a result of the extraordinary stresses thrust upon them by the modern world.
Read more about this topic: A Plague Of Frogs (book)