Is there an infallible and simple method for estimating the imminent disappearance of a species? Outside of molecular biology, which is reliable but costly and rarely within the means of institutions in developing countries, there are no miracles: You have to count and count again. This is a Sisyphean task-not very rewarding, often futile, particularly in dealing with small animals, birds, or insects.
And yet, a method now surely exists. Two Belgian researchers at the University of Antwerp, in Wilrijk, have just developed it. It requires only a graduated caliper rule or a 20-centimeter ruler, as well as a good knowledge of statistics. In short, the method is within everyone's reach and is based on a recent hypothesis, advanced for the first time in 1994, but never proved until now: The closer an animal or plant species is to its extinction, the higher the number of asymmetric individuals within the species. In other words, the last individuals of a race are increasingly lame, and now it has been proved.
Luc Lens and Stefan Van Dongen conducted their research in America as well as in Flanders, but it was in Kenya, in the Taita Hills Reservation, 250 kilometers inland, that they accomplished their goal. "We were looking for a way to show that the fluctuating asymmetry of a species on its way to extinction was correlated to the environmental stress it was undergoing," observed Lens. "The idea was quite theoretical in 1994, and most people wonder why it should have taken so many years to prove something that seems obvious!"
Looking for evidence, the two researchers ran up against some formidable difficulties because of the imprecision of the measurements. "The asymmetry of the legs or the wings, for example, never exceeds 10 percent," he added, "which means that the fluctuating asymmetry of limb that is 10 centimeters long will range between 0.1 and 1 centimeters at the most. Errors in measurement are inevitable."
The two animals that were chosen, however, were not selected randomly. The first is a moth of the Geometridae family that has become exceedingly rare. The other is a bird, the Taita blackbird (Turdus hellen), which gathers seeds from the ground; it is endemic to the last three extensive sections of the primary forest in Kenya: Mbololo, Ngandao, and Chawia. As a species on its way to final extinction, this bird in fact is an excellent model; there remain, all in all, only about 1,350 specimens, all banded, of which 1,059 are in Mbololo, and 250 and 38 respectively in the two other sections of forest. This means that, in Chawia, this blackbird will probably disappear in one or two generations (three to seven years) if nothing is done in the meantime.
"To solve our measurement problems and their statistical repercussions, we had to develop innovative mathematical tools, now completely perfected," explained Lens, "and the results were not long in coming. "The number of asymmetric blackbirds in Chawia is eight times greater than in Mbololo and 2.5 times greater than in Ngandao. Comparable results were obtained with the moth. It seems that the stress on the species as it dwindles toward extinction causes the asymmetry.
There are two possible reasons for this. The first that comes to mind is what biologists call "genetic drift." A restricted and isolated population loses its genetic diversity, particularly because of inbreeding. The number of anomalies thus increases as a result. However, the measurements of instances of genetic drift, using molecular markers, proved to be clearly less precise than those of fluctuating asymmetry. Indeed, from a molecular standpoint, there are practically no differences between Mbololo and Ngandao. "Something [else] must therefore be involved," noted Lens.
The second explanation stems from what is known as epigenetic factors. The disturbances that an organism undergoes in the course of its development may alter its morphology. A genome is not, as people commonly believe, like the set score of a classical symphony. Rather, it is more like a jazz piece, in which only the tones and the motifs are fixed; this is the genotype. The interpretation, which fluctuates to some extent, is the phenotype, the actual shape that the organism will take on.
"In theory, the genotype and the phenotype are identical," Lens explains. "But, in reality, this is never the case. There are, of course, systems, most likely vast complexes of genes that are still little understood, which ensure a great deal of stability in the organism as a whole as it develops. But in the case of prolonged stress-a lack of food, for example-the organism suffering the shortage must allocate to its vital functions the small amount of energy available, at the expense of the system that ensures morphological stability. This is why fluctuating asymmetry increases with stress, when the species is threatened."
The method for measuring fluctuating asymmetry is so simple to use that it has already been applied on other endangered species, such as the Canadian grizzly bear and various aquatic insects, particularly in Belgium, and even to plants, which, like most animals, have a symmetric structure. "With this method, capturing 40 to 50 individuals is sufficient to find out whether the species is really endangered in the short term," the researcher asserts. This is real progress.
Asymmetry is an unrivaled indicator of the failure of a species to adapt to its environment. As everyone suspects, asymmetry is not exactly an "advantage," despite what is said by hunters of the dahu, a legendary animal whose asymmetric legs allow it to live on slopes. "On the contrary, we think that fluctuating asymmetry actually worsens the prognosis of endangered species and seriously jeopardizes their life expectancy," Lens concludes.
source: http://www.sciencesetavenir.com 11may02
|
If you have come to this page from an outside location click here to get back to mindfully.org |