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by Marina KHOLODOVA, Cand. Sc. (Biol.), leading research associate, A.N. Severtsev Institute for Problems of Ecology and Evolution, Russian Academy of Sciences (RAS)
Now why waste time and effort in studying the genetic diversity of wild animals? Is this relevant for their present and future? Such questions have been asked time and again. Why not just protect populations of rare species even if their initial progenitors were few in number-just several individuals?
European bisons (aurochs) are an excellent example illustrating what might seem to be at first sight the small significance of genetic diversity in the animal kingdom. By the onset of the 20th century there were only a few individuals of them, while their present population of three thousand comes from only twelve ancestors. That is why the genetic diversity of the newly reproduced population of aurochs is but very small. Our optimism in the initial period of the struggle for their numbers is giving way to concern about the future welfare of this species.
Such signs as the diminishing survival value of youngsters as well the incidence of diseases detected by Russian and Polish zoologists (caused by microorganisms, these diseases were considered not pathogenic before) go to show that the viability of aurochs whose gene pool is much depleted is declining. Today many facts point to this interdependence. It is particularly evident in rare species and small populations (cheetah, isolated groups of wolves, etc.). The matter involves not only the above negative aftereffects for the newly born younglings (lower weight, resistance to infections). The depleted gene pool also tells on different aspects of the reproduction process-from faulty spermatogeny in males to deviations in the normal sexual behavior and mating. Small isolated populations become prone to inbreeding and incest, something that worsens the animals' morphophysiological characteristics. In some species males come to be superior in numbers amongst younglings. For one, this effect was described in 2003 for the musk deer by our research associate Dr. Vladimir Prikhodko, who has evolved Russia's first animal population multiplying in confinement.
For several years now our Institute has been researching in genetic diversity among wild animals and in mechanisms sustaining it, both in this and neighbor
countries. We have selected three species representing the basic ecological types - the saiga, the musk deer and the moose-for our case studies. In this work we are getting financial support from the Russian Fund of Basic Research, and the Presidium of the Russian Academy of Sciences within the framework of the research program Scientific Principles for Sustained Biodiversity in Russia; we are also aided by the RAS Branch of Biological Sciences involved with the projects Basic Principles for Controlling Biological Resources, and Dynamics of Animal and Plant Genofonds.
The saiga (Saiga tatarica) is a typical representative of nomadic ungulates (hoofed animals) found in open landscapes; evolutionally, it is closely related to the antelope. Saigas occurred in great abundance in the past. According to our biologists, Drs. A. Scher and G. Baryshnikov, expert in the evolution of large mammalians of the past, this species, Saiga tatarica, was found all the way back 500,000 to 700,000 years ago. Its fossil remains are found over large expanses from Western Europe to Alaska. Paleontological data demonstrate that even 12 to 14 thousand years ago the saiga populated a vast circumpolar area in the Holarctic (or the northern part of Eurasia and North America) and was within what we call the mammoth fauna. In contrast to most of the big animals of this fauna that died out in consequence of the disintegration of the tundra-steppe ecosystems caused by climatic warming in the late Pleistocene, the saiga survived and accommodated to different environmental conditions. Small wonder that it is called a living fossil: the animal's appearance has changed little, if any, since the time when it inhabited the high northern latitudes together with mammoths, wooly rhinoceroses, deer and other animals.
Today the saiga populates steppes (plains) and semi-steppes of Kalmykia and Kazakhstan. A small isolated group is found in Mongolia in the basin of the Great Lakes. Saigas are gregarious animals, that is they live in herds: during regular seasonal migrations huge saiga herds can cover hundreds and even thousands of kilometers as they change summertime pastures for winter ones. In mating seasons the males take a harem of as many as twelve females. A herbivore, the saiga feeds on many steppe plants and grasses, including those poisonous to domestic cattle.
In number the saiga population has changed in a wide range during recorded history. As testified by travelers, the saiga population numbered millions even in the recent past (a mere fifty years ago it ran into two million in the Volga region and Kazakhstan). But it has been shrinking every now and then under adverse conditions-summer droughts, harsh winters with abundant snow, "jutes" (springtide ice forming a hard crust over snow), high pressing from predators and excessive hunting. As a result, the overall herd contracts to 1/10th - 1/30th of its original numbers. The saiga's fertility rate is very high: for this reason the species could survive against the heavy odds of the hard and abruptly changing conditions in the subarctic tundra plains of the distant past, and also in present-day deserts and semideserts with their extra-continental climate.
Now about the musk deer (Moschus moschiferus). A denizen of the taiga woodlands and mountains, it is the only representative of the species, and the smallest hoofed animal here in Russia - the adult deer weigh 9 to 14 kg, or less than 28 pounds. Unlike most artiodactyls (cloven-hoofed, or cloven-footed animals), the musk deer has no horns; but its males are armed with impressive tushes making them look quite formidable. We in this country have a population of its northern subspecies; the southern, or Himalayan, occurs in China, Tibet, Korea and in the Himalayas.
The Moschus moschiferus is a very ancient animal. The present type must have been persisting at least ever since the late Pleiocene or early Pleistocene. Paleontologists say it came to Russia from central and eastern Asia.
The ecology and behavior of this singular species are most unusual, characterized by high trophic and bio-typical selectivity. Musk deer prefer wood lichens for food, especially in winter seasons. As shown by our studies, these plants are well digested and assimilated, and their addition to green feeds enhances the nutritional value of the fodder. Since wood lichens are within reach all the year round, in wintertime the musk deer suffers less from food shortages than other herbivores.
Because of its small size the musk deer is an easy prey for many predators, the sable including; therefore it chooses secure landscapes with caves as "safe havens". Such kind of ecology makes for the specific behavioral and populational stereotypes of the species: it is confined to particular territories immune to other animal species, and is broken down into relatively isolated groups. Unlike most ungulates that are polygamous (cohabiting in a harem during mating seasons), the musk deer is a monogamous animal by and large, that is mating in pairs.
Now the moose (Alces alces), the largest representative of the deer family who inhabits most different woodlands of Eurasia and North America-from boggy, water-logged stretches of Siberian taiga forests down to broad-leaved groves of the South. This animal often occurs in other zones, for one, in forest-steppes, forest - tundras and elsewhere.
In evolutionary terms this is a younger species than the musk deer and the saga: it must have been formed in the mid-Pleistocene. It came to populate Eurasia and North America about 100,000 to 150,000 years ago. Not choosy and fastidious in food, the moose show preference for woody and shrubby plants. For the most part they live either as loners or in families, and are not prone to combine in groups which, if formed none the less, are rather unstable. The species is remarkable for a relatively low level of mobility and does not seek secure habitats in contrast to the musk deer. However, in some
areas the moose go on seasonal migrations and travel as far as 100, 200 and 300 km, and even more. During mating the males take one or two females or hold small harems. The fertility rate of moose is rather small, and every year many females stay barren.
Naturally the population dynamics of all the above there species of wild animals not only depends on changing environmental conditions-human activities are also implicated here. Active hunting for moose, saigas and less so for musk deer has been on since the Stone Age: their bones are recovered in diggings on the sites of many encampments of primitive man. By the late 19th century the population of the moose and saiga had dropped to a critical level. The subsequent hunting bans and favorable natural conditions helped these species to rehabilitate. Yet the turn of the 20th and 21st centuries saw another critical period for the Russian population of the saiga and musk deer.
The high demand on the world market for saiga horns and musk-deer ejaculate (secrete of the musk gland of males), which are widely used in traditional Chinese medicine, plus the looser border control over smuggling spurred illicit hunting for these animals in our country. The saiga was hit the hardest because adverse natural conditions conspired with human activities in what we call anthropogenic pressing. Today the overall saiga population in Russia makes up only 5 - 10 percent of what it was in the 1980s and 1990s. Man-caused environmental modification has a pernicious effect, too - the habitation areas of these and other species of wild animals contracts, and boundaries between populations and population groups are changed.
All that has prodded the author of the present article to get down to the genetic diversity of the saiga, musk deer and moose populations proceeding from the level of variability of the most variable fragments of mitochondrial DNA (mtDNA) contained in all male and female cells but passed on along the material line through the egg cell. Thus mtDNA studies apply to inheritance on the motherly line of descent.
Any new mutation in mtDNA fragments means the birth of a new line. The larger the number of mutations, the higher the divergence of one genetic line from another, and the more distant genetic relatedness between them. Consequently, we can compare individuals, groups, populations and species. For one, this very method is used in studying the genesis of human races and the relatedness of different peoples and ethnic groups.*
Our data demonstrate: for migrating species like the saiga, intrapopulational variability is much higher that interpopulational differences. Populations inhabiting Kazakhstan exhibit a particularly close level of relatedness. DNA studies show that populations living at Usty-urt and Betpak-Daly (in the westernmost and southeastern parts of Kazakhstan, respectively), districts which are much far apart from each other, are in fact closely related-not isolated populations but groups within one and the same genetic system. However, a comparison of the European population in Kalmykia with that in Kazakhstan shows a degree of their genetic isolatedness. This phenomenon could be put down to the Volga, a river that serves as a natural water barrier between the European (to the west) and the Kazakhstan (to the east) groups. Vigorous human activities are likewise instrumental in widening the gap.
What about the practical conclusions? First of all, given the downtrend in the saiga population, we should
* See: L. Zhivotovsky, "Genes and Races: We Are of the Same Kith and Kin", Science in Russia, No. 4, 2004 - Ed.
work toward restoring the saiga numbers-say, by importing saigas from other areas with a larger population. In order to preserve the genetic originality of the saiga (which has adjusted to concrete conditions of the habitation medium), it would be most advisable to select donors from closely related groups. For instance, to save the saigas of Betpak-Daly, now in a critical condition, one could bring thither saigas from Ust-yurt.
Now the saiga is a good example of a positive correlation between the numbers of a population and its genetic diversity - the larger the population, the higher its genetic diversity. A comparison of European (Kalmyk) saigas when their population numbers were high and stable (in 1949 - 1980; we took reference DNA from museum samples) with what was obtained at the turn of this century shows clearly that a dramatic fall in the population numbers caused a dramatic drop in genetic diversity.
These interconnected processes, if continued, may have a dire effect on the saiga's viability, for its adaptation to adverse environmental conditions will keep going down (expressed in the lower resistance to infectious diseases typical of diminished genetic variability). Special nurseries have been established in the Republic of Kalmykia, and in the Astrakhan and Rostov regions so as to reverse the downtrend.
Species like the musk deer distinguished for expressly manifest territoriality (confinement to definite territories) run the risk of diminished genetic diversity among isolated groups and its aftereffect, the inbreeding. As we have demonstrated, these animals have a general level of genetic variability proper to ungulates. Hoofed animals inhabiting restricted territories are much akin in this indicator. Such phenomena have been registered for the denizens of Sikhote-Alin, Sakhalin and the Lake Baikal area. In virgin habitats the genetic diversity of separate groups and populations is sustained by an exchange of migrants reducing the probability of inbreeding and its aftermath.
According to Dr. Vladimir Prikhodko, such exchanges are effected largely through narrow zones of contact devoid of natural obstacles, such as mountain ranges, rivers, and so forth. On the other hand, human economic activities, such as road building, timber and lumber industries and the like hamper transition of animals from one group to another. And last, the overall decrease in the musk deer population of Russia restricts a potential number of immigrants. All this combines in decreasing the viability of separate populations up to their total extinction-more than that, it threatens the very existence of the species as a whole. That is why it is important to spot genetically isolated groups and devise methods promoting a free exchange of individuals. Such conclusions likewise hold for other species leading a settled mode of life.
Finally, our study of moose in European Russia and in the Urals has revealed close genetic relatedness of these animals there and a wide geography of some of their genetic lines: identical mtDNAs were found in the Archangel, Yaroslavl, Leningrad, Sverdlovsk and other administrative regions; previously they had been detected in Finland as well. All that attests to a high mobility of the moose species that constitutes a single population in Europe and in the Urals. And yet their genetic diversity is all too low.
The degeneracy of the gene pool of the European moose has deep historical roots. During the recent glacial period the woodland area shrank dramatically and caused an abrupt cut in the moose numbers. Significant depressions occurred in subsequent periods as well, up to the recent times. Considering the fairly uniform distribution of most of the genetic lines and mobility of animals within their habitation area, special attention should be given to sanctuaries as refuges for the moose; that will help preserve its genofond.
The sad story of the European bison (aurochs) whose survival chances are endangered because of its depleted gene pool (genofond) bring home the following self-evident truths. Namely, we should work out a strategy toward preserving the genetic diversity of endangered animals declining in numbers. This strategy should proceed above all from the biological characteristics of species. Say, for the saiga that has high fertility the aftereffects of a drastic drop in numbers will be less destructive than for the moose or the musk deer, what with their sluggish fertility rate. Depressions related to inbreeding and its consequences affect worst of all the territorial (settled) species like the musk deer.
An imbalance in the correlation of the sexes in populations may lead to a downturn in overall genetic diversity. This tendency is more manifest among monogamous species batter than among polygamous ones holding harems in the mating seasons.
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