BIOLOGY Volume 1 - A Guide to General Biology - 2004

10. ORGANISMS AND THE ENVIRONMENT

10.9. Environmental Conservation

10.9.2. Preservation of Genetic Diversity

Rare and Endangered Species

Human impact on the biosphere has led to the extinction of numerous species. The mammoth, dodo, great auk, and Bengal tiger¹ have already been wiped out by human activity. According to existing estimates, an average of one species currently goes extinct every day.

If we want to prevent the rapid, human-induced decline of biological diversity, we must: 1) identify the species at greatest risk; 2) study the causes of their impending extinction; and 3) attempt to eliminate those causes.

The International Union for Conservation of Nature (IUCN) publishes detailed lists of threatened taxa in a series of so-called Red Data Books. It distinguishes four categories of risk.

The Red Data Book for vertebrates includes all known taxa belonging to these four categories. For plants, compiling such a list is practically impossible, since an estimated 10% or more of described taxa (i.e., about 60,000) are already rare or face the threat of extinction within the next 30–40 years.

There are several measures that help prevent extinction:

1) protection and restoration of habitats;

2) establishment of conservation areas (nature reserves, wildlife sanctuaries, national parks, protected areas, etc.);

3) monitoring and reducing The impact of modern intensive agricultural practices on the biota;

4) reducing The Use of toxic substances, particularly pesticides;

5) restricting trade in endangered species;

6) establishing artificial refuges and implementing breeding programs for endangered species, for example in zoos and botanical gardens;

7) creating sperm and seed banks to preserve the maximum genetic diversity of taxa.

The giant panda (Ailuropoda melanoleuca), which has become a symbol of the World Wide Fund for Nature (WWF), is an example of a species whose extinction is being prevented through the protection and restoration of natural habitats combined with captive breeding.

The giant panda, or bamboo bear, is native to eastern Tibet and adjacent mountains in southwestern China. It feeds almost exclusively on young bamboo shoots, the Abundance of which undergoes severe cyclic fluctuations. In Sichuan Province in 1983, bamboo forests died off suddenly over a large area, and at least 59 pandas starved to death. Compounding this is the anthropogenic factor: the species' habitat is shrinking due to population growth and forest clearance for agricultural land. Without the help of conservation organizations, the giant panda would already be extinct.

By the early 1990s, a substantial amount of research had been conducted, bringing scientists closer to understanding the physiology and ecology of the giant panda in the wild. It became clear how such a seemingly ill-adapted animal survives in its changing environment. Adult pandas live solitary lives, pairing only for mating. They spend 95% of their waking hours eating bamboo: it is low in nutrients, so pandas require large amounts of food, meaning vast thickets with The ability to roam freely through them. Forest reserves have been established for this species, and a captive breeding program has been successfully implemented (in Sichuan Province) using modern reproductive techniques, particularly Artificial Insemination and sperm banks. Today, the giant panda population has grown to approximately one thousand individuals.

Genetic Resources in the Service of Humanity

Out of 250,000 known species of higher plants, only 30 currently provide 95% of our plant-based diet (Fig. 10.35). Developed countries utilize a very narrow range of their varieties. For example, in Canada, half of the wheat crop comes from a single variety, 'Neepawa'. This poses a danger because environmental changes can lead to a sharp drop in agricultural output. Outbreaks of pests or pathogens are particularly dangerous for monocultures. This was clearly demonstrated by the catastrophic spread of the late blight fungus that destroyed the potato crop in Ireland in the 1840s, causing widespread famine.

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Fig. 10.35. Average annual global production of major food crops. (Sattaur (1989) The shrinking Gene pool, New Scientist, 29.7.89, 37–41.)

A quick Introduction of new, climate-resilient crop varieties can offer a solution to this problem. Breeding such varieties requires specific genes, which are typically present in wild populations of crop relatives and can be introduced into high-yielding varieties through crossbreeding or Genetic Engineering. Similarly, the traits of domestic animal breeds can be modified.

Obviously, this approach becomes much more difficult if human economic activity leads to the extinction of wild relatives of cultivated plants and domestic animals. Consequently, establishing seed reserves, sperm banks, field gene banks, and cryopreserving Cells from as many taxa as possible is essential for sustainable agriculture. Preserving The Diversity of wild species is also vital because some of them may contain medicinal agents yet unknown to science. For instance, aspirin was synthesized based on a natural antipyretic agent—salicylic acid found in the leaves of the white willow (Salix alba), while the tropical relative of the periwinkle, Catharanthus roseus, yielded a powerful anticancer compound used to treat Hodgkin's disease and certain types of non-Hodgkin's lymphomas. Recently, a variant of this plant containing 10 times more medicinal raw material was discovered in the West Indies.

In 1982, medications of plant origin worth 40 billion US dollars were prescribed worldwide. They were derived from merely 41 out of 5,000 species studied for this purpose. Considering that a total of 250,000 plant species are known, it is highly likely that medicine will discover many more useful properties in them. This potential naturally depends on preserving the maximum genetic Water/126.html">Diversity of the flora.

Botanical Gardens

Plants are best conserved in situ (meaning "in place"), i.e., within their natural habitats. This approach maintains the largest possible population with minimal effort and expense. Furthermore, the taxon will continue its coevolution with pollinators, symbionts, competitors, and herbivores, preventing any decline in its adaptive potential.

However, if a habitat is severely fragmented or undergoes drastic changes, this approach becomes unreliable. Rainforest species, which are currently being destroyed at an alarming rate, face particularly high risks. An alternative is ex situ conservation ("out of place"), i.e., in botanical gardens, arboretums, etc.

Today, there are approximately 1,500 botanical gardens worldwide. Most of them are located in North America, Europe, and the former Soviet republics, whereas plant diversity is highest in the tropics and subtropics. If the goal is not merely to cultivate living specimens temporarily, but to ensure their reproduction—namely, the sustainable renewal of the species—such geographical mismatch creates obvious challenges related to differences in photoperiod and Temperature regimes. These difficulties can be overcome by combining the horticultural expertise of botanical gardens with more modern germplasm preservation Methods, such as seed banks, field gene banks, and Cell cryopreservation (see below).

Seed Banks

A seed bank is a reliable and space-efficient method for storing germplasm. Originally, these were collections of seeds from food crops and their wild relatives, but today it has become standard practice to conserve the gene pools of many endangered species that have no immediate practical value.

Seeds of many plants (known as orthodox seeds) can remain viable in a dormant state for thousands of years if kept under conditions of low humidity (5–10%) and low temperature (—20 °C). This group includes major crops such as cereals, soybeans, cotton, and various vegetables. At Wakehurst Place, the primary seed repository of the Royal Botanic Gardens, Kew, in London, all incoming material is first X-rayed to check for the presence of an embryo. Samples undergo regular germination testing, and if viability drops below an acceptable threshold (to approximately 85%), the batch is renewed by growing the stored seeds to harvest a fresh crop. This is the most complex and expensive part of the process. Even when successful in terms of quantity, Inbreeding is inevitable, which carries the risk of reducing the quality of the renewed reserves.

The situation is even more challenging with so-called "recalcitrant" seeds, which cannot withstand drying and are therefore unsuitable for long-term storage. Such seeds are found in 20% of all plant species and 70% of tropical species, including vital crops such as cacao, rubber, and tea. Other species, such as potatoes—which reproduce primarily vegetatively—also require alternative long-term storage strategies. In principle, these problems can be solved through deep-freezing of germplasm and the establishment of field gene banks.

Cryopreservation

Cryopreservation refers to the storage of embryonic and meristematic cells in liquid nitrogen at —196 °C. This halts all metabolic processes, allowing the material to remain unchanged theoretically for an indefinite period—provided the refrigeration system operates reliably. The main biological drawback of this approach is the "freezing" of evolution: the genotype is no longer involved in adaptation processes and, after long-term storage, may prove unsuited to new environmental conditions on the planet. This means the taxon can no longer be reintroduced into the wild or used in crop breeding.

Field Gene Banks

Field gene banks are permanent living plant collections—not only of trees, as in arboretums, but also of savanna grasses, various varieties of wheat, rice, cotton, etc. They can be established at botanical gardens, not as decorative public displays, but in small plots or beds not intended for public viewing. For example, the International Cocoa Genebank in Trinidad, which specializes in Latin American varieties of this crop, cultivates 16 trees for each of the 2,500 varieties of Theobroma cacao. These plots provide useful information regarding plant traits, particularly yield and seed germination, which is vital for establishing seed banks. The main disadvantage of this approach is the large space required for the collection and its inevitable vulnerability to pests, fires, hurricanes, and other natural disasters.

In 1989, a group of leading international biodiversity conservation agencies developed a botanical garden conservation strategy. Its goal is to ensure cooperation among local, national, and global projects and to standardize ex situ taxon conservation methods. The strategy aims to stimulate the exchange of material and scientific data among collections, as well as the participation of botanical gardens in combating the illegal trade in endangered species.

Zoos

Originally, zoos (or rather, menageries) were established as collections of wild animals to satisfy public curiosity. Species conservation, including captive breeding, is a relatively recent direction in their activities. The main objective of such breeding programs is to maintain populations of endangered animals with the aim of reintroducing them into the wild when suitable conditions arise. Consequently, it is crucial to simultaneously restore the natural habitat or at least eliminate the factors driving the given taxon to the brink of extinction there.

Most zoos house only a few individuals of each species. To prevent inbreeding and the weakening of animals' adaptive traits, inter-zoo exchanges of breeding stock are widely practiced. Their movements are coordinated by the International Species Inventory System (ISIS), headquartered at the Minnesota Zoo.

Transporting breeding animals across the globe is a troublesome and costly endeavor, and despite notable major successes, such as with giant pandas at the London Zoo, success is not guaranteed. Artificial insemination solves this problem. Semen is collected from sedated males using a probe that electrically stimulates the genitals. This method can be applied not only in zoos but also in the wild, allowing the gene pools of captive populations to be augmented without depleting wild populations.

In practice, many zoo breeding programs have proven so successful that they have led to overpopulation issues, particularly in species whose reintroduction into the wild is delayed. This is unsurprising, as captivity typically entails lower environmental resistance and, consequently, lower mortality rates. For instance, lions in the wild rarely live beyond 7 years, whereas 20-year-old individuals are common in zoos. Decreasing the birth rate is not a viable solution, as it shifts the population's age Structure in favor of older animals. This threatens reproductive success and disrupts the natural learning processes of the young through imitation of adult role models, particularly regarding sexual and parental behavior.

Reintroduction involves serious difficulties and is currently practiced on a very limited scale, largely due to the persistence in original habitats of the problems that threatened the species with extinction in the first place. This is clearly illustrated by The history of the nene (Hawaiian goose). By 1949, its wild population had plummeted to 12 birds. Captive breeding programs ensured the survival of the species, and to date, over 3,000 nenes have been reintroduced into their native habitat. However, a viable wild population has never fully recovered because human-introduced predators remain on the Hawaiian Islands, continuing to push these birds to the brink of extinction.

Nevertheless, prompt reintroduction is indispensable. Otherwise, captive-bred populations will lose the traits necessary for Life in the wild. Animals will become tame and incapable of foraging, establishing territories, or avoiding predators—especially humans. As a result, they will be doomed to a semi-domesticated existence. Just as with plants, the successful conservation of animal species requires coordinating efforts undertaken both ex situ and in situ.

10.22. How can sperm banks contribute to the conservation of, say, African rhinoceroses, whose populations are becoming increasingly fragmented, making it difficult for animals from different groups to encounter one another?

¹ The reasons for the mammoth's extinction are hardly purely anthropogenic, and the Bengal tiger is currently the most numerous tiger subspecies. True, the Caspian (Turanian) tiger went extinct not so long ago. — Trans. note