The theoretical Parasitology,

AS IT TO UNDERSTAND, THAT ENTER ITS TASK?

S.A. Be`er

Institute of Parasitology RAS. Moscow

 

The discussion of a theoretical parasitology should begun with fundamental concepts of parasitism, and from a postulate that a synthesis of particular theories of parasitology should at the end lead to foundation of a specific part of science – the theoretical parasitology.

Any parasitic organism (starting with prokaryotes) decreases its entropy using energy of a free-living organism – its host. Stable parasitic (and any other biological) system may be characterized, from the point of view of thermodynamics, by the constant decrease of entropy (as opposed to constant increase of entropy under effects of environment). The exceptions to this rule characterize the loss of system balance and so stability, eventually leading to its disintegration.

The parasitism is a powerful factor that played an important part in development of many groups of both plants and animals. It is characterized by high information content, strong effects on plant and animal genome, their sexual process, and also leads to development of complex mechanisms of defense from invasion of alien proteins.

Nowadays the speed of evolutionary processes in parasite-host systems increases. Furthermore, the character of their entropy changes, by the reason of massive and also multialigned (i.e., chaotic) effects of various in nature and strength of effects anthropogenous factors on components of parasite-host systems.

The parasitism had a serious advantages over other forms of symbiotic relationships in regard to co-evolution of endoparasites and their hosts, particularly on its beginning stages. On these stages, pathogenesity on population level stimulated a number of essential processes, particularly the evolution of mechanisms of immunity. In the further course of evolution, pathogenesity on a population level becomes an obstacle for the formation of a balanced parasitic system. After that, the most evolutionary important factor is no longer a pathogenesity as such, but constantly working mechanism of “deliverance from pathogenesity” as a result of removal of highly virulent individuals from parasite populations, leading to selection of less virulent (and so, more tolerant to the host) parasites.

The problem of parasite biodiversity is considered from 2 aspects: (1) estimation of proper parasite diversity; (2) estimation of parasite role in diversity changes resulting all free-living organisms on the Earth, that is more essential. The paper covers problems of parasite diversity and parasitic systems being formed (parasite communities) which, apart from parasites, are known to include numerous free-living organisms acting as parasite partners in parasitic chains, i.e. different (final, intermediate, additional, etc.) hosts. Parasites are closely associated with the latter by complex parasite-host interrelations and significantly influence them at all levels of organization. Examples are given that illustrating role of parasitic organisms in the problem of biodiversity.

The phenomenon of physical interference of a parasite allocation to that of its host (or, more precisely, their overlapping), is common to all parasitic organisms, irrespective of their systematic arrangement and is observed on all parasitic stages of their life cycles. It may be considered as a universal feature of endo-parasitism. Due to this overlapping, the "start" of the mechanisms responsible for close parasite-host interactions is possible. Spatial overlapping results in a formation of a combined living structure consisting of 2 individuals with their different interacting genomes, morpho-physiological composition and informational connections. The association arisen is likely to have the qualitative features of a "supra-organism" with regard to each constituent. Spatial overlapping of a parasite and its environment is not simply a mechanical interference of their physical parameters. During their coevolution the parasite and its host form a common biologically active formation conditionally named "complicatobiont". Physical overlapping of a parasite with its environment may be regarded as a peculiar feature of living organisms characterized by "parasite congruention" principle. The partners (endoparasite & specific host) form associations in which it is difficult to draw a line between the components. These associations may be characterized by the following features: insertion of fragments of a parasite genome into that of a host, a forming of complex xenoparasitic barriers, very close adhesive connections up to a formation of "perfect concord areas" (chromatophilous adhesion), initiation of 'molecular mimicry" processes (production of antigens common to the parasite and its host), diverse metabolic interactions, synchronized program of partners interaction and self-regulation of their abundance in populations. Based on these grounds we can treat such common parasite-host structures as elements of some superorganism. The characteristics mentioned above may give rise to new emergent features in a functioning (evolving) construction. A parasitism, as compared with a symbiosis, has certain advantages for a complicatobiont forming. It seems likely that parasites had formed their evolution strategy so as to initiate formation of supra-organism associations while not excepting notion of a parasite as an independent organism from among living objects of the Earth. Complex associations formed by them have the characteristics of living systems. Lichen being made up of diverse organisms, which formed them with a parasitism as a basis approximately in late Mesozoic era, may serve as an example of complicatobionts.

Evolution of comlicato-biontes may be explained from the point of view of evolution of complex (“synthetic”) biological systems.

 

 

Успехи общей паразитологии,

/ Отв. ред. С.А. Беэр / Тр. Ин-та паразитологии. Т.44. М.:

Наука, 2003. (в печати)

РОЛЬ ПАТОГЕННОСТИ ПАРАЗИТОВ

В ЭВОЛЮЦИИ ОРГАНИЧЕСКОГО МИРА

С.А. БЕЭР

 

 

В первой четверти XX века академиком К.И. Скрябиным была опубликована книга: "Симбиоз и паразитизм в природе", с подзаголовком: "Введение в изучение биологических основ паразитологии" (Скрябин, 1923), давно уже ставшая раритетом. В ней впервые были описаны, по сути дела, все формы симбиоза и пограничные с ними модусы взаимоотношений организмов. Если мысленно сложить эту книгу с трудами А.А. Филипченко, А.Г. Кнорре, В.Н. Беклемишева, Б.М. Козо-Полянского, А.С. Фаминцина, К.С. Мережковского, ¾ то это и будет та основа, понимания симбиоза и паразитизма, которая позволяет отталкиваясь от неё, развивать уже новые идеи, относительно роли сложных межорганизменных взаимоотношений в эволюции.

За последние примерно 30 лет трактовка паразитизма в известной степени изменилась, точнее - дополнилась. Усилилось понимание того, что сущность явления заключается не только в специфическом симбиотическом взаимодействии генетически разнородных организмов, но и вообще, в более глубоком влиянии паразитизма на эволюцию органического мира.

Становится очевидным, что паразитизм следует признавать, как мощный фактор, сыгравший важную роль в развитии многих групп животных и растений. Он обладает: высокой информативностью, сильным воздействием на геном животных и растений, их половой процесс, способствует формированию сложных защитных механизмов к внедрению чужеродного белка.

Паразитизм тесно связан с понятием "патогенность паразитов", которую можно рассматривать с двух точек зрения, условно говоря: "медика" и "биолога-эволюциониста". Это разные вещи. Медики обычно оценивают патоген-ность на организменном уровне, а биологи эволюционисты ¾ на популяционном. Отсюда и разные подходы к проблеме роли патогенности паразитов в эволюции практически любых живущих на Земле организмов.