The origin of plague. Future perspectives of ecological and molecular-genetic synthesis

Plague, infamous due to three devastating pandemics, remains one of the most dangerous human diseases. Its causative agent, the microbe Yersinia pestis, is a priority in the arsenal of possible biological weapons, which requires increased attention to the development of a system of biological (bacteriological) security. A deep knowledge of the natural processes that facilitate the development of the causative agent of plague may be useful for this. There are currently two alternative approaches to determining the origin of Y. pestis – molecular genetics (MG) and ecological. MG-data has led to the innovative idea of the saltation conversion of the psichrophilic saprozoonotic microbe Yersinia pseudotuberculosis O:1b into a population of the pathogenic plague microbe Y. pestis, by horizontal transfer of two specific plasmids pFra and pPst from the external environment, or from other bacteria and inactivated/deletions of genes that have lost their functions in a new habitat, probably in populations of voles (Microtinae) in Asia. The ecological scenario is based on the idea of Darwinian adaptations by way of a quick "quantum" formation of its properties in a parasitic system; the "marmot–flea" (Marmota sibirica – Oropsylla silantiewi), during the transition between the Pleistocene and Holocene periods. Three important factors of quantum speciation were found: heterothermia of marmot bodies during hibernation, the oxidative "burst" of macrophages in hibernating marmots, and stress-induced mutagenesis initiated by the oxidative "burst" of macrophages. This article asserts the complementarity of the ecological and MG approaches. The prospect of a solution to the problem of quantum speciation of the causative agent of the plague, and the development of methods for the treatment and prevention of disease, can be observed in the synthesis of ecological and MG approaches.

Species concepts and speciation

Some of the recent literature on species concepts and speciation is reviewed. It is evident that there is no single precise and objective definition of the species which is universally acceptable and applicable. Rather than trying to solve the species problem by searching for more definitions or separating the category of nomenclatural taxonomy from that of experimental research, it is suggested that it would be preferable to recognize and indeed stress that not all species are of the same kind. Different sorts of species should be recognized and understood in relation to different inherent characteristics and different strategies of evolution. We should thus recognize palaeospecies, morphospecies, sibling species, ring species, polytypic species, biospecies, introgressed species, hybrid species, compilospecies, agamospecies, gynogenetic species, and so on. It ought to be possible to devise a scheme for designating these and handling them then in a systematic manner.With reference to speciation, it is concluded that no longer should we stress that gradual allopatric speciation is the only or indeed main mode of speciation in animals. We should encompass also the concepts of quantum speciation, gradual sympatric speciation, instant speciation, and speciation by hybridization and polyploidy. There is now experimental evidence to show that these are theoretically possible. However, it is as well to remember that, to date, speciation by hybridization and polyploidy is the only proven method.As noted by many previous authors, there is no single mode of speciation. The process in different groups of animals is liable to be radically different. Further, even in the same family or genus, there is no reason to believe that the mode of speciation will be constant.