Grebelnyi S.D. 2005. [How many clonal species are there in the world. Part 1. The difference between clonal forms and bisexual species] // Invertebrate Zoology. Vol.2. No.1: 79–102 [in Russian, with English summary].
Zoological Institute, Universitetskaya naberezhnaya, 1, Saint-Petersburg 199034 Russia. E-mail: email@example.com
ABSTRACT: When using the term “sexual reproduction” we usually forget that sexual process is not directly bound up with reproduction. Being the main instrument of genetic recombination, in mammals and birds it takes place in every generation and supports the diversity of genotypes. In other cases (Daphniidae, Daphniiformes, Crustacea; Aphididae, Homoptera) it only periodically restores the genetic diversity, which is inevitably lost by population while it reproduces by parthenogenesis. As a result, the population gradually converges to a mixture of a limited number of clones, each of which being comprised of genetically identical individuals. Switching over to long-term parthenogenesis (or other kind of reproduction without recombination) leads to emergence of genetically isolated, generally all-female races. The examples of such phenomenon are the beetles (Otiorhynchus, Curculionidae, and Ptinus, Ptinidae), butterflies (Solenobia, Psychidae), grasshoppers (Saga, Tettigoniidae, and Warramaba, Eumastacidae), woodlice (Trichoniscus, Trichoniscidae, Isopoda, Crustacea). Many of them, having acquired some karyological differences from their closest bisexual relatives, are often considered as separate clonal or hemiclonal species (for example, parthenogenetic lizards of the genera Cnemidophorus, Teiidae; Leiolepis, Uromastycinae; Lacerta, Darevskia, Lacertidae; Heteronotia, Gekkonidae; gynogenetic and hybridogenetic fishes Poecilia and Poeciliopsis, Poeciliidae; caudate amphibian Ambystoma, Ambystomatidae; very common European frog Rana esculenta. Most of non-recombinating races or species are characterized by higher heterozygosity and viability, many of them being of hybridogenous origin. The study of meiosis in parthenogenetic organisms makes it possible to understand the cause of competitive success of such forms in nature and fragility of clones obtained from “normal” bisexual species in the laboratory. The fact is that the animals and plants, which in natural conditions do not have true sexual reproduction, nevertheless pass all their chromosome set (or only a part of it) to their offspring in completely unmodified condition. The necessary condition of successful cloning is a deep deformation of gametogenesis, which disrupts recombination. That preserves the most favorable combinations of characters, which, having arisen by chance, succeeded in clonal competition. By examining different mechanisms of stoppage of recombination in nature (parthenogenesis, gynogenesis, hybridogenesis et ctr.), we elicit the most general features of clones as well as their advantages and limitations in comparison with bisexual Mayr’s “biological species”.
KEY WORDS: clonal competition, all-female races, unisexual species, stoppage of recombination, parthenogenesis, gynogenesis, hybridogenesis, apomixis, geographic distribution of polyploids, “biological species”, climatic changes.