Kravchenko, Shabanov (2010) Levels of biodiversity of the Pelophylax esculentus complex

Kravchenko M. A., Shabanov D. A. Levels of biodiversity of the Pelophylax esculentus complex // Biodiversity and Sustainable Development. Proceedings of the International Scientific‑Practical Conference – Simferopol: KNC, 2010. – pp. 68–71.
UDC 573.22:591.158.1:597.851
Kravchenko M.A., senior lecturer, Shabanov D.A., associate professor; Department of Zoology and Animal Ecology, V. N. Karazin Kharkiv National University; m_kravchenko@inbox.ru; d.a.shabanov@gmail.com
LEVELS OF BIODIVERSITY OF THE PELOPHYLAX ESCULENTUS COMPLEX
This work is devoted to the hybridogenic complex of green frogs, which is characterized by unusual levels of biodiversity. Before discussing these levels, it is necessary to substantiate the very possibility of differences in sets of biodiversity levels among different groups of organisms.
In the “Convention on Biological Diversity”, adopted by the UN (Rio de Janeiro, 1992), a basic definition is given: “‘Biological diversity’ means the whole variety of living organisms from all environments <…>; the diversity within species, between species and ecosystems.” In accordance with this definition many authors distinguish three main levels of biodiversity: genetic (intraspecific), species and ecosystem. Obviously, these three levels of biodiversity correspond to the three basic levels of organization of biosystems: the organism, the species and the ecosystem. At the same time it is clear that this list is incomplete: both the organism, the species and the ecosystem are themselves complex systems composed of an entire hierarchy of subsystems.
To order our concepts of diversity levels, we turn to a cybernetic understanding of the term. From a cybernetic point of view (Ashby, 1959), diversity is the number of possible states of a system. From this perspective one can distinguish potential diversity (the number of possible different states of a set of systems) and realized diversity (the number of observed states adopted by the systems under study). The traits by which a system can assume different states can be called its “degrees of freedom”. Biodiversity is the realized set of states of biosystems according to a certain set of their “degrees of freedom”.
By what traits, “degrees of freedom”, can individuals within a population differ? For example, by sex, age, genetic endowment. At what level are these characteristics determined? Sex in most vertebrates is determined at the genotypic level and depends on the set of genomes of the individual. In some cases sex can be redefined epigenetically (as a result of interaction between the inherited developmental program and environmental conditions in which ontogeny occurs). Age reflects ontogenetic changes over time. Processes influencing survival and mortality of individuals of different sex and age are reflected in the sex and age structure of populations. During sexual reproduction the genotype of an individual is determined by the genomes of the gametes that formed the zygote and by cytoplasmic inheritance. The genetic uniqueness of an individual is defined by the composition of genomes that constitute its genotype, and genetic diversity itself is set at the genome level (Table 1).
Table 1. “Basic set” of biodiversity levels (from the population level and below)

The complex includes two parental species: the pool frog, Pelophylax lessonae (Camerano, 1882) and the marsh frog, Pelophylax ridibundus (Pallas, 1771), as well as their hybrids, called edible frogs, Pelophylax esculentus (Linnaeus, 1758). A remarkable feature of the hybrid frogs is that, in the typical case, the gametes receive not a recombined mixture of the parental genomes but one of the parental genomes in its pure form. For example, in the North‑Donetsk Center of Green‑Frog Diversity (Shabanov, Lytvynchuk, 2010) individuals of P. ridibundus co‑breed together with the following P. esculentus forms: diploids transmitting the P. lessonae genome to gametes; diploids transmitting the P. ridibundus genome; diploids producing both P. lessonae and P. ridibundus gametes simultaneously (!); triploids with two P. ridibundus genomes; triploids with two P. lessonae genomes. In addition, tetraploid P. esculentus sometimes arise in this centre, while adult P. lessonae are absent: their genomes are transmitted clonally from generation to generation among hybrids (Shabanov et al., 2006; Korshunov, 2009). In other regions of green‑frog distribution it has been shown that the mitochondria typical for P. ridibundus have been displaced by mitochondria of P. lessonae, acquired through backcrosses with P. esculentus (Plötner et al., 2008). The result of such peculiarities of green frogs is, for example, the emergence of hemiclonal population systems (HPS), which, unlike ordinary populations, unite individuals of different species that differ in ploidy and the nature of the gametes they produce.
Unusual diversity levels generated by these and other “degrees of freedom” characteristic of green frogs may also be present in other hybridogenic species complexes. Of course, these levels are not equivalent. For instance, the potential diversity of genomes in terms of their clonality and recombinancy is incomparably smaller than the potential genetic diversity of genomes. Different diversity levels interact: clonal transmission of genomes sharply narrows their realized genetic diversity. In any case, all diversity levels, both those common to most organisms and those specific to particular groups, require study and conservation.
The work was carried out with the support of the Fundamental Research Fund of V. N. Karazin Kharkiv National University, as well as grants from the Ukrainian State Fund for Fundamental Research and the Russian Foundation for Basic Research (RFBR).

{
"title": "Levels of Biodiversity in Hemiclonal Population Systems of the Green Frog Complex",
"summary": "The presented set of diversity levels (Table 1) represents a basic framework typical for species with simple life cycles and fertilization, such as the common toad Bufo bufo. Specific groups, like the green frogs (Pelophylax esculentus complex), exhibit additional “degrees of freedom” due to interspecific hybridization, hemiclonal inheritance, and the transfer of nuclear and cytoplasmic genetic material, generating new hierarchical levels of biodiversity (Table 2). The article outlines these levels, their driving factors, and discusses their implications for conservation and research.",
"body": "Age‑related\nBirth and mortality\nSex‑related\nDynamics of sex ratio at different ontogenetic stages\nGene‑pool\nSelection, genetic drift, migrations\nIndividuals\nOntogenetic\nDevelopment and senescence\nEpigenetic\nVariability of developmental processes\nGenotypic\nCombination of genomes at fertilization\nGenomes\nGenetic\nRecombination\nGenes\nAllelic\nMutagenesis\n\nThe set of diversity levels shown in Table 1 can be considered “basic,” characteristic for most species with a simple life cycle and fertilization—for example, the common toad Bufo bufo (Linnaeus, 1758), which spawns in the same water body as the green frogs examined here. Groups of organisms characterized by specific degrees of freedom will also be characterized by specific levels of diversity. For instance, for our species Homo sapiens Linnaeus, 1758, culturally based levels of variability that correspond to populations and individuals are important. The peculiarity of the green frog group lies in the fact that it is characterized by interspecific hybridization, hemiclonal inheritance, interspecific transfer of nuclear and cytoplasmic genetic information, as well as a diversity of hybrids in terms of ploidy and the composition of produced gametes (Plötner, 2005; Shabanov, Lytvynchuk, 2010). These features of green frogs generate new “degrees of freedom” of their variability and give rise to new biodiversity levels (Table 2).\n\nTable 2. Biodiversity levels characteristic for hemiclonal population systems of the hybrid‑genetic complex of green frogs. Levels specific to the Pelophylax esculentus complex are highlighted in semi‑bold type.\n\nSystems\nDiversity level\nLeading factors of variability\nPopulations (population systems)\nAge‑related\nBirth and mortality\nSex‑related\nDynamics of sex ratio at different ontogenetic stages\nSpecies‑level (parental species, hybrids)\nInterspecific hybridization, clonal transmission of genomes of species absent in the hemiclonal population system (HPS)\nCytogenetic\nDynamics of HPS composition due to differences in reproductive efficiency of different forms\nGene‑pool\nSelection, genetic drift, migrations\nIndividuals\nEpigenetic\nVariability of developmental processes\nCytoplasmic inheritance\nTransmission through hybrids of mitochondria from another species, selection of different mitochondrial lineages\nGametic\nElimination of different genomes during gametogenesis\nPloidy\nNumber of genomes\nGenotypic\nCombination of genomes at fertilization\nGenomes\nMode of inheritance\nClonal transmission or recombination\nSpecies‑level\nInterspecific hybridization, semi‑clonal inheritance\nGenetic\nRecombination (including interspecific)\nGenes\nAllelic\nMutagenesis\n\nThe complex includes two parental species: the pool frog Pelophylax lessonae (Camerano, 1882) and the marsh frog Pelophylax ridibundus (Pallas, 1771), as well as their hybrids, called edible frogs Pelophylax esculentus (Linnaeus, 1758). A remarkable feature of the hybrid frogs is that, in the typical case, the gametes receive not a recombined mixture of the parental genomes but one of the parental genomes in its pure form. For example, in the North‑Donetsk Center of Green Frog Diversity (Shabanov, Lytvynchuk, 2010) individuals of P. ridibundus co‑reproduce together with the following P. esculentus representatives: diploids transmitting the P. lessonae genome to gametes; diploids transmitting the P. ridibundus genome; diploids simultaneously producing gametes of both P. lessonae and P. ridibundus (!); triploids with two P. ridibundus genomes; triploids with two P. lessonae genomes. In addition, tetraploid P. esculentus sometimes arise in this center, while adult P. lessonae are absent: their genomes are transmitted clonally from generation to generation among hybrids (Shabanov et al., 2006; Korshunov, 2009). In other regions of green‑frog distribution it has been shown that the mitochondria typical for P. ridibundus have been displaced by mitochondria of P. lessonae, acquired through backcrosses with P. esculentus (Plötner et al., 2008). As a result of these peculiarities, hemiclonal population systems (HPS) arise, which, unlike ordinary populations, unite individuals of different species that differ in ploidy and the nature of the gametes they produce.\n\nUnusual diversity levels generated by these and other “degrees of freedom” characteristic for green frogs may also be present in other hybridogenic species complexes. Of course, these levels are not equivalent. For example, the potential diversity of genomes in terms of their clonality and recombinancy is incomparably smaller than the potential genetic diversity of genomes. Different diversity levels interact: clonal transmission of genomes sharply narrows their realized genetic diversity. In any case, all diversity levels, both those common to most organisms and those specific to particular groups, require study and conservation.\n\nThe work was carried out with the support of the V. N. Karazina Fundamental Research Fund of Kharkiv National University, as well as grants from the Ukrainian State Fund for Fundamental Research (GFFI) and the Russian Foundation for Basic Research (RFBR)."
}

This group includes two parent species: the pond frog, Pelophylax lessonae (Camerano, 1882), and the lake frog, Pelophylax ridibundus (Pallas, 1771), as well as their hybrids, known as edible frogs, Pelophylax esculentus (Linnaeus, 1758). A remarkable feature of hybrid frogs is that, typically, their gametes do not contain a recombined mixture of the genomes they received from their parents, but rather one of the parental genomes in its pure form. For example, at the Seversko-Donetsk Center for Green Frog Diversity (Shabanov, Litvintchuk, 2010), individuals of P. ridibundus co-reproduce with the following representatives of P. esculentus: diploids that pass the P. lessonae genome to gametes; diploids that pass the P. ridibundus genome; diploids that simultaneously produce P. lessonae and P. ridibundus gametes (!); triploids with two P. ridibundus genomes; triploids with two P. lessonae genomes. In addition, P. esculentus tetraploids occasionally arise in this center, while adult P. lessonae are absent: their genomes are transmitted clonally from generation to generation among hybrids (Shabanov et al., 2006; Korshunov, 2009). In other regions where green frogs are found, it has been shown that in P. ridibundus, the mitochondria characteristic of this species have been displaced by P. lessonae mitochondria obtained through backcrossing with P. esculentus (Plötner et al., 2008). The result of such characteristics of green frogs is, for example, the emergence of hemiclonal population systems (HPS), which, unlike ordinary populations, unite individuals of different species that differ in ploidy and the nature of the gametes they produce. The unusual levels of diversity generated by these and other “degrees of freedom” characteristic of green frogs may also be present in other hybridogenic species complexes. Of course, these levels are not equivalent. For example, the potential diversity of genomes based on their clonality and recombinancy is incomparably smaller than the potential genetic diversity of genomes. Different levels of diversity interact: for instance, clonal transmission of genomes sharply narrows their realized genetic diversity. In any case, all levels of diversity—both those common to most organisms and those characteristic of specific groups—require study and conservation. This work was supported by the Fund for Fundamental Research at V. N. Karazin Kharkiv National University, as well as grants from the State Fund for Fundamental Research of Ukraine and the Russian Foundation for Basic Research (Russia).