Evol Ecol Res 8: 1235-1248 (2006)     Full PDF if your library subscribes.

Demography and evolution of pure hybridogenetic frog (Rana esculenta) populations

Christian Som1,2 and Heinz-Ulrich Reyer1*

1Institute of Zoology, University of Zurich, Winterthurerstrasse 190, CH-8057 Zürich and 2World Wide Fund for Nature, Hohlstrasse 110, CH-8010 Zürich, Switzerland

Author to whom all correspondence should be addressed.
e-mail: ulireyer@zool.unizh.ch


Question: How can pure hybrid populations of the hemiclonal frog Rana esculenta persist over time? How can they maintain genetic diversity despite partial clonal inheritance?

Mathematical methods: A deterministic model for identifying the composition of hybrid populations in relation to gamete production and primary fitness of its diploid and triploid members. Computer simulations for testing the effects of population composition on genetic diversity.

Key model assumptions: Pure Rana esculenta populations consist of diploid males and females of the genotype LR and triploid males and females of the type LLR. Triploids of both sexes eliminate the R genome pre-meiotically (hybridogenesis) and produce haploid L gametes. Within the diploids, males produce R sperm and females either haploid R or diploid LR eggs. All individuals mate randomly and generations do not overlap. The overall hybrid population has a constant size with both sexes and ploidies affected equally by the limitation.

Predictions: In pure Rana esculenta populations, the co-existence of diploid and triploid individuals is stable since each ploidy depends on the other for successful reproduction; hence, the mating system is balanced in itself. The genetic diversity and health in these hemiclonal populations resembles the diversity in similar sexual species due to a constant high amount of recombination in one of the parental genomes and a reduced mutation rate in the other. Thus diploid–triploid R. esculenta have become self-sustaining evolutionary units with a potential for new species formation.

Keywords: ecological modelling, evolutionary unit, hybridogenesis, mate choice, ploidy, population dynamics, speciation.

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