Abstract
The widespread South American melanopline grasshopper Dichroplus pratensis is chromosomally polytypic. Seven different Robertsonian translocations between six L-autosomal pairs of the standard all-telocentric karyotype were detected; several races in Argentina are characterized for being polymorphic for one to three of these rearrangements. Within contact zones monobrachial homologies between fusion metacentrics thus occur, and hybrids (complex structural heterozygotes) are formed, in whose meiosis, quadrivalents and quinquivalents prone to non-convergent orientation and unbalanced segregation are produced. We analyse the karyotypic constitution of populations of D. pratensis from a hybrid zone between races that, although sharing the polymorphic 3/4 fusion, differ for fusions with monobrachial homologies as described above. The Sierra de la Ventana hybrid zone has certain distinctive characteristics: the frequencies and type of the fusions vary abruptly within short distances; these fusions show a mosaic pattern distribution; all the monobrachially homologous fusion metacentrics were found in high frequency. The possible origin of this hybrid zone is discussed.
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Acknowledgements
Acknowledgements The authors wish to express their sincere gratitude to those who helped in the collection and processing of grasshoppers: Tati Mirol, Dr Cristina D'Aiutolo and Claudio Jr and Pablo {CJB's sons). Special thanks are also due to Dr Esteban Hasson and Dr Pablo Colombo for reviewing the manuscript, to Dr Demetrio Boltovskoy for assistance with the English language, to Dr Osvaldo Reig for the literature suggested and to Ing. Jorge (Flaco) Maidana for providing computer facilities. CJB is indebted to Professor Dr Juan Hunziker in whose laboratory CJB's work on grasshopper cytogenetics started 10 years ago. Financial support from Buenos Aires University and CON1CET is gratefully acknowledged.
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Tosto, D., Bidau, C. Distribution of chromosome frequencies within a hybrid zone of Dichroplus pratensis (Melanoplinae, Acrididae). Heredity 67, 299–306 (1991). https://doi.org/10.1038/hdy.1991.93
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DOI: https://doi.org/10.1038/hdy.1991.93