Inverted meiosis can rescue fitness of chromosomal hybrids
The article in PNAS provides evidence for a mechanism that rescues fertility of chromosomal hybrids in species with holocentric chromosomes.
Photo description: Cover image of PNAS, Vol. 115, no. 41: Wood White butterflies (Leptidea sinapis) engaged in courtship. Image courtesy of Vlad Dincă.
Chromosomal rearrangements have the potential to drive speciation. However, their accumulation in a population is considered both difficult and unpredictable, because the greatly reduced reproductive fitness of chromosomal hybrids prevents fixation of novel karyotypes. Our study provides evidence for a mechanism that rescues fertility of chromosomal hybrids in species with holocentric chromosomes. We analysed the evolutionary role of the meiotic behaviour of holocentric chromosomes by studying F1 to F4 hybrids between two chromosomal races of the Wood White butterfly (Leptidea sinapis), separated by at least 24 chromosomal fusions/fissions. These chromosomal rearrangements resulted in multiple meiotic multivalents, and, contrary to the theoretical prediction, the hybrids displayed surprisingly high reproductive fitness and regular behaviour of meiotic chromosomes. Here we demonstrate that chromosomal heterozygotes of Leptidea males exhibit inverted meiosis, i.e. they have a reverse order of main meiotic events in which the first and most critical stage of the chromosome number reduction is replaced by the less risky stage of sister chromatid separation. The results suggest that inverted meiosis may facilitate proper chromosome segregation in chromosomal hybrids, preserving fertility and enabling long-term persistence of chromosomal rearrangements, which is a major prerequisite for chromosomal speciation. Our article was selected for the cover image of the 9 October 2018 Issue of PNAS (http://www.pnas.org/content/115/41.cover-expansion).
Lukhtanov V.A., Dincă V., Friberg M., Šíchová J., Olofsson M., Vila R., Marec F., Wiklund C. (2018) Versatility of multivalent orientation, inverted meiosis, and rescued fitness in holocentric chromosomal hybrids. Proceedings of the National Academy of Sciences of the United States of America 115: E9610-E9619. DOI: 10.1073/pnas.1802610115
