Cyto genetic studies in clarkia d section primigenia d part 5 interspecific hybridization between clarkia amoena huntiana d and clarkia lassenensis d
Abdel Hameed, F.
Evolution 25(2): 347-355
ISSN/ISBN: 0014-3820 DOI: 10.2307/2406926
The discovery of a single sympatric association between two diploid species of Clarkia, i. e., C. amoena huntiana and C. lassenensis (2n = 14), marks the first reported case of overlap of their otherwise well separated geographical distributions. Cytological and morphological observations showed no hybrids within this mixed population. Greenhouse interspecific hybridizations involving populations surrounding the area of sympatry did not succeed in setting seeds, whereas some of those between populations well separated geographically set seeds. Of these, two combinations were far more successful than the rest. These two combinations involved certain chromosome end arrangements found in the most southern part of the range of each species. Both C. amoena and C. lassenensis may have in the past enjoyed a relatively wide area of overlap and sympatry. The allotetraploid, C. gracilis, may have originated more than once sometimes during late Pleistocene when the two diploids came together after earlier being well separated geographically and genetically. Greenhouse produced F1-diploid hybrids showed a wide range and a high degree of meiotic irregularities which are probably the main factor causing sterility. No genuine association was observed at M1 with all chromosomes being univalents at this stage in most meiocytes. The few M1 associations encountered were due to heterochromatin stickiness. Meiotic irregularities resulted, in part, from univalent pseudo-associations, precocious division, and fragmentation prior to M1. The absence of homology between the two diploid genomes in F1-meiocytes would define the resulting amphidiploid as a true or genomic allotetraploid.