Hidden deleterious genetic factors affecting post-meiotic viability in zygospore progeny of a unicellular haplontic alga, mating group A of the Closterium ehrenbergii species complex (Chlorophyta)

Abstract

SUMMARY In a haplontic green alga, mating group A of the Closterium ehrenbergii Meneghini ex Ralfs species complex, viability of meiotic progeny was studied by isolating two gone cells from a single germinating zygospore. In F1 progeny of a cross between mating-type plus M-16-4a and mating-type minus M-16-4b, studied in six independent experiments, percentage survivals varied little from 86 to 96 with a mean of 93 ± 1.4 SE. In F2 progenies of crosses among eight mating-type plus and eight mating-type minus F1 clones of the M-16-4a · M-16-4b cross, percentage survival varied considerably from 24 to 100, with a mean of 70.8 ± 2.2. In B1 progenies of the above eight mating-type plus F1 clones, survival values were significantly different between backcrosses to the recurrent M-16-4b (range = 32–83, mean ± SE = 58.3 ± 6.8) and backcrosses to a genetically unrelated mating-type minus, R-13-20, (85–97, 92 ± 1.6). Also in B1 progenies of the above mating-type minus F1 clones, survival values were significantly different between backcrosses to the recurrent M-16-4a (56–90, 68.3 ± 4,4) and backcrosses to a genetically unrelated mating-type plus, R-13-131 (78–93, 86.1 ± 1.6). Clearly, viabilities of meiotic progeny differed considerably between outbreedings (M-16-4a × M-16-4b, and F, clones × R-13-20 or R-13-131) and inbreedings (F2 and F1 clones × M-16-4a, or M-16-4b). These data suggest the presence of hidden deleterious genetic factors that may reduce viability of zygospore progeny if inbred between a pair of wild-type strains from the normally outbreeding mating group A of the C. ehrenbergii species complex.