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Schlagwörter:
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Zusammenfassung:
In some taxa, new emergences of asexual lineages are possible through contagious asexuality, where rare males from obligate asexual lineages can transmit asexuality to new lineages by cross-mating with sexual females. With such ‘contagious asexuality’ scenario, it is often assumed that asexuality can be immediately transmitted intact from the asexual to the new hybrid lineages. In this paper, we investigate in detail whether asexuality is faithfully transmitted in such crosses. We studied the reproductive modes of F1s produced by crossing sexual females to males from an obligate parthenogen lineage in Daphnia pulex. While the parental asexual lineage is an obligate parthenogen reproducing clonally, we find that the F1s show a wide diversity of reproductive modes. We do not find discrete classes of sexual vs. asexual F1s. Rather, some F1s appear to be able to reproduce both sexually and asexually. Moreover, when they are able to reproduce asexually (about 20 % of F1s), they do not reproduce clonally, as shown by frequent loss of heterozygosity (LOH) among their parthenogenetic offspring. Such LOH can lead to large fitness reduction by revealing recessive deleterious mutations, which may therefore largely impact the chance of establishment of contagiously-produced asexual lineages. We also found that these F1s are difficult to produce and have strongly reduced fertility rates, particularly for asexual F1s compared to natural ones, indicating that the initial fitness of these contagiously-produced asexual lineages is also often low. Together, our results indicate that asexuality is not transmitted intact with ‘contagious’ crosses. Such crosses rather result in diverse, non-binary, and non-clonal offspring, on which subsequent selection may act.
