Institut de Systématique, Evolution, Biodiversité (ISYEB), Muséum national d'Histoire naturelle, CNRS, Sorbonne Université, EPHE. CP 75005, 57 rue Cuvier, 75005 Paris, France.
Département de Biologie, Ecole Normale Supérieure, PSL Research University, 75005 Paris, France.
Fungal Genet Biol. 2018 Nov;120:1-8. doi: 10.1016/j.fgb.2018.08.005. Epub 2018 Sep 1.
Most species able to reproduce both sexually and asexually (facultative sexual species) invest more in sexual reproduction in stressful environment conditions. According to the abandon-ship hypothesis, plasticity for investment in sexual reproduction may have been selected in these species, allowing unfit genotypes to generate progeny carrying new advantageous allelic combinations. We tested this hypothesis in Aspergillus nidulans, a fungus able to reproduce asexually, or sexually, by outcrossing and/or haploid selfing (i.e. fusion of genetically identical haploid nuclei, causing immediate genome-wide homozygosity). We crossed various strains of A. nidulans in a non-stressful environment and a stressful environment containing a non-lethal dose of fungicide. Without stress, crosses preferentially generated haploselfed fruiting bodies, whereas stressful conditions significantly increased the outcrossing rate. Our results strongly support the abandon-ship hypothesis and suggest that, for parents with low fitness, the costs of investing in sexual reproduction may be compensated by the production of fitter progeny carrying beneficial allele combinations. Similarly, the progeny generated by outcrossing was less fit than that produced by haploid selfing in non-stressful environments, but fitter in stressful conditions, suggesting that outcrossing may have short-term advantages in stressful environments in A. nidulans.
大多数既能进行有性生殖又能进行无性生殖的物种（兼性有性物种）在压力环境条件下会更多地投资于有性生殖。根据弃船假说，这些物种的有性生殖投资可塑性可能已经被选择，允许不合适的基因型产生携带新有利等位基因组合的后代。我们在能够进行无性生殖或有性生殖（即通过异交和/或单倍体自交的杂交）的真菌 Aspergillus nidulans 中测试了这一假说（即融合遗传上相同的单倍体核，导致立即全基因组纯合）。我们在非压力环境和含有非致死剂量杀菌剂的压力环境中交叉各种 A. nidulans 菌株。在没有压力的情况下，杂交优先产生单倍体自交的果体，而压力条件显著增加了异交率。我们的结果强烈支持弃船假说，并表明对于适合度较低的亲本来说，投资有性生殖的成本可能会通过产生携带有利等位基因组合的更适合的后代来得到补偿。同样，在非压力环境中，与单倍体自交产生的后代相比，异交产生的后代适应性较差，但在压力环境中适应性较强，这表明在 A. nidulans 中，异交可能在压力环境中有短期优势。
