Giraud T, Jonot O, Shykoff J A
Ecologie, Systématique et Evolution, UMR 8079 Université Paris Sud, Université Paris-Sud, Orsay cedex, France.
J Evol Biol. 2006 May;19(3):970-80. doi: 10.1111/j.1420-9101.2005.01032.x.
Microbotryum violaceum is a fungus that causes the sterilizing anther smut disease in Caryophyllaceae. Its diploid teliospores normally produce equal proportions of haploid sporidia of its two mating types. However natural populations contain high frequencies of individuals producing sporidia of only one mating type ('biased strains'). This mating type-ratio bias is caused by deleterious alleles at haploid phase ('haplo-lethals') linked to the mating type locus that can be transmitted only by intra-tetrad selfing. We used experimental inoculations to test some of the hypotheses proposed to explain the maintenance of haplo-lethals. We found a disadvantage of biased strains in infection ability and high intra-tetrad mating rates. Biased strains had no higher competitive ability nor shorter latency and their higher spore production per flower appeared insufficient to compensate their disadvantages. These findings were only consistent with the hypothesis that haplo-lethals are maintained under a metapopulation structure because of high intra-tetrad selfing rates, founder effects and selection at the population level.
堇菜科黑粉菌是一种能引发石竹科花药黑粉菌不育病的真菌。其二倍体冬孢子通常会产生等量的两种交配型单倍体担孢子。然而，自然种群中存在高频率仅产生一种交配型担孢子的个体（“偏态菌株”）。这种交配型比例偏差是由与交配型位点连锁的单倍体阶段有害等位基因（“单倍体致死基因”）导致的，这些基因只能通过四分体内部自交进行传递。我们通过实验接种来检验一些为解释单倍体致死基因的维持而提出的假说。我们发现偏态菌株在感染能力方面存在劣势，且四分体内部交配率较高。偏态菌株没有更高的竞争能力，潜伏期也没有更短，并且它们每朵花更高的孢子产量似乎不足以弥补其劣势。这些发现仅与以下假说一致：由于四分体内部自交率高、奠基者效应以及种群水平的选择，单倍体致死基因在集合种群结构下得以维持。
