Engel C R, Daguin C, Serrão E A
CCMAR-Centre of Marine Sciences, FCMA, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal.
Mol Ecol. 2005 Jun;14(7):2033-46. doi: 10.1111/j.1365-294X.2005.02558.x.
To date, molecular markers have not settled the question of the specific status of the closely related, but phylogenetically unresolved, brown seaweeds, hermaphroditic Fucus spiralis and dioecious Fucus vesiculosus, nor their propensity for natural hybridization. To test the degree of species integrity and to assess effect of the mating system on the population genetic structure, 288 individuals coming from parapatric (discontinuous) and sympatric (contiguous) spatial configurations at two sites were genotyped with five microsatellite loci. Using a Bayesian admixture analysis, our results show that F. spiralis and F. vesiculosus comprise clearly distinct genetic entities (clusters) generally characterized by cosexual and unisexual individuals, respectively. Genetic diversity within each entity suggests that F. spiralis reproduces primarily through selfing while F. vesiculosus is characterized by an endogamous breeding regime. Nevertheless, aberrant sexual phenotypes were observed in each cluster, no diagnostic alleles were revealed and 10% of study individuals were intermediate between the two genetic entities. This pattern can be explained by recent divergence of two taxa with retention of ancestral polymorphism or asymmetrical, introgressive hybridization. However, given (i) coincident monomorphism at three loci in spiralis clusters and (ii) that significantly more intermediates were observed in sympatric stations than in parapatric stations, we argue that interspecific gene flow has occurred after divergence of the two taxa. Finally, we show that whether recently separated or recently introgressive, the divergent breeding systems probably contribute to species integrity in these two taxa.
迄今为止，分子标记尚未解决亲缘关系密切但系统发育尚未明确的褐藻、雌雄同体的旋链岩藻和雌雄异株的泡叶岩藻的具体分类地位问题，也未解决它们自然杂交的倾向问题。为了测试物种完整性的程度并评估交配系统对种群遗传结构的影响，我们对来自两个地点的异域（不连续）和同域（连续）空间配置的288个个体进行了五个微卫星位点的基因分型。通过贝叶斯混合分析，我们的结果表明，旋链岩藻和泡叶岩藻分别由通常以两性个体和单性个体为特征的明显不同的遗传实体（簇）组成。每个实体内的遗传多样性表明，旋链岩藻主要通过自交繁殖，而泡叶岩藻的特征是近亲繁殖。然而，在每个簇中都观察到了异常的性表型，没有发现诊断性等位基因，并且10%的研究个体处于两个遗传实体之间的中间状态。这种模式可以用两个分类群最近的分化并保留祖先多态性或不对称的渐渗杂交来解释。然而，鉴于（i）旋链岩藻簇中三个位点的一致单态性，以及（ii）在同域站点中观察到的中间类型明显多于异域站点，我们认为在两个分类群分化后发生了种间基因流动。最后，我们表明，无论最近是分离还是最近发生渐渗，不同的繁殖系统可能有助于这两个分类群的物种完整性。
