National Herbarium of NSW, Mrs Macquaries Road, Sydney, Australia.
BMC Evol Biol. 2011 May 18;11:126. doi: 10.1186/1471-2148-11-126.
Inter-population distance and differences in breeding times are barriers to reproduction that can contribute to genotypic differentiation between populations. Temporal changes in environmental conditions and local selective processes can further contribute to the establishment of reproductive barriers. Telopea speciosissima (Proteaceae) is an excellent subject for studying the effect of geographic, edaphic and phenological heterogeneity on genotypic differentiation because previous studies show that these factors are correlated with morphological variation. Molecular, morphological and environmental datasets were combined to characterise the relative influence of these factors on inter-population differentiation, and Bayesian analyses were used to investigate current levels of admixture between differentiated genomes.
A landscape genetic approach involving molecular and morphological analyses identified three endpoints of differentiated population groups: coastal, upland and southern. The southern populations, isolated from the other populations by an edaphic barrier, show low migration and no evidence of admixture with other populations. Amongst the northern populations, coastal and upland populations are connected along a skewed altitudinal gradient by genetically intermediate populations. The strong association between temperature and flowering time in Telopea speciosissima was shown to maintain a temporally unstable reproductive barrier between coastal and upland populations.
Substrate-mediated allopatry appears to be responsible for long-term genetic isolation of the southern populations. However, the temperature-dependent reproductive barrier between upland and coastal populations bears the genetic signature of temporal adjustments. The extreme climatic events of the last glacial maximum are likely to have caused more complete allochronic isolation between upland and coastal populations, as well as exerting increased selective pressure upon local genomes. However, at intermediate altitudes, current climatic conditions allow for the incorporation of alleles from previously distinct genomes, generating new, intermediate genomic assemblages and possibly increasing overall adaptive potential.
种群间的距离和繁殖时间的差异是繁殖的障碍，这可能导致种群间的基因型分化。环境条件的时间变化和局部选择过程可以进一步促进生殖障碍的建立。Telopea speciosissima（山龙眼科）是研究地理、土壤和物候异质性对基因型分化影响的绝佳对象，因为先前的研究表明这些因素与形态变异相关。本研究结合分子、形态和环境数据集来描述这些因素对种群间分化的相对影响，并使用贝叶斯分析来研究分化基因组之间当前的混合水平。
涉及分子和形态分析的景观遗传方法确定了分化种群群体的三个终点：沿海、高地和南部。南部种群被土壤障碍与其他种群隔离，显示出低迁移率，没有与其他种群混合的证据。在北部种群中，沿海和高地种群通过遗传上处于中间的种群沿着倾斜的海拔梯度连接。Telopea speciosissima 中温度和开花时间之间的强烈关联表明，在沿海和高地种群之间维持了一个时间不稳定的生殖障碍。
基质介导的异地发生似乎是南部种群长期遗传隔离的原因。然而，高地和沿海种群之间依赖温度的生殖障碍带有时间调整的遗传特征。末次冰盛期的极端气候事件可能导致高地和沿海种群之间更加完全的异时隔离，并对当地基因组施加更大的选择压力。然而，在中海拔地区，当前的气候条件允许以前不同的基因组的等位基因融入，产生新的、中间的基因组组合，并可能增加整体适应潜力。
