窗口期：在柏克西亚杂交区的一个繁殖事件表明持续的杂交和表型可塑性。
Window of opportunity: an episode of recruitment in a Banksia hybrid zone demonstrates continuing hybridization and phenotypic plasticity.
机构信息
School of Biological Sciences, University of Wollongong, Wollongong, NSW 2522, Australia.
出版信息
Ann Bot. 2010 Mar;105(3):419-29. doi: 10.1093/aob/mcq001. Epub 2010 Feb 7.
BACKGROUND AND AIMS
In perennial plants (especially post-fire resprouters), extant populations may reflect recruitment events in the distant past. This is true of hybrid zones formed by two Banksia species of swamps and woodlands in south-eastern Australia, Banksia robur and B. oblongifolia. Both resprout after fire but recruitment is dependent on periodic fires. Although plants of intermediate morphology have also been identified as hybrids using allozyme markers, the extent of ongoing hybridization is unknown. This study investigates whether both microsatellite markers and morphological measurements can be used to distinguish between the two species and their hybrids. A recent recruitment event and microsatellite markers allow the frequency of ongoing hybridization to be estimated, and also the effects of environmental variation on the morphology of plants and seedlings to be tested.
METHODS
Variation at seven microsatellite loci was scored and seven leaf characteristics within putatively pure stands and mixed stands of both species were measured, revealing that the two species were genetically and morphologically distinct and that mixed stands also contained genetically and sometimes morphologically distinct hybrids. An opportunity created by wildfires was used to analyse the genetics and morphometrics of adults and seedlings from two hybrid zones.
KEY RESULTS
Approximately 9 % of adults and 21 % of seedlings were identified as genetic hybrids in both hybrid zones. Within these sites, the genotype of mature plants correlated well with morphology, except for some hybrid plants that had parental morphology. However, seedling morphology was highly variable and insufficient to describe the composition of the hybrid zone in this cohort. Greater phenotypic plasticity was evident among seedlings growing within the hybrid zones than seedlings growing in pots.
CONCLUSIONS
The hybrid zones are complex and the range of genotypes detected in seedlings reveals both continuing hybridization and introgression.
背景与目的
在多年生植物（尤其是火后再生植物）中，现存种群可能反映出过去遥远时期的繁殖事件。这在澳大利亚东南部的沼泽和林地两个 Banksia 物种（Banksia robur 和 B. oblongifolia）形成的杂交区中是真实的。这两个物种都在火灾后再生，但繁殖依赖于周期性的火灾。尽管使用同工酶标记也鉴定出中间形态的植物为杂种，但持续杂交的程度尚不清楚。本研究旨在探讨微卫星标记和形态测量是否可用于区分这两个物种及其杂种。最近的一次繁殖事件和微卫星标记允许估计持续杂交的频率，并检验环境变化对植物和幼苗形态的影响。
方法
在假定的纯种群和两个物种的混合种群中，对七个微卫星位点的变异进行了评分，并测量了七个叶片特征，结果表明，这两个物种在遗传和形态上均有明显差异，并且混合种群中也包含遗传上和形态上有时不同的杂种。利用野火创造的机会，分析了两个杂交区的成年植物和幼苗的遗传学和形态计量学。
主要结果
在两个杂交区中，大约 9%的成年植物和 21%的幼苗被鉴定为遗传杂种。在这些地点，成熟植物的基因型与形态密切相关，但某些杂种植物具有双亲形态。然而，幼苗形态高度可变，不足以描述该队列中的杂交区组成。与在杂交区中生长的幼苗相比，在盆中生长的幼苗表现出更大的表型可塑性。
结论
杂交区很复杂，在幼苗中检测到的基因型范围揭示了持续的杂交和基因渐渗。
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