Morphological and molecular phylogenetic context of the angiosperms: contrasting the 'top-down' and 'bottom-up' approaches used to infer the likely characteristics of the first flowers
Morphological and molecular phylogenetic context of the angiosperms: contrasting the 'top-down' and 'bottom-up' approaches used to infer the likely characteristics of the first flowers
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DOI：
10.1093/jxb/erl128
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发表时间：
2006-01-01
影响因子：
6.9
通讯作者：
Rudall, Paula J.
中科院分区：
文献类型：
--
作者：
Bateman, Richard M.;Hilton, Jason;Rudall, Paula J.
最近，解决长期争论的被子植物“起源”问题的尝试依赖于从类群与性状矩阵衍生的系统发育框架。大多数人假设经验的严格性与矩阵的大小成正比。基于序列的基因型方法增加了矩阵中的特征（核苷酸和插入缺失）的数量，但仅限于现有物种的高度有限的范围，而基于形态的方法增加了系统发育信息类群（包括化石）的数量，但代价是只能访问有限的表型特征。这两种方法目前正在提供截然不同的关系假设。大多数分子研究表明，所有现存的裸子植物形成一个自然群体，这表明导致被子植物的谱系的早期分歧令人惊讶，而仅形态学的系统发育表明，一系列（大部分已灭绝的）裸子植物先于后来的被子植物起源。这种冲突的原因包括：（1）巨大的表型和基因型空白，很大程度上反映了新生代前的灭绝，它将早期分化的现存被子植物与其在现存裸子植物中最接近的亲缘植物分开； (ii) 关于哪些 (a) 现存被子植物和 (b) 灭绝的被子植物与裸子植物关系最密切，存在很大的不确定性； (iii)关于哪些(a)现存的和(b)灭绝的裸子植物与被子植物关系最密切，因此最能作为“外群”来决定早期分化的被子植物中特征转变的进化极性，存在极大的不确定性。这些因素仍然允许关于许多表型性状（生殖性和营养性）的获得顺序的显着对比但可信的假设，这些性状将“经典”被子植物与“经典”裸子植物区分开来。这种花的定义仍然不明确，其起源模式仍然存在激烈争议。进化关系的一些定义和假设排除了花在界定被子植物中的作用。我们主张维持平行的、相互启发的形态学和分子系统发育重建计划，分别通过额外的分类单元（特别是化石）进行同源性测试和探索可能负责主要表型转变的基因的进化发育遗传学研究来支持。
Recent attempts to address the long-debated 'origin' of the angiosperms depend on a phylogenetic framework derived from a matrix of taxa versus characters; most assume that empirical rigour is proportional to the size of the matrix. Sequence-based genotypic approaches increase the number of characters (nucleotides and indels) in the matrix but are confined to the highly restricted spectrum of extant species, whereas morphology-based approaches increase the number of phylogenetically informative taxa (including fossils) at the expense of accessing only a restricted spectrum of phenotypic characters. The two approaches are currently delivering strongly contrasting hypotheses of relationship. Most molecular studies indicate that all extant gymnosperms form a natural group, suggesting surprisingly early divergence of the lineage that led to angiosperms, whereas morphology-only phylogenies indicate that a succession of (mostly extinct) gymnosperms preceded a later angiosperm origin. Causes of this conflict include: (1) the vast phenotypic and genotypic lacuna, largely reflecting pre-Cenozoic extinctions, that separates early-divergent living angiosperms from their closest relatives among the living gymnosperms; (ii) profound uncertainty regarding which (a) extant and (b) extinct angiosperms are most closely related to gymnosperms; and (iii) profound uncertainty regarding which (a) extant and (b) extinct gymnosperms are most closely related to angiosperms, and thus best serve as 'outgroups' dictating the perceived evolutionary polarity of character transitions among the early-divergent angiosperms. These factors still permit a remarkable range of contrasting, yet credible, hypotheses regarding the order of acquisition of the many phenotypic characters, reproductive and vegetative, that distinguish 'classic' angiospermy from 'classic' gymnospermy. The flower remains ill-defined and its mode (or modes) of origin remains hotly disputed; some definitions and hypotheses of evolutionary relationships preclude a role for the flower in delimiting the angiosperms. We advocate maintenance of parallel, reciprocally illuminating programmes of morphological and molecular phylogeny reconstruction, respectively supported by homology testing through additional taxa (especially fossils) and evolutionary-developmental genetic studies that explore genes potentially responsible for major phenotypic transitions.