PHYLOGENETIC SYSTEMATICS AND THE SPECIES PROBLEM

Abstract— A tension has arisen over the primacy of interbreeding versus monophyly in defining the species category. Manifestations of this tension include unnecessary restriction of the concept of monophyly as well as inappropriate attribution of "species" properties, to "higher taxa", and vice versa. Distinctions between systems (wholes) deriving their existence from different underlying. processes have been obscured by failure to acknowledge different interpretations of the concept of individuality. We identify interbreeding (resulting in populations) and evolutionary descent (resulting in monophyletic groups) as two processes of interest to phylogenetic systematists, and explore the relations between the systems resulting from these processes. In the case of sexual reproduction, populations of interbreeding organisms (regardless of whether they are monophyletic) exist as cohesive wholes and play a special role in phylogenetic systematics, being the least inclusive entities appropriate for use as terminal units in phylogenetic analysis of organismal relationships. Both sexual and asexual organisms form monophyletic groups. Accepting the reality and significance of both interbreeding and monophyly emphasizes that a conscious decision must be made regarding which phenomenon should be used to define the species category. Examination of species concepts that focus either on interbreeding or on common descent leads us to conclude that several alternatives are acceptable from the standpoint of phylogenetic systematics but that no one species concept can meet the needs of all comparative biologists.     

中国植物分类学中的物种问题

Nooteboom和Peter Raven都认为中国的分类学家往往持有狭隘的物种概念,而这是由于他们缺 少足够的标本,尤其是模式标本,因而不能充分研究种的变异性。Raven说这使他相信中国植物分类学 中真正的物种概念颇有模式概念的色彩。他们的说法不无道理。的确,中国的植物区系中可能有大量 的种其真实身份还有讨论的余地。根据单个性状或完全按营养器官性状来命名新种是常有的事。有些 学者甚至把发表新种作为其分类工作的主要目标。现有的、为数非常有限的关于中国植物变异式样研 究的证据证明有些“种”实际上是生态宗(Clinopodium)、地理宗(Cunninghamia和Indigofera)或呈地形 梯度变异式样的分类群(Lespedeza和Rhododendron)而已。根据表型的可塑性变化而命名的种曾经或 仍然被作为“好种”对待(Rorippa)。具各种不同叶形特性的种间杂种的分离系被命名为不同的种 (Ilex)。分类学上本来就已经很复杂的无融合生殖复合体由于新种的不断增加而变得更加复杂 (Malus)。对一个具有复杂变异式样的种的精心研究导致对25个种名的归并,其中有10个是80年代 由中国分类学家发表的(Clematoclethra)。诸如此类的例子随着研究工作的扩大而势必大量增加。传统 植物分类学主要或完全以形态性状为依据。外部形态性状具有比较容易观察和记录的优点。分类学种 概念能满足多种用途分类的需要。但如果把分类学种概念说成是完全凭分类学家个人的主观判断或甚 至偏爱而很难有是非之分就颇成问题了。现在比过去任何时候都有条件对种这个分类阶元作客观的解 释。正确的物种概念来自对植物变异式样及其分类学价值的正确和充分的理解。因此,作为标本室分 类学家,首先要研究尽可能多的标本。其次,尽可能收编来自其他方面的证据是十分可取的。这些证据 即使不是很有用的分类性状,对更好地了解或解释类群的变异式样往往具有重要的意义。分类学家可 借以发现他所寻找的分类群在表型或基因型变异上的间断。对这两种间断的合理应用将导致在许多属内种级水平的更加合理的分类。     

闽北森林群落物种多样性的可塑性面积单元问题

分析闽北森林群落物种多样性的可塑性面积单元问题（ＭＡＵＰ）,结果表明,闽北森林群落物种多样性存在尺度效应和划区效应,其影响随着取样面积增大而减小,长期封禁保护的森林群落和森林群落和近期受人为干扰的退化森林群落物种多样性受ＭＡＵＰ影响趋势相同,文中应用ａｃｋｋｎｉｆｉｎｇ方法估计群落物种多样性的近似正态分布置信区间和划区效应。     

SPECIES DISCRIMINATION AMONG PELAGIC HETEROPODS: RESOLUTION OF THE PTEROTRACHEA HIPPOCAMPUS--P. MINUTA PROBLEM

Four species of Pterotrachea are currently recognized, two ofwhich (P. hippocampus Philippi, 1836, and P. minuta Bonnevie,1920) have very similar morphologies. These two species havebeen distinguished mainly on the basis of eye and visceral nucleusshapes; the former with wide, triangular eyes and a short, broadnucleus, and the latter with narrower, triangular eyes and ataller, more slender nucleus. Quantitative and qualitative morphologicaldata were obtained from specimens of P. hippocampus and P. minuta collectedduring two oceanographic sampling programs in the North AtlanticOcean. Comparisons of eye and visceral nucleus shapes (representedby their length to width and length to retinal width ratios,respectively), plotted against body length showed linear decreases,with no justification for the recognition of two separate species.Examination of eye shape across a wide range of body sizes showedthat the width of the retina increases disproportionately with bodygrowth (by elongation and medial upturning) beginning at a length ofabout 21-22 mm. As a result, the overall appearance of the eyeat this body size changes such that smaller animals (less than21-22 mm) have eyes corresponding with those of P. minuta, whilethe eyes of individuals larger than this body length match thoseof P. hippocampus. Several authors have distinguished femalesof the two species by the presence (P. hippocampus) or absence (P.minuta) of cuticular spines anterior to the eyes. Examinationof female specimens showed that those less than about 30 mmlacked these spines, while those above this size possessed them.Thus, cuticular spines represent a secondary female sexual characteristic. Other morphological features that have been used by previousauthors to distinguish the two species were examined and rejected.Because P. hippocampus was described prior to P. minuta, itis herein regarded as the senior synonym of P. minuta. (Received 12 June 1997; accepted 21 May 1999)