支序系统学的原理和方法

（1）同源vs. 同功性状
同源≠相似；非同源≠不相似 Analogous structures may look similar to one another, but are not derived from a common ancestor. When two
organisms have analogous structures, this is an example of
如何判断祖征与衍征 —性状的极性推测 Determining polarity of a character involves determining which state is ancestral.
1. 化石顺序：较早地层中的化石具有的特征一般比较晚地层 中的化石特征更为祖态。 2. 外类群比较：所谓外类群就是研究的类群（内群）关系较 近但一般相对古老的生物类群。它们往往具有更多的祖征。 因此，将某一特征与其比较后可得到演化的极向。
Comparison Between Homology and Analogy
（2）性状趋同
Convergent evolution(趋同进化): describes the acquisition of the same biological trait in unrelated
lineages.
（一）性状类型
Homology（同源）: Similarity resulting from common ancestry. Homoplasy（同功）:Similarity not due to common ancestry Reversal（逆转） – loss of new (apomorphic) feature, resembles ancestral (old) feature. Convergence (趋同) – gain of new, similar features independently. Parallel evolution(平行进化) - the development of a similar trait in related, but distinct, species descending from the same ancestor, but from different clades. (有亲缘关系的物种独立获得类似的适应)
确定同源特征以后，还要确定它们 的演化序列或过程，以根据它们的 变化过程来逐步推断分类单元之间 的系统发育关系。 如果性状2是由性状1演化而来， 那么性状2为衍征/近裔性状（apomorphy, derived character), 性状1为祖征/近祖性状（plesiomorphy, primitive/ancestral character)
从其来源：分为形态性状、生理性状、生态性状、遗传性状、生化性状 从进化的角度：性状可以分为近裔性状、近祖性状和自近裔性状； 从它们在提示进化信息的功能与作用：可以分为共近裔性状、共近祖性状。
Character states(性状状态） = one of two or more forms of a character (e.g., ―red,‖ ―white‖).
Cactus
Euphorb
These two succulent plant genera are only distantly related, but have independently converged on a very similar body form.
Convergent evolution: spines of cacti & euphorbs
the forelimb bone forms
Homologous Structures
All have the same bones, but are used in different ways and for various functions -
remember, homologous
structures have common ancestry!
共有衍征是判断物种亲缘关系的唯一证据
请根据以下性状推测物种 Ⅰ、Ⅱ、Ⅲ之间的关系 其中 0为祖征，1为衍征 。 （1）若根据数值学派观点结果如何？
（2）若根据支序学派观点结果如何？
请根据以下性状推测物种 Ⅰ、Ⅱ、Ⅲ之间的关系 （1）若根据数值学派观点结果如何？ （2）若根据支序学派观点结果如何？
谁和谁的关系更近？
?
共同祖先的相对近度
A
B
AN1
AN1
C t1 t2
Taxon B and Taxon C are more closely relaed to each other than they are to TaxonA
B与C的共同祖先AN1比B与C中任何一个与A之间的共同祖 先AN2距离现今更近，（B与C有最近的共同祖先）即B与C 之间的血缘关系近于A与B 或者A与C之间的关系。
（三）支序系统学派（Cladistics）
也称为系统发育系统学（Phylogenetic systematics）
代表人物：德国昆虫学家Willi Hennig(1913-1976) 代表著作：1950年发表的德文著作《系统发育系 统学原理》
Willi Hennig(1913-1976)
Hennig, W. 1950. Grundzuge einer Theorie der phylogenetischen Systematik. Deutscher Zentralverlag, Berlin.
convergent evolution Independent development of similarity between species due to similar selection pressures.
• Similar structures evolving in separate lineages as adaptations to the same environmental pressures • Convergent structures did not evolve from a common ancestor
☆ Character
groups found in the study groups but not the outgroups are derived（衍生的）.
3. 类群系列对比（comparision of transformation serious)：
Symplesiomorphy（共有祖征）：Character shared by a number of groups Inherited from ancestors older than the last common ancestor.Symplesiomorphies are not helpful in determining evolutionary relationships. A Synapomorphy （共有衍征）is an evolutionary novelty unique tBaidu Nhomakorabea a particular clade.
如图：三角形和五边形都由四边形演化而来，因此，三角形和五边形是衍 征，四边形是祖征。圆形由五边形演化而来，这时圆形为衍征，五边形为 祖征。可见祖征与衍征都是相对的。
共有祖征 Symplesiomorphy
共有衍征 Synapomorphy
独征/自征
毛
硬壳卵 羊膜卵 四肢
Autapomorphy
脊椎
Hennig, W. 1966. Phylogenetic Systematics. University of Illinois Press, Urbana, Illinois.
什么是支序系统学？
（1）进化论是支序系统学的理论基础
（2）共近裔性状、单系是支序系统学的判别准则
（3）简约法是支序系统学理论的分析方法
类群是分类上一类生物的集合，可以是科、属、种或者其它阶元， 在一个已知分类系统中都有相应的阶元位置，具有容易识别的共同 性状。
Character（性状） = a feature or attribute of a taxon (e.g., ―petal color‖)
性状是生物体在形态、行为、生理、生态、遗传、生化等多方面的 表现，是一个或者一群生物体可以观察到或通过实验得到的属性。
谁和谁的关系更近？
什么是支序系统学？
（1）进化论是支序系统学的理论基础
（2）共近裔性状、单系是支序系统学的判别准则
（3）简约法是支序系统学理论的分析方法
（4）系统发育关系树是分类单元关系的表述形式
几个重要概念
Taxon(类群): is a particular group of similar organisms that are assigned a rank and name.
Polarity is determined by using outgroup comparison.
☆An
outgroup is closely related, but not part of the group being examined (the ingroup).
☆ If
a character is found in both the study group and the outgroup, it is considered ancestral for the study group.
euphorb spines
cactus spines
Leg-less lizards
Both examples of reversal within Tetrapods: loss of a derived feature – forelimbs. Example of convergence relative to one another! Independently evolved.
Snake
legged snakes lizards leg-less lizards
*
*
*= loss of legs
gain of legs (Tetrapods)
Convergent evolution：
wings of some animals evolved independently
（二）性状的演化
（4）系统发育关系树是分类单元关系的表述形式
什么是支序系统学？
（1）进化论是支序系统学的理论基础
The basic idea behind cladistics is that members of a group share a common evolutionary history, and are "closely related," more so to members of the same group than to other organisms. These groups are recognized by sharing unique features which were not present in distant ancestors. These shared derived characteristics are called synapomorphies. 支序系统学派研究的核心内容是类群（研究对象）间的系统发育关系， 认为最能体现系统发育关系的依据是分类单元之间的血缘关系；而反 映血缘关系的最确切办法是共同祖先的相对近度（Relative recency of common ancestor)主张以共同祖先的相对近度作为衡量类群间亲 缘关系的唯一标准
硬骨骼
共有祖征:如果两个或两个以上的分类单元具有的某些特征起源于比最近 的共同祖先更早的祖先，则其特征为共有祖征。四肢是哺乳类、爬行类和 鸟类的共有祖征。 共有衍征：如果某一特征起源于最近的共同祖先本身，该特征为共有衍征。 羊膜卵是哺乳类、爬行类和鸟类的共有衍征。 独征/自征：某一支系独有的特征。被体毛是哺乳类的独征。