Data from: The phylogenetic basis of sexual size dimorphism in orb-weaving spiders (Araneae, Orbiculariae)

Extreme sexual body size dimorphism (SSD), in which males are only a small fraction of the size of the females, occurs only in a few, mostly marine, taxonomic groups. Spiders are the only terrestrial group in which small males are relatively common, particularly among orb-weavers (especially in the families Tetragnathidae and Araneidae) and crab spiders (Thomisidae). We use a taxonomic sample of 80 genera to study the phylogenetic patterns (origins and reversals) of SSD in orb-weaving spiders (Orbiculariae). We collected and compiled male and female size data (adult body length) for 536 species. Size data were treated as a continuous character and ancestral sizes, for males and females separately, were reconstructed using Wagner parsimony on a cladogram for the 80 genera used in this study. Of the 80 genera in the analysis, 24 were female-biased dimorphic (twice or more the body length of the male); the remaining 56 genera were monomorphic. Under parsimony only four independent origins of dimorphism are required: in the theridiid genus Tidarren, in the distal nephilines, in the "argiopoid clade," and in the araneid genus Kaira. Dimorphism has reversed to monomorphism at least seven times, all of them within the large "argiopoid clade." The four independent origins of dimorphism represent two separate instances of an increase in female size coupled with a decrease of male size (involving only two genera), and two separate instances of an increase in female size with male size either remaining the same or increasing, but not as much as females (involving 30 genera). In orb-weaving spiders far more taxa are sexually dimorphic as a result of female size increase (22 genera) than as a result of male size decrease (two genera). SSD in orb-weaving spiders encompasses several independent evolutionary histories that together suggest a variety of evolutionary pathways. This multiplicity strongly refutes all efforts to date to find a general explanation for either the origin or maintenance (or both) of SSD, because the different pathways very likely will require distinctly different, possibly unique, explanations. Each pattern must be understood historically before its origin and maintenance can be explained in ecological and evolutionary terms. The most frequently cited example of male dwarfism in spiders, the golden orb spider genus Nephila (Tetragnathidae), is in fact a case of female giantism, not male dwarfism.极端性体大小二态性（SSD）指雄性体型仅为雌性极小一部分的情况，该类二态性仅存在于少数类群中，且多数为海洋类群。蜘蛛是唯一一类雄性体型普遍偏小的陆生类群，这类情况在圆网蛛类（Orbiculariae）中尤为常见，尤其是肖蛸科（Tetragnathidae）、园蛛科（Araneidae）以及蟹蛛科（Thomisidae）。本研究选取80个属作为分类学样本，以探究圆网蛛类中SSD的系统发育模式（起源与反转）。我们收集并整理了536个物种的雌雄体型数据（成虫体长），将体型数据作为连续性状，基于本研究使用的80个属的分支图，采用瓦格纳简约法分别重建雌雄祖先体型。在参与分析的80个属中，24个属为雌性偏态二态（雌性体长为雄性的2倍及以上），剩余56个属为体型单态。基于简约法分析，该二态性仅需四次独立起源：分别在球蛛科的Tidarren属、远端络新妇类、‘园蛛支系（argiopoid clade）’以及园蛛科的Kaira属。二态性至少有7次反转回单态性，且全部发生在大型的‘园蛛支系’内部。四次独立起源的二态性可分为两类：一是雌性体型增大同时雄性体型减小（仅涉及2个属），共2次独立起源；二是仅雌性体型增大，雄性体型保持不变或有所增加但增幅小于雌性（涉及30个属），同样为2次独立起源。在圆网蛛类中，因雌性体型增大而产生性二态的类群（22个属）远多于因雄性体型减小产生二态的类群（2个属）。圆网蛛类的SSD包含多种独立的演化历史，共同指向多样的演化路径。这种多样性有力驳斥了迄今为止所有试图为SSD的起源或维持（或两者兼具）找到通用解释的尝试，因为不同的演化路径很可能需要截然不同、甚至可能是各自独特的解释。在从生态学和演化生物学角度解释其起源与维持机制之前，必须先从历史演化的视角理解每一种模式。蜘蛛中雄性矮化最常被引用的例子——金圆网蛛属（Nephila，肖蛸科）——实际上是雌性体型巨型化的案例，而非雄性矮化。