2005_CoddingtonSNAPhylogeny

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ARACHNIDA

Spiders are one of the eleven orders of the class Arach-nida, which also includes groups such as harvestmen (Opil-iones), ticks and mites (Acari), scorpions (Scorpiones), falsescorpions (Pseudoscorpiones), windscorpions (Solifugae),and vinegaroons (Uropygi). All arachnid orders occur inNorth America. Arachnida today comprises approximately640 families, 9000 genera, and 93,000 described species, butthe current estimate is that untold hundreds of thousandsof new mites, substantially fewer spiders, and several thou-sand species in the remaining orders, are still undescribed(Adis & Harvey 2000, reviewed in Coddington & Colwell2001, Coddington et al. 2004). Acari (ticks and mites) areby far the most diverse, Araneae (spiders) second, and theremaining taxa orders of magnitude less diverse. Discount-ing secondarily freshwater and marine mites, and a fewsemi-aquatic or intertidal forms, all extant arachnid taxaare terrestrial. Arachnida evidently originated in a marinehabitat (Dunlop & Selden 1998, Dunlop & Webster 1999),invaded land independently of other terrestrial arthropodgroups such as myriapods, crustaceans, and hexapods(Labandeira 1999), and solved the problems of terres-trialization (desiccation, respiration, nitrogenous wasteremoval without loss of excess water, and reproduction)in different ways. Although the phylogeny of Arachnida isstill controversial (Coddington et al. 2004), specialists agreethat the closest relative of Araneae is a group of orders col-lectively known as Pedipalpi: Amblypygi, Schizomida, andUropygi (Shultz 1990).

PHYLOGENETIC THEORY AND METHOD

Systematics is the study and classification of the differ-ent kinds of organisms and the relationships among them.Good classifications are predictive: knowing one featurepredicts many others. If one knows that an animal hasspinnerets on the end of the abdomen, it will also havefangs and poison glands (lost in a few spiders), eight legs,two body regions, male palpi modified for sperm transfer,and it will spin silk: in short, it is a spider. All spiders sharethese features because they inherited them from a commonancestor, but todays spiders have evolved to differ amongthemselves. For example, the earliest spiders had fangs thatworked in parallel (orthognath, like tarantulas and theirallies), but later in spider evolution one lineage developed

fangs that worked in opposition (labidognath, like themajority of spiders in North America). Much later withinthe labidognath lineage, some evolved the ability to coat silklines with a viscid, semi-liquid glue, useful for entrappingand subduing prey. This nested pattern of branching lin-eages (phylogeny), results from evolutionary descent withmodification (Fig. 2.1). The vast majority of similaritiesand differences among species are due to phylogeny. Jump-ing spiders (Salticidae) all have huge anterior median eyesbecause they are relatively closely related, and wolf spider(Lycosidae) eyes exhibit their characteristic eye pattern forthe same reason. Phylogeny explains more biological pat-tern than any other scientific theory (e.g., ecology, physiol-ogy, ethology, etc.), and therefore classifications based onphylogeny will be maximally predictive. Besides huge front

PHYLOGENY AND CLASSIFICATIONOF SPIDERS

Chapter 2

eyes, jumping spiders also share many other anatomical,behavioral, ecological, and physiological features. Mostimportant for the field arachnologist they all jump, a usefulbit of knowledge if you are trying to catch one. Taxonomicprediction works in reverse as well: that spider bouncingabout erratically in the bushes is almost surely a salticid.

Another reason that scientists choose to base classifica-tion on phylogeny is that evolutionary history (like all his-tory) is unique: strictly speaking, it only happened once.That means there is only one true reconstruction of evolu-tionary history and one true phylogeny: the existing clas-sification is either correct, or it is not. In practice it can becomplicated to reconstruct the true phylogeny of spidersand to know whether any given reconstruction (or classifi-

cation) is true. Indeed, scientists generally regard truthin this absolute sense as beyond their reach. Instead theystrive to make their hypotheses as simple as possible, and asexplanatory as possible. Simpler and more general hypoth-eses win. They win through comparison of predictionsmade by the hypothesis to factual observation. Scientifichypotheses (e.g., explanations, classifications, taxonomies,phylogenies) are constantly tested by discovery of new traitsand new species. To the extent that the hypothesis is good,it accommodates and comfortably explains new data. If thenew data do not fit the theoretical expectations, sooner orlater a new hypothesis or a revised version of the old onetakes its place. In biological classification, and phylogenyreconstruction in particular, scientists have developed anumber of technical terms to describe the various ways that

classifications or phylogenies do, or do not, correspond tofact (Fig. 2.1). Any group in a classification is said to be ataxon (plural taxa) or clade, and in theory corresponds toone common ancestral species and all of its descendants.Such clades are said to be monophyletic (mono = single,and phylum = race).

In the preceding examples, spiders (Araneae), labido-gnath spiders (now called Araneomorphae), sticky-silkspinners (Araneoidea), jumping spiders (Salticidae) andwolf spiders (Lycosidae) are all thought to be monophyleticgroups, clades, and taxa. Each of these groups is distin-guished by one or more uniquely evolved features or inno-vations. Such characters are said to be derived, becausethey are transformations of a more primitive trait. Orthog-nath chelicerae is the original, primitive (plesiomorphic)

condition for spiders, and labidognath chelicerae is thelater, derived (apomorphic) condition. The only acceptableevidence for monophyletic groups are shared, derived char-acters, or synapomorphies (syn = shared, apomorphy =derived morphology) such as the evolution of viscid silk inAraneoidea (Fig. 2.1).

Sometimes systematists (scientists who infer phylogenyand use the results to classify organisms) make mistakesand group taxa based on primitive characters or plesio-morphies. Such groups, containing a common ancestorand some but not all of its descendants, are then termedparaphyletic. In Figure 2.1, the grouping Orthognatha isparaphyletic because it is based on a primitive character,orthognath or paraxial chelicerae, and because it includesthe common ancestor of all spiders but excludes some

Jonathan A. Coddington

FROM: Ubick, D., P. Paquin, P.E. Cushing, and V. Roth (eds). 2005. Spiders of North America: an

identication manual. American Arachnological Society. 377 pages.


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19Spiders of North America

Fig. 2.1 Taxa are in regular, characters in italic font. Only synapomorphies (shared, derived characters) are valid evidence of monophyletic groups(clades). Paraphyletic groups are usually based on plesiomorphies, polyphyletic groups on convergences.

LabidognathOrthognath

Opisthothelae

Araneae

Spinnerets

primitive derived

plesiomorphic apomorphic

Female fertilization ducts

Clades

Synapomorphy

Time

(Polyphyletic)

Big Spiders

(Paraphyletic)Orthognatha

Cheliceral

Orientation

Viscid silk

(Monophyletic)Entelegynae

Mesothe

lae

Myg

alomorph

ae

Saltic

idae

Lyco

sidae

Aran

eoide

a

descendants, i.e. the Labidognatha. Even worse, sometimesgroups dont even include any common ancestor at all andare then termed polyphyletic (Big Spiders, Lycosidae +Mesothelae in Fig. 2.1 would be polyphyletic). Polyphyleticgroups are usually based on convergent features and para-phyletic groups on primitive features.

Classifications (and phylogenies) need not be strictlybinary or dichotomous: in Figure 2.1 the three-way forkuniting Araneoidea, Lycosidae, and Salticidae intentionallydoesnt indicate which is most closely related to which. Ifnodes are dichotomous, the two daughter lineages are oftencalled sister taxa, or, informally, sisters.

In practice systematists infer phylogeny by compilinglarge tables or matrices of taxa and their traits or fea-tures. Traits may be anything presumed to be geneticallydetermined and heritable, such as morphology, physiol-ogy, behavior, or, increasingly, DNA sequences. The idealapproach would encapsulate all comparative knowledgeabout the group in question. Based on evidence external

to the analysis (or even an a priori assumption) one taxonin the analysis is specified to join at the root of the tree,and powerful computer algorithms are used to find themost plausible tree (or branching diagram, also termed acladogram) that unites all taxa and best explains the data.Systematists adopt the initial null hypothesis that all simi-larities are due to phylogeny. The fit between the tree andthe data decreases to the extent that one must suppose thesame trait arose two or more times independently (con-vergent evolution) or was lost secondarily. An example ofthe former might be big. Not all big spiders are eachothers closest relatives (but some are). An example of thelatter is the absence of true abdominal segmentation in allspiders. Spiders are arthropods and arthropods typicallyhave segmented abdomens; spider relatives also have seg-mented abdomens. Rather than suppose that all arthro-pods with segmented abdomens gained the conditionindependently, and thus that spiders reflect the ancestralunsegmented arthropod, it becomes very much simpler


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LiphistiidaeAtypidae

Barychelidae

Paratropididae

ActinopodidaeMigidae

IdiopidaeCtenizidae

Theraphosidae (Ischnocolinae)

Theraphosidae (Theraphosinae)

Hypochilidae

FilistatidaeCaponiidae

TetrablemmidaeSegestriidae

DysderidaeOrsolobidaeOonopidae

PholcidaeDiguetidaePlectreuridaeOchyroceratidae

LeptonetidaeTelemidae

SicariidaeDrymusidae

Scytodidae

PeriegopidaeOecobiidae

Mimetidae + Malkaridae?

Hersiliidae

Eresidae

DeinopidaeUloboridae

AraneidaeTetragnathidae

NicodamidaePhyxelididae

TitanoecidaeDictynidae

ZodariidaeCryptothelidae

SparassidaeAnyphaenidaeClubionidaeCorinnidaeZoridaeLiocranidaePhilodromidaeSalticidaeSelenopidae

Thomisidae Cithaeronidae

Ammoxenidae

GallieniellidaeTrochanteriidae

Lamponidae

AmaurobiidaeTengellidae

GnaphosidaeProdidomidae

Neolanidae

Zorocratidae

ZoropsidaePsechridae

SenoculidaeOxyopidae

Pisauridae

TrechaleidaeLycosidae

StiphidiidaeAgelenidae

DesidaeAmphinectidaeMetaltellinae

MiturgidaeCtenidae

Ctenidae (Acanthoctenus)

Miturgidae (Mituliodon)

TheridiosomatidaeMysmenidae

Anapidae

PimoidaeLinyphiidae

TheridiidaeNesticidaeSynotaxidae

Cyatholipidae

Symphytognathidae

HuttoniidaePalpimanidaeStenochilidae

MicropholcommatidaeHolarchaeidae

PararchaeidaeArchaeidaeMecysmaucheniidae

AustrochilidaeGradungulidae

AntrodiaetidaeMecicobothriidae

"Dipluridoids" + Hexathelidae

"Nemesiioids" + Microstigmatidae

Mesothelae

Avicularoidea

Atypoidea

Opisthothelae

Araneomorphae

Haplogynae

Mygalomorphae

Neocribellatae

Araneoclada

Eresoidea

Orbiculariae

Divided Cribellum Clade

Titanoecoids

Zodarioids

Dionycha

Amaurobioids

Fused Paracribellar Clade

Gnaphosoidea

Stiphidioids

Agelenoids

Lycosoids

Higher Lycosoids

Ctenoid complex

Deinopoidea

Araneoidea

Derived Araneoids

RTA Clade

Reduced Piriform Clade

Araneoid Sheet Web Weavers

Spineless Femur Clade

Linyphioids

Cyatholipoids

Theridioids

Symphytognathoids

Entelegynae

Canoe Tapetum Clade

Palpimanoidea

Crassitarsae

Theraphosodina Theraphosoidea

Migoidea

Rastelloidina

Domiothelina

"Cyrtaucheniioids"Paleocribellatae

Austrochilioidea

Unplaced familiesChummidaeCybaeidaeCycloctenidaeHahniidaeHalidaeHomalonychidaeSynaphridae

Fig. 2.2 Phylogeny of Araneae


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to suppose that the original arthropod was segmentedand that it was spiders that changed to lack abdominalsegmentation. The tree that requires the fewest hypothesesof convergent evolution and/or secondary loss is preferredas the current working hypothesis. Of course new taxa andcharacters can be added, so that in practice the preferredtree can -and usually does -change at least a little bit witheach new analysis. The best classifications are derived fromphylogenetic analyses, but to date rather few groups of spi-ders have been analyzed phylogenetically.

SPIDER PHYLOGENY

Spiders currently comprise 110 families, about 3,600genera, and nearly 39,000 species (Platnick 2005). Pale-ontologists to date have described roughly 600 fossilspecies (Selden 1996, Dunlop & Selden 1998), but thesehave primarily been significant in dating lineages; thusfar fossils have not seriously challenged or refuted infer-ences based on the recent fauna. Strong evidence supportsspider monophyly: cheliceral venom glands, male pedipalpimodified for sperm transfer, abdominal spinnerets and silkglands, and lack of the trochanter-femur depressor muscle(Coddington & Levi 1991). Roughly 67 quantitative phylo-

genetic analyses of spiders at the generic level or above havebeen published to date, covering about 905 genera (about25% of the known total), on the basis of approximately3,200 morphological characters (summarized in Cod-dington & Colwell 2001 and Coddington et al. 2004). Onthe one hand, overlap and agreement among these studiesis just sufficient to permit stitching the results togethermanually (Fig. 2.2); on the other, they are so sparse thatmany relationships in Fig. 2.2 are certain to change as moreinformation accumulates and more taxa are studied. Figure2.2 is not itself the result of a quantitative analysis but is,essentially, an amalgamation of individual cladogramspublished for particular lineages. Although there are sev-eral spider phylogenies above the species level based onDNA (Huber et al. 1993, Garb 1999, Gillespie et al. 1994,

Piel & Nutt 1997, Hedin & Maddison 2001, Vinket al. 2002,Maddison & Hedin 2003a, b, Arnedo et al. 2004), this fieldis still in its infancy.

The basics of spider comparative morphology have beenknown for over a century, but the first explicitly phyloge-netic treatment of spider classification was not publisheduntil the mid-1970s (Platnick & Gertsch 1976). Thisanalysis resolved a long-standing debate by clearly show-ing a fundamental division between two suborders: theplesiomorphic mesotheles (the southeast Asian Liphisti-idae with two genera and about 85 species) and the derivedopisthotheles (everything else). Whereas mesotheles showsubstantial traces of segmentation, for example in theabdomen and nervous system, the opisthothele abdomenshows no segmentation (although color patterns in many

spider species still reflect ancient segmentation patterns)and the ventral ganglia, or nerve centers, are fused. Opis-thotheles include two major lineages: the baboon spiders(tarantulas) and their allies (Mygalomorphae, 15 familiesworldwide with about 300 genera and 2,500 species) andthe so-called true spiders (Araneomorphae, 94 familiesworldwide with about 3,200 genera and 36,000 species)(Platnick 2005).

Mygalomorphs look much more like mesotheles thanaraneomorphs. They tend to be rather large, often hirsuteanimals with large, powerful chelicerae. Nearly all leadquite sedentary lives, usually in burrows, which they rarelyleave, and they rely little on silk for prey capture. Some dofashion trip-lines from silk or debris, which effectivelyincrease their sensory radius beyond the immediate area

of the burrow entrance, and some diplurid species do spinelaborate sheet webs, but they lack one key innovation pres-ent in araneomorphs: the piriform silk essential to cementsilk to silk, or silk to substrate. Whereas any araneomorphcan dab a tiny dot of piriform cement to anchor its drag-line and almost instantly trust its life to the bond, mygalo-morphs must spin structures several centimeters across toanchor silk to substrate, and that is a long and laboriousprocess. Without piriform silk, substantial innovations inweb architecture are essentially impossible.

Mygalomorphs rarely balloon, and therefore their powersof dispersal are limited to walking. Usually, the juveniles donot walk far, and so mygalomorph populations are highlyclumped: when you find one, its siblings and cousins aregenerally not far away. Mygalomorph known species diver-sity is barely 7% of araneomorph diversity, so the diver-sification rates of these two sister taxa clearly differ, butthe reasons remain mysterious. The contrast in dispersalmechanisms may be a partial explanation, but it also maybe that mygalomorph species are simply much more dif-ficult to discriminate morphologically. Araneomorphs leadmuch more vagile lives (including dispersal by ballooning),and the group is much more diverse.

Within mygalomorphs, the atypoid tarantulas (Atypidae,Antrodiaetidae) seem to be the sister group of the remain-ing lineages (Raven 1985a, Goloboff 1993), although someevidence suggests including Mecicobothriidae in the aty-poids. The sister group to the atypoids is the Avicularioi-dea, of which the basal Dipluridae may be a paraphyleticassemblage (Goloboff 1993). One of the larger problemsin mygalomorph taxonomy worldwide concerns the para-phyletic Nemesiidae, currently 38 genera and 325 species(Goloboff 1995). The remaining mygalomorph families(represented in North America only by Ctenizidae, Cyr-taucheniidae, and Theraphosidae, Fig. 2.2) divide into twodistinct groups: the theraphosodines baboon spiders ortrue tarantulas and their allies (Prez-Miles et al. 1996)and the typically trap-door dwelling rastelloidines (Bond

& Opell 2002). Less work has gone into mygalomorph phy-logeny, and because the diverse Dipluridae, Nemesiidae,and Cyrtaucheniidae seem to be paraphyletic, the numberof mygalomorph families may increase substantially. Forall their size and antiquity, mygalomorphs have remarkablyuniform morphology. Because fewer reliable, distinctivefeatures can be compared, mygalomorph phylogeny hasbeen a difficult and frustrating subject. Perhaps moleculardata will advance the subject.

Araneomorphs include over 90% of known spider spe-cies: they are derived in numerous ways and appear quitedifferent from mesotheles or mygalomorphs. Mesothelesare the only spiders with an anterior median pair of distinctspinnerets and mygalomorphs have lost them completely.A complex, important synapomorphy of araneomorphs is

the fusion and reduction of the anterior median spinneretsto a cribellum, a flat sclerotized plate that bears hundredsto thousands of silk spigots that produces very fine, dry,

yet extremely adhesive, silk (cribellate silk). Spider draglinesilk is justly famous because it is tougher than Kevlar (Craig2003, Gosline et al. 1986, 1999, Scheibel 2004), but in manyways, cribellate silk is even more amazing. Its stickinessseems to be based on electron-electron interactions (vander Waals forces) between the silk and the surface to whichit sticks (Hawthorn & Opell 2002). Insofar as other naturaland man-made glues operate on gross chemical principles,this atomic-level universal glue mechanism also seemsworthy of biotechnological attention.

Other animals use silk throughout their lives, but noother group of animals even comes close to the diversity,


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intricacy, and elegance of silk use by spiders (Eberhard1990, Craig 2003). Systematists first became aware of thisrichness through comparative studies of behavior (Eber-hard 1982, 1987b, 1990, Coddington 1986b, c), and onlylater by paying attention to the morphology that producedall that diversity. Although cytologists had been study-ing spider silk glands since the early 20 thcentury (Kovoor1987), it was not until the advent of the scanning electronmicroscope, and the cladistic reinterpretation of cytologi-cal data in the light of spigot diversity (Coddington 1989)that systematists began to plumb the immense variation inspinneret spigots and silks for phylogenetic research. Nowspigots, silks, and silk use are some of the richest sourcesof comparative data in spiders (e.g., Platnick 1990a, Plat-nick et al. 1991, Eberhard & Pereira 1993, Griswold et al.1999a).

Although many araneomorph lineages independentlyabandoned the sedentary web-spinning lifestyle to becomevagabond hunters, the plesiomorphic foraging mode seemsto be a web equipped with cribellate silk. Paleocribellataecontains just one family, Hypochilidae (two genera, 11species). It is a famous North American taxon because it issister to all remaining araneomorphs (Neocribellatae), and

therefore retains a fair number of primitive traits (Plat-nick et al. 1991, Catley 1994). Within Neocribellatae, themonophyly of Haplogynae is weakly based on cheliceral(chelicerae fused with a lamina instead of teeth), palpal(tegulum and subtegulum fused rather than free), andspinneret characters (vestiges of spigots in former moltslacking) (Platnick et al. 1991, Ramrez 2000). The cribellateFilistatidae (three North American genera) is is sister to theremaining haplogynes, and a quantitative phylogeny of thefamily has been published (Ramrez & Grismado 1997).All haplogynes except Filistatidae evidently lost the cribel-lum, but Pholcidae (Huber 2000), Diguetidae, Ochyroc-eratidae, and, debatably, Scytodidae and Segestriidae stillbuild prey-catching webs. The cellar spiders (Pholcidae)are exceptional for their relatively elaborate, large webs.

Some pholcid genera have independently invented viscidsilk (Eberhard 1992). Some of the most common and ubiq-uitous synanthropic spider species are pholcids, so oneshould not assume that a taxon that branched off relativelyearly in evolution is necessarily primitive, poorly adapted,or non-competitive. The remaining haplogyne families liveeither in tubes (Dysderidae) or are vagabonds that tend tooccur in leaf litter or other soil habitats and are not com-monly encountered by the casual collector. Because theyare still poorly known, many of the new spider species dis-covered each year tend to come from haplogyne families.

The araneomorph Entelegynae is supported by severalimportant, yet poorly understood synapomorphies (Gris-wold et al. 1999a) in reproductive and spinning systems.Entelegynes have more complex reproductive systems

in which the female genitalia (epigynum) has externalcopulatory openings. In all other spiders copulation takesplace through the gonopore. This secondary set of open-ings provides a flow-through sperm management system:the male deposits sperm in the epigynum that connects tospermathecae that connect to the uterus. This has majorimplications for reproductive behavior and the relationbetween the sexes (Eberhard 2004). For one thing, theflow-through system means the first male to mate with afemale usually sires most of the spiderlings (Austad 1984).The copulatory ducts that lead from the epigynum to thespermathecae are often extremely contorted in entelegynefemales. This has led to hypotheses that such complexityactually make it more difficult for males to inseminatefemales (Eberhard 1985, 1996). For whatever reason, fer-

tilization ducts in entelegyne spiders have been secondarilylost only five times and in mostly small groups: twice indistal palpimanoid families (this may be primary absencerather than secondary loss, Huber 2004), a small sub-cladeof uloborids, some anapids, and a rather uniform, if spe-ciose, sub-clade of tetragnathids (Hormiga et al. 1995). Asecond consistent but enigmatic entelegyne synapomorphyis cylindrical gland silk. These glands and spigots appearonly in adult females, and it is thought that the silk is usedonly in egg sacs, but the specific contribution of cylindricalgland silk to egg sac function remains unknown.

Male entelegyne genitalia are also greatly modified. Ple-siomorphic male spider genitalia are usually simple, taper-ing, pyriform bulbs. Pyriform bulbs lack apophyses or, ifapophyses are present, they are small and quite simple(e.g., Fig. 2.3). Other parts of the male palp, such as thecymbium, patella, and tibia, are likewise unadorned. Incontrast, entelegyne male genitalia can be bewilderinglycomplex. The bulb has two or three divisions (alwayssubtegulum and tegulum, sometimes with an elaborateembolic division. The tegulum usually has two apophy-ses (conductor and median apophysis) in addition to theembolus. Any or all of these in entelegynes can be won-

derfully complex, with knobs, levers, grooves, hooks, ser-rations, sinuous filaments, and spiraling parts (e.g., Figs.2.4-2.5). Unraveling the homology of entelegyne malegenitalia is a major problem (Coddington 1990). Entele-gyne bulbs also work differently. The plesiomorphic bulbejaculates via muscles that force the sperm out. Entelegynebulbs lack those muscles and work hydraulically instead.The male pumps blood into the bulb to raise its internalpressure, which serves both to expand and uncoil its vari-ous parts. Glands empty their contents into the sperm ductand force the sperm out (Huber 2004). For sperm transferto occur, this complicated structure must interact preciselywith the correspondingly complex female genitalia (Huber1994, 1995). In addition, the various parts of an entelegynebulb are usually connected only by thin, flexible mem-

branes that inflate like balloons during copulation. As awhole the bulb is so flexible that at least some of the malescomplexity doubtless serves only to stabilize and orient hisown genitalia during copulation.

2.3

2.4

2.5


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Female epigyna have corresponding ledges, pockets,ridges and protuberances externally, and often labyrinthineductwork internally. One hypothesis is that the femalecomplexity is essentially defensive, the result of antagonis-tic co-evolution (Chapman et al. 2003): females as a wholeinvest so much more in their offspring than do males(even in spiders), that they should choose mates carefully(Alexander et al. 1997). Female genitalic complexity maybe a challenge to males such that only high-quality malessucceed, or succeed much better than low-quality males.Males, in turn, have evolved complex and highly flexiblegenitalia, the better to win over choosy females. This expla-nation assumes, of course, that overall quality of males istightly correlated with male copulatory prowess. In anyevent, the difficulty of attaching to and navigating femalegenitalia may give the female more time to assess the maleand break off mating if she chooses.

Three small families, known as eresoids, have thus faralways clustered near the base of Entelegynae in phyloge-netic analyses: Oecobiidae, Hersiliidae, and Eresidae (Cod-dington 1990, Griswold et al. 1999a). Only the first twooccur in North America. Their phylogenetic relationshipsare controversial. Oecobiids (Glatz 1967) and hersiliids (Li

et al. 2003) share a unique attack behavior: they are the onlyspiders known to run swiftly around the stationary preyencircling it with silk as they go. The behavior could also beconvergently evolved, although in accordance with the nullhypothesis of phylogenetics, until proven otherwise, wepresume the similarity is explained by descent. Certainlyno obvious features tie any of these families closely to anyother entelegynes. Because they are entelegyne yet share nomore derived apomorphies with other entelegyne clades,they seem to be the basal entelegyne group.

The Palpimanoidea is a controversial entelegyne group(10 families, 54 genera), of which only the pirate spiders(Mimetidae) occur in North America. For years mimetidswere thought to be araneoids based on setal morphology,general appearance, and the overall complexity of their

palps, but then were transferred to palpimanoids (Forster& Platnick 1984). Recent research, however, suggests thatmimetids are araneoids after all, in which case Palpimanoi-dea is polyphyletic (Schtt 2000, 2003, Huber 2004).

Males can also have knobs or apophyses elsewhere ontheir palpi. About half of entelegyne species have one inparticular, the retrolateral tibial apophysis, that defines aclade of 39 entelegyne families (the RTA clade: Sierwald1990, Coddington & Levi 1991, Griswold 1993, Fig. 2.2).Huber (1994, 1995) found that the RTA usually, but notalways, serves to anchor and orient the male bulb to thefemale genitalia prior to expansion of the hematodochae.

Orbiculariae is one of the largest entelegyne lineages.It consists of two superfamilies, Araneoidea (13 families,1,000 genera), and Deinopoidea (2 families, 22 genera).

The monophyly of Orbiculariae is controversial becausethe strongest apomorphies are all behavioral: both groupsspin orbwebs (Coddington 1986c and references therein).Prior to strictly phylogenetic classification in spiders thetwo groups were thought to be only distantly related. Thecribellate Deinopidae and Uloboridae were included inthe Cribellatae, and authors often commented on thedetailed similarity of these orbs to those of the classical,ecribellate Araneidae (reviewed in Scharff & Coddington1997). However, as noted above, the cribellum is primitivefor Araneomorphae. On the one hand, araneoids or theirancestors must therefore have lost it and, on the other,groups based on plesiomorphies are false. When the old,polyphyletic Cribellatae collapsed (Lehtinen 1967, Forster1967, 1970b), deinopids and uloborids had nowhere else to

go, as it were, and so the form of the web (and the strikingsimilarities in behavioral details) constituted a strong blockof synapomorphies. But if orbweavers were monophyletic,the six araneoid families that spin sheet or cobwebs musthave lost the orbweb. Against this view is the hypothesisthat the orbweb is an unusually efficient and profitabledesign to catch prey. In general the more adaptive a featureis, the more likely it is to evolve independently; perhapsthe araneoid and deinopoid web forms are convergent.This view argues that the orbweb is so superior a preda-tion strategy that any spider lineage capable of it wouldhave evolved it independently (and never lost it). Little evi-dence thus far suggests that orbwebs are drastically betterthan other web architectures (although they are widelyregarded as better-looking!). Indeed, ecological evidencepoints the other way (Blackledge et al. 2003). Another dif-ficulty for the monophyly hypothesis is that the deinopoidorb is cribellate (dry adhesive silk), and the araneoid orbuses viscid silk. The missing link, it is argued, wouldhave had neither. The obvious rejoinder is that perhapsthey had both at one point, but one of the good effects ofmodern quantitative analysis is that people spend less timearguing about irresolvable issues, and more time seeking

new evidence. The orb web diphyly argument particularlyneeds evidence that deinopoids share strong synapomor-phies with some non-orb weaving group. Evidence againstorbweaver monophyly is starting to appear from molecularevidence (Hausdorf 1999, Wu et al. 2002), but these studiesare small, omit many important taxa, and do not confirmeach others results.

Araneoidea (ca. 11,000 species) is much larger thanDeinopoidea (ca. 300 species). Only one deinopid spe-cies occurs in North America (in Florida and, possibly,Alabama). Araneoids are ecologically dominant speciesthroughout the world but especially in north temperateareas such as North America, where Linyphiidae swampsany other spider family in both species diversity and sheerabundance. Current phylogenetic results (Hormiga 1994b,

2000, Griswold et al. 1998) indicate that Linyphiidae andfive other families form the monophyletic araneoid sheetweaver clade, which thus implies that within Araneoidea,the orb was lost only once (or transformed into a sheetweb). Linyphiidae spin sheets as do Pimoidae. The clas-sic cobwebs of Theridiidae and Nesticidae would thenbe derivations from a basic sheet, which, considering theweb of black widows, Steatoda, and other apparently basaltheridiid genera (Benjamin & Zschokke 2002, Agnarsson2004, Arnedo et al. 2004, ), seems plausible. Araneoid sheetweb weavers account for the bulk of araneoid species diver-sity (713 genera, 7,600 species worldwide). Perhaps sheetor cobwebs are not so bad after all (Griswold et al. 1998,Blackledge et al. 2003).

Although the most recent analysis suggests that the

sister taxon of Orbiculariae is approximately all remain-ing entelegyne families (possibly including eresoids andpalpimanoids), the evidence for this is quite weak for sev-eral reasons (Griswold et al. 1999a). First, non-orbicular-ian entelegyne families have received little phylogeneticresearch, so such overarching conclusions are premature.Second, the problem is intrinsically difficult. Resolving theentelegyne node requires an analysis that includes severalrepresentatives from all major entelegyne clades, includingrelevant enigmas such as Nicodamidae (Harvey 1995) andZodariidae (Jocqu 1991a). That means a very large matrixand an even larger scope of characters. Such a matrix is noteasily constructed, and will probably require collaborationof numerous specialists.


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