Substrate selection for web-building in Cyrtophora citricola (Araneae: Araneidae)

2012·1.7 MB·English

by  Ruth Madrigal Brenes

2012. The Journal ofArachnology 40:249-251
SHORT COMMUNICATION
Substrate selection for web-building in Cyvtophora citricola (Araneae: Araneidae)
Ruth Madrigal Brenes: Escuela de Biologia, Universidad de Costa Rica, Ciudad Universitaria Rodrigo Facio, San Jose,
Costa Rica. E-mail: [email protected]
Abstract. In general, spidersthat build long-lastingwebs invest a largeramount ofsilk and consequently a largeramount
ofenergy in their construction than those species that build ephemeral webs. It is expected that spiders that build long-
lasting webs choose rigid substrates for web construction to help preserve their investment. 1 experimentally tested this
prediction by confining Cyrtophora citricola (Forsskal 1775) (Coddington 1989) spiders (n = 32) in containers provided
with firmand unstablesubstratesforthespiderstoconstruct theirwebs. Thisexperimentconfirmsthat C. citricolastrongly
prefers firm substrates to which to attach its web when it must choose between a firm and an unstable substrate.
Keywords: Araneids, spiders, orb-web, web-substrate selection
Thestructureofthehabitatcan beimportant forspiderswhen they width X height X depth); ifa spider did not build its web within four
select sites to build their webs (Janetos 1986). The substrates selected nights, it was released and replaced with another spider.
byspiders forwebconstruction vary across species, and this selection Spiders do not usuallyattach silk threads to tightlystretched plastic
may be especially crucial for spiders that build long-lasting webs. wrappingmaterial,so1coveredtheopen,broadfacesoftheframewith
Within araneids, those species with long-lasting webs in general use this material. 1 also lined one ofthe sides ofthe frame with a sheet of
more silk and invest more time to construct denser webs and are not this material and then hung a sheet ofpaper cut into 12 strips (height
capable of ingesting and recycling a high percentage of the silk of 22cm.width 1.5cm)infrontofthisside(Fig. I).Theoppositesidewas
old webs {Lubin 1986; Townley & Tillinghast 1988; Kawamoto & not lined with plastic wrapping material, thus giving the spider
Japyassu2008),incontrastto thosearaneid speciesthat maketypical, sufficient support to construct its web. Six ofthe strips ofeach sheet
shorterlastingorbsand arecapableofingestingthesilk oftheirwebs. were attached to both ends (giving a firm substrate), and six were
The higher investments of silk, time, and energy by spiders con- attachedonlytotheupperend(givinganunstablesubstrate),following
structing long-lasting webs increase the cost of web relocation an alternate order: one strip attached to both ends (odd numbers in
(Tanaka 1989), likely imposing strong selection on the behaviors Fig. 1)followed byanotherstripattached tooneend(even numbersin
associated with web site choice. Fig. 1). 1 drew horizontal lines 2 cm apart that divided each strip into
Orb-weaving spiders in the genus Cyrtophora construct webs that 1 1 sections (A to K, from top to bottom), allowing me to record the
consist of dense, horizontal orbicular sheets of dry silk with an heights at which spiders attached threads (Fig. 1).
irregulartangleofdrythreadsaboveand below(Wheeler 1926; Lubin I gave each spider four nights to build its web (20 ofthe 32 spiders
1973). Thewebsarestrong, longlasting, and infrequentlyrebuilt, and built a complete web in two nights, 12 more in the next two nights).
are repaired when damage occurs (Lubin 1973, 1980). Thus the After a spider wove the spiral, the tendency for an addition of new
spider’schoice ofappropriate substratesto which to attach theweb is silk threads decreased drastically unless the web was damaged (G.
important in order to decrease the probability ofdamage to the web. Barrantes unpubl. data). On the fifth day, 1 used the coordinates
This paper experimentally examines the selection offirm vs. unstable provided by the numbered and lettered strips to record the location of
substrate as support for the construction of the web by Cyrtophora each thread attachment. The tensions on the threads generally pulled
citricola (Forsskal 1775) (Coddington 1989). the unstable strips out oftheirvertical alignment, toward the spider’s
I collected 32 adult females of C. citricola between April and web. After counting the threads, ! fed the spider a fiy, then cut all
November of 2009 in the Valle Central of Costa Rica (09°56'N, threads that were attached to the paper strips. This made the spider
34°15'W). Iplacedeachspiderinacardboardframe(27 X 22 X 18cm: rebuild the orb ofthe web. though part ofthe scaffolding above the
Stripposition FI Uil IFII UIV FV UVI FVIUV IFV UIII FII UI
Substratetype 45 678 (F=Firm,U=Unstable)
Stripnumber ^ 2 3 9 10 11 12
—
Figure 1. Stylized drawing ofthe arrangement ofthe experimental strips to which spiders attached their threads. F = firm; U = unstable;
positions ofstrips closest to the corners were I, and those nearest the center were VI.
249
250 THE JOURNAL OF ARACHNOLOGY
24
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— Vertical position(Aattop,Katbottom)
Figure 2. Number of threads (mean, SE, and SD, n = 32) —
attached to firm strips (white boxes) and to unstable strips (black Figure 3. Number of threads (mean, SE, SD) attached to the
b(pooxseist)i,onorVdIe)re(dFifrrmomsutbhsetreaxtte:ernBal=po-s0i.t3i2o,n (Rp~os=iti0o.n82I,)Ft\o4th=e c1e8n.t5e1,r sdtirfifpesre(ndtotvteerdticlianle)s.ePctoisointsioonfAthiesaftirtmhesttorippsof(stohleidstrliipnea)nadndposuintsitoanblKe
P < 0.0001; Unstablesubstrate; B = -0.17, Er = 0.70, = 9.19, P at the bottom.
l<ik0el.y00t0o1a;tctoamcphatrhirnegadsslotpoesf,itrm=ve—r7t.i3ca6lPsu<rfa0c.e0s0.1)F.uSrptihdeerrmsowreer,esmtaobrlee ofthe wall may be a consequence ofthe characteristics and shape of
threadsweremorelikelyto belocated inhighand lowpositions,while the orbs ofthis species. Orb-web building spiders tend to build long
unstable threads were more evenly distributed. bridging lines that form part ofthe upper frame and support the rest
ofthe orb web. In general, the attachment points ofthe anchor lines
orbwas not rebuilt (R. Madrigal Brenes pers. observ.). I repeated this that support theframearerelativelyfewand tend to bewell separated
procedure two more times and counted the threads of each of the (Foelix2011). Although construction behaviorisyet unexplored in C.
three webs built by each spider. Webs were rebuilt within the next citricoki, it is possible that this species follows a similar pattern of
three nights in all cases. behavior: first build anchor and/or frame lines that are attached to
To determine ifspiders preferred to attach threads to the firm or extremes, and then use these lines as mechanical support to construct
the rest ofthe web. This possibility remains to be demonstrated.
ct((btfdhhoaiierrnrserdmtaeu)adsnns1psc(oetFa(sniatfgbdti.lfiarenrcm1)gho),emsdwttariotitnthpohdest,hpecabsoioaIrrtnsnhodferniorer.fses1t)s2Ttwrouae(isbvupisensmn.sregataatag1sbaecludtoerph)mae;epifnarot2errhcdae(obeum/ladn-picetsseahtstpratrob.eissldbpieIuit)tdittieohhworneuinsstnhtiocnhufeobmtmtahbhpevneraadrcelraauegde1od1essf swdtsthuehrebmeBasottaMtnhesersseeactrtdytreioooaitntscoheoegelandeernsactttserhgipxuaoeipctnndet,eurCrsi.iastmnsaectdniwnhdtetarttabiUol.clcooaoktAinepbsspotctsrrlrioiewmuaadhicrcaletlhaety,rdhfsuetaaerrhmplaeeipbclsrrltypeoseisahdufwcealierhtvrssbemmsoatoafhsvsyatueithcrmibhisceluoiaannnursssvsteptesasarpdbttuelitcctegetioarestnstluieebooissn-ntsf
troeltahtievceotronetrh)e,p1opseitrifoonrmoefdthaersetgrriepsss(ihoonrifzorontthaelfaixrims,stproispistiaonnd1anclootsheesrt preesnissittaynttoansedlecdturfaibrlmeswubesbtsrat(ee.sg.., Leiiccnige spp.) have a lower pro-
oneforthe unstablestripsand then compared theslopestodetermine
ifthe number ofthreads changed relative to the position ofthe strips ACKNOWLEDGMENTS
in firm vs. unstable strips.
Lastly, for both firm and unstable substrates, I determined if the andI tthwanokaGniolbneyrmtoBuasrrarnetveise,weWrisllfioarmmGa.nyEbehrehlaprfdul, LcionmdmeenntHsiggainnds
spiderattached different numbersofthreadsat differentheightsalong
statistical advice.
the length ofeach strip, using a Kolmogorov-Smirnov test for each
type of substrate. For this test, I averaged the number of threads LITERATURE CITED
attached to unstable and firm substrates at each height (sections from
A to K) for each ofthe three webs ofthe spiders. Coddington, J.A. 1989. Spinneret silk spigot morphology; evidence
All spiders(/; = 32)attachedmore threadstothefirm strips than to for the monophyly oforbweaving spiders, Cyrtophorinae (Aranei-
the unstable strips (mean ± SD; firm = 7.02 ± 1.15, unstable = 4.04 dae), and the group Theridiidae plus Nesticidae. Journal of
± 0.85; paired = 18.96, P < 0.0001). However, spiders did not Arachnology 17:71-95.
distribute their threads evenly along either the horizontal or vertical Foelix, R.F. 2011. Biology of spiders. Third edition. Oxford
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