The impact of UVA on the glycoprotein glue of orb-weaving spider capture thread from a diurnal and a nocturnal species (Araneae: Araneidae)

2016·3.2 MB·English

by  Sarah D Stellwagen

2016. Journal of Arachnology 44:401-404
SHORT COMMUNICATION
The impact of UVA on the glycoprotein glue of orb-weaving spider capture thread from a diurnal and a
nocturnal species (Araneae: Araneidae)
Sarah D. Stellwagen, Brent D. Opell and Mary E. Clouse: Department of Biological Sciences, Virginia Tech, Blacksburg,
Virginia 24061, USA; E-mail: [email protected]
Abstract. We compared the effect of Ultraviolet A radiation on the adhesive droplets of the diurnal orb-web weaver
Argiope trifasciata Forskaal, 1775 and the nocturnal orb-web weaver Neoscona crticifera (Lucas, 1838). We hypothesized
that glycoprotein glue within A. trifasciata droplets will either be unaffected or will benefit from UVA exposure, whereas
the glycoprotein of N. crticifera will be degraded by UVA. In both species, the volume of fresh droplets did not differ from
that of droplets that were exposed to UVA for four hours, or from the volume of droplets kept in the dark for four hours.
This documented that UVA did not affect compounds that confer droplet hygroscopicity. Both dark and UVA treatments
reduced the relative toughness of droplet glycoprotein, though the reductions were not statistically significant, with the
dark treatment exhibiting a greater decrease in relative toughness. This study suggests that ecologically relevant levels of
UVA exposure do not affect the glycoprotein glue of orb-weaver capture silk.
Keywords: Adhesion, biomaterials, toughness, silk, ultraviolet
Ultraviolet radiation (UVR) comes in several forms including including A. trifasciata Forskaal, 1775, are found in habitats where
UVA and UVB, the latter of which is more damaging, although more their webs are exposed to full sun. Others, such as Neoscona crticifera
UVA enters the atmosphere than the other forms of UVR (Rizzo et (Lucas, 1838). are nocturnal and forage from the center of their webs
al. 2011). Ultraviolet radiation induces cross-linking in proteins (Bhat at night and monitor their webs from an adjacent cryptic retreat
& Karim 2009; Hu et al. 2013), and low doses may enhance spider silk during the day. The web’s radial threads extend from the center like
performance by further aligning proteins, similar to the “improve¬ the spokes of a wheel and are largely responsible for absorbing the
ment phase”, during which molecule alignment is hypothesized to force of prey impact (Sensenig et al. 2012), whereas the prey capture
continue after a silk strand is extruded (Agnarsson et al. 2008). Non¬ spiral retains flying insects (Apstein 1889; Sekiguchi 1952; Sahni et al.
adhesive major ampullate spider silk continues to improve mechan¬ 2014). The measure of a capture thread’s ability to overcome the
ically after several hours of natural UVA exposure, hypothesized to efforts of a prey struggling to escape is the droplet’s toughness, the
be the result of free radical generation that induces cross-linking, work required to extend a droplet (Sensenig et al. 2012). This is
however longer exposures do eventually result in degradation (Osaki determined by the extent of droplet stretching (the droplet’s
2004; Osaki & Osaki 2011; Perea et al. 2015). UVA at ~700 W/m' extensibility) and the force required to extend the droplet until it
reduces the molecular weight of spider dragline silk from Nephila pulls from a surface, that is, to overcome the droplet’s adhesion.
clavipes Linnaeus, 1767 more than 30% during the first hour, and
To complement our previous UVB study (Stellwagen et al. 2015),
more than 80% after 5 hours (Matsuhira et al. 2013). However the
we investigated the effects of UVA radiation on the performance of
radiation intensity used was more than 20x the natural incident UVA
viscous glue droplets from A. trifasciata and N. crucifera (family
striking spider webs in the summer. Osaki & Osaki (2011)
Araneidae). We tested the hypothesis that the performance of
demonstrated that ecologically relevant doses of UVA actually serve
droplets from the webs of the full-sun diurnal species, A. trifasciata,
to mechanically strengthen dragline silk of Argiope hriienniclii
is enhanced by UVA exposure; whereas that of droplets from webs of
(Scopoli, 1772) while weakening that of Neoscona naittica (L. Koch,
the primarily nocturnal N. crticifera, is either not affected or is
1875).
degraded by UVA. We did this by comparing several performance
The capture spiral threads of araneoid orb weaver webs differ from
metrics. First, the duration of droplet extension before droplet pull-
the dragline threads that form their radial and frame threads. These
off, a measure of the time over which the work of extension occurs,
adhesive threads are composed of a pair of supporting axial
and second, the angle of axial line deflection, a measure of the force
flagelliform fibers that are covered by aqueous aggregate gland
on an extending droplet. Together, these metrics can be used to
material. Originally deposited as a cylinder of dope, this material
compute relative toughness, a measure of the energy required to
coalesces into regularly spaced droplets, each containing a glycopro¬
extend a droplet to pull-off.
tein glue core (Sahni et al. 2010, 2014). Inorganic salts and low
molecular mass organic (LMMC) compounds within the aqueous Fresh threads collected in the early morning (A. trifasciata) or late
layer that surrounds this glycoprotein core attract atmospheric evening {N. crticifera), soon after they were spun, were compared with
moisture, causing droplet volume to fluctuate with environmental those that were aged in the dark for 4 hours and droplets that were
humidity (Edmonds & Vollrath 1992; Opell et al. 2013; Townley & exposed to 4 hours of UVA. We photographed each thread droplet
Tillinghast 2013). We have shown that diurnal species preferring prior to extension, permitting us to compare the effect of aging and
habitats that expose their webs to full or partial sun produce viscous UVA on droplet volume. This allowed us to test a contending
threads with droplets that are not only resistant to degradation, but hypothesis that differences observed in droplet performance can be
also contain glycoprotein that exhibits an increase in relative explained by the impact of UVA on droplet hygroscopicity through
toughness when exposed to UVB (Stellwagen et al. 2015). This its effect on LMMC and salts in a droplet’s aqueous layer, a
results in more work being required to extend these UVB exposed conclusion that would make it more difficult to ascribe UVA action to
droplets. Species of the genus Argiope Audouin, 1826 (Orbiculariae), its effect on the droplet’s glycoprotein core.
401
402 JOURNAL OF ARACHNOLOGY
= H H eu Thread samples from webs constructed by 13 adult female A.
s (» H S ^ S S trifasdata and 11 adult female N. crucifera were collected on and near
nt oo VOOn fono the Virginia Tech campus in Blacksburg, Montgomery County,
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atm ^ o o o ^ o Vtriirfgaisndiaat, a UwSeAb , safmropmle w15a sA cuoglluesctt edto be2t5w eSeenp t0e5m:3b0ehr a2n0d1 40. 8;E3a0chh anAd.
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d tr aII, aII. a. Q. all images and videos captured by 16;00h the same day. Threads of N.
n crudfera webs were collected between 2I;30h and 23:00h and their
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s m study was completed by i6:00h on the following day. Except for
ecie Hcd, o -PH om differences in irradiance described below, all methods and analyses
oth sp -OJ i-nri rr-^-n1) on-M^i ^vidl oiinol ovidl areT twhoo se1 5d.e0s cwribatetd, b3y5 2S tnelmlw asgpeenc terat la lp. e(a2k0 15U).V A fluorescent tubes
b (F15T8BL; 440.4 mm length, 25.4 mm diameter; USHIO Inc.,
or Cypress, CA, USA) were used to irradiate samples. Irradiance was
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ness5). ^ P fmN fVNOj mPMeaAsu2r2e0d0 ) useiqnugi pap edp howtoitrho .eat erU VraAd iodmeteetcetro r( S(oPlMarA 2L1ig1h0t, CGole.,n sIidnec.,
h1 + 1 +1 -fl il il il
ug20 O — »n cN On VO 05 Pennsylvania, USA) with a spectral sensitivity from 320-400 nm,
ve to al. ( H —OO< VinO VO cTaelcibhrnaotleodg yt r(aNcIeSaTbl)e o nto 1 8t hAeu gNusatt i2o0n1a4l. TInhsrteiatudtse woerfe Sirtraanddiaatredds foarn d4
g relatiLiao et 0O5O rmVoO hlaomuprss ),a t w~h1ic3h Wis /mtw^ o(-tthheir dms axthime umma xliemveulm p rloedvuelc eodf bfyu llt hseu nUliVghAt
o received in Blacksburg in late summer. Conditions in the dark
d l in treatm.ent cylinder and the UV cabinet were recorded every 30
nd a. Q.
m^), ascribe rn CN nt VO s(Hecoobnod®s fmoor dtewl oU h2o3u-0rs0 2b,y O tenmsept eCraotmurpeu/rteelra Ctivoerp h.,u mBoiduirtnye ,d aMtaa slsoagcgheur¬s
N/de \d in sd o ni setts, USA). The dark treatment cylinder maintained ambient
ess (d as Q(2a S53 UQ iinl O+1 r+o1 il riol ^il taet m5p5e%r at±u re1 .3a%t ;2 4fo°Cr th±e 0U.1V3 °cCa b(imneeat,n th±e ScoDr)r easnpdo nrdeilnagti vvea lhuuesm iwdeitrye
hnute W od 'O od 24°C ± 0.08°C and 55% ± 1.7%.
gp
um We used JMP (SAS Institute, Cary, North Carolina) to analyze
o
s), relative tume was co mrO+P1 i+^1 rfiNPl m^—ri-l ^voidl ^roiPl dpS>aah ita0rap. 0it5ra-o)tne.- dWsN tsic.ol okrmNn Wsoaidl nltey-enrs etodsdri mswtcreaoirlbem u vupteasaedlrudi es votsoa nl uwsd eeestwr eewri tmhelo rinegP e-c tnroa<omn rsmp0fao.a0rrle5imtd ye adwos, fi t thsahi ngemdn d iafatiatccgahaa ne(itPdn.
econdet vol tuessitnegd Wfoirlc onxoormn aplaitiyr . teRstesm. Eaiancihn gt renaotnm-neonrt mvaallu ve awluaess cwomerpe acreodm tpoa rtehde
on phase times (sxon pair). Dropl •HSor :ToODj Hop CCi(cid:9632)fnNOl rmn^i-l T—o0iin5lf« ^no(iNdl! ^no^—mil!' 0r^i-5lj^ swosfriunemip dsNiphttlhhe oa,ietrr th ithwt rdyeehr rtaiho ocdtepfhh l,eecv c towado lnianuvttrethoreko,il nnu lw nd maeoihnenariscgdc hth ho thesrfsep y eUaeeprctvioVmtiethehdAesee ,nr sa etwis sxs dpe ptrerhoetoche sipq eualscutre eoitts (nseT tat rwralesotbiaasmlls t.em i adlOaen1rrnudo) .tr p(s TlT LbehahetMba issldlteMe ngfaICagan)itu. lh ege idfenaf e notcdoatf
^), extensiP = Wilco ^ >5 oOos o^^ 0n5j ^nj didtnrrredooaipptclmlaeetttee’ ns pttshoe rauofttno e rratm hnaeayq n gucoleeybo csueomsrp vurelsoadtty e eibenref f caeorcaertt etr aoiwfbff uietatchegtidenind g et abocoy h rt hUdUerV oVApeAlf ef eet.cex txpspo osousfur ere th aenosdne
mW
ume (p pair, o^0—^5 im0n5 o^ooj" eexxptTeenorditeaenld c elaodna ddn eohd ap duti lmle ifetrh oebmre graea lnde raowspehdlee ntf,r oaamnnd taehxneid acel odnl iwtnaehc etiwnn agtsh epa rdot rbo1ep8 l0oe°rt hahnaaddd
m), volmatched rOi-l VoiDl ^ooil m——il mnil] o0Vi5Ol adbxievicaiodlm eldien eisn,o tw ot hhtihicneh tphhraaedt- e ixrte tetnunors niloeondn gptoehr a ase ex1,e 8rb0t°ee fdco orane fmfigoeruacresau toiroannb .tl heTe h fdoisrrc otepi mloeetn wwthaaess
p
m), width (on; MP = f'isvdl4 v—idl, >i0l oriPol oviodl oviodl sagpullh.yf af2csi0oce1ip,e 5rdno)ut.t ertEiionnx g ete wxwntieshtinhiocdinnh t thtdihmere oed pgsrl loepyptrcslooe vpt(’iTrsdo aetgbedlli yenac noe1 lp)io.nr nodFgteeoxairt ne o dtfch ot(ehfr ieegf, u. e al2xln tiedsnnu tsnShi tbeesi lpleliwextyctaie egonsefs,n ito hAenet.
gth (pdeviati min VmO 'sOn 00 etrxipfaossduareta. , Fdorro pNl.e tc reuxdtefnersaio. ne xtitmenes iowna st imreed uwceads ubnya f2f9e%ct edaf tbeyr UUVVAA
end oo exposure.
et ldar Ood rrPn r<Pn d— 0^5 0^5 Plotting the force on an extending droplet against extension time
Dropl stan ti-l- il —il oil <inl 0i5l dcuerpvicet sr ethpere speenrftso rmrealantcivee o tfo aung henxetesns daendd d rios palent . inTdheex aroefa tuhen deenr etrhgiys
— 1 2 ^ m rn m required to extend a droplet (Table 1, Fig. 1). Compared with fresh
1.n ± •S threads, the energy absorbed by threads of A. trifasdata and N.
Table mea "uS. O O Ci ~t2 >D Q^ carnudc if4e5ra% d eacnreda se3d1 %5,5 %r easnpdec t4i3v%el,y ,r esapfetecrti vUelyV,A a fteexr pdoasrukr et.r eaNtmeiethnetsr
13; treatment difference wass significant and. although both treatment
STELLWAGEN ET AL.—IMPACT OF UVA ON ORB-WEB GLYCOPROTEIN GLUE 403
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Figure 1.—Force/extension time plots for viscous droplets and corresponding histograms of relative toughness for droplets in each treatment,
as determined from areas under these curves. Points in force/extension time plots are mean values and are connected by smoothed lines. Relative
toughness values are mean + standard deviation.
values were less than the control, there was no evidence to suggest toughness with aging may indicate that the chemical cross-linking
that that UVA exposure degraded droplet performance beyond the mechanism hypothesized to strengthen dragline silk (Osaki 2004) either
aging that occurred during this time. does not affect the glycoprotein, or that higher doses of UVA not
Retention time is important for prey capture success, and a typically experienced by spider threads are needed to see this effect and
reduction of only a few seconds can mean a lost feeding opportunity sufficiently counteract the effect of aging. Similar to UVB, UVA does
for an orb-weaving spider (Blackledge & Zevenbergen 2006). This not appear to impact the LMMC in droplets, which supports the
study hypothesized that droplets from webs of the diurnal, full sun observation that these compounds resist degradation (Opell et al.
species A. trifcisciata would be more likely to be positively affected by 2015). Thus, our study suggests that ecologically relevant doses of
UVA than those from the nocturnal species N. criicifera, or at least UVA have little impact on spider capture spiral thread function.
would be more resistant to UVA degradation. However, although
droplets from A. Irifasciata webs showed a reduction in droplet ACKNOWLEDGEMENTS
extension time after exposure to UVA, this did not affect the overall
energy absorption of the droplet during its extension. Carlyle C. Brewster assisted with statistical analyses. Author
Interestingly, the relative toughness of both species' droplets contributions: S.D.S. collected and prepared thread samples, per¬
decreased more after dark exposure than after UVA exposure, formed droplet extensions and image measurements, analyzed data,
although these differences were not statistically significant. Threads and prepared the manuscript and figures. B.D.O. designed and
of both species experienced a 4-hour, dark aging treatment, however, constructed the instrumentation used in this study, collected and
for A. trifasciata this occurred approximately 3 hours after a web was helped prepare thread samples, and contributed to data analysis, and
constructed, but for N. crucifera it occurred approximately 11 hours manuscript and figure preparation. M.E.C. assisted with droplet
after a web was constructed. This difference may explain the smaller extension, image measurements, and data entry. Funding: Funds
decrease in energy absorption by N. crucifera droplets. This decrease in from the State Council for Higher Education for Virginia provided
404 JOURNAL OF ARACHNOLOGY
the digital camera used in this study. This study was supported by Osaki, S. 2004. Ultraviolet rays mechanically strengthen spider’s silks.
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Journal of Experimental Biology 216:3023-3034. Manuscript received 13 November 2015, revised 25 April 2016.