The stability of hygroscopic compounds in orb-web spider viscous thread

Animals use adhesive secretions in a plethora of ways, either for attachment, egg anchorage, mating or as either active or passive defence. The most interesting function, however, is the use of adhesive threads to capture prey, as the bonding must be performed within milliseconds and under unsuitable conditions (movement of prey, variable environmental conditions, unfavourable attack angle, etc.) to be nonetheless successful. In the following study a detailed characterization of the prey capture system of the world-renowned glowworm group Arachnocampa from the macroscopic to the ultrastructural level is performed. The data reveal that the adhesive droplets consist mostly of water and display hygroscopic properties at varying humidity levels. The droplet core of Arachnocampa luminosa includes a certain amount of the elements sodium, sulphur and potassium (beside carbon, oxygen and nitrogen), while a different element composition is found in the two related species A. richardsae and A. tasmaniensis. Evidence for lipids, carbohydrates and proteins was negative on the histochemical level, however X-ray photoelectron spectroscopy confirm the presence of peptides within the droplet content. Different to earlier assumptions, the present study indicates that rather than oxalic acid, urea or uric acid are present in the adhesive droplets, presumably originating from the gut. Comparing the capture system in Arachnocampa with those of orb-spiders, large differences appear not only regarding the silky threads, but also, in the composition, hygroscopic properties and size of the mucous droplets.

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“…marmoreus [48; 49; 50]. Also, at low humidities (>20%) the droplets are still visible and adhesive in spiders [51; 82; 83; 84]. …”

Section: Discussionmentioning

confidence: 99%

Characterization of the Fishing Lines in Titiwai (=Arachnocampa luminosa Skuse, 1890) from New Zealand and Australia

et al. 2016

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“…Our finding in experiment 1 of smaller and less spheroid gluey silk droplets in the webs of the spiders fed crickets compared with those fed cockroaches was probably a consequence of more water being lost to the atmosphere. This may explain why the spiral threads in the webs of the spiders fed crickets were less sticky than those of spiders fed cockroaches (Edmonds and Vollrath, 1992;Sahni et al, 2014b;Amarpuri et al, 2015;Opell et al, 2015). Water loss may also explain the greater concentration of inorganic salts in the spiral threads of the spiders fed crickets compared with those of the spiders fed cockroaches (Sahni et al, 2014b;Amarpuri et al, 2015).…”

Section: Discussionmentioning

confidence: 99%

“…Henceforth the differential expression of aggregate glycoprotein (Choresh et al, 2009;Vasanthavada et al, 2012;Collin et al, 2016) remains a plausible alternative explanation for the differences in spiral stickiness between spiders in the cricket and cockroach feeding treatments. Spread and extension of the glycoproteins under load is, nevertheless, enhanced if the glycoproteins are sufficiently hydrated (Stellwagen et al 2014;Opell et al, 2015). Hence a reduction in the amount of hygroscopic salts in the gluey silk droplets of the cricket-fed spiders may be responsible for the differences in adhesion regardless of whether or not they produced droplets with more or less glycoproteins than the cockroach-fed spiders.…”

Section: Discussionmentioning

confidence: 99%

“…The stickiness of the spiral threads is conferred by the presence of the glycoproteins (Bonthrone et al, 1992;Sahni et al, 2010Sahni et al, , 2011Opell, et al, 2013). The salts induce cohesive forces that cause the aggregate silk to coalesce along the flagelliform thread into droplets that resemble beads on a string (Sahni et al, 2014b;Opell et al, 2015). The salts also facilitate water uptake from the environment into the droplets (Vollrath et al, 1990;Sahni et al, 2010Sahni et al, , 2011Townley and Tillinghast, 2013), which keeps the droplets hydrated, and thus solvates the glycoproteins (Sahni et al, 2011(Sahni et al, , 2014a.…”

Section: Introductionmentioning

confidence: 99%

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Diet-induced covariation between architectural and physicochemical plasticity in an extended phenotype

Blamires

Hasemore

Martens

et al. 2016

Journal of Experimental Biology

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The adaptive benefits of extended phenotypic plasticity are imprecisely defined due to a paucity of experiments examining traits that are manipulable and measurable across environments. Spider webs are often used as models to explore the adaptive benefits of variations in extended phenotypes across environments. Nonetheless, our understanding of the adaptive nature of the plastic responses of spider webs is impeded when web architectures and silk physicochemical properties appear to co-vary. An opportunity to examine this co-variation is presented by modifying prey items while measuring web architectures and silk physiochemical properties. Here, we performed two experiments to assess the nature of the association between web architectures and gluey silk properties when the orb web spider Argiope keyserlingi was fed a diet that varied in either mass and energy or prey size and feeding frequency. We found web architectures and gluey silk physicochemical properties to co-vary across treatments in both experiments. Specifically, web capture area co-varied with gluey droplet morphometrics, thread stickiness and salt concentrations when prey mass and energy were manipulated, and spiral spacing co-varied with gluey silk salt concentrations when prey size and feeding frequency were manipulated. We explained our results as A. keyserlingi plastically shifting its foraging strategy as multiple prey parameters simultaneously varied. We confirmed and extended previous work by showing that spiders use a variety of prey cues to concurrently adjust web and silk traits across different feeding regimes.

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“…1A), each composed of an adhesive glycoprotein core surrounded by a hygroscopic aqueous layer (Fig. 1B;Edmonds and Vollrath, 1992;Townley et al, 1991;Sahni et al, 2013;Townley and Tillinghast, 2013;Opell et al, 2015). These threads are spun as a continuous cylinder of aggregate gland dope surrounding a pair of supporting flagelliform fibers.…”

Section: Introductionmentioning

confidence: 99%

Humidity-mediated changes in an orb spider's glycoprotein adhesive impact prey retention time

Opell

Buccella

Godwin

et al. 2017

Journal of Experimental Biology

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Properties of the viscous prey capture threads of araneoid orb spiders change in response to their environment. Relative humidity (RH) affects the performance of the thread's hygroscopic droplets by altering the viscoelasticity of each droplet's adhesive glycoprotein core. Studies that have characterized this performance used smooth glass and steel surfaces and uniform forces. In this study, we tested the hypothesis that these changes in performance translate into differences in prey retention times. We first characterized the glycoprotein contact surface areas and maximum extension lengths of Araneus marmoreus droplets at 20%, 37%, 55%, 72% and 90% RH and then modeled the relative work required to initiate pull-off of a 4 mm thread span, concluding that this species' droplets and threads performed optimally at 72% RH. Next, we evaluated the ability of three equally spaced capture thread strands to retain a house fly at 37%, 55% and 72% RH. Each fly's struggle was captured in a video and bouts of active escape behavior were summed. House flies were retained 11 s longer at 72% RH than at 37% and 55% RH. This difference is ecologically significant because the short time after an insect strikes a web and before a spider begins wrapping it is an insect's only opportunity to escape from the web. Moreover, these results validate the mechanism by which natural selection can tune the performance of an orb spider's capture threads to the humidity of its habitat.

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The stability of hygroscopic compounds in orb-web spider viscous thread

Cited by 3 publications

References 29 publications

Characterization of the Fishing Lines in Titiwai (=Arachnocampa luminosa Skuse, 1890) from New Zealand and Australia

Characterization of the Fishing Lines in Titiwai (=Arachnocampa luminosa Skuse, 1890) from New Zealand and Australia

Diet-induced covariation between architectural and physicochemical plasticity in an extended phenotype

Humidity-mediated changes in an orb spider's glycoprotein adhesive impact prey retention time

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