© 2017. Published by The Company of Biologists Ltd | Journal of Experimental Biology (2017) 220, 2129-2131 INSIDE JEB Ground spiders stones. Returning to Kiel, Wolff pitted the anchor their webs because of their enlarged predators against giant house spiders piriform silk glands, so they are unable to overwhelm victims with (Eratigena atrica), lace webbed spiders anchor structural threads. ‘This is a supersticky silk (Amaurobius fenestralis) and silver-sided textbook example of a trade-off, where a sector spiders (Zygiella x-notata) while highly efficient prey capture mechanism filming the encounters from beneath. ‘The has evolved at the cost of reduced thread attacks can be very quick; it can be hard to attachment, which is a basic function in all distinguish what is going on’, says Wolff, spiders’, he concludes. who slowed the movies down to see Drassodex attach silk to the floor of the 10.1242/jeb.163493 enclosure before running quickly around Wolff, J. O., Rˇ ezáč, M., Krejčı,́ T. and Gorb, S. N. its prey, producing a trail of sticky thread (2017). Hunting with sticky tape: functional shift in that dried quickly, ensnaring the victim’s silk glands of araneophagous ground spiders (Gnaphosidae). J. Exp. Biol. 220, 2250-2259. legs until it was neatly trussed up. Kathryn Knight A ground spider subduing a larger wolf spider. Photo credit: Arno Grabolle. But how did the Drassodex piriform silk differ from the silk produced by web Most spiders are content to sit and wait for spinners? This time, Wolff staged the unsuspecting victims to blunder into their spider ambushes on a sheet of plastic from Paper wasps really silken traps, but webs are only ever as which he could cautiously collect the silk. recognise each other’s good as the structures that secure them to Although isolating individual strands was faces the surfaces that support them. ‘This extremely difficult, Wolff eventually [attachment] is done with a special type of collected 17 straight specimens and silk, called piriform’, says Jonas Wolff, measured the silk’s strength. Comparing from Macquarie University, Australia, the piriform silk with other silks produced adding that most spiders only produce this by web-spinning spiders, he realised that The face of each Polistes fuscatus paper wasp is silk when they need to securely anchor a Drassodex piriform silk combines the unique. Photo credit: Elizabeth Tibbetts. structural thread. However, when Wolff toughness of dragline silk with the and Milan Rezác ,̌ from the Czech remarkable stretchiness of spiral capture Sculpting delicate nests from chewed-up University of Life Sciences, realised that threads from webs. Also, the glue coating wood pulp, Polistes fuscatus paper wasps the piriform silk-producing glands of the thread is extraordinarily deformable are master architects. But the social ground spiders (Gnaphosidae) were and tough, withstanding shear stresses insects have another skill that makes them different from those of other species – that are more than 750 times the stresses appear even more similar to humans: they they had fewer and the glands were that artificial glues can endure. are capable of face recognition. In fact, the significantly larger than those of web- females that found new colonies learn to spinning spiders – the colleagues were After the silk’s material properties had recognise their nestmates’ faces faster intrigued. ‘Why should a lineage of spider been defined, Tomáš Krejcǐ and Rezáč than they learn to distinguish other visual deviate from a pattern that is so investigated the silk-producing glands patterns. ‘Very few animals are known to widespread and hence a long-term and saw that the spigots through which have the special ability to recognize each success story?’, wondered Wolff. That, piriform silk is expelled are much larger other’s faces’, says Ali Berens, from the coupled with the ground spiders’ novel than those of other species; probably to Georgia Institute of Technology, USA, hunting strategy – they actively ambush eject a thick layer of glue at high speed in adding that the skill ‘likely evolved to prey, snaring them with piriform silk, and order to overwhelm victims that may lash reduce costly competitive interactions even pick fights with insects and out and injure them. The team also among nest-founding queens’. However, arachnids that are larger than themselves – realised that the enlarged spigots might other paper wasp species, such as Polistes led Wolff, Rezác ̌and Stanislav Gorb, become clogged by dried silk metricus, are less choosey and never learn from the University of Kiel, Germany, to components, until they noticed that the to recognise each other visually; they find out more about the ground spider’s spinnerets have a unique anti-clogging simply learn to recognise patterns. extraordinary silk and the glands that mechanism. They remain closed until just Realising that the difference in the wasps’ produce it. before they deploy the silk, when the fluid facial recognition abilities presented the pressure in the arachnid’s body rises and ideal opportunity to begin dissecting the However, ground spiders are not very the spigot pops open. essential components of wasp face common in northern Germany. It was recognition, Berens and her colleagues only while collecting animals in the Wolff adds that Drassodex spiders are Elizabeth Tibbetts, from the University of Southern Alps that Wolff stumbled across unable to spin the densely packed piriform Michigan, and Amy Toth, from Iowa Drassodex heeri concealed beneath silk disks used by web-spinning spiders to State University, USA, decided to Inside JEB highlights the key developments in Journal of Experimental Biology. Written by science journalists, the short reports give the inside viewof the science in JEB. Journal of Experimental Biology 2129 INSIDE JEB Journal of Experimental Biology (2017) 220, 2129-2131 discover which genes are essential for behavioural phenotype. However, it is not based at the University of Windsor, wasp face recognition. out of the realm of possibility that some of Canada, Butts, Galina Prokopchuk and the genes might be shared’, Berens Vojtecȟ Kašpar caught male and female Tibbetts and members of her lab collected concludes. fish from the Credit River in Canada to females of both species from under the compare the performance of jack and eaves of local buildings as the insects 10.1242/jeb.163477 hooknose male sperm in water and dilute founded new colonies and began Berens, A. J., Tibbetts, E. A. and Toth, A. L. ovarian fluid. constructing nests in spring. Back in the (2017). Cognitive specialization for learning faces lab, they patiently trained some of the is associated with shifts in the brain transcriptome Analysing the tail beat patterns and of a social wasp. J. Exp. Biol. 220, 2149-2153. insects to recognise simple black-and- calculating the speed at which the sperm white patterns, while others had to learn to Kathryn Knight could swim, their efficiency and the identify P. fuscatus faces from their power required to propel the sperm distinctive coloured markings. Once the Jack Chinook’s sperm through the water, it was clear that the jack wasps had completed their training and sperm outperformed the sperm of the their memories were secure, Tibbetts beat hooknose’s to the more robust older fish. The length of the froze them and shipped the insects to ultimate reward wriggling wave that passes along each Berens and Toth in Iowa, where the duo beating sperm tail was longer in the analysed the wasps’ brain gene expression jack sperm than the hooknose, and patterns. Jacky Cosson calculated that the jack sperm beat their tails faster to propel Comparing the gene expression patterns them through the water at 161 μms−1, in the brains of the P. fuscatus wasps that while the hooknose sperm only had learned to recognise simple shapes reached 155 μms−1. In addition, the with those of P. fuscatus that had learned jack sperm swam more efficiently in to recognise faces, the team was dilute ovarian fluid, with the hooknose impressed to find differences in 257 sperm using 45% more energy. It was genes, including genes that are involved AChinook salmon. Photo credit: Vojtěch Kašpar. also apparent that the fluid released in neuron signalling – such as the with the females’ eggs impacted the serotonin receptor and tachykinin. Life is beset with competition, from the performance of both males’ sperm, However, when Berens searched the P. sprint for victory to a tasty morsel to slowing the beat of the sperm’stail metricus gene expression patterns for stylish preening to attract mates, but one while increasing the sweep from side to evidence of the 257 P. fuscatus face of the most fundamental contests must side. ‘Each female creates a unique recognition genes, none cropped up. ‘This occur in the microscopic realm where fish spawning environment by suggests […] that there is something sperm battle to penetrate an egg first. simultaneously expelling ovarian fluid special about face learning – that it is not ‘Males often exhibit different tactics to along with an egg batch’, says Butts. just hyper-developed visual learning, but increase their reproductive success’,says a highly specialized learning response’, Ian Butts, from Auburn University, USA. So although it might look at first glance as says Berens. Some male fish pass themselves off as if the reproductive odds are stacked females to outsmart rivals guarding against smaller younger jack salmon Having identified the genes that lie at the harems, while others try sneaking behind males, they have a stealthy card up their heart of P. fuscatus’s ability to recognise opponents’ backs. Small Chinook salmon sleeves in the form of their super- individuals, Toth is now keen to learn males – known as ‘jacks’, which return to competitive sperm, which outperform the more about how these genes function in the river of their birth a year or two before sperm of apparently more superior facial recognition.