© 2015. Published by The Company of Biologists Ltd | The Journal of Experimental Biology (2015) 218, 961-963

INSIDE JEB

Tarantula coordination painstakingly digitising the position of Hairy big-eyed bats are the spiders’ limbs on the movies to disintegrates in heat accurately track their movements. seed predators

After months of patient analysis, it was clear that the spiders’ hydraulic limbs were affected by temperature. Going full out at the lowest temperatures, the spiders could only manage a relatively sedate top speed of 20 cm s−1.But,bythetimetheyhad warmed up to 40°C, they were rocketing Texas brown tarantula (Aphonopelma hentzi). along at a startling 53 cm s−1. And, instead Photo credit: Anna Ahn. of increasing their stride length as they speeded up, the animals increased the Scuttling across the floor, a spider’s Chiroderma villosum, hairy big-eyed bat, eating frequency of each stride from a leisurely a fig. Photo credit: Marco Tschapka. movements have more in common with 4 strides s−1 at 17°C to an impressive robots than you may at first realise. Instead 10 strides s−1 at the highest temperature. of contracting muscles to extend a limb, But, when the team analysed how the If you think feeding your picky toddler spiders inflate their joints with haemolymph spiders coordinated the extension of their is tough, spare a thought for Insa to straighten them – in much the same way Wagner. ‘Chiroderma villosum [hairy joints along the length of their legs, they ’ that hydraulic fluid propels robot limbs. And found that the animals were becoming more big-eyed bats] insist on fresh figs ,says temperature fluctuations may affect the uncoordinated at the highest temperatures: Wagner from the University of Ulm, movements of spiders and robots alike: fluid at the lowest temperatures, the spiders Germany, adding that windfalls and viscosity can increase dramatically as managed to extend the third and fifth joints frozen fruits are unacceptable to the temperature falls, prompting undergraduate fussy eaters. Wagner initially became at almost the same instant, but as the ’ Nick Booster from Pitzer College, USA, to temperature increased, their control began interested in the bats diet when she ask whether spider movements are affected noticed their fiddly eating habit – it took ‘ ’ to fall apart and the animals had more by temperature change. I ve always wanted difficulties coordinating the two joints. them nearly an hour to eat one fig. to study spiders because they use She also says, ‘Most bats use fruit as hydraulics’, says Anna Ahn from Harvey chewing gum: they take a bite, chew it Initially, the team had suspected that the Mudd College, USA, so when Booster until all of the sugar is gone and then spiders may be hampered at lower approachedAhnandSteveAdolphwithhis spit out the fibrous remains’, adding that temperatures by the increased viscosity of idea to study the effects of temperature on the animals often swallow intact seeds the haemolymph. Instead, the spiders’ the arachnid’s movements, they jumped at along with the juice or spit the seeds out coordination was restricted at higher the chance. ‘This is a fascinating question’, untouched. However, in addition to temperatures, because there may not be Ahn chuckles, adding, ‘We wanted to processing the fruit pulp to extract the enough time for the haemolymph to flow understand how temperature affects the juice, the big-eyed bats separated the through the leg and back to initiate the haemolymph and whether impaired seeds from the fruit flesh before next stride at the spiders’ blisteringly fast haemolymph movement might influence pulverising them with their teeth and high temperature stride rate. the spiders’ ability to run’. spitting the fragments away. Could the bats be chewing the goodness out of the ‘Hydraulic extension may allow spiders to Choosing to test the athletic abilities of seeds for nourishment? Wagner, her PhD save space and mass in their limb, but it may Texas brown tarantulas at temperatures supervisor Elisabeth Kalko, and Marco come at the expense of control’, says Ahn. that the animals encounter naturally (15, Tschapka, also from the University of And she adds that the inability of tarantulas 24, 31 and 40°C), Booster and Harvey Ulm, decided to find out. to coordinate joint extension at high Mudd College undergraduate Frances Su temperatures may partly explain why, painted white dots at four locations on the But working with the bats and their instead of taking advantage of the heat of arachnids’ forelegs and hindlegs before favourite figs proved challenging. Figs the day, her local tarantulas emerge at dusk filming the animals as they scampered fruit asynchronously, so there are always when temperatures are cooler. along a runway. Su recalls that the team some trees bearing ripe fruit in a forest: had no problems getting the spiders to 10.1242/jeb.122218 the challenge was finding them. ‘I had a sprint when startled with a gentle puff of list of about one-hundred fig trees [Ficus Booster, N. A., Su, F. Y., Adolph, S. C. and Ahn, air, although collecting movies with a A.N.(2015). Effect of temperature on leg kinematics obtusifolia] along the coastline of the clear view of at least four strides was more in sprinting tarantulas (Aphonopelma hentzi): high Barro Colorado Monument that I had to troublesome. ‘It was difficult when the speed may limit hydraulic joint actuation. J. Exp. check at least once a week for nearly ripe spiders didn’t run in the right direction’, Biol. 218, 977-982. fruit’, recalls Wagner, who foraged says Su; then Booster spent hours Kathryn Knight constantly for ripe figs to satisfy her bats.

Inside JEB highlights the key developments in The Journal of Experimental Biology. Written by science journalists, the short reports give the inside view of the science in JEB. The Journal of Experimental Biology

961 INSIDE JEB The Journal of Experimental Biology (2015) 218, 961-963

And collecting the fig-mad bats was also Optimistic future for sea potential is high. Then, after allowing tricky. Wagner explains that hairy big- 15 min for the stain to penetrate the eyed bats are relatively scarce compared urchins sperm, the team set the gametes a with the more common Artibeus watsoni swimming test – they filmed the sperm (Thomas’s fruit-eating bat). However, inadropofseawaterundera after patiently staking out ripe fruit trees microscope – to find out how well they and collecting individual animals, performed and recorded the ratio of Wagner was ready to start investigating green to orange/green fluorescence in how they masticated each mouthful and order to measure the membrane how efficiently they extracted the seeds’ potential of the sperm mitochondria in nutrients. all three environmental scenarios.

Analysing how 12 bats chewed their fig Not surprisingly, the sperm mitochondria meals, Wagner realised that the big-eyed became increasingly unhappy as the pH bats spent three times as long chewing the dropped, with the membrane potential Centrostephanus rodgersii sperm. Photo credit: – seeds as they did the fruit pulp. And when Monique Binet. falling up to 42% at 0.3 pH units, and she compared the number of seeds in the plunging by as much as 55% in the 2300 pellets of discarded pulp produced by When you cast your seed into the open, pH scenario. However, the –0.3 pH unit C. villosum with the number of seeds in you’d better be sure that the conditions reduction did not appear to impact the the fruit pulp pellets of A. watsoni, the will be ideal to ensure the success of the sperm swimming speed adversely – C. villosum fruit pellets were almost seed next generation. And that approach sperm swam even faster than under free. She also found that the A. watsoni seems to have served sea urchins present day conditions – but the poo contained four times as many intact perfectly well: that was until now. As performance of the –0.5 pH unit sperm seeds as that of C. villosum. So, instead of global sea temperatures rise and the suffered as their swim speed plummeted. distributing the seeds in their faeces, the oceans begin to acidify, the tiny gametes Although the sperm were not equally big-eyed bats appeared to be consuming that sea urchins entrust to the waves are affected by the adverse conditions; there them, but were the bats deriving any under increasing risk. Monique Binet were large variations in swimming speed benefit from the seeds? from CSISO, Australia, and an in both of the future climate conditions. international team of collaborators say, Teaming up with Irene Tomaschewski ‘Under near-future scenarios of ocean So, even though the sperms’ and Jörg Ganzhorn from the University of acidification, the swimming behaviour of mitochondria were impaired, and Binet Hamburg, Germany, Wagner analysed marine invertebrate sperm is altered’. and her colleagues point out that the the nutrient content of the seed remains Sperm use a pH gradient (from low to sperm are currently near their pH and discovered that the big-eyed bats high pH) to activate the energy- tolerance tipping point, the team were extracting almost all of the goodness supplying mitochondria that power the is optimistic about the future of from them (over 85% of the lipids, gametes when released into the ocean, so C. rodgersii sea urchins. Explaining that protein and sugars). And when Wagner the team decided to test how future lower mitochondrial activity will allow ’ tested the bats fig preferences, she climate scenarios might affect the the sperm to eke out their meagre energy found that the bats always preferred membrane potential of mitochondria that reserves for longer and extend their F. obtusifolia figs, which have a higher produce ATP, and how individual longevity, the team says, ‘Increased seed content than the figs of other swimming performance is affected by sperm longevity increases fertilisation species. What is more, the bats were only acidification. success when sperm–egg encounter rates interested in the seeds from strangler figs, remain high over prolonged periods’. which are covered in a slimy gel that the After collecting Centrostephanus Andtheyalsosuggestthatthebroad seed uses to attach itself to the trunk of a rodgersii sea urchins from the rocky range of sperm responses may provide host tree to grow on. shoreline of Sydney’s North Harbour the sea urchins with an opportunity to and transporting them back to the lab at side-step their apparently bleak future. ‘Chiroderma villosum acts more as a Macquarie, the team encouraged the sea The team says, ‘Substantial inter- seed predator than a seed distributor’, urchins to release sperm ready to test the individual variation in responses of says Wagner, who also suspects that the effects of environmental acidification. sperm swimming to ocean acidification gel coating on F. obtusifolia seeds helps Next, they exposed the fresh sperm to may increase the scope for selection of the bats to separate the seeds from the seawater from one of three scenarios – resilient phenotypes, which, if heritable, fruit flesh, allowing them to extract current ocean pH, –0.3 pH units below could provide a basis for adaptation to more from their fig meals than other current ocean pH (the projected coastal future ocean acidification’. bats. – water conditions in 2100) and 0.5 pH 10.1242/jeb.122200 10.1242/jeb.122192 units below current ocean pH (the projected coastal water conditions in Schlegel, P., Binet, M. T., Havenhand, J. N., Wagner, I., Ganzhorn, J. U., Kalko, E. K. V. and – Doyle, C. J. and Williamson, J. E. (2015). Tschapka, M. (2015). Cheating on the mutualistic 2300) before adding JC-1 stain to the Ocean acidification impacts on sperm contract: nutritional gain through seed predation sperm, which fluoresces green when the mitochondrial membrane potential bring sperm in the frugivorous bat Chiroderma villosum mitochondrial membrane potential is swimming behaviour near its tipping point. J. Exp. (Phyllostomidae). J. Exp. Biol. 218, 1016-1021. low, but produces orange/green Biol. 218, 1084-1090.

Kathryn Knight fluorescence when the membrane Kathryn Knight The Journal of Experimental Biology

962 INSIDE JEB The Journal of Experimental Biology (2015) 218, 961-963

Magnetic sense essential for correct turtle turning

It’s one of the greatest ocean odysseys: when the consequences of ignoring the magnetic lingering longer than was safe in the cold tiny loggerhead turtles strike out from their field at the locations where the hatchlings’ northern waters near Portugal and failing to birth beaches on the coast of North America responses to the magnetic field were enter the Antilles Current – that would bear into the Atlantic, their migration will take strongest. them home – in the waters off Barbados. them all the way to Europe and back before Next, the team set the simulated turtles they return home. Nathan Putman and Testing which directions the tiny reptiles swimming strongly in the directions that colleagues from the University of North swam in when they experienced the theyselected when exposed to the magnetic Carolina, Chapel Hill, USA and the Centre magnetic fields that exist near Portugal, the fields near Portugal and Barbados, and this de Recherche Halieutique Méditerranéenne Straits of Gibraltar, the Canary Islands, time the youngsters stayed on track. et Tropicale, France, explain that the tiny Suriname and Barbados, the team found The team says, ‘Our findings suggest that voyagers use a range of senses to guide them that the hatchlings in the Portuguese the magnetic navigation behaviour of sea on their way, including detecting and magnetic field swam in a southerly turtles is intimately tied to their oceanic responding to the local magnetic field. direction, while those experiencing the ecology and is shaped by a complex However, untangling the relative magnetic field near Barbados swam interplay between ocean circulation and contributions of different sensory northwards. And when they simulated the geomagnetic dynamics’. mechanisms at individual locations along turtles’ route as they moved passively in the the way is tricky. So, Putman and his strong ocean currents, going with the flow 10.1242/jeb.122226 colleagues decided to take a hybrid in regions where the turtles did not respond Putman,N.F.,Verley,P.,Endres,C.S.and approach: integrating lab-based to the magnetic field did not pose Lohmann, K. J. (2015). Magnetic navigation experimental observations of hatchling problems: the currents simply carried them behavior and the oceanic ecology of young loggerhead sea turtle responses to the in their preferred direction. However, the loggerhead seaturtles.J. Exp. Biol. 218, 1044-1050. magnetic fields at specific locations along youngsters appeared to encounter Kathryn Knight their route with simulations that investigated problems near Portugal and Barbados, [email protected] The Journal of Experimental Biology

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