© 2015. Published by The Company of Biologists Ltd | Journal of Experimental Biology (2015) 218, 3711-3713

INSIDE JEB

Alcoholic pupfish kick Breukelen. However, after testing 295 the fish drunk”’, recalls van Breukelen. animals, van Breukelen and Hillyard had And when the team added ethanol to the breathing oxygen to concede that the phenomenon was real. fish’s water, even the fish that were The fish were somehow switching from adapted to cooler water switched to aerobic metabolism to anaerobic paradoxical anaerobism. So Devils Hole metabolism, which was perplexing as pupfish switch off aerobic metabolism to anaerobic metabolism is nowhere near as avoid the toxic side-effect of an aerobic effective as aerobic metabolism – only lifestyle, despite the expense. yielding 1/15 the amount of ATP per glucose molecule generated by aerobic 10.1242/jeb.134619 metabolism. Why were the fish indulging Heuton, M., Ayala, L., Burg, C., Dayton, K., Cyprinodon nevadensis mionectes in such a profligate practice? McKenna, K., Morante, A., Puentedura, G., from Ash Urbina, N., Hillyard, S., Steinberg, S. and van Meadows: Photo credit: Frank van Breukelen. Breukelen, F. (2015). Paradoxical anaerobism in Deep in a warm pool in a limestone cavern Intrigued, the team tested whether the desert pupfish. J. Exp. Biol. 218, 3739-3745. in the Mojave Desert lives one of the phenomenon was the result of the refuge Kathryn Knight rarest species on earth: the Devils Hole C. diabolis population breeding with pupfish (Cyprinodon diabolis). With a another closely related species, current population of just 131 adults, the Cyprinodon nevadensis mionectes. It takes personality for race is on to secure the fish’s future. ‘One van Breukelen explains that it has been possible cause for the small population suggested that interbreeding with other catfish to breathe air size of C. diabolis is limited food pupfish could have compromised the availability’, says Frank van Breukelen function of the mitochondria that generate Life is full of risks. Getting the next meal from the University of Nevada Las Vegas, ATP. However, when the team measured or defending your territory can be USA. Realising that the dark conditions the oxygen consumption patterns of the hazardous. David McKenzie from the dramatically limit the amount of food that two species, they both performed CNRS Montpellier, France, explains that grows in the cavern to support the fish, paradoxical anaerobism, so there was no animals gamble with fate for several van Breukelen and his colleague, Stanley mitochondrial disruption. And when the reasons. Some animals have to place Hillyard, were curious to know how many team tested whether C. diabolis were themselves at risk when foraging to pupfish the restricted ecosystem could switching to paradoxical anaerobism satisfy a high metabolic rate, while sustain. However, before they could do because they had depressed metabolism, others are simply bolder: and fish are no the calculation, the duo needed to they found that the fish were still wafting exception. McKenzie is also intrigued by measure the scarce fish’s metabolic rate. their gill covers to take in oxygen, so they air-breathing fish and was puzzled why ’ As the native Devils Hole pupfish weren t depressing their metabolism. less than 2% of fish have evolved the population is too endangered to study Finally, the team checked whether ability. ‘Air is a rich source of oxygen directly, van Breukelen and Hillyard C. diabolis were switching to paradoxical but breathing it is risky, so it made me measured the metabolic rate of a refuge anaerobism because there simply was not wonder if it might be linked to population of the fish that had been enough oxygen to sustain aerobic personality’, says McKenzie, explaining established as an insurance policy should metabolism in the warm conditions. that fish that breathe at the surface are the population ever be wiped out. But However, even that theory did not hold vulnerable to predation. Knowing that when they performed the measurement, water. Brazil is gripped by an invasion of air- the duo stumbled across an unexpected breathing African sharptooth catfish paradox. ‘We were going nuts trying to figure out (Clarias gariepinus), McKenzie decided what triggers paradoxical anaerobism’, to visit his collaborator Tadeu Rantin at Recording the fish’s oxygen consumption admits van Breukelen, until he and the Federal University of São Carlos, at temperatures ranging from 25 to 38°C, Heuton embarked on an animated brain- Brazil, to find out whether it takes Matt Heuton found that they consumed storming session one night. It occurred to courage for the catfish to breathe air or oxygen at a stable rate of around them that the fish may be switching to whether they simply surface to satisfy a 300 μlh−1 when they came from a paradoxical anaerobism to avoid the toxic fast metabolism. population that had been raised at 28°C. side-effects of aerobic metabolism, However, when Heuton measured the producing ethanol instead. They knew Collecting feral fish in São Paulo state and oxygen consumption rate of fish raised at that the 33°C-acclimated fish naturally transporting them back to the lab, 33°C – the temperature in the Devils Hole produced high levels of ethanol – 7.3 McKenzie, Rantin and Thiago Belão then spring – something went wrong. The fish times more than the fish from cooler developed a bimodal respirometer – with appeared to stop consuming oxygen. ‘My water: could the ethanol be switching off a space to allow individual catfish to initial reaction was that there was a aerobic energy production and stalling breathe air – to measure the animal’s air- malfunction of the electrode’, laughs van oxygen consumption? ‘I said, “Let’s get and water-oxygen consumption

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

3711 INSIDE JEB Journal of Experimental Biology (2015) 218, 3711-3713 simultaneously. After allowing the fish to others seem to take risks just because they between 2.5 and 3.5 m deep, ready to rest for 24 h in the respirometer, want to’. observe the females as they spawned. And McKenzie and Belão then recorded the then Puneeta repeated the experiment in amount of oxygen that they consumed 10.1242/jeb.134627 water where the temperature was a from air and water to determine their McKenzie, D. J., Belao,̃ T. C., Killen, S. S. and uniform 22°C across the entire depth. metabolic rates. Next, they startled the Rantin, F. T. (2015). To boldly gulp: standard fish by tapping on the respirometer and metabolic rate and boldness have context- Filming the females in the water with a dependent influences on risk-taking to breathe recorded how long it took the animals to air in a catfish. J. Exp. Biol. 218, 3762-3770. thermocline, Puneeta and her colleagues pluck up the courage to return to the Sakurai, Dharmamony Vijai, Hae-Kyun surface. ‘We assumed that how quickly Kathryn Knight Yoo and Hajime Matsui saw the squid they returned to air breathing was a descend into the cool water beneath the measure of how bold they were’,says thermocline where they produced egg McKenzie. masses ranging in diameter from 17 to Thermocline essential for 80 cm containing 38,000–200,000 eggs. Initially, they found that the fish in fully squid egg survival Explaining that the animals could only use oxygenated water did not need to breathe their fins to swim as they produced the egg oxygen from the air during the day, masses – because the mantles were used to although they did so anyway. However, pump water into the jelly surrounding the the fish in oxygen-depleted water were egg mass – Puneeta describes how each clearly struggling to meet their metabolic animal cradled the egg mass in their arms demands and resorted to air breathing and tentacles as it was extruded. In often. And when the team plotted a graph addition, the squid sank gradually to near of the fish’s metabolic rate against the the bottom of the tank during the 7 min it time that it took them to resume air took for them to produce each egg mass. breathing after a fright, they could see that However, she never saw the squid sit in the the fish that had the highest metabolic Japanese flying squid inside an experimental posture that Sakurai had suggested they rates breathed air the most. ‘There was an tank. Photo credit: Hae-Kyun Yoo. adopt before spawning. Puneeta also element of strong drive of individual By terrestrial standards, the Japanese flying noticed that initially the egg masses were metabolic rate to air breathe’,says squid (Todarodes pacificus)israthershy. elongated, although they eventually McKenzie. Little is known about the elusive animals’ became more spherical and then their reproduction, despite tons of them density changed and they floated up into But McKenzie also wondered whether appearing on dining tables every year. the thermocline, where the eggs boldness could be another factor affecting Pandey Puneeta from Hokkaido University, developed and hatched 5–6 days later. how swiftly the fish resumed air Japan, says, ‘A full understanding of its life breathing. Maybe some of the fish were history is hampered because observation is However, the eggs that were laid in the more courageous than others and this was difficult at the depths at which spawning tank with uniform temperature water did being obscured by the fish’s strong urge to occurs’, adding that the squid were not hatch successfully. They failed to breathe air. Recalling colleagues assumed to spawn in shallow coastal waters become buoyant, remaining at the bottom suggesting a technique to help tease apart above the continental shelf surrounding of the tank until 2–3 days later, when the the impact of boldness from the metabolic Japan. Previous attempts to observe egg masses collapsed and were consumed drive to breathe air, McKenzie and Shaun spawning in the field and the lab had led by microorganisms. Killen from the University of Glasgow Yasunori Sakurai to suggest that the squid scrutinised the data again and realised that migrated above the layer of water separating The team suspects that in addition to the fish could be divided into two groups the cold deep waters from the warmer spawning in shallow coastal waters, the – – one timid and the other bold with the surface waters (the thermocline) to spawn, squid may head further offshore to spawn. bold fish returning to the surface to with the egg masses sinking down later into They also suggest that the thermocline is breathe within 75 min of a fright, while the thermocline where the eggs would responsible for maintaining the buoyancy the timid animals remained cowering at develop prior to hatching. However, when of the egg mass and preserving the outer the bottom for at least 115 min. Also, the the Hakodate Research Centre for Fisheries jelly layer that protects the eggs from bold animals tended to air breathe more and Oceans opened in Japan in June 2014, microorganism damage. during the day and they chose to breathe Sakurai finally had access to a 6 m deep, air in well-oxygenated water, even though 300 m3 tank where he and Puneeta could 10.1242/jeb.134601 there was no need to place themselves at test the theory. risk. ‘The bold individuals were Puneeta, P., Vijai, D., Yoo, H.-K., Matsui, H. and ‘ ’ Sakurai, Y. (2015). Observations on the apparently just choosing to [put Having collected male and female squid spawning behavior, egg masses and paralarval themselves at risk]’, says McKenzie. by hand jigging and in traps in the waters development of the ommastrephid squid Adding that physiology and personality off Hokkaido, Puneeta pumped warm and Todarodes pacificus in a laboratory mesocosm. J. Exp. Biol. are not necessarily linked, he says, ‘Some cold seawater into the colossal reinforced 218, 3825-3835. animals take risks because they have to, concrete tank to create a thermocline Kathryn Knight Journal of Experimental Biology

3712 INSIDE JEB Journal of Experimental Biology (2015) 218, 3711-3713

Aphids reconstruct amino acids from scratch

It’s a gardener’s worse nightmare: your (Buchnera aphidicola) convert the four instead of building the amino acids newly planted seedlings become infested non-essential amino acids into the directly from the skeletons of the four by a horde of aphids. With unlimited sap essential amino acids that are necessary plant-derived amino acids, the aphids on tap, aphids should have a ticket to the for the aphid’s survival. were breaking down the plant-derived good times, but Meena Haribal and amino acids into small components which Georg Jander from the Boyce Thompson Feeding the aphids a series of diets laced they then used to synthesise the essential Institute for Plant Research, USA, with amino acids fortified with heavy amino acids that were not provided by explain that the sugary fluid is far from nitrogen and carbon isotopes, the duo their diet. The duo was also surprised that nutritious. Plant roots primarily produce then embarked on a brain-teasing set of instead of directly using the amino acids four amino acids – glutamine, glutamate, gas chromatography–mass spectrometry that they consumed in sap, the aphids asparagine and aspartate – which experiments to untangle the amino acid were resynthesising them too. ‘Even provide the voracious insect’s only synthetic web linking the aphid to its when there is an excess of an amino acid source of nitrogen. To overcome the symbiotic bacteria. Scrutinising hundreds in the diet, it gets broken down and re- restrictions of their diet, many aphid of mass spectra and tracing the paths of synthesised by the aphids’, says Jander. species have struck a cooperative deal nitrogen and carbon atoms, the duo found with symbiotic bacteria: providing their that the amine nitrogen of asparagine was 10.1242/jeb.134635 lodgers with food and security in return incorporated more readily into other Haribal, M. and Jander, G. (2015). Stable isotope for nutritional supplements that the amino acids than the amide nitrogen. studies reveal pathways for the incorporation of aphids cannot provide for themselves. However, the duo was intrigued to see that non-essential amino acids in Acyrthosiphon Haribal and Jander were curious to find most of the amino acids in the aphids’ pisum (pea aphids). J. Exp. Biol. 218, out how the pea aphid (Acyrthosiphon bodies were composed of combinations of 3797-3806. pisum) and its bacterial lodger normal and heavy carbon, suggesting that Kathryn Knight Journal of Experimental Biology

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