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The Subtle Art of Electro-Flirting in Wild Knifefish

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The Subtle Art of Electro-Flirting in Wild Knifefish © 2018. Published by The Company of Biologists Ltd | Journal of Experimental Biology (2018) 221, jeb170084. doi:10.1242/jeb.170084 OUTSIDE JEB The subtle art of electro- with high precision. They found that each may interfere with natural courtship. This fish emitted electric discharges at their study highlights the importance of flirting in wild knifefish own unique frequency, producing investigating physiological phenomena in ‘electrical fingerprints’ that they used to natural habitats. The team also note that identify and track individuals, as well as the insights into how weak electrical distinguish between the sexes. signals are interpreted by the fish’s brains may help us to improve the design of The team discovered that the electric bionic devices, such as retinal and discharges were closely associated with – cochlear implants for people with two types of behaviour: male female impaired vision and hearing. courting and male–male aggression. During courting, males would hound 10.1242/jeb.170084 females with short electric ‘chirps’ that Henninger, J., Krahe, R., Kirschbaum, F., Grewe, lasted less than 20 ms, until the female J. and Benda, J. (2018). Statistics of natural responded with a long chirp that lasted communication signals observed in the wild COMMUNICATION over 150 ms, signalling her intention to identify important yet neglected stimulus regimes in weakly electric fish. J. Neurosci. release eggs. These long chirps were doi:10.1523/JNEUROSCI.0350-18.2018. What do James Brown and ghost knifefish responded to with precisely timed (Apteronotus) have in common? They’ve response ‘doublet’ chirps, which Alex Evans (0000-0002-5655-012X) both harnessed the power of electric indicated the intention of the male to University of Leeds organs in order to deliver declarations of release sperm, resulting in a tightly [email protected] adoration. As close relatives of the electric synchronised fertilisation event. As well eel (Electrophorus electricus), it’s as courtship, the team found interesting probably not too shocking that ghost patterns of electro-communication How ticks put the B in knifefish also possess an electric organ between males competing for access to blood that generates an electrical discharge. As females. These events occurred when the well as emitting electricity, ghost electric discharges of a rival male knifefish are covered in electro-sensitive interfered with the signals emitting from a receptors that allow them to sense their male courting a female and tended to end surroundings, detect the presence of other with the rival male submissively individuals and communicate with other retreating from the area. fish through electric organ discharge. As ghost knifefish are nocturnal and The team was also able to demonstrate frequently hide amongst rocks and roots, how these short and long chirps were their natural behaviours are rarely ever closely linked to spawning behaviours in observed and the characteristics of their another species of brown ghost knifefish Apteronotus leptorhynchus electrical discharges have previously been ( ) in a more NUTRITION examined almost exclusively through closely monitored laboratory laboratory-based tank studies. Until now, environment. By simultaneously filming Few things wreck a picnic faster than the the natural electric conversations of ghost and recording the fish’s electric discovery of a poppy seed tucked into the knifefish and their role in wild behaviours discharges for over 5 months, collecting a warm folds behind your knee that turns out have largely remained a mystery. staggering 1.3 million individual chirps in to be a tick. If left undisturbed, it will the process, the team demonstrated that slowly gorge on your blood until it A recent study reveals the importance of the same short and long chirps recorded in resembles a flattened jelly bean – with legs. subtle bio-electric communication during the wild were closely correlated with For picnickers and parents, it’s a revolting the courting and aggression behaviours of critical mating events such as the transformation fraught with dangers, wild weakly electric fish. Lead authors of synchronised release of eggs and sperm. because ticks are major vectors of a range of the study, Jörg Henninger and Jan Benda, debilitating illnesses, including Lyme from the Eberhard Karls University of However, in contrast to previous disease; yet, for biologists, the Tübingen, Germany, set out deep into the laboratory-based tank studies, many of transformation is nothing short of rainforests of Panama to record the the EOD signals detected in the wild were remarkable. electro-communications of wild brown much weaker than expected and barely ghost knifefish (Apteronotus rostratus). activated the fish’s own electro-receptors. Ticks can endure weeks of starvation Using a grid of electrodes placed in a These subtle electric whispers had never while awaiting the chance arrival of new knifefish-inhabited creek, the team were previously been recorded in laboratory hosts, but even after tapping into a vein, able to record electric organ discharges experiments as the artificial conditions all they get is a diet of blood, upon which Outside JEB reports on the most exciting developments in experimental biology. The articles are written by a team of active research scientists highlighting the papers that JEB readers can’t afford to miss. Journal of Experimental Biology 1 OUTSIDE JEB Journal of Experimental Biology (2018) 221, jeb170084. doi:10.1242/jeb.170084 they would surely starve. Although ticks with a B vitamin supplement and this species (ROS), a by-product of electron blood is rich in proteins and lipids, it solved everything! The ticks on drugs and movement through the respiratory chain lacks other key nutrients required for vitamins were as healthy as wild-type ticks. that supports ATP production. The dual survival. However, a fascinating new role of mitochondria intrigued Karine Salin study – by Olivier Duron from the CNRS This and countless other studies make clear and her colleagues from the University of in Montpellier, France, and his team of the numerous essential roles that bacteria Glasgow, UK, and Semmelweis colleagues from across the country – play in animal well-being. In addition, this University, Hungary, so they investigated shows how ticks overcome this nutritional study highlights the massive evolutionary whether the metabolic adjustments made deficiency. flexibility of some bacterial groups. Within by mitochondria during fasting also caused Francisella, there are both mutualists and oxidative stress in brown trout (Salmo Ticks are arachnids, but they aren’t the pathogens that are nasty enough to be used trutta), a species that naturally experiences only creepy-crawlies that suck. Several as bioweapons. Interestingly, some other periods when food is scarce. insect families are exclusive blood feeders tick species harbor nutritional symbionts and others live on a diet of plant sap; but from another genus, Coxiella,thatalso The team either fed trout fry as much as their survival doesn’t depend on this contain species used as bioweapons. they could eat or deprived them of food in alone. Typically, these beasts rely on Remarkably, both were tamed by ticks – a realistic simulation of the natural food microbial lodgers, known as mutualists, which is exciting news for biologists, but shortages experienced by these animals. to supply their missing dietary probably not enough to calm panicked After 2 weeks, the team collected the requirements. To test whether a similar parents after a day in the woods. mitochondria from the fish’s livers and symbiosis was at play in ticks, Duron and measured how much oxygen they his colleagues treated ticks with 10.1242/jeb.170068 consumed as they produced energy-rich antibiotics to kill off potential bacterial Duron, O., Morel, O., Noel, V., Buysse, M., ATP (known as state 3 respiration) and symbionts. The response was dramatic. Binetruy, F., Lancelot, R., Loire, E., Menard, while maintaining the electric gradient Male juvenile ticks fed with antibiotics C. Bouchez, O., Vavre, F. and Vial, L. (2018). that counteracts proton leak across the Tick-bactertia mutualism depends on B vitamin were 10 times less likely to reach synthesis pathways. Curr. Biol. 28, 1-7. mitochondrial inner membrane (state 4 adulthood than their untreated respiration). The team also measured the counterparts and the ticks that did survive Daniel E. Rozen (0000-0002-7772-0239) size of the electric gradient directly using Leiden University were smaller and deformed. For females, [email protected] the fluorescent probe safranin. it was even worse. Of 120 treated females, not a single one reached adulthood. So, Comparing the sizes of the livers, the team bacteria matter, but what do they provide found that those from the fasted fish were for their hosts? Fasting fish risk oxidative about one-third the size of those from the stress well-fed fish and had fewer mitochondria, To answer this question, the team leading to a 50–70% reduction in respiration dissected ticks and discovered that they rate. However, the story was very different were all colonized with a strain from the at the level of the individual mitochondria: bacterial genus Francisella. These fasted mitochondria increased state 3 bacteria are usually vertebrate pathogens, respiration and reduced state 4 respiration, but in ticks they showed the hallmarks of meaning they selectively increased their long-term mutualists. First, they were capacity
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