The human eye can see and sense light, which is made of electric and magnetic fields. However, humans can’t sense electric fields alone – whereas sharks, electric eels, dolphins, platypus, echidna, cockroaches, and mosquitos can. They use this ability to find prey, evade predators, communicate with each other, and to navigate.To this list we can now add a small insect called the fruit fly (Drosophila melanogaster) – at least in one form. On April 1, researchers at the University of California, Santa Barbara, the Barcelona Institute for Science and Technology, and the Universitat Pompeu Fabra (the latter two in Barcelona, Spain) reported in Current Biology evidence of fruit fly larvae being able to sense electric fields.Fruit flies are much easier to study than sharks, eels or echidna – and this is why the researchers were also able to pinpoint the sensory neurons that mediated the larva’s ability to sense electric fields.These findings have raised the prospects of researchers soon identifying the very molecules that underlie electrosensation in fruit flies.The larva that turnedThe research article included a short video of a fruit fly larva crawling about on the surface of a slab of agarose gel. The short ends of the slab were partly immersed in reservoirs of a phosphate buffer. Wires connected one reservoir to the anode (positive element) of a battery, and the other reservoir to the cathode (negative element). The battery produced an electric field of about 3.6 V/cm along the length of the slab. The experimenter could interchange the anode and cathode at will.Whenever the field switched direction, the larva almost instantaneously switched the direction in which it was crawling — always towards wherever the cathode was. It was convincing evidence that the larvae could sense the electric field and respond quickly.Movement in response to an electric field is called electrotaxis.The game changerThe fruit fly is a favourite organism of geneticists, and over the years researchers have accumulated large collections of different resources to work with this lifeform. Among them are tens of thousands of fly strains called driver lines. Each driver line is a fruit fly whose genome has been modified to express a protein called GAL4 in particular cells.The GAL4 protein causes a target gene bearing a sequence called UAS to be expressed. The latter is simply called the responder.For example, say the GAL4 protein targets the gene corresponding to the UAS-GFP protein. This protein emits a green glow when hit with ultraviolet light, so researchers can easily check where the gene is active in a fruit fly’s body under a microscope.In their study, the scientists used specific driver lines and responders to find the neurons in fruit fly larvae that respond to electric fields. First, they used a driver line called NP2729-Gal4 to turn on a gene that blocks neurons from talking to each other. The larvae in this group had trouble with electrotaxis.Then the researchers tested other driver lines that controlled smaller sets of these neurons. When they used two called Gr66a and Gr33a to activate the same gene, the larvae completely lost their ability to respond to electric fields. The different neurons affected in the three driver lines pointed the researchers to six neurons on each side of the larva’s body involved in sensing bitter taste.Finally, the team examined just these six neurons in the Gr66a driver line while watching them under a microscope. Only one neuron reacted to a rotating electric field. In sum, just two specific neurons – one on each side of the larva’s body – were responsible for sensing electric fields.Future prospectsIn future research, the researchers have said they may be able to identify the exact genes involved in these neurons using a technology called scRNA-Seq. scRNA-Seq is short for “single-cell RNA sequencing”. Here, scientists first break apart the brain and nerve tissue of fruit fly larvae into individual cells. These cells are then placed inside tiny droplets using a special device. Inside each droplet, the RNA – the molecule that helps turn genes into proteins – from one cell is turned into DNA. Each droplet also adds a unique barcode, a short DNA tag, that marks all the DNA from that one cell.After this step, the DNA from all the cells is mixed and read (or sequenced) together. The barcodes let scientists know which cell each piece of DNA came from. If a cell is using the Gr66a-Gal4 driver line, for example, then both the GAL4 RNA and the RNA from other important genes in that cell will have the same barcode. This helps scientists figure out which receptor genes are active in specific neurons, like those that sense electricity.Sharks and electric eels are charismatic animals and many of them are endangered. The first step in the conservation of such species is to understand them inside-out, including where they are and aren’t, what resources they need during different parts of their life cycle, and how they feed and protect themselves and their offspring. Understanding how an endangered species may be using electric fields as part of these tasks will be helpful.Fruit flies are nowhere as charismatic as many of these species. However, they hold a special place among geneticists: they have only four pairs of chromosomes yet their genes and human genes function in similar ways; their short lifespan allows scientists to study multiple generations in a short period; and they’re low-maintenance in the lab.Fruit-fly researchers thus went from “0-to-60” with just this one study. Conceivably, these diminutive insects studies may reveal the science behind yet more abilities in other animals in future.D.P. Kasbekar is a retired scientist.