Animals have many ways of sensing their chemical environments that vary across species. While mammals rely on their tongues for tasting, aquatic creatures like fish use their skin to taste. Conversely, insects have taste buds outside their bodies, not just in their mouths.
Researchers have shown that fruit flies, scientifically known as Drosophila melanogaster, have developed unique ways to find food and avoid danger using their senses of smell and taste in habitats ranging from forests to deserts. By studying how their senses have changed over time, scientists hope to learn how fruit flies adapted to their surroundings.
To investigate the sensory capabilities of fruit flies, scientists from the University of Lussane in Switzerland compared how different fruit flies smell and taste. They collected 5 distinct body parts essential for the flies’ senses. These included 1) the heads of their babies, or larvae, 2) the part where their females lay eggs, 3) their front legs, 4) their antennae, and 5) their mouthparts with structures like tiny fingers called palps. They collected these body parts from 6 different kinds of fruit flies that are related to each other but live in different places and eat different things.
The researchers separated the male and female fruit flies, which included 3 repeats per sex and species. They knocked out the adult flies with CO2 gas so they could collect samples and perform experiments without harming them. They separated the larvae from their food source and removed their heads. They did this 3 times for each adult body part, 3 times for each larvae, and 3 times for each egg-laying part.
The researchers examined the genes in the fruit flies’ body parts using RNA sequencing techniques. RNA sequencing is like decoding an encrypted message to understand what’s happening inside a cell at the molecular level. First, scientists isolated the RNA, which is like the parchment carrying the encrypted message. Then, they converted it into a more readable synthetic form, called copy DNA or cDNA, like translating the secret code into a legible alphabet. Next, they broke the cDNA into smaller sections of nucleotides, represented by the letters A, C, G, or T, and read the order of nucleotides in each section.
The scientists analyzed these nucleotides, like the letters in an alphabet, to figure out which genes, similar to words, were “on” or “off” in the fruit flies’ body parts. They used this method to examine how many genes were active or inactive in the flies’ cells, helping them understand how fruit flies adapt and respond to their environment. Finally, they stored the flies’ RNA data in a genomics database called ArrayExpress for future scientists to study and learn from.
The researchers found that the body parts responsible for smelling and tasting things in fruit flies differed in terms of how certain genes were switched on or off. They found some genes in the fruit flies’ sensory organs remained the same. Still, thousands of genes in each fly’s body part changed depending on stimuli, like temperature, humidity, pollutants, and interactions with other organisms. They found that when a gene’s activity changed in one part of a fruit fly’s body, it often changed in other parts too, but not always in the same way.
The researchers also used their data to compare how specific genes control the fruit flies’ senses in different parts of their bodies. For example, they found that male fruit flies had more active sensory genes in their front legs than female fruit flies. They proposed these differences could affect how fruit flies choose their mates.
The researchers concluded the way genes are switched on or off in fruit flies’ sensory organs is complex and can vary between different species and between males and females. They acknowledged they could not determine how the genetic differences in smell and taste help the fruit flies adapt to changes in their diets or habitats. They proposed that future researchers continue analyzing their data and collect similar data from a larger sample size of fruit fly species to find the reasons behind the different smelling patterns and how they help flies adapt.
