Scientists tested spiders as living DNA traps; their stomach contents can reveal which insects and other animals are living around them |
A study published in ‘Experimental and Applied Entomology’ has explored how spiders could tell what animals are living around them by examining traces of prey DNA left inside their bodies. The research tested how ‘reliable prey DNA’ could be found in wolf spiders after feeding and how long that genetic evidence remained detectable. The experiments showed that DNA from some prey could still be detected several days after a meal, although the chances fell as digestion progressed. The findings suggest that spiders could become useful biological samplers for studying food webs and the small creatures living in an area. At the same time, the research shows why timing and laboratory methods matter when scientists use a spider’s stomach contents as a window into their surroundings and nearby ecosystems too.
Scientists can now identify a spider’s prey by analysing DNA from its body
Spiders are predators, so every meal can leave behind a small genetic record of what they have eaten. Instead of trying to observe every tiny insect in a habitat, scientists can examine the DNA remaining in a spider after it has consumed prey. The idea is particularly useful because spiders do not leave behind neat, recognisable pieces of food. As the study explains, spiders digest their prey externally and consume it in liquid form, which makes traditional analysis of what they have eaten difficult. DNA-based methods provide another way to identify those meals. The research by Jeffery Marker and colleagues at Karlstad University focused on wolf spiders belonging to the family Lycosidae. These spiders are generalist predators, meaning they can feed on a variety of prey. That makes them potentially useful for studying relationships between predators and the wider animal community.
Female wolf spider of the species Hogna lenta. Image Credit: Patrick Edwin Moran/Wikipedia
How the scientists prepared spiders before testing for DNA
The scientists wanted to answer a fairly practical question of ‘how long does prey DNA remain detectable inside a spider.’ To find out, they collected Pardosa spiders from forested areas in southern Sweden. The spiders were kept individually in lab containers and were given controlled meals. Three types of prey were used which included the fruit fly ‘Drosophila hydei,’ the cricket ‘Gryllus bimaculatus’ and the springtail ‘Coecobrya tenebricosa.’ Before feeding, the spiders were starved for at least 8 days, with the average starvation period being about 17 days. After the spiders had eaten, researchers examined different groups at intervals ranging from immediately after feeding to eight days later. In total, 203 spiders were included in the final analysis. This gave the researchers a controlled way to watch the genetic evidence of a meal gradually disappear.
Method used by scientists to find the prey DNA
The team used a technique called ‘DNA metabarcoding.’ Put simply, it allows researchers to look for short pieces of genetic material and use them to work out which species they came from. The researchers tested two combinations of laboratory primers, which act like molecular starting points for copying a particular section of DNA. Both were designed to target a part of the ‘mitochondrial COI gene,’ a commonly used genetic region for identifying animals. One combination performed better than the other. The researchers therefore used the more successful pair for their DNA metabarcoding work. The difference mattered because prey DNA becomes increasingly broken down as digestion continues. A method that can detect shorter pieces of DNA can therefore be especially useful when the genetic material has already begun to degrade.
How long could the spiders reveal what they had eaten
The results showed that time was the most important factor affecting whether prey DNA could still be detected. Using the more successful primer combination, Drosophila DNA could be detected for up to 120 hours, or five days, after feeding. Gryllus DNA could be detected for up to 96 hours, or four days. However, the likelihood of finding the DNA decreased as more time passed after the meal. The researchers calculated DNA detection half-lives of about 41.6 hours for Drosophila and 15.2 hours for Gryllus. In other words, the genetic evidence did not simply disappear at once. Instead, the likelihood of detecting it gradually declined. The third prey, Coecobrya, produced much weaker results. Its DNA was detected in fewer than 9% of the spiders, meaning there was not enough consistent evidence to calculate a reliable detection half-life.
Mapping the animals in the spider’s ecosystem
The research does not show that spiders can immediately be used as complete surveys of every animal in an ecosystem. Instead, the study demonstrates that prey DNA can survive inside wolf spiders long enough to be detected using molecular techniques. That creates an opportunity for scientists to use predators as indirect sources of information about prey communities. A spider collected from a particular environment may carry genetic evidence of recent meals. By examining that evidence, researchers could potentially learn more about predator-prey relationships without having to find and identify every small animal directly. However, the study also highlights an important limitation. A negative DNA result does not necessarily mean that a particular prey species was absent. The genetic evidence may simply have degraded beyond detection, or the chosen laboratory method may not have worked equally well for that prey.
Wolf spider on a web. Image Credit: Charles J. Sharp/Wikipedia
Importance of timing of a spider’s meal
The study makes clear that a spider’s stomach is not a permanent record. It is more like a short-lived biological diary. The longer the time between feeding and collection, the greater the chance that the prey’s DNA will become difficult to detect. The choice of laboratory primers also matters. The researchers argue that future studies should take factors such as previous gut contents, starvation periods and possible differences in metabolism into account. The work by Marker and colleagues ultimately shows why a spider can be more than just a predator in an ecosystem study. Its latest meal can carry a small genetic record of the life around it. With careful sampling and the right DNA methods, those tiny traces could give scientists another way to understand the hidden communities of insects and other animals that are otherwise difficult to observe.
Source link
