Have you ever bitten into a slice of bread, only to find out that it’s gone mouldy? Yuck! But what causes mould, and how does it spread? This was a mystery solved by scientists in the 1800s.
Mould in bread is caused by a fungus (fungi for multiple). Fungi are made of many tiny branches that grow into a huge maze. These branches reach out to find food from the environment around them; the branches spread from a central point to search for food at the edges. As resources run low, the middle of the fungus dies, creating an expanding ring of live branches. There are many types of fungi out there, and mould is one type that we try to avoid when we store our fruit, vegetables, and bread. When scientists discovered fungi, they solved one mystery, but there are new questions to be answered.
One mystery involves a type of insect that loves to eat fungi: beetles! Specifically, beetles in the group called Brontini. These little guys eat fungi when they are larvae (baby beetles before they’ve become adults). Usually, the these larvae eat fungi under the bark of trees, but recently a special Brontini beetle was found. This beetle, called Protodendrophagus antipodes by scientists, lives up in the mountains of New Zealand, above the treeline in the alpine zone. Protodendrophagus antipodes is a long name, so we’ll call them Anti.
Anti are special for more than one reason. First, they live way up in the cold alpine area, which is a harsh environment to live in. The freezing temperatures and dry environment even stop trees from growing there! Second, every other species of Brontini beetle feeds on fungi under tree bark. Confusingly, the area where Anti lives doesn’t have these fungi. Since it’s too high up the mountain for trees to grow, there’s no fungi under tree bark for the beetles to munch on. And so, one group of enthusiastic scientists decided to figure out what these little guys eat. Let’s meet our investigators!
Our team is made up of three skilled diet detectives: John Marris (“The Mastermind”) – the strategic leader who knows the ins and outs of beetles; David Hawke (“The Brains”) – a science whiz with a flair for chemistry; and David Glenny (“The Sidekick”) – your friendly neighbourhood plant expert. Together, the team solved the mini mystery in the mountains: where is the food for Anti?
In 2018, the team went into the Southern Alps on an exciting trip to examine the scene and gather more evidence. They found two very important clues. First, there were lots of lichens in the areas where the beetles live. Second, sometimes the beetles lived where there wasn’t anything else to eat. I bet you can guess what our prime menu suspect is!
You’ve probably seen lichens around, though you may not have known what they were. Lichens grow on trees and rocks, but they’re not just one species; lichens are an example of a “symbiotic relationship”. This is when two organisms work together to boost each other’s chance of survival. In this case, the organisms work so closely together that the lichen itself is actually made up of both species! The body of the lichen is a strong skeleton built from fungus. Inside that skeleton live algae, plant-like organisms that can use the sun to make food. In this way, the fungus keeps the algae safe, and the algae feed the fungus. Win win! Cha-ching!
Since lichens are made up of fungi, this seemed like a pretty good place for our detectives to start. Every good private eye needs evidence to make their case. Thankfully, our clever detectives saw a way to test their theory: the stomach contents of the beetles! They collected some Anti as “evidence” and looked at the food in their stomachs. Inside they found spores that came from a lichen fungus.
“What is a spore?” you may ask. Remember that maze of branches that make up a fungus? Well, sometimes the branches can’t find enough food for the fungus to eat. If that happens, the fungus has a new strategy to survive: spores! These are little circular pieces of fungus that can spread to new areas and find the fungus a better home.
But their work wasn’t done yet: the detectives found more than just lichen spores in their beetle stomachs. They also found a whole bunch of mystery food which they couldn’t identify. The scientists needed to confirm that lichens really are the only food eaten by Anti. So, the scientists put their thinking hats on and decided to find a new way to solve this puzzle. They chose to use an approach called the “stable isotope test”.
An isotope is a special form of elements, such as nitrogen and carbon, and organisms at the bottom of the food chain absorb them from the environment. If an animal eats something, then the isotopes of the animal should be pretty similar to its food.To solve this mystery, the scientists tested the isotopes of Anti and all of the potential foods in the area. A good detective looks at all the possible solutions, so they tested the soil, the mosses, the lichens, the tiny mountain plants, and even a type of spider.
At last, the detective work was done. Their test showed just what we’re all thinking: the Anti beetle really does eat lichen. The link was so clear that David Hawke called it a “textbook example” of the test in action. The scientists were very excited because lichen-eating is pretty rare for beetles.
After all their investigation, the detectives could finally declare: “case closed!” Now we have a new mystery: how do these beetles survive in the extreme cold of the alpine zone?
This article was prepared by Master of Science student Heidi Allan as part of the ECOL608 Research Methods in Ecology course.
