Hirtodrosophila mycetophaga facts for kids

The Hirtodrosophila mycetophaga is a type of fruit fly. It's quite large for a fly, usually about 4.0 to 4.5 millimeters long. So far, these flies have only been found in Australia. They are special because they mate on bracket fungi, which are mushroom-like growths found on trees. They prefer fungi with lighter colors to make their mating dances easier to see!

In a lab, these flies live for about 17 days. They are one of only three Australian fly species known to use a special mating system called lekking. This means males gather in one spot to show off to females.

What it Looks Like and Where it Lives

Male H. mycetophaga flies are about 4.0 millimeters long from head to wing tip, and females are a bit longer at 4.5 millimeters. We don't know how long they live in the wild, but in a lab, they live for about 17 days.

These flies mostly live in Australian rainforests. You can find them from eastern Victoria up to south-central Queensland. They were first discovered near the Ourimbah Creek in New South Wales way back in 1924.

Home and Habitat

Hirtodrosophila mycetophaga flies love places that are naturally wet and humid. This is because they can dry out very easily. Young flies especially need fresh food within a day of hatching, or they will quickly dehydrate.

A bracket fungus like the ones these flies use for mating.

These flies do their courtship and mating on the flat underside of a specific type of bracket fungus called Ganoderma applanatum. These fungi often grow on the sides of fallen trees and are common in wet forests. This means the flies usually have many places to spread out. On a single bracket fungus, the flies are spread out pretty evenly.

Some of these fungi get a white layer on their underside with small holes. The color of the fungus can change as it grows. However, H. mycetophaga flies only use fungi that are white or grey. This helps the flies stand out against the background, making their mating displays easier to see. Flies also tend to pick fungi that are ripe and releasing spores. They also need some light, so you might find them in spots where sunlight can get through the thick forest trees.

Scientists think that adult flies prefer to live on fresh mushrooms, while their young (larvae) like to live in decaying fungi. The flies also use the bracket fungus to hide. When you look at a group of flies from the side, they are harder to spot. This helps them stay safe from predators like spiders and lizards.

Fly Gathering Spots

When a male H. mycetophaga fly arrives at a lek (a special gathering spot), he usually stays in the same place all day. Males show off by bobbing and holding their wings apart. They tend to claim a small area on the fungus, but these areas can shift as males move around and defend their "moving territories." Researchers found that most flies (nine out of ten) came back to the same fungus, or one nearby, the next day.

During courtship, female flies move less on the fungus. Males, however, move around a lot, usually sideways. But females do spread their wings to respond to the males' courtship moves.

Finding Mates in Leks

When females visit a lek, they usually appear at the edges and don't stay as long as the males. There are also fewer females than males. Some males get better access to females than others. Certain males tend to be at the edges where females first arrive, while others are stuck in less good spots toward the center of the lek. The male closest to a new female will approach her and do a special "wing-scissoring" dance.

Females tend to gather where there are more males. The chance of a fungus being used by flies increases with its size; bigger bracket fungi have more flies. However, scientists found that females don't choose bigger fungi just because they are big. They choose them because more males are present there.

Male Defense of Space

Scientists also believe that males don't gather in certain spots just because there are good breeding sites or resources for females there. They saw groups of flies in areas without special resources, and fungi with lots of resources weren't used more often. Males even spread themselves out more evenly than you'd expect if they were just randomly placed. This suggests that males try to keep a distance from each other. This pattern, along with how females spread out, supports the idea that they use a lek mating system. We don't know if other things in the environment affect which specific spots H. mycetophaga uses.

What They Eat

Many, but not all, H. mycetophaga flies eat fungi. Scientists have found bits of wood and fungal mycelia (the root-like parts of fungi) in their stomachs. Young flies (larvae) have been successfully raised in a mix of bran and agar (a jelly-like substance) that had molds growing on it. Most of the fungal material these flies eat grows on wood.

Courtship Dances

Males also show off with other courtship moves like wing vibration and scissoring. When a male vibrates, he holds his wings about 45 degrees apart. When he scissors, he holds his wings 90 degrees apart, making a straight line across his body. Scissoring usually lasts longer than vibrating.

Mating Sounds

Sounds happen during vibration and scissoring, but not when the male just extends his wings. The vibration sound of H. mycetophaga is like a series of pulses. The time between each pulse is about 46 milliseconds. The scissoring sound is a smooth, wave-like sound. A male's aristae (a large bristle on its antennae) are better at picking up the sounds from the pulse song than the wave-like song. The usual sound frequency for this call is 180 Hz.

Lek Behavior

For males, the chance of mating successfully goes up as the size of the lek (the gathering spot) increases. This means more males in one spot lead to more mating success.

Leks might have developed away from food sources because mating displays would be hard to see in the dark forest. The fact that flies tend to gather only on lighter-colored fungi, which makes their displays more visible, supports this idea. Visual showing-off seems very important in leks, but chemical signals called pheromones might also play a role.

H. mycetophaga is one of the few Hirtodrosophila species that uses lek mating. There's a related lekking species in Hawaii that belongs to a different group of Drosophila flies. It's possible that lekking developed separately in these related species, which is called convergent evolution. However, the Hawaiian Drosophila flies use the smooth surface of a fern leaf for their leks, not the underside of a bracket fungus.

Why Males Gather

One idea, called the "hotspot model," suggests that males gather in areas where many females are present. However, this model might not fully explain what happens with H. mycetophaga. Scientists have seen that the presence of certain fluids (exudates) that would attract females doesn't affect where the males display. So, this model can't fully explain why these flies gather for mating. It's possible that where certain food or resources are located might influence where the first groups form.

Challenges of Grouping

Even though larger groups of males are generally more successful, there can be downsides to joining. As a group gets bigger, males might fight more with each other. Males who aren't as strong in the group might suffer more from these fights, which could outweigh the benefits of being in the lek. These males might even be forced away from the display spots. Even if these males aren't much smaller than others, other things like their age or past fights might make them less able to defend their spot. Evidence of fights within the lek suggests that a "competition model" might better explain their behavior. Less competitive males are found on smaller leks. The strongest males are found in the best spots on the lek. Females are attracted to these males because they can pass on good genes to their babies.

Social Life

H. mycetophaga are generally not considered social insects, except for their lekking behavior where they group together. Even so, groups of two or more adults have been seen in different places. However, other adult flies of the same species have been seen avoiding joining these groups. Flies purposely keep themselves and their young spaced out from other flies. Only about 6% of males were seen outside leks, which shows a clear benefit to grouping. Males in groups have a better chance of finding females ready to mate than isolated males do. As many as 70 male H. mycetophaga flies have been seen on a single bracket fungus at one time!

Protecting Them

While not just about H. mycetophaga, these flies are part of general reports that Drosophila can be used as a "biological indicator." This means they can help us understand how healthy an ecosystem or environment is, especially with climate change happening. Studies show that rare rainforest species, like H. mycetophaga, might disappear and then reappear during times of environmental stress. This information can help us see the overall impact on biodiversity (the variety of life). Drosophila flies in rainforests are especially important because they often interact closely with the flora (plants) of the rainforests. Scientists looked closely at H. mycetophaga collections in Palmerston National Park, north Queensland. These flies were found 500 meters inside the forest.