Dung Beetles Written Report

Dung Beetle Written Report

Biology 1010

MacKenzie Waldon, Natalia Wingo, Morgan Oliphant, and Samuel Nay

African Dung Beetles are some of the most interesting insects in the animal kingdom. Their peculiar nature of traveling has made them an intriguing subject of study to scientists. They are the first demonstration of insects to orientate with the starry sky and the first documented species in the animal kingdom to orient using the Milky Way. In the scientific paper, “Dung Beetles Use the Milky Way for Orientation” by Marie Dacke, Emily Baird, Marcus Byrne, Clarke H. Scholtz, and Eric J. Warrant, they explain how dung beetles obtain food and energy, reproduce, and navigate efficiently using the starry lit sky and/or the Milky Way.

The African Dung beetle fits into the following classification:

Domain: Eukaryote

Kingdom: Animalia

Phylum: Arthropda

Class: Insecta

Order: Coleoptera

Family: Scarabaeidae

Genus: Scarabaeus

Species: Scarabaeus satyrus

The Dung Beetle obtains energy in a rather odd yet intriguing manner in the eyes of scientists. To survive, dung beetles feed on the feces of other animals. They form the excrement into a ball shape in order to roll it home efficiently. Dung beetles are capable of eating more than their own weight in 24 hours, obtaining enough energy to perform this task for the day. This act takes up an immense amount of energy so some dung beetles have adapted to waiting for other beetles to form the dung balls and then stealing it for themselves. This competitive manner adaptation does not benefit the species as a whole but rather to the individual beetle that is saving as much energy as it can.

Dung beetles reproduce sexually. Typically, when male beetles are rolling the dung ball back to its nest female beetles will ride on top of the ball for the journey back home. Once they arrive at their destination they bury the dung underneath some soft soil while the female beetle lays her fertilized eggs within the ball. Once the eggs are hatched, the larva relies on the warm environment and nutrients that the dung provides in order to develop into adult beetles. Once they are adults they emerge from their dung piles and build their own nests to continue the cycle of reproduction. Adaptations that would be necessary for this would include the ability to dig and get the ball below the surface of the ground. Another adaption would be the ability for the eggs to grow with only what the dung produces in order survive in the burrow.

The authors undertook this work because they noticed that the dung beetles were able to transport their dung balls in a fairly straight path on typical clear-sky nights. Their initial assumption was they orient themselves using the moon. Then they observed that the dung beetles were still able to travel in a linear path even on moonless nights. However, when the sky was overcast the beetle’s ability to transport their dung balls in a straight path had dramatically altered in a negative way. This is what enabled scientists to start questioning and looking for answers. This type of behavior in insects had not been observed before, thus making it a study that scientists had to undertake.

In the scientific paper, the authors are trying to explain why the dung beetles are able to navigate without the moon but are not able to without the stars. The authors wondered what all the factors were that contributed to the dung beetle’s efficient travels of straight pathways. They ultimately hypothesized that the “dung beetles exploit the starry sky for orientation.” This was something that intrigued the scientific community because it was something that, to our present knowledge, had never been done by an insect until this point.

Scientists conducted two different experiments with dung beetles to test this hypothesis. They began the first experiment by placing the beetles in an arena and timed how long it took the beetles to roll their dung balls to the edge of the arena. This Arena was designed to obscure the surrounding environment from the beetles. They tested all the effects that celestial and terrestrial cues could have on the dung beetle’s navigation. There were different stages where the beetles were exposed to each cue at a time and filmed above to see the differences; if any at all. Dung Beetles have two sets of eyes; the supernal eyes which lay on top of their head and the duodenal eyes that are on the bottom of their head. So, in order for scientists to observe the influence a starry night sky has on dung beetles they constructed tiny cardboard hats to cover the vision of their supernal eyes. However, the duodenal eyes of the beetle would be left uncovered, allowing them to still see the ground and area around them.

In the second experiment the beetles were moved from the arena to the Johannesburg planetarium where a starry night sky could be projected along with the Milky Way onto the ceiling. The scientists observed the effects of projecting different amounts of stars with and without the Milk Way and the Milky Way all by itself. The experiment was conducted with five specific conditions: (1) starry night sky and Milky Way (2) just Milky Way (3) dim stars (4) bright stars (5) complete darkness. These experimental methods helped the authors to answer their initial question.

In the first experiment, the authors concluded that relying on only terrestrial cues took the dung beetles a much longer time to reach the edge of the arena than when celestial cues were exposed. When the beetle’s supernal eyes were obscured by the cardboard cap, they were severely disabled in orienting themselves. The researchers also found that the beetles took about the same amount of time on nights when the moon was out, as on nights that it was absent from the sky.

In the second experiment it was found that the beetles took the same amount of time to reach the edge of the arena, whether they could see the full starry sky, or just the dim glow of the Milky Way. However when the Milky Way was removed, they found that it took the beetles slightly longer to reach the edge. As long as the beetle’s supernal vision can see the glow of stars, preferably from the Milky Way, they will be able to use the night sky to efficiently orient themselves.

From the results of these experiments, the researchers were able to conclude that dung beetles rely on their celestial cues like stars and the Milky Way in order to orientate themselves (rather than the moon or any terrestrial cues.) It was also concluded that even though dung beetles can orient themselves with any of the stars, they exclusively exploit the Milky Way’s general shape and glow in order to navigate with the most efficiency. Before this experiment, this type of behavior was only observed in birds, seals, and humans. Even though bidirectional celestial cues for orientation have been proposed in the past it had never been proven at this point. Thus making the African dung beetle the only known insect in the animal kingdom to use the Milky Way for direction.

The scientific paper was very interesting because it demonstrates the amazing abilities that even small organisms are able to do. The paper exercises the scientific method in very specific and practical ways while explaining it simply for all readers to understand. It sheds a whole new light on the capability of not only what the African dung beetle can do but what the entire class of insects could do as well. It has opened up the discussion of what adaptations are possible and what hypothesis’ can be experimented next in order to continue this research.

#Biology #Fall2016