How to Find a Mate When You Smell Like Dung

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Let's Talk Science
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Some dung beetles use alternative reproductive tactics to increase their chances of finding a mate. Learn what this tells us about evolution and biodiversity.

Think of the couples in your life. Do you know how these people found each other?

Different people use different strategies when they look for love. These strategies (or tactics) depend on what the person is like. For example, think of two high school students. One is a star football player. The other is a bookworm. The football player might be able to impress potential dates by scoring the final point in the big game. Meanwhile, the bookworm might try to use his or her literary knowledge to woo fellow students in English class.  

These two strategies are very different, but they can both work!

Something very similar happens in the animal kingdom. Different types of individuals within the same species are called morphs. If humans were different morphs, football players might be one morph and bookworms would be another. Both the number of species and the number of morphs in each species contribute to the planet’s biodiversity.

There is usually one main strategy that most individuals use to impress members of the alternate sex. When there are different morphs, the morphs may court differently. Scientists call these strategies reproductive tactics.  To understand how this might work, let’s look at an example from the animal kingdom: dung beetles.

Dung beetle basics

  • There are many types of dung beetles, most of which eat dung (animal feces) or at least the liquid parts of it.
  • Dung beetles use their antennae to smell for dung piles. Once a beetle has found a pile, it will form a ball of dung that can be even bigger than it is! Then, it will stand on its front legs and push the ball around with its back legs. It’s sort of like they’re doing a handstand!
  • Many male dung beetles give females nuptial gifts, or courtship gifts. This is a little like giving your crush flowers on your first date. The nuptial gift of choice for many species of dung beetle is - you guessed it - balls of dung! These balls provide the females with nutrients, which is important for egg production.
Dung Beetle Rolls Enormous Dung Ball with Difficulty (2019) by Smithsonian Channel (1:14 min.).

The horned vs. the hornless 

Sometimes, one species has multiple body types within it. This is called polymorphism (many morphs). For example, in dung beetle species such as Onthophagus acuminatis, some males have horns, and others do not. Those with horns court females differently from those without.

Small-horned (left) and large-horned (right) morphs of the dung beetle Onthophagus nigriventris
Small-horned (left) and large-horned (right) morphs of the dung beetle Onthophagus nigriventris (Source: Alex Wild, Symposium: The Impacts of Developmental Plasticity on Evolutionary Innovation and Diversification 2012, The Society for Integrative & Comparative Biology).

 

Females in many dung beetle species create elaborate burrows in the ground. They roll dung balls into these burrows, and that’s where they lay their eggs.

In some dung beetle species, male horned beetles will wait at the entrance to a female’s tunnel. They’ll fight off other dung beetles that try to get in and mate with the female inside.The two male beetles push each other around, almost wrestling, until the smaller or less dominant beetle gives up and retreats.

Occasionally, these horned beetles walk around in the tunnels to look for intruders, then go back to their posts.

Did you know?

Dung beetles can be found in every continent around the world except Antarctica.

Hornless males have no chance of fighting off one of these big guys. But they still end up having offspring. How could this be?

Well, hornless males have ways of getting at the females. They might sneak past the guarding male through an existing tunnel to mate with the female inside. They might also dig tunnels down into the ground that intersect with the tunnels that the female has created. This is a bit like a human tunneling into a bank vault to steal all the money!

Sometimes, a hornless male tries to slip right under the guard’s nose (so to speak). If it is lucky, the guard will not catch it. If the guard does see it, then it will chase it out of the burrow. But the sneaky male may just go back to a side tunnel and wait until it thinks the coast is clear, then try again.

Did you know?

Dung beetles are the world’s strongest animals relative to their weight. They are able to pull over a thousand times their weight! 

Why do animals develop alternative reproductive tactics? 

These types of polymorphisms and alternative reproductive tactics tend to evolve when there is more than one way for a species to succeed. For example, they tend to evolve when:

  • signals that attract mates also attract predators. For example, many species of frogs will call (sing) to attract mates, but this also lets predators know where they are! That’s why some frogs will use different tactics. For example, non-calling frogs may stand near the calling frogs so they can still find females, but stay quiet to lower their chances of being eaten.
  • physical structures that cost energy to grow are helpful in attracting mates (like the horns we’ve seen in dung beetles). Since they need to find more food to help them to grow horns, they are at a disadvantage competing with hornless beetles for survival. But as you’ve seen with male dung beetles, having horns sure can help males gain more mates!  
  • attracting mates means also helping to take care of the offspring afterwards. Taking care of offspring also costs energy. This can lead to the alternative reproductive tactic: sneaking in to see the female. Her partner may fight him off, but that’s okay: the sneakier male gets the reward of having offspring, but not needing to put energy into raising them!  
There's more than one way to succeed as a dung beetle
Infographic showing the pros and cons of horns for dung beetles (© 2019 Let’s Talk Science).

 

It is fascinating to see how animals of the same species can work in different ways to achieve the same result! 

Starting Points

Connecting and Relating

  • What thoughts come to mind when you hear the term “dung beetle?”
  • What animal courtship behaviours do you know about?

Connecting and Relating

  • What thoughts come to mind when you hear the term “dung beetle?”
  • What animal courtship behaviours do you know about?

Relating Science and Technology to Society and the Environment

  • Do you think spending time and money to study the mating behaviour of dung beetles is a good use of public funds? Why/why not?

Relating Science and Technology to Society and the Environment

  • Do you think spending time and money to study the mating behaviour of dung beetles is a good use of public funds? Why/why not?

Exploring Concepts

  • Other than dung and dung beetles, what are some other nuptial gifts members of other species present prior to mating?
  • What is a morph? How might polymorphism be considered a genetic advantage when it comes to reproduction?
  • Deception is an important strategy for reproduction. What are some of the ways some animals use deception to increase their chances of mating?
  • What are some different reproductive tactics found in the animal kingdom? Why do you think these strategies evolved? (e.g. male emperor penguins incubate the eggs, pair-bonding dances in certain species of birds and insects, male against male combats prior to mating, etc.)

Exploring Concepts

  • Other than dung and dung beetles, what are some other nuptial gifts members of other species present prior to mating?
  • What is a morph? How might polymorphism be considered a genetic advantage when it comes to reproduction?
  • Deception is an important strategy for reproduction. What are some of the ways some animals use deception to increase their chances of mating?
  • What are some different reproductive tactics found in the animal kingdom? Why do you think these strategies evolved? (e.g. male emperor penguins incubate the eggs, pair-bonding dances in certain species of birds and insects, male against male combats prior to mating, etc.)

Nature of Science/Nature of Technology

  • A question often posed about scientific research is ‘’how does the knowledge gained from the research benefit people/society’’?  Is it important that people find an application for new scientific knowledge such as the different mating rituals of insects?  Or is it okay to gain knowledge simply for the sake of gaining knowledge? Explain.

Nature of Science/Nature of Technology

  • A question often posed about scientific research is ‘’how does the knowledge gained from the research benefit people/society’’?  Is it important that people find an application for new scientific knowledge such as the different mating rituals of insects?  Or is it okay to gain knowledge simply for the sake of gaining knowledge? Explain.

Media Literacy

  • Anthropomorphism is a term that describes the human action of giving human traits to other animals. This can be found in media from children’s cartoons to some documentaries. How might the media’s anthropomorphizing of animals influence how we perceive their mating rituals? Explain.

Media Literacy

  • Anthropomorphism is a term that describes the human action of giving human traits to other animals. This can be found in media from children’s cartoons to some documentaries. How might the media’s anthropomorphizing of animals influence how we perceive their mating rituals? Explain.

Teaching Suggestions

  • This article supports teaching and learning in biology related to animal reproduction, biodiversity and evolution. The concepts of alternative reproductive tactics, morphs and polymorphism are introduced. Teachers could use this article to introduce sexual reproduction tactics. The dung beetles’ polymorphisms and alternative mating tactics provide an excellent example of an evolutionary survival strategy.
  • After reading the article, teachers could use a Key Ideas Round Robin strategy to help students consolidate their understanding of the main points in the article. Download ready-to-use reproducibles using the Key Ideas Round Robin learning strategy for this article in [Google doc] and [PDF] formats.
  • To go further, teachers could have students, individually or in groups, conduct research on the morphs and alternative reproductive tactics of a selected animal species. Students could then combine their completed research to create a collaborative graphic organizer that summarizes the research.

Teaching Suggestions

  • This article supports teaching and learning in biology related to animal reproduction, biodiversity and evolution. The concepts of alternative reproductive tactics, morphs and polymorphism are introduced. Teachers could use this article to introduce sexual reproduction tactics. The dung beetles’ polymorphisms and alternative mating tactics provide an excellent example of an evolutionary survival strategy.
  • After reading the article, teachers could use a Key Ideas Round Robin strategy to help students consolidate their understanding of the main points in the article. Download ready-to-use reproducibles using the Key Ideas Round Robin learning strategy for this article in [Google doc] and [PDF] formats.
  • To go further, teachers could have students, individually or in groups, conduct research on the morphs and alternative reproductive tactics of a selected animal species. Students could then combine their completed research to create a collaborative graphic organizer that summarizes the research.

Learn more

Dung Beetles

Information on dung beetles from the San Diego Zoo, including habitat and diet, family habits, and where you can find them.

Polymorphism

Article from Encyclopedia Britannica explains how polymorphism differs from continuous variation and links to related concepts

Kung Fu Dung Beetles - Operation Dung Beetle

A video (2:23 min.) from BBC Earth with more information on dung beetles.

References

Emlen, D. (1997). Alternative reproductive tactics and male-dimorphism in the horned beetle onthophagus acuminatus (coleoptera: Sarabaeidae). Behavioral Ecology And Sociobiology, 41(5), 335-341. doi: 10.1007/s002650050393

Taborsky, M., Oliveira, R. F., & Brockmann, H. J. (2008). The evolution of alternative reproductive tactics: concepts and questions. In Oliveira, R. F., Taborsky, M., & Brockmann, H. J. (Eds.), Alternative Reproductive Tactics: An Integrative Approach, 1-21. Cambridge University Press.