How to Find a Mate When You Smell Like Dung

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.

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.

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!  

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