Think of the couples you know, do you know how they found each other? Was it the same way every time?

Cirellium Bachuss, a species of dung beetle, rolls a dung pile. Image © Kay-africa, Wikimedia Commons.

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 their 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 different morphs. If humans were different morphs, football players might be one morph and bookworms would be another.

Some morphs court differently than others. There is usually one main strategy that most individuals use. Scientists call all other strategies alternative 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 (or at least the liquid parts of it).

Dung beetles use their antennae to smell for dung piles. Once they find a pile, they’ll form a ball of dung that can be even bigger than they are! Then, they’ll stand on their front legs and push the ball around with their back legs. It’s sort of like they’re doing a handstand!

Many male dung beetles give females nuptial gifts, or courtship gifts (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.

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. Male dung beetles with horns court females differently than male dung beetles without horns.

Believe it or not, the two ants in this picture are from the same species! The one on the left is a minor worker and the one on the right is a major worker. They are both fully grown (the minor worker will not grow into a major worker later on in its life). This is an example of polymorphism. Image © Bob Peterson, Wikimedia Commons

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.

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, hornless males can slip right under the guard’s nose (so to speak), but the guard may catch them. If this happens, the guard chases them out of the burrows. But they’ll just go back to their side tunnel and wait until they think the coast is clear, then try again.

Did you know? Some dung beetles use the stars to find their way home, similar to how humans used celestial navigation hundreds of years ago!

Why do animals develop alternative reproductive tactics?

These types of polymorphisms and alternative reproductive tactics only evolve in very specific situations:

  1. When signals that attract mates also attract predators. For example, many species of frogs will “sing” to attract mates, but this also lets predators know where they are! That’s why some frogs will choose different tactics: they’ll stand near the singing frogs so they can still find females, but stay quiet to lower their chances of being eaten.
  2. When physical structures that cost energy to grow are helpful in attracting mates (like the horns we’ve seen in dung beetles!) It costs energy to grow physical structures like horns, and the males don’t need these structures to survive. But as you’ve seen with male dung beetles, having horns sure can help males gain more mates!
  3. When attracting mates means also helping to take care of the offspring afterwards. Taking care of offspring also costs energy. When a male may have to care for his offspring, he may take on an alternative reproductive tactic: he may sneak in to see the female. Her partner may fight him off, but that’s okay: the sneaker 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!

Can you think of any other animals that use alternative reproductive tactics? Why do you think they evolved these strategies?

Did You Know? Chameleons change their colour during mating season. Different coloured chameleons have different reproductive strategies when it comes to courting females.

Learn More!

Visit CurioCity today to read more interesting articles on various Science, Technology, Engineering, and Math (STEM) topics! There are also many great educator resources for those looking to share this information with their students.

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