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

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

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.

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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

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 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!
  2. 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!

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

Author: Brittany Smale
Originally Published: 20 October 2017

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