Animal Weapons

What’s the deal with fiddler crabs?


Image: CC via Wikimedia Commons

We have a new case study lesson that was published last week over at the National Center for Case Study Teaching in Science. The center is run through the University of Buffalo and is supported by the National Science Foundation. This collection is very beneficial to any science teacher, and I encourage you to look through the topics for use in your classroom.

Our case (which you can find here) deals with animal weapons, specifically extreme weapons. Our minds typically go to moose or elk antlers, but there are lots of examples from the animal world. The case looks at this from a bioenergetic perspective. For example, male moose have large antlers even though allocating resources towards growing those antlers deplete their bones in other areas by 60%. That’s incredible! It seems like their has to be a better answer than just for fighting. This case looks at fiddler crabs. Why do males have one large claw that sometimes is as big as their whole body? This large claw would seem to come with some disadvantages.

Screenshot 2016-03-10 09.06.20

This case is designed to be used in a flipped classroom. However, there are many different ways you can use it. Take it, and make it your own. Here’s the abstract:

In most animals, the drive to breed and produce offspring is strong. However, most males live their whole lives without having the chance to breed. The events leading up to mating can be very dangerous and also very costly to an individual. Some males have evolved elaborate structures, or weapons, as a result. The structures do help males in both combative situations and with attracting females, but ironically, the structures themselves come with certain costs. This flipped case study provides students with the opportunity to not only see how animal structures and functions are linked, but also to see how certain animal structures are needed and costly. There are videos that students are expected to view before the case. The case was initially designed for a second semester college general biology class for majors. However, it can also be used in non-major biology classes. Students should have some background knowledge of natural selection, specifically sexual selection as well as energetic demands of certain structures.