Testing the pheromone hypothesis

Oliver Trottier (Leigh Marine Laboratory) set out to test whether pea crabs use pheromones at mating time. In this video, Oliver talks us through his experimental set-up. He demonstrates how male and female pea crabs (each in their host mussels) were placed close to each other in flowing seawater and shows how he used a trap to test whether male crabs were leaving their hosts in response to a signal from female crabs.

Teaching point:
Try showing this clip without sound. You could ask students to write about, draw a sketch of or explain Oliver’s experimental design. What are the strengths of Oliver’s experimental set-up?

Point of interest:
Leigh Marine Laboratory is situated right beside the sea, within the Cape Rodney-Ōkakari (Goat Island) Marine Reserve. This site means that the laboratory has access to piped seawater from the ocean. It is this seawater that is flowing through the pheromone tubes in Oliver’s experiment.

Transcript

Oliver Trottier (Leigh Marine Laboratory)
So I’ve got a series of tubes here which I called pheromone tubes. What happens is this water floats from the upper tank down through these clear tubes you see here, into the pheromone tubes and then out the other side like this into the tank. What I did was I put different females in their host mussels in the upstream section of the tubes at different egg stages – so early stage, late stage, about to give birth, about to burst – as well as females that didn’t have eggs. So I put them in the upper section of the tubes, and then in the lower section, I placed a male.

What happens if you look at this tube is the water flows through this side, flows past the female in her host like this, picks up all the scents and smells that she’s giving off, flows through the tube into this section where there’s a male inside his host and then out the end. And what happens is if the female in the upstream section is producing the pheromone and the male picks up on it, he’ll climb out of his host, trundle along the pheromone trap and he’ll actually fall into the bottom section of the trap.

And of course, I had a control tube which had no female but a mussel host in this end and the male here, and of course over the 9 months I was doing this, that male actually never came out whereas in all the other tubes that had females at different stages, they were coming out.

I’ll just give you a little look of what would happen if you got a positive result. So you come out in the morning, and if the female had been releasing a pheromone, hopefully the male would be trapped, and that’s what you’d find.

Acknowledgements:
Oliver Trottier – Leigh Marine Laboratory, Auckland University.