Assignment 2: Paper Review

Electroreception and electroreception in platypus

Henning Scheich, Gerald Langner, Chris Tidemann, Roger B. Coles, and Anna Guppy

(Click paper title for link)

Summary 

In 1986, Scheich et al. were the first to discover that the bill of the platypus contained electroreceptors. (Previously it was thought that the bill only contained mechanoreceptors.) They were able to prove this through 5 behavioural and electrophysiological experiments on 4 platypuses, 1 male and 3 female, in a 40 cm deep tank with a 3m diameter.

As preliminary work to the experiments, it was determined that there are 2 phases in the foraging behaviour of platypuses. The first is a general "patrol" phase, where the platypus is trying to detect food, and the second is a more specific "search" phase when the platypus has detected the prey items. Scheich et al. (1986) determined that live prey and electric dipoles evoked a search response, whereas NaCl tablets did not.

In the first experiment, changes in foraging behaviour were used to measure the ability of the platypuses to detach a miniature 1.5 V alkaline battery. When the battery was 10cm away, the platypuses were able to locate the battery 100% of the time. The experiment was repeated, offering a choice between a piece of shrimp tail, a dead battery, and a live battery: platypuses always preferred the live battery. 

The second experiment tested the ability of the platypuses to detach electric fields. To do this, 2 aluminium plates were placed inside on two opposite sides of the tank and connected to a 1.5V battery. As the electric field was switched from plate to plate, the platypuses showed head and tail reflex movements, showing they could detect the switching field. 

In the third experiment, Scheich et al. determined the platypuses' ability to locate and avoid objects using electroreception. A plastic plate with carbon electrodes carrying current was placed in the tank while the platypus was in the patrol phase. When the electrodes were turned on, the platypus was able to avoid and navigate around the plate; however, when the electrodes were turned off, the platypus would not detect the plate and bumped into it. 

Like the first experiment, the fourth experiment looked at foraging behaviour in relation to the presence and absence of an electric field. Scheich et al. observed that the platypuses would turn over hollow bricks while foraging, especially when there was prey hiding inside. When electrodes were placed inside the bricks instead of prey items, the same response was seen.

Lastly, Scheich et al. used cortical evoked potentials to determine how electrically sensitive the platypus bill is, and to map out where on the brain these signals were detected. When 1 millisecond pulses were applied to the proximal third of the bill, brain activity was concentrated in the posterior-lateral hemisphere. The threshold needed to stimulate the bill was less than 180 microvolts/cm^-1.

Critique 

Overall, I thought that this paper was an enjoyable read. At the time it was published, it was quite innovative, as it was originally thought that that platypus bill only contained mechanoreceptors, so it was interesting to see how electroreception in the platypus bill was discovered. I thought that the experiments were a simple, yet clever way to show that platypuses used electrolocation and electroreception; all 4 of the experiments were successful in showing this.

The written results were succinct, easy to understand, and were not filled with jargon. Nevertheless, I found that the figures that accompanied the paper were hard to read and somewhat confusing. Some of the graphs did not have labelled axes, and none of the graphs had titles. Although the graphs were explained in a single text box next to the graphs, I think it would have helped to have labelled axes and titles on each of the graphs. In the experiment where the electrosensitivity was monitored and signals to the brain mapped out, it would have been nice to have pictures of the experiment setup, and sketch of the areas of the brain that responded when the bill was stimulated. 

In terms of organization, the paper did not follow the usual organizational scheme, where the Introduction, Materials and Methods, Results, and Discussion are labelled using subheadings. Instead, it was organized in paragraphs, where each paragraph discussed a different experiment that was completed. Although I can understand why this was done, I think that the use of subheadings would help to make things more organized, either by using the ones described above, or by using them to title each experiment. I would have also liked to have seen a more detailed description of the materials and methods used. 


Reference

Scheich, H., Langner, G., Tidemann, C., Coles, R. B., & Guppy, A. (1986). Electroreception and electrolocation in platypus. Nature, 319(6052), 401-402. doi:10.1038/319401a0