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Labra, A., & Hoare, M. (2014). Chemical recognition in a snake–lizard predator–prey system. acta ethologica, 1-7.

Introduction

In the recent article by Labra & Hoare they looked to observe whether chemical signals of the prey can be sensed by the predator and whether chemical signals of the predator can be sensed by the prey. In this experiment they used one snake Philodryas chamissonis to discriminate between scents of two lizard prey species which it preys on, Liolaemus nitidus and L. chiliensis. These lizard species belong to same genus and live in the same area except L.chiliensis which mainly is on trees whereas L.nitidus is present in the same habitat as the snakes e.g. mainly on rocks. The researchers wanted to learn whether the snake can distinguish the scents of these species of lizard as it might not encounter one (L.chiliensis) as frequently as the other. They expected that the snake might respond more to L.nitidus as it might frequently encounter it thus giving the snake an easy meal. This is the life-dinner principle. Secondly they wanted to observe whether the two congeneric lizard species could sense the snake scent (and whether the L.chiliensis might sense the snake scent even if there is not a perceived risk). Secondly they wanted to observe the behavior once the prey sensed the predator. Methods
In general they found 10 adult males of L. chiliensis nine (not sexed) individuals (prey) nine of P. chamissonis (predator), four adult males of L. nitidus (prey). For the snake they made it first hungry then they put it in a cage of either the reptiles or an odourless control. They measured the tongue flicks and motion of the snake in the different conditions. They performed a similar experiment with the two reptiles but with a snake scent, (conspecific scent for Liolaemus chiliensis) or odorless. They measured the tongue flicks, temperature, and behavior.

Scents significantly affected the number of tongue flicks of the snake. Lizards made slow motions in the snake enclosure and some even tried to jump the fence. Interestingly the lizard tongue flicked more in the conspecific enclosure. The snake tongue moved less in the L-nitidus than in the presence of L-chiliensis (less encountered lizard)
The snake discriminated between congeneric lizard prey, showing less exploratory behavior (i.e., number of tongue flicks and motion time) in the presence of L. nitidus scents. L.chiliensis, recognized the snake scents, displaying a reduction of activity but did not react otherwise because it likely encounters the snake at a low frequency as it is in the bushes.
On the other hand P. chamissonis exhibits this fine-tuned response to the different lizard scents when it seems it would be advantageous to react to any lizard scent. There may be a novelty factor here. The snake largely does not want to search for difficult prey. Liolaemus species can discriminate scents of snakes effectively and scents from its own species.

Critique

Within this article it shows an interesting experiment to understand predator-prey relationships and evaluate the life-dinner principle. It was a simple setup. Although they did not mention how they could know that all the scents were taken out of the enclosure. If there were scents left on the inside of the enclosure the study would fail. Secondly, it would have made sense to take the same number of males or females with the same number of 10. This would increase the variability in the study. Lastly, it would have been nice to include another analytical factor within the study. They are measuring tongue flicks, behavior and temperature under the three conditions. The study was limited in some parts of the setup that the authors could have designed better. Although the data made sense there could have been more of it. For future experiments it would be interesting to see other predator-prey relationships. Additionally, it would be interesting to see more data collected. It was unclear why they did not the lizard experiments a little different.