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Big brained invaders do better

10. April, 2011
Eleutherodactylus johnstonei

Image via Wikipedia

This had me go “oh, that’s quite interesting”, but I’m not sure if I really learned much from it. Below is the reference with a link to the original work, should you want to read it.

Amiel JJ, Tingley R, Shine R (2011) Smart Moves: Effects of Relative Brain Size on Establishment Success of Invasive Amphibians and Reptiles. PLoS ONE 6(4): e18277. doi:10.1371/journal.pone.0018277


Now, they start out with something quite obvious in the introduction, which is that bigger brains in relation to body size leads to what non-academics would call higher intelligence. It has to do with cognitive function and behavioural plasticity… and stuff.

Now, these things would be useful for an animal, that has ended up in a foreign environment. Since humans started to reign over the earth, this has happened a lot, so we need to know as much about this as possible.

Now, based on previous knowledge the authors predicted that reptiles and amphibians with larger relative brains size would “do better” than those with smaller relative brains sizes when introduced to a strange environment. My definition of “doing well”, is establishing a breeding population.

Their data is from surveys carried out on animals that had already been introduced in various places (no, they didn’t go out and release lots of amphibians and reptiles in places they didn’t belong). This type of non-experimental research means that you have limited data and you basically just have to work with what you get.

They did a reasonable job at it, however. They used the much revered R for data analysis and the lme4 package, which I also find quite useful in my data analysis. This allowed them to carry out mixed effects models including all of their different variables and to then do a model simplification to a minimum adequate model, which all seems pretty straight forward to me, without knowing more detail than they give in the methods section.

What I find quite interesting, is that although there was as expected an overall trend for a correlation between bigger brain to body size ratio and probability of success, it was negative in Australasia unlike in the rest of the world. This might just be due to limited data, which they can’t randomise or structure much, if they don’t have a say in where which animals are introduced, but it does lead to speculation about why it might be that having a big brain is harmful to reptiles and amphibians in Australasia.

This is where we get to the discussion, and I have to say that although this is an interesting piece of science, I think it needs a bit more substantial evidence. The authors agree, but they also start talking about forebrain sizes, which I find a bit redundant since they also mention that reptiles and amphibians don’t have a structure that corresponds to the forebrain in mammals and birds.

Their ideas on how to expand study are sensible, but I think a little more knowledge, perhaps using short experimental trials with amphibians on their ability to carry out certain tasks, might shed more light on what it is about larger brained reptiles and amphibians that makes them more successful in some areas and not in others. They mention that a larger medial cortex may lead to better spatial memory in reptiles, but they then do not go ahead to suggest testing spatial memory of reptiles with varying brain to body ratio. This should be a relatively simple behavioural test. They like to get neuroscientists in on the act and although that is really interesting, and understanding brain function and so on is necessary, if you’re interesting in what it is about bigger brains that helps animals survive in strange environments, why not test out their abilities to carry out necessary tasks (such as remembering where home is and where they saw a source of food).

The authors do mention one good reason why it might be, that the bigger brained reptiles did worse in Australasia, which is that big brains are costly (we know this) and that in Australasia, a big brain may not make up for the cost of having it. Basically, being clever won’t make you less hungry in Australasia. However, as I said before, I think they need more data before they can really speculate on something like that.

2 Comments leave one →
  1. 18. April, 2011 20:39

    Maybe Australasia is just a really, really angsty place and you need a sufficiently large brain in order to develop suicidal tendencies.

    “I’m in a new environment far away from home. Bugger this! I’ll just off myself…”

  2. 18. April, 2011 22:12

    Well, if it’s anything like mainland Australia, it’s enough to cause some serious paranoia. *Everything* is out to get you there.

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