Saturday, April 9, 2011

Invasive Herps & Brain Size

Why is it that some amphibian and reptile species become invasive, while others do not? The anwer to this question may rest in the relative brain size of the species. This question is addressed in a new article by Joshua J. Amiel, Reid Tingley, and Richard Shine of the University of Syndney.  They report that amphibians and reptiles have smaller forebrains than birds and mammals, and are often viewed to have less behavioural complexity. In an effort to examine the relationship between larger brain size and capacity to thrive in a novel environment, the authors analysed data on human introductions of amphibians and reptiles to areas outside of their native geographic ranges. They assumed that if a larger brain facilitates dealing with new challenges, success in establishing feral populations following a human introduction will be higher in amphibians and reptiles with large brains relative to their body sizes.

They found brain size relative to body size was, in fact, larger in species of amphibians and reptiles reported to be successful invaders, compared to species that failed to thrive after translocation to new sites.
This was the same evolutionary trend previously found in birds and mammals suggesting that larger brain size enhances the ability to deal with novel environmental challenges in all major clades of terrestrial vertebrates. Interestingly, this pattern was present in all biogeographic regions, except Australasia. Introduced amphibians and reptiles with smaller (rather than larger) brains were more successful at establishing populations in Australasia. This may result from environmental factors selecting against larger brain size where a lack of resources exacerbates the energetic costs of maintaining such an energy expensive organ. The authors prpose that low resource availability in Australasia may favour small brain size and other traits that reduce an animal's total energy requirements. They note evolutionary trends towards reduced fecundity levels in rodents and in birds that have invaded Australia over longer time periods reinforce this hypothesis.

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

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