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Friday, May 11, 2012

Sending Sharks to School: Brain Evolution in Sharks and Their Relatives

Whale sharks and basking sharks have very similar brain organisation.

Here are a few things I just learnt from an interesting seminar by UWA Researcher Dr. Kara Yopak.
- Manta rays have the biggest brain to body size ratio of all the cartilaginous fish.
- There is interspecific variation in brain organisation which is correlated with ecological parameters such as feeding habits and locomotory style. It doesn't necessarily track phylogenetic relationships. Through her work Kara has shown that whale sharks and basking sharks have similar brain organisation. The convergence in their lifestyle (notice how they feed in a similar manner?) appears to parallel a convergence in their brain morphology.
- Species that occupy complex reef or oceanic habitats (e.g. blue shark) have larger brains with well-developed and large, highly foliated cerebella.
-  Benthic and benthopelagic demersal species such as the Pacific angelshark have the smallest brains.
- Species such as great white sharks have disproportionately big bodies to brain size vs. their terrestrial counterparts with comparable brain size because marine species are not constrained by gravity. 
- A study on London taxi drivers showed that the part of the brain used for spatial cues enlarged in size as they spent more time on the job. 

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