Previous work by Cox and Calsbeek has shown that ovariectomized lizards grow faster and survive longer than lizards with intact ovaries. Ovariectomized lizards also develop larger fat bodies, and a reasonable explanation is that it is the greater fat that these lizard accumulate that allows them to survive better over the winter. To test this hypothesis, the authors experimentally removed fat bodies from some lizards and not others. They found that this treatment had no effect on survival, thus disproving the hypothesis. In other words, removal of the ovaries both increases fat body buildup and survival, but the two phenomena are not related, a nice demonstration of the importance of experimental manipulation to understand disentangle correlation from causation and elucidate physiological mechanisms.
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