Several hypotheses have been proposed to explain genome size variation in birds. However, no general consensus has been reached thus far. In this study, we analysed the inter- and intraspecific variation of genome size in some parrot species, and we tested the hypotheses that (1) weaker fliers have larger genomes, and (2) long-living species have lower DNA content. In general, parrots have a mean genome size (2.93 pgucleus) comparable to that of other avian orders. Amazona ochrocephala tresmariae has the highest genome size (4.30 pgucleus) among parrots. As expected, weaker flyers have larger genomes than better ones. In contrast to our prediction, we found a positive correlation between genome size and longevity. Finally, the species-group Amazona has a higher DNA content than the two groups Ara and Cacatua. Since oxidative stress is causally related to longevity, we suggest that DNA oxidative damage could have acted to some extent as a constraint on GS variation in parrots and perhaps also in other avian orders.
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