SIMILAR-sized animals have wildly different genome sizes, but no one has
known why. Now researchers from Glasgow University have found that, in birds at
least, genome size is related to longevity.
In vertebrates, genome size, known as the C-value, varies enormously, from
0.4 picograms in a pufferfish to 142 pg in the African lungfish. This variation,
mainly due to differing amounts of non-coding DNA, seems unrelated to an
animal鈥檚 complexity, a puzzle dubbed the C-value paradox.
Bird genomes, which vary from 2 pg to 3.8 pg, also seem unrelated to species
size. For instance, the black-headed gull has a much larger genome than the
similarly sized sparrowhawk. So biologists Pat Monaghan and Neil Metcalfe
wondered whether a bird鈥檚 C-value could be related to its maximum potential
lifespan.
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They analysed the variation in genome size and longevity in 67 bird species
from 28 different families, ranging from tiny wrens to huge condors, and found
that species with larger genomes do indeed live longer. As they will say in a
future issue of Trends in Genetics, the team used genome length to
predict accurately that different bird species weighing 500 grams have lifespans
varying between 7.2 to 19.4 years.
鈥淏eyond a certain point, reductions in genome size may carry a cost in terms
of organism function,鈥� says Metcalfe. But uncertainties remain, says Andrew
Leitch from Queen Mary and Westfield College, London. 鈥淲hy do so many tree
species, which are scarcely short-lived, have rather small genomes?鈥� he asks.