evolution - What are the costs associated with carrying lots of genetic material

What are the costs (if any) associated with carrying lots of genetic material (Big genome size)?

• energy for copying?


• raw material for copying?


• space in the cell?


• Maintenance cost (matter and energy)?


• time to copy is a limiting factor for the minimum generation time?



• Less robustness?


• More likely to evolve a gene that spreads well but has a negative fitness impact on the rest of the genome (selfish gene or outlaw)?

The answer probably depends on the organism. I am interested about any information concerning uni- or multi-cellular eukaryotes, bacteria or viruses.

Do we have any knowledge about how important are these costs or is it pure guesses?

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^{This post comes in reaction to @AlanBoyd comments on this post.}

Answer

It is generally known that the smaller (or less complex) an organism is, the more "condensed" it's genome is. For example, bacteria (or some eukaryotes) have operons (http://en.wikipedia.org/wiki/Operon) or overlapping genes using different and they don't have introns, which alltogether saves a lot of space.

There are many reasons for that. Available space in the cell is definitely not one if it, however. Energy for copying and maintenance is a good point, but you have to keep in mind how evolution works. Bacteria and unicellular eukaryotes are usually adapted to a very specific environment in which they can reproduce rapidly. This means, they only need a small set of genes, specific for this environment and they have to reproduce very frequent, which means they are very prone to mistakes during DNA-copying. Such a mistake can lead to the death of the cell, which in this case equals the death of the organism.

In higher organisms however, the advantages of a bigger genome outweigh the disadvantages by far. Evolution can happen much faster because and mistake while copying does not necessarily lead to the death of the whole organism. Adaptation to a much greater variety of conditions is also necessary, e.g. when you look at plants: Their genomes are (on avarage) much bigger than the ones we mammals have, because they cannot move if the conditions around them become unpleasent. Instead, they need to find a way to adapt. This means, a big genome is in this case a fitness bonus. More interestingly, plant genoms are highly mutable (http://en.wikipedia.org/wiki/Transposable_element), which was originally thought to be a huge disadvantage.