The genomes of salamanders contain ten times more dna than the genomes of humans because salamanders?

This is because they lose DNA at a slower rate compared to other vertebrates. DNA is lost over time than it is gained through more deletion mutations than insertions. According to the following peer-reviewed journal ( http://gbe.oxfordjournals.org/content/early/2012/11/22/gbe.evs103.abstract), salamanders have had fewer deletion events on their DNA over their evolutionary timescale compared to other vertebrates. Yet insertion events have been significantly similar between Salamanders and other vertebrates.

the answer would be 3