CRISPR-arrays not only contain bits and pieces of virus DNA to protect against infections. They may also contain pieces from the own genome or that of closely related species. This is strange and implies something like suicide or the killing of relatives.
Archaea do not take the concept of species as serious as plants and animals: a lion and a leopard do not mate but Haloferax mediterranei and Haloferax volcanii do. And they exchange genetic material. This is good when they share viral CRISPR sequences since they acquire protection against viruses without going through a dangerous infection. It is really nasty when they transfer CRISPR sequences that match the genome of the mating partner! Sex is in most cases not successful and one of the partners dies because the DNA is cut up by CRISPR.
What’s the consequence? These CRISPR sequences have nothing to do with defense against viruses. They rather seem to set up barriers between species and thus contribute to evolution: though Haloferax mediterranei and Haloferax volcanii “want” to mate, they may fail because of their CRISPR sequences.
Sex is a risky thing: for the better or for the worse!
This work was done by Uri Gophna’s group (Tel Aviv) in our SPP 2141 research consortium. The artwork by Raya Gov illustrate sex with knives and scissors.