Wolbachia pipientis is a species of bacteria that infect fruit flies. When the genome of the fruit fly was sequenced, it was found that most of the genome of the bacteria had been integrated into the fruit fly genome. Describe what has happened between these two organisms.

A. This passing of genes between organisms of different species is caused by mutations. This type of gene transfer can increase genetic variation only, if it happens in the cells that produce eggs and sperm.

B. This passing of genes between organisms of different species is called gene recombination and happens during sexual reproduction. This type of gene transfer has no effect on genetic variation.

C. This passing of genes between organisms of different species is caused by gene duplications. This type of gene transfer can increase genetic variation, if the duplicated genes acquire new functions.

D. This passing of genes between organisms of different species is called lateral gene transfer. This type of gene transfer can increase genetic variation, and therefore diversity.