The only way to achieve genetic variation in a genome was previously thought to be solely through sexual reproduction. However, there is one species that proves this thought untrue. This species is a microscopic animal known as the rotifer. Rotifers are known to reproduce in an asexual manner, meaning that the female passes all of her genes onto her offspring because her gametes never undergo meiosis, and no fertilization event occurs. Recently the sequencing of the genome of this microscopic animal revealed that an unexpected 8% of the species genome was foreign. These foreign genes varied but were primarily characteristic of fungi and bacteria. These foreign genes from different species gave the rotifer’s traits uncommon to them such as the ability to break down toxins and utilizing new foodstuffs. But how did this species come to obtain this foreign DNA?
Rotifer are known to inhabit shallow ponds or puddles, however, when the pond dries up the rotifer dehydrates and shrinks and pieces of DNA are broken, but the individual does not die. They in fact can stay in this sort of dormant form for very long periods of time and can be blown to different pools of water where they will rehydrate and repair their broken parts of DNA. It would appear that during these dehydration events holes are made in the cell membrane and DNA can be sucked up into the cell through these holes utilizing horizontal transfer. Their ability to quickly and efficiently repair broken DNA after dehydration makes incorporating these foreign pieces of DNA very easy. The new DNA lines up with the appropriate DNA sequence in the already existing DNA, so potentially old genes can be replaced with new ones. This appears to have been done by this species for centuries, and may be exactly why an organism that reproduces asexually has existed for so long. They receive the necessary genetic variation without exerting all the energy of sexual reproduction.
These small organisms developed a way to increase their genetic variation in the absence of sexual reproduction. Due to this they have created doubt that sexual reproduction is essential in evolutionary adaptation. This adaptation in this microscopic animal is quite intriguing.