A tiny invertebrate, that has lost the ability to have sex, can steal DNA from its food. Bdelloid rotifers are microscopic creatures found throughout the world in fresh water and damp soil. They are also are all female and only reproduce asexually, having lost sex and males millions of years ago. However, they can inherit new genes from other non-animal species such as bacteria and fungi.
Researchers studied the rotifers’ mRNA, a molecule similar to DNA that only contains genes currently being used to make proteins. The mRNA was compared to a database containing the mRNA of thousands of other species. When a section of mRNA from the rotifers matched a section in the database, scientists looked up where the genes came from. Using this method they found that about 10% of the genes were alien - coming from non-rotifer species, that included bacteria, fungi and algae. Scientists suspect that the rotifers are acquiring these genes from the organic debris they eat.
Even more unusual is that because this method only looked at genes being expressed, we know that this alien DNA is not just sitting in cells, it is being used to make proteins. Most of these proteins are enzymes, molecules that enable chemical reactions to occur. These enzymes, which couldn't be made without the foreign genes,, may explain the amazing capabilities of bdelloid rotifers.
Despite living in aquatic and damp environments bdelloid rotifers can survive drying out. The dehydrated rotifers lie dormant until they’re rehydrated when the environment gets wetter. The enzymes made, using foreign genes, enable the rotifers to use otherwise unusable substances as food, and to manufacture protective molecules. This could be important for surviving dehydration.
The consumption of DNA may also account for the number of bdelloid rotifer species. Bdelloid rotifers reproduce without sex. This is not unusual as many organisms reproduce asexually, but bdelloid rotifers are the only animals to exclusively reproduce this way. Theory predicts that this lack of sex should limit their ability to adapt to changing conditions, and therefore limit their evolution into new species. However, there are over 300 species of bdelloid rotifer.
Sex mixes genes from different individuals creating new combinations that might be useful. This mixing also creates variety within a species, helping species to evolve by increasing the chance of some individuals being adapted to current conditions. Bdelloid rotifers can create new combinations of genes without sex by horizontal gene transfer – where genes are transferred between two rotifers. But horizontal gene transfer alone, between rotifers, isn’t expected to have resulted in the diversity of bdelloid rotifers seen throughout the world. The introduction of new genes from other life forms increases the variation between bdelloid rotifers, and may explain the large number species seen.
So not only does stealing genes from their food add to the weirdness of these already unique creatures, it may explain their millennia of survival and evolution.
Boschetti C. et al. PLoS Genet 8(11) e1003035 (2012)