For the past 80 million years, a tiny water-borne organism called the bdelloid rotifer has lived and thrived without the benefits of sexual reproduction. Now, while asexual reproduction is nothing new to science, the way that these rotifers go about it is particularly unique: They eat DNA found in organic debris. The discovery shows that sex may not be as important to reproduction as previously assumed. Gasp!
In this international study, a research team led by Chiara Boschetti and Alan Tunnacliffe of Cambridge University conducted the first large scale analysis of the mysterious rotifer. What they learned was that the all-female microinvertebrates get about 10% of their active genes by ingesting bacteria, fungi, protists, algae, and other organisms that are found in their aquatic environments. Once they've eaten this foreign DNA, they then 'transcribe' the genetic information in a way that scientists don't quite understand — a process that's being called 'horizontal gene transfer' (HGT).
But what the researchers do know is that, of this genetic material, about 80% codes for enzymes (which makes a considerable contribution to the bdelloid biochemistry), and that 39% of enzyme activity has a foreign contribution. In 23% of cases the activity is uniquely driven by a foreign gene.
And what's just as fascinating is how the HGT process allows the bdelloid to continually evolve and adapt to changing conditions over time. One of the primary benefits of sexual reproduction is that it leads to subtle mutations that allow a species to change and adapt to new environments. With HGT, variations are still happening — but as the result of integrating new DNA from other species.
And indeed, the researchers have cataloged over 400 different species of this rotifer, many of which have developed remarkable adaptations. For example, one varient has developed a tolerance for high levels of ionizing radiation that kills other animals, and others can withstand extreme dehydration. As a result, the researchers have concluded that horizontal gene transfer is a viable mechanism for survival without sex — one that works by diversifying capacities and even replacing defective genes with foreign counterparts.
The entire study can be found at PLOS.
Image: Marine Biological Laboratory.