To keep you entertained about invertebrates when we are not in the field, I will write regularly about invertebrates that made the news recently. On the menu today: a summary of a story published today about rotifers and a video of a tiny sea anemone.
How do bdelloid rotifers do without sex?
There are less than 1% of all animal species that don't use sex at all to reproduce. And, for most of them it seems that they gave it up fairly recently. This suggests that, in the long run, species that do not use sex to reproduce end up extinct. By not reproducing sexually, species accumulate deleterious mutations, and cannot exchange mutations that could help them to adapt to changes in their environment -- such as new diseases.
Bdelloid rotifers are an exception, as it seems that they have been reproducing strictly asexually for tens of millions of years. A study published today in the journal Science by Wilson & Sherman sheds some light on the cause of this exception.
Bdelloid rotifers are microscopic animals that live in any kind of moist habitat all around the globe. In addition to their mode of reproduction, bdelloid rotifers are also exceptional in their ability to stay alive out of the water for up to 9 years (at any of their life stages). This ability might be one of the factors explaining why they do well without sex.
The authors of the study showed that staying out of the water for a few weeks reduced drastically the number of individuals killed by a pathogenic fungus. By staying dry for an extended period of time, they can get rid of the the fungus and reduce the selective pressure that these pathogens impose to these asexual rotifers.
Video of Corynactis viridis
Have a look at this video of this small sea anemone feeding on plankton. Note how it can change the shape of its tentacles and its mouth (in the center). This video has been filmed under fluorescent light and is played 1200 times faster.