All the Single Ladies: Bdelloid Rotifers

Lean este artículo en español.

Although it is not yet February, you may have noticed that the candy isle at your local grocery store is already fully stocked with mystery chocolates in heart-shaped boxes and chalky candies in pastel colors. Whether you love, hate, or are simply ambivalent about Valentine’s Day, you have to agree that humans are fairly unique in their approach to courtship and romance. In fact, a good look at the animal kingdom will tell you that are as many ways to woo, mate, and reproduce as there are species to do it! Over the next few posts, No Bones will look at some of the weird and wonderful ways that invertebrates ensure the continuation of their genetic line. Today, we look at all the single ladies--or the world of bdelloid rotifers. 

 

Picture of a bdelloid rotifer Habrotrocha rosa (Rkitko, Wikimedia Commons)

A rotifer is a small, often microscopic animal that lives in freshwater, brackish and marine environments. Commonly called “wheel animals,” these little critters are mostly omnivorous, feeding on organic detritus, dead bacteria, algae and protozoans. They eat pretty much anything small enough to fit into their mouths. Bdelloid rotifers (Bdelloidea) are a class of rotifers (approximately 450 species!) entirely made up of females. That’s right, there are no male bdelloids. These females have been going without male counterparts, and consequently sex, for about 80 million years. Like the Amazon warriors of legend these are some seriously tough ladies. Bdelloid rotifers have an incredible ability to survive harsh environments that are devoid of water by entering a state of dormancy that occurs in cases of extreme desiccation (anhydrobiosis).

Scanning electron micrographs, showing the morphological variation of bdelliod rotifers and their jaws. (Diego Fontaneto, Wikimedia Commons)

Bdelloids reproduce through a type of asexual reproduction called parthenogenesis. This means that eggs can develop into embryos without any need for fertilization. Biologically speaking, there are a lot of advantages to sex. For example, during sexual reproduction, the offspring receives one pair of genes from the mother and one from the father, and as these genes come together, they are often rearranged into new combinations. While asexual reproduction allows organisms to propagate quickly, it also yields clones with low genetic diversity. In turn, low genetic diversity hinders the ability to adapt quickly when conditions change. As a result, it is thought that animals that lose the ability to reproduce asexually are eventually headed for extinction. This hypothesis is supported for several other lineages lacking sexual reproduction, which are evolutionarily young. Bdelloids, however, buck this trend because they have been around for so long. How could they do it?

Lateral view of a bdelloid rotifer (Damian H. Zanette, Wikimedia Commons)

The reason for these animals’ evolutionary longevity is an area of continuing investigation among scientists. However, one of the secrets to their success may be that they “steal” genes from other critters, possibly through ingestion. (Yep, some scientists think that bdelloids steal the genetic material of the stuff they eat!). This process is called horizontal gene transfer. Studies have shown that perhaps up to 10% of the active genes in these rotifers are pirated from other species. These pilfered genes may even contribute to their amazing abilities to withstand desiccation.

So whether you are counting the days till February 14^th or you could care less, just remember to be yourself this season. The females of Bdellodia have been doing their own thing for 8 million years, and they are doing just fine!

By Frances Farabaugh, Intern Invertebrate Zoology Department NMNH

Comments

[Stella Maris Stevenson]

David Baxter: Would you kindly explain for me concept of convergent evolution? I am a neophyte in all branches of human
knowledge and too old to begin now. I hardly read one of books by Isaac Asimov long time ago. Nothing else. Thanks.
Stella Maris Stevenson.

[David Baxter]

I love the idea of horizontal gene transfer. If you like science fiction then take a look at the Polity novels of Neal Asher, especially those dealing with the Spatterjay virus and the Jain. I wonder if his ideas were inspired by this process or whether we just had some convergent evolution!

[Josh]

Awesome article!

[Mari Chapa]

Female power!