A nematode worm that has evolved the ability to breed itself has lost even a quarter of its genetic heritage, including the genes that make its spermatozoa more competitive than those of competing species.
Caenorhabditis briggsae is a creature about 1 mm long, very similar to Caenorhabditis elegans, whose DNA has been completely sequenced: for this reason both species are often used as models in genetic studies.
Something is changed. A million years ago C. briggsae developed the ability to reproduce itself: the specimens of this species are therefore hermaphrodites, with male and female sexual organs. Scientists at the University of Maryland wanted to investigate how this ability influenced the genetics of the creature.Curiosity: animals that need a partner. |
They compared its DNA with that of a similar species, the worm Caenorhabditis nigoni, which reproduces in the traditional way, and found that the genetic heritage of the first is in deficit of 7, 000 genes: since the two species are different above all in the reproductive method, it would seem that self-fertilization has wiped out a quarter of the nematode's DNA.
better get rid of it. In particular, a group of genes that encodes particular proteins on the surface of the spermatozoa would disappear and give the non-hermaphrodite species a competitive advantage over their opponents. This characteristic is useless and even harmful for the nematodes that reproduce on their own - it seems to encourage the birth of male specimens and therefore causes a gender imbalance within the species.
The discovery represents a sort of evolutionary snapshot of how a species perfects its reproduction. As Eric Haag, biologist and author of the study explains, "genes that are essential for tens of millions of years can suddenly become useless or even disadvantageous when the sexual system changes".