José Cerca, Christian Meyer, Günter Purschke, Torsten H. Struck
A significant fact about the history of life is the many situations in which evolution doesn’t happen. Needless to say, in a Darwin-dominated environment, that fact and its significance is understated and understudied:
That size, shape and structure of organisms can evolve at different speeds is well known, ranging from fast-evolving adaptive radiations to living fossils such as cichlids or coelacanths, respectively.
A team lead by biologists at the Natural History Museum (University of Oslo) has uncovered a group of species in which change in appearance seems to have been brought to a complete halt.
The tiny annelid worms belonging to the genus Stygocapitella live in sandy beaches around the world. In their 275-million-year-old history the worms have evolved ten distinct species.
But what makes the group stand out is its presence of only four different appearances, or morphotypes. Such absence of morphological change has lately proven to be a common feature of many so-called cryptic species complexes, for example, in mammals, snails, crustaceans or jellyfishes.
– Cryptic species are species which have already been distinct species for a substantial amount of time, but have accumulated very little or no morphological differences.
Natural History Museum, University of Oslo, “Ghost worms mostly unchanged since the age of dinosaurs” at Eurekalert
So “cryptic species” means “didn’t really evolve much in form.” Let’s make a note of that. And now get this:
– Such species can help us understand how evolution proceeds in the absence of morphological evolution, and which factors might be important in these cases, explains professor Torsten Struck at the Natural History Museum (University of Oslo)
Two of the Stygocapitella species that were investigated split apart at the same time when the Stegosaurus and Brachiosaurus roamed about.
But despite 140 million years of evolution, these ghost worms today look almost exactly the same. However, looks may be deceiving. Molecular investigations reveal that they are highly genetically distinct, and considered reproductively isolated species.
In comparison to other cryptic-species complexes that are separated by a maximum of a couple million years, the time span in this complex is ten times longer, which makes the lack of change in ghost worms extreme.
Natural History Museum, University of Oslo, “Ghost worms mostly unchanged since the age of dinosaurs” at Eurekalert
So “these ghost worms today look almost exactly the same” but “they are highly genetically distinct”? Which means that genetics and morphology (body form) don’t have much to do with each other? The researchers admit, more or less, that they really don’t know.
Yes, that is odd. So many lecterns splintered in vain. But, one wants to ask, how distinct are the genomes of these species that all look the same?
Would it be like mapping a cat’s genome and finding a German Shepherd’s GATTACA in there? What that level of distinction really tells us goes well beyond cats and German Shepherds. Or do the researchers really mean something less highly distinct? What? We search for analogies here.
See also: Stasis: When life goes on but evolution does not happen