Comments on: Bdelloid rotifers – 80 million years without sex

By: alexandra

alexandra — Sat, 30 Jan 2010 02:37:25 +0000

So , BEFORE 80 million years ago??? What prodded the evolution away from sexual reproduction to female cloning?
Too many orgies?

By: Jason

Jason — Thu, 15 Oct 2009 06:26:08 +0000

Well, Mayr was wrong, and probably didn’t take bdelloids into consideration when he came up with his definition. Furthermore, many other species that were supposedly asexual were found to have males. However, there should be genomic “footprints” if sexual reproduction occured, and as Meselson and co. have shown, these are absent in bdelloids. These gals are the real deal when it comes to asexuality. And if you ever look at the different species under a microscope, some are so different in appearance, morphology, behavior, etc, that there is no doubt that they can be classified as separate species.

By: David

David — Sun, 04 Oct 2009 19:45:44 +0000

Of course, if you happen to use Facebook, you could always try this species model approach: http://apps.facebook.com/qwhat-species-dfidic/?start=1&target=home (can't claim credit for it but I am determined to be closest to Salmonella typhi!

By: David

David — Sun, 04 Oct 2009 19:39:15 +0000

DJ translated~
Biological Species Concept (BSC): reproductive isolation is the centerpiece, i.e. the failure of populations to interbreed or to form viable or fertile hybrids (insert Ernst Mayr here)
Phylogenetic Species Concept (PSC): monophyly is the centerpiece, i.e. the populations of each species should share a common ancestor (insert DJ here)
then we also have-
Ecological Species Concept (ESC) which defines a species as a set of organisms exploiting a single niche (adaptive zone), i.e. it supposes that ecological niches in nature occupy discrete zones (kinda almost insert me here!)

By: DJ

DJ — Sun, 04 Oct 2009 18:09:39 +0000

@John S. Wilkins,
The Biological Species Concept (BSC) is just one of many. In the paper: Concepts of Species by James Mallet (2001). He attempts to discuss all of the current concepts and their implications with regard to evolutionary and conservation sciences. It is a great paper with a concise description of species concepts.
I am a fan of the Phylogenetic Species Concept (PSC) over the BSC because it is much more precise: ” A phylogenetic species is an irreducible (basal) cluster of organisms, diagnosably distinct from other such clusters, and wthin which there is a parental pattern of ancestry and descent”(Carcraft, 1989, Speciation and its ontology: The empirical concequences of alternative species concepts for understanding patters and processes of differentiation).
The PSC has its own disadvantages, namely it could be used to parse smaller and smaller groups until we classify individuals as species unto themselves. But I think with a reasonable adherence we stand the best shot of perceiving monophyletic groups using this method. Which in the long run will be more useful I think. Not that my opinion means much. hehe.
Anyway, the question of what exactly constitutes a species remains unsettled. There are many ideas, and many adhere to the BSC because of its historical popularity (and lets face it, Ernst Mayr was an amazing scientist)though I’m guessing the BSC won’t be the definitive concept used to express the idea of discrete groups we call species.

By: Brian Schmidt

Brian Schmidt — Fri, 02 Oct 2009 20:34:57 +0000

Mark: bdelloids haven’t maintained their identity as a single species, instead they’ve differentiated into a variety of species.
The concept of species is somewhat theoretical under normal circumstances but for these ladies it’s even more theoretical, merely describing groups of similar individuals that were related in the past but (obviously) don’t interbreed. Similar objections are made to describing bacteria as species, although bacteria at least have a few mechanisms for lateral gene flow.
I’m curious why the gene differentiation trick works for bdelloids and not for other multicelluar animals. I’m guessing that others undergo meiosis and then recombine the genes internally, mimicking sex, while bdelloids skip that step entirely.

By: David

David — Thu, 01 Oct 2009 17:53:53 +0000

Mark,
Genetic diversity is maintained through the mechanism as outlined in Ed’s article above: “but in the asexual bdelloids, a daughter inherits both copies of each gene from its mother and they never mingle. This frees them to evolve in their own directions and take on new roles, irrespective of the destinies of their partner.”
Further, “Pouchkina-Stantcheva found evidence of this in a gene called lea from the bdelloid Adineta ricciae. The two copies of this gene differ by about 14% of their sequence, and these small differences translate to proteins with substantially different structures and functions.”
What this means is that there is at least as much genetic differentiation as would exist between sexually-reproducing humans and as also stated above, those small variations can account for substantial differences (unless you have an identical twin, look at your own siblings, or even the next door neighbors! [and "monkey business" inferred from that is purely coincidental!])
Your argument would probably hold more true for other species that clone exact copies of mom through parthenogenesis (called “obligate parthenogenesis” if only females are produced) and therefore do not have the ability to keep the mom’s and offspring’s genes separate as rotifers do, then they would indeed be very prone to react negatively to sudden changes in their environment.

By: Mark Dow

Mark Dow — Thu, 01 Oct 2009 16:47:49 +0000

How is it that they can maintain their identities as species? Wouldn’t the genome of separate family trees of individuals slowly and amorphously diverge, resulting in a broad class of organisms with less commonality as time goes on? Do they converge on similar solutions to environmental challenges?

By: David

David — Thu, 01 Oct 2009 13:13:33 +0000

LOL! I believe Ernst Mayr’s answer to the “species problem” is to define species as “groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups” which stresses reproduction as opposed to gender- rotifers obviously reproduce… however the common accepted interpretation of species is “populations of organisms that have a high level of genetic similarity” but I would agree that in microbiology there is a clear argument for the entire bacterial domain being a single gene pool which would probably support the contention of many entomologists who would argue that most, if not all mammal “species” should really be classified into one genus!
Is science supposed to be an exact science?

By: John S. Wilkins

John S. Wilkins — Thu, 01 Oct 2009 10:24:42 +0000

Dare I ask how these can bear species names if they have no sex? Mayr said they aren’t species!