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All rotifers are female (we think) – but the underlying explanation has been challenged

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Rotaria macrura, a rotifer species/ Michael Plewka

And maybe they are not all female.

From ScienceDaily:

A new study has cast doubt on leading theory for how tiny creatures have evolved for tens of millions of years — without ever having sex.

they are all female, and their offspring are clones of their mothers. Bdelloids are microscopic animals that live in freshwater and damp habitats across the world. Despite their apparent lack of sex, we know they have evolved for tens of millions of years into more than 500 species.

By studying their genomes — the set of all the genes that define an animal’s characteristics — researchers thought they had identified an explanation for how bdelloids had ‘gotten away’ with no sex for millions of years.

However, a new study, published today in PLOS Biology and led by Imperial College London researchers, reveals this mechanism may not be the main explanation for the bdelloids’ success.

Many species of bdelloid endure periods of drying out, called desiccation. Although they survive desiccation, the process damages their DNA, which they need to repair when dehydrated.

Based on a previous study of the genome of a species that survives desiccation, researchers had proposed that the repair of DNA might remove some of the problems of being asexual, for example by removing harmful mutations and possibly allowing occasional recombination of genes to occur.

This theory made key predictions about what the genomes of the small number of bdelloid species that cannot survive desiccation should look like. The new study looked at the genomes of three further species, including some that do not undergo desiccation.

The researchers found that the predicted differences between species that can and cannot survive desiccation were not observed. This suggests that DNA repair following desiccation may not be as important as previously thought, and that other factors may need to be considered to explain bdelloid evolution.

Finally, although no males have ever been found, this new study of rotifers’ genomes suggests scientists can’t rule out sex as firmly as previously thought. Previous evidence had suggested that the structure of the bdelloid genome made conventional sex impossible.

Sexual animals have two copies of each gene arranged along matching chromosomes, one from the father and one from the mother. The first bdelloid genome sequenced revealed that the two copies of genes were often on the same chromosome, which is incompatible with their inheritance on chromosomes from a father and a mother. The new study, however, did not find these same patterns in the three new genomes.

Lead author Dr Reuben Nowell said: “We haven’t proved they are having sex, it’s just that we can’t prove that they aren’t based on the current genome results. Other species of rotifers have identifiable males, but no bdelloid rotifer males have ever been found. Paper. open access – Reuben W. Nowell, Pedro Almeida, Christopher G. Wilson, Thomas P. Smith, Diego Fontaneto, Alastair Crisp, Gos Micklem, Alan Tunnacliffe, Chiara Boschetti, Timothy G. Barraclough. Comparative genomics of bdelloid rotifers: Insights from desiccating and nondesiccating species. PLOS Biology, 2018; 16 (4): e2004830 DOI: 10.1371/journal.pbio.2004830
More.

The bad news is that the simple explanation probably isn’t the answer. The good news is that we found out that it probably isn’t the answer. We could have been content to make up a Darwinian just-so story and insert it into the textbooks for memorization.

See also: Bdelloid rotifer uses horizontal gene transfer (HGT), dispenses with sex

and

Top life sciences micro photo: The rotifer, filtering water for food, like a vacuum cleaner

3 Replies to “All rotifers are female (we think) – but the underlying explanation has been challenged

  1. 1
    bornagain77 says:

    A few notes:

    How did the sexes originate? Why is it that the vast majority of living things require a “male and female” to reproduce? If evolution were true – doesn’t it make much more sense that EVERY living organism was self-replicating and required no useless energy expenditure? When did the first male get here? When did the first female get here? How? Why? Wouldn’t they have had to appear fully functional and at the same time in order for the next generation of organisms to arrive? Of course, they would. So, how is it that the first male and female for almost 2 million living organisms arrived together and fully functional so that reproduction could take place? “Sex is the QUEEN of evolutionary biology problems.”
    Dr. Graham Bell – In his book, ‘The Masterpiece of Nature’

    Knowledge gap on the origin of sex – May 26, 2017
    Excerpt: There are significant gaps in our knowledge on the evolution of sex, according to a research review on sex chromosomes. Even after more than a century of study, researchers do not know enough about the evolution of sex chromosomes to understand how males and females emerge.
    https://www.sciencedaily.com/releases/2017/05/170526084533.htm

    Various Modes of Reproduction in Phylums
    https://quizlet.com/17313821/reproduction-in-phylums-flash-cards/
    One of the most enigmatic ‘novelties’ of the Cambrian explosion was the appearance of a wide variety of methods of reproduction for a such wide variety of different multicellular species/phyla in such a short time:
    http://www.uncommondescent.com.....ent-563050

    Another whack at the “sex paradox” – July 1, 2014
    Excerpt: The article is most informative about tests done on the various theses but in the end (they state). And so the paradox of sex lives on. “We still really don’t know the answer to this very most basic question,” says Mark Welch. “We don’t know why sex exists.”
    http://www.uncommondescent.com.....x-paradox/

    Ian Juby’s sex video – (Can sexual reproduction plausibly evolve?) – video
    http://www.youtube.com/watch?v=Ab1VWQEnnwM

    Irreducible Complexity in Male Sexual Function – Howard Glicksman – July 10, 2016
    http://www.evolutionnews.org/2.....02983.html

    Surprise: Men and Women Greatly Differ Genetically | Jerry Bergman – May 8, 2017
    Excerpt: An article in New Scientist titled “Sex Differences in Human Gene Expression” concluded that “Researchers uncover thousands of genes whose activity varies between men and women.”[1] Specifically, their study found 6,500 genes were differentially expressed. They concluded that men and women are distinctly dimorphic, consequently one result of this fact is that they have very dissimilar disease susceptibilities.[2] The sexual dimorphic traits result mainly from differential expression of the genes that exist in both sexes. These results strongly go against the current politically correct view that the only differences between males and females are a few minor plumbing variations and a couple of small hormones.
    http://crev.info/2017/05/men-w.....netically/

    Verse:

    Mark 10:6
    However, from the beginning of creation, ‘God made them male and female.’

    Supplemental note on how ‘sexual selection’ is used as a ‘just so story’ in combination with natural selection as the supposed ‘designer substitute’.

    Brangelina Fever Gets Its Own Darwinian Just-So Story – Jonathan Witt – September 29, 2016
    Excerpt: What about all those zany things on the nature shows so impractical that natural selection would never vote them on to the next round of mother nature’s great big unmerciful game of Jeopardy? Well then, Darwinism has just the little beauty you’re looking for. That’s right, folks, sexual selection — natural selection’s winsome, whimsical, and wondrous assistant. Sexual selection is where, say, peahens prefer the peacocks with the bigger tail feathers, never mind how impractical those tails might become for running and flying. Presto! Peacocks have evolved whimsically enormous peacock tails.
    Together, natural and sexual selection can whip up a just-so story or any biological marvel you want to throw at them.
    http://www.evolutionnews.org/2.....03177.html

  2. 2
    polistra says:

    If other species have both males and females, maybe those other species are fertilizing the bdelloid eggs. In other words, maybe the bdelloid type isn’t a species in the traditional sense but just one form in a complex life-cycle that we don’t understand yet.

    We should connect them to Microfacebook. Then we’ll know all about every moment of their lives, and we can use the knowledge to sell them cilia stiffener pills and Bdellcoin.

  3. 3
    Allan Keith says:

    All rotifers are female (we think)

    Actually, we do not think this. Pathogenic species typically produce males at one time in the annual cycle. For eukaryote species that are largely asexual, it is common for there to be a sexual stage at periodic intervals.

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