Super-successful self-cloning crayfish highlights evolutionary problem of sex
Since its discovery in Germany in 1995, the marbled crayfish has spectacularly spread across Europe and parts of Africa in huge numbers. Because it reproduces asexually (i.e. only a female is needed), this ‘self-cloning’ crayfish can establish a population in a lake or waterway starting with just one individual. Bearing a large number of young, the marbled crayfish appears to be out-competing ‘native’ crayfish, and some authorities have officially declared it a pest.
Recent genetic analysis has found that the marbled crayfish has three sets of 92 chromosomes rather than the usual two. With two of these sets being identical to each other and only slightly different from the third set, researchers surmise that the marbled crayfish arose from a mating between two slough crayfish, Procambarus fallax. They say that one of those parents must have had an abnormal egg or sperm with two copies of its chromosomes rather than the usual single set., And so the marbled crayfish now can copy itself as many other asexually-reproducing organisms do via apomictic parthenogenesis. Its eggs do not need to be fertilized by sperm, and all contain the same three sets of chromosomes. Genetic analysis of marbled crayfish from various locations in Europe and Africa confirms that they are indeed all clones—genetically identical.
The marbled crayfish has now been declared a new species, Procambarus virginalis, and is said by the researchers to “illustrate a unique path of animal genome evolution”.1
But nowhere in this ‘evolution’ is there any evidence of anything that could have turned microbes into marbled crayfish, or any other of the multiplicity of plant, animal, and other creature kinds. Marbled crayfish have an extra set of genes, but no new ones (i.e. that didn’t already exist in crayfish populations)—how did crayfish get any of their genes originally?
In fact, calling examples like this (and e.g. polyploidy, where a new plant species can arise from doubling the chromosome numbers of an existing one) ‘evolution’ is not just inaccurate but seriously misleading. This is because it will make many think that it is a ‘little bit’ of the same sort of process that, extended by millions of years, could turn worms into walruses. But this latter evolutionary story requires vast amounts of new information to arise, information that did not previously exist. For instance, information coding for eyes had to arise in a world that had never had such information before, and similarly for a mindboggling array of new systems and structures. However, such examples as the marbled crayfish obviously tell us absolutely nothing about any new information arising.
What’s more, this new example of the success of asexual reproduction adds to the existing problem that evolutionists have (and many acknowledge) of explaining how and why sexual reproduction arose. If it is supposed to have been because of the alleged advantage of sex, this crayfish shows that an organism can be spectacularly successful just by cloning itself. So why should evolution ‘bother’ to evolve sexual reproduction in the first place?
References and notes
- Gutekunst, J., and 6 others, Clonal genome evolution and rapid invasive spread of the marbled crayfish, Nature Ecology and Evolution 2:567–573, 2018 | doi:10.1038/s41559-018-0467-9. Return to text.
- Pennisi, E., An aquarium accident may have given this crayfish the DNA to take over the world, sciencemag.org, 5 February 2018. Return to text.
- Parthogenesis = reproduction without sexual intercourse, apomictic is from Greek ‘without mixing’, it refers to parthenogenesis where there is no meiosis: a process that mixes the genes on chromosomes and produces cells with half the number of chromosomes. Return to text.