Wednesday, 7 February 2018

Yet Another Newly Evolved Species

Marbled crayfish, Procambarus virginalis
By Chucholl C. (Own work) [CC BY-SA 3.0],
via Wikimedia Commons
An aquarium accident may have given this crayfish the DNA to take over the world | Science | AAAS

Like most weeks, it's been a pretty dreadful one for creationists so far as scientific research is concerned. Another week and still not one iota of support for creationism or its lab-coated mock-science version, intelligent (sic) design. Instead we have the usual plethora of papers which quite incidentally, and with no effort or intent on the part of the authors, refutes creationism and confirms evolution.

I've already written about two - bacteria evolving to digest plastic and the extraordinary evolutionary history of the house dust mite. Now we have this observed evolution of a new species of crayfish which fills all the criteria for what creationists call 'macro-evolution', which they claim is impossible. Later, I'll be writing about a beautiful example of a fossil of an intermediate ancestor of both spiders and scorpions - again, something creationists tell their dupes don't exist. That one 'impossible' thing and one 'nonexistent' thing in the same week!

The new species of crayfish, the marbled crayfish (Procambarus virginalis), evolved in a German aquarium and is the only known all-female, asexual species of decapod crustacean. It reproduces parthenogenetically by cloning itself, and is spreading at an alarming rate, out-competing and exterminating other species of crayfish as it goes. It now threatens the existence of seven species of crayfish in Madagascar. The new species came about when two American slough crayfish (Procambarus fallax), imported into Germany for the aquarium trade, mated.

Since it's discovery in Germany in 1995 the marbled crayfish has spread across Europe and into Africa. The European Union has now banned the species from being sold, kept, distributed, or released to the wild. It came to the interest of medical science because there were thought to be similarities in how it clones itself and how cancer cells clone themselves. Frank Lyko, a molecular geneticist at the German Cancer Research Center in Heidelberg, and his colleagues wanted to study the epigenetics of cloning so they sequenced genomes of about a dozen marbled crayfish from different parts of the world and performed less detailed genetic analyses of two dozen more from across Madagascar. Although it contains about the same number of genes, the genome of the marbled crayfish is larger than the human genome, at about 3.5 million DNA bases. Lyko and his team published their findings yesterday in Nature Ecology & Evolution.

The marbled crayfish Procambarus virginalis is a unique freshwater crayfish characterized by very recent speciation and parthenogenetic reproduction. Marbled crayfish also represent an emerging invasive species and have formed wild populations in diverse freshwater habitats. However, our understanding of marbled crayfish biology, evolution and invasive spread has been hampered by the lack of freshwater crayfish genome sequences. We have now established a de novo draft assembly of the marbled crayfish genome. We determined the genome size at approximately 3.5 gigabase pairs and identified >21,000 genes. Further analysis confirmed the close relationship to the genome of the slough crayfish, Procambarus fallax, and also established a triploid AA’B genotype with a high level of heterozygosity. Systematic fieldwork and genotyping demonstrated the rapid expansion of marbled crayfish on Madagascar and established the marbled crayfish as a potent invader of freshwater ecosystems. Furthermore, comparative whole-genome sequencing demonstrated the clonality of the population and their genetic identity with the oldest known stock from the German aquarium trade. Our study closes an important gap in the phylogenetic analysis of animal genomes and uncovers the unique evolutionary history of an emerging invasive species.

Analysis shows that the new species is triploid, i.e. it has three copies of each chromosome instead of the usual two. It is also highly heterogenous, i.e., it often has two or more alleles of each gene rather than three copies of the same allele. It has 276 chromosomes instead of the normal 184 of its parent species, Procambarus fallax. This means it can't reproduce with its parent species or any other related species so is genetically isolated. It is highly fecund and can adapt rapidly to new environment because it will eat just about anything from dead plant matter to small insects, snails, fish eggs and even small fish. There is no wasted energy finding a mate and with the inevitable loss of external fertilisation.

So how does this refute creationism?

Creationists (or at least those who know they can no longer get away with arguing that evolution can't occur at all) claim that evolution can only occur within a species so no new species can arise by evolution. This new species arose by evolution because is was a change in allele frequency and it produced a genetically isolated population that can't interbreed with its parent species or any other related species.

Creationists claim that macro-evolution, i.e., an evolutionary change in a structure or function, can't occur because this needs an increase in genetic information, and this is impossible because no new information can be created. This change involved a fifty percent increase in information due to the genome increasing from diploid to triploid. This allowed a new reproductive function to arise which no longer requires mating or fertilisation of the ovum by sperm.

Creationists claim that all mutations are harmful, resulting in a degradation of genetic information and reduced fitness. This mutation was highly beneficial to the new species, enabling it to out-compete other species and increase rapidly from a single individual.

So, we have a new species which arose recently by mutation. It has fifty percent more information and a new reproductive function. The mutation was hugely beneficial and we know exactly how it arose. Exactly what creationists tell us can't happen so never happens.

The question is, will any creationist accept that seeing something happen refutes their claim that it can't and doesn't happen? Any bets?

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