Marmorkrebs, giant marbled crayfish

In 2018, scientists reported that the giant marbled crayfish (Marmorkrebs [German]: Procambarus fallax f. virginalis) recently developed the strategy of being entirely female and cloning itself via parthenogenesis¹; the female doesn’t require a male crayfish to fertilize its eggs. Despite the cloning procedure that makes them virtually identical genetically, the crayfish vary in size and pattern—no doubt due to epigenetics.²

First discovered by a German aquarium in the mid-1990s, these crayfish that developed from Florida-Native crayfish have migrated into the wild and are aggressively spreading in Europe, at the expense of the native European crayfish. The 8 to 12 cm long Marmorkrebs has been observed in Germany, Italy, Slovakia, Sweden, Japan, and Madagascar. The marbled crayfish prefers a warm and humid climate, suggesting that climate change may influence its distribution and success. The clones also thrive in a wide range of habitats—from abandoned coal fields in Germany to rice paddies in Madagascar, writes Carl Zimmer of the New York Times.

Given that every individual Marmorkrebs can reproduce (the advantage of parthenogenesis is that the female crayfish doesn’t need to find a mate—it just gives birth), one European scientist has dramatically suggested that, “we’re being invaded by an army of clones.” Zimmer shares the results of Dr Lyko and his team on how the all-female Marbokrebs came to be:

“Scientists concluded that the new species got its start when two slough crayfish mated. One of them had a mutation in a sex cell — whether it was an egg or sperm, the scientists can’t tell. Normal sex cells contain a single copy of each chromosome. But the mutant crayfish sex cell had two. Somehow the two sex cells fused and produced a female crayfish embryo with three copies of each chromosome instead of the normal two. Somehow, too, the new crayfish didn’t suffer any deformities as a result of all that extra DNA.” 

In its first couple decades, [Marmorkrebs] is doing extremely well, writes Zimmer. But sooner or later, the marbled crayfish’s fortunes may well turn, he adds. “Maybe they just survive for 100,000 years,” Dr. Lyko speculated. “That would be a long time for me personally, but in evolution it would just be a blip on the radar.”

Marmorkrebs

But what if this speculation isn’t the whole scenario? What if Marmorkrebs is just another example of climate change-induced adaptation and change through epigenetics? While climate forcing and habitat destruction is causing the extinction of many species; other species are, no doubt, adapting and exploiting the change. These generalists (born with change inside them) are poised to take over in Nature’s successional march.³

Bdelloid rotifer

Parthenogenesis and epigenetic change isn’t new. In fact, it’s very old … All-female bdelloid rotifers have been cloning a sisterhood for millions of years and using incorporated foreign genes through horizontal gene transfer4 (essentially stealing genetic material from their environment) to maintain a healthy diverse population. What’s new and weird is that this crayfish “suddenly” developed this ability—probably through epigenetic means (given this entire group is versatile in reproductive strategies in general). The real question none of the articles that covered this phenonemon ask is: WHY? Why is it happening NOW?

In my latest book “A Diary in the Age of Water” (due for release in May 2020 by Inanna Publications) I explore this “change” in a unique way:

Kyo finds a copy of Robert Wetzel’s Limnology on a lower shelf of the “L” section. It stands tall with a thick green-coloured spine. This is the book that Hilda, one of the Water Twins, had saved from the book burnings of the Water Age. A present from her limnologist mother. Hilda kept it hidden under her mattress. When CanadaCorp police burst into their home and dragged her mother away, Hilda was left alone with Wetzel. The limnology textbook was forbidden reading because its facts were no longer facts. 

After some coaxing, Myo shared a most bizarre tale of that time which led to the catastrophic storms and flood. What the governments hadn’t told their citizens—but what each citizen felt and knew—was that humans had lost the ability to reproduce. Then a spate of “virgin births” throughout the world spawned what seemed a new race of girls—‘deformed’, blue and often with strange abilities. Many considered them abominations, a terrible sign of what was in store for humanity—a punishment for their evil ways. Then, as quickly as they’d populated the world, these strange blue girls all disappeared without a trace. They simply vanished and became the Disappeared. Myo told her that some people called it a Rapture, a portent of the end times. Others suggested that the girls had all been murdered—a genocide, organized by what was left of the world government. 

Then … the storms … changed the world.

–“A Diary in the Age of Water” 

1. Spontaneous Parthenogenesis: From the Greek Parthenon “virgin” and genesis “creation”, parthenogenesis is a natural form of asexual reproduction in which growth and development of embryos occur without fertilization. In animals it involves development of an embryo from an unfertilized egg; in plants it proceeds through apomixis. The production of only female offspring by parthenogenesis (such as with bdelloid rotifers) is called thelytoky.
2. Epigenetics is the study of changes in organisms caused by the modification of gene expression (such as environmental triggers) rather than alteration of the genetic code itself. If genetics represents the hardrive of a computer, epigenetics is its software.
3. Niche (the role or job of an organism or population) can be broad (for generalists) or narrow (for specialists). A specialist has superior abilities to exploit the narrow environmental conditions it lives in and is splendidly adapted to a fixed stable environment; generalists, less successful at exploiting than the specialist but more widely adaptive, can thrive in less stable environments that present a wider range of conditions.
4. Horizontal gene transfer is the movement of genetic material between organisms other than by the vertical transmission of DNA from parent to offspring through reproduction. HGT is an important factor in the evolution of many organisms.

A Diary in the Age of Water will be released in May 2020 by Inanna Publications, Toronto, Canada.

Nina Munteanu is a Canadian ecologist / limnologist and novelist. She is co-editor of Europa SF and currently teaches writing courses at George Brown College and the University of Toronto. Visit www.ninamunteanu.ca for the latest on her books. Nina’s bilingual “La natura dell’acqua / The Way of Water” was published by Mincione Edizioni in Rome. Her non-fiction book “Water Is…” by Pixl Press (Vancouver) was selected by Margaret Atwood in the New York Times ‘Year in Reading’ and was chosen as the 2017 Summer Read by Water Canada. Her novel “A Diary in the Age of Water” will be released by Inanna Publications (Toronto) in June 2020.