The Unexpected Origin of Marbled Crayfish: An Accidental Process Leading to a New Species
Background: I run the Crustacean Chronicles website and have published a few scientific papers about marbled crayfish. These animals are fascinating and I've come to know them well through my research.
Crustaceans, such as crayfish, can be found in a wide variety of habitats, from shallow lakes to deep oceans. While most crustaceans have two sets of chromosomes (2n), the marbled crayfish (Crystal Cave Marbled Crayfish) is a remarkable exception. It is a triploid species (3n), meaning it has three sets of chromosomes.
The Accident
The marbled crayfish species came into existence through a series of unexpected biological events. The origin story begins with the accidental fertilization of an egg from the Russian sturgeon by the sperm of the Paddlefish. This rare fusion led to the creation of the "Sturdlefish," a term coined to describe the resulting offspring. However, the Sturdlefish was not chosen to be the focus of this article. Instead, the focus is on the Marbled Crayfish, which emerged from a similar, albeit more common, biological phenomenon.
Marbled crayfish, abbreviated as 3n, have three sets of chromosomes. Most animals have two sets (2n). During the process of cell division, chromosomes normally divide to form one set of chromosomes in each resulting cell. However, in some rare cases, something goes wrong during this division, resulting in a sperm or egg cell with double the normal number of chromosomes (2n). When such a cell fertilizes a normal egg (1n), the resulting offspring has three sets of chromosomes (3n).
What makes the Marbled Crayfish remarkable is that this triploid state developed into a fully reproductive adult. This is described in the technical term autopolyploidy, a phenomenon that is relatively common in plants but less so in animals. In the case of the Marbled Crayfish, this autopolyploidy event is thought to have led to “instant speciation”—a rare and rapid process where a new species emerges from a single event.
The Technical Details
Autopolyploidy has been documented in humans as well, but in a far less remarkable manner. A triploid human abortus due to dispermy (the fertilization of one egg by two different sperm cells) has been documented. However, this condition did not allow the organism to survive beyond a very early stage in development.
The Timing of the Event
The exact time when the Marbled Crayfish originated is uncertain. Strictly speaking, nobody knows for sure. However, we can make some educated guesses based on the observations of the closely related species, the Slough Crayfish.
People who study the Slough Crayfish have always seen a 50-50 split of males and females. If the Marbled Crayfish had existed before the mid-1990s, this would be quite notable, as such a mix of genders is not typical for other crayfish species.
Another clue comes from genetic similarity among individuals. If the split happened long ago, you would expect more diversity among lineages. However, the individuals are genetically very similar, suggesting that the event might have been as recent as the mid-1990s. Even in cloning, mutations happen and accumulate at a low rate. So, if the split happened long ago, the expected diversity among lineages would be present.
Conclusion
The Marbled Crayfish's origin remains a mystery. It’s a fascinating example of nature’s unpredictable and adaptive processes. Whether it emerged 25 years ago or later, the speciation event that created this unique animal is a testament to the complexity and marvel of biological evolution.
As researchers continue to study these fascinating creatures, we may uncover more secrets about the Marbled Crayfish and its origins.