Science Matters – week 36

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Scary mutants

The multi-million dollar international trade in exotic pets has long been a bugbear of mine.

Not only does it promote wild animals as (eminently unsuitable) fashion accessories, but it also allows potentially dangerous microbes to jump to, and cause epidemics in, other species including humans. What’s more, even if they don’t mutate as occurred in the case outlined here, if released into the wild either by design or mistake these foreigners can cause havoc to local ecosystems.

In a letter to the scientific journal Nature in 2003, a group of German scientists began ‘it has been rumoured that an unidentified crayfish…of marbled appearance and uncertain geographical origin that was introduced into the German aquarium trade in the mid 1990s, is capable of unisexual reproduction (parthenogenesis)’.

The authors ended by warning that: ‘This crayfish…could become a menace to European freshwater systems, as the release of even one specimen into the wild would be enough to found a population that might out-compete native crayfish’.

Now, 23 years later, this all-female crayfish has escaped into the wild.  Identified as a descendent of the fresh water slough crayfish from Florida, it is now called the marbled crayfish or Marmokrebs. So far it has invaded the waterways of at least nine European countries as well as Japan and Madagascar. Unravelling its origin reveals that a unique macro-mutation must have occurred in a single slough crayfish egg; probably caused by heat or cold shock whilst in transit from Florida to Germany for the pet market.

The resulting female hatchling possessed three sets of chromosomes per cell (triploidy) and the ability to produce clones of itself without a mate and at very high frequency.

Because of its warm climate and abundant freshwater habitats, Madagascar has seen the most rapid colonisation with Marmokrebs. Millions of the animals have invaded the countries lakes, rice paddies and swamps and are threatening its seven endemic crayfish species.

It is only a matter of time before this scenario is repeated in other locations, destroying valuable ecosystems and eliminating indigenous species.