Rare venomous mammal reveals genetic secrets

Scientists compiling the genome of a rare venomous mammal have been assisted in their quest by the fact that it is extremely inbred.

The bizarre and critically endangered Hispaniolan solenodon (Solenodon paradoxus) has become the latest mammal species to have its whole genome sequenced. The achievement, published in the journal GigaScience, will not only aid in efforts to save the animal from extinction, but will also help answer important questions about mammal evolution.

The solenodon, native to Cuba and Hispaniola, represents an ancient mammal lineage. Analysing the genome, the researchers, led by Taras Oleksyk from the University of Puerto Rico at Mayagüez, conclude that its line diverged from other mammals some 73.6 million years ago.

Despite their superficial similarity to shrews, solenons are only distantly related. They have several unusual characteristics, including a flexible snout that moves courtesy of a ball-and-socket joint, very large claws, and teats positioned at the rear. 

It has venomous saliva, which is delivered along grooves in their incisor teeth.

Venom is an unusual attribute in mammals, but not one confined to a single evolutionary group. As well as solenons, it is found in Australia’s platypus (Ornithorhyncus anatinus), and a few species of shrew. Some definitions also classify the anticoagulants contained in vampire bat saliva as venom.

The case has also been made to include a primate called the slow loris (Nycticebus coucang) in the venom club, but this is contested. The species produces a substance from glands inside its elbows, which, if licked by the loris and then transferred to another species, can induce anaphylaxis.

The rarity of the solenodon and the rugged and remote habitat in which lives posed significant challenges for Oleksyk and his team when it came to gathering enough samples for genetic sequencing. Transporting the samples resulted in considerable degradation, and the laboratory used could only produce limited information from each.

However, the researchers reasoned that because the species had been isolated on a couple of islands for tens of millions of years, it must by now be extremely inbred. That means that genome variation between individuals must be very limited – they are “homozygous”, in the jargon – and therefore the partial information obtained from each sample could be combined and the result seen as accurate for the entire species.