Contrary to conventional wisdom, non-parasitic invertebrates such as sea cucumbers can clone themselves, biologists in Alberta have found.

After more than 100 years of observations, scientists had thought the tiny sea creatures only rarely reproduce.

Now researchers have determined that three new groups of echinoderms – sea cucumbers, sand dollars and sea urchins – can spontaneously clone themselves.

Sea urchin larva with a clone (ball on bottom) about to separateCourtesy/copyright: Alexandra Eaves

Prof. Richard Palmer of the department of biological sciences at the University of Alberta and graduate student Alexandra Eves describe their findings in Thursday's issue of the journal Nature.

Larval echinoderms usually swim and feed for several months before switching into miniature adult form.

Palmer and Eves watched hundreds of larvae form a ball of tissue that pitched off, growing into a second creature: a clone.

Adult sea urchinCourtesy/copyright: Alexandra Eaves

"These data make it clear that people have likely seen this spontaneous cloning for many years but have not recognized it," said Palmer.

"This is a dramatic example of what terrifies scientists the most – when you see things with your own eyes but refuse to acknowledge it. It's a classic example of how deeply held beliefs may actually prevent you from seeing things."

The pair found cloning in up to 12 per cent of lab-reared sea cucumber larvae and 10 to 90 per cent of sea star larvae from the field.

They suggest larval cloning may offer three potential ecological advantages:

• help increase fertility under ideal conditions
• increase chances of settlement after the larval stage
• recycling of larval tissue

At least one earlier report of larval cloning was dismissed as a lab culturing error.

Eaves says larval cloning may have helped echinoderm diversity to persist over hundreds of millions of years.

The researchers point out that since acorn worms are the nearest relatives of echinoderms, scientists should test if their larvae can clone themselves.

The research was sponsored by the government of Alberta and the Natural Sciences and Engineering Research Council of Canada.