Some sea stars can reproduce both sexually and asexually through cloning. Propagating sexually offers more genetic variation, but according to a recent Heredity study, sea stars seem to avoid aging to some extent when they clone themselves instead.
Telomeres, the little caps at the ends of chromosomes, shorten as cells divide over the course of an organism’s life. Researchers have been using telomeres as a marker of both aging and health. In sexually reproducing species like us, telomere length is "restored" during the embryo’s development. But little is known about aging in asexual organisms that propagate by budding or fission: Does the new animal have restored telomeres? Previous work with flatworms in the lab revealed that clones avoid aging by regulating telomeres.
To see if this holds true in wild populations, a team led by Álex Garcia-Cisneros from the University of Barcelona compared the telomere lengths of 58 Coscinasterias tenuispina sea stars from four populations in the Atlantic Ocean and the Mediterranean Sea. When these stars divide or fragment themselves into multiple parts, new parts regenerate.
The team also used 12 individuals to compare telomere lengths in two different tissues – tube feet (for climbing) and pyloric cecum (for digesting) – from both regenerating and non-regenerating arms.
Sea stars in the Mediterranean were smaller and more inclined to clone themselves, while those living in the Atlantic were bigger and tended to reproduce sexually. The team found a clear link between telomere length and the level of clonality: The Mediterranean populations sported longer telomeres, while those of the Atlantic sea stars were shorter.
"We also noted that the telomeres were longer in the newly formed tissue than in the 'old' tissue in the same starfish," study coauthor Helen Nilsson Sköld from the University of Gothenburg said in a statement. The formation of new tissue during cloning seems to rejuvenate the telomeres.
Images: University of Gothenburg (top), A. Garcia-Cisneros et al./Heredity 2015 (middle)