Sexless Starfish Reveals Why Sex Is So Great

//

We examine the dire state of perhaps the most interesting and diverse part of our planet.
iStockphoto.com/sweetlifephotos

Single parenting takes on new extremes for certain starfish that are hermaphrodites -- male and female at the same time and, in some cases, self-fertilizing. The species faces high risk of extinction, according to new research.

The dire situation faced by the non-mating starfish, Parvulastra parvivipara and Parvulastra vivipara, helps to explain why so many organisms, including humans, have sex. Genetic diversity and the dispersal of youngsters support population growth.

PHOTOS: Life on the Ocean Floor Garbage Patch

The plight of the starfish, documented in the latest issue of the journal Biology Letters, reveals how a life without sex but with self-fertilization could result in eventual oblivion.

“There are quite a few reasons why these species are vulnerable,” senior author Michael Hart of Simon Fraser University’s Department of Biological Sciences told Discovery News. “The whole species could be wiped out.”

Hart and his team studied the starfish, which are restricted to high intertidal pools of South Australia and Tasmania. These starfish also go by the nickname "sea cushions," since they look a bit more like a cushion than a star when viewed from the side.

Most adult starfish of other species do reproduce via a separate male and female. Females usually produce eggs that males fertilize in the seawater. At that point, the fertilized eggs develop and grow before becoming little starfish that will attach themselves to the substrate and start the whole process over again.

The extreme self-parenting starfish often have no such male-female interaction.

As a hermaphrodite, the individual produces its own eggs, which are then fertilized right inside the body, likely with that same individual’s own sperm.

“The fertilized eggs are not sent out into the environment for development, and instead the parent keeps the developing embryos inside its body, where they complete their embryonic development and become juvenile sea stars (starfish),” Hart explained.