Captain Phasmatodea and the Attack of the (Not Really) Clones

Star Wars excitement just won’t seem to quit for our Life Sciences Team. Several of us have commented that the Imperial Storm Troopers seem to come in two flavors: clone and not-clone. Simple. But for the Phasmatodae, it’s complicated.

Phasmatodea is the group of insects that include all the stick insects. Here at Pacific Science Center you can see three representatives, Medauroidea extradentata and Lonchodiodes samarensis (Vietnamese and Samar stick insects) and Extatosoma tiaratum (Australian prickly sticks).

Some species of stick insects can reproduce without males, a process called parthenogenesis. Our Vietnamese stick insect population has not produced a male in years.

This is a fast way for a female to make her own “clone army”, producing large numbers of offspring without the risks and lost energy of seeking a mate. For an insect with an abundant food source, this lets her colonize it faster. So why do some of their near relatives go through the entire mating thing?

It turns out that the stick insects’ process is little more complex and varied than creating identical clones as single cells do (or sea anemones). The female doesn’t make duplicates of herself, but instead generates a bit of diversity by creating eggs with different combinations of her own chromosomes. Like shuffling the same cards again and again, she will produce many combinations. As long as the combinations fit the environment, this is a speedy and efficient system.

But there is no room for new genes to be introduced. Over time, species that become parthenogenic become less and less able to mate and get locked into their reproductive pattern. When the environment changes, it may be harder for these species to adapt, as they have a smaller group of genes to draw on. Under such circumstances, a similar species that reproduced sexually might prevail.

Again, it’s complicated.

For the in depth story please see the following articles:

http://phasmid-study-group.org/sites/phasmid-study-group.org/files/More1996.pdf

http://link.springer.com/article/10.1007%2FBF00328476

http://rspb.royalsocietypublishing.org/content/280/1764/20130823.abstract