Lauren Vandepas: "Behold, comb jelly poo!"
The ctenophore (comb jelly) species used in this study
were the lobate ctenophore Mnemiopsis leidyi
and the cydippid Pleurobrachi bachei.
In a study published in Current Biology this year, my colleagues and I demonstrated that comb jellies do, in fact, definitely poop. They have an anus! They’re even overachieving in the anus department – they have two anal pores. At the University of Miami Professor Bill Browne and his grad student, Jason Presnell, saw ctenophore pooping in action while they were observing their animals. While taking a larval invertebrate class in Panama, my course mini-project on how ctenophore larvae feed went in an unexpected direction when I watched the larvae expel digested shrimp through their anal pores. What. We discussed these odd observations we’d made, and after seeing how varied the literature was with respect to what the heck ctenophores are using their aboral pores for, we decided to tackle the mysterious “poo” problem.
|Diagram showing ctenophore digestion in three parts: |
ingestion of prey, break-down and distribution of digestible food,
and expulsion of undigested wastes.
Bill, Jason, and I wanted to show that two different ctenophore species that aren’t closely related use their anal pores in the same way – as anuses. We fed the jellies fluorescent shrimp or fish and watched the food pass through the ctenophores’ guts and out the anal pores. Behold, comb jelly poo! Ctenophores have a mouth on one end and anal pores at their other end – a through-gut! Demonstrating that through-guts aren’t just for bilaterian animals raised some interesting questions about when through-guts appeared during animal evolution. It’s already widely thought that this trait arose separately several times in different lineages within bilaterians. Ctenophores split off way before bilaterians evolved – do they have the same type of through-gut as bilaterians? Are ctenophore through-guts built in the same ways as bilaterians’ during embryonic development? Is this another independent evolution of the through-gut? We don’t yet have an answer for how homologous the ctenophore through-gut is to other animals’, but we’re looking at what genes ctenophores use to form their gut during development, and examining their digestive cells for clues.
Contrary to the popular belief that “Everybody Poops”, not all animals can – but ctenophores definitely do.