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Dr. Richard Palmer, University of Alberta – Barnacle Reproduction

In today’s Academic Minute, Dr. Richard Palmer of the University of Alberta reveals a surprising find about how some barnacles reproduce.

Richard Palmer is a professor of biology at the University of Alberta where his research interests include Comparative and experimental studies of biological asymmetries, developmental plasticity, and the evolution of marine invertebrates. His ongoing research projects are focused on understanding developmental plasticity in starfish tube feet and body form and mating behavior in gooseneck and acorn barnacles. He earned his Ph.D. at the University of Washington.

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Dr. Richard Palmer – Barnacle Reproduction

You would think that after 200 years of intensive study, barnacles wouldn’t yield any more big surprises.  But they do.  Recent research from the Bamfield Marine Sciences Centre on Canada’s rugged west coast, has yielded another huge surprise that changes the way we think about how crustaceans mate. 

Ever since Darwin spent 8 years of his life studying barnacles — as he postponed writing the Origin of Species — they have fascinated biologists.  They are exceedingly peculiar crustaceans, related to crabs & shrimp, that are glued to the rocks unable to move.  Think of a shrimp-like animal, attached on it’s back inside a ring of shell plates, kicking food out of the water into its mouth with its legs.  Add to this a curious fact about barnacles:  like other crustaceans they must copulate to mate. 

This leads to the first big barnacle surprise.  Because they must reach a neighbor to mate, they have some of the longest penises, relative to their body size, of any animal.  In some species it can be up to 8 times the body length.  But what happens when one barnacle is too far away from a neighbor to copulate? 

Gooseneck Barnacles

Textbooks tell us they then self-fertilize, which is certainly possible as they are hermaphrodites.  But DNA evidence has revealed a second big barnacle surprise.  Marjan Barazandeh and her colleagues found that one gooseneck barnacle has a third way of mating:  sperm capture from the water.  Solitary barnacles were found to carry many eggs that they did not fertilize themselves.  Therefore they must have captured sperm from the water.  This so-called spermcast mating happens in some other marine invertebrates like sponges, corals, clams, and sea squirts, but no biologists ever thought it happened in crustaceans.  This simple observation that one species of barnacle can capture sperm from the water overturns a century of beliefs about what a barnacle, or for that matter any crustacean, is capable of when it comes to mating.

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