April 10 2013

12:00 LSB 2320

Robert Vrijenhoek
Senior Scientist, Monterey Bay Aquarium Research Institute

Resolving sexual conflicts: the evolution of bone-eating worms with dwarf males


Bone-eating Osedax worms were first described in 2004 from Monterey Bay, CA. We are now aware of at least 19 species worldwide. Osedax exhibit extreme male dwarfism. The males are arrested metatrochophore larvae that live on stored yolk and start making sperm after they colonize the host females. Male dwarfism reduces sexual competition for limted food resources, sunken bones. The sexes are hypothesized to be environmentally determined, based on where the worm larvae first settle. Those settling on bones develop as females and those settling on females transform into dwarf males. Fifteen species known to occur in Monterey Bay tend to segregate partially by depth (above and below 1000 m) and by stages of bone decomposition. Some Osedax species are early colonizers of bones and others dominate later stages of bone decomposition. Osedax do not depend entirely on whale bones, as they can also grow on fish, turtle, bird, seal and terrestrial mammal bones. Lacking mouths and digestive tracts, the females grow invasive "roots" that digest bones to extract organic compounds. Endosymbiotic bacteria that aid in nutrition infect the developing females after they settle on bones. The genomes of two symbiont phylotypes are now sequenced, providing insights into their respective physiological roles. Fossil evidence indicates that Osedax were already involved in degrading whale and flightless bird bones during the Oligocene. However, alternative molecular evidence suggests that Osedax might have arisen during the Cretaceous before the origin of large marine mammals. Fossilized bones from Cretaceous marine reptiles and late Oligocene cetaceans should be examined to test the latter hypothesis.















































































































































































































































































































































































































































































































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