Amidst the animal kingdom’s menagerie of sexual practices, those of Corbicula clams stand out.
A common freshwater genus about the size of a half-dollar, nearly all Corbicula species are clones. That’s odd, albeit not extraordinary. They’re also physically hermaphroditic but genetically male — again odd, but not extraordinary.
What’s really strange is that, once in a great while, they hijack fresh DNA from other clams.
“They can steal the eggs of other species,” said David Hillis, a University of Texas at Austin computational biologist whose Corbicula investigations are described May 23 in the Proceedings of the National Academy of Sciences. “Usually, the whole maternal genome is then kicked out. But sometimes they keep some of the genes, and incorporate them into their own genome.”
At a glimpse, Corbicula reproduction seems to be of the unexceptional, sperm-meets-egg-in-the-water marine variety. But in most cases, sperm and egg come from the same clam, which produces both. Then, after fertilization, egg genes are ejected from the embryo. Should currents happen to mix sperm and egg from different clams, the same happens. In either case the result is a clone descended from one original clam’s sperm.
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