This New Scientist article (Michael Marshall, 28 April 2011) on the interbreeding of shrews despite the fact that their chromosomes have been rearranged does not use the “biological species concept” (it’s hard to know how to do so under the circumstances). Stuck for a term, Marshall calls the differently arranged groups “races” instead. Anyway,
Searle of Cornell University in Ithaca, New York, and colleagues studied two neighbouring races in Siberia. Despite the shrews’ different chromosome Jeremy arrangements, they manage to interbreed. Their hybrid offspring are less fertile than their parents, however.
That’s because the offspring do not have matching pairs of chromosomes, so it is hard for them to make eggs or sperm that have the full complement of genes. But although their fertility is lower, it isn’t zero: they can still have litters of their own. Somehow they are able to assemble up to nine chromosomes in the centre of a dividing cell, and pull them apart one by one in the right way to make viable sperm and eggs. “I think it’s fairly astonishing that they manage it,” Searle says.
Eventually the different races may become separate species. Searle says there are shrews that look just like the common shrew, but do not breed with them – and the only difference is how they arrange their chromosomes.
But are we missing something here? Does anyone remember when the concept of “species” was meaningful?