The New York Times has an informative and thoughtful article by Sean Carroll about interspecific hybrids this week. The article starts with photographs of a range of remarkable animal hybrids, then moves on to the science and evolutionary implications with plants and insects. The article quotes James Mallet as saying that perhaps 10 percent of animal species and up to 25 percent of plant species can form hybrids between different species, although, like the Crocus hybrid shown above, most do not produce seeds and must be multiplied vegetatively (in situ hybridization by Farah Badakshi in my lab, following work by Marian Orgaard published here).
Although inability to form interspecific hybrids is often quoted as a definition of a species, this is frequently not the case! Hybrids that are sterile are most likely to be evolutionary dead-ends, even if successful locally and for many decades.
However, other hybrids, particularly when the chromosome number doubles, may give rise to new species – speciation – and have selective advantages over the parents, often colonizing new areas. Wheat, named Triticum aestivum, derived from three ancestors, is a particularly well known example.
The New York Times article discussed sunflower (Helianthus species) hybrids, and has quotations from Loren Riesenberg, University of British Columbia, Editor of Molecular Ecology, and co-author of this month’s freely available review on “Speciation genes in plants” in Annals of Botany.