What’s the Difference between a Species and a Variety?
– November 29, 2011Posted in: Animals and Plants, Conservation, Conservation at the Zoo, Plants, Uncategorized
Wild buckwheat Eriogonum fasciculatum
Miguel Kaminsky and Lauren Anderson are interns at the San Diego Zoo Institute for Conservation Research through the Bureau of Land Management’s Seeds of Success Program. As part of the internship, they make collections of seeds from plant species vital to southern California habitats. The seeds will be preserved and studied and eventually help restore habitats damaged by fire or during development projects.
This internship has provided a lot of new experiences and opportunities for learning. Specifically, events during the collection of wild buckwheat Eriogonum fasciculatum seeds at El Capitan Open Space Preserve compelled me to review some basic biological concepts regarding speciation. The whole exercise began when Lauren and I went on a seemingly routine mission to collect Eriogonum seeds. By the time we each filled a quarter of a bucket with seeds and associated material, Lauren pointed out extensive variation in the leaf morphology of the plants we were collecting. Some plants had linear, light green leaves while others had much wider, blue-green leaves with an almost woolly layer of flattened hairs. To make matters more confusing, some plants had shoots exhibiting both leaf types. This made us think there was hybridization of some sort going on, so we decided to do some further research before packaging this collection to ensure we had seeds from just one species.
Upon consulting a plant atlas, we learned that there are three varieties of Eriogonum fasciculatum in the area we were sampling. These are var. fasciculatum, var. foliolosum, and var. polifolium. Var. polifolium has the wider, oblong, woolly leaves while var. foliolosum has the linear leaves that aren’t nearly as woolly on their upper surface. In turn, we inferred that the individuals we encountered were vars. foliolosum, polifolium, and mixes of the two.
Although we determined the collection was not useful to us because we needed seeds with a varietal lineage free of comingling, this left me with some fundamental questions. Why aren’t these morphologically distinct populations classified as different species? What is the difference between a species and a variety?
Lauren Riesberg, in her extensive writings addressing speciation and hybridization, cited Mayr’s definition of a species as “groups of interbreeding natural populations reproductively isolated from other such groups.” However, species that are not geographically isolated have been known to interbreed and produce hybrid offspring. Wikipedia defines a variety as a genetically, and in turn, morphologically distinct subset of a species that is geographically isolated from other populations within that species. However, when the geographic barrier is removed, this subset interbreeds with the rest of the species, resulting in an influx of genes that erodes the variety’s distinct features, thus reintegrating it into the greater species group. With this in mind, I distinguish species and varieties based on the fact that a hybrid of two species produces offspring with reduced fertility, such as malformed pollen grains, while a hybrid of two subspecific varieties produces offspring that show no such deformities and reflects the traits of the original species.
El Capitan Open Space Preserve
In light of these considerations, I came to the conclusion that the El Capitan Open Space Preserve is a very special place in the origins and family history of Eriogonum fasciculatum. According to “Flora of North America,” Eriogonum fasciculatum var. folilosum came about from an ancient hybridization event between vars. fasciculatum and polifolium. This event likely happened at places much like the El Capitan Open Space Preserve, where these populations intermingle. Eventually, isolated populations of these varieties might inbreed to the point that they become reproductively isolated from the parent varieties, giving rise to new species through divergent evolution.
El Capitan offers a living snapshot into the evolutionary history that drives speciation. In conclusion, this experience reminds me that speciation is a dynamic process taking place in our backyards, in present times, while we go about our daily lives.
