Do you eat the red ones last? I’ve often wondered why some Rubus spectabilis berries are red and some are yellow, so I thought I would write an entry that answers the question.
Rubus spectabilis is a polymorphic species. That is, there are multiple phenotypes, or visible genetic traits, that occur within the same population, and members with different phenotypes (red or yellow berries) are able to breed freely. This characteristic is similar to the variability in hair colour found in people of European descent. In fact, polymorphism is very common in the natural world: sexual dimorphism, or the differences between males and females of a species, is another example.
Polymorphism arises when a genetic mutation occurs within an individual (or individuals), and is spread through a population. In the case of Rubus spectabilis, we do not know which morph was the original and which was the mutation. It is also unclear which factors allowed both morphs to become fairly evenly represented through the species’ western North American range.
In order to better understand why Rubus spectabilis displays fruit-colour polymorphism, I turned to an article written by Anna Traveset and Mary Willson, titled Ecology of the Fruit-Colour Polymorphism in Rubus spectabilis. The two ecologists examined the effects of fructivore preference, seed dispersers, soil type, and seed predation on the yellow and red morphs. They found that a greater number of fruit-eating birds preferred red berries to yellow, but that overall this preference was minor and unlikely to exert a strong selective pressure. Seed dispersers and seed predation had no effect, but soil type was a key factor in determining the germination, and therefore the range for each morph. Overall, soil type (likely coupled with other, unstudied factors) determines whether an area is likely to have more red or yellow-berried Rubus spectabilis plants.
To answer the question I first posed–I do eat the red ones last. I find that along my heavily-used urban trail, the red salmonberries are picked much more frequently than the yellow ones. Whether my fellow trail-walkers prefer the red ones or just don’t realize the yellow berries are ready, I am not sure, but I am quite happy to eat my fill of juicy, golden berries while everyone else searches high and low for the red ones.
For those of you on the west coast of North America, salmonberry season is upon us! Let me know if you manage to try out this recipe for salmonberry pie.