In the fall, many plants in western Oregon (and elsewhere) produce brightly-colored fruits. These attract fruit-eating animals, which eat the fruits and move their seeds to new locations, potentially better sites for germination and survival. By and large, such fruits are red, blue, or purple – colors that contrast with surrounding vegetation and appeal to birds, but snowberries (Symphoricarpos albus) buck the trend, producing white fruits about the size of huckleberries that dangle on the ends of flimsy stems.
Why are snowberries white when so many other plants produce red berries? If the red of other fruits has been selected to enhance seed dispersal by birds, maybe the white of snowberry has been selected for dispersal by another agent. In the tropics, white or green fruits are commonly eaten by bats. Flying through a dark forest, a bat may detect a white fruit more easily than a red one, particularly if it has a strong odor and is hanging at the end of a long branch. Unfortunately, there are no tropical fruit bats in western Oregon*, but there are nocturnal fruit-eaters. Perhaps woodrats or flying squirrels cue in on snowberries.
Alternatively, snowberries might be white because why not? Presumably red fruit pigmentation exacts some energetic toll from plants, so all else being equal, a white fruit should cost less than a red one. Pheasants and turkeys appear content to eat unadorned snowberries, and some of their seeds are able to germinate following gut passage**. Selection on snowberry’s dispersal mechanism may also be weaker than for other plants; S. albus seems to reproduce more commonly via spreading rhizomes than from seeds.
*Though a vampire bat in the same family existed in northern California during the Pleistocene.
**Based on the results of a seed viability study from turkey feces conducted by Sara Evans-Peters at OSU.