Fruit color polymorphism in a bird-dispersed shrub (Rhagodia parabolica) in Australia

Summary

We examined the selective basis of fruit color, a trait assumed to affect the attractiveness of fruits to avian dispersal agents, inRhagodia parabolica in Victoria, Australia. The fleshy fruits ofR. parabolica are highly polymorphic in color; individual plants may bear red, white, or yellow fruits, or some combination of these. Red color is produced by betacyanins, yellow by betaxanthins, and white by some other flavonoid compounds. Red is the most common color, white less common, and yellow is relatively rare; red and white is the most common color combination. Fruits of these color-morphs do not differ in maximum size, weight, pulp-seed ratio, water content, or content of major nutrients (sugars, N, and lipids). The most common avian consumer,Zosterops lateralis, foraged at random on the color-morphs, although all fruit-eaters, collectively, slightly favored white fruits. Weekly fruit removal rates were equivalent for all four morphs. Seeds from color-morphs differed in seed germination behavior: seeds from red fruits germinated faster than seeds from yellow fruits, and seeds from white fruits showed the greatest response to passage throughZ. lateralis guts. Lack of strong foraging preferences by birds and the different germination behaviors may contribute to the maintenance of the color polymorphism.