6.8. Polymorphism and polyphenism
The existence of several generations per year often is associated with morphological change between generations. Similar variation may occur contemporaneously within a population, such as the existence simultaneously of both winged and flightless forms (“morphs”). Sexual differences between males and females and the existence of strong differentiation in social insects such as ants and bees are further obvious examples of the phenomenon.
The term polymorphism encompasses all such discontinuities, which occur in the same life-history phase at a frequency greater than might be expected from repeated mutation alone. It is defined as the simultaneous or recur- rent occurrence of distinct morphological differences, reflecting and often including physiological, behavioral, and/or ecological differences among conspecific individuals.