Wing dimorphism as an adaptive strategy in water‐striders (Gerris)

Abstract

Several hypotheses have been suggested to account for the adaptive significance of the different wing morphs in water‐striders (Gerris, Heteroptera). Stability and isolation of population sites should favour short‐wingedness; increased rates of population extinction should increase the fitness of the long‐winged individuals. Further, if the populations are often resource (food) limited, dimorphism may be optimal. Combinations of other selective pressures can also produce local dimorphism, which need not be optimal — dimorphism can result from mixing of individuals from different population sites. The term morphism cycle is coined to express a cyclical change: when a region (comprising a great number of population sites) is initially colonized, long‐wingedness is favoured, but short‐wingedness becomes more advantageous after the colonization phase. However, if the populations become totally short‐winged, they probably face a relatively high risk of extinction, and the cycle may begin anew. The ecological genetics of the Finnish water‐striders (nine species) is discussed in connection with the numerous predictions suggested by the original cluster of wing‐dimorphism hypotheses. © 1976 Mendelian Society of Lund