Drivers of polymorphism dynamics in pygmy grasshoppers

Sammanfattning: In this thesis, I used colour polymorphism in pygmy grasshoppers as a model system to study the influence of selection, developmental plasticity, mating behaviour and gene flow on patterns of phenotypic and genetic diversity within and among populations in changing environments.Data for more than 5,000 individuals collected from natural populations showed that the incidence of black (melanic) pygmy grasshoppers was higher in burnt than in non-burnt areas, and rapidly declined over time within populations in post-fire environments. A common garden experiment confirmed that differences among populations were genetically determined. A split brood experiment further uncovered no developmental plasticity in response to rearing substrate, but a high resemblance between mothers and their offspring thus indicating that colour morphs are under strong genetic control.To investigate the role of polyandry, I experimentally mated virgin females to multiple males; genotyped families using microsatellite markers developed for this purpose, and demonstrated that polyandrous females can produce offspring sired by different males. Analysis of families produced by females collected from a natural population confirmed that multiple paternities can increase colour morph diversity among half-siblings in the wild. Analysis of 130 AFLP (Amplified Fragment Length Polymorphism) markers in individuals from 5 localities uncovered two distinct gene clusters, as well as high genetic diversity within and significant divergence among populations within each cluster.My studies of colour polymorphism dynamics demonstrate an important role of population differentiation and rapid adaptive evolution in response to selection in heterogeneous environments, indicate limited effects of plasticity and gene flow, and implicate multiple mating as promoting diversity within populations in this pygmy grasshopper system.