Maintenance of diapause variability in the two‐spotted spider mite, tetranychus urticae, in a heterogeneous and stochastic environment

Abstract

AbstractA simple nongenetic mathematical model analyzed the processes responsible for the variations in the diapause percentage among populations of the two‐spotted spider mite, Tetranychus urticae Koch. This model incorporates the following assumptions. 1) Mites have diapause (DD), non‐diapause (NN), and “plastic” (DN) populations (plasticity exists in the phenotypic expression of diapause in response to habitat conditions at the time of diapause induction). 2) A heterogeneous mite habitat consists of microhabitat L, in which all the non‐diapausing mites die during the winter due to the lack of winter host plants, and microhabitat O with winter hosts capable of supporting some of the non‐diapausing mites overwinter. 3) Temporal fluctuation of winter conditions which affect the survival and reproduction of non‐diapausing mites. Using these assumptions, we compared the fitness functions of the three populations and analyzed the conditions under which each population is favoured over the other two, thereby elucidating the processes involved in the maintenance of variability in diapause. Our analysis revealed: 1) frequent mild winters are of primary importance for the non‐diapause trait to be maintained, 2) the existence of winter hosts is also important for the nondiapause trait to be favoured, and this importance depends greatly on the degree of the adaptive diapause expression in the DN mites in response to habitat conditions, i.e., the better the phenotypeenvironment matching in DN, the higher the probability that DN will be favoured, 3) The combined effect of the temporal and spatial variation enhances the maintenance of variablity in the diapause trait of the mites.