Life-history evolution in spatially heterogeneous environments,with and without phenotypic plasticity

Summary The formulation of Kawecki and Stearns (1993) adapted for sexual populations is used to characterize lifehistory evolution in spatially heterogeneous environments comprising a number of distinct habitats. Three types of evolutionary outcome/optimal strategy are distinguished, appertaining to populations with phenotypic plasticity, populations without it (here called aplastic) and to populations that are reproductively isolated. In general plastic and isolated optima differ, but do not differ if none of the habitats provide source or sink populations. Plastic, aplastic and isolated optima are calculated and compared in three numerical examples representing trade-offs involving reproductive effort, egg size and defence. Locating the aplastic optimum involves numerical construction of a fitness landscape showing how allelic fitness depends on aplastic strategy and on the relative frequencies of the habitats. In all three examples the aplastic optimum lies between or almost between the plastic optima. In two cases the aplastic optimum switches abruptly between the plastic optima as the relative frequencies of the habitats change, and in the third case the switch is gradual. The abruptness or otherwise of the switch depends on the position and structure of the valleys in the fitness landscape and this in turn depends on how sharply the fitness peaks are differentiated.