Variable offspring size as an adaptation to environmental heterogeneity in a clonal plant species: integrating experimental and modelling approaches

Summary 1.  The production of variably sized offspring has been hypothesized to be adaptive to temporal variability in environmental conditions. 2.  This is difficult to verify empirically, and theoretical models are typically generic and not parameterized with data from real populations; studies integrating theoretical and empirical approaches to this problem are rare. 3.  Here, we present experimental data on the growth of Scirpus maritimus , a clonal aquatic macrophyte that grows through vegetative extensions involving tubers. 4.  The experiments show that offspring fitness (biomass productivity) is dependent on environmental conditions (water depth). 5.  Experimental data indicate that variation in offspring (tuber) sizes can be approximated by a lognormal distribution. 6.  We use these data to develop a different equation model of S .  maritimus growth to test whether producing variably sized offspring is adaptive. The model compares fitness under the lognormal strategy to several hypothetical strategies with qualitatively different variance in offspring size. 7.  The model results suggest that lognormal variation in S .  maritimus tuber size may be adaptive to the temporal variation in water levels that characterize its natural Mediterranean environment. 8.  We illustrate how the underlying principles that lend adaptive value to offspring size variation may apply to other species experiencing similar environmental conditions. 9.   Synthesis . Close integration of data and theoretical models creates a unique tool for investigating the adaptive value of life‐history traits in clonal aquatic plants.