Environmental, genetic, and seed mass effects on winged seed production in the heteromorphic Spergularia marina (Caryophyllaceae)

Summary1 Spergularia marina (L.) Grieseb. is a cosmopolitan, autogamous herb that produces winged and unwinged seeds. In Europe, large‐seeded populations tend to produce a higher proportion of winged seeds than small‐seeded populations. 2 This pattern has prompted speculation that winged seeds evolved because they increase the dispersability of large‐seeded genotypes. Alternatively, winged seed production may be an adaptive plastic response to stress, resulting in increased dispersal. A third hypothesis is that wing production is favoured among maternal plants with high fecundity because it reduces postdispersal sibling competition. 3 We present the results of a greenhouse experiment conducted to test these hypotheses using California genotypes of S. marina . Twenty‐four maternal families ( N  = 230 plants) were replicated across three nutrient treatments. Within treatments, large‐seeded fruits, individuals and families tended to produce a higher proportion of winged seeds than small‐seeded ones. We found no evidence that winged seeds are induced by stress or high fecundity. 4 These results are consistent with evidence that winged seed production in S. marina is positively associated with the evolution of mean seed mass, representing an adaptation that enhances the dispersability of large seeds. The low frequency of winged seeds in the population sampled here suggests that the heteromorphism may not be an important current adaptation in small‐seeded populations of S. marina .