High morphological diversity in remote island populations of the peat moss Sphagnum palustre: glacial refugium, adaptive radiation or just plasticity?

Abstract

Abstract Many islands are characterized by high biological diversity, and both adaptive and non-adaptive factors have been found to contribute to island richness. Here we study extensive color morph variability in the allopolyploid peat moss Sphagnum palustre on the Azores Islands. By comparing genetic diversity patterns in island and mainland populations we evaluate various hypotheses for the high diversity observed within and between islands. We conclude that the diversity observed cannot be explained by Azores Islands having acted as refugia for morphotypes during Pleistocene glacial periods. Furthermore, high island diversity is not the result of past or ongoing adaptive radiations. Lack of genetic differentiation and free reproduction among morphs growing closely together is not consistent with adaptive differentiation in space or time to changing environmental conditions. We conclude that high island diversity in this species likely reflects phenotypic plasticity, possibly in response to unfavourabl...