Data from: Evolutionary determinants of morphological polymorphism in colonial animals

Colonial animals commonly exhibit morphologically polymorphic modular units that are phenotypically distinct and specialize in specific functional tasks. But how and why these polymorphic modules have evolved is poorly understood. Across colonial invertebrates there is wide variation in the degree of polymorphism. Bryozoa are a phylum of exclusively colonial invertebrates that uniquely exhibit almost the entire range of polymorphism. Previous approaches to understanding the evolution of polymorphism have been based upon analyses of (1) the functional role of polymorphs or (2) presumed evolutionary costs and benefits based upon evolutionary theory that postulates polymorphism should only be evolutionarily sustainable in more "stable" environments because polymorphism commonly leads to the loss of feeding and sexual competence. Here we use bryozoans from opposite shores of the Isthmus of Panama to revisit the environmental hypothesis by comparison of faunas from distinct
oceanographic provinces that differ greatly in environmental variability and we then examine the correlations between the extent of polymorphism in relation to patterns of ecological succession and variation in life histories. We find no support for the environmental hypothesis. In contrast, the temporal position of species in a successional sequence is collinear with the degree of polymorphism. The association between degrees of polymorphism and variations in life histories is fundamental to understanding of the macroevolution of polymorphism.