Fitting and evaluating univariate and multivariate models of within-lineage evolution

The nature of phenotypic evolution within lineages is central to many unresolved questions in paleontology and evolutionary biology. Analyses of evolutionary time series of ancestor-descendant populations in the fossil record are likely to make important contributions to many of these debates. However, the limited number of models that have been applied to these types of data may restrict our ability to interpret phenotypic evolution in the fossil record. Using uni- and multivariate models of trait evolution that make different assumptions regarding the dynamics of the adaptive landscape, I evaluate contrasting hypotheses to explain evolution of size in the radiolarian Eucyrtidium calvertense and armor in the stickleback Gasterosteus doryssus. Body-size evolution in E. calvertense is best explained by a model in which the lineage evolves as a consequence of a shift in the adaptive landscape that coincides with the initiation of neosympatry with its sister lineage. Multivariate evolution of armor traits in a stickleback lineage (G. doryssus) shows evidence of adaptation toward independent optima on the adaptive landscape at the same time as traits change in a correlated fashion. The fitted models are available in the R package evoTS, which builds on the paleoTS framework.