PASTIS: an R package to facilitate phylogenetic assembly with soft taxonomic inferences
- Tweetable abstract: PASTIS for R integrates taxa lacking genetic data into MrBayes version 3.2 input using topology constraints.
- Phylogenetic trees that include all member lineages are necessary for many questions in macroevolution, biogeography and conservation. Currently, producing such trees when genetic data or phenotypic characters for some tips are missing generally involves assigning missing species to the root of their most exclusive clade, essentially grafting them onto existing and static topologies as polytomies.
- We describe an R package, ‘PASTIS’, that enables a two-stage Bayesian method using MrBayes version 3.2 (or higher) to incorporate lineages lacking genetic data at the tree inference stage. The inputs include a consensus topology, a set of taxonomic statements (e.g. placing species in genera and aligning some genera with each other or placing subspecies within species) and user-defined priors on edge lengths and topologies. PASTIS produces input files for execution in MrBayes that will produce a posterior distribution of complete ultrametric trees that captures uncertainty under a homogeneous birth-death prior model of diversification and placement constraints. If the age distribution of a focal node is known (e.g. from fossils), the ultrametric tree distribution can be converted to a set of dated trees. We also provide functions to visualize the placement of missing taxa in the posterior distribution.
- The PASTIS approach is not limited to the level of species and could equally be applied to higher or lower levels of organization (e.g. accounting for all recognized subspecies or populations within a species) given an appropriate choice of priors on branching times.