Aim To describe a protocol for incorporating a temporal dimension into historical biogeographical analysis, while maintaining the essential independence of all datasets, involving the generation of general area cladograms.
Methods General area cladograms (GACs) are a reconstruction of the evolutionary history of a set of areas and unrelated clades within those areas. Nodes on a GAC correspond to speciation events in a group of taxa; general nodes are those at which multiple unrelated clades speciate. We undertake temporal calibration of GACs using molecular clock estimates of splitting events between extant taxa as well as first appearance data from the fossil record. We present two examples based on re-analysis of previously published data: first, a temporally calibrated GAC generated from secondary Brooks parsimony analysis (BPA) of six extant bird clades from the south-west of North America using molecular clock estimates of divergence times; and second, an analysis of African Neogene mammals based on a phylogenetic analysis for comparing trees (PACT) analysis.
Results A hypothetical example demonstrates how temporal calibration reveals potentially critical information about the timing of both unique and general events, while also illustrating instances of incongruence between dates generated from molecular clock estimates and fossils. For the African Neogene mammal dataset, our analysis reveals that most mammal clades underwent geodispersal associated with the Neogene climatic optimum (c. 16 Ma) and vicariant speciation in central Africa correlated with increased aridity and cooler temperatures around 2.5 Ma.
Main conclusions Temporally calibrated GACs are valuable tools for assessing whether coordinated patterns of speciation are associated with large-scale climatic or tectonic phenomena.