Résumé
Aim: Different species assemblages of annual killifish possess replicated
body size distributions yet have unique sets of species in each area of
endemism. Here, we use models of trait evolution and historical
biogeography to discover how size variation originated and has been
restructured. Location: South America. Taxon: Austrolebias
(Cyprinodontiformes). Methods: We sampled 63 individuals from 26
Austrolebias species. Using phylogenetic trees (BEAST2), data on
environmental variables at sampling locations and size data we compare
different models for trait evolution (SURFACE, l1OU) of body size and
niche traits. We model the historical biogeography of the areas of
endemism (BioGeoBEARS) and use both analyses in combination to reconstruct
the history of four species assemblages. Results: We present new
phylogenetic trees for Austrolebias and use them to show that large size
principally arose within a single area driven by a shifted selection
optimum for a subset of the species in that area. We suggest that
ecological interactions triggered size divergence and that this
large-bodied lineage subsequently spread to two other areas. A second
assemblage may have been shaped by adaptation to a new environment without
an associated increase in size divergence. A third assemblage, which has
the smallest size range and the most recent origin, is phylogenetically
clustered and we found no evidence of environmental filtering. Main
conclusions: Assemblage similarity in Austrolebias is the result of
contrasting ecological, evolutionary and historical processes. Modelling
trait evolution together with historical biogeography can help to
disentangle the complex histories of multispecies assemblages. This
approach provides context to commonly used tests investigating the role of
ecological processes from phylogenetic data and generates new testable
hypotheses on the processes that generated trait diversity and assemblage
similarity.