Data from: Locating evolutionary precursors on a phylogenetic tree

Conspicuous innovations in the history of life are often preceded by more
cryptic genetic and developmental precursors. In many cases, these appear
to be associated with recurring origins of very similar traits in close
relatives (parallelisms) or striking convergences separated by deep time
(“deep homologies”). Although the phylogenetic distribution of gain and
loss of traits hints strongly at the existence of such precursors, no
models of trait evolution currently permit inference about their location
on a tree. Here we develop a new stochastic model which explicitly
captures the dependency implied by a precursor and permits estimation of
precursor locations. We apply it to the evolution of extrafloral nectaries
(EFNs), an ecologically significant trait mediating a widespread mutualism
between plants and ants. In legumes, a species-rich clade with
morphologically diverse EFNs, the precursor model fits the data on EFN
occurrences significantly better than conventional models. The model
generates explicit hypotheses about the phylogenetic location of
hypothetical precursors, which may help guide future studies of molecular
genetic pathways underlying nectary position, development and function.