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The role of biotic and abiotic factors in evolution of ant dispersal in the milkwort family (Polygalaceae)

Journal article
Authors F. Forest
M. W. Chase
Claes Persson
P. R. Crane
J. A. Hawkins
Published in Evolution
Volume 61
Issue 7
Pages 1675-1694
ISSN 0014-3820
Publication year 2007
Published at Department of Plant and Environmental Sciences
Pages 1675-1694
Language en
Links <Go to ISI>://000247576400013
Keywords Bayesian methods, diversification rates, elaiosomes, key innovation, likelihood optimization, molecular dating, myrmecochory, EOCENE THERMAL MAXIMUM, DIFFERENTIAL DIVERSIFICATION RATES, PALEOCENE-EOCENE, SEED DISPERSAL, DNA-SEQUENCES, PHYLOGENETIC-RELATIONSHIPS, MOLECULAR EVOLUTION, FLOWERING PLANTS, DIVERGENCE TIMES, CHLOROPLAST DNA
Subject categories Biological Sciences

Abstract

A phylogenetic approach was taken to investigate the evolutionary history of seed appendages in the plant family Polygalaceae (Fabales) and determine which factors might be associated with evolution of elaiosomes through comparisons to abiotic (climate) and biotic (ant species number and abundance) timelines. Molecular datasets from three plastid regions representing 160 species were used to reconstruct a phylogenetic tree of the order Fabales, focusing on Polygalaceae. Bayesian dating methods were used to estimate the age of the appearance of ant-dispersed elaiosomes in Polygalaceae, shown by likelihood optimizations to have a single origin in the family. Topology-based tests indicated a diversification rate shift associated with appearance of caruncular elaiosomes. We show that evolution of the caruncular elaiosome type currently associated with ant dispersal occurred 54.0-50.5 million year ago. This is long after an estimated increase in ant lineages in the Late Cretaceous based on molecular studies, but broadly concomitant with increasing global temperatures culminating in the Late Paleocene-Early Eocene thermal maxima. These results suggest that although most major ant clades were present when elaiosomes appeared, the environmental significance of elaiosomes may have been an important factor in success of elaiosome-bearing lineages. Ecological abundance of ants is perhaps more important than lineage numbers in determining significance of ant dispersal. Thus, our observation that elaiosomes predate increased ecological abundance of ants inferred from amber deposits could be indicative of an initial abiotic environmental function.

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