Evolutionary Ecology Research, 2007, 9: 1349–1362
Convergent evolution of an ant–plant mutualism
across plant families, continents, and time
Robert R. Dunn,1,2 Aaron D. Gove,1,2 Tim G. Barraclough,3,4
Thomas J. Givnish5 and Jonathan D. Majer6
1
Department of Zoology, North Carolina State University, Raleigh, NC, USA,
Department of Environmental Biology, Curtin University of Technology, Perth, WA, Australia,
3
Division of Biology, Imperial College London, London, UK,
4
Jodrell Laboratory, Royal Botanic Gardens, Kew, Richmond, Surrey, UK,
5
Department of Botany, University of Wisconsin, Madison, WI, USA and
6
Centre for Ecosystem Diversity and Dynamics in the Department of Environmental Biology,
Curtin University of Technology, Perth, WA, Australia
2
ABSTRACT
Questions: How often has dispersal of seeds by ants evolved in monocots and is the timing
of origins associated with changes in the ant community or instead with the rise of forests?
Are patterns in the origin of elaiosomes (the trait associated with the dispersal of seeds by ants)
through time similar to those for the origins of fleshy fruits?
Data studied: We estimate the timing of the origin of elaiosomes and fleshy fruits respectively
by mapping seed morphology onto a recent phylogeny based on ndhF sequence data for
the monocots (Givnish et al., 2005). For comparison, we use fossil data on ant relative
abundance through time and phylogenetic data for the timing of the origin of seed-dispersing
ant lineages.
Search method: We mapped origins of both elaiosomes and fleshy fruits onto the phylogeny
using parsimony in the program Mesquite (Maddison and Maddison, 2005). We analysed the
relationship between ant relative abundances, the number of origins of seed-dispersing ants,
and the rate of origination of elaiosomes using randomization-based Monte Carlo regression
in the program R (Cliff and Ord, 1981). Using the program Discrete (Pagel, 2006), we test whether
fleshy fruits or elaiosomes and shaded forest understoreys show correlated evolution.
Conclusions: Morphological features for the dispersal of seeds by ants (myrmecochory) have
evolved at least twenty times within the monocots. Origins of myrmecochory are not associated
with the rise of forests during the Cretaceous or with subsequent transitions of plant lineages
into closed canopy habitats, nor are they contemporaneous with the origins of fleshy fruits.
Instead, the origins of myrmecochory are closely associated with the rise in relative abundance
of ants (proportion of all individual insects in fossils) towards the end of the Eocene and more
recently.
Keywords: ant, convergent evolution, dispersal, diversity, Formicidae, mutualism,
myrmecochory, seed.
* Address all correspondence to Robert R. Dunn, Department of Zoology, North Carolina State University,
120 David Clark Labs, Raleigh, NC 27695-7617, USA. e-mail: [email protected]
Consult the copyright statement on the inside front cover for non-commercial copying policies.
© 2007 Robert R. Dunn
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