Evol Ecol Res 9: 1349-1362 (2007) Full PDF if your library subscribes.
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
1Department of Zoology, North Carolina State University, Raleigh, NC, USA, 2Department of Environmental Biology, Curtin University of Technology, Perth, WA, Australia, 3Division of Biology, Imperial College London, London, UK, 4Jodrell Laboratory, Royal Botanic Gardens, Kew, Richmond, Surrey, UK, 5Department of Botany, University of Wisconsin, Madison, WI, USA and 6Centre for Ecosystem Diversity and Dynamics in the Department of Environmental Biology, Curtin University of Technology, Perth, WA, Australia
Address all correspondence to Robert R. Dunn, Department of Zoology, North Carolina State University, 120 David Clark Labs, Raleigh, NC 27695-7617, USA.
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.
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