title: Evolutionary dynamics of a cycad obligate pollination mutualism - Pattern and process in extant Macrozamia cycads and their specialist thrips pollinators.
abstract: Obligate pollination mutualisms are rare and few have been investigated deeply. This paper focuses on one such mutualism involving thrips in the genus Cycadothrips that pollinate cycads in the genus Macrozamia. Both represent old lineages relative to insects and plants generally, are endemic to Australia, and are mutually co-dependent. The phylogenetic analyses presented here demonstrate that the pollinator is much more diverse than previously considered, with each pollinator lineage being extremely specific to between one and three host species where these latter share part of their distribution. The new species diversity we demonstrate in Cycadothrips all presently falls under the species name C. chadwicki, and these different lineages diversified during two periods. An older divergence, beginning 7.3Mya (4.4-11.1, 95% HPD), resulted in three major lineages, and then further diversification within each of these three lineages took place at most 1.1Mya (0.6-1.8, 95% HPD). These divergence estimates correspond to times when aridification was increasing in Australia, suggesting that population fragmentation following climatic change has played a significant role in the evolutionary history of Cycadothrips and Macrozamia. This means that co-diversification of the host and pollinator in allopatry appears to be the dominant process affecting species diversity. Host switching is also clearly evident in the discrepancy between the divergence times of the C. chadwicki lineage and C. albrechti, about 10.8Mya (6.0-17.1, 95% HPD), and their hosts, at about 1.1Mya (0.2-3.4Mya, 95% HPD), in that the pollinator split pre-dates the origin of the associated host species of each. These results add to the body of evidence that the evolutionary processes important in obligate pollinator mutualisms are more varied than previously assumed.
authors.affiliation: The University of Queensland, School of Biological Sciences, Brisbane, 4072 Queensland, Australia. Electronic address: dean.brookes@uqconnect.edu.au.
authors.forename: D R
authors.initials: DR
authors.lastname: Brookes
authors.affiliation: The University of Queensland, School of Biological Sciences, Brisbane, 4072 Queensland, Australia. Electronic address: j.hereward@uq.edu.au.
authors.forename: J P
authors.initials: JP
authors.lastname: Hereward
authors.affiliation: University of Utah, Department of Biology, 257 S. 1400 E., Salt Lake City, UT 84112, USA. Electronic address: g.walter@uq.edu.au.
authors.forename: L I
authors.initials: LI
authors.lastname: Terry
authors.affiliation: The University of Queensland, School of Biological Sciences, Brisbane, 4072 Queensland, Australia. Electronic address: irene.terry@utah.edu.
authors.forename: G H
authors.initials: GH
authors.lastname: Walter
mesh_terms: D000818:Animals; D001315:Australia; D005075:Biological Evolution; D051456:Gene Flow; D005828:Genetics, Population; D005843:Geography; D006239:Haplotypes / Q000235:genetics; D018895:Microsatellite Repeats / Q000235:genetics; D010802:Phylogeny; D054817:Pollination; D013045:Species Specificity; D013559:Symbiosis; D061149:Thysanoptera / Q000502:physiology*; D013997:Time Factors; D032481:Zamiaceae / Q000235:genetics / Q000502:physiology*
keywords: Biogeography; Coevolution; Cycadothrips; Host specificity; Phylogeny; Species diversification