title: Interpreting the modern distribution of Myrtaceae using a dated molecular phylogeny.
abstract: The angiosperm family Myrtaceae has extant and fossil taxa from all southern continents and is assumed to be of Gondwanan origin. Many modern groups contain sister taxa that have disjunct transoceanic distributions, which can be interpreted as a result of either vicariance or long-distance dispersal and establishment (LDDE). Further, some Myrtaceae groups occur on Pacific islands with enigmatic geological histories. We tested hypotheses of vicariance and LDDE by estimating divergence times using a relaxed molecular clock calibrated with 12 fossils. In total, 88 genera and 202 species were sampled, representing both subfamilies and all tribes of Myrtaceae. We reconstructed the family as Gondwanan in origin. Of the 22 geographically disjunct sister groups in our study, up to six are potentially explained as the product of vicariance, three resulting from overland dispersal via new land connections, and 13 due to LDDE events. Nine of the 13 hypothesized LDDE events occurred in fleshy-fruited taxa. Our results indicate that most of the transoceanic distribution patterns in Myrtaceae have occurred since the Miocene due to LDDE, whereas inferred vicariance events all occurred before the Late Eocene. There are many instances of sister relationships between species-poor and species-rich groups in Myrtaceae, and at least three occurrences of geographically isolated taxa on long branches of the phylogeny (Arillastrum, Myrtus, and Tepualia), whose modern-day distributions are difficult to explain without additional fossil or geological evidence.
authors.affiliation: Research School of Biology, The Australian National University, Canberra, ACT 2601, Australia; Centre for Australian National Biodiversity Research, National Research Collections, Black Mountain, Canberra, ACT 2601, Australia; Australian Tropical Herbarium, James Cook University, Cairns, QLD 4870, Australia. Electronic address: Andrew.Thornhill@gmail.com.
authors.forename: Andrew H
authors.initials: AH
authors.lastname: Thornhill
authors.affiliation: School of Biological Sciences, University of Sydney, Sydney, NSW 2006, Australia.
authors.forename: Simon Y W
authors.initials: SY
authors.lastname: Ho
authors.affiliation: Research School of Biology, The Australian National University, Canberra, ACT 2601, Australia.
authors.forename: Carsten
authors.initials: C
authors.lastname: Külheim
authors.affiliation: Research School of Biology, The Australian National University, Canberra, ACT 2601, Australia.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Crisp
mesh_terms: D001499:Bayes Theorem; D005580:Fossils; D005843:Geography; D027822:Myrtaceae / Q000145:classification*; D010139:Pacific Islands; D010802:Phylogeny; D013997:Time Factors
keywords: Biogeography; Fossil calibration; Long-distance dispersal and establishment; Molecular dating; Myrtaceae; Vicariance