Relaxed Molecular Clock Provides Evidence for Long-Distance Dispersal of Nothofagus (Southern Beech)

Nothofagus (southern beech), with an 80-million-year-old fossil record, has become iconic as a plant genus whose ancient Gondwanan relationships reach back into the Cretaceous era. Closely associated with Wegener's theory of “Kontinentaldrift”, Nothofagus has been regarded as the “key genus in plant biogeography”. This paradigm has the New Zealand species as passengers on a Moa's Ark that rafted away from other landmasses following the breakup of Gondwana. An alternative explanation for the current transoceanic distribution of species seems almost inconceivable given that Nothofagus seeds are generally thought to be poorly suited for dispersal across large distances or oceans. Here we test the Moa's Ark hypothesis using relaxed molecular clock methods in the analysis of a 7.2-kb fragment of the chloroplast genome. Our analyses provide the first unequivocal molecular clock evidence that, whilst some Nothofagus transoceanic distributions are consistent with vicariance, trans-Tasman Sea distributions can only be explained by long-distance dispersal. Thus, our analyses support the interpretation of an absence of Lophozonia and Fuscospora pollen types in the New Zealand Cretaceous fossil record as evidence for Tertiary dispersals of Nothofagus to New Zealand. Our findings contradict those from recent cladistic analyses of biogeographic data that have concluded transoceanic Nothofagus distributions can only be explained by vicariance events and subsequent extinction. They indicate that the biogeographic history of Nothofagus is more complex than envisaged under opposing polarised views expressed in the ongoing controversy over the relevance of dispersal and vicariance for explaining plant biodiversity. They provide motivation and justification for developing more complex hypotheses that seek to explain the origins of Southern Hemisphere biota

Origins and evolution of the New Zealand forest flora : a molecular phylogenetic approach : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Biology at Massey University, Palmerston North, New Zealand

The origins and evolution of the New Zealand flora have puzzled the imagination of botanists world-wide. Competing hypotheses have sought to explain the floristic relationships between New Zealand and other Southern Hemisphere landmasses. Scientific approaches have involved geology, plant morphology, palynology and palaeobotany in investigations of the distribution patterns of these floras. Analyses presented in the current thesis use molecular data to investigate phylogenetic relationships of plant lineages native to the New Zealand forest flora. In the present thesis, molecular work included amplification and sequencing of standard DNA markers such as nuclear ribosomal DNA, ndhF and rbcL gene sequence. These data were obtained for New Zealand and overseas species of Myrsinaceae, Nothofagaceae and genus Agathis (Araucariaceae). Analyses of these data have been presented alongside results and re-analyses of genetic data for Podocarpaceae, Proteaceae, Winteraceae and genus Metrosideros (Myrtaceae). These analyses aimed to synthesise recent work and provide a framework for further molecular investigations into the origins of the New Zealand woody forest flora. Amplified fragment length polymorphism (AFLP) was used to locate polymorphic genome regions that were converted into sequence specific DNA markers. Information from AFLP and AFLP derived markers was used to elucidate evolutionary processes as well as interspecific and intraspecific relationships between closely related taxa of Myrsine and Nothofagus. DNA analyses showed that the New Zealand forest hosts plants with very different origins and evolutionary histories. Results presented in the current thesis support hypotheses of vicariance and long-distance dispersal across Southern Hemisphere lands. Molecular data are consistent with a continuous presence of Agathis (Araucariaceae), Dacrydium (Podocarpaceae) and Pseudowintera (Winteraceae) on the New Zealand archipelago since the break-up of the Gondwanan supercontinent. It is proposed that extant species of these lineages have evolved from ancestors that arrived on the New Zealand landmass during the Cretaceous. In contrast, divergence time estimates on Nothofagus suggest that relationships between extant Fuscaspora and Lophozonia beeches date back to the Mid Tertiary and are not explained by vicariance and continental drift. Phylogenetic analyses substantiate fossil evidence of a Tertiary arrival of Metrosideros (Myrtaceae), Myrsine (Myrsinaceae). Knightia and Toronia (both Proteaceae). Similarly, dispersal from New Zealand to other southern lands has been inferred for Metrosideros and Myrsine. These findings and those reported earlier for alpine plant groups suggest that trans-oceanic dispersal is likely to be an important explanation of floristic relationships between New Zealand and other distant landmasses. Molecular studies on New Zealand Myrsine suggest recent speciation events, geographic differentiation and ongoing hybridisation between some morphologically and ecologically distinct species Intraspecific analyses on Myrsine divaricata and Nothofagus menziesii show that extant distribution patterns within New Zealand are relatively recent and may have developed during the Quaternary. Although both lineages have an ancient history on the New Zealand archipelago, it is concluded that species and their distributions - including that of the monotypic genera Elingamita - are of recent origin

ML Tree Indicating Evolutionary Relationships for <i>Nothofagus</i> Species Based on the <i>atpB–psaI</i> and <i>trnL–trnF</i> Region of the Chloroplast Genome (7,269 bp)

<p>Divergence dates (in Myr) were obtained with an F84+ Γ₈ substitution model using the BRMC approach of Thorne et al. [<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.0030014#pbio-0030014-b29" target="_blank">29</a>]. For the dates indicated, the age of the root node and that of F/N1 were constrained to 70–80 Myr; L2 was also constrained in accordance with fossil data [<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.0030014#pbio-0030014-b26" target="_blank">26</a>] at 20 Myr. Violet numbers show bootstrap values. The pollen grains represent the first appearance of the respective pollen type in the New Zealand fossil record. Plio, Pliocene; Oligo, Oligocene; Palaeo, Palaeocene; Ma, Maastrichian; Campan, Campanian. L1–L4, <i>Lophozonia</i> 1–4; F1–F2, <i>Fuscospora</i> 1–2; F/N1, <i>Fuscospora</i>/<i>Nothofagus</i> 1.</p