Late-Cenozoic origin and diversification of Chatham Islands endemic plant species revealed by analyses of DNA sequence data

Abstract

The relationships of 35 taxa endemic to the Chatham Islands and their close relatives were investigated using DNA sequence data. This study implies that the closest relatives of many of the endemic species are widespread and common species that occur on either of the main New Zealand islands. Hypotheses that the majority of the Chatham Island endemic plants have their closest relatives in northern North Island or southern South Island are not supported. The closest relative for the monotypic Myosotidium hortensium occurs in the Mediterranean, indicating successful long-distance transoceanic dispersal. Patterns of dispersal and estimates of divergence times were determined, and we relate these data to hypotheses of the islands' lateCenozoic geological history. The Chatham Island endemic taxa differ from their closest relatives by between 0.0 and 6.4% sequence divergence (mostly B1.5%). Divergence time estimates determined for 19 taxa using molecular clock analyses identified a large group of taxa whose divergence times wereB2.4 Myr, and four species with divergence times!3.54 Myr. Divergence time estimates for Chatham Island endemic plants are congruent with two late-Cenozoic geological events. First, the emergence of land 6.0 Myr following eruption of the Mangere Volcano, and second, uplift of the submerged Southern Volcanics, Mangere Volcano and Rangitihi Volcanics between 3.0 and 2.0 Myr.Keywords: Chatham Islands; dispersal; DNA sequence data; geology; molecular clock; New Zealand flora; speciation Introduction Phylogenetic studies of vascular plants endemic to isolated oceanic islands such as the Hawaian archipelago (Baldwin et al. 1991; Wagner & Funk 1995), Canary Islands (GJ Allan et al. 2004; Moore et al. 2002) and Juan Fernandez Islands (Crawford et al. 1998) have advanced understanding and facilitated the development of hypotheses on the evolutionary history of oceanic islands and their biotas (Chen & He 2009; Heaney 2007;Whittaker et al. 2008). New Zealand is also cited as an important biogeographic region and there has been much discussion about the flora having a Gondwanan ancestry and being vicariant (Craw 1989) or being more recent and having arrived primarily by dispersal (McGlone et al. 2001;Pole 1994). Within New Zealand, there has been debate about the effects of glaciation and glacial refugia on plant distributions (Burrows 1965;Wardle 1963Wardle , 1988 and the importance of the Alpine Fault (Heads 1998; McGlone 1985). Most of this debate has focused on the two main islands, North Island and South Island. Often overlooked biogeographic features of New Zealand are the more distant *Corresponding author. Email: heenanp@landcareresearch.co.nz Vol. 48, No. 2, June 2010, 83Á136 island groups of the Kermadec Islands, subantarctic islands and Chatham Islands. New Zealand Journal of BotanyThe Chatham Island archipelago (1768W and 448S; Fig. 1) is located at the eastern end of the Chatham Rise, some 850 km to the east of the main islands of New Zealand, and is the easternmost extension of th...

Jurassic primates, immobile ducks and other oddities: a reply to Heads’ review of The Monkey’s Voyage

“…The flora and fauna of the Chathams are in keeping with the hypothesised young age of the current islands (as subaerial land); in particular, molecular-dating studies of various plant and animal groups (see below), and the observation that there are few endemic genera (Holdaway et al 2001;Emberson 1998;de Lange et al 2011) argue against ancient origins of the biota. In fact, most Chathams populations are classified as conspecific with ones found elsewhere (Emberson 1998;Holdaway et al 2001;Heenan et al 2010;de Lange et al 2011).…”

“…Geological 'evidence' for prior land that can plausibly explain the biota of the islands by normal dispersal and vicariance amounts to wishful thinking, and molecular phylogenetic results, far from countering origins by LDD, collectively provide strong support for that explanation (Trewick 2000;Chambers et al 2001;Heenan et al 2010;Mitchell et al 2014b).…”

“…Many investigators, not just Heads, have interpreted divergences in this way (e.g. Ericson et al 2002;Nagy et al 2003;Vences et al 2003;Allwood et al 2010;Heenan et al 2010). Thus, as with the probable bias of molecular methods to overestimate the ages of divergences in birds, mammals and flowering plants, this logical error, if anything, has led to underestimating the importance of LDD.…”

“…Within the Hikurangi Plateau, the volcanic activity that formed the current guyots is thought to have occurred some 89-99 million years ago or even earlier (Davy et al 2008), and is thus irrelevant to the origins of the much younger biota of the Chathams. Finally, parts of the Mernoo and Veryan Banks did become emergent land during recent glacial periods (Heenan et al 2010), but these islands were much closer to the main islands of New Zealand than to the Chathams; thus, if Chathams ancestors lived on these intermittent islands, LDD would still have been required for them to colonise the Chathams. In short, the geological 'evidence' cited by Heads for the Chathams suggests few if any routes of normal dispersal, which is the type of dispersal required by vicariance scenarios.…”

A new species of rust fungus on the New Zealand endemic plant, Myosotidium, from the isolated Chatham Islands

“…& Link (1811) from Portugal and Spain is the closest relative of Myosotidium, which appears to represent a Chatham Island-Mediterranean disjunction (Heenan et al 2010). It is also related to Lappula squarrosa and Trichodesma scottii (Heenan et al 2010).…”