ORIGINAL ARTICLE: Cycads in the insular South‐west Pacific: dispersal or vicariance?

Abstract

Aim Cycads constitute an ancient plant group that is generally believed to disperse poorly. However, one group of cycads (subsection Rumphiae) is thought to have dispersed relatively recently from a Malesian source area westwards to East Africa and eastwards into the Pacific, using a floatation-facilitating layer in their seeds. We use morphological and allozyme characters to investigate the relationships among the species within this group and to deduce whether the wide distribution was achieved by recent dispersal (as evidenced by high genetic similarity) or more distant vicariance events (high genetic differentiation).Location We examined specimens collected throughout the range of subsection Rumphiae, from East Africa through Southeast Asia to Tonga in the South-west Pacific.Methods We investigated relationships within subsection Rumphiae of the genus Cycas by analysing 18 variable (11 informative) morphological characters and 22 allozyme loci for seven of the 10 species currently assigned to this taxon.Results Distinctive morphological characters are few and fail to resolve relationships within the group. Allozyme data show that species within this subsection are closely related and suggest that there are two groups within the subsection, one comprising Cycas thouarsii (East Africa) and C. edentata (the Philippines), and the other the remaining species (from Malesia and the Pacific). The Australian species C. silvestris is sister to subsection Rumphiae in the morphological analysis but is closely allied to C. rumphii (nested within the subsection) in the allozyme analysis, suggesting that Rumphiae may be paraphyletic and that characters thought to be taxonomically important may need to be re-evaluated.Main conclusions Cycads within subsection Rumphiae are closely related, and the wide distribution of this group was probably achieved through relatively recent oceanic dispersal events. Separate events probably account for the dispersal of these cycads into the Pacific and to Africa. The origin and distribution of C. silvestris (Australia) could be explained by a dispersal event from New Guinea or may have resulted from a former land connection between Australia and New Guinea.

Bees in the Southwest Pacific: Origins, diversity and conservation

“…The complex geological history of the Pacific, particularly in the Southwest, means that this issue has not been conclusively resolved for this region. Keppel et al (2008) showed that genetic similarity in a broadly distributed group of SWP cycads (subsection Rumphiae) revealed a likely recent oceanic dispersal rather than vicariance. In contrast, Heads (2008) presented vicariance arguments for a number of patterns that were previously thought to comprise 'dispersal' examples, including the Australia/Pacific Lotus australis complex, focused around New Caledonia and the SWP.…”

The Cycad Genus Cycas May Have Diversified From Indochina and Occupied Its Current Ranges Through Vicariance and Dispersal Events

“…This is an additional but essential justification for the present study to re-investigate the biogeography of the genus Cycas. Indeed, the biogeography of the genus Cycas has been investigated in recent studies (e.g., Keppel et al, 2008;Xiao and Möller, 2015). In their study, Xiao and Möller (2015) indicated, with high level of confidence (∼94%), that South China is the origin of the genus.…”

“…In Asia, the genus is distributed across the Red River Fault between South China and the Indochina block, with Red River potentially constituting a geographical barrier for gene flow (Xiao and Möller, 2015). If this barrier was effective, we would expect to detect the signature of vicariance events in the evolutionary history of the genus Cycas (Keppel et al, 2008;Xiao and Möller, 2015). Then, the widespread distribution of Cycas from Asia to Africa, Australia and across the Pacific regions might have been mediated through long distance dispersal events across the ocean.…”

Changing perspectives on the biogeography of the tropical South Pacific: influences of dispersal, vicariance and extinction

“…For example, the conifer genus Agathis, often cited in support of the vicariance origin of Pacific island biotas (Whitmore, 1969;de Laubenfels, 1996), was found to have recently speciated in the Pacific, with the likely source being New Caledonia (Setoguchi et al, 1998). Similarly, Pacific cycads (genus Cycas) appear to have recently expanded their distribution following the evolution of adaptations that facilitate oceanic dispersal (Hill, 1996;Keppel et al, 2008). In addition, LDD and recent divergence are now known to have played a major role in determining the current distribution of Nothofagus Cook & Crisp, 2005a;Knapp et al, 2005), long considered to support vicariance scenarios (Linder & Crisp, 1995;).…”