Cryptic adaptive radiation in tropical forest trees inNewCaledonia

Abstract

SummaryThe causes of the species richness of tropical trees are poorly understood, in particular the roles of ecological factors such as soil composition. The nickel(Ni)-hyperaccumulating tree genus Geissois (Cunoniaceae) from the South-west Pacific was chosen as a model of diversification on different substrates.Here, we investigated the leaf element compositions, spatial distributions and phylogeny of all species of Geissois occurring on New Caledonia.We found that New Caledonian Geissois descended from a single colonist and diversified relatively quickly into 13 species. Species on ultramafic and nonultramafic substrates showed contrasting patterns of leaf element composition and range overlap. Those on nonultramafic substrates were largely sympatric but had distinct leaf element compositions. By contrast, species on ultramafic substrates showed similar leaf element composition, but occurred in many cases exclusively in allopatry. Further, earlier work showed that at least three out of these seven species use different molecules to bind Ni.Geissois qualifies as a cryptic adaptive radiation, and may be the first such example in a lineage of tropical forest trees. Variation in biochemical strategies for coping with both typical and adverse soil conditions may help to explain the diversification and coexistence of tropical forest trees on similar soil types.

Hidden diversity in the morphologically variable script lichen (Graphis scripta) complex (Ascomycota, Ostropales, Graphidaceae)

“…In many cases, the discovery of cryptic lineages leads to discovery of other subtle, previously unknown characters that characterize those lineages. Such characters may include differences in ecology, chemistry, physiology, microstructures, biogeography, or even a combination of these traits (Arup and Åkelius 2009;Czarnota and Guzow-Krzemińska 2010;Lendemer 2011;Parnmen et al 2012;Pillon et al 2014;Vondrák et al 2009;Yost et al 2012).…”

Interpreting the modern distribution of Myrtaceae using a dated molecular phylogeny

“…As we have not been able to estimate this crown age, we cannot currently use it to test the hypothesis of a persistent land mass (Ladiges and Cantrill, 2007). Estimated ages from previous studies of New Caledonian taxa have suggested that speciation events there are not older than 37 Ma (Barrabé et al, 2014;Bartish et al, 2011;Pillon, 2012;Pillon et al, 2014Pillon et al, , 2010, when New Caledonia has been proposed to have emerged above the sea (Grandcolas et al, 2008). Furthermore, thorough genetic sampling of Myrtaceae species in tribes Xanthostemoneae (22 spp.…”

A revision of Mezoneuron (Leguminosae: Caesalpinioideae) in New Caledonia, with perspectives on vegetation, geology, and conservation

“…According to Pillon et al 2009, species occurring on both ultramaphic and non-ultramaphic soil are not uncommon. For example two of the 13 species of the genus Geissois Labillardière (1825: 50) (Cunoniaceae) occur on both ultramaphic and non-ultramaphic soils (Pillon et al 2014). Pillon et al (2009) also noted that some species having a broad soil tolerance within the Cunoniaceae were complex and taxonomically challenging; this situation reflects the one discussed here.…”

“…It has been suggested that other groups of New Caledonian plants may harbour cryptic species due to adaptive radiation to different soil types, such as ultramaphic vs. non-ultramaphic soils (Pillon et al 2009;Pillon et al 2014). This contrasts with other known examples of cryptic species in the Caesalpinia group, such as in the Caesalpinia hintonii Sandwith (1937: 303) complex (Sotuyo et al 2007) and Arquita grandiflora Gagnon et al (Gagnon et al 2015, in press), which are thought to have arisen through vicariance due to mountain uplift, followed by low selective divergence of lineages.…”