Spatial and ecological population genetic structures within two island‐endemic Aeonium species of different niche width

Abstract

The Crassulacean genus Aeonium is a well‐known example for plant species radiation on oceanic archipelagos. However, while allopatric speciation among islands is documented for this genus, the role of intra‐island speciation due to population divergence by topographical isolation or ecological heterogeneity has not yet been addressed. The aim of this study was to investigate intraspecific genetic structures and to identify spatial and ecological drivers of genetic population differentiation on the island scale. We analyzed inter simple sequence repeat variation within two island‐endemic Aeonium species of La Palma: one widespread generalist that covers a large variety of different habitat types (Ae. davidbramwellii) and one narrow ecological specialist (Ae. nobile), in order to assess evolutionary potentials on this island. Gene pool differentiation and genetic diversity patterns were associated with major landscape structures in both species, with phylogeographic implications. However, overall levels of genetic differentiation were low. For the generalist species, outlier loci detection and loci–environment correlation approaches indicated moderate signatures of divergent selection pressures linked to temperature and precipitation variables, while the specialist species missed such patterns. Our data point to incipient differentiation among populations, emphasizing that ecological heterogeneity and topographical structuring within the small scales of an island can foster evolutionary processes. Very likely, such processes have contributed to the radiation of Aeonium on the Canary Islands. There is also support for different evolutionary mechanisms between generalist and specialist species.

Local Climate Heterogeneity Shapes Population Genetic Structure of Two Undifferentiated Insular Scutellaria Species

“…This phenomenon is very like the case of Aeonium davidbramwelii and A. nobile on the island of La Palma in the Canarian archipelago: the former is an ecological generalist while the latter is an ecological specialist. There is a lack of species divergence but an obvious population structure exists (Harter et al, 2015 ). However, in our case, although the niche space of tpe is smaller than that of bar , their spatial distribution predicted by ENM on the basis of six bioclimatic variables is almost overlapping (Supplementary Figure 1 ).…”

Climate vs. topography – spatial patterns of plant species diversity and endemism on a high‐elevation island

“…; Harter et al . in press). Thus, the concept of presumed stability (or variability) on islands might need a re‐evaluation, as hot spots of neo‐endemism tend to form in moderately variable conditions on the continent, indicating the importance of variability for speciation (Fjeldså et al .…”

The role of geography, ecology, and hybridization in the evolutionary history of Canary Island Descurainia

“…Climatic variation within the Canary Islands has often been seen as a major driver of diversification within endemic plant lineages (Harter et al, 2015; Irl et al, 2015). Climatic variation, especially along elevation gradients, promotes ecological shifts and speciation (Hua and Wiens, 2013); for example, precipitation gradients have played a significant role in the radiation of Aeonium (Crassulaceae; Harter et al, 2015). Our results indicate that for Descurainia , precipitation and temperature are strongly linked phylogenetically.…”