Reconstruction of the spatio-temporal diversification and ecological niche evolution of Helianthemum (Cistaceae) in the Canary Islands using genotyping-by-sequencing data

Abstract

Background and aims: Several biogeographical models have been proposed to explain the colonization and diversification patterns of Macaronesian lineages. In this study, we calculated the diversification rates and explored what model best explains the current distribution of the 15 species endemic to the Canary Islands belonging to Helianthemum sect. Helianthemum (Cistaceae).

Methods: We performed robust phylogenetic reconstructions based on genotyping-by-sequencing data and analysed the timing, biogeographical history and ecological niche conservatism of this endemic Canarian clade.

Key results: Our phylogenetic analyses provided strong support for the monophyly of this clade, and retrieved five lineages not currently restricted to a single island. The pristine colonization event took place in the Pleistocene (~1.82 Ma) via dispersal to Tenerife by a Mediterranean ancestor.

Conclusions: The rapid and abundant diversification (0.75-1.85 species per million years) undergone by this Canarian clade seems the result of complex inter-island dispersal events followed by allopatric speciation driven mostly by niche conservatism, i.e. inter-island dispersal towards niches featuring similar environmental conditions. Nevertheless, significant instances of ecological niche shifts have also been observed in some lineages, making an important contribution to the overall diversification history of this clade.

Keywords: Helianthemum; Allopatric speciation; Canary Islands; diversification; genotyping-by-sequencing; niche conservatism; phylogenomics.

Fig. 1.

Geographical location of all 22 populations of the 15 species of Helianthemum sect. Helianthemum endemic to the Canary Islands included in this study. Note that only H. broussonetii is found on two different islands. Species labels are coloured to denote the lineage to which the species was retrieved in the phylogenetic reconstruction (Fig. 2).

Fig. 2.

Majority-rule consensus tree estimated under concatenation analyses (ML conducted in RAxML and BI in Exabayes) from the dataset min50% including the species of Helianthemum sect. Helianthemum in the Canary Islands and the outgroup species. PP/BS are shown above or below branches only when PP < 0.95 and BS < 75 %. Dashes indicate nodes not recovered by RAxML. The five lineages retrieved are identified with capital letters from A to E and coloured accordingly. Nodes with low QC (<0.5) and QD (<0.75) scores after the quartet sampling analyses are indicated by asterisks. The island of origin of the studied populations is also shown: GO, La Gomera; TF, Tenerife; LP, La Palma; GC, Gran Canaria; FT, Fuerteventura; LZ, Lanzarote.

Fig. 3.

Spatio-temporal reconstruction of the diversification of Helianthemum sect. Helianthemum in the Canary Islands. (A) Arrows represent the most parsimonious dispersal events that best explain the current distribution of these species in the archipelago, and are coloured according to the lineage involved in each event. Numbers above or below arrows are the mean estimated ages (in Ma) for each dispersal event. The number of species and the lineage to which they belong are indicated by dots inside the outlines of the island. (B) Ancestral area reconstruction under the DEC analysis with founder-event speciation parameters (DEC+j) conducted in BioGeoBEARS using the MCC tree obtained with BEAST from the dataset min50%. Arrows show inter-island dispersal events and indicate either an east–west or west–east direction of dispersal. Black lines, arrowheads and nodes correspond to ancestral (not extant) species or lineages: W, Western Mediterranean; E, Eastern Mediterranean; GO, La Gomera; TF, Tenerife; LP, La Palma; GC, Gran Canaria; FT, Fuerteventura; LZ, Lanzarote. Oldest island ages (van den Bogaard, 2013) are shown near the island’s abbreviated name.

Fig. 4.

Climatic niche reconstruction analysis of Helianthemum sect. Helianthemum in the Canary Islands. (A) Representation of the PCA obtained using climatic data from the occurrence points of the study species. (B) Character state reconstruction of species’ climatic niche (according to the values on the first axis of the PCA) on the MCC tree obtained with BEAST from the dataset min50%. The ML reconstruction is represented as gradational colours along the branches (warmer and drier climatic conditions in red, colder and wetter in blue and intermediate values in green). The lengths of the horizontal bars at the nodes represent the 95 % confidence intervals of the ancestral niche estimates (error range).