Phylogenetics and phylogeography of Euphorbia canariensis reveal an extreme Canarian-Asian disjunction and limited inter-island colonization

Abstract

Euphorbia canariensis is an iconic endemic species of the Canary Islands and one of the most characteristic species of lowland xerophytic communities known, in Spanish, as cardonal-tabaibal. This species is widely distributed in the archipelago, which contrasts with the theoretically low dispersal abilities suggested by its unspecialized diasporas. Furthermore, the phylogenetic relationships of this species are unclear, although it is thought to be related to the Indian E. epiphylloides and not to other cactus-like Euphorbia of the Canary Islands (E. handiensis) and Africa. Here we aimed to reconstruct the evolutionary history of E. canariensis at two levels: (i) a phylogenetic approach aimed at unravelling relationships of this species and large-scale biogeographic patterns, and (ii) a phylogeographic approach focused on the history of colonization between islands of the Canarian archipelago in relation to habitat availability for this species through time. Based on previous phylogenetic studies of Euphorbia, we sequenced the ITS region for E. canariensis and several potentially related species to build a phylogenetic framework. We also sequenced two cpDNA regions for 92 individuals from 29 populations of E. canariensis representing its distribution range. We estimated the number of inter-island colonization events using PAICE, a recently developed method that includes a sampling effort correction. Additionally, we used species distribution modelling (SDM) to project current habitat availability for E. canariensis to past periods. Phylogenetic results supported the Canarian E. canariensis as closely related to the Southeast Asian E. epiphylloides and E. sessiliflora. In the Canarian archipelago, E. canariensis displayed a surprising west-to-east colonization pattern. The estimated number of inter-island colonization events was c. 20 - 50, and SDM suggested an increase in habitat availability in recent times. In summary, in this study we confirmed an extreme biogeographic disjunction between Macaronesia and Southeast Asia, described only for a small number of plant species, and estimated relatively low dispersal capabilities for E. canariensis, with a west-to-east colonization pattern in the Canary Islands. HighlightsO_LIThe Canarian Euphorbia canariensis is sister to Southeast Asian species. C_LIO_LIThis lineage shows one of the widest disjunctions affecting Macaronesian plants. C_LIO_LIThe lack of intermediate relatives could be the result of extinction events. C_LIO_LIE. canariensis displays low colonization ability in the Canarian archipelago. C_LI