The path followed by species in the colonization of remote oceanic islands ultimately depends on their phylogenetic constraints and ecological responses. In this study, we aim to evaluate the relative role of geographical and ecological forces in the origin and evolution of the Madeiran ivy (Hedera maderensis), a single-species endemic belonging to the western polyploid clade of Hedera. To determine the phylogenetic placement of H. maderensis within the western polyploid clade, we analyzed 40 populations (92 individuals) using genotyping-by-sequencing and including Hedera helix as outgroup. Climatic niche differences among the study species were evaluated using a database with 867 records representing the entire species ranges. To test species responses to climate, 13 vegetative and reproductive functional traits were examined for 70 populations (335 individuals). Phylogenomic results revealed a nested pattern with H. maderensis embedded within the south-western Iberian H. iberica. Gradual niche differentiation from the coldest and most continental populations of H. iberica to the warm and stable coastal population sister to H. maderensis parallels the geographical pattern observed in the phylogeny. Similarity in functional traits is observed for H. maderensis and H. iberica. The two species show leaves with higher specific leaf area (SLA), lower leaf dry matter content (LDMC) and thickness and fruits with lower pulp fraction than the other western polyploid species H. hibernica. Acquisition of a Macaronesian climatic niche and the associated functional syndrome in mainland European ivies (leaves with high SLA, and low LDMC and thickness, and fruits with less pulp content) was a key step in the colonization of Madeira by the H. iberica/H. maderensis lineage, which points to climatic pre-adaptation as key in the success of island colonization (dispersal and establishment). Once in Madeira, budding speciation was driven by geographical isolation, while ecological processes are regarded as secondary forces with a putative impact in the lack of further in situ diversification.
AimEvolutionary studies of oceanic island endemics are usually focused on lineages that have experienced in situ radiation, while those that speciated once on the island or archipelago but have not further diversified (single‐species endemics) remain understudied. The Macaronesian archipelagos, in the Atlantic Ocean, are home to significant numbers of single‐species endemics. The genus Hedera L. (12 species) includes three single‐species endemics from three Macaronesian archipelagos with putatively independent origins. Here, we tested the role of phylogenetic niche conservatism in their evolution. To that end, we (1) reconstructed the spatio‐temporal origin of Macaronesian ivies using phylogenomics, and (2) assessed the role of climatic niche during their colonization and speciation.LocationAzores, Canary Islands, Madeira, western Mediterranean.TaxonHedera spp.MethodsWe used 166 samples representing all Hedera species to generate genotyping‐by‐sequencing (GBS) libraries and performed time‐calibrated phylogenomic and biogeographic analyses. Climatic preferences and climatic niche evolution were assessed using a geo‐referenced database of the western ivy species (2,297 records).ResultsIndependent and asynchronous colonization and speciation were estimated for the three Macaronesian ivies, resulting in different degrees of phylogenetic and climatic niche differentiation: H. canariensis displayed an early divergence (7.5–12 Ma) and high phylogenetic and niche isolation; H. azorica had intermediate phylogenetic isolation and niche divergence from its closest relative H. helix (4.4–6.8 Ma) and H. maderensis was embedded within the climatically similar H. iberica (2.8–4.6 Ma). A strong phylogenetic signal was suggested for climatic niche in the western clade of Hedera, where the three Macaronesian ivies are placed.Main ConclusionsThe three Macaronesian ivies represent the evolutionary stages leading to the emergence of single‐species island endemics. Climatic niche conservatism appears to be involved in the evolution of single‐species endemics, first by facilitating island colonization, and then by limiting in situ diversification.
Background and aims: The way plants cope with biotic and abiotic selective pressures determines their success in the colonization of remote oceanic islands, which ultimately depends on the phylogenetic constrains and ecological response of the lineage. In this study we aim to evaluate the relative role of geographical and ecological forces in the origin and evolution of the Madeiran ivy (H. maderensis). Methods: To determine the phylogenetic placement of H. maderensis within the western polyploid clade of Hedera (three species), we analysed 40 populations (92 individuals) using genotyping-by-sequencing and including H. helix as outgroup. Climatic niche differences among the four study species were evaluated using a database with 706 records representing the entire species ranges. To test species responses to climate, a set of 19 vegetative and regenerative functional traits were examined for 70 populations (335 individuals). Key results: Phylogenomic results revealed a nested pattern with H. maderensis embedded within H. iberica. Gradual niche differentiation from the coldest and most continental populations of H. iberica to the warm and stable coastal population sister to H. maderensis parallels the geographical pattern observed in the phylogeny. Similarity in adaptive traits is observed for H. maderensis and H. iberica. The two species show leaves with higher SLA, lower LDMC and thickness and smaller fruits than those of H. hibernica. Conclusions: Acquisition of the Macaronesian climatic niche and the associated functional syndrome in mainland European ivies (small fruits, leaves high SLA, and low LDMD and thickness) was a key step in the colonization of Madeira 1 by the H. iberica/H. maderensis lineage, which points to climatic pre-adaptation as a driver of island colonization (dispersal and establishment). Once in Madeira, speciation was driven by geographical isolation, while ecological processes are regarded as secondary forces with a putative impact in the lack of further in situ diversification.
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