Phylogenetic perspectives on biome shifts in Leucocoryne (Alliaceae) in relation to climatic niche evolution in western South America

Abstract

Aim Shifts between the western South American sclerophyll and winter-rainfall desert biomes and their relationship to climatic niche evolution and aridity development were investigated in the South American endemic geophytic Leucocoryne (Alliaceae) clade. Location Western South America. Methods We constructed a molecular phylogeny (internal transcribed spacer, ITS), estimated lineage divergence times, and identified ancestral biomes and biome shifts. The multivariate climatic niche of present-day species was described using occurrence data and bioclimatic variables. Climatic niche similarity was evaluated using Mahalanobis and Fisher distances. Brownian motion (BM) and Ornstein–Uhlenbeck (OU) models of evolution were used to characterize temperature and precipitation niche evolution. Ancestral temperature and precipitation were estimated using the phylogenetic generalized leastsquares method. Results Leucocoryne exhibits a low level of phylogenetic biome conservatism. The clade arose in the early Miocene in an ancestral sclerophyll biome and subsequently moved northwards into the arid winter-rainfall biome on two separate occasions, during the late Miocene and Pliocene, respectively, with very recent diversification of species in the winter-rainfall desert. Overall, the multivariate climatic niche showed significant differentiation, and phylogenetic and climatic niche distances were correlated. Temperature and precipitation niche evolution within lineages followed a pattern that is consistent with stabilizing selection (OU model). Main conclusions The low level of phylogenetic biome conservatism found in Leucocoryne is associated with considerable expansion of the precipitation and temperature niche axes. Unidirectional biome shifts from a wetter biome characterized by higher species richness and more continuous vegetation cover, into a drier biome with lower species richness and much sparser vegetation cover, suggest that the availability of and lower biotic resistance within open habitats facilitated biome shifts in Leucocoryne. Incursion into the arid winterrainfall desert and diversification there may have been facilitated by the conservative geophytic life-form of Leucocoryne, the generally cool coastal conditions, and the wet/dry climatic cycles occurring since the late Miocene.