Climatic and edaphic niche shifts during plant radiation in the Mediterranean biodiversity hotspot.

Abstract

Background and aims: Ecological speciation is frequently invoked as a driver of plant radiation, but the behaviour of environmental niches during radiation is contentious, with patterns ranging from niche conservatism to niche divergence. Here we investigated climatic and edaphic niche shifts during radiation in a western Mediterranean lineage of the genus Linaria (Plantaginaceae).

Methods: Detailed distributional, phylogenomic and environmental data were integrated to analyse changes in climatic and edaphic niches in a spatiotemporal context, including calculation of niche overlap, niche equivalency and similarity tests, maximum entropy modelling, phylogenetic comparative methods and biogeographic analyses.

Key results: Active divergence of climatic and edaphic niches within a limited subset of available conditions was detected among the eight study species, and particularly between sister species. Speciation and niche divergence is estimated to have happened in the southern Iberian Peninsula under Mediterranean conditions, followed by waxing and waning of distribution ranges resulting from the Quaternary climatic cycles.

Conclusions: Results support the idea that the prevalence of niche conservatism or niche divergence patterns is a matter of phylogenetic scale. Habitat isolation pertaining to both climatic and soil conditions appears to have played a role in plant speciation in the western Mediterranean biodiversity hotspot, most likely in combination with pollinator isolation and some degree of geographic isolation. These findings are in agreement with an adaptive radiation scenario incorporating certain non-adaptive features.