Do patterns of leaf trait variation, ecological strategies and population genetic structure differ in endemic vs. sister widespread species? Evidence from the forest species pair Aegonychon calabrum-A. purpurocaeruleum (Boraginaceae)

Why endemic species exhibit restricted geographical ranges is a key question in biogeography and ecology. Several historical, ecological or biological factors can contribute to the phenomenon of geographical range restriction. Among these, a relatively recent origin, a narrow ecological niche, a limited dispersal capacity, a low adaptive phenotypic plasticity or genetic variability are often involved. Understanding the role of these factors is crucial to support and plan conservation actions of endemic plant species, which often represent the most valuable and fragile components of native flora in a given region. Within the framework of a project on the Italian forest endemics, we attempted to bring light on this question by using trait-based and population genetics approaches in species of Apiaceae and Boraginaceae. These two families include several remarkable endemics in the forests of southern Italy. The idea was to compare the patterns of infraspecific variation in functional traits, ecological strategies and genetic structure in a selected number of species-pairs, each including a narrow endemic and a closely related wide-ranging species. One specific pair under investigation includes two species from the small genus Aegonychon Holub (Boraginaceae-Lithospermeae): A. calabrum (Ten.) Holub and A. purpurocaeruleum (L.) Holub. The former is confined to few isolated sites in the mountain forests of southern Italy, while the latter occurs in the understorey of thermophilous forests across many European countries and all Italian regions except Sardinia. Analyzing representative population samples of the two species, we could test the hypothesis that these species differ in the range and patterns of infraspecific variation in key leaf traits (LA, SLA, LDMC, LMA, LNC, LPC), Grime’s ecological strategies and genetic structure, which was examined with AFLP fingerprinting. In addition, we could compare genetic and phenotypic traits at the intraspecific level to evaluate the roles of genetic drift and natural selection in population differentiations.