Strong conservatism of floral morphology during the rapid diversification of the genus Helianthemum

Abstract

Premise: Divergence of floral morphology and breeding systems are often expected to be linked to angiosperm diversification and environmental niche divergence. However, available evidence for such relationships is not generalizable due to different taxonomic, geographical and time scales. The Palearctic genus Helianthemum shows the highest diversity of the family Cistaceae in terms of breeding systems, floral traits, and environmental conditions as a result of three recent evolutionary radiations since the Late Miocene. Here, we investigated the tempo and mode of evolution of floral morphology in the genus and its link with species diversification and environmental niche divergence. Methods: We quantified 18 floral traits from 83 taxa and applied phylogenetic comparative methods using a robust phylogenetic framework based on genotypingby-sequencing data. Results: We found three different floral morphologies, putatively related to three different breeding systems: type I, characterized by small flowers without herkogamy and low pollen to ovule ratio; type II, represented by large flowers with approach herkogamy and intermediate pollen to ovule ratio; and type III, featured by small flowers with reverse herkogamy and the highest pollen to ovule ratio. Each morphology has been highly conserved across each radiation and has evolved independently of species diversification and ecological niche divergence. Conclusions: The combined results of trait, niche, and species diversification ultimately recovered a pattern of potentially non-adaptive radiations in Helianthemum and highlight the idea that evolutionary radiations can be decoupled from floral morphology evolution even in lineages that diversified in heterogeneous environments as the Mediterranean Basin.

A phylogenetic perspective on ecological specialisation reveals hummingbird and insect pollinators have generalist diets

“…Closely related plants are often hypothesized to interact with similar sets of pollinators, but this idea has only mixed empirical support (Cirtwill et al 2020). We used a phylogenetic approach to test whether closely related plant species had more similar pollinator faunas in terms of richness and/or composition, which may be due to specific flower phenotypes preferred by pollinators (Kantsa et al 2018) and floral trait conservatism (Martín-Hernanz et al 2023). Thus, we used Blomberg's K (Blomberg et al 2003) to analyse whether closely related plants were visited by a similar number of pollinator species (phylogenetic signal of the pollinator richness) at each community.…”