Evolution of pollination in prostanthera labill. (lamiaceae)

Abstract

Prostanthera Labill. (Lamiaceae) is traditionally divided into section Klanderia (F. Muell.) Benth. and section Prostanthera based on floral characteristics that correspond to putatively ornithophilous or entomophilous pollination syndromes. To better understand these pollination syndromes and how they evolved, the phylogenetic relationships, floral morphology, and pollination of Prostanthera were investigated. Maximum parsimony and Bayesian phylogenies for 66 (~75%) species of Prostanthera were constructed using chloroplast (trnT-F, nth-rpl32) and nuclear (ETS) genomes. In all cases Prostam‘hera was found to be paraphyletic with respect to Wrixonia. Prostanthera section Prostanthera was revealed to be paraphyletic relative to section Klanderia. A multivariate morphometric analysis of floral characteristics was also congruent with the molecular phylogenies and identified a single putatively ornithophilous group and two putatively entomophilous groups. Quantitative analyses of pollinator visitation further supported hypotheses derived from the analysis of nucleotide data and multivariate morphometrics and identified functional pollinator groups for each clade. Ancestral state reconstruction using squared-change parsimony of geometric morphometric landmark data provided insights into the ancestral pollination syndrome and evolutionary changes necessary to optimise corolla morphology for each clade. It is concluded that ancestral Prostanthera was likely pollinated by a diverse range of insects and possibly even birds. The evolution of an ornithophilous clade and a generalist entomophilous clade correspond with separate modifications to the lobes and tube of the corolla. The combination of phylogenetic and morphological data from this study provides a robust understanding of relationships and an insight to the structural changes in the evolution of pollination.