Trap diversity and character evolution in carnivorous bladderworts (Utricularia, Lentibulariaceae)

Anna Sofia Westermeier,Andreas Fleischmann,Simon Poppinga,Kai Müller,Thomas Speck,Carmen Rubach,Bastian Schäferhoff

doi:10.1038/s41598-017-12324-4

Abstract

Bladderworts (Utricularia, Lentibulariaceae, Lamiales) constitute the largest genus of carnivorous plants but only aquatic species (about one fifth of the genus) have so far been thoroughly studied as to their suction trap functioning. In this study, we comparatively investigated trap biomechanics in 19 Utricularia species to examine correlations between life-forms, trapping mechanisms, and functional-morphological traits. Our investigations show the existence of two functional trap principles (passive trap in U. multifida vs. active suction traps), and – in active suction traps – three main trapdoor movement types (with several subtypes). The trapdoor movement types and their corresponding functional-morphological features most presumably represent adaptations to the respective habitat. We furthermore give insights into fluid dynamics during suction in three representatives of the main types of trapdoor movement. The results on functional morphology and trapdoor movement were mapped onto a new phylogenetic reconstruction of the genus, derived from the rapidly evolving chloroplast regions trnK, rps16 and trnQ-rps16 and a sampling of 105 Utricularia species in total. We discuss potential scenarios of trap character evolution and species radiation, highlighting possible key innovations that enable such a unique carnivorous lifestyle in different habitats.

Highlights

Bladderworts (Utricularia) belong to the most recently evolved group of carnivorous plants, the Lentibulariaceae within the order Lamiales[1]
In the ‘Utricularia vulgaris trap type’, the free edge of the trapdoor rests on the threshold at an obtuse angle of about 90°, and the trap entrance is shaped like a short tube
Based on our comparative biomechanical and functional-morphological studies, we propose the distinction between Utricularia trap and trapdoor movement types based on differences in functional principle, entrance morphology, angles between the doors and the thresholds, and trapdoor motion (Fig. 1)

Summary

Introduction

Bladderworts (Utricularia) belong to the most recently evolved group of carnivorous plants, the Lentibulariaceae within the order Lamiales[1]. The trigger hairs, the trapdoor abruptly inverts its curvature to concave (when seen from the outside), which is hypothesized to be facilitated by concentric cellular constrictions on its inner surface[17] It swings open, the trap walls relax, and water and prey rush into the trap due to the sudden increase of bladder volume, all within only a few milliseconds. In the ‘Utricularia vulgaris trap type’, the free edge of the trapdoor rests on the threshold at an obtuse angle of about 90° (as seen in sagittal section), and the trap entrance is shaped like a short tube. This applies to all species of Utricularia sect. In the second (unnamed) type, to which many non-aquatic species are attributed to, the trap entrance is long and tubular with the door standing obliquely at an acute angle of about 30°

Methods

Results

Conclusion