Grants and current projects
2020: DFG grant BR 2930/6-1
The prothoracic repellent glands of stick and leaf insects: Reconstructing the morphological and chemical evolution of an elaborate arthropod defensive system
Animals are permanently under strong selection to avoid predation, therefore predator-prey interactions are major driving forces of evolution and have given rise to a plethora of effective defensive strategies. Colouration is arguably the most obvious among primary defenses and might enhance crypsis to reduce detection or warn predators of the prey’s unpalatability or toxicity. Both strategies can be found in stick and leaf insects (Phasmatodea), a mesodiverse lineage of large terrestrial herbivorous arthropods well known for their remarkable capability to camouflage themselves as plant parts. Most species are nocturnal, remain motionless during the day and exhibit masquerade crypsis by mimicking twigs, leaves and bark. In contrast, a minority of species such as the Peruvian fire stick (Oreophoetes) displays striking forms of aposematism (warning colouration) insinuating the use of their efficient prothoracic repellent glands. Chemical spraying from these glands is just one of numerous secondary defense mechanisms in phasmatodeans (i.e., those initiated when a predator attacks), comprising startle display, defensive stridulation, thanatosis or escape by flight, limb autotomy or counterattack via heavily armend legs. Although most species largely rely on cryptic appearance to avoid predator detection, their secondary defense system is quite elaborate, and repugnatorial glands in the prothorax are supposed to be widely present among extant species, in fact constituting a derived ground pattern feature (autapomorphy) of all Phasmatodea.The chemical substances involved in this powerful defensive mechanism are known only for a dozen species out of the 3.000+ described taxa, so far with no information available for major and pivotal lineages. The goal of the present project is (i) to generate a profound information base for the presence and anatomical diversity of the prothoracic repellent glands across a broad and representative taxon sampling of 100 stick and leaf insect species, (ii) to identify the chemical substances involved, and (iii) to reconstruct the step-wise anatomical and chemical evolution of this elaborate defense system and to detect key innovations in a phylogenetic framework. The obtained information will be correlated with further data on body form and size, armature, colouration and behavioural observations of the examined specimens in order to reveal transformations of crucial traits and to detect key innovations that might have had an effect on diversification rates and shaped the evolution of stick and leaf insects. Since the few hitherto reported repellent substances show an unexpectedly huge diversity between taxa, exhibiting highly specific characteristics such as odor or causing skin irritations (as perceived by humans), and include some previously unreported natural products, we also expect our project to demonstrate the value of stick and leaf insects as sources of new bioactive compounds.
Stick and leaf insects, or Phasmatodea, are a mesodiverse lineage of large terrestrial herbivores that exhibit extreme forms of masquerade crypsis, imitating twigs and leaves to deceive visually hunting predators. Phasmatodea comprises ~3000 extant species and stands out as one of the last remaining insect orders for which a robust higher-level phylogenetic hypothesis is lacking, and we have only rudimentary understanding of the basal phylogeny for these insects. Yet, phasmatodeans serve as a model system to address important questions in evolutionary biology, such as speciation, evolution of asexuality, loss and regain of morphological traits, and clade diversification or, more precisely, repeated adaptive radiations in geographic isolation. New research suggests that the extant diversity is the result of a surprisingly recent rapid radiation and that geographical distribution rather than traditional taxonomic grouping and morphological similarity reflects the evolutionary relationships among stick and leaf insects. An extensive temporally calibrated phylogenetic analysis based on a combination of transcriptomic and Sanger sequence data selected for maximum phylogenetic coverage from >600 taxa (~20% of the known species diversity) is supposed to reliably resolve the relationships among stick and leaf insects. The obtained tree will provide an evolutionary framework for (i) tracing the global historical biogeography of phasmatodeans, (ii) assessing rates of speciation and extinction, and (iii) reconstructing ancestral character states and transformations of crucial traits that have an effect on diversification rates. These traits comprise flight capability and the presence of associated structures, such as ocelli and wind-sensitive hairs, body size and form, and the capacity for asexual reproduction. A plethora of mostly undescribed fossil specimens will be incorporated in the study, serving as calibration points for the phylogeny and also allowing comparison of quantitative morphometric and discrete anatomical traits between extinct and extant forms. The project is designed to significantly advance our understanding of adaptive clade diversification across space and time in this largely neglected group of insects.
2016: NSF (Nation Science Foundation) grant with Prof. Dr. Michael F. Whiting and Dr. James A. Robertson (Brigham Young University, Utah, USA) Award #1557114
Stick and leaf insects are large, tropical herbivores with an incredible ability to mimic twigs, bark, and leaves. Despite being important players in tropical ecosystems, stick insect diversity and evolution is the least understood of any large insect group. Many stick insects rely on ants to help disperse their eggs, but little is known about how this complex interaction evolved. The project will result in a greater understanding of stick insect evolution and the first, comprehensive understanding of species diversity. Because stick insects are common and diverse in the tropics, this research will provide critical baseline data for ongoing tropical conservation efforts. Four undergraduate students will gain training in all aspects of the scientific process using stick insects as a focal group. An interactive museum exhibit targeted to K-12 students will present the evolution of stick insect camouflage, ant associations, and the role these insects play in the natural world. The exhibit will also focus on conservation issues in the tropics, using the Lord Howe Stick Insect as an example of species rescue and recovery.
The project will reconstruct a robust phylogeny for stick insects based on DNA sequence data, document the parallel evolution of the different stick insect body types, investigate shifts from crypsis to aposematism, and determine whether these shifts are correlated with other life history traits and species radiations. The project will decipher the evolution of stick insect oviposition techniques, determine how many times egg dispersal via ants has evolved, investigate correlates of adult dispersal ability and reliance on ant-mediated egg dispersal, and study the temporal and geographic overlap of particular plant and phasmid species. It will also provide the baseline data to understand a fascinating cross-kingdom convergence on reliance on ant-mediated egg dispersal in both stick insects and angiosperms. This project will provide the scaffolding for future taxonomic work, revisionary systematics, and studies into the evolution of their unique forms.
DFG Grant BR 2930/2-1