The prothoracic repellent glands of stick and leaf insects: Reconstructing the morphological and chemical evolution of an elaborate arthropod defensive system
Dissertation
Datum der mündl. Prüfung:2023-11-24
Erschienen:2024-03-11
Betreuer:Dr. Sven Bradler
Gutachter:Dr. Sven Bradler
Gutachter:PD Dr. Alexander R. Schmidt
Dateien
Name:Dissertation Marco Niekampf.pdf
Size:11.1Mb
Format:PDF
Zusammenfassung
Englisch
Stick and leaf insects (Phasmatodea) form a diverse lineage of large herbivorous arthropods inhabiting predominantly tropical and subtropical regions. These insects are well known for their impressing camouflage capabilities, exhibiting extreme forms of crypsis and masquerade whereby they disguise themselves by mimicking twigs, bark, leaves, lichens or mosses. In addition to this and a rich repertoire of further primary and secondary defensive strategies, these insects defend themselves using irritating and malodorous chemicals from prothoracic repellent glands. These glands are considered as a derived autapomorphic trait of the Phasmatodea and are widely distributed among these insects. However, detailed knowledge of the glandular anatomy and chemical compounds is scarce and only a few taxa have been studied thus far. In order to generate a profound information base for the presence as well as anatomical and biochemical diversity of the prothoracic repellent glands, I used micro-computed tomography (μCT) and gas chromatography coupled with mass spectrometry (GC-MS) for a global sampling of stick and leaf insects. For the first time, the glands were analyzed in size and structure in comparative studies of major lineages, leading to the categorization into four distinct types (Chapter 1). The phylogenetic comparison of gland types and sizes clearly indicates a convergent evolution in the Euphasmatodea. Moreover, the chemical analyses revealed the monoterpene peruphasmal as the ancestral defensive substance that has been conserved for millions of years and is still prevalent in many extant subgroups (Chapter 2). Contrary to this, individual taxa evolved novel chemicals in the repellent secretions and diverged from the ancestral substance, eventually highlighting a high degree of chemical diversity in stick and leaf insects (Chapter 3). Chemical disparities do not only occur in distantly related taxa, but as exemplarily shown for the leaf insects (Phylliidae), are also found within closely related and phenotypically uniform groups (Chapter 4).
Keywords: defensive strategies; insect evolution; chemical defense; comparative morphology; repellent glands