Showing papers by "Hans Pohl published in 2019"

The evolution and genomic basis of beetle diversity.

Abstract: The order Coleoptera (beetles) is arguably the most speciose group of animals, but the evolutionary history of beetles, including the impacts of plant feeding (herbivory) on beetle diversification, remain poorly understood. We inferred the phylogeny of beetles using 4,818 genes for 146 species, estimated timing and rates of beetle diversification using 89 genes for 521 species representing all major lineages and traced the evolution of beetle genes enabling symbiont-independent digestion of lignocellulose using 154 genomes or transcriptomes. Phylogenomic analyses of these uniquely comprehensive datasets resolved previously controversial beetle relationships, dated the origin of Coleoptera to the Carboniferous, and supported the codiversification of beetles and angiosperms. Moreover, plant cell wall-degrading enzymes (PCWDEs) obtained from bacteria and fungi via horizontal gene transfers may have been key to the Mesozoic diversification of herbivorous beetles—remarkably, both major independent origins of specialized herbivory in beetles coincide with the first appearances of an arsenal of PCWDEs encoded in their genomes. Furthermore, corresponding (Jurassic) diversification rate increases suggest that these novel genes triggered adaptive radiations that resulted in nearly half of all living beetle species. We propose that PCWDEs enabled efficient digestion of plant tissues, including lignocellulose in cell walls, facilitating the evolution of uniquely specialized plant-feeding habits, such as leaf mining and stem and wood boring. Beetle diversity thus appears to have resulted from multiple factors, including low extinction rates over a long evolutionary history, codiversification with angiosperms, and adaptive radiations of specialized herbivorous beetles following convergent horizontal transfers of microbial genes encoding PCWDEs.

The phylogeny of Coleopterida (Hexapoda) – morphological characters and molecular phylogenies

Abstract: Coleopterida (Coleoptera + Strepsiptera) has been established as the sister group of Neuropterida (Megaloptera + Neuroptera + Raphidioptera) based on recent phylogenetic analyses of DNA sequence data obtained from genomes and transcriptomes. However, within the resulting clade (Neuropteroidea) the proposed sister‐group relationship between the highly specialized endoparasitic Strepsiptera and the megadiverse Coleoptera still lacks convincing morphological support. Furthermore, relationships among the four suborders of Coleoptera remain controversial, with morphological characters strongly conflicting with results suggested by molecular evidence. A large morphological dataset comprising external and internal features of adults and immature stages is presented here and analysed phylogenetically. Our study is focused on deep splits in Coleopterida and on reconstructing character evolution on the phenotypic level. Parsimony analyses clearly support a sister‐group relationship between Strepsiptera and monophyletic Coleoptera. Presumptive synapomorphies are characters linked with posteromotorism, but also features of the head and prothorax. We recover Archostemata as sister group of the remaining extant Coleoptera, and Polyphaga as sister group of the species‐poor suborder Myxophaga. The most important character complex of Coleoptera is heavy sclerotization without exposed membranes and a simplification of the thoracic muscle apparatus. Non‐archostematan beetles are characterized by further simplifications of the thoracic locomotor apparatus. This trend reaches its peak in Myxophaga and Polyphaga, and these suborders also share apomorphies of the larval legs. A pattern with Polyphaga as sister to all other suborders and a clade Myxophaga + Archostemata (as in recent molecular phylogenetic studies) requires ten additional steps with our dataset. This scenario implies that various simplifications of the thoracic exoskeleton and musculature have taken place several times independently, and also that a complex feeding apparatus suitable for saprophagy and sporophagy was ancestral in Coleoptera, with secondary reduction (or modification) in Archostemata and Adephaga. The coleopteran subordinal relationships remain a challenge, with morphological and molecular data suggesting distinctly different patterns. The earliest evolution of Coleopterida is not documented in the fossil record. The exploration of potential stem‐group fossils is a high priority, as is the study of species from the Permian–Triassic transition zone, which are apparently important in the context of evaluating the relationships among beetle suborders.

Highly specialized Cretaceous beetle parasitoids (Ripiphoridae) identified with optimized visualization of microstructures

Abstract: Extremely miniaturized longipedes insects (body length c. 0.3 mm) embedded in two pieces of Cretaceous amber from Myanmar are described and interpreted. Using inverted fluorescence and light microscopy for detailed analysis of microstructures, the inclusions were identified as primary larvae of the beetle family Ripiphoridae, subfamily Ripidiinae. While the structure of thoracic and abdominal segments including appendages corresponds well with the groundplan known in recent members of Ripidiinae, a curved prosternal ridge with prominent spines (each c. 5 μm), the reduced condition of stemmata and antennae and the lack of sharp mandibles are unique features within the entire family, apparently apomorphies of the longipedes larvae. A sinuate prosternal edge with a dense row of spines (prosternoctenidium) might be homologous with ‘head ctenidia’ in some previously described miniaturized conicocephalate larvae, but further investigation is needed. The morphological differences between the head of longipedes larvae and extant Ripidiinae are interpreted as adaptations to different groups of hosts and life strategies. Palaeoethology of the longipedes larvae is briefly discussed. In addition, the systematic placement of conicocephalate larvae from Canadian, Myanmar and Russian Cretaceous ambers, already interpreted by various authors as primary instars within Coleopterida (assigned to either Strepsiptera or to the coleopteran Tenebrionoidea: Ripiphoridae), is discussed.

The abdomen of a free-living female of Strepsiptera and the evolution of the birth organs.

Abstract: Mengenillidae is a small, basal family of Strepsiptera, mainly characterized by free-living females in contrast to the endoparasitic females of Stylopidia. Here, we describe external and internal structures of the female abdomen of Eoxenos laboulbenei (Mengenillidae). The external morphology was examined and documented using microphotography. Internal structures were reconstructed three-dimensionally using a μCT-data set. The morphologically simplified abdomen comprises 10 segments. The integument is weakly sclerotized and flexible. Spiracles are present dorsolaterally on segments I-VII. Segment VII bears the posteroventral birth opening and the small abdominal segment X carries the anus at its apex. Numerous eggs float freely in the hemolymph. The musculature of segments I-IV is composed of ventral and dorsal longitudinal muscle bundles, strongly developed paramedial dorsoventral muscles and a complex meshwork of small pleural muscles, with minimal differences between the segments. Segments V-X contain more than 50 individual muscles, even though the musculature as a whole is weakly developed. Even though it is not involved in processing food, the digestive tract is well-developed. Its postabdominal section comprises a part of the midgut and the short hindgut. The midgut fills a large part of the postabdominal lumen. The lumina of the midgut and hindgut are not connected. Five or six nodular Malpighian tubules open into the digestive tract at the border region between the midgut and hindgut. The birth organ below the midgut releases the primary larvae after hatching via the birth opening at segment VII. It is likely derived from primary female genital ducts. The presence of six additional birth organs of segments I-VI are de novo formations and a groundplan apomorphy of Stylopidia, the large strepsipteran subgroup with endoparasitic females. The loss of the primary birth organ of segment VII is an apomorphy of Stylopiformia (Stylopidia excl. Corioxenidae).