The evolution of complete metamorphosis in insects

Metamorphosis, the change (meta) in form (morphe), is a common phenomenon in the animal kingdom, where it has evolved several times independently. The most dramatic metamorphic changes occur in the most successful group of animals: the insects, which comprise more than 60% of all living animals. Within the group of insects, the Holometabola (e.g. beetles, butterflies, flies and bees) comprise more than 80% of all insect species. Holometabolous insects undergo complete metamorphosis. In a non-feeding pupal life stage, intercalated between the larval and adult stages, their entire anatomy is radically remodelled, including the digestive tract, which undergoes apoptosis and proliferation. The second major group of insects, the Hemimetabola (e.g. grasshoppers, true bugs, and dragonflies), undergo incomplete metamorphosis. Compared to Holometabola, hemimetabolous insects metamorphose more gradually, less drastically and without a pupal stage. Holometaboly is one of the key evolutionary innovations explaining insects' enormous and unique biodiversity. However, how the evolution of the pupal stage is related to the success of insects is unknown. The remodelling of the larval gut poses a significant challenge to the gut microbiota, as the gut is replaced during pupation, which does not occur in Hemimetabola. It gives holometabolous insects the unique opportunity to drive a change between the larval and adult microbiota, facilitating niche shifts by allowing the insect to acquire specialised symbionts for a life-stage specific diet, ecology and physiology- one barely studied adaptive hypothesis explaining the evolution of the pupa. In chapter II, using 16S rRNA gene metabarcoding, I studied 18 different herbivorous insect species from five orders of holometabolous and three orders of hemimetabolous insects. Comparing larval and adult specimens, I found a much higher beta-diversity and hence microbiota turnover in holometabolous insects than in hemimetabolous insects. My results support the idea that the pupa offers the opportunity to change the gut microbiota and hence facilitates niche shifts. This possible effect of niche shift facilitation could explain a selective advantage of the evolution of complete metamorphosis. The unique opportunity to change the microbial composition throughout insect development by gut remodelling during complete metamorphosis also puts holometabolous insects at a higher risk of infections. Holometabola must control their gut microbiota and initiate an immune response to avoid infectious diseases during metamorphosis. In chapter III, using RNAseq, I compared the expression of immune effector genes in the gut during metamorphosis in two holometabolous and a hemimetabolous insects. I found high read count abundances of differentially expressed immune effectors in the gut at the larval-pupal moult in the two Holometabola; no such high abundances were observed at the nymphal-adult moult in Hemimetabola. My findings confirm that only complete metamorphosis elicits a prophylactic immune response as an adaptive response in holometabolous insects, which controls the microbiota during gut replacement. Another barely studied and not mutually exclusive hypothesis explaining the success of holometabolous insects could be that intercalating the pupal stage decouples growth and differentiation. Most growth is confined to the larval stages in holometabolous insects, while most development occurs in the pupa, allowing for fast larval growth. In chapter IV, I conducted a literature review and calculated growth rates and ratios. I compared 33 species from three holo- and seven hemimetabolous insect orders. I found faster larval growth, higher growth ratios, and much higher variances for those traits in holometabolous than hemimetabolous insects. I also found much shorter growth periods of the larval stages in holometabolous than hemimetabolous insects. My results support the decoupling of the growth and differentiation hypothesis in holometabolous insects, allowing fast larval growth. In this thesis, I investigated two barely studied and not mutually exclusive hypotheses explaining the evolution of the pupa in holometabolous insects, which constitute the majority of animal diversity. I could show a microbiota turnover in holometabolous insects, which is also under the control of the host gut immunity and allows the Holometabola to occupy different niches throughout development. The second hypothesis, which proposes that decoupling growth and differentiation allows for fast larval growth, is supported by my findings of faster larval growth rates in holometabolous than hemimetabolous insects. The facilitation of niche shifts by changes in the gut microbiota could be considered an essential driver of the evolution of the pupa. The microbiota turnover could also be driven by other selective factors such as growth rate. Fast larval growth could be a selective factor for decoupling growth and differentiation, ultimately resulting in the evolution of the pupa in holometabolous insects

Complete metamorphosis and microbiota turnover in insects

The insects constitute the majority of animal diversity. Most insects are holometabolous: during complete metamorphosis their bodies are radically reorganized. This reorganization poses a significant challenge to the gut microbiota, as the gut is replaced during pupation, a process that does not occur in hemimetabolous insects. In holometabolous hosts, it offers the opportunity to decouple the gut microbiota between the larval and adult life stages resulting in high beta diversity whilst limiting alpha diversity. Here, we studied 18 different herbivorous insect species from five orders of holometabolous and three orders of hemimetabolous insects. Comparing larval and adult specimens, we find a much higher beta-diversity and hence microbiota turnover in holometabolous insects compared to hemimetabolous insects. Alpha diversity did not differ between holo- and hemimetabolous insects nor between developmental stages within these groups. Our results support the idea that pupation offers the opportunity to change the gut microbiota and hence might facilitate ecological niche shifts. This possible effect of niche shift facilitation could explain a selective advantage of the evolution of complete metamorphosis, which is a defining trait of the most speciose insect taxon, the holometabola

Complete metamorphosis and microbiota turnover in insects

This study was funded by the DFG (Deutsche Forschungsgemeinschaft, RO 2284/2-1).The insects constitute the majority of animal diversity. Most insects are holometabolous: during complete metamorphosis their bodies are radically reorganized. This reorganization poses a significant challenge to the gut microbiota, as the gut is replaced during pupation, a process that does not occur in hemimetabolous insects. In holometabolous hosts, it offers the opportunity to decouple the gut microbiota between the larval and adult life stages resulting in high beta diversity whilst limiting alpha diversity. Here, we studied 18 different herbivorous insect species from five orders of holometabolous and three orders of hemimetabolous insects. Comparing larval and adult specimens, we find a much higher beta-diversity and hence microbiota turnover in holometabolous insects compared to hemimetabolous insects. Alpha diversity did not differ between holo- and hemimetabolous insects nor between developmental stages within these groups. Our results support the idea that pupation offers the opportunity to change the gut microbiota and hence might facilitate ecological niche shifts. This possible effect of niche shift facilitation could explain a selective advantage of the evolution of complete metamorphosis, which is a defining trait of the most speciose insect taxon, the holometabola.Peer reviewe

Chytrid parasitism facilitates trophic transfer between bloom-forming cyanobacteria and zooplankton (Daphnia)

Parasites are rarely included in food web studies, although they can strongly alter trophic interactions. In aquatic ecosystems, poorly grazed cyanobacteria often dominate phytoplankton communities, leading to the decoupling of primary and secondary production. Here, we addressed the interface between predator-prey and host-parasite interactions by conducting a life-table experiment, in which four Daphnia galeata genotypes were maintained on quantitatively comparable diets consisting of healthy cyanobacteria or cyanobacteria infected by a fungal (chytrid) parasite. In four out of five fitness parameters, at least one Daphnia genotype performed better on parasitised cyanobacteria than in the absence of infection. Further treatments consisting of purified chytrid zoospores and heterotrophic bacteria suspensions established the causes of improved fitness. First, Daphnia feed on chytrid zoospores which trophically upgrade cyanobacterial carbon. Second, an increase in heterotrophic bacterial biomass, promoted by cyanobacterial decay, provides an additional food source for Daphnia. In addition, chytrid infection induces fragmentation of cyanobacterial filaments, which could render cyanobacteria more edible. Our results demonstrate that chytrid parasitism can sustain zooplankton under cyanobacterial bloom conditions, and exemplify the potential of parasites to alter interactions between trophic levels

Comprehensive analysis of chemical and biological problems associated with browning agents used in aquatic studies

Inland waters receive and process large amounts of colored organic matter from the terrestrial surroundings. These inputs dramatically affect the chemical, physical, and biological properties of water bodies, as well as their roles as global carbon sinks and sources. However, manipulative studies, especially at ecosystem scale, require large amounts of dissolved organic matter with optical and chemical properties resembling indigenous organic matter. Here, we compared the impacts of two leonardite products (HuminFeed and SuperHume) and a freshly derived reverse osmosis concentrate of organic matter in a set of comprehensive mesocosm- and laboratory-scale experiments and analyses. The chemical properties of the reverse osmosis concentrate and the leonardite products were very different, with leonardite products being low and the reverse osmosis concentrate being high in carboxylic functional groups. Light had a strong impact on the properties of leonardite products, including loss of color and increased particle formation. HuminFeed presented a substantial impact on microbial communities under light conditions, where bacterial production was stimulated and community composition modified, while in dark potential inhibition of bacterial processes was detected. While none of the browning agents inhibited the growth of the tested phytoplankton Gonyostomum semen, HuminFeed had detrimental effects on zooplankton abundance and Daphnia reproduction. We conclude that the effects of browning agents extracted from leonardite, particularly HuminFeed, are in sharp contrast to those originating from terrestrially derived dissolved organic matter. Hence, they should be used with great caution in experimental studies on the consequences of terrestrial carbon for aquatic systems

Tackling the critical hurdles – revising technology-based ideation processes

Technological innovations are crucial for a country’s economic growth as they often have radical innovation potential. Although recognized as a key role in the innovation process, lots of technologies remain unexploited. University spin-offs (USOs) have the potential to transfer technologies into technological innovations. Often though, in universities there is a lack of consideration of potential implementation right from the start. The so-called fuzzyfront end (FFE) stage is crucial for successful innovation, as no commercialization can be achieved without the identification of a suitable application. This represents a critical hurdle, as of to date appropriate approaches for a successful systematic identification and validation of technology applications are missing. Furthermore, most investigating studies rely on data from spin-offs that are already operating successfully on the market and have therefore survived the critical initial stages of development, without highlighting the FFE of their process. This fact makes the pre-development activity of opportunity recognition appear to be a scientifically neglected topic. In this research a mixed-method approach is conducted to investigate the critical hurdles in the technology application selection (TAS) process of technologies, consisting of an extended literature review, completed by interviews with stakeholder involved in the USOs ecosystem. Striving to uncover the black box of the FFE, the study aims to specify and operationalize requirements for application identification of technologies. These findings are of relevance for researchers and practitioners which like to facilitate the exploration of potential technological innovation

Comprehensive analysis of chemical and biological problems associated with browning agents used in aquatic studies

Inland waters receive and process large amounts of colored organic matter from the terrestrial surroundings. These inputs dramatically affect the chemical, physical, and biological properties of water bodies, as well as their roles as global carbon sinks and sources. However, manipulative studies, especially at ecosystem scale, require large amounts of dissolved organic matter with optical and chemical properties resembling indigenous organic matter. Here, we compared the impacts of two leonardite products (HuminFeed and SuperHume) and a freshly derived reverse osmosis concentrate of organic matter in a set of comprehensive mesocosm- and laboratory-scale experiments and analyses. The chemical properties of the reverse osmosis concentrate and the leonardite products were very different, with leonardite products being low and the reverse osmosis concentrate being high in carboxylic functional groups. Light had a strong impact on the properties of leonardite products, including loss of color and increased particle formation. HuminFeed presented a substantial impact on microbial communities under light conditions, where bacterial production was stimulated and community composition modified, while in dark potential inhibition of bacterial processes was detected. While none of the browning agents inhibited the growth of the tested phytoplankton Gonyostomum semen, HuminFeed had detrimental effects on zooplankton abundance and Daphnia reproduction. We conclude that the effects of browning agents extracted from leonardite, particularly HuminFeed, are in sharp contrast to those originating from terrestrially derived dissolved organic matter. Hence, they should be used with great caution in experimental studies on the consequences of terrestrial carbon for aquatic systems