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Our Research Unit FOR2281, which we nicknamed the "So-Long" project, comprises 12 projects. Nine are focused on specific organisms or models and three aim at performing comparative analyses. In addition, So-Long includes a variety of associated projects that support the main research momentum of the unit. Transcriptome sequencing (RNA-Seq) is being undertaken at BGI.

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Remoulding of the fecundity/longevity trade-off in a fungus-growing termite

Project TP05, Organism: Macrotermes bellicosus (Isoptera, Termitidae)

The aim of the Research Unit is to study the apparent remoulding of the fecundity/longevity trade-off in social insects at the ultimate and proximate levels. Almost all studies on ageing in social insects concentrated on social Hymenoptera.
The second largest social insect taxon, the termites, has been much neglected although it convergently evolved similar divergent lifespans between reproducing and non-reproducing castes. We recently started studying ageing and the fecundity/longevity trade-off in the lower termite, Cryptotermes secundus, which is socially less complex and has less pronounced differences in longevity between queens and workers than seen in higher termites. Within the framework of the Research Unit (RU), we also investigate the remoulding of the fecundity/longevity trade-off in the fungus-growing higher termite Macrotermes bellicosus. Macrotermes termites live in complex societies; their queens have a lifespan of up to 20 years and they are the most fertile individuals among all animals. This study allows for testing of commonalities and lineage-specific idiosyncrasies of the remoulding of the fecundity/longevity trade-off in social insects.

Contributors: Prof. Dr. Judith Korb, Daniel Elsner

The fecundity/longevity trade-off in a clonal ant

Project TP04, Organism: Platythyrea punctata (Hymenoptera, Formicidae, Ponerinae)

Colonies of social insects are characterised by a division of labour, with one or a few individuals specialising in reproduction and the majority of the colony members – the workers – handling all other tasks. Reproductives of perennial social insects are famous for their very long lifespan. Furthermore, they appear to avoid or even reverse the fundamental trade-off between fecundity and longevity: reproductives by far outlive their non-reproductive nestmates. However, reproductives and non-reproductives of most advanced social insect differ tremendously in ontogeny, morphology, physiology, behaviour and resource availability. This all may affect the interrelation between fecundity and longevity. The clonal ant Platythyrea punctata is a suitable model to study the trade-off without these confounding traits: workers are all morphologically and genetically identical. However, its colonies are characterized by a well-ordered reproductive division of labour based on rank orders established by young workers through fighting. As a consequence, each colony contains only one, rarely several, reproductive workers, while the majority of individuals has inactive ovaries. Interestingly, reproductive individuals (that lay unfertilized eggs) survive significantly longer than their coeval, non-reproductive clonemates. In this project we combine behavioural assays and molecular tools to analyze the interplay between longevity and fecundity in Platythyrea punctata.
Contributors: Prof. Dr. Jürgen Heinze, Dr. Abel Bernadou

Ageing and fecundity in Cardiocondyla ants

Project TP08, Organism: Cardiocondyla obscurior (Hymenoptera, Formicidae, Myrmicinae)

The life history trade-off between reproduction and longevity appears to be fundamental across animals and plants. Numerous studies document that reproduction is usually costly and therefore reduces future lifespan. Interestingly, the trade-off seems to be reversed in social insects, where reproducing queens outlive non-reproducing workers. Although data are scarce and the mechanisms still unknown, a few studies suggest a key role of vitellogenin in queen longevity, and, in addition, involvement of the TOR and IIS pathways. Both have also been shown to be of importance in solitary model organisms, which are subject to the trade-off. In our model system, the ant Cardiocondyla obscurior, we have already collected an extensive data set on life history traits and we were able to identify factors that impact queen lifespan. By doing so, we could confirm that queens do not suffer as a consequence reproduction in terms of reduced longevity. C. obscurior is particularly appropriate for life-history studies as, in contrast to most other social insects, mating and reproduction can be observed and conducted in the laboratory, queen longevity can be easily monitored due to a relatively short lifespan, and the genome is available. Hence, our existing data provide an excellent source to explore the molecular basis of the association between ageing and reproduction. Within the research unit’s research programme, we manipulate reproduction and food availability to detect the genetic pathways that impact queen longevity. As we could previously show that colony structure has a notable influence on queen lifespan, we in addition investigate how social structure affects age and fecundity.

Contributors: Dr. Alexandra Schrempf, PD Dr. Jan Oettler, Prof. Dr. Jürgen Heinze

Fecundity/longevity reversal in a social insect with alternative reproductive strategies

Project TP03, Organism: Temnothorax rugatulus (Hymenoptera, Formicidae, Myrmicinae)

Organisms clearly face a trade-off in allocating resources to either fecundity or longevity. In social insects this ubiquitous trade-off seems to be reversed. The queen - the most fecund individual of the colony - lays thousands of eggs and concurrently can live for decades, whereas the sterile workers only live for a few weeks or months. Social insects are ideal to study the molecular basis of longevity, not only because they exhibit strong intraspecific variation in longevity but also because this variation is mainly due to phenotypic plasticity as queens and workers develop from the same genetic background. Moreover, comparative studies revealed that variation in queen lifespan is influenced by social and ecological factors. Monogynous queens, which are the sole reproductive individual in their colonies, live much longer than polygynous ones, which reproduce alongside of other queens.
Our model, the ant Temnothorax rugatulus, exhibits a fecundity-longevity gradient with three morphologically distinct female castes. The large, macrogyne queens live in monogynous societies, whereas the smaller microgynes occur mainly in polygynous nests and show a lower fecundity and probably also reduced longevity. We manipulate the number of queens, food availability and egg presence and determine the effects on fecundity and survival in the two queen phenotypes. If the queen dies or is removed from Temnothorax colonies, workers become fertile. We analyse how and to what extent fertility positively influences lifespan in workers. Moreover, we study gene expression and identify genes and pathways underlying fecundity and longevity differences. In addition, we determine the level of oxidative stress, which is known to reduce longevity. Our framework allows us to quantify the influence of social and ecological parameters affecting fecundity and longevity in T. rugatulus and the underlying genetic networks. Together with other projects in the Research Unit, we gain insights into the molecular basis of the fecundity-longevity reversal in social insects, and we compare our findings to other model systems. Our long-term goal is to understand the association between fecundity and longevity on the proximate and the ultimate level.

Contributors: Prof. Dr. Susanne Foitzik, Dr. Barbara Feldmeyer, Matteo Negroni

The genomic tool box to transform a short-lived social bee into a long-lived parasite

Project TP06, Organism: Apis mellifera capensis, Bombus terrestris, Bombus vestalis (Hymenoptera, Apidae, Apinae)

The honeybee, as one of the most highly derived and highly eusocial insect species, may not appear very suitable at first sight to deal with trade-offs between longevity and fecundity. Colonial life in honeybees evolved well after the uncoupling of the trade-off between longevity and fecundity in its social ancestors. However, even though the honeybee queen seems to be in strict control of reproduction, the honeybee colony provides some elegant ways to test such trade-offs using the worker caste as a model system. Although worker sterility is the rule, workers can occasionally activate their ovaries to produce own offspring. This occurs whenever the queen is lost and cannot be replaced. In the extreme, worker reproduction can turn into social parasitism, as in the Cape Honeybee Apis mellifera capensis. Its parasitic workers invade a host colony, kill the resident queen and establish themselves as pseudoqueens therein. These pseudoqueens regain fertility, which may also interfere with their lifespan since it has been shown that they can function as pseudoqueens for up to five months. The comparison of worker pseudoqueens with sterile social workers therefore forms an ideal model system to test for the molecular basis of the uncoupling of life history trade-offs, independent of the nutrient-dependent morphological caste differences exhibited by queen and workers. We can not only test if egg laying workers live longer than sterile ones but also manipulate reproduction by experimental applications of queen pheromones that can inhibit pseudoqueen reproduction at various life stages.
Contributors: Prof. Dr. Robin Moritz, Denise Aumer

Phenotypic plasticity and the fecundity/longevity trade-off: investigating the underlying genetic basis in an orchid bee at the cusp of sociality

Project TP09, Organism: Euglossa viridissima (Hymenoptera, Apidae, Apinae, Euglossini)

Socially polymorphic species, in which different members of the same species exhibit either solitary or social behaviour, provide unrivalled model systems for exploring the role of sociality in fundamental biological processes. Using a socially polymorphic orchid bee species, Euglossa viridissima, which can be induced to nest in artificial observation boxes in the field, we describe the gene expression profiles of solitary and eusocial (worker and queen) phenotypes so as to identify key genes underpinning the different life history trajectories of the two castes. By experimental manipulation of brood cell provisioning, we test the fecundity/longevity trade-off in the solitary phenotype and define how it is modulated in the eusocial phenotype, using gene expression profiles and key ageing markers to explore its genetic basis. Comparison of these data with fully solitary and permanently eusocial species will demonstrate where along the sociality continuum remoulding of the fecundity/longevity trade-off has occurred.
Contributors: Prof. Dr. Robert Paxton, Alice Séguret

The physiological and metabolic basis of the fecundity/longevity trade-off in Drosophila

Project TP02, Organism: Drosophila melanogaster (Diptera, Drosophilidae)

In many organisms, curtailed reproduction increases lifespan. Conversely, extended lifespan is often accompanied by reduced reproduction. The overarching aim of our Research Unit is to investigate the evolution and mechanisms of the fecundity/ longevity trade-off in insects by comparing experimental manipulations in social insects, where – remarkably – the fecundity/longevity trade-off is typically absent, with data from solitary insects (e.g., Drosophila), where this trade-off is common and well-established. As a model for understanding the mechanisms underlying the fecundity/longevity trade-off, we perform experiments in the fruit fly (Drosophila melanogaster), which serves as a “solitary insect” reference system or “control” for the research undertaken on social insects in the So-Long project. The fact that decreased food intake without malnourishment (dietary restriction) extends lifespan while concomitantly reducing reproduction suggests that the longevity-reproduction trade-off might represent an energetic resource allocation trade-off. If so, food limitation might divert resources away from reproduction and make them available for somatic maintenance and survival. However, the trade-off in energy allocation between fecundity and metabolic storage is not quantitatively exact, and dietary restriction can increase lifespan in gonadectomized worms (Caenorhabditis elegans) and sterile flies (D. melanogaster), findings which are at odds with the resource allocation model. In contrast to C. elegans that lacks the entire gonad, worms that lack germ cells only are long-lived, and dietary restriction cannot further extend longevity in these individuals, suggesting that signals from the germline may oppose those of the somatic gonad to regulate ageing in the worm. Therefore, although current knowledge indicates that nutrient metabolism, reproduction and ageing represent interconnected regulatory axes, the actual mechanisms underlying the trade-off between reproduction and longevity remain largely unknown. The main goal of the research proposed here to use the genetically powerful fruit fly model Drosophila melanogaster to test whether the reproductive and nutritional regulatory axes converge onto the same mechanisms that affect ageing. Specifically, we will use a sterile mutant with oogenic arrest and a germline-less, long-lived transgenic strain as experimental tools to discover how reproduction interacts with diet to affect lifespan and physiology. To systematically characterise the global physiology underlying the fecundity/longevity trade-off in Drosophila, we will combine transcriptomics, metabolomics, endocrine assays and RNAi silencing of candidate genes.

Contributors: Prof. Dr. Thomas Flatt, Marisa Rodrigues


Comparative analysis of the fecundity/longevity trade-off in social insects: Convergent evolution of longevity in eusocial cockroaches and HymenopteraProject TP01, genome analyses, Organism: all

A hallmark of ageing is the trade-off between longevity and fecundity. However, reversals of this trade-off and the concomitant escape from ageing have convergently evolved in taxa as distantly related as the social Hymenoptera (bees, ants, wasps) and the social cockroaches (termites). Indeed, the lifespan of queens and kings (in termites) that monopolise reproduction within insect societies can exceed that of sterile individuals by up to two orders of magnitude. A recent surge in genomic resources has boosted studies into the molecular mechanisms underlying reproductive division of labour among the social Hymenoptera; yet, how the longevity/fecundity trade-off changes with sociality has received less attention. Moreover, the termites have been largely neglected, despite their independent evolutionary origin of similar lifespan divergence between reproductive and non-reproductive individuals. We aim to identify the molecular toolkit underlying the reversal of the fecundity/longevity trade-off in social insects, focusing on both Hymenoptera and cockroaches. Our comparative analyses include the first genome of the non-social, close relative of termites, the German cockroach (Blattella germanica). This approach helps us gain a deeper understanding into the molecular, evolutionary and genetic basis of how social insects escape the longevity/fecundity trade-off in distantly related taxa.

Contributors: Prof. Dr. Erich Bornberg-Bauer, Dr. Mark Harrison;
associated: Dr. Evelien Jongepier

Comparative transcriptome analyses of the fecundity/longevity trade-off in social insects

Project TPZ, transcriptome analyses, Organism: all

As in project TP01, this project aims to identify the molecular toolkit underlying the reversal of the fecundity/longevity trade-off in social insects using comparative approaches and analytic methods based on transcriptome data. Sequencing techniques (RNA-Seq) and subsequent data usage have become major tools for investigating differences and changes in transcriptomes between samples (see Wang et al. 2009). We aim to conduct comparative analyses across all samples of the social and non-social individuals of different age with and without stress (food availability, direct oxidative stress, work load) and manipulation of fecundity generated in the So-Long project. One approach we employ is differential gene expression analysis for which we will most likely focus on orthologous genes (transcripts that can be compared across taxa) including the genetically well characterised non-social dipteran fruitfly Drosophila melanogaster (see TP02).

Contributors: Prof. Dr. Judith Korb, Florentine Schaub, Dr. Karen Meusemann in collaboration with all projects

Towards a quantitative evolutionary theory of caste specific ageing

Project TP10, transcriptome analyses, Organism: all

The extraordinarily long lifespans of queens (and kings) in eusocial insects and the strikingly large differences in life expectancy between workers and queens challenge our understanding of the evolution of ageing. This enormous intraspecific variation makes social insects ideal model systems for ageing research and for studying the causes underlying adaptive variation in lifespan within species, without the limitations of interspecific comparison which suffers from confounding factors such as genetic architecture, physiology, ecology and so on. Although verbal arguments from classical evolutionary theories of ageinge.g. the mutation accumulation, antagonistic pleiotropy and disposable soma theories (reviewed in Rose 1991) – have been used to qualitatively explain the divergence in longevity between castes, there are no quantitative models to accurately predict the degree of divergence and its covariance with species-specific physiological, life-history, social and ecological characteristics. For example, it has been proposed that selection favours a lower rate of ageing in reproductives because they are less exposed to external hazards than workers (Keller & Genoud 1997). However, it is currently impossible to verify to what extent this explanation can account for the large quantitative divergence in ageing, nor is it clear which of the proposed ageing mechanisms are consistent with it. This project makes an attempt to do just that, and meet the challenges of providing a quantitative theoretical framework for the experimental and comparative projects in the Research Unit. We fully expect the insights from our studies to generalize beyond the scope of social insects and boost progress in ageing research in general. We aim to address the following main research questions:
Is caste-specific variation in external mortality sufficient to explain quantitatively the divergence in ageing between workers and reproductives in social insects?
  • Which of the proposed ageing mechanisms (mutation accumulation, antagonistic pleiotropy, optimal resource allocation), or which combination of mechanisms, can best explain the divergence in ageing between workers and reproductives in social insects?
  • Is condition-dependence of sensitivity to external hazards necessary to explain the caste-specific divergence in ageing? If so, what kind of condition-dependent traits are most likely to be involved?
  • How important is the role of genetic architecture? Does the evolution of extreme caste-specific divergence in ageing require the evolution of caste-specific regulatory networks that operate semi-independently, or can largely overlapping networks accomplish the divergence?
  • Can we accurately predict the caste-specific ageing profiles of the study species in the RU, based on experimental and life-history data? If so, does it require a single general model with species-specific fine-tuning of parameters, or is it necessary to construct structurally different models for different species?<\span>

Contributors: Prof. Dr. Franjo Weissing, Prof. Dr. Ido Pen, Dr. G. Sander van Doorn, Dr. Boris Kramer
in collaboration with TP01, TPZ, and all project focusing on an (model) organism.