Raum: NW I, 5.0 01 06
Ecological Immunity and Reproductive Ecology Group
My interest in science is centred on the evolutionary and ecological aspects of sexual selection, host-parasite interactions and immunity. Over the past years I have worked extensively on evolutionary and behavioural ecology, in particular on the conflict between individuals or species, whether it be conflicts between host and parasite or between male and female. Sexual reproduction and parasitism have always been the central interests in my life as a biologist. Moreover, it is increasingly being recognised that female responses to sexual conflict and host responses to parasites are not mutually exclusive topics, but rather are intimately connected. I am convinced that linking reproduction with host-microbe interactions will give many novel insights on how individuals deal with opportunistic infections and parasites and optimize reproductive investment.
Left) Copulating Bedbugs, top right) Activity of antibacterial substance measured in an immune assay and bottom right) Male reproductive organs.
My current research focuses on sexual conflict in the bedbug Cimex lectularius. While males have control over mating, the genetic contribution of males to the offspring generation is entirely unexplored as are the mechanisms leading to sperm selection by females. By experimentally separating male and female effects on fertilisation, I want to quantify sperm killing in bed bug females, investigate its mechanism, study competitive fertilisation after copulation inside and outside the supposed cryptic female choice organ and quantify sperm killing with respect to male and female genotype. Further, I am also interested in the relationship between the reproductive system and immunity, which seem to be tightly linked in bedbugs.
My work has been mentioned on BBC online, VBiO, Uni Bayreuth, TU Dresden, Research Features.
See here my latest publication
Current group members
Sara Bellinvia (PhD student) Disentangling host-parasite and male-female coevolutionary effects on host fitness
TBA (PhD student co-supervised with Klaus Reinhardt) The role of sperm phenotypic plasticity in speciation, University of Bayreuth and Technical University Dresden
Gitta Baeuerle (MSc student) Interspecific variation of antimicrobial venom and immune function in bumblebees
Bosert, S. (MSc student) Biodiversity and conservation along motorways
Nagl, L. (BSc student) Mating rate and reproductive output as drivers of sexual size dimorphism in the bedbug Cimex lectularius
Seltman, T. (BSc student) Effect of septic and aseptic mating on reproductive immune traits
Wieprecht, S. (BSc student) Sexual transmission of microbes in bedbugs
Christina Tilgen (student research assistant) conducting paternity analyses
Jörg Hager (technician)
Sperm-microbe interactions (DFG grant)
Males have been proposed to protect their sperm with antimicrobial substances from sexually transmitted microbes or microbes encountered in the females. We tested this ejaculate protection hypothesis where the two basic components are examined in conjunction, 1) microbes damage sperm and 2) antimicrobial ejaculate substances prevent such microbe-induced sperm damage. For our experiments we used the common bedbug, Cimex lectularius, which mates by traumatic insemination and possesses an antibacterial ejaculate substance. We exposed bedbug sperm to microbes either with or without antibacterial substance and measured the proportion of dead sperm. Exposure to microbes alone induced high sperm mortality, while in combination with antibacterial substance sperm survived as well as a control group of sperm without antibacterial substance and microbes. We also asked ourselves if male provisioning of antibacterial substance is a nuptial gift, leading to higher offspring numbers in females. Counting eggs showed a higher egg number laid over the first few weeks, and a faster decrease in egg numbers later on in the provisioned females compared to control groups not receiving the antibacterial substance. Sperm protection seems to be the more likely candidate for the evolution of antimicrobial substances in the seminal fluid than a nuptial gift. Although females do not seem to benefit directly from antibacterial substances, the protective effect on sperm might also reduce microbe numbers transmitted during mating. We are currently investigating to what extent the microbe-induced sperm mortality translates into male fitness and in general how microbes affect reproductive traits of both sexes. link to paper
Cimex lectularius paramere
The role of sperm adaptation and sperm plasticity in ecological speciation
(Collaboration with Dr. Ondrej Balvin, Czech University of Life Sciences, Dr. Tomáš Bartonička, Masaryk University Brno and Prof. Dr. Klaus Reinhardt, Technical University Dresden)
Speciation, the emergence of new species, is the ultimate source of biodiversity. Its most important step is that populations become reproductively isolated, i.e. their interbreeding is reduced, or results in reduced fitness. Characters that cause reproductive isolation before mating have been intensively studied, but reproductive isolation may also occur post mating, either before or after fertilisation, called gametic isolation (prezygotic) and hybrid disadvantage, respectively. Gametic isolation is heavily understudied and current models exclusively describe its genetic component of incompatibilities. Drawing on substantial evidence that all aspects of sperm functioning do not only depend on genetic but environmental factors, we here propose that environmental effects on sperm contribute to reproductive isolation, and test it for the first time. We will investigate the relative contribution the environment has on the functioning of sperm (which, by definition corresponds to sperm phenotypic plasticity) on reproductive isolation, compared to the (male) genetic component of sperm. We will compare the fitness outcome of population crosses in a natural system that currently undergoes speciation. We will use populations of bedbug host races that live on human or on bat hosts (bat-associated lines BL and human-associated lines HL).
External immune defence and its integration into the classical immune system
(Collaboration with Simon Tragust, University of Halle, and Heike Feldhaar, University of Bayreuth, Germany)
In recent years, evidence has accumulated that antimicrobials not only act internally, but are also deployed to the environment of an individual. Given that these antimicrobials form a defence against microbes, they should be considered part of the immune system. In addition to antimicrobials any trait affecting the pathosphere and microbial composition in the environment of an organism forms part of an external immune defence. Antimicrobials can be self-produced, symbiont derived or environment derived. A genetic basis and heritable variation for self-produced antimicrobials can be assumed but needs to be shown. Therefore, to understand the evolution of the external immune defence involving environment and symbiont-derived antimicrobials, investigations have to focus on the traits leading to the acquisition of symbionts or the collection of antimicrobials and their variation.
External immune defences might include not only the use of antimicrobials, but also behavioural adaptations, such as sanitary behaviours. Both are intimately linked, because behavioural adaptations are required to apply and distribute secreted compounds. By identifying antimicrobials and behaviours as traits of the external immune defence, we use tractable experimental framework in which costs and benefits for each individual can be assessed. Thereby, we also integrate the idea of social immunity where immune services are aimed at related group members as well as non-immunological defences into our definition of external immune defence. External immune defences defining the microbial environment of an individual can be viewed as the mechanisms leading to an extended immune phenotype. link to paper
Female gene expression responses to sperm phenotype and genotype
(Collaboration with Klaus Reinhardt, TU Dresden, Germany and Paul Johnston, Free University Berlin, Germany)
Reproductive success is highly variable between individuals. To date the main reason for such variation is appointed to genotype by genotype interactions of the mating partners, whereas the ecological context in which mating takes place has been widely neglected. For example, the duration of pre-copulatory sperm storage, i.e. the environment sperm are exposed to prior to copulation, potentially could have effects on how females process relatively older sperm compared to younger sperm. We are testing this by measuring female transcriptomes after exposing them to different sperm genotypes and different pre-copulatory sperm environments. Our results suggest that neglecting sperm environment might be one explanation for the small explanatory power of variation in reproductive success in previous studies. link to paper
Immunity to sperm
Reproductive immunity combines probably the two most important aspects of biological life: reproduction and the immune system. Reproduction incorporates highly complex processes that are mostly still unrevealed. Sexual reproduction is further complicated by antagonistic interest of the sexes in the amount and quality of investment for reproductive output. Due to the conflicting interests both sexes have evolved mechanisms to turn the odds of reproduction to their favour, which leads to an evolutionary arms race between the sexes. The immune system is actively involved in the processes of reproduction, mainly after insemination and during fertilisation. Post-mating processes and their relationship to immune function have just started to be described by researchers, yet without separating the effects of sperm, seminal fluid and male effects on mating. The paragenital system of female bedbugs, into which males transfer sperm, is filled with haemocytes, suggesting that it evolved partly to reduce the immunological consequences of hypodermic sperm transfer. Different sexual selection pressures could affect the evolution of sexually transmitted diseases, adaptive suppression of immunity, sexual conflict, genetic compatibility and cryptic female choice (CFC). CFC could drive the evolution, as immune cues potentially are able to provide the basis for female choice: females could directly assess male ‘quality’ by the ability of sperm to withstand, or escape, female-derived immunological attack. Sperm are non-self to a female’s immune system, and so phagocytosis may potentially act specifically on sperm. Using a phagocytosis assay we test the selection potential of the female immune organ (mesospermalege), which was identified by Eberhard (1996) as the cryptic female choice organ. Investigating the interaction between the immune system and mating will give new insight into the processes of cryptic female choice and sperm competition within the female. Ejaculates are not only necessary for reproduction, but also potentially dangerous to females. Especially, dead sperm or very old sperm should not linger around too long. Further, sperm is non-self to the female and might elicit an immune reaction, which then will kill sperm.
Outbreeding effects in an inbreeding insect
(Collaboration with Toby Fountain, University of Uppsala, Sweden)
Most populations exist with some form of spatial structure due to subdivided habitat. The common bedbug, Cimex lectularius, is rapidly re-emerging as a prominent public health and economic pest. Due to repeated founder events, frequent local extinctions due to pest control operations and restricted dispersal, bedbugs exist in highly structured metapopulations. The number of founders has been estimated as being as low as a single mated female. Therefore, close inbreeding is likely to be a very common feature of bedbug infestations and very high levels of differentiation have been observed between infestations. Whilst the majority of infestations seem to result from a single introduction, multiple introductions may be more common in buildings with a high turnover of people. Long distance passive dispersal gives the opportunity for individuals from highly differentiated populations to meet, and therefore introduces the possibility of heterosis and/or outbreeding depression. Whilst it is likely that bedbugs are resilient to inbreeding, as it appears that they frequently go through severe bottlenecks. What is not known is whether outbreeding can lead to a significant improvement in offspring fitness. One hypothesis may be that the increased connectivity between populations through an increase in global travel, has led to a rise in outbreeding events, which in turn has resulted in increased population growth and contributing to their resurgence. In this project, we investigate the effect of outbreeding of bed bugs on a number of different fitness correlates. We also test whether we could experimentally purge deleterious mutations with two generations of consanguineous mating. link to paper
Sexual size dimorphism in the cimicidae
(Collaboration with Dirk J. Mikolajewski, Free University Berlin, Germany and Klaus Reinhardt, TU Dresden, Germany)
Sexual dimorphism is the difference between the sexes of the same species and is extremely widespread and variable in animals. It includes differences in colour, exaggerated sexually selected traits, behaviour, body structure and size. In this project we concentrate on sexual size dimorphism (SSD), which in invertebrates is often female biased. SSD is thought to evolve through differential selective pressures on the sexes including fecundity selection on female size, sexual selection on male size and genetic correlation as well as multiple constraining factors. We are especially interested in investigating the mechanism that is central to the establishment of the size difference. Previously both development time and growth rate have been hypothesized to be important parameters in defining SSD. We investigate this by manipulating developmental time via different temperature regimes. Lower than optimal temperatures often prolong developmental times in ectothermic animals. Due to size constraints females might be less plastic in their response to environmental stress in both these traits. Therefore, under temperature stress SSD should be smaller at lower than optimal temperatures. Also growth rate should define SSD at lower than optimal temperatures rather than developmental time.
Please contact me if you are interested in doing a project in my group. I am happy to discuss ideas within the framework of my current projects. If you consider working with me please have a look at this and this.
>> Curriculum Vitae