Department of Biology & Biochemistry
A Turandot family gene promotes immunity against sexually transmitted fungal infections in Drosophila melanogaster
Author(s): Zhong, W, McClure, CD, Immonen, E, Ritchie, MG, Priest, NK
Although it is well known that mating increases the risk of infection, we do not know whether females have adaptive responses to mitigate the fitness costs of sexually transmitted infections (STIs). The major problem has been that we lack a suitable model host/pathogen system for studying the costs of STIs. Recently, Turandot-M (TotM), a member of the Turandot family of genes involved in immune and stress response, has been shown to be upregulated in female Drosophila melanogaster when they hear male courtship songs. Here we use the Gal4/UAS RNAi gene knockdown system to test whether TotM provides survival and fecundity benefits for females that mate with fungus-infected males. We show that when the fungus, Metarhizium robertsii, is sexually transmitted it reduces female reproductive output across all fly lines. By comparing the knockdown line (Gal4/UAS-TotM) with control lines (Gal4/+ and UAS-TotM/+), we found that TotM provides a survival benefit for females infected with an STI and a survival cost for healthy females. Interestingly, TotM does not provide a benefit for females under direct topical infection with M. robertsii. Together these results show that TotM plays a previously-overlooked role in defence against STIs and it suggests that females use auditory cues to anticipate the immune challenges that come with mating.
Department of Veterinary Medicine
A microcosm approach to understand the effects of host demography on disease transmission
Author(s): Diaz, A, Restif, O
One key aspect of the evolution of virulence is the rate of transmission between susceptible hosts. In theory, a virulent strain may increase in frequency if selection favours its transmission. However, it is not always know what host traits positively select for transmission and how individual variation and population demography affect its evolution. We are working with an experimental system in which specific aspects of infectious disease dynamics can be measured. We use the nematode Caenorhabditis elegans and fluorescent pathogenic bacteria (Salmonella enterica Typhimurium) to tract the spread of infection. In the soil, C. elegans lives in contact with many microorganisms, including pathogenic bacteria. It is known that similar to the mammalian innate immune response, C. elegans is able to mount a response to Salmonella. Despite this, Salmonella can colonise the worm intestine and increases death. Yet, it is not understood if and how the pathogenic effects of Salmonella can contribute the transmission of the disease in a population. We have characterised in detail C. elegans demography in response to the pathogen and varying conditions (i.e. age of infection, worm population size and genetic background). As reported before we found that Salmonella reduces worm survival. However, we found no reduction in the reproduction as a consequence of the pathogen, but a strong negative population density-dependence feedback on C. elegans. As a consequence of the high bacteria shedding of worms and little effects on its reproduction, Salmonella is very likely to thrive in the population
Evolutionary and Behavioral Biology
A stumbling Red Queen: host-parasite coevolution handicapped by Feeble males
Author(s): Masri, L, Schulte, RD, Timmermeyer, N, Thanisch, S, Crummenerl, L, Jansen, G, Michiels, NK, Schulenburg, H
Our work highlights the potential influence of intra-specific variations among the sexes in immunocompetence on host-parasite coevolution. In particular, the Red Queen hypothesis proposes that coevolving parasites select for outcrossing in the host. Outcrossing relies on males, which often show lower immune investment as a consequence of sexual selection. Here, we show that such sex-specific variation in immunity significantly interferes with parasite-mediated selection. Two independent coevolution experiments with Caenorhabditis elegans and its microparasite Bacillus thuringiensis produced a decreased yet stable frequency of outcrossing male hosts. Subsequent tests verified that male C. elegans suffered from a direct selective disadvantage. In the presence of its microparasite, males showed lower survival, decreased sexual activity, and altered escape behavior. Each of these responses can reduce outcrossing frequencies. At the same time, males also offered an indirect selective benefit, because male-mediated outcrossing increased offspring resistance. As such intra-specific variations in immunity are widespread among animals, the resulting interference of opposing selective constraints may impose a fundamental limit to host adaptation during antagonistic coevolution.
Adaptation of a fungal pathogen to individual versus social immunity in ants
Author(s): Stock, M, Grasse, AV, Cremer, S
Social insects fight diseases not only by the hygiene behaviour and physiological immune system of the individual group members, but also by their collectively performed, social defences ranging from sanitary behaviours, use of antimicrobials and organisational adaptations. Parasites infecting social insect colonies thus have to overcome both individual and social immune responses, which likely exert very different selection pressures on the parasite. To disentangle these effects and to understand the complexity of host-parasite-coevolution in social insect hosts, we performed a selection experiment on parasite adaptation towards solitary reared ants and ants in a social group, i.e. individual immune defence only or both, individual and social defences. We used the Argentine ant, Linepithema humile, and its fungal pathogen Metarhizium as our study system. Metarhizium is a soil-born entomopathogen and obligate killer of a broad range of insect hosts. It was recently found that the previously named M. anisopliae in fact is a species complex comprising a diversity of different Metarhizium species, which differ in ecological dominance and virulence against insects. To reflect this natural diversity, we used a mix of both M. roberstii and M. brunneum to perform ten passages through both solitary and grouped ants (10 replicates each). We found that fungal species composition and virulence changed over the ten generations, revealing a difference in the adaptation potential of the two sympatric fungal species, as well as an effect of the evolution regime. We can thus conclude that the ecological diversity of the different generalist Metarhizium species may reflect adaptations to a diversity of host species, and that the additional group level defences in insect societies adds new selection pressures for their coevolving pathogens with measurable effects on disease dynamics.
An invasive species reverses the roles in a host-parasite relationship
Author(s): Vrtilek, M, Vrtilek, M, Douda, K, Smith, C
Host-parasite relationships are often characterized by coevolutionary dynamics of parasite adaptations to exploit their host, and counter-adaptations in the host to avoid the costs imposed by parasitism. Such dynamic can be severely affected by introduction of a non-native species. We used a unique reciprocal host-parasite relationship between European bitterling fish, Rhodeus amarus, and European unionid mussels to study the effect of an invasive mussel species on bitterling oviposition behaviour and its consequences. Bitterling lay their eggs into gills of live mussels and, in turn, mussel larvae parasitize fish. The European bitterling colonized most of Europe relatively recently and parasitize all sympatric European mussels, which are evolutionarily naive and have not evolved strong defences (egg rejection) against bitterling parasitism. The parasitic larvae of European mussels are unable to utilize the bitterling, although readily parasites most other European fishes. The Chinese pond mussel, Anodonta woodiana, recently colonized European freshwaters from the region of high abundance and diversity of Asian bitterling species where it evolved strong adaptations against bitterling parasitism. We found that European bitterling behaviourally responded to A. woodiana as to a potential host, but failed to use it properly for oviposition (one population) or used it but all the eggs were lost due to rejections by the mussel (second population). Another experiment revealed that parasitic larvae of A. woodiana can develop on the European bitterling successfully, and hence effectively reversed the host-parasite relationship between the bitterling and mussels. We also discuss potential long-term consequences on population dynamics of the bitterling fish.
Department of Animal Biology/Centro de Investigação das Ferrugens do Cafeeiro
Analysis of Illumina RNA-seq data from a susceptible vs resistant coffee - Colletotrichum kahawae interaction
Author(s): Fino, J, Figueiredo, A, Loureiro, A, Silva, MC, Batista, D, Paulo, OS
Coffee berry disease (CBD), caused by the fungus Colletotrichum kahawae, is considered one of the biggest threats to Arabica coffee production in Africa at high altitude. Some coffee genotypes are known to be resistant to CBD, but the molecular genetic basis of coffee resistance is still unknown. With the purpose of gaining some insights on this process, a RNA Illumina sequencing approach was used to characterize the defense response of two coffee genotypes, respectively resistant and susceptible to C. kahawae, during the early stages of the infection process. Three inoculation time-points were selected (24, 48 and 72 hpi) and two biological replicates were collected. Twenty four independent cDNA libraries were sequenced and data is being analyzed to assess differential gene expression when comparing inoculated with control samples. The data was trimmed, and two assemblies were made: one with the control libraries and the other with the inoculated libraries. The first was used in expression quantification for both gene and isoform, by using statistical methods. Particular attention was paid to data normalization, using FPKM algorithm in gene quantification, and a Maximum Likelihood statistical model in isoform quantification. The other assembly is being used to discover C. kahawae genes by codon usage frequency (ECLAT). Although fungal transcripts are weakly represented in the samples, we expect to detect new and unknown genes of C. kahawae. The identification and characterization of expression differences between these contrasting situations will allow us to understand which genes are potentially involved in the resistance response of coffee to C. kahawae. The subsequent identification of the predicted proteins and their location in the metabolic networks could provide new relevant knowledge able to support and improve coffee breeding for resistance to CBD.
Funded by FCT (project PTDC/AGR-GPL/112217/2009)
Centre for Immunity, Infection and Evolution
Are tolerant hosts more likely to be super-shedders of disease?
Author(s): Vale, PF
Understanding the causes of individual variation in transmission could improve the success of disease management, by allowing to target the most infectious hosts. Disentangling the causes of this variation is challenging in the context of epidemics, but an alternative is to study disease transmission (or transmission potential) under a variety of genetic and environmental contexts in controlled experimental conditions. During infection, hosts may recover by eliminating pathogens (resistance mechanisms) or by controlling damage caused by infection without eliminating pathogens (tolerance mechanisms). Because they suffer less for a given parasite load, very tolerant hosts may experience infections for longer and have more opportunities for disease transmission. I present experimental data from Daphnia-microparasite and rodent malaria systems testing the link between tolerance and transmission potential. These results may be particularly relevant in understanding the epidemiological consequences of anti-virulence therapies of infection, that essentially increase host health without eliminating parasites.
Institute of Environmental Sciences
Avian malaria parasites and paternity in the blue tit
Author(s): Podmokła, E, Dubiec, A, Arct, A, Drobniak, SM, Gustafsson, L, Cichon, M
Monogamous bird species commonly adopt extra-pair mating as an alternative reproductive strategy. Since such behavior is potentially associated with very high costs in terms of desertion by the social male, it should be balanced by benefits, which may be either of direct or indirect origin. In the latter case, females may benefit from engaging in mating outside the pair bond if extra-pair males pass to the offspring genes of superior quality. One of the main determinants of individual quality is resistance to parasites. Therefore, if the social mate of the female is parasitized, she might be willing to seek resistance genes for her offspring through matings with other males. However, despite the strong theoretical prerequisites, robust empirical data verifying this prediction is lacking. Here, we test this hypothesis using infection status with malaria parasites as an index of genetic resistance. Blood parasites causing avian malaria (genus Plasmodium and Haemoproteus) are widespread among passerine birds and they may negatively affect fitness of the host by either reducing survival or reproductive success. We verified whether the occurrence of extra-pair offspring in the brood was related to infection status with avian malaria parasites of the social father in the wild blue tit (Cyanistes caeruleus) population characterized by relatively high frequency of extra-pair matings (40% of nests contain at least 1 extra-pair offspring) and approximately 60% infection rate with malaria parasites among adult males and females. Additionally, we examined whether the occurrence of extra-pair young is affected by infection status of the mother and the interaction between the infection status of both social parents.
department of Evolutionary and Environmental Biology
Can parasitoid recognition of hosts be improved by conditioning to host mate-recognition cues?
Author(s): Keinan, Y, Harari, A, Keasar, T
Species-specific semiochemicals, such as mate recognition pheromones, are often exploited by predators and parasitoids as cues for recognizing their prey. Generalist predators, unlike their prey, respond to pheromones of many prey species. Therefore, generalist natural enemies used for pest management tend to search for alternative prey. This reduces biocontrol efficiency and harms non-target species. We tested whether generalist parasitoids increase parasitism on a specific host after conditioning to its synthetic sex pheromone. Parasitoids learn to associate host presence with related environmental cues. We hypothesized that the efficiency of host search and parasitism would increase at repeated encounter with the learned pheromone odor. Two-phase laboratory experiments tested whether the generalist egg parasitoid Trichogramma cacoeciae (Hymenoptera: Trichogrammatidae) can be conditioned to the synthetic sex pheromone of its host, Lobesia botrana (Lepidoptera: Tortricidae). In the conditioning phase, parasitoids oviposited in L. botrana eggs in the presence or absence of the host's pheromone. In the test phase, wasps of both treatments encountered additional L. botrana eggs, in the presence or absence of the pheromone. Parasitism rates were compared among treatments. Wasps exposed to the pheromone did not increase parasitism rates, neither in the conditioning nor in the test phase. Possibly, the wasps innately responded to the pheromone, which masked their response to conditioning. To examine this possibility, we tried to condition the wasps to rum extract, a neutral olfactory stimulus, foreign to their natural environment. No conditioning occurred in this experiment either, suggesting poor odor learning in T. cacoeciae. We now ask whether chemicals, associated with hosts or host plants, attract the wasps when no conditioning occurs. Olfactometer bioassays are underway to identify environmental cues that guide T. cacoeciae to its L. botrana hosts.
Deciphering the impact of Plasmodium parasites on bird odorant profile: what makes infected birds more attractive to mosquitoes?
Author(s): Vézilier, J, Nicot, A, Romain, P, Nicolas, B, Bruno, B, Rivero, A, Gandon, S
It was recently demonstrated, using the avian malaria system (Plasmodium relictum SGS1 lineage), that infected birds are more attractive than non-infected birds to host-seeking Culex pipiens mosquitoes (Cornet et al. 2013 Ecology Letters). These results suggest that malaria parasites might manipulate bird traits that are used by mosquitoes to locate their host. This previous experiment eliminated visual or behavioural cues as potential signals, leaving olfactory cues as the most likely mechanism responsible for this enhanced attractiveness. To elucidate the proximal mechanisms of this fascinating manipulation, we characterised bird odorant profiles before and after a Plasmodium infection. The volatile organic compounds (VOC) emitted by hosts were captured on a solid phase (odour trap) using an innovative experimental setup. Gas chromatography was used for identification (mass spectrometry) and quantification (flame ionization detector) of VOCs. Cx. pipiens mosquito feeding preference (between infected and non infected birds) was simultaneously recorded following the protocol described in Cornet et al.. Here we correlate bird odour profiles and mosquito choice measurements, in order to identify VOC candidates susceptible to manipulation by Plasmodium parasites to render their hosts more attractive to mosquitoes.