Abstracts (first author)

Talk 

The reproduction-survival trade-off at the transcriptional level

Author(s): Zwaan B, Doroszuk A, Jonker M, Breit T

Summary:

To reproduce, organisms typically compromise their own immediate and future survival. Trade-offs are pervasive and form an important component of many biological theories. Despite the considerable attention dedicated to trade-offs over last years and sufficient genomic tools, it remains unclear how the patterns in gene expression translate to life-history trade-offs observed at the phenotypic level, and to what extent the knowledge at the molecular and theoretical levels can be integrated. Here, we report that the genes functionally linked to reproduction and survival in Drosophila melanogaster show negatively correlated expression patterns, mirroring the reproduction-survival trade-offs observed at the phenotypic level. We further show that the expression trade-off mediates responses to food and age in accordance with life history theory. This includes a parallel shift of the trade-off in females on different diets complying with the acquisition-allocation theory, and a trade-off release in males on high food levels following the notion of lower reproductive investments in males. Taken together, our findings (i) indicate that life history trade-offs can be interpreted as conflicts over gene expression, (ii) extend the interpretations of basic concepts in biology to the transcriptional level, and, (iii), suggest mechanisms of how these trade-offs are regulated. Up to date, trade-offs have either mostly been approached from a purely phenotypic perspective without much attention to the underlying mechanisms, or conclusions have been drawn about trade-offs from molecular studies without considering the functional phenotype. Our study clearly bridges these views and provides a novel molecular perspective for interpretation and testing of classical biological theories.



Abstracts (coauthor)

The fate of seasonal plasticity under relaxed selection

Author(s): Brattstrom, O, Oostra V, Brakefield PM, Hiltemann Y, Zwaan BJ

Summary:

Phenotypic plasticity of wing patterns is a widespread phenomenon among butterflies. Species occurring in seasonal habitats, where larval food plants dry out for an extended part of the year, often have a distinct dry season morph that is sedentary and delay reproduction until fresh plants are available. The dry season morph has a cryptic wing pattern to avoid detection by predators, while the wet season morph instead have conspicuous eyespots to deflect predator attacks.

The butterfly Bicyclus anynana is a model system for studies of phenotypic plasticity. In this species the plasticity affects more than just wing pattern so that the wet season morph allocates more of its available resources for quick reproduction. Wing pattern polyphenism is found in most Bicyclus species, but has not been well studied in species from less seasonal habitats.

We studied the phenotypic responses to different rearing conditions in the rainforest species B. martius and compared them to B. anayana. The wing pattern responses were similar despite the fact that true dry season conditions never occur in the forest habitat. Other traits showed limited response, suggesting that B. martius is adapted for continuous breeding. Surprisingly, the relative reproductive investment from the larval resources was smaller than in wet season morphs of B. anynana. Knowing that B. martius is a long-lived butterfly this can be seen as an adaption for spreading investments over time while maintaining an optimal fat load for flight performance.

Phenotypic responses are known to be under developmental hormonal control and it is thought that changes in hormone levels control a whole suite of correlated traits. In B. martius the life history traits seem uncoupled from the wing pattern polyphenism that still remains despite the presumed relaxed selection. This might be due to a relatively low fitness cost of expressing the wrong phenotype in a constant wet season environment.

The scent of inbreeding: a male sex pheromone betrays inbred males

Author(s): Van Bergen, E, Brakefield P, Heuskin S, Zwaan B, Nieberding C

Summary:

Inbreeding depression results from mating among genetically related individuals and impairs reproductive success. The decrease in male mating success is usually attributed to an impact on multiple fitness-related traits that reduce the general condition of inbred males. However, the reduced mating success of inbred males could also be a consequence of strong selection on females to avoid mating with an inbred male. This is especially relevant if females gain direct benefits through appropriate mate choice (parental care, territory defences, nuptial gifts) or if they suffer direct costs should they mate with an inbred male (decreased offspring viability and fertility). Here we find that the production of the male sex pheromone is reduced significantly by inbreeding in the butterfly Bicyclus anynana. Other traits indicative of the general condition, including flight performance, are also negatively affected in male butterflies by inbreeding. Yet we unambiguously show that only the production of male pheromones affects mating success. Thus, this pheromone signal informs females about the inbreeding status of their mating partners. We also identify the specific chemical component, hexadecanal, likely responsible for the decrease in male mating success. Our results advocate giving increased attention to olfactory communication as a major causal factor of mate-choice decisions and sexual selection.

Summary:

In most long-term laboratory evolution experiments, organisms are exposed to a constant selection regime that initially causes a large reduction in fitness. However, the ecological relevance of this treatment may be questioned: under natural circumstances, environmental variables likely vary with time. We were interested in how the rate of directional environmental change affects the evolution of heavy metal tolerance in Saccharomyces cerevisiae. To this end, we grew replicate lines of yeast for 500 generations in the presence of (i) a constant high concentration of Cd, Ni or Zn or (ii) gradually increasing concentrations of these metals. We anticipated that these contrasting selection regimes would result in different adaptive dynamics and evolutionary endpoints, as the shape of the fitness landscape changes as a function of metal concentration. More specifically, we propose the following alternative scenarios: 1) the most resistant genotype is most fit at all metal concentrations, but strength of selection is proportional to concentration 2) the optimal genotype changes with concentration, such that the optimal genotype at intermediate concentrations will confer an intermediate level of tolerance. These scenarios predict that a gradual increase of metal concentration (as opposed to a constant high concentration) causes mutations of large effect to be fixed at later time points (scenario 1), only mutations of small or intermediate effect to be fixed (scenario 2) and, if the fitness landscape is rugged, evolutionary endpoints to be fitter and more diverse (both scenarios). Here, we present results from competition assays that were used to determine the relative fitness of evolved and ancestral isolates and thus differentiate between the alternative hypotheses. Although evolutionary dynamics differed between the treatments, evolutionary endpoints had a similar fitness, reflecting a smooth fitness landscape that changes as a function of metal concentration.

Summary:

Environmental conditions experienced during development are known to influence the phenotype but also the different components of heritability, including genetic variance (VG). Here, phenotypic as well as genetic responses of life-history traits to two different developmental conditions, temperature and food limitation were assessed. The former represents an environment that defines seasonal polyphenism in our study organism, the tropical butterfly Bicyclus anynana, whereas the latter represents a more unpredictable environment. While development time, pupal mass, and resting metabolic rate showed no genotype-by-environment interaction for genetic variation, for thorax ratio and fat percentage the VG increased under the cool temperature, dry season environment. Additionally, for fat percentage, VG increased under food limitation. Hence, the traits most intimately related to the polyphenism in B. anynana show the most environmental specific genetic variance as well as some indication of cross-environmental genetic correlations. I will relate these results and the observed phenotypic responses to temperature (season) and food limitation to our recent RNA-Seq analyses on 72 individuals from the same families. We find substantial genetic variation for gene expression variation, affecting 1225 genes significantly (FDR<5%), while seasonal and food conditions affected much fewer genes. Interestingly, we also identified a number of genes whose expression was affected by the interaction between developmental conditions and genetic background, indicating genetic variation for environmental responses.

Summary:

Dietary restriction (DR), a reduction in food intake without malnutrition, is a well-studied topic in ageing research. However, knowledge about mechanisms mediating this response is scarce. We know the Insulin-IGF Signalling (IIS) pathway is involved in ageing in many organisms. In Drosophila, insulin-like peptides (DILPs), upstream components of IIS, respond to different food conditions and a dilp2-3,5 knockout extends lifespan. This suggests that dilps can have a role in mediating the DR response. We investigated the role of dilps in nutrient-altered ageing by determining lifespan, fecundity and brain-dilp expression of the long-lived dilp2-3,5 knockout mutant (d235∆)and its genetic control (wDah) on a range of food types that differed in sugar and yeast concentration. We showed that d235∆ flies had an increased lifespan and decreased reproduction on all food types compared to wDah flies. There was still a nutrient-dependent lifespan and reproduction response for d235∆ flies, but the effect of the highest sugar and yeast concentrations was reduced for both lifespan and fecundity. For gene expression, in wDah flies dilp2 and -3 expression increased on high yeast and lower sugar concentrations, dilp5 expression increased on high yeast concentrations and dilp6 expression did not change on different sugar or yeast concentrations. Interestingly, in d235∆ flies dilp6 expression increased on high yeast concentrations. This data shows that dilp2, 3 and 5 may have a role but are not the key in mediating the DR response. We hypothesize that dilp6 expression may take over expression of dilp2, -3 and -5 in the d235∆ flies, but not sufficient to maintain the same lifespan and reproduction on every food type.

Sexually antagonistic genes in a natural population of African buffalo

Author(s): Van-Hooft, P, Greyling BJ, Getz WM, Van-Helden PD, Zwaan BJ, Bastos ADS

Summary:

The view is emerging that intralocus sexual conflict at so-called sexually antagonistic genes is a fundamental factor for the genetic architecture of fitness. However, we do not know of any study on a natural population which has been able to analyse sexually antagonistic genes directly. Here, we analysed heterozygosity-fitness correlations (HFC) using microsatellites to show the occurrence of sexually antagonistic genes in the African buffalo (Syncerus caffer) of Kruger National Park. Additional analyses provided new insights into the characteristics of these genes and the selection pressures involved. Expected heterozygosity increased in low body condition (LBC) females relative to high body condition (HBC) females, i.e. a negative HFC, while the opposite was observed in males, i.e. a positive HFC. Alleles with a high frequency in HBC relative to LBC females tended to have a low frequency HBC relative to LBC males. This observation indicates that the particular group of sexually antagonistic alleles linked to the studied microsatellites are beneficial to females and deleterious to males. Furthermore, sexual antagonism was strongest among the high frequency alleles, indicating that they are under positive selection. The sexually antagonistic alleles were dominant in females, indicated by LBC-HBC allele frequency differences among heterozygotes, but less dominant and possibly recessive in males. This sex-specific inheritance pattern may result in protected polymorphism. Pregnant females with relatively many sexually antagonistic alleles, expected to be beneficial to their daughters, were mostly carrying female foetuses, while those with relatively few sexually antagonistic alleles mostly male foetuses. Thus mothers try to improve the chances that sexually antagonistic alleles are transmitted to the sex they benefit. This shows that the genetic load of sexually antagonistic variation can be high enough to interfere with the sexual selection of good genes.

Summary:

Malaria is a vector-borne disease that causes a huge burden to humanity, causing around 600 thousands deaths each year, of which 80% are children under the age of five years. Action to interrupt malaria transmission can be achieved by drugs and vector control. Current tools for vector control involve the use of insecticides though impregnated bed nets (ITNs) or indoor residual spraying (IRS). Unfortunately, these strategies have limitations because of the rapid spread of insecticide resistance in mosquitoes. New tools have to be employed to effectively combat malaria, such as entomopathogenic fungi that could be more sustainable and safe for the environment. To make this approach more effective and evolution proof, is crucial to study the components and mechanisms of fungal virulence by exploring the potential development of fungal resistance by the mosquito. We focus on the cosmopolitan fungus Beauveria bassiana which has already been successfully tested in field-based trials. In this study we characterized the natural variation of virulence of 20 isolates of B. bassiana that come from distinct regions of the world against the malaria mosquito Anopheles gambiae. Our results showed pronounced differences in virulence between isolates. Interestingly, there was no clear trend concerning geographic origin of isolates and virulence. We further evaluated the relationships between virulence and several fungal characteristics such as spore size, hyphal growth, UV resistance and conidiation production, among others. The contribution of these components to the overall virulence is elucidated. This study highlights the need of further multidisciplinary approaches for understanding the interaction among the many mechanisms shaping the virulence of B. bassiana against the insect An. gambiae.

Spatio-temporal compartmentalization of ecdysteroid effects on post-growth patterning

Author(s): Mateus, AA, Marques-Pita M, Oostra V, Lafuente E, Brakefield P, Zwaan B, Beldade P

Summary:

Developmental plasticity is a phenomenon whereby a single genotype produces distinct phenotypes depending on environmental conditions experienced during development. This process is regulated by changes in endocrine physiology, and has one of its most compelling examples in butterfly wing patterns that differ dramatically across seasons. In the butterfly Bicyclus anynana, larvae that develop during the wet season produce adults with conspicuous wing patterns, while those that develop during the dry season produce adults with cryptic patterns. The temperature regulation of the alternative adult phenotypes is mediated by changes in the internal ecdysteroid hormone dynamics. Manipulation of hormone titers copy the effects of temperature. However, little is known about hormonal sensitivities in relation to different external temperatures, to when the manipulations are done in terms of developmental timing, and to how different regions of the same tissue respond. Our aim was to investigate the compartmentalization of the effects of manipulations of systemic hormone levels during pupal development on adult wing patterns. We manipulated external temperatures (representing the natural extremes and an intermediate temperature) and internal levels of 20-hydroxyecdysone (via hormone injections at different developmental time points), and analyzed phenotypic effects on different wings, wing surfaces, color pattern elements, repeated elements of the same type, and groups of cells of the same repeat. Our results show that the effects of hormone manipulations depend on temperature and time point, and is highly compartmentalized in space: with specific epidermal cells responding in specified ways. We also show that this compartmentalization does not reflect compartmentalization of expression of hormone receptor. It remains to be seen whether the spatial compartmentalization of hormone effects is determined upstream or downstream of the binding of the hormone to its receptor.

Summary:

Populations of laboratory animals that are selected for increased lifespan often show correlated negative responses in early fecundity. However in some cases late fecundity, or total lifetime fecundity, is higher in the populations selected for increase lifespan. By some, this has been interpreted as a falsification of the disposable soma theory. According to the Y–model, in which the effects of variation in allocation and acquisition on life histories are studied, an alternative is suggested. A negative relationship between lifespan and reproduction can be viewed as variation in allocation, whereas a positive relationship is the result of variation in acquisition. We have analyzed age specific fecundity and lifespan in a cohort of Drosophila melanogaster flies which were individually housed. Early fecundity related negatively with lifespan, while late fecundity related positively with lifespan in the same cohort. We show that a model which incorporates the ideas of the Y-model, disposable soma theory and a decrease in physiological performance when age increases, can explain how the relationship between fecundity and lifespan changes with age. Furthermore, we modeled different environments in which there is variation in extrinsic mortality rates. In high mortality environments there was selection for high early fecundity, low late fecundity and low lifespans, whereas the opposite was true for low mortality environments. Our laboratory population of D. melanogaster was founded from a combination of flies from different areas in Europe and therefore is heterogeneous in genotype. We conclude that the differences in life history strategies found in one cohort of laboratory flies are the result of a mosaic of selection on the relationship between fecundity and lifespan over age.

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Address

XIV Congress of the European Society for Evolutionary Biology

Organization Team
Department of Animal Biology (DBA)
Faculty of Sciences of the University of Lisbon
P-1749-016 Lisbon
Portugal

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