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Stephen Stearns
Yale University
Department of Ecology and Evolutionary Biology
United States

Comparing phenotypic, quantitative genetic, and genomic approaches to measuring tradeoffs in a contemporary human population

talk 

Author(s): Stearns, SC

Summary:

In women born before 1940 in Framingham, Massachusetts, there was a significant negative correlation between number of children ever born and lifespan. Each additional child was associated with a reduction of about one year of life. Analysis of the 1500+ pedigrees containing 15,000+ people with an animal model that partially controlled for cultural and environmental effects yielded a large, significant, negative genetic correlation between children ever born and lifespan. A genome wide association study that looked for genes that alter the slope of the relationship between those two traits discovered several genes, some of which have previously been identified as involved in cancer. One, EOMES, has the sort of function one would expect of a gene that influences a tradeoff: its product affects many different processes. Statistical models with and without education as a covariate yielded results consistent with the idea that education is a cultural mimic of antagonistic pleiotropy: increases in level of education are associated with fewer children and longer life.

Alexandre Jousset
Georg August University Göttingen
Institute for Zoology
Germany

Evolution of food preferences drives pleiotropic fitness trade-offs in bacteria

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Author(s): Jousset, A, Fernkorn, F, Lapouge, K, Stefan, S

Summary:

Bacteria face trade-offs between life history strategies, among which the choice of a generalist or specialist resource use strategy has important effects on fitness. Bacteria bypass this problem by prioritizing nutrient utilisation. They highly specialise on preferred nutrients when available, and invest in a generalist way of life when only second-choice nutrients are left. Here we show that bacteria rapidly evolve new food preferences as an adaptation to a new substrate. We follow the expression of the small regulatory RNA crcZ in Pseudomonas fluorescens which is expressed in absence of preferred resources. It activates the translation of genes involved in alternative resource use. We show that the substrates inhibiting crcZ levels rapidly change when bacteria are confronted with second-choice subtrates, indicating that bacteria evolve new preferences. We further show that these altered food preferences affect the use of complex substrates by bacteria as well as their coexistence with competitors. Evolution of food preferences by bacteria appear therefore as efficient strategy to adapt to new conditions by readjusting the regulation of genes linked to substrate uptake and catabolism.

Howard Rundle
University of Ottawa
Department of Biology
Canada

Experimental insight into condition-dependent trait expression: near-orthogonal effects of environmental vs. genetic manipulations in Drosophila melanogaster

talk 

Author(s): Rundle, H, Mallet, M, Arbuthnott, D, Pawlowsky-Glahn, V, Egozcue, JJOSE, Bonduriansky, R

Summary:

Differences in condition among individuals arise from both genetic and environmental variance in their acquisition and/or assimilation of resources. Such variation in condition can weaken or otherwise obscure the physiological trade-offs among competing life history traits that are thought to necessarily arise from the allocation of finite resources. The nature and extent of among-individual variation in condition will therefore determine whether life history traits co-vary positively or negatively and is therefore central to our understanding of life history trade-offs. Our understanding of condition-dependent trait expression derives almost exclusively from environmental manipulations, yet it is the underlying genetic basis of condition, and the pleiotropy this generates among life history traits, that may have fundamental evolutionary consequences. A comprehensive understanding of life history traits, their trade-offs, and their evolution, will therefore require a detailed knowledge of the impacts on trait expression of both environmental and genetic variation in condition. Here we use a two-way factorial design to provide some of the first experimental data comparing the effects of diet and mutation-accumulation (i.e. environmental and genetic) manipulations of condition on a suite of sexual displays (epicuticular pheromones) and morphological traits in Drosophila melanogaster. Our results reveal that condition is multi-dimensional, with the effect of the environmental manipulation being almost orthogonal to that of the genetic manipulation for both sets of traits in both sexes. Only body size showed concordant effects of diet and mutation accumulation. This suggests that environmental manipulations alone may provide misleading insight into condition-dependence and its effects on the expression, evolution, and trade-offs among competing traits.

Adam Hayward
University of Sheffield
Department of Animal and Plan Sciences
United Kingdom

Genetic trade-offs and the evolution of human life-histories

talk 

Author(s): Hayward, AD, Lummaa, V

Summary:

Understanding life-history trade-offs is fundamental to explaining the diversity of life-history strategies in nature, and determining the genetic basis of trade-offs can identify how evolutionary constraint maintains life-history variation. Humans have evolved an unusual life-history compared to other primates, characterized by the menopause and long female post-reproductive lifespan (PRL). These have been hypothesized to evolve to enable (i) reduced reproduction when the costs of reproducing exceed the benefits, and (ii) enhanced grandchild survival. Previous tests of these hypotheses have examined phenotypic correlations between female reproductive rate and (i) PRL and (ii) offspring survival. However, environmental effects can mask genetic associations, and the direction and magnitude of these genetic correlations must be examined to determine the evolutionary potential of such traits. Using genealogical data from preindustrial Finnish church records for eight populations, we applied a multivariate quantitative genetic framework to examine the genetic basis of female reproductive rate, measured by inter-birth interval (IBI). We examined how additive genetic effects on IBI changed with age, and how age-specific genetic effects varied across environmental conditions. We determined the genetic trade-offs between IBI and both PRL and offspring survival, and how these trade-offs varied across ages and environments. Pilot analyses on four populations show a genetic basis to all traits, and suggest that genetic trade-offs between IBI and the other traits increased with age in poor environmental conditions, but were weak and age-independent in good conditions. IBI and PRL were positively related to lifetime fitness, suggesting that genetic trade-offs act as an evolutionary constraint. Our results will reveal new insight into human life-history evolution and generally highlight the fact that genetic correlations between traits may be age- and environment-dependent.

Colin McClure
Faculty of Science, University of Bath
Department of Biology & Biochemistry
United Kingdom

Hsp83 and TotC are Required for Pathogen-Induced Hormesis in the Fruit Fly

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Author(s): McClure, CD, Zhong, W, Priest, NK

Summary:

Hormesis contradicts the fundamental evolutionary concept that organisms can’t have it all. Many studies have found that treatments, such as limited stress and diet restriction, can enhance Darwinian fitness without obvious costs. This is a problem for our understanding of trade-offs as it suggests both that organismal fitness is sub-optimal, and that organisms can avoid trade-offs between life history traits. However, few studies have considered the possibility that hormesis is driven by a trade-off between Darwinian fitness and pathogen resistance. Here we show that topical treatment with an inactive fungus increases the survival and fecundity of various strains of the fruit fly. Using mutant strains and the Gal4::UAS knockdown system, we show that the heat shock protein Hsp83, and the generalist stress gene TotC, are required for this response. Preliminary evidence suggests that this hormetic response depends both on the temperature and diet of the host. These results are important as they identify the genetic basis of a novel hormetic response and provide a potential explanation for phenomena which appear to defy the constraints apparent in life history trade-offs: that hormetic responses are only beneficial under a narrow range of ecological conditions. Thus, our results are consistent with the hypothesis that hormesis also involves trade-offs.

Michael Garratt
University of New South Wales
School of Biological, Earth and Environmental Sciences
Australia

Life-history constraints are exposed when genetically-modified mice compete with con-specifics

talk 

Author(s): Garratt, M, Pichaud, N, Brooks, RC

Summary:

An organism’s investment in life history traits such as growth, reproduction and lifespan will be constrained by a variety of physiological factors. With regards to constraints on lifespan, genetic modification of gene expression has been successfully used to uncover some of the molecular pathways that influence how long an organism lives. These techniques have the potential to reveal constraints on other life history traits as I will demonstrate in this talk. We used a genetically-modified strain of mouse to test how various components of life history are constrained by oxidative stress, a physiological condition also implicated in ageing. Mice that did not express a key antioxidant enzyme used to protect against oxidative stress, copper-zinc superoxide dismutase (Sod1), showed altered investment in behavioural, morphological and molecular aspects of reproduction and sexual signalling. These effects were also found to be more prominent when animals were maintained in a competitive environment. We then used phenotypic manipulations to increase investment in various reproductive traits in both genetically-modified and wild-type animals. This allowed us to determine how oxidative stress, the outcome of this gene knockout, influences an organism’s ability to increase metabolic rate, adjust mitochondrial function and limit further oxidative damage when investing in demanding periods of reproductive effort. Our results reveal that oxidative stress is one aspect of physiology that can directly reduce investment in reproduction. The examination of genetically modified animals in more ecologically-relevant conditions offers exciting opportunities to uncover the mechanistic constraints on life history evolution.

Delphine Sicard
University Paris Sud
France

Linking protein structure and trade-off between life-history traits

talk 

Author(s): Sicard, D, Albertin, W, Spor, A, Kvitek, D, Wang, S, Nidelet, T, Martin, J, Marullo, P, Bely, M, Bourgais, A, Langella, O, Balliau, T, Valot, B, Da Silva, T, Dillmann, C, Gavin, S, De Vienne, D

Summary:

Metabolic pathways implicated in external resource consumption are expected to have an essential role in the evolution of life-history traits. Two extreme life-history trait strategies related to different resource exploitation strategies have been described in the yeast, Saccharomyces cerevisiae : The "grasshoppers" have a high specific glucose consumption rate in fermentation, a large cell size but a low reproduction rate and carrying capacity, while the "ants" have a low specific glucose consumption rate, a small cell size and a high reproduction rate and carrying capacity (Spor et al. 2008, 2009). We have explored the genetic and metabolic bases of « ant » and « grasshopper » life-history strategies. Using mutant analysis, we have shown that variation of expression of glycolytic encoding genes allow moving on the continum between these two extreme life-history strategies (Wang et al. 2011). Using proteomics appoaches we have revealed that not only glycolytic gene expression is involved in the control of yeast life-history strategies but also post-traductionnel modification of specific glycolytic enzymes (Albertin et al. 2013). Finally using experimental evolution, we have found that the evolution towards « ant » or « grashopper » strategies can be explained partly by mutations in a highly pleiotropic gene involved in a hub of more than 200 protein interaction network. This gene is recurrently mutated in the laboratory evolution. The location of the mutations in the gene, and thus in the protein, changes the effect of the mutation on several traits. Altogether, our data highlight the role of both variation in gene expression and also protein structure in the trade-off between life-history traits.

Staffan Jacob
Laboratoire Evolution & Diversité Biologique
Université Paul Sabatier
France

Microbiome mediates oxidative costs of reproduction

talk 

Author(s): Jacob, S, Parthuisot, N, Callat-Michel, A, Helfenstein, F, Heeb, P

Summary:

Parasites exert important selective pressures on host life-history traits. By affecting allocation trade-offs between reproduction and self-maintenance, they have major consequences for host reproductive success and survival. Microbiome is a major part of earth biomass, including pathogenic and commensal microorganisms. To date experimental studies that examine how the microbiome shapes host life-history traits are still lacking. Here we modified nest microbial communities of wild breeding great tits (Parus major) to test whether the microbiome mediates the oxidative cost of reproduction. We found that microbiome affected the relationship between fledgling number and adult oxidative damage. Adults raising a large number of nestlings show higher oxidative damage in control and high bacterial density treatments, whereas this trade-off was absent when decreasing bacterial densities. This study provides the first experimental evidence for a role of environmental microbiome in mediating the oxidative costs of reproduction. Our results show that the microbiome may constitutes a fundamental factor shaping animal life-history traits that need to be considered in future studies.

Lukas Schärer
University of Basel
Zoological Institute
Switzerland

Phenotypic engineering of testicular and ovarian function reveals a sex allocation trade-off in a simultaneously hermaphroditic flatworm

talk 

Author(s): Schärer, L, Sekii, K, Arbore, R, Berezikov, E, Ladurner, P

Summary:

A resource allocation trade-off between investment towards the male and the female function is a fundamental assumption of sex allocation theory for simultaneous hermaphrodites, but there is currently limited empirical support for it, especially among animals. Here we experimentally manipulated testicular and ovarian function in the free-living flatworm, Macrostomum lignano, and subsequently tested for the occurrence of the sex allocation trade-off. Specifically, we used RNA interference—by soaking worms in a solution of double-stranded RNA—to knock down the expression of specific candidate genes, which we identified in two ways. First, we screened 11 gonad-specific candidate genes obtained from a published microarray study in the distantly related planarian flatworm, Schmidtea mediterranea. Seven of these candidate genes had testis-specific expression in M. lignano, and the knockdown of five of these had evident effects on testicular function. The most prevalent effect was a disruption of sperm production, which for one candidate gene was accompanied by an increase in ovary size. Second, using an RNA-Seq screen in M. lignano we identified a candidate gene with ovary-specific expression, knockdown of which prevented the formation of yolk in developing oocytes and also resulted in larger testes (and a trend for a higher sperm production rate). Both of our approaches thus yielded candidate genes whose knockdown uncovered sex allocation trade-offs (notably via manipulation of both the male and the female function). This, to our knowledge, is the first study to use phenotypic engineering of testicular and ovarian function to empirically test the trade-off assumption of sex allocation theory. Furthermore, our results suggest that disrupting the function of one gonad does not necessarily lead to a trade-off, possibly because some types of disruption do not liberate resources that become available to the opposite function.

Jennifer Sanderson
University of Exeter (Cornwall Campus)
Centre for Ecology and Conservation
United Kingdom

Testosterone mediation of a trade-off between offspring care and reproduction in the cooperatively-breeding banded mongoose (Mungos mungo).

talk 

Author(s): Sanderson, JL, Young, AJ, Hodge, SJ, Walker, SL, Cant, MA

Summary:

Investment in offspring care commonly leads to a reduction in survival and fecundity, generating a trade-off between care of current young and future reproduction. Theory suggests that variation in this trade-off may explain the conspicuous individual differences in helping effort observed in cooperative breeders. In non-social species, testosterone is often found to mediate the trade-off between offspring care and reproduction. However, little is known about the mechanism mediating the trade-off between helping and future reproduction in cooperatively-breeding vertebrates. Here, we investigate testosterone as a candidate mechanism mediating trade-offs between cooperative offspring care and reproduction in the banded mongoose (Mungos mungo). Periods of high investment in offspring care are preceded by low faecal testosterone metabolite (fT) concentrations, suggesting that testosterone may inhibit offspring care in this species. During group oestrous, high ranking individuals with access to mates show elevated fT concentrations and a concurrent decrease in offspring care investment. However, outside of group oestrous, when there are no available mating opportunities, we find no correlations between individual rank and fT concentrations or investment in offspring care. These results provide evidence for testosterone mediation of the trade-off between offspring care and current reproduction in the banded mongoose, similar to that seen in non-social species. However, the mechanism mediating the trade-off between offspring care and future reproduction remains unknown. Together, these results highlight understanding the role of physiological mechanisms in mediating behavioural trade-offs as a key area of study to explain within-group variation in cooperative investment.

Contacts

Chairman: Octávio S. Paulo
Tel: 00 351 217500614 direct
Tel: 00 351 217500000 ext22359
Fax: 00 351 217500028
email: mail@eseb2013.com

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

Website

Computational Biology & Population Genomics Group 
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