Abstracts (first author)

Talk 

The maintenance of mitochondrial genetic variation by negative frequency-dependent selection

Author(s): Arnqvist G, Kazancıoğlu E

Summary:

The processes that maintain biological and genetic diversity are not fully understood. Mitochondrial genes, which encode proteins involved in a key energetic pathway in eukaryotic cells, often show high levels of standing genetic variation. This observation is especially puzzling, given the accumulating evidence for life history and fitness effects of mitochondrial genetic variation, because selection should rapidly exhaust genetic variation in the mitochondrial genome. Negative frequency-dependent selection, where the relative fitness of a genotype is inversely related to its frequency in a population, provides a potent and potentially general process that can maintain mitochondrial genetic polymorphism. However, empirical tests of this possibility are lacking. Here, we present experimental evidence that negative frequency-dependent selection acts to maintain polymorphism in mitochondrial genes. We assessed the change in mitochondrial haplotype frequencies over 10 generations of experimental evolution in a large number of seed beetle populations, where haplotypes competed for propagation to subsequent generations. We found that haplotypes consistently increased in frequency when they were initially rare and decreased in frequency when initially common. Furthermore, the strength of frequency-dependent selection was contingent upon epistatic mitonuclear interactions, directly supporting the tenet that intergenomic epistasis is important in mtDNA evolution. Our results have important implications for the use of mtDNA haplotype frequency data to estimate population level phenomena and they revive the general hypothesis that negative frequency-dependent selection may commonly facilitate genetic polymorphism in life history traits.


Video


Abstracts (coauthor)

Summary:

Classic sex role theory predicts that sexual selection should be stronger in males in taxa showing conventional sex roles and stronger in females in role reversed mating systems. I present the results of a study that tested this very central prediction and assessed the utility of different measures of sexual selection. We estimated sexual selection in both sexes in four seed beetle species with divergent sex roles using a novel experimental design. We found that sexual selection was sizeable in females, and that the strength of sexual selection in females and males varied with mating system and species. Residual selection formed a substantial component of net selection in both species. Further, we compared variance-based measures of sexual selection (the Bateman gradient and selection opportunities) with trait-based measures (selection differentials) in their ability to predict sexual dimorphism in reproductive behavior and morphology across species. Our results 1) highlight the importance of using assays that incorporate components of fitness manifested after mating, and 2) allow us to identify the generally most informative measure of the strength of sexual selection in comparisons across sexes and/or species.

Summary:

Despite the longstanding perception of the selective neutrality of mitochondrial genes, there is a growing awareness of their influence on life-history traits via interaction with the nuclear genome. Due to their effect on traits such as metabolism and growth rates, cyto-nuclear interactions are affecting variation predicted to explain the evolution of behavioural types or personalities (i.e. behavioural variation that is consistent within individuals, but differs among individuals). However, while cyto-nuclear interactions have significant potential to explain variation in behaviours, this line of research remains poorly explored. We used nine cyto-nuclear integression lines, where three cytoplasmic genomes were introgressed into three nuclear backgrounds, to disentangle genetic effects on both life-history traits and behavioural variation in the seed beetle (Callosobruchus maculatus). We show that life-span, but also activity of individuals in behavioural assays are influenced by the interaction of nuclear and cytoplasmic genes. Variation in activity level is consistent among individual beetles, suggesting that intergenomic interactions can also explain variation in animal personality. These results advance our understanding of the functionality of mitochondrial genes and their non-neutrality, and highlight the importance of cyto-nuclear interactions in explaining variation in behaviour and personality.

Summary:

In organisms with internal fertilization, males transfer seminal fluids to females during copulation. Specific proteins secreted by the male accessory glands (Acps) have profound impact in female reproductive physiology and behavior, affecting fecundity and female remating rate. Thus, these proteins may mediate postcopulatory sexual selection and may generate sexual conflict. Such selection can lead to their rapid evolution, with consequences for speciation. Despite their importance, Acps have been identified and their function elucidated in few cases and our understanding of the genetic variation in Acps production and the selection upon their encoding loci is still incomplete. The main goal of this study is to elucidate the level of genetic variation for Acps across populations in a seed beetle species, Callosobruchus maculatus, and to identify the Acps that mediate the effects upon female fitness through comparative quantitative proteomics studies. By using 7 different populations, we performed an experiment to estimate genetic variation in the Acps that regulate offspring production and female longevity. To obtain the Acp-proteome profile from each population we performed two-dimensional gel electrophoresis (2D-PAGE) and we generated the proteomic fingerprint needed for quantitative comparative analyses. Preliminary results showed that males from different populations have differentially affected female fecundity and longevity. Our results suggest the presence of genetic variation across populations for the effects of the Acps upon the studied female traits. 2D-proteomics comparative analyses showed differences in the Acp-proteome profile across populations, revealing a potential correlation between changes in the proteome and the female fitness. This finding is essential to identify the Acps that mediate the effects upon female fitness. This novel information will offer new insights into the evolution of Acps.

Summary:

The rapid divergent evolution of genital morphology is largely attributable to postmating sexual selection through cryptic female choice. Yet, our understanding of the evolutionary mechanisms of cryptic female choice for male genital traits is very incomplete. In the seed beetle Callosobruchus maculatus previous research has shown that male reproductive fitness increases with genital spine length. Here, we investigate the effects of artificial selection for male genital spine length on female fitness. We first show that, remarkably, females from lines in which males were artificially selected for longer genital spines exhibited comparatively greater fitness (life-time reproductive success). One explanation for this is that male genital spines in C. maculatus are condition dependent. That is, selecting for longer male genital spines may indirectly select for male genetic quality, and differences in female fitness across these selection lines may be due to shared genetic architecture between the sexes. We test the hypothesis that male genital spines in C. maculatus are condition dependent by rearing genetically independent families (derived from the same base population as the selection lines) through a series of substrates that vary in nutritional value. Differences in genital spine size across developmental substrates indicate condition dependence of the trait. Variation in the degree of condition dependence across genetic families indicates standing genetic variation for condition dependence (G x E), which could account for the fact that artificial selection on male genitalia generates a correlated response in female fitness. We discuss our findings in terms of the origin and maintenance of traits selected via cryptic female choice.

Summary:

It is now well recognized that exaggerated sexual signalling traits occur in females across many taxa. However, it remains empirically true that such traits are less common in females than in males. Their relative rarity in females is attributed to more restrictive conditions under which they can evolve: theoretically, female investment into signals of mate quality should be restricted due to trade offs with investment into fecundity. The conditions necessary for the evolution and maintenance of exaggerated female traits are not fully understood and their exact signalling function is not always clear. We investigated the chemical signalling role of a conspicuous, female-limited trait in a beetle showing female courtship and male mate choice. Megabruchidius tonkineus females court males by repeatedly presenting their abdomen, which bears two large, dark, pore-enriched patches that the male probes and antennates before deciding whether to copulate. We manipulated female mating status, age, and size, measured male mating preferences and compared female chemical profiles to determine whether this exaggerated female trait functions to signal female fecundity.

Genetic conflict between the sexes and rates of adaptation to climate warming

Author(s): Berger, D, Grieshop K, Lind M, Goenaga J, Maklakov A, Arnqvist G

Summary:

Intralocus sexual conflict (IASC) occurs when selection favors sex-specific optima in traits that have a shared genetic basis in males and females. This form of genetic conflict plays a key role in evolution and is likely to cause a gender load on population fitness. However, even though theory predicts that IASC may hamper adaptation under environmental change, we know very little about its potential role in affecting evolutionary rates under climate warming. We quantified the intersexual genetic correlation for fitness itself at a benign (29˚C) and a stressful (36˚C) temperature in the seed beetle Callosobruchus maculatus, by measuring offspring production of males and females from isofemale lines. In the studied population, there is a substantial gender load on fitness at the benign temperature, signified by a negative genetic correlation between male and female fitness. However, the correlation changed sign and became positive at stressful temperature conditions, suggesting that novel conditions may reduce genetic conflict between the sexes and increase rates of adaptation to climate warming. We estimate intersexual genetic correlations for, and sex-specific selection on, key traits likely to be involved in responses to climate warming (metabolic rate, lifespan, water loss, locomotor activity and body size). These data allow testing of two mechanisms that each predicts reduced conflict at stressful temperatures: 1) a release of cryptic genetic variation that has similar effects on fitness in both sexes and increases the opportunity for selection, and 2) a change and alignment of sex-specific selection differentials under stress.

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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