Evolution Letters最新文献

Changes in gene expression levels are central to adaptation, yet predicting and understanding their evolution remains challenging. Here, we used transcriptome-wide variation in the red flour beetle Tribolium castaneum to identify genes under selection for expression changes during adaptation to heat and drought stress and to uncover the mechanisms driving these changes. We found that estimates of genetic selection on expression levels were predictive of their evolutionary changes after 20 generations across seven independent selection lines. Evolution was largely caused by indirect selection acting on genetically correlated genes rather than by direct selection on individual genes. Consequently, central genes in co-expression networks experienced stronger selection and larger expression changes. Our genomic analysis revealed that selection on expression levels is associated with parallel allele frequency changes in the respective genes, especially in pleiotropic genes and those carrying expression quantitative trait loci, with stronger genetic selection corresponding to greater parallelism. Contrary to previous evidence of constrained evolution at more connected genes, adaptation was driven by selection acting disproportionately on genes central to co-expression gene networks. Overall, our results demonstrated that selection measured at the transcriptome level not only predicts future gene expression evolution but also provides mechanistic insight into the genetic architecture of adaptation.

Understanding the drivers of biodiversity is a central goal in evolutionary biology. In particular, sexual selection has long been proposed as a potential catalyst of speciation, but empirical evidence remains inconclusive. Here, we present a comprehensive meta-analysis synthesizing 145 effect sizes from 50 comparative studies testing the relationship between proxies of sexual selection and species diversity across the animal kingdom. Our results reveal a modest but consistent positive association (global effect size: r = 0.201; 95% confidence interval: 0.035-0.366), supporting the hypothesis that sexual selection contributes to speciation. However, the global effect size corresponds to an R ² of only 0.04, suggesting that sexual selection is not a dominant driver of speciation. We also uncover substantial heterogeneity among effect sizes, largely attributable to between-study variation and taxonomic affinities of effect sizes. Studies that fail to account for phylogenetic non-independence tend to report stronger effects. In contrast, other tested methodological and biological moderators, such as the proxies used to estimate the strength of sexual selection or proxies of speciation, do not explain the observed heterogeneity in effect sizes. Sensitivity analyses confirm the robustness of our results, and we find no signatures of publication bias. We highlight the need for broader taxonomic coverage and a greater focus on understudied mechanisms, such as post-copulatory sexual selection, to refine our understanding of the role of sexual selection in shaping species diversity.

Genetic covariance matrices (G-matrices) are a key focus for research and predictions from quantitative genetic evolutionary models of multiple traits. There is a consensus among quantitative geneticists that the G-matrix can evolve through deep time. Yet, quantitative genetic models for the evolution of the G-matrix are lacking. In contrast, the field of macroevolution has several stochastic models for univariate traits evolving on phylogenies. However, analytical models of how multivariate trait matrices might evolve on phylogenies have not been considered. Here, we show how three analytical models for matrix evolution can be combined to unify quantitative genetics and macroevolutionary theory in a coherent mathematical framework. The models provide a basis for understanding how G-matrices might evolve on phylogenies. We fit models to data via simulation using Approximate Bayesian Computation. Such models can be used to generate and test hypotheses about the evolution of genetic variances and covariances, together with the evolution of the traits themselves, and how these might vary across a phylogeny. This unification of macroevolutionary theory and quantitative genetics is an advance in the study of phenotypes, allowing for the construction of a synthetic quantitative theory of the evolution of species and multivariate traits over deep time.

Phenotypic plasticity is a widespread strategy used by organisms to cope with environmental fluctuations. Empirical studies have mostly focused on describing the amplitude of phenotypic change through reaction norms, which ignore the temporal dynamics of plasticity. Although the speed of plastic responses has recurrently been predicted to modulate their adaptiveness, it remains largely understudied. Here, we retraced the time course of plasticity across four traits in 12 isogenic strains of the ciliate Tetrahymena thermophila to test how the temporal dynamics of plasticity mediate its adaptiveness under fluctuations. We decomposed plastic responses into 3 parameters: a lag and a rate describing their temporal dimension and the canonical plastic capacity. All showed high intraspecific variability. We found the plastic capacity to be positively correlated to the rate of plasticity and not to the time required for plastic changes to be implemented. We then linked the dynamics of plasticity to how strains performed across a gradient of fluctuation periods. The temporal parameters of plasticity significantly explained performance in fluctuating conditions, more so than the plastic capacity alone. Interestingly, strains mounting morphological plasticity at a slower rate tended to be less sensitive to fluctuations. This study demonstrates that a better understanding of how organisms cope with environmental change requires us to consider and incorporate the temporal dynamics of plasticity in theories and experiments.

Polyploids are organisms with three or more chromosome sets, which often give them different physiology, morphology, and evolutionary properties. The impact of polyploidy on the genetic load dynamics, in terms of accumulation, fixation, and purging of deleterious mutations, is largely unknown. Here, we use forward-in-time genomic simulations to compare the fitness effects of genetic load components assuming diploid and tetraploid populations under different demographic scenarios. Under partial recessiveness, we show that tetraploids tend to accumulate a higher genetic load than diploids in small and large populations, with negative consequences on their fitness. Under complete recessiveness, the same pattern is observed only in small populations, but similar load effects are found in large diploid and tetraploid populations under mutation-drift equilibrium. The only scenario where tetraploids suffered less from the effects of genetic load was in bottlenecked populations under complete recessiveness. Our results highlight the importance of factors such as demography, dominance and selection coefficients, and genetic drift in shaping the different patterns of accumulation of deleterious mutations in diploids and tetraploids. While some studies have suggested that tetraploids might have a reduced genetic load because recessive mutations could be masked more efficiently, our findings align more closely with evidence that tetraploids frequently accumulate a higher genetic load than diploids. This insight is significant for assessing the role of ploidy in the conservation of endangered species.

Post-copulatory sexual selection, comprised of sperm competition and cryptic female choice, is a powerful evolutionary force that can drive the rapid diversification of reproductive traits across taxa. In birds, the female reproductive tract provides the arena for post-copulatory sexual selection, yet we lack a comprehensive understanding of the female specific processes that shape the evolution of sexually selected traits. Here, we use a comparative approach to explore the relationships between female reproductive tract morphology, sperm competition intensity, and sperm traits across Galliformes. Accounting for phylogenetic and allometric relationships, we find that species with relatively larger testes for their body size-a proxy for intense sperm competition-have relatively longer vaginas, suggesting that important co-evolutionary dynamics exist between male and female reproductive physiology. Surprisingly, we find no link between sperm length and sperm storage tubule morphology, challenging existing predictions. Our findings suggest that the vagina has a significant but currently overlooked influence on post-copulatory processes and emphasizes the need to better integrate female morphology into models of sexual selection.

Non-invasive methods for measuring thermal tolerance and thermoregulation in large numbers of individuals under natural environmental conditions are useful to understand the capacity of species to adapt to future climate scenarios. Infrared thermography (IRT) is one such tool in research on thermal adaptation, but concerns have been raised about its reliability, specifically the correlation between surface temperature (T _s) and body temperature (T _b) (Monge et al., (2025). What does IRT tell us about the evolutionary potential of heat tolerance in endotherms? Evolution Letters, 9(2),184-188). Here, we discuss the biological inferences that can be made from data on T _s and T _b, and whether T _s needs to be correlated with T _b to be informative in studies of thermoregulation in free-living organisms. We also present a framework illustrating biological insights that can be gained by integrating IRT with data on different phenotypic traits, fitness metrics, pedigree information and other physiological traits, including T _b. We illustrate the utility of this new framework by demonstrating how it has increased our understanding of the evolution of thermal tolerance in a large animal where T _b is not easily measured, the ostrich (Struthio camelus) (Svensson et al., (2024). Heritable variation in thermal profiles is associated with reproductive success in the world's largest bird. Evolution Letters, 8(2), 200-211). Integrating IRT with individual fitness data and pedigree information in field studies can aid our biological interpretation of T _s in future research on the ecology and evolution of thermal tolerance in both endotherms and ectotherms.

Natural populations often experience heterogeneity in the quality and abundance of environmentally acquired resources across both space and time, and this variation can influence population demographics and evolutionary dynamics. In this study, we directly manipulated diet in replicate populations of Drosophila melanogaster cultured in experimental mesocosms in the field. We found no significant effect of resource variation on estimates of adult census size. Resource variation altered patterns of phenotypic and genomic evolution across replicate populations; however, we find that this effect is secondary to selection driven by the fluctuating seasonal environment. Seasonal adaptation was observed for all traits assayed and elicited genome-wide signatures of selection. In contrast, adaptation to the resource environment was trait-specific and exhibited an oligogenic architecture. This illustrates the capacity of populations to adapt to a specific axis of variation (the resource environment) without hindering the adaptive response to seasonal change. This, in turn, suggests that resource variation may be an important force driving fluctuating selection across natural populations, ultimately contributing to the maintenance of genetic and phenotypic variation.

The evolution of eusociality, characterized by cooperative brood care, reproductive division of labor, and overlapping generations, represents a major evolutionary transition. A central paradox is that early models suggested diminishing returns to helping, making solitary reproduction seemingly more efficient. Here, we experimentally demonstrate increasing returns to scale from early-season helping in the primitively eusocial wasp Polistes gallicus. By manipulating the proportion of females allowed to remain as helpers, we show that while reproductive output scales linearly with worker numbers, total sexual productivity increases convexly with helper probability, thereby showing that early-season helping leads to compounding effects on reproductive output. Using these data, we parameterize a dynamic population genetic model and show that this convex relationship facilitates the spread of eusociality alleles more readily under monandry than polyandry, contrary to the conclusions of some prior models. Importantly, we show that compounding effects can cause eusociality to evolve even when helpers are no more efficient at rearing brood than solitary breeders. Our findings emphasize the value of integrating experimental data with mechanistically motivated theoretical models to study social evolution.

Evolutionary trade-offs-opposing trait effects on total fitness via different fitness components-are likely to be widespread. Some key trade-offs are expected to be the result of chains of causation acting across an organism's lifetime. For example, a trait imparting reproductive benefits early in life may trade off against reduced survival to attain later-life reproductive opportunities. Tools in evolutionary quantitative genetics have recently been developed to formally characterize selection acting through different causal pathways throughout the life cycle and, therefore, to formally characterize evolutionary trade-offs. We use these methods to investigate a trade-off between early life reproduction and survival and how that trade-off affects selection on body size in the Soay sheep population inhabiting St Kilda (Outer Hebrides, Scotland). We decompose and quantify the total effects of first-year female body mass on lifetime fitness, with particular attention to the effect of body mass on early-life reproduction and the potential survival cost of early-life reproduction. Our results establish that the total effect of body mass on lifetime fitness is positive, despite the strong negative contribution acting via early life reproduction. Moreover, we show that the magnitude of the selection on body mass acting through different causal paths highly depends on population density. At higher densities, the cost of early-life reproduction is higher, and therefore, it contributes a strong negative component to the total selection of body mass-i.e., at higher population density, selection on body mass is weaker than it is when the population density is smaller. By decomposing total selection and quantifying selection acting through different causal paths, we expose the underlying mechanics shaping body mass in Soay sheep female lambs, and we provide a meaningful contribution to the understanding of the evolution of body size in this population.