Journal of Evolutionary Biology最新文献

Parasitoids are important natural enemies of insects, imposing strong selection for the evolution of resistance. In aphids, the heritable endosymbiont Hamiltonella defensa is a key determinant of resistance, making symbiont-conferred defence a potential target for specific adaptation by parasitoids. We tested this hypothesis in the aphid parasitoid Lysiphlebus fabarum and four of its host species, Aphis fabae fabae, A. hederae, A. urticata, and A. ruborum. The parasitoids show host-associated genetic differentiation indicative of host specialization, and each of these aphid species harbours their own 1-3 distinct strains of H. defensa. We introduced eight H. defensa strains from all four aphid species into a common host background (a laboratory strain of symbiont-free A. fabae fabae) and then tested the ability of 35 field-collected L. fabarum lines from the same four hosts to parasitize the H. defensa-carrying aphids. The origin of symbionts affected parasitism success, with strains from A. fabae fabae and A. hederae conferring strong protection, and strains from A. urticata and A. ruborum providing virtually no protection. For one strain each from A. fabae fabae and A. hederae, we found a signature of specific adaptation by parasitoids, as parasitoids able to overcome their protection mostly came from the same hosts as the symbiont strains. Two other strains were so strongly protective that they permitted very little parasitism independent of where parasitoids came from. While not fully conclusive, these results are consistent with specialized parasitoids adapting to certain defensive symbionts of their host species, supporting the notion of symbiont-mediated coevolution.

Spermatozoa exhibit striking morphological variation across the animal kingdom. In passerine birds, sperm exhibit considerable variation in size, yet the basic sperm phenotype is highly conserved; sperm are filiform, the head is corkscrew-shaped, and the midpiece is elongated and twisted around the flagellum. A significant departure from this typical sperm morphology has been reported in the sister species, the Eurasian bullfinch (Pyrrhula pyrrhula) and Azores bullfinch (P. murina). Here, we report a second evolutionary shift in passerine sperm phenotype in the nominate subspecies of the red-browed finch (Neochmia temporalis temporalis); sperm are nonfiliform, with an ellipsoid head and an extremely short midpiece restricted to the nuclear-axoneme junction. Additionally, we show that the sperm phenotype of the red-browed finch is similar to the putatively neotenous sperm described in the two bullfinch species. Using whole-genome data, we found no evidence that the unusual sperm phenotype of the red-browed finch is associated with reduced genetic variation or a population bottleneck. In contrast, using data on relative testes size, we find some support for the hypothesis that relaxed postcopulatory sexual selection, via a lack of sperm competition, may, at least in part, explain the unusual sperm of the red-browed finch. We also discuss the possible roles of mutation, genetic drift, and genetic hitchhiking in the evolutionary origins and maintenance of neotenous sperm phenotypes. Finally, we suggest that these dramatic evolutionary shifts in sperm phenotype warrant further investigation and highlight the need for a greater understanding of the developmental and genomic basis of sperm phenotype.

Sex differences in cooperation are widespread, but their evolution remains poorly understood. Here, we use comparative analyses of the cooperatively breeding birds and mammals to formally test the leading Dispersal Hypothesis for the evolution of sex differences in cooperation. The Dispersal Hypothesis predicts that, where both sexes delay dispersal from their natal group, individuals of the more dispersive sex should contribute to natal cooperation at lower rates (either because leaving the natal group earlier reduces the downstream direct benefit from natal cooperation or because dispersal activities trade-off against natal cooperation). Our comparative analyses reveal support for the Dispersal Hypothesis; sex biases in dispersal predict sex biases in helper contributions to cooperative care within the natal group across cooperative birds and mammals. Strikingly, in every species that showed significant sex biases in both dispersal and natal helping, the direction of sex bias in dispersal predicted that in natal helping in the manner predicted by the Dispersal Hypothesis. Our analyses also suggest that these patterns cannot be readily attributed instead to alternative hypothesized drivers of sex differences in cooperation (kin selection, heterogamety, paternity uncertainty, patterns of parental care, or differences between birds and mammals). These findings help to clarify the evolutionary drivers of sex differences in cooperation and highlight the need for single-species studies to tease apart whether sex differences in dispersal predict sex differences in natal cooperation because dispersal impacts the direct benefits of natal cooperation (as is often proposed) or because activities that promote dispersal trade off against natal cooperation.

Predator-prey systems often feature periodic population cycles. In an empirical system with a heritable prey defence trait, ecological oscillations were previously shown to cause evolution of prey defence on the timescale of the population cycles. In this paper, we develop a phenotypically structured model comprising partial differential equations to investigate the evolutionary dynamics of prey defence during population cycles for a clonally reproducing prey species. We reveal that ecological population cycles induce evolutionary oscillations not only of the mean prey defence trait but also of trait variance. We show that both eco-evolutionary oscillations and stable dynamics lead to high trait variance for a wide range of parameters. For stable dynamics, we show that this is caused by a mutation-selection balance whose impact is larger than in the absence of predators. For oscillatory dynamics, we show that high trait variance is caused by perpetual changes in the direction of selection. Finally, we highlight that switches between stable and oscillatory dynamics depend on the functional form of the cost and efficiency functions of prey defence.

Life-history traits such as body size, reproduction, survival, and stress resistance are fundamental to an organism's fitness and are highly influenced by nutritional environments across life stages. In this study, we employed a full factorial experimental design to investigate the effects of isocaloric diets (diets with equal caloric content but differing macronutrient composition) on key life-history traits in an outbred Drosophila melanogaster population. Our results demonstrated significant diet-induced plasticity, with males reared on carbohydrate-rich developmental diets had larger wings as adults. Fertility increased with protein-rich diets at both developmental and adult stages, reaffirming the critical role of dietary protein in enhancing reproductive success. Lifespan exhibited sexually dimorphic responses: carbohydrate-rich developmental diets extended male lifespan, while carbohydrate-rich adult diets reduced lifespan in both sexes. Stress resistance traits, including starvation and desiccation resistance, were unaffected by developmental diets but influenced by adult diets, with carbohydrate-rich adult diets enhancing survival under both stress conditions in males and females. While most traits exhibited additive effects of nutrition across life stages, a marginal interaction for male starvation resistance suggests that developmental and adult diets can interact in a trait- and sex-specific manner. Moreover, associations between dietary effects on life-history traits were context-dependent, driven primarily by adult diets and varying by sex. These findings emphasize the role of stage-specific nutritional environments in modulating life-history traits and their correlations, offering insights into how organisms may adapt to changing ecological conditions and the importance of considering both developmental and adult dietary contexts in evolutionary studies.

Adaptive plasticity allows organisms to interact with heterogenous environments and respond to environmental change. Population-level comparisons of plasticity provide insights into the selective factors driving plasticity evolution and properties of reaction norms likely to evolve. We test how thermal environments shape melanin plasticity in response to a seasonal cue in the white-lined sphinx moth, Hyles lineata. We compare how photoperiod affects melanization in two populations that experience different thermal environments: Colorado and Arizona. If thermal environment drives differences in melanin plasticity in response to photoperiod, then the reaction norms should differ in intercept (higher melanization in Colorado larvae across photoperiods, due to colder temperatures), slope (steeper in Arizona larvae, due to a larger range of temperatures across relevant photoperiods), and shape (linear in Arizona larvae and quadratic in Colorado larvae, due to the relationship between photoperiod and temperature). Results are partially consistent with these predictions: the Arizona population had a steeper slope, but a higher intercept. The Colorado population likely relies more heavily on temperature cues to inform melanization, requiring lower temperatures to increase melanin. Populations did not differ in reaction norm shape, suggesting that while slope and intercept are labile, there may be constraints on the evolution of shape. Because only two populations were compared in this study, replication at the population level is needed to corroborate the generality of these results. This study highlights the complexity of plasticity evolution and the need to consider multiple cues and selective pressures, as well as potential constraints on the evolution reaction norms.

Evolution in variable environments is predicted to disfavour genetic canalization and instead select for alternative strategies, such as phenotypic plasticity or possibly bet-hedging, depending on the accuracy of environmental cues and type of variation. While these two alternatives are often contrasted in theoretical studies, their evolution are seldom studied together in empirical work. We used experimental evolution for 30 generations in the nematode worm Caenorhabditis remanei to simultaneously study the evolution of plasticity and bet-hedging in environments differing only in their temperature variability, where one regime is exposed to faster temperature cycles between 20 and 25 °C, with little autocorrelation between parent and offspring environment, while the other regime had slowly increasing temperature with high autocorrelation in temperature between parent and offspring. These two environments had the same average temperature over evolutionary time, but one varied with larger magnitude on a shorter time scale. After experimental evolution, we scored adult size and fitness in full siblings reared in two different temperatures, optimal 20 °C and mildly stressful 25 °C. Experimental evolution in fast temperature cycles resulted in the evolution of increased body size plasticity but not increased bet-hedging, compared to evolution in the slowly changing environment. Plasticity followed the temperature-size rule as size decreased with increasing temperature and this plastic response was adaptive. In addition, we documented substantial standing genetic variation in body size, which represents a potential for further evolutionary change.

New genes can emerge de novo from non-genic genomic regions. In budding yeast, computational predictions have shown that intergenic regions harbour a higher-than-expected propensity to encode transmembrane domains, if theoretically translated into proteins. This propensity seems to be linked to the high prevalence of predicted transmembrane domains in evolutionarily young genes. However, what accounts for this enriched propensity is not known. Here, we show that specific arrangements of polyA/T tracts, which are abundant and enriched in yeast intergenic regions, explain this observation. These tracts are known to function as nucleosome-depleted regions, which prevent or reduce nucleosome formation to enable transcription of surrounding genes. We provide evidence that these polyA/T tracts have been repeatedly coopted through de novo gene emergence for the evolution of novel small genes encoding proteins with predicted transmembrane domains. These findings support a previously proposed "transmembrane-first" model of de novo gene birth and help explain why evolutionarily young yeast genes are rich in transmembrane domains. They contribute to our understanding of the process of de novo gene evolution and show how seemingly distinct but potentially interacting levels of functionality can exist within the same genomic loci.

This study explores the thermal tolerance of geographically isolated Mediterranean fruit fly, Ceratitis capitata (Wiedemann) populations and examines how response to thermal stress is associated with its capacity to invade cooler temperate regions. The remarkable invasion success of C. capitata, facilitated by global fruit trade and human activity, offers an opportunity to explore the role of phenotypic plasticity in shaping invasion dynamics. We assessed critical thermal limits across populations from varying latitudes, examining the effects of latitude, climate, and thermal acclimation. Critical thermal minimum (CTmin) was lower in populations obtained from colder, higher-latitude regions and influenced by climatic variability. While acclimation temperature had a marginally non-significant effect on CTmin, its interaction with latitude was significant, showing a pronounced increase in CTmin with acclimation at higher latitudes. Critical thermal maximum (CTmax) was influenced by microclimatic variability, with higher values in populations originating from colder, higher-latitude sites. Acclimation temperature increased CTmax across populations, with females exhibiting higher CTmax values than males. Significant interactions between latitude and climatic variability (PC1) for both CTmin and CTmax underscore the role of local climate conditions in shaping thermal tolerance. These findings enhance our understanding of the physiological mechanisms driving the invasive potential of C. capitata and its adaptation to temperate climates.