Evolution Letters最新文献

Trait variation along environmental gradients can indicate the different strategies that organisms have evolved in response to environmental heterogeneity. So far, many inferences on trait-environment associations come from global studies performed at high taxonomic levels, and their transferability to lower evolutionary and spatial scales is unclear. Here, we tested for alignment in trait-environment relationships in 13 life-history and physiological traits among and within 7 Brassicaceae species over elevational gradients. Species and source populations originated from different elevations in the central Alps, and plants were raised under benign and warm conditions in greenhouse chambers. Some traits showed alignment in both within- and among-species trait clines, with even higher alignment on the level of trait complexes. There was high parallelism in resource allocation to leaves, particularly of carbon, with allocation decreasing with elevation. Size and biomass also decreased with elevation at the species and within-species level, respectively. Overall, the concordance in resource investment strategies when coping with lower as compared to higher elevations across evolutionary and spatial scales highlights their general role in adaptation to elevation.

Understanding the structural changes that enable enzymes to remain active in extreme thermal conditions is of broad scientific interest for both fundamental and applied biological research. Three key mechanisms that underlie the thermal adaptation of enzymes are modifications in structural flexibility, compactness, and the contacts formed among amino acids. However, most previous studies on these topics have been limited to small sample sizes or a narrow taxonomic focus, and the importance of these factors to thermal adaptation remains poorly understood. In this study, we combined molecular dynamics simulations and phylogenetic comparative analyses to thoroughly analyze the structural factors underlying thermal adaptation in adenylate kinase-a key enzyme involved in cellular energy balance and homeostasis-across 70 prokaryotic species. We detect systematic increases in the flexibility of the enzyme with temperature, both across and within species. In contrast, structural compactness appears to be almost completely independent of temperature. Finally, we uncover a remarkable diversity in the number and types of amino acid contacts observed in different adenylate kinases that cannot be explained solely by temperature. Our results suggest that there are multiple paths toward the adaptation of prokaryotic adenylate kinases to extreme thermal environments and that these paths are generally accessible through changes in flexibility.

Fundamental traits of genes, including function, length, and Guanine-Cytosine (GC) content, all vary with gene age. Pleiotropy, where a single gene affects multiple traits, arises through selection for novel traits and is expected to be removed from the genome through subfunctionalization following duplication events. It is unclear, however, how these opposing forces shape the prevalence of pleiotropy through time. We hypothesized that the prevalence of pleiotropy would be lowest in young genes, peak in middle-aged genes, and then either decrease to a middling level in ancient genes or stay near the middle-aged peak, depending on the balance between exaptation and subfunctionalization. To address this question, we have calculated gene age and pleiotropic status for several model multicellular eukaryotes, including Homo sapiens, Mus musculus, Danio rerio, Drosophila melanogaster, Caenorhabditis elegans, and Arabidopsis thaliana. Gene age was determined by finding the most distantly related species that shared an ortholog using the Open Tree of Life and the Orthologous Matrix Database. Pleiotropic status was determined using both protein-protein interactions (STRINGdb) and associated biological processes (Gene Ontology). We found that middle-aged and ancient genes tend to be more pleiotropic than young genes, and that this relationship holds across all species evaluated and across both modalities of measuring pleiotropy. We also found absolute differences in the degree of pleiotropy based on gene functional class, but only when looking at biological process count. From these results, we propose that there is a fundamental relationship between pleiotropy and gene age, and further study of this relationship may shed light on the mechanism behind the functional changes genes undergo as they age.

Sexual conflict frequently gives rise to adaptations that increase male reproductive success at the expense of harming females ("male harm") and decreasing population growth. Studying the ecology of male harm is paramount to understand how sexual conflict unfolds in nature, and its consequences for populations viability. Here, we used seed beetles (Callosobruchus maculatus), a species where males harm females via both harassment and traumatic male insemination, to study whether temperature (24, 28, or 32 °C) can modulate male harm. We disentangled temperature effects on male harm via pre- and postcopulatory mechanisms ("harassment and mating") vs. precopulatory mechanisms (i.e., "harassment" only; ablated males). These treatments were applied under different levels of sexual conflict, with females continuously exposed throughout their lifespan to either no males (control; "no harm"), 1 male (low sexual conflict), or 2 males (high sexual conflict). Constant exposure to males decreased female fitness at warmer environments, particularly at 28 °C and when females were subject to constant harassment and mating under high sexual conflict. In contrast, constant exposure to male harassment and mating increased female fitness at 24 °C, particularly under low sexual conflict (significant ~14% increase vs. control females). At the population level, not being exposed constantly to males resulted in higher net reproductive rates at 28 and 32 °C, whereas constant male-female cohabitation resulted in optimal net reproductive rates at 24 °C, rescuing estimated population growth rate and thus reversing the cost/benefit balance of exposure to males. Our findings show that, by dictating the outcome of female fitness under constant male exposure, temperature can modulate sexual conflict to the point of reversing it and facilitating population growth. Our results support the emerging notion that environmental variation can significantly decrease overall levels of sexual conflict in nature.

Microbial adaptation is driven by the circulation of mobile genetic elements (MGEs) among bacteria. On the one hand, MGEs can be viewed as selfish genes that spread like infectious diseases in a host population. On the other hand, the horizontal transfer and the loss of these MGEs are often viewed as a form of sexual reproduction that reshuffles genetic diversity in a way that may sometimes be adaptive for bacteria cells. Here, we show how these 2 perspectives can be reconciled using a single unified framework capturing the dynamics of multiple, interacting MGEs. We apply this framework to study how interactions between MGEs affecting rates of horizontal gene transfer and segregation loss shape the short- and long-term evolutionary dynamics of MGEs and the bacteria population. We show that these interactions produce nonrandom MGE associations that can speed up or slow down microbial adaptation depending on the evolutionary conflicts between MGEs as well as between MGEs and their bacterial hosts. Moreover, we show how these interactions affect the evolutionary potential of the bacteria population. We discuss the implications of these predictions for the community response to environmental stressors such as antibiotic treatment or vaccination campaigns as well as the evolution of accessory genomes.

Effects of parental age on juvenile survival are well documented, but whether parental age has long-term consequences for the fitness of surviving offspring remains poorly understood. This is particularly the case for polygynous mammals, where differential impacts on sons versus daughters are predicted. Here, we investigate the effects of maternal and paternal age on offspring first-year survival, longevity, lifetime reproduction, and annual reproduction in a wild Soay sheep population. We find that younger and older mothers produced offspring that were less likely to survive their first year than middle-aged mothers, and this effect was independent of offspring sex. However, among offspring that survived their first year, adult lifespan and lifetime reproductive success were only influenced by maternal age in sons and not in daughters. Increased adult reproductive success in sons of middle-aged mothers, compared to young and old mothers, was not driven by maternal age effects on offspring reproductive ageing patterns, but potentially by consistent effects on offspring average annual reproductive performance. There was weak evidence of a paternal age effect on offspring longevity but no effect on other offspring traits. Our study shows long-lasting, sex-dependent maternal age effects on offspring fitness traits in the wild, adding to the growing body of literature that highlights the potential importance of intergenerational effects in natural populations.

Plant propagules are frequently relocated between populations for restoration, especially in fragmented ecosystems like prairies, where few pristine patches remain. While research shows that plant populations often perform better in their native environments than in foreign sites, this pattern is not universal. The extent to which plant population fitness varies with distance from its site of origin remains unclear. Using aster models, we investigated the relationship of fitness with geographic distance and climate differences between the source and experimental sites for four perennial prairie forbs by planting 12 populations of each species at a north and south experimental site in the tallgrass prairie of Minnesota, USA. At both experimental sites, individuals from warmer and southern source sites had greater fitness, but the deviations of population mean fitnesses from the fitted relationships were substantial and idiosyncratic. Our results suggest limited effectiveness of geographic distance and temperature difference in predicting population mean fitness. This challenges the efficacy of long distance seed transfers as seed sourcing strategies to promote population persistence in prairie restorations.

Cyanobacteria blooms pose a substantial threat to freshwater systems globally. While zooplankton grazers such as Daphnia can have an important role in suppressing cyanobacteria blooms, cyanobacteria can adversely impact Daphnia fitness and even kill them. Earlier work has shown an evolutionary increase in tolerance to cyanobacteria across years and strong genotype × genotype interactions determining the interaction between Daphnia and the cyanobacterium Microcystis. Here, we test the hypothesis that Daphnia magna can adapt during 1 growing season to changes in dominant strains of Microcystis. Over 2 consecutive years, we collected D. magna clonal lineages and Microcystis strains from a single pond early and late in the growing season and we assessed whether Daphnia survival differed when exposed to Microcystis strains from either the same or a different time point within the growth season. Our findings reveal important Daphnia genotype × Microcystis genotype interactions, with Daphnia survival being higher when exposed to Microcystis from the same time point than when exposed to Microcystis of a different time point. Our results extend earlier findings to variation within 1 single natural system and growth season, and suggest an important impact of rapid (co)evolutionary dynamics shaping the tolerance of zooplankton grazers to cyanobacteria.

Colonization of new habitats is typically followed by divergent selection acting on traits that are immediately important for fitness. For example, differences between sensory environments are often associated with variation in sensory traits critical for navigation and foraging. However, the extent to which the initial response to novel sensory conditions is mediated by phenotypic plasticity, and the contribution of sensory or neural adaptation to early species divergence remains unclear. We took advantage of repeated cases of speciation in Heliconius butterflies with independent allopatric distributions in the west of the Colombian and Ecuadorian Andes. Using volumetric brain measurements, we analyzed patterns of investment in primary sensory processing areas of the brain across different localities and habitats. We find that a higher altitude species, Heliconius chestertonii, differs in levels of investment in visual and olfactory brain components compared with its lower altitude relative H. erato venus, mainly attributable to broad-sense heritable variation as inferred from comparisons between wild and common-garden-reared individuals. We provide evidence that this variation is consistent with divergent selection, and compare these shifts with those reported for another high-altitude species, H. himera, and its parapatric lowland counterpart, H. erato cyrbia, to demonstrate parallel reductions in the size of specific optic lobe neuropils. Conversely, for the antennal lobe, we detected different trait shifts in H. himera and H. chestertonii relative to their lowland H. erato neighbors. Overall, our findings add weight to the adaptive potential of neuroanatomical divergence related to sensory processing during early species formation.