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Sexual selection can be an engine of divergent evolution between closely related lineages, as a result of idiosyncratic coevolution of male and female reproductive traits. The possibility that this can contribute to speciation has ample support from comparative studies but very few experimental evolution studies have addressed the role of sexual selection in very early stages of divergent evolution. Here, we use experimental evolution to study divergent evolution between replicate lines of the seed beetle Acanthoscelides obtectus evolving under strong or weak sexual selection for >190 generations. We first confirm that the experimental regimes employed resulted in marked differences in the strength of sexual selection. We then indirectly assess the degree of divergent evolution of those male and female traits that affect postmating sexual selection, by crossing replicate lines. We find that lines evolving under strong sexual selection are more divergent in reproductive traits, as evidenced by a stronger male × female interaction for male sperm competition success. Finally, we assess the degree of divergent evolution in the expression of candidate genes for male seminal fluid proteins and female reproductive proteins. We find that lines evolving under strong sexual selection are more divergent in the expression of reproductive proteins, providing a possible causal mechanism contributing to the results seen in the reproductive phenotype. Our findings provide evidence for more divergent evolution of reproductive traits under stronger sexual selection, in line with the tenet that sexual selection may promote divergence even in the absence of environmental differences between populations.
BACKGROUND: Patients’ and relatives’ feedback is used by hospitals to improve the quality and safety of care. It can be solicited, as in the case of satisfaction questionnaires or complaints collected by mediation centers. Hospital users also provide unsolicited feedback by writing compliment letters, which are generally considered as expressions of gratitude. This study investigated compliment letters received by a neonatology service from parents with a twofold objective: first, to investigate compliment letters’ content regarding parents’ experiences and second, to explore underlying needs that motivated parents to provide feedback. METHODS: This qualitative descriptive study was based on the analysis of 573 compliment letters collected by the neonatology service of Lausanne University Hospital in Switzerland between 2009 and 2020. The parents’ lived experiences contained in compliment letters were analyzed using framework analysis. The needs and functions that their feedback fulfilled were examined through a custom analysis method, combining psychological and socio-anthropological perspectives, and informed by the results of the framework analysis. RESULTS: Five core themes characterized parents’ experiences: recall of the care and hospital stay (contextual information to refer to the children’s stays in the service), life after the hospital discharge (children’s health evolution and development), parents’ feelings (how parents experienced their children’s care), perception of the healthcare professionals (healthcare professionals ways of being and doing), parents’ gratitude (thanks to healthcare professionals for their acts or their qualities). Five underlying needs were identified: thanking the team, closure (claim that the children were no longer patients), partial closure (feedback on the state of the children), taking its own place in the care (parent’s account of the impact of children’s hospitalization), managing the sense of indebtedness (parents’ acknowledgement that they owe something to the team). CONCLUSION: When parents write compliment letters, they mostly express how they experienced their children’s hospitalization and how they managed to make sense out of it. Compliment letters thus have other functions than expressing gratitude. They allow parents to sustain relationships with healthcare professionals, support the normalization of their children’s situation and their recovery or provide testimony of experiences. They contain important information about the writers, health care professionals, the relationship they have established, hospital operations and healthcare organization. As hospital users' experiences are thought to contribute to health care quality, it matters that health services consider the information they convey.
Sensory traits shape animal lifestyles due to the central role they play in retrieving and processing environmental information. However, being some of the most energetically expensive tissues to build and maintain, ecological demands often modulate investment in these organs. Evidence that ecology shapes the evolution of sensory traits is plenty, but is heavily biased towards vertebrates and has only recently begun to emerge in invertebrates. Here, we elucidate the macroevolution of a key sensory organ-eye size-using temperate butterflies as models. Using micro-CT X-ray imaging of pinned museum specimens, we quantified the eye size of 443 individuals comprising 59 species. Further, using 12 years of long-term monitoring data to quantify species habitat, we tested the hypothesis that forest-associated species, likely experiencing dimmer light conditions, should have larger eyes than those from open habitats. Our comparative analyses revealed tight allometric scaling between eye and wing size, and phylogeny alone explained 74% of eye size variation, with low heterogeneity in the evolutionary rates. Further, we found that habitat structure had no association with eye size. Overall, our findings indicate that allometry and shared ancestry, not ecology, shape the macroevolution of 3D eye size in temperate butterflies. We also demonstrate how non-invasive microCT imaging can be used on pinned museum specimens for studying phenotypic evolution on a macroevolutionary scale.
This contribution is a comment on a simulation study of Robert J. Knell and Jonathan M. Parrett (Evo. Lett. 8, 539-349, 2024). There is growing evidence that in ecological adaptation, sexual selection is a "double-edged sword"-it can fuel adaptation and population persistence, or hinder adaptation and lead to population extinction. Knell and Parrett explore this topic, using an individual-based model to investigate how alternative reproductive tactics (ARTs) affect adaptation to changing environments. They find that in the presence of ARTs, extinction can be averted, as fixed ARTs facilitate evolutionary rescue. While we appreciate their research question and approach, we question the generality of this result. First, some of their conclusions hinge on the parameter values chosen. In their model, individuals express one of two reproductive tactics (fighting or sneaking) depending on whether their condition exceeds a given threshold. We demonstrate that their conclusions rely strongly on this threshold value. For high values (i.e., when most individuals sneak), they observe evolutionary rescue-however, for values lower than those explored in K&P, fixed ARTs do not impact extinction. When we allow the threshold to evolve, it evolves to take low values, indicating that when fixed ARTs are adaptive, they do not promote evolutionary rescue. Second, K&P assume that the sneaking strategy results in considerably lower mating success than the fighting strategy. We show that, if the average mating success of the sneaking strategy is increased, fixed ARTs again do not cause evolutionary rescue. Finally, we show that varying the degree of influx of variation or the inheritance process similarly breaks the association between fixed ARTs and evolutionary rescue. Overall, we agree with K&P that ARTs may influence evolutionary rescue, but possibly in different contexts than those considered in their manuscript. Thus, whether and how ARTs shape extinction risk remains an open question.
The vertebrate skull originates from two embryonic lineages, the mesoderm and the neural crest, offering a unique framework to study how developmental mechanisms connect phenotypic variation and evolutionary diversification. Using 3D geometric morphometrics, we analysed skull shape variation in lacertid lizards. Mesoderm- and neural crest-derived bones formed two distinct, conserved modules at both micro- and macroevolutionary scales. In the common wall lizard (Podarcis muralis), rapid evolution of skull shape under sexual selection was primarily driven by neural crest-derived bones. While the primary axis of shape divergence in P. muralis aligned with a major axis of variation across lacertids, neural crest-derived bones exhibited overall slower evolutionary rates and lower morphological disparity than mesodermal-derived bones. We propose that this discrepancy between the role of the neural crest for skull evolution on micro- and macroevolution reflects developmental bias imposed by neural crest cell biology. By enabling developmental coupling of skull shape, body colouration and behaviour, the neural crest cells can facilitate rapid, correlated responses under sexual selection but may limit long-term evolvability in the skull.
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.
Interdiscursivity refers to the blending of multiple discourses, genres, or styles within a single communicative event. This study investigates the interdiscursivity of Chinese public health risk communication letters issued during major health crises over the past two decades, including SARS, H1N1, COVID-19 and seasonal influenza. It examines how multiple discourse types-advice-giving, scientific, literary, authoritative, affective and informal-are interwoven and strategically adapted across different crises to guide public behaviour, mobilise communities and foster trust. Using qualitative document analysis combined with thematic analysis, the study traces the historical evolution of these interdiscursive patterns and situates them within China's broader public health documentary heritage. The findings demonstrate that these letters not only translate abstract risks into actionable guidance but also serve as instruments for documenting sociocultural shifts and governance practices, and for supporting collective memory and institutionalised learning. By linking the diachronic evolution of interdiscursive strategies to the social and documentary functions of public health communication, this study highlights the dual role of risk communication letters as both practical tools and enduring public health documents, offering insights for future communication strategies in health crises.
Human communication is generally overt: We address each other with verbal cues, use eye contact, and point for each other, all to be understood and avoid misunderstandings. What are the cognitive underpinnings and evolutionary roots of overt communication? For decades, the Gricean interpretation of overt communication was taken for granted, despite two widely recognized problems: a developmental paradox in language acquisition and a methodological barrier to identifying the presence of its signature features in nonhuman animals. We introduce a further challenge: the "signaler assumption problem." This concerns the mechanism of how signalers are supposed to establish "common ground." We avoid these problems by replacing the Gricean approach with an evolutionarily grounded version of script theory, originally developed to model procedural knowledge. Our updated version of script theory posits that individuals recognize recurring situations as belonging to basic event schemata that form larger sets of patterned social interactions. In social interactions, individuals follow a finite number of scripts and understand others as following the same scripts. If the scripts of different individuals align during a social interaction, common ground is established. It is this common ground rather than mutual higher order mentalizing that renders a predominantly overt communication system possible. We review the theoretical and empirical literature and argue that the perception of social events as hierarchically structured scripts fostered the evolution of overt communication. Script theory offers an empirically more plausible and more parsimonious evolutionary explanation of the emergence of human linguistic communication than Gricean assumptions of complex mentalizing abilities. (PsycInfo Database Record (c) 2026 APA, all rights reserved).
The evolution of novel animal signals is critical to the generation of biodiversity. Here, we explore how new sexual signals become established. This process is challenging to explain because if receiver preferences are coupled with existing signals, then most receivers should discriminate against new signals. We investigated an underappreciated hypothesis: relaxed receiver preferences facilitate novel signal evolution by allowing new signals to establish a foothold. Further, we probed the mechanistic underpinnings of relaxed preferences by combining field-based and common garden approaches, allowing us to investigate evolution and plasticity as mechanisms. We capitalized on the Pacific field cricket, Teleogryllus oceanicus, a species that has recently evolved multiple novel acoustic signals (e.g., purring and rattling) in response to an eavesdropping parasitoid fly only found in the crickets' introduced range in Hawaii. To test the hypothesis that selection associated with high search costs in introduced populations leads to relaxed mating preferences and determine whether such relaxation is plastic, we conducted sound preference (phonotaxis) trials with females from the cricket's native range (Australia and French Polynesia, where the fly is absent) and its introduced range (Hawaii, where the fly is present). We presented females with novel songs plus the typical, ancestral song. Differences in phonotactic behavior between the lab and field settings would indicate plasticity in preferences. We found that Australian and French Polynesian females were quite plastic; they discriminated strongly against most songs in the field, but were much more phonotactic to rattling and the typical song in the lab. However, Hawaiian females exhibited little plasticity and were consistently highly responsive to the rattling and typical songs in the lab and field. This pattern points to a loss of ancestral plasticity in female preferences sometime after colonizing Hawaii, resulting in heightened responsiveness to all songs-allowing novel signals to establish.
As large-scale genomic datasets are becoming abundant, new questions can now be posed in evolutionary biology. Although innovative methodological approaches are constantly developed to test these new hypotheses, their application to the study of nonmodel species is hampered by technical challenges associated with such systems. In recent years, artificial intelligence (AI) solutions, mostly in the form of deep neural networks, have been successfully introduced to analyse genomic data from nonmodel species. Here, we highlight the latest trends in deep learning to infer demographic history and signals of natural selection, and offer novel research directions to develop AI algorithms for the study of nonmodel organisms. Specifically, we identify strategies to process data missingness and uncertainty, to infer selective events in the face of unknown genomic and demographic parameters, and to generate interpretable and explainable predictions. We demonstrate our arguments by showcasing an original implementation to detect selective sweeps from an experimental setting with low sample size, uncertain sequencing data, and unknown demographic model, as typical in studies of nonmodel species. We argue that the study of nonmodel organisms is an opportunity to develop general-purpose data-driven methodologies for evolutionary inferences. Fair sharing of resources and inclusive frameworks are key to enabling researchers to benefit the most from this new wave of technologies.
Theories on the evolutionary origins of human aggression have often implicitly assumed that conspecific aggression is a single behavioral trait. However, different types of aggression can be described, based upon their intensity, frequency, as well as the age and sex of the opponents. The phylogenetic relationships between different types of aggression remain poorly understood. We tested the strength of correlated evolution between five distinct types of aggression in primates, namely, between- and within-group mild (i.e., not life-threatening) aggression, between- and within-group adulticide, and infanticide. We collected data on 100 free-ranging, non-provisioned and group-living species, including humans. Phylogeny had a weaker effect on mild than on lethal aggression; the effect of phylogeny was greater for adulticide, especially when we partitioned our analyses by the sex of the attacker. Furthermore, we found a positive correlation between within- and between-group adulticide, and with infanticide; these results were mostly confirmed when we considered the sex of the attacker. Conversely, the two types of mild aggression were weakly related with lethal aggression. Our study highlights the importance of treating aggression as a complex set of interrelated traits in comparative analyses. Our findings indicate that mild aggression is not closely linked to killing; thus, the escalation of aggression may follow more complex patterns that what predicted by current socio-ecological models.
The spatiotemporal evolution characteristics and influencing factors of sudden environmental accidents are analyzed by employing exploratory spatial analysis and Pearson correlation analysis, based on the statistical data of sudden environmental accidents in 31 provinces, municipalities, and autonomous regions in China from 2008 to 2022. The results provide valuable insights for the prevention and treatment of sudden environmental pollution emergencies. The results showed that: (1) the total of sudden environmental accidents exhibited an inverted V shaped structure with 2013 as the turning point, showing an overall decreasing trend in China. (2) The seasons when the sudden environmental accidents occurred from the highest to lowest proportions were autumn (29.01%), summer (26.29%), spring (24.80%), and winter (20.19%). The months with the highest frequency were May and July, while October and December had the lowest. The dates with the most occurrences were the 5th, 7th, 4th, 2nd, 11th, and 9th, while the 31st, 30th, 29th, and 27th were the lowest. Regarding weekdays, Monday (16.56%), Wednesday (15.94%), and Thursday (14.38%) were the highest proportions, while Sunday (12.50%) was the lowest. (3) Spatial distribution revealed an overall imbalance, with the eastern coastal comprehensive economic zone being the highest frequency of environmental accidents, followed by the middle reaches of the Yellow River comprehensive economic zone, and the northeast comprehensive economic zone having the lowest. Provinces with the highest number of sudden environmental accidents were mainly in Shanghai (1129), Shaanxi Province (472), and Jiangsu Province (419). Based on the cold and hot spot analysis, H-H areas were mainly located in the southeast coastal regions, L-L areas were concentrated in the western and northeastern regions, and L-H areas were distributed in the central regions. (4) Pearson correlation analysis indicated that investment in the treatment of industrial pollution as percentage of GDP and secondary industry output value as Percentage of GDP were the main driving factors for sudden environmental accidents in China. Per capita GDP, pollutant emissions, and the total of letters and phone calls regarding environmental pollution had inhibitory effects on the occurrence of sudden environmental accidents, while single factors had relatively minor impacts. To effectively prevent and control sudden environmental accidents, it is necessary to improve the risk management system for sudden environmental accidents and strengthen monitoring and management of accident-prone industries, dates, and regions.
The rapid pace of environmental change has prompted pressing concerns about the persistence of wild populations. For plants, because they move from one place to another only passively between generations, their persistence is especially likely to depend on their capacity for ongoing adaptive evolution. There are numerous examples of rapid adaptation in the recent past, but evidence about rates of adaptation in the wild is limited. Previously, to assess the capacity for genetic adaptation of three wild plant populations growing in their source locations, we have estimated their additive genetic variance for fitness in three successive years. Here, we present the actual difference between successive generations in their average absolute fitness. We partition this change into components resulting from genetic change and due to environmental difference, as well as a residual component. In each of six cases of intergenerational change, we have detected evolutionary adaptation as genetic increase in average fitness during the first generation, while also finding generally greater effects of differences in environment between years. Nevertheless, we show that when environmental change reduces a population's average fitness, these adaptive genetic responses often substantively ameliorate its deleterious impact.
The National Board of Medical Examiners and the American Board of Surgery created a series of examinations including Subject Exams, United States Medical Licensing Examination Steps 1-3, ABS In-Training Exam, and the ABS Qualifying and Certifying Exams originally designed as staged assessments of clinical competence. These exams have evolved beyond licensure requirements into high-stakes screening tools for residency and even surgical fellowship selection. Recent efforts to de-emphasize standardized testing have sparked substantial debate within the medical community. We examine whether standardized tests reflect a true measure of trainee competence and its impact on trainees from low socioeconomic status. We also explored the downstream impact of de-emphasizing standardized testing, shifting selection from objective test scores towards more subjective factors such as research experience, letters of recommendations, and medical school reputation.
To develop, implement, and assess the utility of a standardized letter of evaluation (SLOE) for OBGYN residency applicants in the US. OBGYN program directors (PDs) were surveyed over 2 consecutive years and asked to estimate the percentage of applicants submitting an SLOE and to indicate its helpfulness compared to traditional letters of recommendation. Sub-group analysis by program type was performed. In 2023, comments for improvement were collected and analyzed for themes using a large language model. OB/GYN residency programs in the United States. OB/GYN PDs in the United States. The survey was completed by 254 of 293 (86.7%) of PDs in 2022 and 253/293 (86.3%) in 2023. From 2022 to 2023, there was no difference in the estimated percentage of applicants who submitted an SLOE to a program (median 50%-74%), though in 2023, university and combined university-community programs estimated receiving higher percentage of applicants submitting SLOEs compared to community and military programs (p < 0.001). Over the study period, the favorability of the SLOE improved, and feedback indicates a need for continued improvement in the SLOE process, including faculty development, standardization, and more honest assessment of applicants. An SLOE was submitted by most applicants to OBGYN residency programs. Iterative modification of the SLOE based on PD, applicant, and faculty advisor feedback is needed to assess its utility in the application process.
Bahrain reports the highest age-standardized cancer incidence among Gulf Cooperation Council (GCC) countries, but its oncology research output has not been comprehensively mapped. We profiled four decades of Bahrain-linked cancer publications to describe growth, contributors, collaboration, impact, and gaps. We searched Scopus and PubMed from inception to December 2024 using cancer-related terms combined with "Bahrain". We included articles, reviews, editorials, letters, conference papers, and book chapters. After deduplication, screening, and manual supplementation, 502 publications were analyzed by year, document type, journal quartile, SCImago Journal Rank (SJR), Bahraini authorship and first-author affiliation, geographic scope, study design, citations, and cancer site grouped using the ICD-O (3rd edition). The first indexed paper appeared in 1981. Output was low until 2010, then increased sharply; 77.7% of publications appeared from 2011 to 2024, peaking at 66 papers in 2024. Articles accounted for 69.3% of the outputs, and reviews accounted for 21.7%, with greater diversity after 2010. The Bahrain Medical Bulletin was the most common outlet (20.2%). Salmaniya Medical Complex led in first-author output, followed by Arabian Gulf University and King Hamad University Hospital. Bahraini first authorship was observed in 66.7% of papers, and most studies were conducted exclusively in Bahrain (65.3%), although the proportion of global collaborations increased to 17.0% from 2021 to 2024. Descriptive designs predominated (57%, including 25.5% case reports), whereas analytic studies were uncommon (4.3%). Breast cancer was the most studied site-specific cancer (23.3%), followed by digestive organ cancers (11.4%); 27.1% of the papers addressed "unspecified" cancer. Respiratory and intrathoracic cancers remain persistently underrepresented despite a high mortality burden. Journal quality improved after 2010, reflected by increasing Q1/Q2 representation and higher SJR distributions. The citation peaks from 2014 to 2018 were driven by highly cited multinational collaborative publications. Bahrain's oncology research output has increased more than 30-fold over four decades, with expanding institutional participation and increasing international collaboration. Persistent reliance on descriptive designs and gaps in high-burden cancers-especially lung cancer-highlights priorities for capacity building, targeted funding, and a nationally aligned oncology research agenda for policy action.
Phenotypic plasticity enables organisms to produce better-suited phenotypes when the environment changes, improving fitness under adverse conditions. Yet responding to environmental cues may provide little use in a constant environment, where organisms already express optimal phenotypes. The forces that sustain plasticity and account for its widespread presence, thus, remain unclear, as plasticity must remain advantageous to persist. Although typically associated with changing environments, maintenance of plasticity requires generational turnover such that parents and offspring regularly encounter different conditions. Here, we demonstrate that even a low number of migrants between locally adapted populations, in constant environments, can promote the emergence and persistence of phenotypic plasticity even when plasticity is costly and never associated with the fittest genotype, independent of its genetic architecture. We support this conclusion by exploring the parameter space of a two-locus, two-deme model using stochastic simulations and analytical approximations. We derive analytical conditions under which plasticity is adaptively maintained as a function of selection strength, migration, and fitness trade-offs. These findings reveal new potential evolutionary origins of plasticity and offer insight into how maladaptive traits can invade adapted populations in stable environments.
Insects comprise one of Earth's most diverse animal groups, but the adaptive capacity of most species, especially those with weak genetic structure, remains understudied. Psolodesmus mandarinus is an endemic damselfly in Taiwan, where its populations show latitudinal variation in wing traits despite limited genetic differentiation in mitochondrial and ribosomal sequences. We hypothesised that weak genome-wide structure may obscure the signals of local adaptation driven by environmental variation. To test this, we integrated genome-wide SNPs, phenotypic measurements, environmental associations, and species distribution models. Although genome-wide population structure was generally weak, pairwise FST values exceeded 0.35 between southeastern and northeastern populations, and genetic-environment association analyses identified outlier loci and individuals associated with environmental variables. Wing traits, particularly wing colours, exhibited a latitudinal divergence and exceeded expectations from neutral structure (PST >FST), indicating selection. Species distribution models showed ecological differentiation and predicted range expansion for clear-winged individuals but range contraction for dark-winged individuals under future climate scenarios. Our findings demonstrate that phenotypic divergence can arise and persist under weak genetic structure, highlighting the evolutionary potential for local adaptation in structured environments even in species with high dispersal potential. An integrative framework provides essential insights for predicting biodiversity responses to environmental change and guiding climate-resilient conservation strategies.
Climate change is altering thermal environments, yet we know little about how environmental predictability shapes species' adaptive responses. Different species may rely on plasticity or evolution to survive environmental change, but how these strategies depend on environmental predictability remains unclear. Experimental evidence that distinguishes between plastic and evolutionary responses to different patterns of environmental variability has been lacking. Here, we present the first experimental demonstration that compares adaptive responses to predictable versus unpredictable thermal variation, disentangling plastic from evolutionary changes. Using Drosophila melanogaster populations evolved for 11 generations under constant, predictably fluctuating, and randomly fluctuating thermal regimes, we assessed survival and fecundity: a plasticity assay testing flies directly from their evolutionary environments to capture total phenotypic responses, and a common garden assay after two generations of standardized rearing to isolate genetic changes. Strikingly, environmental predictability shaped divergent life-history strategies that were only revealed by comparing our two assays. Populations from predictably fluctuating environments evolved enhanced survival, but this benefit was only visible in the common garden assay, not when tested directly from their evolutionary environment. Conversely, populations from randomly fluctuating environments showed reduced survival in the plasticity assay and consistently lower fecundity in the common garden assay, though this reproductive cost was completely masked in the plasticity assay. These contrasting responses demonstrate that environmental predictability fundamentally determines life-history evolution: predictable variation favors investment in stress-resistant longevity, while unpredictable variation imposes both immediate survival costs and constitutive reproductive constraints. Our findings challenge the traditional view that environmental variation uniformly selects for increased plasticity, instead revealing that the predictability of environmental change determines both the target and mechanism of adaptation. As climate change increases environmental variability and reduces environmental predictability, these insights provide crucial guidance for predicting species persistence and developing effective conservation strategies.
Understanding how genotype-by-environment (G × E) interactions influence evolutionary trajectories and contribute to historical contingency is key to predicting adaptation. In structured environments, populations often diversify into ecotypes. This specialization depends on ecological opportunity and also hinges on the adaptive landscape, as early beneficial mutations may restrict access to new niches unless alternative trajectories or compensatory mutations arise. Previous studies demonstrated that Escherichia coli populations rapidly diversify into two coexisting ecotypes in nutrient-rich, spatially structured environments, mediated by first-step mutations that upregulate type 1 fimbriae, a pilus involved in biofilm formation that enables surface colonization. Here, we investigated how first-step mutations shape evolutionary trajectories by experimentally evolving wild-type and fimbrial-deficient (ΔfimA) E. coli in structured and unstructured environments. In structured environments, ΔfimA initially confers a fitness benefit by eliminating the energetic cost of weak biofilm formation, but ultimately prevents range expansion, constraining adaptation relative to wild-type populations. In unstructured environments, where biofilms provide no advantage, both genotypes evolved similarly, with sequencing revealing parallel early mutational trajectories. Our findings provide one of the first experimental demonstrations that a single, clinically relevant first-step mutation in a non-essential gene can create an evolutionary "dead end," constraining subsequent diversification. These results highlight the ruggedness of adaptive landscapes in structured environments and show how early beneficial mutations can trap lineages on local fitness peaks, underscoring the role of G × E interactions in shaping the predictability and contingency of evolution.