Gene Expression Divergence in Eugenia uniflora Highlights Adaptation across Contrasting Atlantic Forest Ecosystems.

Understanding the evolution and the effect of plasticity in plant responses to environmental changes is crucial to combat global climate change. It is particularly interesting in species that survive in distinct environments, such as Eugenia uniflora, which thrives in contrasting ecosystems within the Atlantic Forest (AF). In this study, we combined transcriptome analyses of plants growing in nature (Restinga and Riparian Forest) with greenhouse experiments to unveil the DEGs within and among adaptively divergent populations of E. uniflora. We compared global gene expression among plants from two distinct ecological niches. We found many differentially expressed genes between the two populations in natural and greenhouse-cultivated environments. The changes in how genes are expressed may be related to the species' ability to adapt to specific environmental conditions. The main difference in gene expression was observed when plants from Restinga were compared with their offspring cultivated in greenhouses, suggesting that there are distinct selection pressures underlying the local environmental and ecological factors of each Restinga and Riparian Forest ecosystem. Many of these genes engage in the stress response, such as water and nutrient transport, temperature, light intensity, and gene regulation. The stress-responsive genes we found are potential genes for selection in these populations. These findings revealed the adaptive potential of E. uniflora and contributed to our understanding of the role of gene expression reprogramming in plant evolution and niche adaptation.

Behavioural Thermoregulation of Flowers via Petal Movement.

Widely documented in animals, behavioural thermoregulation mitigates negative impacts of climate change. Plants experience especially strong thermal variability but evidence for plant behavioural thermoregulation is limited. Along a montane elevation gradient, Argentina anserina flowers warm more in alpine populations than at lower elevation. We linked floral temperature with phenotypes to identify warming mechanisms and documented petal movement and pollinator visitation using time-lapse cameras. High elevation flowers were more cupped, focused light deeper within flowers and were more responsive to air temperature than low; cupping when cold and flattening when warm. At high elevation, a 20° increase in petal angle resulted in a 0.46°C increase in warming. Warming increased pollinator visitation, especially under cooler high elevation temperatures. A plasticity study revealed constitutive elevational differences in petal cupping and stronger temperature-induced floral plasticity in high elevation populations. Thus, plant populations have evolved different behavioural responses to temperature driving differences in thermoregulatory capacity.

Spatially heterogeneous selection and inter-varietal differentiation maintain population structure and local adaptation in a widespread conifer.

BACKGROUND: Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) plays a critical role in the ecology and economy of Western North America. This conifer species comprises two distinct varieties: the coastal variety (var. menziesii) along the Pacific coast, and the interior variety (var. glauca) spanning the Rocky Mountains into Mexico, with instances of inter-varietal hybridization in Washington and British Columbia. Recent investigations have focused on assessing environmental pressures shaping Douglas-fir's genomic variation for a better understanding of its evolutionary and adaptive responses. Here, we characterize range-wide population structure, estimate inter-varietal hybridization levels, identify candidate loci for climate adaptation, and forecast shifts in species and variety distribution under future climates. RESULTS: Using a custom SNP-array, we genotyped 540 trees revealing four distinct clusters with asymmetric admixture patterns in the hybridization zone. Higher genetic diversity observed in coastal and hybrid populations contrasts with lower diversity in inland populations of the southern Rockies and Mexico, exhibiting a significant isolation by distance pattern, with less marked but still significant isolation by environment. For both varieties, we identified candidate loci associated with local adaptation, with hundreds of genes linked to processes such as stimulus response, reactions to chemical compounds, and metabolic functions. Ecological niche modeling revealed contrasting potential distribution shifts among the varieties in the coming decades, with interior populations projected to lose habitat and become more vulnerable, while coastal populations are expected to gain suitable areas. CONCLUSIONS: Overall, our findings provide crucial insights into the population structure and adaptive potential of Douglas-fir, with the coastal variety being the most likely to preserve its evolutionary path throughout the present century, which carry implications for the conservation and management of this species across their range.

Response of wild aquatic insect communities to thermal variation through comparative landscape transcriptomics.

Fluctuations in temperature are recognized as a potent driver of selection pressure, fostering genomic variations that are crucial for the adaptation and survival of organisms under selection. Notably, water temperature is a pivotal factor influencing aquatic organism persistence. By comprehending how aquatic organisms respond to shifts in water temperature, we can understand their potential physiological adaptations to environmental change in one or multiple species. This, in turn, contributes to the formulation of biologically relevant guidelines for the landscape scale transcriptome profile of organisms in lotic systems. Here, we investigated the distinct responses of seven stream stonefly species, collected from four geographical regions across Japan, to variations in temperature, including atmospheric and water temperatures. We achieved this by assessing the differences in gene expression through RNA-sequencing within individual species and exploring the patterns of community-genes among different species. We identified 735 genes that exhibited differential expressions across the temperature gradient. Remarkably, the community displayed expression levels differences of respiration and metabolic genes. Additionally, the diversity in molecular functions appeared to be linked to spatial variation, with water temperature differences potentially contributing to the overall functional diversity of genes. We found 22 community-genes with consistent expression patterns among species in response to water temperature variations. These genes related to respiration, metabolism and development exhibited a clear gradient providing robust evidence of divergent adaptive responses to water temperature. Our findings underscore the differential adaptation of stonefly species to local environmental conditions, suggesting that shared responses in gene expression may occur across multiple species under similar environmental conditions. This study emphasizes the significance of considering various species when assessing the impacts of environmental changes on aquatic insect communities and understanding potential mechanisms to cope with such changes.

Sex-specific life-history trait expression in hybrids of a cave- and surface-dwelling fish (Poecilia mexicana, Poeciliidae).

Evaluating the fitness of hybrids can provide important insights into genetic differences between species or diverging populations. We focused on surface- and cave-ecotypes of the widespread Atlantic molly Poecilia mexicana and raised F1 hybrids of reciprocal crosses to sexual maturity in a common-garden experiment. Hybrids were reared in a fully factorial 2 × 2 design consisting of lighting (light vs. darkness) and resource availability (high vs. low food). We quantified survival, ability to realize their full reproductive potential (i.e., completed maturation for males and 3 consecutive births for females) and essential life-history traits. Compared to the performance of pure cave and surface fish from a previous experiment, F1s had the highest death rate and the lowest proportion of fish that reached their full reproductive potential. We also uncovered an intriguing pattern of sex-specific phenotype expression, because male hybrids expressed cave molly life histories, while female hybrids expressed surface molly life histories. Our results provide evidence for strong selection against hybrids in the cave molly system, but also suggest a complex pattern of sex-specific (opposing) dominance, with certain surface molly genes being dominant in female hybrids and certain cave molly genes being dominant in male hybrids.

Local adaptation of Pinus leiophylla under climate and land use change models in the Avocado Belt of Michoacán.

Climate change and land use change are two main drivers of global biodiversity decline, decreasing the genetic diversity that populations harbour and altering patterns of local adaptation. Landscape genomics allows measuring the effect of these anthropogenic disturbances on the adaptation of populations. However, both factors have rarely been considered simultaneously. Based on a set of 3660 SNPs from which 130 were identified as outliers by a genome-environment association analysis (LFMM), we modelled the spatial turnover of allele frequencies in 19 localities of Pinus leiophylla across the Avocado Belt in Michoacán state, Mexico. Then, we evaluated the effect of climate change and land use change scenarios, in addition to evaluating assisted gene flow strategies and connectivity metrics across the landscape to identify priority conservation areas for the species. We found that localities in the centre-east of the Avocado Belt would be more vulnerable to climate change, while localities in the western area are more threatened by land conversion to avocado orchards. Assisted gene flow actions could aid in mitigating both threats. Connectivity patterns among forest patches will also be modified by future habitat loss, with central and eastern parts of the Avocado Belt maintaining the highest connectivity. These results suggest that areas with the highest priority for conservation are in the eastern part of the Avocado Belt, including the Monarch Butterfly Biosphere Reserve. This work is useful as a framework that incorporates distinct layers of information to provide a more robust representation of the response of tree populations to anthropogenic disturbances.

Evidence that variation in root anatomy contributes to local adaptation in Mexican native maize.

Mexican native maize (Zea mays ssp. mays) is adapted to a wide range of climatic and edaphic conditions. Here, we focus specifically on the potential role of root anatomical variation in this adaptation. Given the investment required to characterize root anatomy, we present a machine-learning approach using environmental descriptors to project trait variation from a relatively small training panel onto a larger panel of genotyped and georeferenced Mexican maize accessions. The resulting models defined potential biologically relevant clines across a complex environment that we used subsequently for genotype-environment association. We found evidence of systematic variation in maize root anatomy across Mexico, notably a prevalence of trait combinations favoring a reduction in axial hydraulic conductance in varieties sourced from cooler, drier highland areas. We discuss our results in the context of previously described water-banking strategies and present candidate genes that are associated with both root anatomical and environmental variation. Our strategy is a refinement of standard environmental genome-wide association analysis that is applicable whenever a training set of georeferenced phenotypic data is available.

Genomic signatures of ecological divergence between savanna and forest populations of a Neotropical tree.

BACKGROUND AND AIMS: In eastern Neotropical South America, the Cerrado, a large savanna vegetation, and the Atlantic Forest harbour high biodiversity levels, and their habitats are rather different from each other. The biomes have intrinsic evolutionary relationships, with high lineage exchange that can be attributed, in part, to a large contact zone between them. The genomic study of ecotypes, i.e. populations adapted to divergent habitats, can be a model to study the genomic signatures of ecological divergence. Here, we investigated two ecotypes of the tree Plathymenia reticulata, one from the Cerrado and the other from the Atlantic Forest, which have a hybrid zone in the ecotonal zone of Atlantic Forest-Cerrado. METHODS: The ecotypes were sampled in the two biomes and their ecotone. The evolutionary history of the divergence of the species was analysed with double-digest restriction site-associated DNA sequencing. The genetic structure and the genotypic composition of the hybrid zone were determined. Genotype-association analyses were performed, and the loci under putative selection and their functions were investigated. KEY RESULTS: High divergence between the two ecotypes was found, and only early-generation hybrids were found in the hybrid zone, suggesting a partial reproductive barrier. Ancient introgression between the Cerrado and Atlantic Forest was not detected. The soil and climate were associated with genetic divergence in Plathymenia ecotypes and outlier loci were found to be associated with the stress response, with stomatal and root development and with reproduction. CONCLUSIONS: The high genomic, ecological and morphophysiological divergence between ecotypes, coupled with partial reproductive isolation, indicate that the ecotypes represent two species and should be managed as different evolutionary lineages. We advise that the forest species should be re-evaluated and restated as vulnerable. Our results provide insights into the genomic mechanisms underlying the diversification of species across savanna and forest habitats and the evolutionary forces acting in the species diversification in the Neotropics.

Local adaptation to hummingbirds and bees in Salvia stachydifolia: insights into pollinator shifts in a Southern Andean sage.

BACKGROUND AND AIMS: Differences among populations in pollinator assemblages can lead to local adaptation mosaics in which plants evolve different floral morphologies and attractive traits. Mountain habitats may promote local adaptation because of differences in environmental conditions with altitude, causing changes in pollinators, and because mountaintops can act as isolated habitats. We studied if the differences in floral shape, size and nectar traits in Salvia stachydifolia can be attributed to variations in the relative contribution of hummingbirds and insects. METHODS: We studied eight populations of S. stachydifolia in natural and under common garden conditions, to assess whether population differences have a genetic component. We recorded pollinators, their behaviour and visitation rates, and characterized pollinator assemblages. In addition, we measured nectar volume and concentration, and collected flowers to describe floral shape and size variation using geometric morphometric methods. We then applied an unsupervised learning algorithm to identify ecotypes based on morphometric traits. Finally, we explored whether populations with different pollinator assemblages had different climatic and/or elevation preferences. KEY RESULTS: We found that variation in the identity of the main pollinators was associated with differences among populations in all traits, as expected under a local adaptation scenario. These differences persisted in the common garden, suggesting that they were not due to phenotypic plasticity. We found S. stachydifolia populations were pollinated either by bees, by hummingbirds or had mixed pollination. We identified two ecotypes that correspond to the identity of the main pollinator guilds, irrespective of climate or altitude. CONCLUSIONS: Variation in S. stachydifolia floral traits did not follow any evident association with bioclimatic factors, suggesting that populations may have diverged as the product of historical isolation on mountaintops. We suggest that differences among populations point to incipient speciation and an ongoing pollinator shift.

The Genomic Basis of Adaptation to High Elevations in Africanized Honey Bees.

A range of different genetic architectures underpin local adaptation in nature. Honey bees (Apis mellifera) in the Eastern African Mountains harbor high frequencies of two chromosomal inversions that likely govern adaptation to this high-elevation habitat. In the Americas, honey bees are hybrids of European and African ancestries and adaptation to latitudinal variation in climate correlates with the proportion of these ancestries across the genome. It is unknown which, if either, of these forms of genetic variation governs adaptation in honey bees living at high elevations in the Americas. Here, we performed whole-genome sequencing of 29 honey bees from both high- and low-elevation populations in Colombia. Analysis of genetic ancestry indicated that both populations were predominantly of African ancestry, but the East African inversions were not detected. However, individuals in the higher elevation population had significantly higher proportions of European ancestry, likely reflecting local adaptation. Several genomic regions exhibited particularly high differentiation between highland and lowland bees, containing candidate loci for local adaptation. Genes that were highly differentiated between highland and lowland populations were enriched for functions related to reproduction and sperm competition. Furthermore, variation in levels of European ancestry across the genome was correlated between populations of honey bees in the highland population and populations at higher latitudes in South America. The results are consistent with the hypothesis that adaptation to both latitude and elevation in these hybrid honey bees are mediated by variation in ancestry at many loci across the genome.

Local adaptation to aridity in a widely distributed angiosperm tree species is mediated by seasonal increase of sugars and reduced growth.

Trees in dry climates often have higher concentrations of total non-structural carbohydrates (NSC = starch + soluble sugars) and grow less than conspecifics in more humid climates. This pattern might result from growth being more constrained by aridity than the carbon (C) gain, or reflect local adaptation to aridity, since NSC fuel metabolism and ensure adequate osmoregulation through the supply of soluble sugars (SS), while low growth reduces water and C demands. It has been further proposed that C allocation to storage could come at the expense of growth (i.e., a growth-storage trade-off). We examined whether NSC and growth reflect local adaptation to aridity in Embothrium coccineum (Proteaceae), a species with an exceptionally wide niche. To control for any influence of the phenotypic plasticity on NSC and growth, we collected seeds from dry (500 mm year-1) and moist (> 2500 mm year-1) climates and grew seedlings in a common garden experiment for 3 years. We then compared NSC and SS concentrations and pools (i.e., total contents), and the biomass of seedlings at spring, summer, and fall. Seedlings from the dry climate had significantly lower biomass and similar NSC concentrations and pools than seedlings from moist climate, suggesting that reduced growth in arid environments does not result from a prioritization of C allocation to storage but it confers advantages under aridity (e.g., lower transpiration area). Across organs, starch and NSC decreased similarly in seedlings from both climates from spring onward. However, root and stem SS concentrations increased during the growing season, and these increases were significantly higher in seedlings from the dry climate. The greater SS accumulation in seedlings from the dry climate compared to those from the moist climate demonstrates ecotypic differentiation in the seasonal dynamics of SS, suggesting that SS underlie local adaptation to aridity. (298 words).

The importance of cryptic diversity in the conservation of wide-ranging species: The red-footed tortoise Chelonoidis carbonarius in Colombia.

Wide-ranging species are seldom considered conservation priorities, yet they have the potential to harbour genetically deeply differentiated units across environments or ecological barriers, including some that warrant taxonomic recognition. Documenting such cryptic genetic diversity is especially important for wide-ranging species that are in decline, as they may comprise a set of even more endangered lineages or species with small distributions. However, studies of wide-ranging species, particularly when they cross political borders, are extremely challenging. One approach to overcoming these challenges is to conduct detailed local analyses in combination with less detailed, range-wide studies. We used this approach with the red-footed tortoise (Chelonoidis carbonarius), a threatened species likely to contain cryptic diversity given its vast range and the distinctive ecoregions that it inhabits. Previous single-gene molecular studies indicated the presence of at least five lineages, two of which occur in different ecoregions separated by the Andes within Colombia. We used a comprehensive genomic analysis to test the hypothesis of cryptic diversity within the single jurisdiction of Colombia. We used a combination of restriction-site-associated DNA sequencing and environmental niche modelling to provide three independent lines of evidence that support the presence of important cryptic diversity that may deserve taxonomic recognition: allopatric reproductive isolation, local adaptation and ecological divergence. We also provide a fine-scale genetic map with the distribution of conservation units in Colombia. As we complete ongoing range-wide analyses and make taxonomic adjustments, we recommend that the two lineages in Colombia be treated as separate units for conservation purposes.

Las especies con distribuciones amplias rara vez son consideradas prioridades de conservación, sin embargo, tienen el potencial de albergar unidades genéticamente diferenciadas que en algunos casos justifican reconocimiento taxonómico. Documentar dicha diversidad genética críptica es especialmente importante para las especies de rangos amplios que ya están en peligro de extinción, pues pueden comprender un conjunto de linajes o especies aún más amenazadas y con distribuciones más pequeñas. Sin embargo, los estudios de especies de rangos amplios, particularmente cuando cruzan fronteras políticas, son extremadamente desafiantes. Un enfoque para superar estos desafíos es realizar análisis locales detallados en combinación con estudios en todo el rango de distribución menos detallados. Nosotros usamos este enfoque con la tortuga de patas rojas (Chelonoidis carbonarius), una especie amenazada que probablemente contiene diversidad genética críptica dada su amplia distribución y las distintas ecorregiones en las que habita. Estudios moleculares previos de un solo gen indicaron la presencia de al menos cinco linajes, dos de los cuales ocurren en diferentes ecorregiones separadas por los Andes en Colombia. En este estudio utilizamos una combinación de secuenciación de ADN asociada a sitios de restricción (RADseq) y modelamiento de nicho ecológico para proporcionar tres líneas independientes de evidencia que respaldan la presencia de diversidad críptica importante que puede merecer reconocimiento taxonómico: aislamiento reproductivo alopátrico, adaptación local y divergencia ecológica. También proporcionamos un mapa genético a escala fina con la distribución de unidades de conservación en Colombia. Mientras completamos análisis genómicos en todo el rango de distribución y hacemos ajustes taxonómicos, recomendamos que los dos linajes en Colombia se traten como unidades independientes para fines de conservación.

Understanding the Geographic Patterns of Closely-Related Species of Paspalum (Poaceae) Using Distribution Modelling and Seed Germination Traits.

The sexual species of the Dilatata complex (Paspalum dasypleurum, P. flavescens, P. plurinerve, P. vacarianum, and P. urvillei) are closely related phylogenetically and show allopatric distributions, except P. urvillei. These species show microhabitat similarities and differences in germination traits. We integrated species distribution models (SDMs) and seed germination assays to determine whether germination divergences explain their biogeographic pattern. We trained SDMs in South America using species' presence-absence data and environmental variables. Additionally, populations sampled from highly favourable areas in the SDMs of these species were grown together, and their seeds germinated at different temperatures and dormancy-breaking conditions. Differences among species in seed dormancy and germination niche breadth were tested, and linear regressions between seed dormancy and climatic variables were explored. SDMs correctly classified both the observed presences and absences. Spatial factors and anthropogenic activities were the main factors explaining these distributions. Both SDMs and germination analyses confirmed that the niche of P. urvillei was broader than the other species which showed restricted distributions, narrower germination niches, and high correlations between seed dormancy and precipitation regimes. Both approaches provided evidence about the generalist-specialist status of each species. Divergences in seed dormancy between the specialist species could explain these allopatric distributions.

Unraveling Signatures of Local Adaptation among Indigenous Groups from Mexico.

Few studies have addressed how selective pressures have shaped the genetic structure of the current Native American populations, and they have mostly limited their inferences to admixed Latin American populations. Here, we searched for local adaptation signals, based on integrated haplotype scores and population branch statistics, in 325 Mexican Indigenous individuals with at least 99% Native American ancestry from five previously defined geographical regions. Although each region exhibited its own local adaptation profile, only PPARG and AJAP1, both negative regulators of the Wnt/ß catenin signaling pathway, showed significant adaptation signals in all the tested regions. Several signals were found, mainly in the genes related to the metabolic processes and immune response. A pathway enrichment analysis revealed the overrepresentation of selected genes related to several biological phenotypes/conditions, such as the immune response and metabolic pathways, in agreement with previous studies, suggesting that immunological and metabolic pressures are major drivers of human adaptation. Genes related to the gut microbiome measurements were overrepresented in all the regions, highlighting the importance of studying how humans have coevolved with the microbial communities that colonize them. Our results provide a further explanation of the human evolutionary history in response to environmental pressures in this region.

Priming by Insects: Differential Effects of Sympatric and Allopatric Priming upon Plant Performance and Tolerance to Herbivory.

Plants have evolved multiple mechanisms to defend themselves from their multiple herbivores. Thus, being able to recognise among them and respond accordingly is fundamental for plant survival and reproduction. Defence priming prepares the plant to better or more rapidly respond to future damage; however, while it is considered an adaptive trait, to date, no studies have evaluated the extent and specificity of the priming recognition. To estimate the costs, benefits and specificity of priming, we used a highly specialist plant-insect system (Datura stramonium-Lema daturaphila) and performed a reciprocal transplant experiment with two populations where a priming stimulus (sympatric vs. allopatric) and a damage treatment (sympatric) were applied. We found no evidence of a fitness cost of priming, given that primed plants without damage showed no reduction in fitness. In contrast, our treatments affected the probability of bud abortion. That is, when damaged plants received no priming or the priming came from an allopatric insect, the likelihood of aborting the first bud was 1.9 times greater compared to plants being primed by their sympatric insect. We also found that damaged plants primed with an allopatric insect produced 14% fewer seeds compared to plants receiving a sympatric priming stimulus. Tolerance to herbivore damage was also the lowest when plants received the priming stimulus from an allopatric insect. Overall, these results suggest that, in our study system, plants recognise their local insect population reducing the negative effect of damage through a tolerance response.

Seed Weight and Trade-Offs: An Experiment in False Rhodes Grasses under Different Aridity Conditions.

The false Rhodes grasses [Leptochloa crinita (Lag.) P.M. Peterson and N.W. Snow and Leptochloa pluriflora (E. Fourn.) P.M. Peterson and N.W. Snow] are considered valuable native forage resources for arid and semiarid rangelands in Argentina and the United States. Effectively using plant materials as forage under aridity conditions requires understanding their resource allocation under those conditions. In the present study, plant functional traits were evaluated in six populations of each false Rhodes grass species from different geographic origin in a humid and an arid region. The evaluation was focused on seed weight, due to the key role of this trait in plant survival. The implication of seed weight in germination under osmotic stress and trade-off relationships between functional traits were also analysed. A fixed ontogenetic variation was found in both species, since populations maintained a stable seed weight across environments. The tolerance to osmotic stress at germination stage was more related to seed weight than to population origin or maternal environment of seeds; heavier-seeded populations produced heavier seedlings instead of a higher number of germinated seeds or higher germination rates. Some traits varied between environments but other traits exhibited a fixed response. Variation patterns among populations were similar within environments and in some cases even for populations from the same geographic origin, revealing a fixed ontogenetic variation; this phenomenon was clearer in L. crinita than in L. pluriflora. Moreover, several different trade-off strategies were detected in both species. These results reinforce the knowledge about the key role of seed weight in survival and performance of seedlings at initial growth stages under arid conditions; however, at advanced stages, other traits would have an important function in growth and development of false Rhodes grasses.

Signatures of Convergent Evolution and Natural Selection at the Alcohol Dehydrogenase Gene Region are Correlated with Agriculture in Ethnically Diverse Africans.

The alcohol dehydrogenase (ADH) family of genes encodes enzymes that catalyze the metabolism of ethanol into acetaldehyde. Nucleotide variation in ADH genes can affect the catalytic properties of these enzymes and is associated with a variety of traits, including alcoholism and cancer. Some ADH variants, including the ADH1B*48His (rs1229984) mutation in the ADH1B gene, reduce the risk of alcoholism and are under positive selection in multiple human populations. The advent of Neolithic agriculture and associated increase in fermented foods and beverages is hypothesized to have been a selective force acting on such variants. However, this hypothesis has not been tested in populations outside of Asia. Here, we use genome-wide selection scans to show that the ADH gene region is enriched for variants showing strong signals of positive selection in multiple Afroasiatic-speaking, agriculturalist populations from Ethiopia, and that this signal is unique among sub-Saharan Africans. We also observe strong selection signals at putatively functional variants in nearby lipid metabolism genes, which may influence evolutionary dynamics at the ADH region. Finally, we show that haplotypes carrying these selected variants were introduced into Northeast Africa from a West-Eurasian source within the last ∼2,000 years and experienced positive selection following admixture. These selection signals are not evident in nearby, genetically similar populations that practice hunting/gathering or pastoralist subsistence lifestyles, supporting the hypothesis that the emergence of agriculture shapes patterns of selection at ADH genes. Together, these results enhance our understanding of how adaptations to diverse environments and diets have influenced the African genomic landscape.

Divergence in Heliconius flight behaviour is associated with local adaptation to different forest structures.

Microhabitat choice plays a major role in shaping local patterns of biodiversity. In butterflies, stratification in flight height has an important role in maintaining community diversity. Despite its presumed importance, the role of behavioural shifts in early stages of speciation in response to differences in habitat structure is yet to be established. Here, we investigated variation in flight height behaviour in two closely related Heliconius species, H. erato cyrbia and H. himera, which produce viable hybrids but are isolated across an environmental gradient, spanning lowland wet forest to high-altitude scrub forest. Speciation in this pair is associated with strong assortative mating, but ecological isolation and local adaptation are also considered essential for complete reproductive isolation. We quantified differences in flight height and forest structure across the environmental gradient and tested the importance of resource distribution in explaining flight behaviour. We then used common garden experiments to test whether differences in flight height reflect individual responses to resource distribution or genetically determined shifts in foraging behaviour. We found that the two species fly at different heights in the wild, and demonstrated that this can be explained by differences in the vertical distribution of plant resources. In both the wild and captivity, H. himera choose to fly lower and feed at lower positions, closely mirroring differences in resource availability in the wild. Given expectations that foraging efficiency contributes to survival and reproductive success, we suggest that foraging behaviour may reflect local adaptation to divergent forest structures. Our results highlight the potential role of habitat-dependent divergence in behaviour during the early stages of speciation.

La elección de microhábitat juega un papel determinante en los patrones locales de biodiversidad. En las mariposas, la estratificación (entendida como altura de vuelo) cumple un rol importante al promover la diversidad de las comunidades. A pesar de esta asumida importancia, todavía está por establecerse el rol de los cambios comportamentales en estadios tempranos de especiación en respuesta a diferencias en la estructura del hábitat. Aquí investigamos la variación en el comportamiento de estratificación en dos especies de mariposas Heliconius cercanamente emparentadas: H. erato cyribia y H. himera, las cuales producen híbridos viables, pero están aisladas a lo largo de un gradiente ambiental que va desde el bosque húmedo tropical de tierras bajas hasta el bosque de matorrales de altitud. La especiación en esta pareja de mariposas está asociada con un alto grado de emparejamiento selectivo, pero el aislamiento ecológico y la adaptación local también son considerados esenciales para un aislamiento reproductivo completo. Mostramos que las dos especies vuelan a alturas distintas, y demostramos que esto se explica por diferencias en la distribución vertical de los recursos florísticos. Posteriormente, usando experimentos controlados de jardín, exploramos si esta divergencia en altura de vuelo está determinada ambientalmente. Tanto en la naturaleza como en cautividad, H. himera escoge volar más bajo y alimentarse en lugares más bajos, lo que es consistente con las diferencias en la disponibilidad de recursos en la naturaleza. Dada la expectativa de que la eficiencia en el forrajeo contribuye al éxito reproductivo y de supervivencia, sugerimos que el comportamiento de forrajeo podría reflejar adaptación local a estructuras de bosque divergentes. Nuestros resultados resaltan el potencial rol de la divergencia dependiente del hábitat en el comportamiento en estadios tempranos de especiación.

A B73×Palomero Toluqueño mapping population reveals local adaptation in Mexican highland maize.

Generations of farmer selection in the central Mexican highlands have produced unique maize varieties adapted to the challenges of the local environment. In addition to possessing great agronomic and cultural value, Mexican highland maize represents a good system for the study of local adaptation and acquisition of adaptive phenotypes under cultivation. In this study, we characterize a recombinant inbred line population derived from the B73 reference line and the Mexican highland maize variety Palomero Toluqueño. B73 and Palomero Toluqueño showed classic rank-changing differences in performance between lowland and highland field sites, indicative of local adaptation. Quantitative trait mapping identified genomic regions linked to effects on yield components that were conditionally expressed depending on the environment. For the principal genomic regions associated with ear weight and total kernel number, the Palomero Toluqueño allele conferred an advantage specifically in the highland site, consistent with local adaptation. We identified Palomero Toluqueño alleles associated with expression of characteristic highland traits, including reduced tassel branching, increased sheath pigmentation and the presence of sheath macrohairs. The oligogenic architecture of these three morphological traits supports their role in adaptation, suggesting they have arisen from consistent directional selection acting at distinct points across the genome. We discuss these results in the context of the origin of phenotypic novelty during selection, commenting on the role of de novo mutation and the acquisition of adaptive variation by gene flow from endemic wild relatives.

The thermal tolerance of a tropical population of blue crab (Callinectes sapidus) modulates aerobic metabolism during hypoxia.

The blue crab Callinectes sapidus is a widespread ectothermic species that supports large fisheries. Physiology of temperate and subtropical populations of blue crabs are well studied; however, a lack of information exists on tropical populations. Given the low locomotion capabilities of C. sapidus adult blue crabs, natural selection should favor traits that shape a particular thermal niche reflected through tolerance modulation to dissolved oxygen (DO). This study was designed to evaluate the thermal window and hypoxia sensitivity of the blue crab population in the southern Gulf of Mexico. The effect of acclimation temperatures from 20 °C to 34 °C on thermal preference (TP), critical thermal limits (CT), and thermal metabolic scope (TMS) was assessed in normoxia. Metabolic rate regulation over oxygen partial pressure (pO2) gradient was evaluated through oxygen consumption measurements at different degrees of acute hypoxia. Callinectes sapidus was observed tending to specialize towards higher temperatures, showing a mean TP from 26 °C to 33 °C. The lowest performance of aerobic pathways was observed at the coldest regimes and the highest at the warmest ones with mean TMS value being 35 % greater at 34 °C than 20 °C. Patterns for metabolic regulation were dependent on the interaction between environmental temperature and DO, in which the interval from 29 °C to 34 °C provoked a 50 % reduction in oxygen consumption when exposed to ∼20% air saturation levels. The results obtained showed that blue crabs distributed in the southern Gulf of Mexico could be close to their oxygen-temperature tolerance limits, which has important implications when climate change effects on species re-distribution is considered.