Academic literature on the topic 'Multiple Selection Pressures Shape Traits'

The development of frameworks for better-understanding ecological syndromes and putative evolutionary strategies of plant adaptation to fire has recently received a flurry of attention, including a new model hypothesizing that plants have diverged into three different plant flammability strategies due to natural selection. We provide three case studies of pyromes/taxa (Pinus, the Proteaceae of the Cape Floristic Region, and Eucalyptus) that, contrary to model assumptions, reveal that plant species often exhibit traits of more than one of these flammability and post-fire recovery strategies. We propose that such multiple-strategy adaptations have been favoured as bet-hedging strategies in response to selective pressure from mixed-fire regimes experienced by these species over evolutionary time.

Abstract Most biological structures carry out multiple functions. Focusing on only one function to make adaptive inferences overlooks that manifold selection pressures and tradeoffs shape the characteristics of a multifunctional structure. Focusing on single functions can only lead to a partial picture of the causes underlying diversity and the evolutionary origin of the structure in question. I illustrate this discussion using bark as a study case. Bark comprises all the tissues surrounding the xylem in woody plants. Broadly, bark includes an inner and mostly living region and an outer, dead one. Of all plant structures, bark has the most complex anatomical structure and ontogenetic origin involving two (and often three) different meristems. Traditionally, the wide diversity in bark traits, mainly bark thickness, has been interpreted as the result of the selective pressures imposed by fire regime. However, recent research has shown that explanations based on fire regime cannot account for salient patterns of bark variation globally including the very strong inner bark thickness–stem diameter scaling, which is likely due to metabolic needs, and the very high intracommunity variation in total, inner, and outer bark thickness, and in inner:outer proportions. Moreover, explanations based on fire disregard that in addition to fire protection, bark carries out several other crucial functions for plants including translocation of photosynthates; storage of starch, soluble sugars, water, and other compounds; protection from herbivores, pathogens, and high temperatures; wound closure, as well as mechanical support, photosynthesis, and likely being involved in xylem embolism repair. All these functions are crucial for plant performance and are involved in synergistic (e.g., storage of water and insulation) and trade-off relationships (e.g., protection from fire vs photosynthetic activity). Focusing on only one of these functions, protection from fire has provided an incomplete picture of the selective forces shaping bark diversity and has severely hindered our incipient understanding of the functional ecology of this crucial region of woody stems. Applying a multifunctional perspective to the study of bark will allow us to address why we observe such high intracommunity variation in bark traits, why some bark trait combinations are ontogenetically impossible or penalized by selection, how bark is coordinated functionally with other plant parts, and as a result, to understand how bark contributes to the vast diversity of plant ecological strategies across the globe.

Maximum lifespan in birds and mammals varies strongly with body mass such that large species tend to live longer than smaller species. However, many species live far longer than expected given their body mass. This may reflect interspecific variation in extrinsic mortality, as life-history theory predicts investment in long-term survival is under positive selection when extrinsic mortality is reduced. Here, we investigate how multiple ecological and mode-of-life traits that should reduce extrinsic mortality (including volancy (flight capability), activity period, foraging environment and fossoriality), simultaneously influence lifespan across endotherms. Using novel phylogenetic comparative analyses and to our knowledge, the most species analysed to date ( n = 1368), we show that, over and above the effect of body mass, the most important factor enabling longer lifespan is the ability to fly. Within volant species, lifespan depended upon when (day, night, dusk or dawn), but not where (in the air, in trees or on the ground), species are active. However, the opposite was true for non-volant species, where lifespan correlated positively with both arboreality and fossoriality. Our results highlight that when studying the molecular basis behind cellular processes such as those underlying lifespan, it is important to consider the ecological selection pressures that shaped them over evolutionary time.

Synopsis Mechanical tradeoffs in performance are predicted to sculpt macroevolutionary patterns of morphological diversity across environmental gradients. Water depth shapes the amount of wave energy organisms’ experience, which should result in evolutionary tradeoffs between speed and maneuverability in fish swimming morphology. Here, we tested whether morphological evolution would reflect functional tradeoffs in swimming performance in 131 species of wrasses and parrotfish (Family: Labridae) across a water depth gradient. We found that maximum water depth predicts variation in pectoral fin aspect ratio (AR) in wrasses, but not in parrotfish. Shallow-water wrasses exhibit wing-like pectoral fins that help with “flapping,” which allows more efficient swimming at faster speeds. Deeper water species, in contrast, exhibit more paddle-like pectoral fins associated with enhanced maneuverability at slower speeds. Functional morphology responds to a number of different, potentially contrasting selective pressures. Furthermore, many-to-one mapping may release some traits from selection on performance at the expense of others. As such, deciphering the signatures of mechanical tradeoffs on phenotypic evolution will require integrating multiple aspects of ecological and morphological variation. As the field of evolutionary biomechanics moves into the era of big data, we will be uniquely poised to disentangle the intrinsic and extrinsic predictors of functional diversity.

Plant-herbivore interactions shape community dynamics across marine, freshwater, and terrestrial habitats. From amphipods to elephants and from algae to trees, plant-herbivore relationships are the crucial link generating animal biomass (and human societies) from mere sunlight. These interactions are, thus, pivotal to understanding the ecology and evolution of virtually any ecosystem. Here, we briefly highlight recent advances in four areas of plant-herbivore interactions: (1) plant defense theory, (2) herbivore diversity and ecosystem function, (3) predation risk aversion and herbivory, and (4) how a changing climate impacts plant-herbivore interactions. Recent advances in plant defense theory, for example, highlight how plant life history and defense traits affect and are affected by multiple drivers, including enemy pressure, resource availability, and the local plant neighborhood, resulting in trait-mediated feedback loops linking trophic interactions with ecosystem nutrient dynamics. Similarly, although the positive effect of consumer diversity on ecosystem function has long been recognized, recent advances using DNA barcoding to elucidate diet, and Global Positioning System/remote sensing to determine habitat selection and impact, have shown that herbivore communities are probably even more functionally diverse than currently realized. Moreover, although most diversity-function studies continue to emphasize plant diversity, herbivore diversity may have even stronger impacts on ecosystem multifunctionality. Recent studies also highlight the role of risk in plant-herbivore interactions, and risk-driven trophic cascades have emerged as landscape-scale patterns in a variety of ecosystems. Perhaps not surprisingly, many plant-herbivore interactions are currently being altered by climate change, which affects plant growth rates and resource allocation, expression of chemical defenses, plant phenology, and herbivore metabolism and behavior. Finally, we conclude by noting that although the field is advancing rapidly, the world is changing even more rapidly, challenging our ability to manage these pivotal links in the food chain.

The dispersal-syndrome hypothesis posits that fruit traits are a product of selection by frugivores. Although criticized as adaptationist, recent studies have suggested that traits such as fruit or seed size, colour and odour exhibit signatures that imply selection by animal mutualists. These traits imply nutritional rewards (e.g. lipid, carbohydrate), attracting frugivores; however, this remains incompletely resolved. Here, we investigated whether fruit nutrients (lipid, sugar, protein, vitamin C, water content) moderate the co-adaptation of key disperser-group mutualisms. Multivariate techniques revealed that fruit nutrients assembled non-randomly and grouped according to key dispersal modes. Bird-dispersed fruits were richer in lipids than mammal-dispersed fruits. Mixed-dispersed fruits had significantly higher vitamin C than did mammal- or bird-dispersed fruits separately. Sugar and water content were consistently high irrespective of dispersal modes, suggesting that these traits appeal to both avian and mammalian frugivores to match high-energy requirements. Similarly, protein content was low irrespective of dispersal modes, corroborating that birds and mammals avoid protein-rich fruits, which are often associated with toxic levels of nitrogenous secondary compounds. Our results provide substantial over-arching evidence that seed disperser assemblages co-exert fundamental selection pressures on fruit nutrient trait adaptation, with broad implications for structuring fruit–frugivore mutualism and maintaining fruit trait diversity.

Abstract Background and Aims Angiosperms vary remarkably in traits such as colour, size and shape of flowers, yet such variation generally tends to be low within species. In deceptive orchids, however, large variation in floral traits has been described, not only between but also within populations. Nonetheless, the factors driving variation in floral traits in deceptive orchids remain largely unclear. Methods To identify determinants of variation in floral traits, we investigated patterns of fruit set and selection gradients in the food-deceptive orchid Orchis purpurea, which typically presents large within-population variation in the colour and size of the flowers. Using long-term data, fruit set was quantified in two populations over 16 consecutive years (2004–2019). Artificial hand pollination was performed to test the hypothesis that fruit set was pollinator-limited and that selfing led to decreased seed set and viability. Annual variation (2016–2019) in selection gradients was calculated for three colour traits (brightness, contrast and the number of spots on the labellum), flower size (spur length, labellum length and width) and plant size (number of flowers, plant height). Key Results Fruit set was, on average, low (~12 %) and severely pollinator-limited. Opportunities for selection varied strongly across years, but we found only weak evidence for selection on floral traits. In contrast, there was strong and consistent positive selection on floral display. Selfing led to reduced production of viable seeds and hence severe inbreeding depression (δ = 0.38). Conclusion Overall, these results demonstrate that the large variation in flower colour and size that is regularly observed in natural O. purpurea populations is maintained by the consistent lack of strong selection pressures on these traits through time.

The transition from outcrossing to selfing is a common evolutionary trend in flowering plants, and floral traits change significantly with the evolution of selfing. Whether or not plant traits are subjected to selection remains an open question in species with mixed mating systems. We examined phenotypic selection in two populations of Halenia elliptica with different selfing rates. We found that the pollen–ovule ratio, seed size, plant height, spur length, and pollinator visitation rate in the population with the higher selfing rate were lower than those in the population with the lower selfing rate. Selfing provides reproductive assurance for populations when pollinator service is low, and the floral traits that are associated with selfing syndrome are evident in populations with a higher selfing rate but are subjected to weak selection in each of the two populations with different selfing rates. Directional selection for an early flowering time indicated that late blooming flowers could experience a risk of seed development in alpine environments, and for large plants, selection indicated that seed production could be limited by the available resources. The floral traits that are associated with pollinator attraction and specialization could be subjected to weak selection at the plant level as selfing evolves, and the selective pressures that are independent of pollinators might not change significantly; highlighting the selective biotic and abiotic pressures that shape the morphological traits of plant species and their independence from the mating system.

Abstract Feralization is the process by which domestic animals return to the wild and produce self-sustaining populations. It is often considered as a model in understanding the permanence of morphological changes associated with domestication; however, it is still unclear how much the release of anthropogenic selective pressures affects domestic traits. Here, we assessed the influence of feralization on the domestic morphological traits acquired through selective breeding using craniomandibular differences in shape and size between populations of feral pigs, wild boar and domestic pigs, using landmark-based geometric morphometrics. Our results suggest that numerous cranial and mandibular traits associated with domestication still exist in feral specimens, corroborating that domestication-induced changes in the shape of morphological elements are broadly maintained in feral populations. This is not the case for size variations, however, as the cranium is significantly smaller in feral pigs than in domesticated breeds, which could be due to the selective pressures associated with founding events. Our exploratory study, therefore, underlines the complexity of feral population history, the intricate influence of variations in genetic diversity, and novel selection pressures in the morphology of these groups. Future studies will need to expand the sample to take into account the diversity of morphotypes.

It is well recognized that differences in environmental selection pressures among populations can generate phenotypic divergence in a suite of morphological characteristics and associated life history traits. Previous analysis of mitochondrial DNA and body size have suggested that Black Bears (Ursus americanus) inhabiting the island of Newfoundland represent a different subspecies or ecotype from mainland populations. Assuming that body size covaries positively with skull size, we predicted that skull size would be greater for bears on the island than the mainland, and the distribution of size-related shape components in multivariate space should show a distinct separation between Newfoundland and mainland populations. Measurements of 1080 specimens from Newfoundland, Alberta, New York, and Quebec did not provide unequivocal support for our prediction that skull size in Newfoundland bears would be larger than bears from the mainland populations. After removing ontogenetic effects of skull size, between-population variation in skull shape was greater in females than males, and the analysis significantly separated Newfoundland bears from mainland populations. Explanations for this pattern are numerous, but currently remain hypothetical. Limited covariation between skull size and body size suggests that genetic traits regulating the size of Black Bear skulls are more heritable (i.e., less influenced by environmental selection pressures) than characteristics affecting body size. We hypothesize that if gape size does not limit prey size in solitary terrestrial carnivores, large degrees of among-population variation in body size should be coupled with little covariation in skull size. In general, sexual dimorphism in skull size and shape was marginal for the phenotypic characters measured in our study. We believe that sexual dimorphism in skull size in Black Bears is primarily driven by intrasexual selection in males for increased gape size display, while similarity in skull shape between sexes is associated with the constraints of a temporally-selective, but similar diet.

A focus in evolutionary biology is to understand the drivers of diversity in animal behavioural traits in the living world. Animals facing similar problems in the environment, such as the problem of how much to invest in parental care, can have very different solutions to the same problem. This large diversity in traits can be explained by a reasonable proposition that this diversity is of adaptive value and is a result of selection pressures acting in a given environment. In wild populations, multiple selection pressures are likely to shape trait evolution. While these multiple selection pressures can manifest through different ecological or demographic conditions, these conditions themselves could vary predictably over space or time, or in an unpredictable manner, a relatively less studied form of environmental variability. While predictable variation in the environment could shape traits through adaptive phenotypic plasticity, traits could also be shaped by unpredictable variation in environment. Unpredictable variation in environments could lead to the evolution of strategies, such as evolutionary bet-hedging or spreading the risk. In my thesis, I attempt to understand how oviposition site selection, a behaviour where multiple selection pressure regimes are rarely considered, is shaped by multiple selective factors in a variable environment. Oviposition site selection is a form of habitat selection where a female chooses a site for laying eggs. This decision can have important fitness consequences for the female because the quality of the site selected can influence the quality (e.g., survival, growth, size at maturation) of her offspring, and thereby their reproductive value (the number of offspring that they are capable of producing). In my thesis, I test how oviposition site selection decisions in the mosquito Aedes aegypti are influenced by variation in three important ecological factors, namely risk of larval predation, risk of competition, and risk of pool desiccation. To investigate the factors influencing evolution of oviposition site selection decisions, I first measured fitness trade-offs associated with larval predation risk and conspecific competition risk at potential oviposition sites through experimental manipulation in the laboratory. I found that larval performance reduced substantially under predation, as predicted. I also found surprisingly strong negative effects of competition, and most importantly, an interaction between predation and competition effects such that under high larval densities, predators may have a positive effect by providing a release from intense effects of competition. In the next chapter, I investigate female oviposition behaviour in the light of these tradeoffs in an artificial pool experiment conducted in field conditions. My findings indicate that females showed a complex oviposition response towards the risk of predation, displaying attraction towards pools with low predator densities and aversion towards pools with high predator density. I explain this complex oviposition behaviour using my findings concerning a predation competition trade-off. I propose that larval predators can provide positive fitness benefits when coupled with other risks, in this case, conspecific density effects. I next focussed on spatial and temporal patterns under natural conditions in two risk factors, namely, pool desiccation risk and larval predation risk. I quantified variation in these risk factors across multiple natural breeding sites (rock pools) over the breeding season of Aedes vexans, the dominant rock pool breeding species at the field site. I report predictable variation in both risk factors and unpredictable patterns of variability in larval predation risk. I used these patterns of variability in risk factors to predict and test female oviposition site selection response to these varying multiple risk factors through manipulative experiments using natural breeding sites (rock pools) in the field. I found signals of complex oviposition site selection response towards multiple risk factors: larval predation risk and pool desiccation risk. I found that females avoided large pools that permanently harbour predators in natural settings. Females did not show a strong preference for small pools that naturally do not harbour predators, indicating that multiple factors – desiccation risk and larval predation risk - could interact to influence female decision making. Overall, my findings indicate that oviposition site selection responses are complex, sensitive to interactions between multiple selective factors, and influenced by patterns in variability in some of these factors.
DBT-IISc, CSIR and MHRD

Abstract Drift of the multivariate mean provides an important baseline against which we can gauge the effects of multivariate selection. Multivariate drift is a function of elapsed time, effective population size, and the G-matrix. In the two-trait case at any given time, we can visualize the trait means of replicate populations as a cloud of points in bivariate trait space. Although each mean takes an erratic path through trait space as time unfolds, the statistical behaviour of the cloud is highly predictable. The dispersion cloud retains its shape and orientation, as it gradually expands in size from generation to generation. Moreover, the cloud shares its characteristic shape and orientation with the G-matrix. Tests of these predictions in natural populations reject drift as an explanation for trait radiation. In particular, the observed dispersion cloud is smaller, sometimes much smaller than expected by neutral drift of the trait means. The need for models that include selection as well as drift is also suggested by the empirical result that the major axis of the dispersion cloud can be aligned with the major axes of inheritance and/or selection.

Abstract Selection is often viewed and analyzed as a single-trait phenomenon or multiple traits are treated as isolated, single traits. This univariate focus is unfortunate because it misses crucial aspects of selection that are only revealed in a multivariate treatment of the problem. Crucial new aspects uncovered in multivariate selection analysis allow us to: (1) distinguish between direct and indirect targets of selection, (2) diagnose the correct shape of the selection surface and hence the shape of the adaptive landscape, (3) estimate the force of directional selection in units that can be used to assess evolutionary responses of trait means to selection, and (4) estimate the force of nonlinear selection in units that can be used to assess immediate effects on genetic variance and covariance, as well as long-term contributions to evolutionary patterns, such as stasis. However, all of these selling points are subject to provisos and limitations. Nevertheless, the case for pursuing multivariate rather than univariate selection analysis is compelling.

As shown throughout this book, urbanization moulds evolutionary processes in many biological systems. But what are its effects on the species that is itself the cause of this radical habitat modification? At least two major cultural transitions in history have involved urbanization: the transition to agriculture, and the continuing transition to modernity. Humans both endure and create the selective pressures associated with urbanization, a process of niche construction with complex evolutionary consequences. Urbanization modifies extrinsic mortality, nutrition, hygiene, demography, the toxicity of air, our microbiota, social interactions, and other factors known to shape selection on morphological, physiological, immunological, life-history, and behavioural traits. Today more than half of humanity lives in cities and is exposed to this new evolutionary context. This chapter presents the elements needed to understand the evolutionary potential of humans living in cities, focusing on traits affecting health. Urbanization can alter the expression of tradeoffs and the selection on traits in ways that change the prevalence of both infectious and non-communicable diseases. The chapter identifies several challenges for research. These include the difficulty of separating the effects of urbanization per se from those of modernization in general, and the need to better integrate eco-evolutionary feedbacks, culture, and learning into microevolutionary models to understand how urban life modifies selection on health. Finally, the chapter discusses why the application to humans of gene editing technologies, such as CRISPR-Cas9, is likely to interact with natural selection, an issue deserving closer attention from evolutionary biologists.

There is now overwhelming evidence that the recent rapid climate change has multiple consequences for birds: their abilities to adapt to climate change is thus a major issue. To understand the evolutionary consequences of climate change, an assessment of how it alters selection pressures is needed. As expected, climate change increases selection for earlier breeding but non-intuitive selection patterns are likely to arise for traits other than phenology. Evolutionary responses to these new selection pressures depend on the evolutionary potential in wild bird populations. Heritability alone is not sufficient to predict responses to selection, as many genetic factors (e.g., genetic correlations, indirect genetic effects) can affect evolutionary trajectories. Altogether, studies investigating the nature of responses to climate change in wild populations (plastic vs microevolutionary responses) are still scarce but suggest that the majority of responses would be due to plasticity.

Abstract The theoretical evolution of the multivariate trait mean has been most explored in the case of a hill-shaped adaptive landscape that has a consistent position, shape, and orientation. Under particular but general conditions, the mean tends to evolve uphill on this stationary landscape, towards the adaptive peak. When two or more traits are genetically correlated, the evolutionary path towards the peak is generally curved rather than straight. The big challenge is to develop generalizations about how multivariate evolution will proceed on different kinds of adaptive peaks. The effect of peak configuration on multivariate trait radiations has been explored by assuming that the peak is multivariate Gaussian. Theory is especially well developed for systems in which a single male trait (ornament) evolves in response to sexual selection exerted by a second, female trait (sexual preference). Under these conditions, the equilibrium of the bivariate mean may be a stable point, a line or an elliptical cycle. Unstable dynamics are also possible, but probably unlikely. Finite population size adds an element of uncertainty to the outcome, changing stable points into clouds, for example. Predictions from these models are consistent with important features of actual sexual radiations, but only a few discriminating, quantitative tests have been conducted.

This chapter examines how phylogenetic approaches can address both ecological character displacement and community-wide character displacement. In ecological character displacement, selection might drive the divergence of ecological phenotypes by negative antagonistic interactions that reduce competition between sympatric populations utilizing the same resource base. In community-wide character displacement, ecological divergence occurs in allopatry, and competition filters species into communities based upon their trait values. The geographic distribution of a species reflects multiple factors, including its strength of phylogenetic niche conservatism and the geography of present day climate, its dispersal ability, and the history of speciation. This chapter considers the effect of competition in the native range, focusing on a scenario in which the evolution of species traits may itself be a product of species interactions. It shows that phylogenetic methods can additionally provide insights into how species interactions might shape trait evolution and even illuminate the process of speciation itself.

Abstract Lost circulation remedial techniques will be effective when they are tailored for the specific challenge. Examples of factors that govern the remedial technique are the type of losses (induced vs. natural fractures, permeable formations, etc.), characteristic size of loss zone, difference between equivalent circulation density and pore pressure gradient, etc. Typically, localized workflows are designed based on experience from wells where these factors are within certain limits. These workflows are limited to the new wells where these factors are within the same limits. Additionally, these workflows usually involve the selection of certain type/size of lost circulation materials (LCMs) with less emphasis on tuning fluid density, rheology, and pump rates. A comprehensive approach, one that caters to a wide range of loss scenarios and allows tuning all engineering parameters available for tailoring the unique solution is needed. The work method discussed herein is built using the principles of mass and momentum conservation. These hydraulic calculations also account for rheology changes due to temperature. The domain of analysis is both the wellbore and the loss zone. Thus, any changes in the wellbore will impact the loss rate and vice-versa. To such a two-way coupled system, a cake buildup model is added in the loss zone to describe the role of filter cake resistance on loss rate. Thus, the proposed method is the most comprehensive approach available to model losses based on wellbore pressures, temperatures and plugging of the loss zone. Such a method allows for greater design flexibility to the engineer in tailoring wellbore fluids during drilling or cement operations. The proposed method is used to understand the sensitivity of the loss zone size to the loss type, loss rate and the depth at which losses occur. This helps engineers highlight the critical information needed from job location to tailor the remedial treatment. The effect of loss zone size on the efficacy of an LCM is demonstrated by evaluating the performance of LCMs of different size and shape. This analysis is useful in tailoring blends made up of different LCMs. Moreover, this work method is used to also compare the impact of rheology and density modification vs. LCMs addition on loss control. This provides greater flexibility in tailoring different aspects of wellbore fluids and placement characteristics. The understanding gained from the above analysis is used in predicting the loss control performance across multiple jobs. These jobs varied in loss rate and loss type. The proposed methodology presented herein revealed an optimum match with actual field observation for all the evaluated jobs. For an example job, the model was able to predict the observed surface pressure. All this analysis further demonstrates the capability of the work method in combating losses by tailoring different aspects of a cement job.

The Cucurbitaceae family includes a broad array of economically and nutritionally important crop species that are consumed as vegetables, staple starches and desserts. Fruit of these species, and types within species, exhibit extensive diversity as evidenced by variation in size, shape, color, flavor, and others. Fruit size and shape are critical quality determinants that delineate uses and market classes and are key traits under selection in breeding programs. However, the underlying genetic bases for variation in fruit size remain to be determined. A few species the Cucurbitaceae family were sequenced during the time of this project (cucumber was already sequenced when the project started watermelon and melon sequence became available during the project) but functional genomic tools are still missing. This research program had three major goals: 1. Develop whole genome cucumber and melon SNP arrays. 2. Develop and characterize cucumber populations segregating for fruit size. 3. Combine genomic tools, segregating populations, and phenotypic characterization to identify loci associated with fruit size. As suggested by the reviewers the work concentrated mostly in cucumber and not both in cucumber and melon. In order to develop a SNP (single nucleotide polymorphism) array for cucumber, available and newly generated sequence from two cucumber cultivars with extreme differences in shape and size, pickling GY14 and Chinese long 9930, were analyzed for variation (SNPs). A large set of high quality SNPs was discovered between the two parents of the RILs population (GY14 and 9930) and used to design a custom SNP array with 35000 SNPs using Agilent technology. The array was validated using 9930, Gy14 and F1 progeny of the two parents. Several mapping populations were developed for linkage mapping of quantitative trait loci (QTL) for fruit size These includes 145 F3 families and 150 recombinant inbred line (RILs F7 or F8 (Gy14 X 9930) and third population contained 450 F2 plants from a cross between Gy14 and a wild plant from India. The main population that was used in this study is the RILs population of Gy14 X 9930. Phenotypic and morphological analyses of 9930, Gy14, and their segregating F2 and RIL progeny indicated that several, likely independent, factors influence cucumber fruit size and shape, including factors that act both pre-anthesis and post-pollination. These include: amount, rate, duration, and plane of cell division pre- and post-anthesis and orientation of cell expansion. Analysis of F2 and RIL progeny indicated that factors influencing fruit length were largely determined pre-anthesis, while fruit diameter was more strongly influenced by environment and growth factors post-anthesis. These results suggest involvement of multiple genetically segregating factors expected to map independently onto the cucumber genome. Using the SNP array and the phenotypic data two major QTLs for fruit size of cucumber were mapped in very high accuracy (around 300 Kb) with large set of markers that should facilitate identification and cloning of major genes that contribute to fruit size in cucumber. In addition, a highly accurate haplotype map of all RILS was created to allow fine mapping of other traits segregating in this population. A detailed cucumber genetic map with 6000 markers was also established (currently the most detailed genetic map of cucumber). The integration of genetics physiology and genomic approaches in this project yielded new major infrastructure tools that can be used for understanding fruit size and many other traits of importance in cucumber. The SNP array and genetic population with an ultra-fine map can be used for future breeding efforts, high resolution mapping and cloning of traits of interest that segregate in this population. The genetic map that was developed can be used for other breeding efforts in other populations. The study of fruit development that was done during this project will be important in dissecting function of genes that that contribute to the fruit size QTLs. The SNP array can be used as tool for mapping different traits in cucumber. The development of the tools and knowledge will thus promote genetic improvement of cucumber and related cucurbits.