Genetic Variation and the Role of Insect Life History Traits in the Ability of Drosophila Larvae to Develop in the Presence of a Competing Filamentous Fungus

Competitive interactions between organisms from distantly related phylogenetical branches have been suggested as being one of the most pervasive forms of interspecific competition. However, so-called inter-kingdom competition has rarely been the focus of ecological and evolutionary studies. Thus, a relatively novel hypothesis has been proposed on the basis that saprophagous insects might intensively compete with filamentous fungi for ephemeral resources (e.g. decaying plant tissue). Consideration that life history traits (e.g. developmental time) are adaptive in determining developmental success in the presence of con- or hetero-specifics competitors implies that these traits have been progressively established by natural selection. Because a similar scenario may apply to antagonistic interactions between saprophagous insects and filamentous fungi, one can expect the existence of heritable variation in developmental success when insect larvae are forced to grow in the presence of noxious mould. Therefore, this study aimed at discovering whether a local population of Drosophila melanogaster indeed harbours genetic variation in developmental success in the presence of the mould Aspergillus niger. By using the isofemale line technique, single larvae forced to feed on fungal infected or uninfected substrate were analysed for variation in survival probability to the adult stage, developmental time and body size of emerged adults. I found genetic variation in survival probability in fungal infected substrates but not in uninfected larval food sources. Mean developmental time and body size varied significantly among isofemale lines in both types of larval environment. Survival was negatively correlated with developmental time on fungal infected substrate, but variation in developmental time on fungal-free substrates was not correlated with survival on fungal infected food patches. Within-trait correlation between fungal infected and uninfected substrates was surprisingly weak, and developmental time was not correlated with body size. The results of this study demonstrate (a) the existence of genetic variation for larval developmental success in the presence of A. niger in a Drosophila population, and (b) heritability of important insect life history traits differed as a function of the larval environment (fungal infected or uninfected feeding substrate). I discuss models that might explain heritability differences and the evolutionary consequences of these results.     

Developmental plasticity and acclimation both contribute to adaptive responses to alternating seasons of plenty and of stress in <Emphasis Type="Italic">Bicyclus</Emphasis> butterflies

Plasticity is a crucial component of the life cycle of invertebrates that live as active adults throughout wet and dry seasons in the tropics. Such plasticity is seen in the numerous species of Bicyclus butterflies in Africa which exhibit seasonal polyphenism with sequential generations of adults with one or other of two alternative phenotypes. These differ not only in wing pattern but in many other traits. This divergence across a broad complex of traits is associated with survival and reproduction either in a wet season that is favourable in terms of resources, or mainly in a dry season that is more stressful. This phenomenon has led us to examine the bases of the developmental plasticity in a model species, B. anynana, and also the evolution of key adult life history traits, including starvation resistance and longevity. We now understand something about the processes that generate variation in the phenotype, and also about the ecological context of responses to environmental stress. The responses clearly involve a mix of developmental plasticity as cued by different environments in pre-adult development, and the acclimation of life history traits in adults to their prevailing environment.     

Explaining adaptive shifts in body size on islands: a life history approach

The tendency for island populations to differ in body size from their mainland relatives has been well documented, but the mechanisms for these size changes remain speculative. Explanations have typically been based on ecological interactions that directly favor either an increase or decrease in body size. While it is clear that direct ecological interactions can influence body size, life history shifts present an alternative explanation for observed insular size trends across phylogenetic groups and trophic levels. Here I describe how decreased resource availability and reduced predation pressure, the same selective forces invoked by previous hypotheses, can operate to produce body size changes via the evolution of life history traits. This mechanism is more generally applicable than previous explanations and is consistent with much of the available data.     

Phylogentic constraints,adaptive syndromes,and emergent properties: From individuals to population dynamics

The hypothesis is developed that there are causal linkages in evolved insect herbivore life histories and behaviors from phylogenetic constraints to adaptive syndromes to the emergent properties involving ecological interactions and population dynamics. Thus the argument is developed that the evolutionary biology of a species predetermines its current ecology.Phylogenetic Constraints refer to old characters in the phylogeny of a species and a group of species which set limits on the range of life history patterns and behaviors that can evolve. For example, a sawfly is commonly limited to oviposition in soft plant tissue, while plants are growing rapidly.Adaptive Syndromes are evolutionary responses to the phylogenetic constraints that minimize the limitations and maximize larval performance. Such syndromes commonly involve details of female ovipositional behavior and how individuals make choices for oviposition sites relative to plant quality variation which maximize larval survival. Syndromes also involve larval adaptations to the kinds of choices females make in oviposition. The evolutionary biology involved with phylogenetic constraints and adaptive syndromes commonly predetermines the ecological interactions of a species and its population dynamics. Therefore, these ecological interactions are calledEmergent Properties because they are natural consequences of evolved morphology, behavior, and physiology. They commonly strongly influence the three-trophic-level interactions among host plants, insect herbivores, and carnivores, and the relative forces of bottom-up and top-down influences in food webs. The arguments are supported using such examples as galling sawflies and other gallers, shoot-boring moths and beetles, budworms, and forest Macrolepidoptera. The contrasts between outbreak or eruptive species and uncommon and rare species with latent population dynamics are emphasized.     

Flight performance in the altricial zebra finch: Developmental effects and reproductive consequences

The environmental conditions animals experience during development can have sustained effects on morphology, physiology, and behavior. Exposure to elevated levels of stress hormones (glucocorticoids, GCs) during development is one such condition that can have long‐term effects on animal phenotype. Many of the phenotypic effects of GC exposure during development (developmental stress) appear negative. However, there is increasing evidence that developmental stress can induce adaptive phenotypic changes. This hypothesis can be tested by examining the effect of developmental stress on fitness‐related traits. In birds, flight performance is an ideal metric to assess the fitness consequences of developmental stress. As fledglings, mastering takeoff is crucial to avoid bodily damage and escape predation. As adults, takeoff can contribute to mating and foraging success as well as escape and, thus, can affect both reproductive success and survival. We examined the effects of developmental stress on flight performance across life‐history stages in zebra finches (Taeniopygia guttata). Specifically, we examined the effects of oral administration of corticosterone (CORT, the dominant avian glucocorticoid) during development on ground‐reaction forces and velocity during takeoff. Additionally, we tested for associations between flight performance and reproductive success in adult male zebra finches. Developmental stress had no effect on flight performance at all ages. In contrast, brood size (an unmanipulated variable) had sustained, negative effects on takeoff performance across life‐history stages with birds from small broods performing better than birds from large broods. Flight performance at 100 days posthatching predicted future reproductive success in males; the best fliers had significantly higher reproductive success. Our results demonstrate that some environmental factors experienced during development (e.g. clutch size) have stronger, more sustained effects than others (e.g. GC exposure). Additionally, our data provide the first link between flight performance and a direct measure of reproductive success.     

Towards an integrated understanding of the structure and mechanics of the cell nucleus

Changes in the shape and structural organization of the cell nucleus occur during many fundamental processes including development, differentiation and aging. In many of these processes, the cell responds to physical forces by altering gene expression within the nucleus. How the nucleus itself senses and responds to such mechanical cues is not well understood. In addition to these external forces, epigenetic modifications of chromatin structure inside the nucleus could also alter its physical properties. To achieve a better understanding, we need to elucidate the relationship between nuclear structure and material properties. Recently, new approaches have been developed to systematically investigate nuclear mechanical properties. These experiments provide important new insights into the disease mechanism of a growing class of tissue-specific disorders termed 'nuclear envelopathies'. Here we review our current understanding of what determines the shape and mechanical properties of the cell nucleus.     

The effect of developmental nutrition on life span and fecundity depends on the adult reproductive environment in Drosophila melanogaster

Both developmental nutrition and adult nutrition affect life‐history traits; however, little is known about whether the effect of developmental nutrition depends on the adult environment experienced. We used the fruit fly to determine whether life‐history traits, particularly life span and fecundity, are affected by developmental nutrition, and whether this depends on the extent to which the adult environment allows females to realize their full reproductive potential. We raised flies on three different developmental food levels containing increasing amounts of yeast and sugar: poor, control, and rich. We found that development on poor or rich larval food resulted in several life‐history phenotypes indicative of suboptimal conditions, including increased developmental time, and, for poor food, decreased adult weight. However, development on poor larval food actually increased adult virgin life span. In addition, we manipulated the reproductive potential of the adult environment by adding yeast or yeast and a male. This manipulation interacted with larval food to determine adult fecundity. Specifically, under two adult conditions, flies raised on poor larval food had higher reproduction at certain ages – when singly mated this occurred early in life and when continuously mated with yeast this occurred during midlife. We show that poor larval food is not necessarily detrimental to key adult life‐history traits, but does exert an adult environment‐dependent effect, especially by affecting virgin life span and altering adult patterns of reproductive investment. Our findings are relevant because (1) they may explain differences between published studies on nutritional effects on life‐history traits; (2) they indicate that optimal nutritional conditions are likely to be different for larvae and adults, potentially reflecting evolutionary history; and (3) they urge for the incorporation of developmental nutritional conditions into the central life‐history concept of resource acquisition and allocation.     

Selective processes in development: implications for the costs and benefits of phenotypic plasticity

Adaptive phenotypic plasticity, the ability of a genotype to develop a phenotype appropriate to the local environment, allows organisms to cope with environmental variation and has implications for predicting how organisms will respond to rapid, human-induced environmental change. This review focuses on the importance of developmental selection, broadly defined as a developmental process that involves the sampling of a range of phenotypes and feedback from the environment reinforcing high-performing phenotypes. I hypothesize that understanding the degree to which developmental selection underlies plasticity is key to predicting the costs, benefits, and consequences of plasticity. First, I review examples that illustrate that elements of developmental selection are common across the development of many different traits, from physiology and immunity to circulation and behavior. Second, I argue that developmental selection, relative to a fixed strategy or determinate (switch) mechanisms of plasticity, increases the probability that an individual will develop a phenotype best matched to the local environment. However, the exploration and environmental feedback associated with developmental selection is costly in terms of time, energy, and predation risk, resulting in major changes in life history such as increased duration of development and greater investment in individual offspring. Third, I discuss implications of developmental selection as a mechanism of plasticity, from predicting adaptive responses to novel environments to understanding conditions under which genetic assimilation may fuel diversification. Finally, I outline exciting areas of future research, in particular exploring costs of selective processes in the development of traits outside of behavior and modeling developmental selection and evolution in novel environments.     

Effects of food variability on growth and reproduction of Aedes aegypti

Despite a large body of knowledge about the evolution of life histories, we know little about how variable food availability during an individual's development affects its life history. We measured the effects of manipulating food levels during early and late larval development of the mosquito Aedes aegypti on its growth rate, life history and reproductive success. Switching from low to high food led to compensatory growth: individuals grew more rapidly during late larval development and emerged at a size close to that of mosquitoes consistently reared at high food. However, switching to high food had very little effect on longevity, and fecundity and reproductive success were considerably lower than in consistently well‐fed mosquitoes. Changing from high to low food led to adults with similar size as in consistently badly nourished mosquitoes, but even lower fecundity and reproductive success. A rapid response of growth to changing resources can thus have unexpected effects in later life and in lifetime reproductive success. More generally, our study emphasizes the importance of varying developmental conditions for the evolutionary pressures underlying life‐history evolution.     

The evolution of parental care in insects: the roles of ecology,life history and the social environment

相似文献   

Induced hatching to avoid infectious egg disease in whitefish.

Reacting to a threat before physical contact, e.g., induced by air- or water-borne substances, appears to be an elegant way of defense. The reaction may be behavioral, developmental, morphological, or physiological, and it can involve a shift in niche or life history. Hatching from eggs is a shift in niche and in life history. From niche shift and life history models, one would predict that the timing of hatching is, to some degree, phenotypically plastic, i.e., early or delayed hatching is likely to be inducible. Temporary increased larval mortality (e.g., increased predation on larvae) would favor delayed hatching, while relatively high egg mortality would favor early hatching. Here, I show experimentally that eggs of the whitefish (Coregonus sp.) hatch earlier in the presence of a virulent egg parasite and that this early hatching is induced by water-borne cues emitted from infected eggs.     

Modeling the effects of Aedes aegypti’s larval environment on adult body mass at emergence

Mosquitoes vector harmful pathogens that infect millions of people every year, and developing approaches to effectively control mosquitoes is a topic of great interest. However, the success of many control measures is highly dependent upon ecological, physiological, and life history traits of mosquito species. The behavior of mosquitoes and their potential to vector pathogens can also be impacted by these traits. One trait of interest is mosquito body mass, which depends upon many factors associated with the environment in which juvenile mosquitoes develop. Our experiments examined the impact of larval density on the body mass of Aedes aegypti mosquitoes, which are important vectors of dengue, Zika, yellow fever, and other pathogens. To investigate the interactions between the larval environment and mosquito body mass, we built a discrete time mathematical model that incorporates body mass, larval density, and food availability and fit the model to our experimental data. We considered three categories of model complexity informed by data, and selected the best model within each category using Akaike’s Information Criterion. We found that the larval environment is an important determinant of the body mass of mosquitoes upon emergence. Furthermore, we found that larval density has greater impact on body mass of adults at emergence than on development time, and that inclusion of density dependence in the survival of female aquatic stages in models is important. We discuss the implications of our results for the control of Aedes mosquitoes and on their potential to spread disease.     

Charr truth: sympatric differentiation in Salvelinus species

Charrs, Salvelinus species, are characteristic fishes of northern freshwater lakes and rivers. They are highly variable in almost every aspect of their behaviour, morphology and life history. Several possible explanations have been proposed to account for this variability and resolve the taxonomic confusion in this genus. I propose that sympatric trophic polymorphism, in the ecological context of these species, can make sense of this variability. I use examples from charr in Canada and Iceland to construct an evolutionary scenario for this genus.     

Plant eco-devo: the potential of poplar as a model organism

Ecological developmental genetics is the study of how ecologically significant traits originate in the genome and how the allelic combinations responsible are maintained in populations and species. Plant development involves a continuous feedback between growth and environment and the success of individual genotype x environment interactions determines the passage of alleles to the next generation: the adaptive recursion. Outbreeding plants contain a large amount of genetic variation, mostly in the form of single nucleotide polymorphisms (SNPs). One of the challenges of eco-devo is to distinguish neutral SNPs from those with ecological consequences. The complete genome sequence of Populus trichocarpa Torr. & A. Gray will be a significant aid in this endeavour. Occurring from California to Alaska, this is the first ecologically 'keystone' species to be sequenced. It has a rich natural history and is an obligate outbreeder. The individual sequenced, Nisqually-1, appears to be heterozygous on average about every 100 bp over the c. 500 million bp of the genome. Overlaid on this within-individual variation is some ecologically based between-individual genotypic variation evident across the distribution of the species. The synthesis of information from genomics and ecology is now in prospect. This 'ecomolecular synthesis' is likely to provide a rich insight into the genomic basis of plant adaptation.     

Differences in Growth Generate the Diverse Palate Shapes of New World Leaf-Nosed Bats (Order Chiroptera,Family Phyllostomidae)

New World leaf-nosed bats (Family Phyllostomidae) display incredible craniofacial diversity that is associated with their broad range of dietary preferences. The short and broad palates of highly frugivorous bats are functionally linked to high bite forces, and the long and narrow palates of nectarivorous bats to flower feeding. Although the functional correlates and evolutionary history of shape variation in phyllostomid palates are beginning to be understood, the specific developmental processes that govern palate diversification remain unknown. To begin to resolve this issue, this study quantified palate morphology in seven phyllostomid species from a range of developmental stages and in adults. This sample includes species with short and broad, long and narrow, and intermediate palate shapes, and thereby covers the range of palate shapes displayed by phyllostomids. Results indicate that while initial palate shape (i.e., width vs. length) varies among species, the pattern of this variation does not match that observed in adults. In contrast, the relative growth of palate width and length in developing phyllostomids and the ratio of these axes in adults are significantly correlated. These and other results suggest that evolutionary alterations in patterns of palate growth have governed the diversification of palate shapes in adult phyllostomids. This implies that the diverse palate shapes of phyllostomids are the result of relatively subtle evolutionary changes in later rather than earlier development events.     

Alternative parasite development in transmission strategies: how time flies!

Among parasitic platyhelminths with complex life cycles, it has been well documented that transmission opportunities are the main forces shaping the diversity of life‐history traits and parasite developmental strategies. While deviations in the development pathway usually involve shortening of life cycles, their extension may also occur following perception of remaining time by parasites. Polystoma gallieni, the monogenean parasite of Hyla meridionalis, is able to trigger two alternative developmental strategies depending on the physiological stage of the tadpoles upon which larvae attach. The distribution and reproductive outputs of both resulting phenotypes were surveyed to address questions about the dynamics of transmission in natural environments. Because modifications in the completion of life cycles can have drawbacks which may perturb the dynamic equilibrium of the resulting host–parasite systems, experimental infestations were also performed to assess parasite–parasite interactions. Our results suggest that the bladder adult phenotype, which involves transmission between frogs and tadpoles, is supplied secondarily by the branchial phenotype which involves transmission between tadpoles and metamorphs. They also support the occurrence of finely tuned trade‐offs between hosts and parasites and highlight positive trends behind the extension of direct life cycles, in which host‐derived signals account for the remaining time to achieve parasitic transmission.     

Evo-Devo: evolutionary developmental mechanisms

Evolutionary developmental biology (Evo-Devo) as a discipline is concerned, among other things, with discovering and understanding the role of changes in developmental mechanisms in the evolutionary origin of aspects of the phenotype. In a very real sense, Evo-Devo opens the black box between genotype and phenotype, or more properly, phenotypes as multiple life history stages arise in many organisms from a single genotype. Changes in the timing or positioning of an aspect of development in a descendant relative to an ancestor (heterochrony and heterotopy) were two evolutionary developmental mechanisms identified by Ernst Haeckel in the 1870s. Many more have since been identified, in large part because of our enhanced understanding of development and because new mechanisms emerge as development proceeds: the transfer from maternal to zygotic genomic control; cell-to-cell interactions; cell differentiation and cell migration; embryonic inductions; functional interactions at the tissue and organ levels; growth. Within these emergent processes, gene networks and gene cascades (genetic modules) link the genotype with morphogenetic units (cellular modules, namely germ layers, embryonic fields or cellular condensations), while epigenetic processes such as embryonic inductions, tissue interactions and functional integration, link morphogenetic units to the phenotype. Evolutionary developmental mechanisms also include interactions between individuals of the same species, individuals of different species, and species and their biotic and/or abiotic environment. Such interactions link ecological communities. Importantly, there is little to distinguish the causality that underlies these interactions from that which underlies inductive interactions within embryos.     

Nematode biphasic ‘boom and bust’ dynamics are dependent on host bacterial load while linking dauer and mouth-form polyphenisms

Cross-kingdom interactions involve dynamic processes that shape terrestrial ecosystems and represent striking examples of co-evolution. The multifaceted relationships of entomopathogenic nematodes with their insect hosts and symbiotic bacteria are well-studied cases of co-evolution and pathogenicity. In contrast, microbial interactions in soil after the natural death of insects and other invertebrates are minimally understood. In particular, the turnover and succession of nematodes and bacteria during insect decay have not been well documented - although it represents a rich ecological niche with multiple species interactions. Here, we utilize developmentally plastic nematode Pristionchus pacificus and its associated scarab beetles as models. On La Réunion Island, we collected rhinoceros beetle Oryctes borbonicus, induced death, and placed carcasses in cages both on the island and in a mock-natural environment in the laboratory controlling for high spatial and temporal resolution. Investigating nematode population density and dispersal dynamics, we were able to connect two imperative plasticities, dauer and mouth form. We observed a biphasic ‘boom and bust’ dispersal dynamic of dauer larvae that corresponds to bacterial load on carcasses but not bacterial type. Strikingly, all post-dauer adults have the predatory mouth form, demonstrating novel intricate interactions on decaying insect hosts. Thus, ecologically relevant survival strategies incorporate critical plastic traits.     

Sociogenetic structure, kin associations and bonding in delphinids

Social systems are the outcomes of natural and sexual selection on individuals' efforts to maximize reproductive success. Ecological conditions, life history, demography traits and social aspects have been recognized as important factors shaping social systems. Delphinids show a wide range of social structures and large variation in life history traits and inhabit several aquatic environments. They are therefore an excellent group in which to investigate the interplay of ecological and intrinsic factors on the evolution of mammalian social systems in these environments. Here I synthetize results from genetic studies on dispersal patterns, genetic relatedness, kin associations and mating patterns and combine with ecological, life history and phylogenetic data to predict the formation of kin associations and bonding in these animals. I show that environment type impacts upon dispersal tendencies, with small delphinids generally exhibiting female-biased philopatry in inshore waters and bisexual dispersal in coastal and pelagic waters. When female philopatry occurs, they develop moderate social bonds with related females. Male bonding occurs in species with small male-biased sexual size dimorphism and male-biased operational sex ratio, and it is independent of dispersal tendencies. By contrast, large delphinids, which live in coastal and pelagic waters, show bisexual philopatry and live in matrilineal societies. I propose that sexual conflict favoured the formation of these stable societies and in turn facilitated the development of kin-biased behaviours. Studies on populations of the same species inhabiting disparate environments, and of less related species living in similar habitats, would contribute towards a comprehensive framework for the evolution of delphinid social systems.     

Adaptive evolution of butterfly wing shape: from morphology to behaviour

Butterflies display extreme variation in wing shape associated with tremendous ecological diversity. Disentangling the role of neutral versus adaptive processes in wing shape diversification remains a challenge for evolutionary biologists. Ascertaining how natural selection influences wing shape evolution requires both functional studies linking morphology to flight performance, and ecological investigations linking performance in the wild with fitness. However, direct links between morphological variation and fitness have rarely been established. The functional morphology of butterfly flight has been investigated but selective forces acting on flight behaviour and associated wing shape have received less attention. Here, we attempt to estimate the ecological relevance of morpho‐functional links established through biomechanical studies in order to understand the evolution of butterfly wing morphology. We survey the evidence for natural and sexual selection driving wing shape evolution in butterflies, and discuss how our functional knowledge may allow identification of the selective forces involved, at both the macro‐ and micro‐evolutionary scales. Our review shows that although correlations between wing shape variation and ecological factors have been established at the macro‐evolutionary level, the underlying selective pressures often remain unclear. We identify the need to investigate flight behaviour in relevant ecological contexts to detect variation in fitness‐related traits. Identifying the selective regime then should guide experimental studies towards the relevant estimates of flight performance. Habitat, predators and sex‐specific behaviours are likely to be major selective forces acting on wing shape evolution in butterflies. Some striking cases of morphological divergence driven by contrasting ecology involve both wing and body morphology, indicating that their interactions should be included in future studies investigating co‐evolution between morphology and flight behaviour.