GENOMIC BASIS OF AGING AND LIFE‐HISTORY EVOLUTION IN DROSOPHILA MELANOGASTER

Natural diversity in aging and other life‐history patterns is a hallmark of organismal variation. Related species, populations, and individuals within populations show genetically based variation in life span and other aspects of age‐related performance. Population differences are especially informative because these differences can be large relative to within‐population variation and because they occur in organisms with otherwise similar genomes. We used experimental evolution to produce populations divergent for life span and late‐age fertility and then used deep genome sequencing to detect sequence variants with nucleotide‐level resolution. Several genes and genome regions showed strong signatures of selection, and the same regions were implicated in independent comparisons, suggesting that the same alleles were selected in replicate lines. Genes related to oogenesis, immunity, and protein degradation were implicated as important modifiers of late‐life performance. Expression profiling and functional annotation narrowed the list of strong candidate genes to 38, most of which are novel candidates for regulating aging. Life span and early age fecundity were negatively correlated among populations; therefore, the alleles we identified also are candidate regulators of a major life‐history trade‐off. More generally, we argue that hitchhiking mapping can be a powerful tool for uncovering the molecular bases of quantitative genetic variation.     

INDIRECT GENETIC EFFECTS INFLUENCE ANTIPREDATOR BEHAVIOR IN GUPPIES: ESTIMATES OF THE COEFFICIENT OF INTERACTION PSI AND THE INHERITANCE OF RECIPROCITY

How and why cooperation evolves, particularly among nonrelatives, remains a major paradox for evolutionary biologists and behavioral ecologists. Although much attention has focused on fitness consequences associated with cooperating, relatively little is known about the second component of evolutionary change, the inheritance of cooperation or reciprocity. The genetics of behaviors that can only be expressed in the context of interactions are particularly difficult to describe because the relevant genes reside in multiple social partners. Indirect genetic effects (IGEs) describe the influence of genes carried in social partners on the phenotype of a focal individual and thus provide a novel approach to quantifying the genetics underlying interactions such as reciprocal cooperation. We used inbred lines of guppies and a novel application of IGE theory to describe the dual genetic control of predator inspection and social behavior, both classic models of reciprocity. We identified effects of focal strain, social group strain, and interactions between focal and group strains on variation in focal behavior. We measured ψ, the coefficient of the interaction, which describes the degree to which an individual's phenotype is influenced by the phenotype of its social partners. The genetic identity of social partners substantially influences inspection behavior, measures of threat assessment, and schooling and does so in positively reinforcing manner. We therefore demonstrate strong IGEs for antipredator behavior that represent the genetic variation necessary for the evolution of reciprocity.     

LIFE‐HISTORY EVOLUTION AND DENSITY‐DEPENDENT GROWTH IN EXPERIMENTAL POPULATIONS OF YEAST

We studied the evolution of the correlation between growth rate r and yield K in experimental lineages of the yeast Saccharomyces cerevisiae. First, we isolated a single clone every approximately 250 generations from each of eight populations selected in a glucose‐limited medium for 5000 generations at approximately 6.6 population doublings per day (20 clones per line × 8 lines) and measured its growth rate and yield in a new, galactose‐limited medium (with ～1.3 doubling per day). For most lines, r on galactose increased throughout the 5000 generations of selection on glucose whereas K on galactose declined. Next, we selected these 160 glucose‐adapted clones in the galactose environment for approximately 120 generations and measured changes in r and K in galactose. In general, growth rate increased and yield declined, and clones that initially grew slowly on galactose improved more than did faster clones. We found a negative correlation between r and K among clones both within each line and across all clones. We provide evidence that this relationship is not heritable and is a negative environmental correlation rather than a genetic trade‐off.     

THE ROLES OF LIFE‐HISTORY SELECTION AND SEXUAL SELECTION IN THE ADAPTIVE EVOLUTION OF MATING BEHAVIOR IN A BEETLE

Although there is continuing debate about whether sexual selection promotes or impedes adaptation to novel environments, the role of mating behavior in such adaptation remains largely unexplored. We investigated the evolution of mating behavior (latency to mating, mating probability and duration) in replicate populations of seed beetles Callosobruchus maculatus subjected to selection on life‐history (“Young” vs. “Old” reproduction) under contrasting regimes of sexual selection (“Monogamy” vs. “Polygamy”). Life‐history selection is predicted to favor delayed mating in “Old” females, but sexual conflict under polygamy can potentially retard adaptive life‐history evolution. We found that life‐history selection yielded the predicted changes in mating behavior, but sexual selection regime had no net effect. In within‐line crosses, populations selected for late reproduction showed equally reduced early‐life mating probability regardless of mating system. In between‐line crosses, however, the effect of life‐history selection on early‐life mating probability was stronger in polygamous lines than in monogamous ones. Thus, although mating system influenced male–female coevolution, removal of sexual selection did not affect the adaptive evolution of mating behavior. Importantly, our study shows that the interaction between sexual selection and life‐history selection can result in either increased or decreased reproductive divergence depending on the ecological context.     

CONVERGENT AND CORRELATED EVOLUTION OF MAJOR LIFE‐HISTORY TRAITS IN THE ANGIOSPERM GENUS LEUCADENDRON (PROTEACEAE)

Natural selection is expected to cause convergence of life histories among taxa as well as correlated evolution of different life‐history traits. Here, we quantify the extent of convergence of five key life‐history traits (adult fire survival, seed storage, degree of sexual dimorphism, pollination mode, and seed‐dispersal mode) and test hypotheses about their correlated evolution in the genus Leucadendron (Proteaceae) from the fire‐prone South African fynbos. We reconstructed a new molecular phylogeny of this highly diverse genus that involves more taxa and molecular markers than previously. This reconstruction identifies new clades that were not detected by previous molecular study and morphological classifications. Using this new phylogeny and robust methods that account for phylogenetic uncertainty, we show that the five life‐history traits studied were labile during the evolutionary history of the genus. This diversity allowed us to tackle major questions about the correlated evolution of life‐history strategies. We found that species with longer seed‐dispersal distances tended to evolve lower pollen‐dispersal distance, that insect‐pollinated species evolved decreased sexual dimorphism, and that species with a persistent soil seed‐bank evolved toward reduced fire‐survival ability of adults.     

LOCAL ADAPTATION AND THE EVOLUTION OF PHENOTYPIC PLASTICITY IN TRINIDADIAN GUPPIES (POECILIA RETICULATA)

Divergent selection pressures across environments can result in phenotypic differentiation that is due to local adaptation, phenotypic plasticity, or both. Trinidadian guppies exhibit local adaptation to the presence or absence of predators, but the degree to which predator‐induced plasticity contributes to population differentiation is less clear. We conducted common garden experiments on guppies obtained from two drainages containing populations adapted to high‐ and low‐predation environments. We reared full‐siblings from all populations in treatments simulating the presumed ancestral (predator cues present) and derived (predator cues absent) conditions and measured water column use, head morphology, and size at maturity. When reared in presence of predator cues, all populations had phenotypes that were typical of a high‐predation ecotype. However, when reared in the absence of predator cues, guppies from high‐ and low‐predation regimes differed in head morphology and size at maturity; the qualitative nature of these differences corresponded to those that characterize adaptive phenotypes in high‐ versus low‐predation environments. Thus, divergence in plasticity is due to phenotypic differences between high‐ and low‐predation populations when reared in the absence of predator cues. These results suggest that plasticity might initially play an important role during colonization of novel environments, and then evolve as a by‐product of adaptation to the derived environment.     

LIFE-HISTORY EVOLUTION IN GUPPIES: 2. REPEATABILITY OF HELD OBSERVATIONS AND THE EFFECTS OF SEASON ON LIFE HISTORIES

Natural populations of guppies that co-occur with the pike cichlid Crenicichla alta and associated predators mature at smaller body sizes, produce more and smaller offspring per litter reproduce more frequently, and have higher reproductive allotments (weight of developing embryos/total body weight) than guppies that co-occur with just the killifish Rivulus harti (Reznick and Endler, 1982). I here consider three forms of repeatability in these life-history patterns: i) among replicate samples collected on the same day from the same locality, ii) between Crenicichla and Rivulus communities among a new series of localities, and iii) among a smaller series of Crenicichla and Rivulus localities sampled in two wet and two dry seasons. In the analysis of replicate collections from two localities, seven of eight statistical comparisons revealed no significant difference. The usual methodology for estimating these variables therefore accurately represents guppy life-history patterns at a given locality. Differences among guppies from Rivulus and Crenicichla localities, covering a wider geographical area than considered by Reznick and Endler (1982), were virtually identical to the previous comparison. Wet-season samples were associated with significant decreases in reproductive allotment and fecundity and significant increases in the size of mature males and the minimum size of reproducing females. Differences between guppies from Rivulus and Crenicichla localities persisted across all samples and were consistent with all other observations, although they tended to be smaller during the wet season. Discriminant analyses on female reproductive traits showed that fecundity and offspring size made strong, independent contributions to discriminating between guppies from the two types of localities. The contribution from reproductive allotment was considerably smaller. There was more overlap between predator treatments during the wet season. Only 8.5% of the individuals were misclassified during the dry season, but 19.5% were misclassified during the wet season.     

PATHOGEN LIFE‐HISTORY TRADE‐OFFS REVEALED IN ALLOPATRY

Trade‐offs in life‐history traits is a central tenet in evolutionary biology, yet their ubiquity and relevance to realized fitness in natural populations remains questioned. Trade‐offs in pathogens are of particular interest because they may constrain the evolution and epidemiology of diseases. Here, we studied life‐history traits determining transmission in the obligate fungal pathogen, Podosphaera plantaginis, infecting Plantago lanceolata. We find that although traits are positively associated on sympatric host genotypes, on allopatric host genotypes relationships between infectivity and subsequent transmission traits change shape, becoming even negative. The epidemiological prediction of this change in life‐history relationships in allopatry is lower disease prevalence in newly established pathogen populations. An analysis of the natural pathogen metapopulation confirms that disease prevalence is lower in newly established pathogen populations and they are more prone to go extinct during winter than older pathogen populations. Hence, life‐history trade‐offs mediated by pathogen local adaptation may influence epidemiological dynamics at both population and metapopulation levels.     

PHENOTYPIC DIVERSIFICATION ACROSS AN ENVIRONMENTAL GRADIENT: A ROLE FOR PREDATORS AND RESOURCE AVAILABILITY ON THE EVOLUTION OF LIFE HISTORIES

Changes in age/size‐specific mortality, due to such factors as predation, have potent evolutionary consequences. However, interactions with predators commonly impact prey growth rates and food availability and such indirect effects may also influence evolutionary change. We evaluated life‐history differences in Trinidadian killifish, Rivulus hartii, across a gradient in predation. Rivulus are located in (1) “high predation” sites with large piscivores, (2) “Rivulus/guppy” sites with guppies, and (3) “Rivulus‐only” sites with just Rivulus. Rivulus suffer higher mortality with large predators, and guppies may prey upon small/young Rivulus in Rivulus/guppy environments. In turn, population densities decline while growth rates increase in both localities compared to Rivulus‐only sites. To explore how the direct and indirect effects of predators and guppies influence trait diversification in Rivulus, we examined life‐history phenotypes across five rivers. High predation phenotypes exhibited a smaller size at reproduction, a greater number of eggs that were smaller, and increased reproductive allotment. Such changes are consistent with a direct response to predation. Rivulus from Rivulus/guppy sites were intermediate; they exhibited a smaller size at reproduction, increased fecundity, smaller eggs, and larger reproductive allotment than Rivulus‐only fish. These changes are consistent with models that incorporate the impacts of growth and resources.     

斑苦竹无性系生长与水分供应及其适应对策的研究

 根据对混生型斑苦竹(Pleioblastus maculata)移栽于不同土壤水分含量的微生境中的野外实验,分析了斑苦竹的无性系生长对水分资源供应的形态可塑性反应和能量投资对策。研究结果表明,水分资源供应水平越高,斑苦竹无性系的总生物量越大,同时,无性系分株的数目越少,而个体增大。在不同水分供应条件下,无性系的隔离者(地下根茎)长度和分株大小都具有显著的差异,而隔离者的节间长度则无明显差别。在低水分资源的生境中,斑苦竹无性系具有投资更多的能量于地下部分,尤其是根茎节间,从而伸长根茎,以获取资源的觅养生长对策;在高水分资源的生境中,其无性系的能量则主要投资于分株的生长。     

EVOLUTION OF GIGANTISM IN NINE‐SPINED STICKLEBACKS

The relaxation of predation and interspecific competition are hypothesized to allow evolution toward “optimal” body size in island environments, resulting in the gigantism of small organisms. We tested this hypothesis by studying a small teleost (nine‐spined stickleback, Pungitius pungitius) from four marine and five lake (diverse fish community) and nine pond (impoverished fish community) populations. In line with theory, pond fish tended to be larger than their marine or lake conspecifics, sometimes reaching giant sizes. In two geographically independent cases when predatory fish had been introduced into ponds, fish were smaller than those in nearby ponds lacking predators. Pond fish were also smaller when found in sympatry with three‐spined stickleback (Gasterosteus aculeatus) than those in ponds lacking competitors. Size‐at‐age analyses demonstrated that larger size in ponds was achieved by both increased growth rates and extended longevity of pond fish. Results from a common garden experiment indicate that the growth differences had a genetic basis: pond fish developed two to three times higher body mass than marine fish during 36 weeks of growth under similar conditions. Hence, reduced risk of predation and interspecific competition appear to be chief forces driving insular body size evolution toward gigantism.     

MATERNAL EFFECTS AND THE PERVASIVE IMPACT OF NESTLING HISTORY ON EGG SIZE IN A PASSERINE BIRD

Environmental conditions experienced during ontogeny may have important and permanent consequences for life-history traits of individuals. The aim of this work was to determine whether conditions experienced during early life, as expressed by prefledgling condition, have any bearing on the volume of eggs subsequently laid by females in a small passerine bird species, the pied flycatcher (Ficedula hypoleuca). I first show a genetic influence on egg volume by dam-offspring regression. The existence of maternal effects is shown by comparing resemblances between average egg volumes of offspring to those of their paternal and maternal grandmothers. Path analysis shows that when controlling for the influence of maternal egg volume, the average volume of eggs produced in a lifetime is positively related to the body condition of a female measured while she is still at the nest. Thus, body condition at fledgling affects egg volume beyond the ability of maternal egg volume to predict offspring egg volume. Although there may be a persistent maternal effect of egg volume on itself or linked to a property correlated with egg volume, the maternal performance trait involved remains unknown, except for maternal egg volume itself. Given the effects that egg volume may have on reproductive success, which are partly determined prior to leaving the nest, maternal effects may have important consequences for lifetime fitness of offspring.     

THE IMPACT OF ELECTROPHORETIC GENOTYPE ON LIFE HISTORY TRAITS IN PINUS TAEDA

Reports of positive associations between allozymic heterozygosity and measures of fitness are routine, but it has not been possible to distinguish between the two preeminent explanations of the phenomenon, dominance and overdominance. We tested several of the assumptions of these hypotheses in our study of the relationship between electrophoretic genotype and three life history traits in loblolly pines (Pinus taeda L.). Traits examined included the survival and growth of selfed and outcrossed progeny of 45 maternal trees, and maternal fecundity, measured as the number of surviving progeny per mother tree. Inbreeding depression was severe; the relative fitness of the selfed progeny was only 8% that of the outcrossed progeny. We found a heterozygote fecundity advantage, which should have resulted in an excess of rare alleles in the progeny. Instead, there was evidence of severe survival selection against rare alleles in both heterozygous and homozygous forms. The deficit of rare alleles averaged 69 and 50% in the selfed and outcrossed progeny, respectively. The one allele in the sample that we should have suspected of being maintained by overdominance (a PGI2 mid-frequency allele) appeared to be overdominant for outcrossed height growth and probably for fecundity as well. Multiple-locus genotype explained very little of the variation in growth, however, and rather than seeing evidence for overdominance as a force in maintaining most of the observed polymorphism, we were left to explain, in the face of the severe survival selection, why the rare alleles were present at all. Projection of the stand into the future through computer simulation showed how balancing selection acting on differential growth, fecundity, and mortality among genotypes could, over the life of the stand, account for the maintenance of the rare alleles in the population.     

GENETICS OF INCIPIENT SPECIATION IN DROSOPHILA MOJAVENSIS. III. LIFE‐HISTORY DIVERGENCE IN ALLOPATRY AND REPRODUCTIVE ISOLATION

We carried out a three‐tiered genetic analysis of egg‐to‐adult development time and viability in ancestral and derived populations of cactophilic Drosophila mojavensis to test the hypothesis that evolution of these life‐history characters has shaped premating reproductive isolation in this species. First, a common garden experiment with 11 populations from Baja California and mainland Mexico and Arizona reared on two host species revealed significant host plant X region and population interactions for viability and development time, evidence for host plant adaptation. Second, replicated line crosses with flies reared on both hosts revealed autosomal, X chromosome, cytoplasmic, and autosome X cactus influences on development time. Viability differences were influenced by host plants, autosomal dominance, and X chromosomal effects. Many of the F₁, F₂, and backcross generations showed evidence of heterosis for viability. Third, a QTL analysis of male courtship song and epicuticular hydrocarbon variation based on 1688 Baja × mainland F₂ males also revealed eight QTL influencing development time differences. Mainland alleles at six of these loci were associated with longer development times, consistent with population‐level differences. Eight G × E interactions were also detected caused by longer development times of mainland alleles expressed on a mainland host with smaller differences among Baja genotypes reared on the Baja host plant. Four QTL influenced both development time and epicuticular hydrocarbon differences associated with courtship success, and there was a significant QTL‐based correlation between development time and cuticular hydrocarbon variation. Thus, the regional shifts in life histories that evolved once D. mojavensis invaded mainland Mexico from Baja California by shifting host plants were genetically correlated with variation in cuticular hydrocarbon‐based mate preferences.     

LABORATORY EVOLUTION OF LIFE-HISTORY TRAITS IN THE BEAN WEEVIL (ACANTHOSCELIDES OBTECTUS): THE EFFECTS OF SELECTION ON DEVELOPMENTAL TIME IN POPULATIONS WITH DIFFERENT PREVIOUS HISTORY

In this study we examined the direct and correlated responses for fast and slow preadult development time in three laboratory populations of the bean weevil (Acanthoscelides obtectus). The first population (“base,” B) has experienced laboratory conditions for more than 10 years; the second (“young,” Y) and the third (“old,” O) populations were selected for early and late reproduction, respectively, before the onset of the present experiments. All three populations are successfully selected for both fast and slow preadult development. The realized heritabilities are very similar in all populations, suggesting a similar level of the additive genetic variance for preadult development. We studied the correlated responses on the following life-history traits: egg-to-adult viability, wet body weight, early fecundity, late fecundity, total realized female fecundity, and adult longevity. All life-history traits examined here, except for the egg-to-adult viability, are affected by selection for preadult development in at least in one of the studied populations. In all three populations, beetles selected for slow preadult development are heavier and live longer than those from the fast-selected lines. The findings with respect to adult longevity are unexpected, because the control Y and O populations, selected for short- and long-lived beetles, respectively, do not show significant differences in preadult development. Thus, our results indicate that some kind of asymmetrical correlated responses occur for preadult development and adult longevity each time that direct selection has been imposed on one or the other of these two traits. In contrast to studies with Drosophila, it appears that for insect species that are aphagous as adults, selection for preadult development entails selection for alleles that also change the adult longevity, but that age-specific selection (applied in the Y and O populations) mostly affects the alleles that have no significant influence on the preadult development. Implications of these findings on the developmental and evolutionary theories of aging are also discussed.     

TESTING THE EFFECTS OF MATING SYSTEM VARIATION ON RATES OF MOLECULAR EVOLUTION IN PRIMATES

Post‐copulatory sexual selection has been proposed to drive the rapid evolution of reproductive proteins, and, more recently, to increase genome‐wide mutation rates. Comparisons of rates of molecular evolution between lineages with different levels of female multiple mating represent a promising, but under‐utilized, approach for testing the effects of sperm competition on sequence evolution. Here, I use comparisons between primate species with divergent mating systems to examine the effects of sperm competition on reproductive protein evolution, as well as on sex‐averaged mutation rates. Rates of nonsynonymous substitution are higher for testis‐specific genes along the chimpanzee lineage in comparison to the human lineage, consistent with expectations. However, the data reported here do not allow firm conclusions concerning the effects of mating system on genome‐wide mutation rates, with different results obtained from different species pairs. Ultimately, comparative studies encompassing a range of mating systems and other life history traits will be required to make broad generalizations concerning the genomic effects of sperm competition.     

改变食物组成对大鼠胃肠道嗜铬细胞的影响

为研究食物组成对肠嗜铬（ＥＣ）细胞的影响，用免疫组织化学方法（ＰＡＰ法）对４组食物组成不同大鼠的胃肠道５－羟色胺免疫反应阳性（５－ＨＴＩＲ）细胞的数量和分布作了观察。发现食物改变会引起大鼠摄食量和胃肠形态的变化，但未见其生长发育异常。食物中米糠含量加倍后，大鼠５－ＨＴＩＲ细胞数量无显著增加，但分布型有明显的变化。食物中米糠含量或米糠和麦麸含量都减少到１０％后，大鼠５－ＨＴＩＲ细胞数量和分布都有明显     

寡聚糖生物农药对棉花体内细菌数量和作物生长的作用

通过常规分离方法,测定寡聚糖生物农药对中棉12品种的棉茎体内细菌群落数量的影响。2批实验结果表明喷寡聚糖后棉茎体内细菌群落数量均低于对照,喷寡聚糖10d后棉茎体内细菌群落数量显著下降(8.0×10