LABORATORY EVOLUTION OF LONGEVITY AND REPRODUCTIVE FITNESS COMPONENTS IN MALE FRUIT FLIES: MATING ABILITY

Populations of Drosophila melanogaster that had been selected for divergent rates of senescence were compared with respect to age-specific male mating ability. The competitive mating ability of males from populations with delayed senescence was inferior to that of males from populations with higher rates of senescence when males were young. This relationship was reversed when males were older. For noncompetitive mating ability and for recovery of fertility after an exhaustive mating bout, there was no difference between populations with different rates of senescence when males were young. However when males were older, flies from populations selected for delayed senescence again had superior mating ability. Thus, rates of male reproductive senescence can be altered in predictable ways by natural selection. The results for the competitive mating tests are consistent with the hypothesis that antagonistic gene action between early- and late-life fitness components influences the evolution of senescence in these populations.     

The experimental assessment of fitness in Drosophila. I. Comparative measures of competitive reproductive success

Strains of D. melanogaster, representing a range of genetic diversity, were systematically subjected to each of several techniques that have been devised to assess total or net fitness. All of these techniques operationally define fitness in terms of reproductive success under competitive conditions. For the set of strains tested, an excellent correlation was obtained between the competitive indices produced by two single-generation intraspecific competitions, despite fundamental differences in the strains used as competitive standards. The results of two interspecific tests were also correlated, but the intraspecific vs. interspecific test result comparisons ranged from highly significant to nonsignificant correlations. For the fitness estimates, the overall variances produced by the intraspecific tests were greater than those obtained in the interspecific competitions. No significant correlations were found between the results of a long-term (multi-generation) competitive assessment of fitness and any of the single-generation tests. Therefore, although all of these tests refer to a net parameter called "fitness", they are clearly not all measuring the same thing. Differences in the competitive interactions operative in each technique are suggested to account for these results.     

The Effects of Interspecific Competition on the Dynamics of a Polymorphism in an Experimental Population of DROSOPHILA MELANOGASTER

Populations of Drosophila melanogaster with a fourth-chromosome polymorphism were subjected to different levels of competition with Drosophila simulans. The dynamics of the polymorphism and the equilibrium frequencies of the sparkling allele were seen to depend on the competitive level, while the higher productivity of the competing populations was shown to be due to the initial parental density. The effects of competition on fitness components were quantified by fitting the data to both a two-stage selection model and a fertility model. Additional experiments were performed to verify that the interspecific competition caused the changes in fitness. The results are discussed in light of the importance of considering selection components in models of ecological genetics.     

Effects of larval crowding on quantitative variation for development time and viability in Drosophila melanogaster

Competition between individuals belonging to the same species is a universal feature of natural populations and is the process underpinning organismal adaptation. Despite its importance, still comparatively little is known about the genetic variation responsible for competitive traits. Here, we measured the phenotypic variation and quantitative genetics parameters for two fitness‐related traits—egg‐to‐adult viability and development time—across a panel of Drosophila strains under varying larval densities. Both traits exhibited substantial genetic variation at all larval densities, as well as significant genotype‐by‐environment interactions (GEIs). GEI was attributable to changes in the rank order of reaction norms for both traits, and additionally to differences in the between‐line variance for development time. The coefficient of genetic variation increased under stress conditions for development time, while it was higher at both high and low densities for viability. While development time also correlated negatively with fitness at high larval densities—meaning that fast developers have high fitness—there was no correlation with fitness at low density. This result suggests that GEI may be a common feature of fitness‐related genetic variation and, further, that trait values under noncompetitive conditions could be poor indicators of individual fitness. The latter point could have significant implications for animal and plant breeding programs, as well as for conservation genetics.     

Measurement of Fitness and Its Components in Six Laboratory Strains of DROSOPHILA MELANOGASTER

Six laboratory strains of Drosophila melanogaster were used to measure "net fitness" and its components by interspecific competition with D. hydei using 100 experimental populations. The "total competitive ability," an estimate of net fitness measured in these competition experiments, was tightly correlated with another measure of net fitness, the population size, in single-species experiments (phenotypic correlation r_p = 0.675 and genotypic correlation r_g = 0.997). Other components of fitness were also measured simultaneously, and the correlation with the net fitness was calculated. The very high correlation between two measurements of net fitness and lower correlations between net fitness and components of fitness suggests that these net fitness measures are more reliable estimates of the "real net fitness" than the components of fitness.     

Genetic Control of Insect Populations: I. Cage Studies of Chromosome Replacement by Compound Autosomes in DROSOPHILA MELANOGASTER

A genetic method for insect control was evaluated using the test organism, Drosophila melanogaster. The technique involved the displacement under a system of continuous reproduction, of standard strains by those carrying compound autosomes. The eradication of the replacements could subsequently be achieved through the use of temperature-sensitive lethal mutations.-While certain compound autosome strains failed to displace standards in population cages, even at the initial release ratio of 25:1, others were highly successful. Indeed, for some strains when the ratio of compounds to standards was as low as 9:1, the population rapidly went to fixation in favor of the compound line.-Hatchability was found to be an insufficient index of fitness to estimate the initial ratios of compounds to standards that would guarantee fixation of the former. Differences in other fitness components, such as development time, were detected that could seriously modify displacement, especially with continuous overlapping generations. The importance of examining the fitness of various compound lines and selecting the most competitive in cages, prior to field tests, cannot be overemphasized.     

Coexistence of ecologically similar colonising species. II. Population differentiation in Drosophila aldrichi and D. Buzzatii for competitive effects and responses at different temperatures and allozyme variation in D. aldrichi

Drosophila aldrichi and D. buzzatii are cactophilic species that colonised Australia about 55–60 years ago. They are sympatric only in Australia. Thus they may be in the process of adapting to new environments and to each other, and diversifying among local, possibly isolated, populations. Larval competitive effects for three populations of each species (Roma, Planet Downs, and Binjour) were measured on semi-natural cactus rots at three temperatures, with preadult viability, developmental time and adult body weight scored for each sex and species. Populations of both species varied in their responses to the other species as competitor, and one D. buzzatii population (Roma) reduced larval performance of D. aldrichi significantly more than did other D. buzzatii populations. Geographic divergence for the three traits was similar in both species, with a relative performance index derived from these traits highest for Roma, second for Binjour, and least for the Planet Downs population of each species. The Roma D. aldrichi population was the most different from the other populations for the performance index and in terms of genetic distances derived from allozyme frequencies. Additionally, comparisons of climatic variables among the population localities showed that the Roma environment was most different from the others. Differential natural selection in different areas of the cactus distribution may be a major cause of population divergence in both species. Drosophila aldrichi is superior for some fitness components at the highest temperature. Thus temperature variation throughout the cactus distribution may contribute to the different ranges of these two species, with competitive exclusion of D. aldrichi in the southern, cooler region of the cactus distribution, but coexistence in the northern, warmer region.     

Genetic Adaptation to Captivity and Inbreeding Depression in Small Laboratory Populations of Drosophila Melanogaster

The rate of adaptation to a competitive laboratory environment and the associated inbreeding depression in measures of reproductive fitness have been observed in populations of Drosophila melanogaster with mean effective breeding size of the order of 50 individuals. Two large wild-derived populations and a long-established laboratory cage population were used as base stocks, from which subpopulations were extracted and slowly inbred under crowded conditions over a period of 210 generations. Comparisons have been made of the competitive ability and reproductive fitness of these subpopulations, the panmictic populations produced from them by hybridization and random mating and the wild- or cage-base populations from which they were derived. After an average of ~180 generations in the laboratory, the wild-derived panmictic populations exceeded the resampled natural populations by 75% in fitness under competitive conditions. The cage-derived panmictic population, after a total of 17 years in the laboratory, showed a 90% superiority in competitive ability over the corresponding wild population. In the inbred lines derived from the wild-base stocks, the average rate of adaptation was estimated to be 0.33 +/- 0.06% per generation. However, the gain in competitive ability was more than offset by inbreeding depression at an initial rate of ~2% per generation. The effects of both adaptation and inbreeding on reproductive ability in a noncompetitive environment were found to be minor by comparison. The maintenance of captive populations under noncompetitive conditions can therefore be expected to minimize adaptive changes due to natural selection in the changed environment.     

Measurement and Selection of Parasitoid Quality for Mass-Reared Trichogramma minutum Riley Used in Inundative Release

Parasitoid quality, subject to both genetic and environmental influences, is critical to the success of any biological control program, however, its measurement and improvement is poorly understood. In this study, a classic genetic approach is taken to develop two indices, namely a character index and a fitness index, for the measurement and selection of high quality parasitoids used in inundative release. Six life-history traits and corresponding fitness components in 33 inbred strains of Trichogramma minutum were used to generate both genotypic and phenotypic variance-covariance matrices that then allowed for the construction of the indices. Most traits and their fitness components were positively correlated, both phenotypically and genotypically, with lifetime fecundity and the number of female offspring appearing to have an important influence. Selection of the top three strains showed that parasitoid quality could be improved by 36% using the character index and possibly up to 150% using the fitness index. The two indices were linearly correlated suggesting that either could be used to measure quality. The character index is recommended because it requires information on only three life-history traits (fecundity, number of female offspring, and number of male offspring) and has highly correlated responses of fitness components. Our work demonstrates that the best quality T. minutum will be obtained by using the character index to select for inbred strains which have high fecundity and number of female offspring.     

EXPERIMENTAL STUDIES OF PLEIOTROPY AND EPISTASIS IN ESCHERICHIA COLI. II. COMPENSATION FOR MALADAPTIVE EFFECTS ASSOCIATED WITH RESISTANCE TO VIRUS T4

Mutations in Escherichia coli that confer resistance to virus T4 also have maladaptive effects that reduce competitive fitness. After resistant populations had evolved for 400 generations in the absence of T4, their fitness approached that of sensitive populations allowed to evolve under identical conditions. However, the resistant populations had not reverted to sensitivity. Instead, this convergence in fitness resulted from genetic changes that compensated for maladaptive pleiotropic effects of the resistance mutations. An allele selected in an evolving resistant population reduced the competitive disadvantage associated with resistance by almost half. Interestingly, this allele was also beneficial in sensitive populations, although its fitness advantage was only about one-fifth as great as it was in the resistant population. These results run counter to a commonly held view that trade-offs between components of fitness should become more pronounced as populations approach their “selective equilibria.” If a trade-off derives from some limiting energetic or material currency, then it is likely to become more pronounced as a population becomes more finely adapted. If a trade-off derives from the disruption of genetic integration, then it is likely to be diminished with further adaptation.     

Genetic variation in tolerance of competition and neighbour suppression in Arabidopsis thaliana

Intraspecific competitive interactions can profoundly influence phenotypic evolution. However, prior studies have rarely evaluated the evolutionary potential of the two components of competitive ability, tolerance of competition and suppression of neighbours. Here, we grow a set of 20 Arabidopsis thaliana recombinant inbred lines in three competitive treatments (noncompetitive, intra‐genotypic competition and inter‐genotypic competition) to examine if there is genetic variation for the components of competitive ability and whether neighbour relatedness has an effect on fitness. We find evidence for genetic variation in tolerance of competition and neighbour suppression and that these two competitive strategies are correlated, such that genotypes that tolerate competition will also strongly suppress neighbours. We further observe that the effect of neighbour relatedness on fitness of target individuals depends on neighbour identity, i.e. whether target individuals perform better when competing against self vs. nonself individuals depends on the genotypic identity of the nonself neighbour. The results are particularly relevant to evolutionary responses under multi‐level selection.     

An analysis of continent-wide patterns of sexual selection in a passerine bird

Patterns of selection are widely believed to differ geographically, causing adaptation to local environmental conditions. However, few studies have investigated patterns of phenotypic selection across large spatial scales. We quantified the intensity of selection on morphology in a monogamous passerine bird, the barn swallow Hirundo rustica, using 6495 adults from 22 populations distributed across Europe and North Africa. According to the classical Darwin-Fisher mechanism of sexual selection in monogamous species, two important components of fitness due to sexual selection are the advantages that the most attractive males acquire by starting to breed early and their high annual fecundity. We estimated directional selection differentials on tail length (a secondary sexual character) and directional selection gradients after controlling for correlated selection on wing length and tarsus length with respect to these two fitness components. Phenotype and fitness components differed significantly among populations for which estimates were available for more than a single year. Likewise, selection differentials and selection gradients differed significantly among populations for tail length, but not for the other two characters. Sexual selection differentials differed significantly from zero across populations for tail length, particularly in males. Controlling statistically for the effects of age reduced the intensity of selection by 60 to 81%, although corrected and uncorrected estimates were strongly positively correlated. Selection differentials and gradients for tail length were positively correlated between the sexes among populations for selection acting on breeding date, but not for fecundity selection. The intensity of selection with respect to breeding date and fecundity were significantly correlated for tail length across populations. Sexual size dimorphism in tail length was significantly correlated with selection differentials with respect to breeding date for tail length in male barn swallows across populations. These findings suggest that patterns of sexual selection are consistent across large geographical scales, but also that they vary among populations. In addition, geographical patterns of phenotypic selection predict current patterns of phenotypic variation among populations, suggesting that consistent patterns of selection have been present for considerable amounts of time.     

Fluctuating asymmetry and fitness correlations in two Engraulis encrasicolus populations

Correlations among several measures of fluctuating asymmetry (FA) and fitness‐related variables were assessed in two populations of the European anchovy Engraulis encrasicolus with fast growth (Aegean Sea) and slow growth (Ionian Sea), respectively. FA levels were borderline significantly higher in the Ionian than in the Aegean for some variables. Variation in otolith shape (deviation from population norm) was lower in the Ionian than the Aegean, contrary to expectation. Within the Aegean, there was no relation between any of the FA indexes and fitness estimators, while in the Ionian a composite otolith FA index was significantly negatively correlated to standard length at age only in 2 year‐old individuals. This difference between the Aegean and Ionian may have been related to the lower growth rate in the Ionian, as FA–fitness relations may be more apparent in less‐beneficial environments. The absence of significant correlations in the Aegean and the low correlation in one age group in the Ionian suggests that FA is not a sensitive indicator of individual fitness in adult E. encrasicolus.     

Multilevel selection and neighbourhood effects from individual to metapopulation in a wild passerine

Multilevel selection has rarely been studied in the ecological context of animal populations, in which neighbourhood effects range from competition among territorial neighbours to source-sink effects among local populations. By studying a Dupont's lark Chersophilus duponti metapopulation, we analyze neighbourhood effects mediated by song repertoires on fitness components at the individual level (life-span) and population level (growth rate). As a sexual/aggressive signal with strong effects on fitness, birdsong creates an opportunity for group selection via neighbour interactions, but may also have population-wide effects by conveying information on habitat suitability to dispersing individuals. Within populations, we found a disruptive pattern of selection at the individual level and an opposite, stabilizing pattern at the group level. Males singing the most complex songs had the longest life-span, but individuals with the poorest repertoires lived longer than 'average' males, a finding that likely reflects two male strategies with respect to fitness and sexual trait expression. Individuals from groups with intermediate repertoires had the longest life-span, likely benefitting from conspecific signalling to attract females up to the detrimental spread of competitive interactions in groups with superior vocal skills. Within the metapopulation selection was directional but again followed opposite patterns at the two levels: Populations had the highest growth rate when inhabiting local patches with complex repertoires surrounded by patches with simple repertoires. Here the song may impact metapopulation dynamics by guiding prospecting individuals towards populations advertising habitat quality. Two fitness components linked to viability were therefore influenced by the properties of the group, and birdsong was the target of selection, contributing to linking social/sexual processes at the local scale with regional population dynamics.     

Ecological determinants of life-history evolution.

Density-dependent natural selection has been studied, empirically with laboratory populations of Drosophila melanogaster. Populations kept at very high and low population density have become differentiated with respect to important fitness-related traits. There is now some understanding of the behavioural and physiological basis of these differences. These studies have identified larval competitive ability and efficiency of food utilization as traits that are negatively correlated with respect to effects on fitness. Theory that illuminates and motivates additional research with this experimental system has been lacking. Current research has focused on models that incorporate many details of Drosophila ecology in laboratory environments.     

Inbreeding depression in male gametic performance

One key objective in evolutionary ecology is to understand the magnitude of inbreeding depression expressed across sex‐specific components of fitness. One major component of male fitness is fertilization success, which depends on male gametic performance (sperm and pollen performance in animals and plants, respectively). Inbreeding depression in male gametic performance could create sex‐specific inbreeding depression in fitness, increase the benefit of inbreeding avoidance and reduce the efficacy of artificial insemination and pollination. However, there has been no assessment of the degree to which inbreeding generally depresses male gametic performance and hence post‐copulatory or post‐pollination fertilization success. Because inbreeding depression is understood to be a property of diploid entities, it is not clear what degree of inbreeding depression in haploid gametic performance should be expected. Here, we first summarize how inbreeding depression in male gametic performance could potentially arise through gene expression in associated diploid cells and/or reduced genetic diversity among haploid gametes. We then review published studies that estimate the magnitude of inbreeding depression in traits measuring components of sperm or pollen quantity, quality and competitiveness. Across 51 published studies covering 183 study traits, the grand mean inbreeding load was approximately one haploid lethal equivalent, suggesting that inbreeding depresses male gametic performance across diverse systems and traits. However, there was an almost complete lack of explicit estimates from wild populations. Future studies should quantify inbreeding depression in systematic sets of gametic traits under naturally competitive and noncompetitive conditions and quantify the degree to which gamete phenotypes and performance reflect haploid vs. diploid gene expression.     

The impact of genetic parental distance on developmental stability and fitness in Drosophila buzzatii

Measures of genetic parental distances (GPD) based on microsatellite loci (D (2) and IR), have been suggested to be better correlated with fitness than individual heterozygosity (H), as they contain information about past events of inbreeding or admixture. We investigated if GPD increased with increasing genetic divergence between parental populations in Drosophila buzzatii and if the measures indicate past events of admixture. Further we evaluated the relationship between GPD, fitness and fluctuating asymmetry (FA) of size and shape. We investigated three populations of Drosophila buzzati, from Argentina, Europe and Australia. From these populations two intraspecific hybridisation lines were made; one between the Argentinean and European populations, which have been separated 200 years and one between the populations from Argentina and Australia, which have been separated 80 years. By doing this we obtained hybrid progeny having different levels of GPD. We found that D (2) and H can be used as indicators of admixture when comparing hybrid individuals with their parentals. IR was not informative. Our results does not exclude the presence of genetic fitness correlations (GFC) over individuals with a broad fitness range from populations in equilibrium, but we doubt the presence of GFC using GPD measures in admixed populations. Shape FA could be a relevant measure for fitness, however, only when comparing populations, not at individual level.     

Plant aspartate transcarbamylase: kinetic properties of the enzyme from mung bean (Phaseolus aureus) seedlings

Aspartate transcarbamylase (EC 2.1.3.2) catalyzes the bi substrate reaction—carbamyl phosphate+ L-aspartate ? carbamyl aspartate ? phosphate, The order of addition of substrates and release of products for the homogeneous aspartate transcarbamylase fromPhaseolus aureuss eedlings has been investigated by using the kinetic methods of analysis. p ]Initial velocity studies indicated that the mechanism might be a sequential one. Product inhibition studies showed that phosphate was a linear competitive inhibitor with respect to carbamyl phosphate and was anS (slope) andI (intercept) linear noncompetitive inhibitor with respect to aspartate. Carbamyl aspartate was a noncompetitive inhibitor with respect to both the substrates. These inhibition patterns agreed with an ordered mechanism of reaction with carbamyl phosphate as the leading substrate and phosphate as the last product to leave the enzyme surface. The presence of dead end complexes and the rapid equilibrium random mechanism were ruled out by the absence of inhibition by the substrate(s) and the linear replot slopevs. the inhibitor concentration. Acetyl phosphate, an analog ue of carbamyl phosphate was a non-competitive inhibitor with respect to aspartate. This result could be explained both in terms of an ordered as well as a random mechanism. On the other hand, succinate, an analog ue of aspartate was an uncompetitive inhibitor with respect to carbamyl phosphate, indicating that the mechanism was ordered. p ]The transition state analog ue, N-(phosphonoacetyl)-L-aspartate, binds much more tightly than either of the two substrates. This analog ue was a linear competitive inhibitor with respect to carbamyl phosphate and a linear noncompetitive inhibitor with respect to aspartate. These results are compatible with an ordered mechanism rather than a random one.     

Studies on the color variation in larvae ofEphestia kühniella Zeller (Lepidoptera: Phycitidae) III. Fitness of different larval color strains

The population fitness in terms of the intrinsic rate of increase r_m was measured in eight pure (homogenic) strains of Ephestia kühniellaZeller with different larva color at an optimal temperature of 25°C, and in three strains at unfavorble temperatures of 15, 17, 28, and 30°C, to understand a mechanism of maintenance of a larval color variation found in wild populations. The survival rate, hatchability, and gross rate of reproduction were poorly correlated with the fitness but the mean generation time and net reproduction rate were correlated with the fitness significantly at 25°C. Intermediate color (pink) strain(s) grew faster, initiated reproduction earlier and had shorter longevities than other strain(s) under the range of 15 and 28°C; the fitness was highest in the intermediate larval color strains except at 30°C in which all strains had a negative rate of increase. The results were discussed with reference to the relationship between the larval color and fitness along with a maintenance mechanism of the variation.     

Ecological Similarity and Coexistence of Epiphytic Ice-Nucleating (Ice) Pseudomonas syringae Strains and a Non-Ice-Nucleating (Ice) Biological Control Agent

De Wit replacement series were used to study competitive interactions between epiphytic IcePseudomonas syringae strains and the biological frost control agents IceP. syringae TLP2del1 and Pseudomonas fluorescens A506. Mixtures containing two strains in different proportions but at a constant total population size were inoculated onto potato leaves. The population sizes of each strain and the total population size were determined when the community had reached equilibrium. A near-isogenic P. syringae strain pair exhibited an interaction similar to that expected for strains competing equally for limiting environmental resources. Replacement series with nonisogenic Ice and IceP. syringae strain pairs suggested that these strains competed for limiting resources according to their relative competitive abilities. There was no evidence of any niche differentiation between the IceP. syringae strains and the IceP. syringae strain. The growth responses of epiphytes following addition of nutrients to the phyllosphere indicated that the epiphytic P. syringae populations were nutrient limited and that, under growth chamber conditions, the populations were more limited by the availability of carbon than by the availability of nitrogen. Determination of in vitro carbon source utilization profiles provided further evidence for the lack of niche differentiation between the Ice and the IceP. syringae strains. Niche overlap indices calculated for the IceP. syringae strains with respect to IceP. syringae TLP2del1 were uniformly high, indicating ecological similarity, and were consistent with the observed low level of coexistence. The biological frost control agent P. fluorescens A506 replaced P. syringae. This was correlated with a high degree of niche overlap between these species.