MEASURING PHENOTYPIC SELECTION ON AN ADAPTATION: LAMELLAE OF DAMSELFLIES EXPERIENCING DRAGONFLY PREDATION

Previous studies suggest that the evolution of increased caudal lamellae size to increase swimming speed was an adaptation of Enallagma damselflies for coexisting with large, predatory dragonflies in fishless lakes. To test whether dragonfly predation still exerts selection pressures for increased lamellae size, I performed a field experiment in which I manipulated the abilities of dragonfly larvae to inflict mortality on Enallagma boreale larvae and compared differences in lamellae size and shape between treatments. In cages where dragonflies were free to forage on damselflies, surviving E. boreale larvae had lamellae that were larger in lateral surface area, and that were wider relative to their length, as compared with larvae recovered from treatments in which dragonflies were not permitted to forage on damselflies. Selection differentials of about 0.25 phenotypic standard deviation units were measured for both of these characters. These results indicate that dragonfly predation still exerts significant selection pressures on damselfly antipredator adaptations. The results of this study are discussed in the context of studies of adaptation.     

SEXUAL SELECTION AND SURVIVAL SELECTION ON WING COLORATION AND BODY SIZE IN THE RUBYSPOT DAMSELFLY HETAERINA AMERICANA

I review methodological problems that can lead to false evidence for selection on secondary sexual characters and present a study of selection in rubyspot damselflies (Hetaerina americana) that avoids these pitfalls. Male rubyspots have a large red spot on each wing that grows to a terminal size after sexual maturity. Selection gradient analyses revealed evidence for positive sexual and survival selection on both terminal wing spot size and body size. Phenotype manipulations confirmed that wing spot size was subject to direct sexual selection, but showed that the positive slope of survival on wing spot size was an indirect effect of selection on unmeasured traits. This study provides the strongest evidence yet for sexual selection on coloration in Odonata, but also provides clear examples of why phenotypic selection statistics must be calculated and interpreted cautiously.     

SPECIES RECOGNITION AND PATTERNS OF POPULATION VARIATION IN THE REPRODUCTIVE STRUCTURES OF A DAMSELFLY GENUS

The selection pressures imposed by mate choice for species identity should impose strong stabilizing selection on traits that confer species identity to mates. Thus, we expect that such traits should show nonoverlapping distributions among closely related species, but show little to no variance among populations within a species. We tested these predictions by comparing levels of population differentiation in the sizes and shapes of male cerci (i.e., the clasper structures used for species identity during mating) of six Enallagma damselfly species. Cerci shapes were nonoverlapping among Enallagma species, and five of six Enallagma species showed no population variation across their entire species ranges. In contrast, cerci sizes overlapped among species and varied substantially among populations within species. These results, taken with previous studies, suggest that cerci shape is a primary feature used in species recognition used to discriminate conspecific from heterospecifics during mating.     

MEASURING NATURAL SELECTION ON PHENOTYPIC PLASTICITY

To understand natural selection we need to integrate its measure across environments. We present a method for measuring phenotypic selection that combines the potential for both environmental variation and phenotypic plasticity. The method uses path analysis and a measure of selection that is analogous to selection on breeding values. For individuals growing in alternative environments, paths are created that represent potential changes in the environment. The probabilities for these changes are then multiplied by the path coefficients to calculate selection coefficients. Selection on plasticity is measured as the difference in selection within each environment. We illustrate these methods using data on selection in an experimental population of Arabidopsis thaliana. Individuals from 36 families were grown in one of four environments, a factorial combination of shaded/open and early/late shading. For final height of the inflorescence, there was positive selection in both the open and shaded environments and negative selection on plasticity of height. For bolting time, there was also positive selection in both environments, but no selection on plasticity. We show how to use this information to examine how selection would change with changes in environmental frequencies and their transition probabilities. These methods can be expanded to encompass continuous traits and continuous environments as well as other complexities of natural selection.     

NONCONSUMPTIVE PREDATOR‐DRIVEN MORTALITY CAUSES NATURAL SELECTION ON PREY

Predators frequently exert natural selection through differential consumption of their prey. However, predators may also cause prey mortality through nonconsumptive effects, which could cause selection if different prey phenotypes are differentially susceptible to this nonconsumptive mortality. Here we present an experimental test of this hypothesis, which reveals that nonconsumptive mortality imposed by predatory dragonflies causes selection on their damselfly prey favoring increased activity levels. These results are consistent with other studies of predator‐driven selection, however, they reveal that consumption alone is not the only mechanism by which predators can exert selection on prey. Uncovering this mechanism also suggests that prey defensive traits may represent adaptations to not only avoid being consumed, but also for dealing with other sources of mortality caused by predators. Demonstrating selection through both consumptive and nonconsumptive predator mortality provides us with insight into the diverse effects of predators as an evolutionary force.     

NATURAL SELECTION ON FLORAL TRAITS IN TWO SPECIES OF LOBELIA WITH DIFFERENT POLLINATORS

Using both multivariate and univariate regression techniques, I measured selection acting through female reproductive success in two hermaphroditic species with precise pollen placement but different pollinators: hummingbird-pollinated Lobelia cardinalis and bumblebee-pollinated L. siphilitica. Six traits were analyzed in two populations of L. cardinalis and one population of L. siphilitica: flower number, mean number of flowers open per day, inflorescence height, number of days in flower, median-flower date and nectar-stigma distance. In another study it was found that female reproductive success in one population of L. cardinalis was much less pollen limited than in the other two populations, and it was therefore expected that selection of female reproductive traits in this population would be weaker. In the univariate analyses correlations caused nearly all traits to have significant directional selection coefficients. However, in the multivariate analyses no traits in L. siphilitica experienced directional or quadratic selection. Selection acted differently in the two L. cardinalis populations. The less pollen-limited population experienced positive directional selection on flower number and median-flower date, while in the other L. cardinalis population there was positive directional selection on flower number and nectar-stigma distance and both positive directional and positive quadratic selection on height. The functional significance of floral traits in these two species and the probable effect of increased sample sizes are discussed.     

A TEST AND REVIEW OF THE ROLE OF EFFECTIVE POPULATION SIZE ON EXPERIMENTAL SEXUAL SELECTION PATTERNS

Experimental evolution, particularly experimental sexual selection in which sexual selection strength is manipulated by altering the mating system, is an increasingly popular method for testing evolutionary theory. Concerns have arisen regarding genetic diversity variation across experimental treatments: differences in the number and sex ratio of breeders (effective population size; N_e ) and the potential for genetic hitchhiking, both of which may cause different levels of genetic variation between treatments. Such differences may affect the selection response and confound interpretation of results. Here we use both census-based estimators and molecular marker-based estimates to empirically test how experimental evolution of sexual selection in Drosophila pseudoobscura impacts N_e and autosomal genetic diversity. We also consider effects of treatment on X-linked N_e s, which have previously been ignored. Molecular autosomal marker-based estimators indicate that neither N_e nor genetic diversity differs between treatments experiencing different sexual selection intensities; thus observed evolutionary responses reflect selection rather than any confounding effects of experimental design. Given the increasing number of studies on experimental sexual selection, we also review the census N_e s of other experimental systems, calculate X-linked N_e , and compare how different studies have dealt with the issues of inbreeding, genetic drift, and genetic hitchhiking to help inform future designs.     

THE FIRST DAMSELFLIES FROM THE LOWERMOST EOCENE OF DENMARK, WITH A DESCRIPTION OF A NEW SUBFAMILY (ODONATA, ZYGOPTERA: DYSAGRIONIDAE)

Abstract:  Eodysagrion mikkelseni gen. et sp. nov., type species of the new subfamily Eodysagrioninae, and the dysagrionine Primorilestes madseni sp. nov., the first thaumatoneurid damselflies from the lowermost Eocene of Denmark, are described. They confirm the presence of this American family in the Palaeogene of Western Europe.     

CONSTANCY OF POPULATION PARAMETERS FOR LIFE-HISTORY AND FLORAL TRAITS IN RAPHANUS SATIVUS L. II. EFFECTS OF PLANTING DENSITY ON PHENOTYPE AND HERITABILITY ESTIMATES

To determine the effect of growing conditions on population parameters in wild radish, (Raphanus sativus L.: Brassicaceae), we replicated maternal and paternal half-sib families of seed across three planting densities in an experimental garden. A nested breeding design performed in the greenhouse produced 1,800 F₁ seeds sown in the garden. We recorded survivorship, measured phenotypic correlations among and estimated narrow-sense and broad-sense heritabilities (h²) of: days to germination, days to flowering, petal area, ovule number/flower, pollen production/flower, and modal pollen grain volume. Survivorship declined with increasing density, but the relative abundances of surviving families did not differ significantly among densities. Seeds in high-density plots germinated significantly faster than seeds sown in medium- or low-density plots, but they flowered significantly later. Plants in high-density plots had fewer ovules per flower than those in the other treatments. Petal area and pollen characters did not differ significantly among densities. Densities differed with respect to the number and sign of significant phenotypic correlations. Analyses of variance were conducted to detect additive genetic variance (V_a) of each trait in each density. At low density, there were significant paternal effects on flowering time and modal pollen grain volume; in medium-density plots, germination time, flowering time and ovule number exhibited significant paternal effects; in high-density plots, only pollen grain volume differed among paternal sibships. The ability to detect maternal effects on progeny phenotype also depended on density. Narrow-sense h² estimates differed markedly among density treatments for germination time, flowering time, ovule number and pollen grain volume. Maternal, paternal and error variance components were estimated for each trait and density to examine the sources of variation in narrow-sense h² across densities. Variance components did not change consistently across densities; each trait behaved differently. To provide qualitative estimates of genetic correlations between characters, correlation coefficients were estimated using paternal family means; these correlations also differed among densities. These results demonstrate that: a) planting density influences the magnitude of maternal and paternal effects on progeny phenotype, and of h² estimates, b) traits differ with respect to the density in which heritability is greatest, c) density affects the variance components that comprise heritability, but each trait behaves differently, and d) the response to selection on any target trait should result in different correlated responses of other traits, depending on density.     

高产磷酯酶C菌株筛选及其抗血小板功能的研究

在湖北省、湖南省、江苏省、山东省、广东省156个点采土样1268份,利用卵黄琼脂的LB培养基初筛获得产生乳白色晕圈的菌株648株;再用卵黄琼脂滤纸圆片检测获得产生乳白色晕圈和透明圈菌株266株;这些菌株用卵黄琼脂杯蝶法筛选出产生大于13．0mm乳白色晕圈及少量透明圈共73株,经过菌生物量、卵黄杯碟法和抗兔血小板聚集率的测定,从73株菌中筛选出15株,菌号为：183,198,247,424,587,596,692,744,754—1,791—2,779,970,998,1107,1182;将此15菌株经菌生物量、卵黄琼脂杯碟法、NPPC法和抗人血小板聚集率的测定,从中选出754—1,779,970,1107四株菌进行分类鉴定和已知菌CW—W—90—3菌对照比较的研究。     

SEQUENTIAL FEMALE ASSESSMENT DRIVES COMPLEX SEXUAL SELECTION ON BOWER SHAPE IN A CICHLID FISH

In many animals, sexual selection on male traits results from female mate choice decisions made during a sequence of courtship behaviors. We use a bower‐building cichlid fish, Nyassachromis cf. microcephalus, to show how applying standard selection analysis to data on sequential female assessment provides new insights into sexual selection by mate choice. We first show that the cumulative selection differentials confirm previous results suggesting female choice favors males holding large volcano‐shaped sand bowers. The sequential assessment analysis reveals these cumulative differentials are the result of selection acting on different bower dimensions during the courtship sequence; females choose to follow males courting from tall bowers, but choose to engage in premating circling with males holding bowers with large diameter platforms. The approach we present extends standard selection analysis by partitioning the variances of increasingly accurate estimates of male reproductive fitness and is applicable to systems in which sequential female assessment drives sexual selection on male traits.     

MEASURING THE EFFECTS OF PAIRING SUCCESS,EXTRA-PAIR COPULATIONS AND MATE QUALITY ON THE OPPORTUNITY FOR SEXUAL SELECTION

Sexual selection can act through variation in the number of social mates obtained, variation in mate quality, or variation in success at obtaining extra-pair fertilizations. Because within-pair fertilizations (WPF) and extra-pair fertilizations (EPF) are alternate routes of reproduction, they are additive, rather than multiplicative, components of fitness. We present a method for partitioning total variance in reproductive success (a measure of the opportunity for selection) when fitness components are both additive and multiplicative and use it to partition the variance into components that correspond to each mechanism of sexual selection. Computer simulations show that extra-pair fertilizations can either increase or decrease total variance, depending on the covariance between within-pair and extra-pair success. Simulations also suggest that for socially monogamous species, extra-pair fertilizations have a greater effect than variation in mate quality or pairing status on the opportunity for selection. Application of our model to data gathered for a population of red-winged blackbirds (Agelaius phoeniceus) indicates that most of the variance in male reproductive success was attributable to within-pair sources of variance. Nevertheless, extra-pair copulations increased the opportunity for selection because males varied both in the proportion of their social young that they sired and in the number of extra-pair mates that they obtained. Furthermore, large and positive covariances existed between the number of extra-pair mates a male obtained and both social pairing success and within-pair paternity, indicating that, in this population, males preferred as social mates also were preferred as extra-pair mates.     

THE DESIGN OF A BEAUTIFUL WEAPON: COMPENSATION FOR OPPOSING SEXUAL SELECTION ON A TRAIT WITH TWO FUNCTIONS

Male fiddler crabs, genus Uca, have one greatly enlarged claw with which they court females and threaten and fight other males. Longer claws are more effective signals but are thought to be less effective weapons because the relative closing force at the tip of the claw decreases with claw length. We studied claw morphology and fighting in Uca terpsichores and Uca beebei and found a mechanism that may resolve opposing selection for signaling and fighting ability. When males fought they delivered gripping forces not at the tips but at the tubercles on the inner margins of their claws’ fingers. As claws grow, these tubercles remain relatively close to the apex of the gape. Consequently, the mechanical advantage that governs the forces that can be delivered at these tubercles decreases only slightly with increasing claw length allowing the claw to be an effective signal and a powerful weapon. Animal weapons are exceptionally diverse in form and detail of armature and the causes of this diversity are poorly understood. We suggest that the designs of weapons may often reflect compensatory patterns of growth and placement of armature that enhances the weapon's overall utility for multiple uses in competition for mates.     

VARIABLE SELECTION ON EUROSTA'S GALL SIZE,I: THE EXTENT AND NATURE OF VARIATION IN PHENOTYPIC SELECTION

Natural fluctuations in environmental conditions are likely to induce variation in the intensity or direction of natural selection. A long-term study of the insect, Eurosta solidaginins Fitch (Diptera; Tephritidae), which induces stem galls on the perennial herb Solidago altissima (Asteraceae) was performed to explore the patterns of variation in phenotypic selection. The intensity of selection imposed by parasitoids and predators on gallmaking larvae, for gall size, was measured across 16 populations over the course of 4 generations, for a total of 64 population-generations. Directional selection was quantified by i, the selection intensity, and variance selection by j‘, a measure of the intensity of selection on phenotypic variance. Size-dependent attack by parasitoids caused upward directional selection (mean i_p = 0.42; SE = 0.023), while size-dependent bird attack favored larvae that induced smaller galls (mean i_b = -0.07; SE = 0.013. The mean net directional selection intensity was 0.35 (SE = 0.030), which indicates that insects inducing larger galls are generally favored by selection. The opposing patterns of size-dependent attack resulted in stabilizing selection in half the population generations, with an overall average. j‘ of -0.11 (SE = 0.078). The magnitude of directional selection was strongly influenced by the population mean gall size and weakly by the optimal gall size. The intensity of variance selection was strongly influenced by the shape of the fitness function, with sigmoidal and Gaussian-like shapes causing greater depletion of phenotypic variance.     

VARIABLE SELECTION ON EUROSTA'S GALL SIZE. II. A PATH ANALYSIS OF THE ECOLOGICAL FACTORS BEHIND SELECTION

We examined phenotypic selection exerted by natural enemies on the gall-making fly Eurosta solidaginis in an extensive field study of 16 populations, spanning four generations. Gall-makers that induce small galls are vulnerable to the attack of Eurytoma gigantea. This imposes upward directional selection on gall size. Insectivorous birds, predominantly the downy woodpecker, are more likely to attack larvae that induce large galls than small ones, and this imposes downward directional selection. We used path analysis to explore the relative contributions of these natural enemies to the net directional selection on gall size. The path models further examined several ecological factors that influence selection intensity through their effects on parasitoid and bird attack rates. Net directional selection varied more strongly with E. gigantea attack than bird attack. Competitive interactions among birds and the three parasitoid species, including E. gigantea, were evidenced by low winter bird attack rates in fields where a high proportion of galls contained the overwintering parasitoids. Eurytoma gigantea attack was heavier in fields where mean gall size was small and bird attack heavier in fields where mean gall size was large. Neither birds nor E. gigantea showed simple density-dependent attack. Data suggested a form of frequency-dependent attack by birds but not by E. gigantea.     

BODY SIZE DECLINES DESPITE POSITIVE DIRECTIONAL SELECTION ON HERITABLE SIZE TRAITS IN A BARNACLE GOOSE POPULATION

Analyses of more than 2000 marked barnacle geese (Branta leucopsis) in the largest Baltic colony, Sweden, showed that structurally large females generally produced larger clutches and larger eggs, hatched their broods earlier in the season, and produced more and heavier young than smaller females. In males, the corresponding relationships between reproductive parameters and structural body size were weaker or nonsignificant. Because structural body size traits have previously been found to be significantly heritable and positively genetically correlated, an increase in mean structural body size of individuals as a response to selection might have been expected. By contrast, we found that the mean adult head length and mean adult tarsus length decreased significantly in the largest colony by approximately 0.7 and 0.5 standard deviations, respectively, in both males and females during the 13-year study period. Environmental factors, such as the amount of rain in different years, were found to affect the availability of high-quality food for growing geese. As a consequence of this temporal variability in the availability of high-quality food, the mean adult structural body size of different cohorts differed by up to 1.3 standard deviations. Comparisons of mean body size of cohorts born in different colonies suggest that the most likely explanation for the body-size decline in the main study colony is that a density-dependent process, which mainly was in effect during the very early phase of colony growth, negatively affected juvenile growth and final size. We conclude that large environmental effects on growth and final structural body size easily can mask microevolutionary responses to selection. Analyses of environmental causes underlying temporal and spatial body size variation should always be considered in the reconstruction and prediction of evolutionary changes in natural populations.