Patterns of fluctuating asymmetry in flowers: Implications for sexual selection in plants

Characters in animals used in signalling and subjected to strong directional selection often demonstrate (i) an elevated level of fluctuating asymmetry (small random deviations from bilateral symmetry) and (ii) a negative relationship between the degree of individual fluctuating asymmetry and the size of a given character. We tested these two predictions in plants since flowers are subjected to strong directional selection and are involved in signalling to pollinators, whereas leaves are supposed not to be directly involved in signalling. The overall level of fluctuating asymmetry in a number of plant species with bilaterally or radially symmetric flowers was not generally higher in floral traits than in leaves. The level of fluctuating asymmetry in plants was sometimes significantly consistent within individuals. The absolute degree of individual fluctuating asymmetry in floral traits was generally negatively related to the size of the trait, while there was a positive relationship for leaves. The degree of individual fluctuating asymmetry in floral traits was marginally negatively related to the degree of individual fluctuating asymmetry in leaf traits. These patterns of fluctuating asymmetry in plants suggest that (i) the degree of asymmetry in flowers signals different aspects of quality than does the degree of asymmetry in leaves, and that (ii) fluctuating asymmetry in flowers often reflects the phenotypic quality of individual plants.     

Enzymatic synthesis of poly(hydroxyalkanoates) in ionic liquids

Ring-opening polymerization of five lactones catalyzed by Candida antarctica lipase B in ionic liquids yielded poly(hydroxyalkanoates) of moderate molecular weights up to Mn=13,000. In the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethane)-sulfonimide and with a low weight ratio of enzyme to lactone (1:100) we obtained polymers from beta-propiolactone, delta-valerolactone, and epsilon-caprolactone with degrees of polymerization as high as 170, 25, and 85, respectively; oligomers from beta-butyrolactone and gamma-butyrolactone with degrees of polymerization of 5; and a copolymer of beta-propiolactone and beta-butyrolactone with a degree of polymerization of 180. Water-immiscible ionic liquids were superior to water-miscible ionic liquids. Reducing the water content of the enzyme improved the degree of polymerization by as much as 50% for beta-propiolactone and epsilon-caprolactone.     

Sexual selection, stabilizing selection and fluctuating asymmetry in two populations of pupfish (Cyprinodon pecosensis)

Fluctuating asymmetry of morphological traits is thought to reflect the capacity of a genotype to produce an integrated, functional phenotype. I tested three predictions. (1) In a polygynous breeding system, under intense sexual selection on males, breeding males should show greater symmetry in bilaterally symmetrical traits than non-breeding males or females. (2) If these traits are under stabilizing selection, highly symmetrical individuals also should be modal phenotypes, thus near the mean value for that trait, whereas individuals with increased asymmetry should represent marginal phenotypes, near the extremes of the distribution for that trait. (3) Differences in the intensity of sexual selection should be reflected in differences in the degree of fluctuating asymmetry between sexes among populations. I examined the relationship between male breeding status and the degree of fluctuating asymmetry of four bilaterally symmetrical- traits, preorbital and preopercular pores and pectoral and pelvic fin rays, in two populations of Pecos pupfish which differed in the intensity of sexual selection. These traits do not function in male-male competition or female choice, thus are not directly affected by sexual selection. In Mirror Lake breeding males, as a group, were most symmetrical for all four traits, while non-breeding males and females showed higher levels of fluctuating asymmetry. Similarly, symmetrical individuals also represented modal phenotypes for four traits (breeding males), and for three traits (non-breeding males and females). These patterns were not seen in the Lake Francis population, where breeding males were as asymmetrical as non-breeding males and females, and the degree of fluctuating symmetry did not differ between modal and marginal phenotypes for any of the four traits. When ecological conditions favour intense sexual selection, either through female choice, male-male competition, or both, breeding males represent the most fit phenotypes. Thus sexual selection reinforces the effects of stabilizing selection on characters that do not function as secondary sexual traits. However, when sexual selection is relaxed, differences between sexes disappear.     

Parasites increase fluctuating asymmetry of maleDrosophila nigrospiracula: Implications for sexual selection

Fluctuating asymmetry (minor deviations from perfect bilateral symmetry) is manifested by individuals less able to buffer environmental stress during development. I utilized a system of two naturally-occurring parasites ofDrosophila nigrospiracula to test whether parasitic infection during host development yields elevated degrees of fluctuating asymmetry in two morphological traits of males. This hypothesis has important implications for sexual selection, as it may explain why asymmetric males are often found to be sexually disadvantaged. In my system, nematodes infect larvae and therefore are more likely to disrupt development than mites which only parasitize adult flies. As predicted, nematode-infected maleD. nigrospiracula had a higher degree of bristle asymmetry than did mite-infested and control (carrying neither parasite) males. There was also a significant relation between nematode number and degree of asymmetry. There was a significant negative relation between nematode load and size of adult males, implicating a causal link between nutritional stress during host development and fluctuating asymmetry. Patterns of wing length asymmetry were inconsistent with those of bristle asymmetry. Nematode-infected males did not differ in wing length asymmetry relative to mite-infested and control males, nor was there a significant relation between nematode number and wing asymmetry. This inconsistency in expression of asymmetry may reflect different intensities of selection operating on each morphological trait.     

A meta-analysis of the heritability of developmental stability

The existence of additive genetic variance in developmental stability has important implications for our understanding of morphological variation. The heritability of individual fluctuating asymmetry and other measures of developmental stability have frequently been estimated from parent-offspring regressions, sib analyses, or from selection experiments. Here we review by meta-analysis published estimates of the heritability of developmental stability, mainly the degree of individual fluctuating asymmetry in morphological characters. The overall mean effect size of heritabilities of individual fluctuating asymmetry was 0.19 from 34 studies of 17 species differing highly significantly from zero (P < 0.0001). The mean heritability for 14 species was 0.27. This indicates that there is a significant additive genetic component to developmental stability. Effect size was larger for selection experiments than for studies based on parent-offspring regression or sib analyses, implying that genetic estimates were unbiased by maternal or common environment effects. Additive genetic coefficients of variation for individual fluctuating asymmetry were considerably higher than those for character size per se. Developmental stability may be significantly heritable either because of strong directional selection, or fluctuating selection regimes which prevent populations from achieving a high degree of developmental stability to current environmental and genetic conditions.     

Glycidol-modified gels for molecular-sieve chromatography. Surface hydrophilization and pore size reduction

Divinyl sulfone-crosslinked agarose gels were made hydrophilic by coupling glycidol to the agarose chains. The concentration of glycidol in the reaction mixture determines the pore size of the gels (the glycidol molecules probably form polymers, the degree of polymerization increasing with the glycidol concentration). Gels prepared with moderate glycidol concentrations are still porous enough to be used for separation of proteins and peptides. Gels with a high degree of glycidol polymerization are suited for desalting of low-molecular-weight compounds, for instance peptides.     

Parasites differentially increase the degree of fluctuating asymmetry in secondary sexual characters

The degree of fluctuating asymmetry has been demonstrated to reflect the ability of individuals to cope with different kinds of environmental stress (Parsons 1990). Parasites and diseases are one kind of environmental stress which most individuals encounter during their lifetime. Parasites have also been suggested to play an important role in sexual selection and the development of ornaments, since the full expression of ornaments may reflect the ability of hosts to cope with the debilitating effects of parasites. Here I report for the first time that a parasite, the haematophagous tropical fowl mite Ornithonyssus bursa (Macronyssidae, Gamasida), directly affects the degree of fluctuating asymmetry in a secondary sexual character of its host, the elongated tail of the swallow Hirundo rustica (Aves: Hirundinidae). I experimentally manipulated the mite load of swallow nests during one season by either increasing or reducing the number of mites, or keeping nests as controls. The degree of fluctuating asymmetry was measured in the subsequent year after the swallows had grown new tail ornaments under the altered parasite regime. The degree of fluctuating asymmetry was larger at increasing levels of parasites for male tail length, but not for the length of the shortest tail feather or wing length or for tail and wing length in females. These results suggest that the degree of fluctuating asymmetry in tail ornaments, but not in other feather traits, reliably reveals the level of parasite infestation. This has important implications for the ability of conspecifics to use the size and the expression of ornaments in assessment of phenotypic quality and thus in sexual selection.     

Behavioral and morphological asymmetry in brain weight selected mice

Mice selected for large and small brain weight preferred to move rightwards in two cognitive paradigms, food-motivated T-maze performance and extrapolation ability tests. The degree of asymmetry in choices of movement direction varied in selection generations and sometimes was accompanied by asymmetry in the weight of the left and right hippocampi and other forebrain structures and different numbers of right and left neocortical cells.     

Structure of branched poly-α-amino acids in dimethylformamide. I. Light scattering

Light scattering of multichain poly-α-amino acids was studied in dimethylformamide (DMF). The polymers consisted of a backbone of poly-L -lysine of degree of polymerization n with side chains of benzyl L -glutamate and benzyl L -aspartate of degree of polymerization, m, on each ε-amino group. The backbone length n is known and m is obtained by amino acid analysis. The results on a series of such materials confirm this structure and show that the molecules are dissolved in highly compacted conformations. It was found that DMF is a poor solvent for these polymers. In the case of the higher molecular weight polymers, the solutions initially were not molecularly disperse. The aggregates were resistant to dilution in the experimental range. Mild heat treatment, however, disaggregated the solutions irreversibly, and the light-scattering data indicated that a structural rearrangement of the molecules had occurred.     

Fluctuating asymmetry in antlers of fallow deer (Dama dama): the relative roles of environmental stress and sexual selection

Antler lengths were recorded of a total of 250 male fallow deer (Dama dama (L)). Animals sampled were from marked populations where the majority of individuals were of known age. Asymmetry in antler length was normally distributed with a mean not significantly different from zero, confirming that differences in length between the antler pair constitute a true fluctuating asymmetry (FA). We found no clear relationship between the degree of asymmetry in antler length of an individual male and either population density or actual body mass. We did, however, detect a significant relationship between asymmetry and deviation from maximum cohort bodyweight. If deviation from maximum weight within a cohort may be considered some index of competitive success or increasing environmental stress, this may suggest that asymmetry in antler length relates in some way to developmental stress suffered by the individual concerned. The degree of asymmetry recorded in antler length also showed a significant decline with animal age, with antlers of animals of 2 years or older showing significantly greater symmetry. This is consistent with a hypothesis that despite continued competition for resources, there is a changing balance of selection pressure as animals reach maturity, with increased pressure from sexual selection requiring males to produce significantly more symmetrical ornaments.     

Molecularly imprinted micro and nanospheres for the selective recognition of 17beta-estradiol

A one-step precipitation polymerization procedure for the synthesis of molecularly imprinted polymers selective for 17beta-estradiol yielding imprinted micro and nanospheres was developed in this study and compared to templated materials obtained by conventional bulk polymerization. The polymer particles prepared by precipitation polymerization exhibited a regular spherical shape at the micro and nanoscale with a high degree of monodispersity. Moreover, the influence of the polymerization temperature, and the ratio of functional monomer to cross-linker on the size of the obtained particles was investigated. The selectivity of the imprinted micro and nanospheres was evaluated by HPLC analysis and via radioligand binding assays. HPLC separation experiments revealed that the imprinted microspheres provide higher or similar affinity to the template in contrast to imprinted polymers prepared by conventional bulk polymerization or synthesized by multi-step swelling/polymerization methods. The dimensions of the imprinted nanospheres facilitate suspension in solution rendering them ideal for binding assay applications. Results from saturation and displacement assays prove that the imprinted nanospheres exhibit superior specific affinity to the target molecule in contrast to control materials. The binding properties of the nanospheres including binding isotherms and affinity distribution were studied via Freundlich isotherm affinity distribution (FIAD) analysis. Moreover, release experiments show that 70% of rebound 17beta-estradiol was released from the imprinted nanospheres within the first 2 h, while more intimately bound 17beta-estradiol molecules (approx. 16%) were released in the following 42 h. Fitting Brunnauer-Emmet-Teller (BET) multi-point adsorption isotherms to the obtained results indicated that the micro and nanospheres are characterized by a comparatively homogenous and narrow distribution of mesopores in contrast to the corresponding bulk polymers.     

Structure and functional properties of temperature-sensitive derivatives of immobilized proteins

Polydiethylacrylamides (degree of polymerization, 13-470) containing a terminal carboxyl group were obtained by the method of radical polymerization of N,N-diethylacrylamide in the presence of mercaptoacetic acid. In the presence of 1-ethyl-(3,3-dimethylaminopropyl)-carbodiimide, these polymers reacted with ovomucoid to produce its polymeric derivatives. The values of the lower critical mixing temperature of these derivatives and the inhibitory activities of immobilized ovomucoid were determined by the length and amount of polydiethylacrylamide macromolecules bound to the molecule of ovomucoid.     

The stationary distribution of an asymmetrical model of selection in a random environment

The stationary distribution for the asymmetrical form of the SAS-CFF model of selection in a random environment is presented. Also presented are the conditions for the stable coexistence of K alleles. These conditions are the same as the conditions obtained from the classical constant-fitness model with the formal substitution of geometric mean fitnesses for the constant fitnesses of the classical model. Two examples are explored. In the “equally spaced” example, increases in the degree of asymmetry raise the homozygosity, which is accompanied by loss of alleles from the population. In the “best allele” example, increases in the degree of asymmetry raise the homozygosity without the loss of alleles. In both cases the frequency spectra are altered by the changes in the degree of asymmetry.     

Floral symmetry is associated with flower size and pollen production but not insect visitation rates in Geranium robertianum (Geraniaceae)

The degree to which fine‐scaled variation in floral symmetry is associated with variation in plant fitness remains unresolved, as does the question of whether floral symmetry is in itself a target of pollinator‐mediated selection. Geranium robertianum (Geraniaceae) is a broadly distributed species whose five‐petaled flowers vary widely with respect to their degree of rotational asymmetry. In this study, we used a naturally occurring population of plants to investigate whether floral rotational asymmetry and leaf bilateral symmetry were phenotypically correlated with a series of fitness‐related traits, and also used an experimental array with model flowers to investigate the preference of insect visitors for varying degrees of floral size and symmetry. We found that leaf asymmetry was not associated with any of the phenotypic traits measured, and that the degree of floral rotational asymmetry was strongly associated with decreased flower size and decreased pollen production. Our experimental arrays showed that insect visitors did not discriminate among model flowers on the basis of size or symmetry alone; however, insect visitors preferentially visited smaller, symmetric model flowers over larger, severely asymmetric model flowers. Taken together, our results suggest that floral and leaf symmetry in G. robertianum are not likely strong indicators of phenotypic quality, and that floral symmetry is unlikely to be a target of pollinator‐mediated selection. However, the relationship between floral asymmetry and pollen production may provide a role for fecundity selection on symmetry in this species. These data importantly add to the growing literature on the adaptive nature of floral symmetry in the wild.     

Asymmetric selection in the copolymerization of N-carboxyl-L- and D-alanine anhydride

The copolymerization of N-carboxy-L - and D -alanine anhydride with methanol as initiator was carried out. The enantiomer excess in the starting monomer mixture is preferentially incorporated into polymer chains, demonstrating asymmetric selection during the D - and L -copolymerization. The mechanism of asymmetric-selective polymerization of α-amino acid NCA is discussed in terms of the stereoregulation by molecular asymmetry of the growing polymer chain.     

The metabolism of fructose polymers in plants. Transfructosylation in tubers of Helianthus tuberosus L

1. A transfructosylase was separated from Jerusalem artichoke-tuber extracts. The partially purified enzyme was practically free from fructosans and its specific activity was increased more than sevenfold. 2. The enzyme was highly specific for terminal β-(2→1′)-linked fructofuranosyl residues. 3. The most active donor found was 1^F-fructosylsucrose, which had about five times the reactivity of the next higher homologues (degree of polymerization 4–6); (1-fructosyl)₂fructose was intermediate in reactivity; sucrose was inactive. 4. Sucrose, and polymers of high degree of polymerization (>20), were the most efficient acceptors for transferred fructosyl residues of the compounds tested. 5. A variety of transferase activities appeared to be catalysed by the enzyme, namely, dismutation (`self-transfer') giving rise to a series of polymers ranging in degree of polymerization both above and below that of the original substrate, transfer to polymer giving rise to limited quantities of higher polymers, and transfer to sucrose; in the last case 1^F-fructosylsucrose/sucrose transfer (resulting in exchange labelling of sucrosyl groups) was used to investigate the mechanism of the reaction more fully. 6. Since fructose transfer can be demonstrated in the living plant tissue, the inter-relationships of the various activities and their significance in fructosan metabolism are discussed.     

Effects of Silicate Polymers on Erythrocytes in Presence and Absence of Complement

The effects of silicates upon erythrocytes depend upon the degree of polymerization. Monomeric silicate does not appear to be taken up by red cells. Polymerized silicates are taken up and bound tightly. In the presence of small polymeric forms erythrocytes are lysed by complement. Larger polymers are bound to erythrocytes but do not sensitize to complement hemolysis. Larger polymers, however, are directly toxic and cause hemolysis in the absence of complement. Red cells exposed to complement-active polymers show characteristic alteration in morphology with the assumption of irregular bell shapes. Larger polymers cause the cells to become spherical before spontaneous rupture occurs. Large polymers cause erythrocyte agglutination but this is minimal or absent with small complement-active polymers. Complement-active polymers cause little or no change in osmotic fragility. Increase in mechanical fragility is a sensitive indication of the presence of larger, agglutinating polymers. The conversion of pneumococci from Gram positivity to negativity appears to be caused principally by complement-active polymers. Possible implications of polymer size and complement activity are discussed in relation to production of silicotic lesions by silica-containing ores.     

Structure and functional properties of temperature-sensitive derivatives of immobilized proteins

Polydiethylacrylamides (degree of polymerization, 13–470) containing a terminal carboxyl group were obtained by the method of radical polymerization of N,N-diethylacrylamide in the presence of mercaptoacetic acid. In the presence of 1-ethyl-(3,3-dimethylaminopropyl)-carbodiimide, these polymers reacted with ovomucoid to produce its polymeric derivatives. The values of the lower critical mixing temperature of these derivatives and the inhibitory activities of immobilized ovomucoid were determined by the length and amount of polydiethylacrylamide macromolecules bound to the molecule of ovomucoid.     

A new genus of long-legged flies displaying remarkable wing directional asymmetry

A previously unknown group of flies is described whose males exhibit directional asymmetry, in that the left wing is larger than, and of a different shape from, the right wing. To our knowledge, wing asymmetry of this degree has not previously been reported in an animal capable of flight. Such consistent asymmetry must result from a left-right axis during development, a level of differentiation whose existence has been questioned for insects. Wing asymmetry of this magnitude has implications for questions in areas of development, natural selection, flight, mate selection and communication in insects. The 'handicap principle' provides a possible explanation: females will choose a mate with the greatest handicap because his survival, in spite of his handicap, is a measure of his genetic superiority.     

THE FITNESS OF MANIPULATING PHENOTYPES: IMPLICATIONS FOR STUDIES OF FLUCTUATING ASYMMETRY AND MULTIVARIATE SELECTION

Phenotypic manipulation (or phenotypic engineering) that alters trait distributions provides a way to increase the statistical power of detecting relationships between traits and fitness. Manipulations relying on plastic responses, however, assume a specific relationship between the perturbation and the alteration of the traits when multiple traits are involved. We measured several traits, including condition measured as fluctuating asymmetry, in the ladybird beetle Harmonia axyridis under six different diets to examine how altered environments affected multiple traits and their distributions. Although diet affected fluctuating asymmetry, we found no consistent relationship between degree of asymmetry and other phenotypic measures. As expected, individual traits were altered by our treatments. Contrary to expectation, relationships among traits were not constant among diets. Our results suggest that assumptions about the relationship between condition and trait values, especially fluctuating asymmetry, cannot be made. Further, studies that use manipulated phenotypes to statistically determine the form of selection must first demonstrate that the pattern of the phenotypic correlation matrix is not itself altered by the manipulation. If the phenotypic correlation matrix is not constant, then experimental estimates of selection coefficients may not reflect selection that occurs in the wild.