Novel cuticular hydrocarbons from the cane beetle Antitrogus parvulus - 4,6,8,10,16-penta- and 4,6,8,10,16,18-hexamethyldocosanes - Unprecedented anti-anti-anti-stereochemistry in the 4,6,8,10-methyltetrad

[GRAPHICS] The major cuticular hydrocarbons from the cane beetle species Antitrogus parvulus are 4,6,8,10,16-penta- and 4,6,8,10,16,18-hexamethyldocosanes, I and 2, respectively. Stereoisomers of 2,4,6,8-tetramethylundecanal of established relative stereochemistry were derived from 2,4,6-trimethylphenol and were then coupled with appropriate methyl-substituted phosphoranes 62 and 25 to furnish alkenes, which on reduction provided diastereomers of I and 2, respectively. Capillary gas chromatography, mass spectrometry, and high resolution C-13 NMR spectroscopy confirmed 1 as either 84a or 84b and 2 as either 15a or 15b. The novelty of these structures and their relative stereochemistry is briefly related to polyketide assembly.

Orientation of the genetic variance-covariance matrix and the fitness surface for multiple male sexually selected traits

Stabilizing selection has been predicted to change genetic variances and covariances so that the orientation of the genetic variance-covariance matrix (G) becomes aligned with the orientation of the fitness surface, but it is less clear how directional selection may change G. Here we develop statistical approaches to the comparison of G with vectors of linear and nonlinear selection. We apply these approaches to a set of male sexually selected cuticular hydrocarbons (CHCs) of Drosophila serrata. Even though male CHCs displayed substantial additive genetic variance, more than 99% of the genetic variance was orientated 74.9degrees away from the vector of linear sexual selection, suggesting that open-ended female preferences may greatly reduce genetic variation in male display traits. Although the orientation of G and the fitness surface were found to differ significantly, the similarity present in eigenstructure was a consequence of traits under weak linear selection and strong nonlinear ( convex) selection. Associating the eigenstructure of G with vectors of linear and nonlinear selection may provide a way of determining what long-term changes in G may be generated by the processes of natural and sexual selection.

Multivariate quantitative genetics and the Lek Paradox: Genetic variance in male sexually selected traits of Drosophila serrata under field control

Single male sexually selected traits have been found to exhibit substantial genetic variance, even though natural and sexual selection are predicted to deplete genetic variance in these traits. We tested whether genetic variance in multiple male display traits of Drosophila serrata was maintained under field conditions. A breeding design involving 300 field-reared males and their laboratory-reared offspring allowed the estimation of the genetic variance-covariance matrix for six male cuticular hydrocarbons (CHCs) under field conditions. Despite individual CHCs displaying substantial genetic variance under field conditions, the vast majority of genetic variance in CHCs was not closely associated with the direction of sexual selection measured on field phenotypes. Relative concentrations of three CHCs correlated positively with body size in the field, but not under laboratory conditions, suggesting condition-dependent expression of CHCs under field conditions. Therefore condition dependence may not maintain genetic variance in preferred combinations of male CHCs under field conditions, suggesting that the large mutational target supplied by the evolution of condition dependence may not provide a solution to the lek paradox in this species. Sustained sexual selection may be adequate to deplete genetic variance in the direction of selection, perhaps as a consequence of the low rate of favorable mutations expected in multiple trait systems.

Contrasting mutual sexual selection on homologous signal traits in Drosophila serrata

The nature of male mating preferences, and how they differ from female mating preferences in species with conventional sex roles, has received little attention in sexual selection studies. We estimated the form and strength of sexual selection as a consequence of male and female mating preferences in a laboratory-based population of Drosophila serrata. The differences between sexual selection on male and female signal traits (cuticular hydrocarbons [CHCs]) were evaluated within a formal framework of linear and nonlinear selection gradients. Females tended to exert linear sexual selection on male CHCs, whereas males preferred intermediate female CHC phenotypes leading to convex (stabilizing) selection gradients. Possible mechanisms determining the nonlinear nature of sexual selection on female CHCs are proposed.

Divergent selection and the evolution of signal traits and mating preferences

Mating preferences are common in natural populations, and their divergence among populations is considered an important source of reproductive isolation during speciation. Although mechanisms for the divergence of mating preferences have received substantial theoretical treatment, complementary experimental tests are lacking. We conducted a laboratory evolution experiment, using the fruit fly Drosophila serrata, to explore the role of divergent selection between environments in the evolution of female mating preferences. Replicate populations of D. serrata were derived from a common ancestor and propagated in one of three resource environments: two novel environments and the ancestral laboratory environment. Adaptation to both novel environments involved changes in cuticular hydrocarbons, traits that predict mating success in these populations. Furthermore, female mating preferences for these cuticular hydrocarbons also diverged among populations. A component of this divergence occurred among treatment environments, accounting for at least 17.4% of the among- population divergence in linear mating preferences and 17.2% of the among-population divergence in nonlinear mating preferences. The divergence of mating preferences in correlation with environment is consistent with the classic by- product model of speciation in which premating isolation evolves as a side effect of divergent selection adapting populations to their different environments.

Determining the effective dimensionality of the genetic variance-covariance matrix

Determining the dimensionality of G provides an important perspective on the genetic basis of a multivariate suite of traits. Since the introduction of Fisher's geometric model, the number of genetically independent traits underlying a set of functionally related phenotypic traits has been recognized as an important factor influencing the response to selection. Here, we show how the effective dimensionality of G can be established, using a method for the determination of the dimensionality of the effect space from a multivariate general linear model introduced by AMEMIYA (1985). We compare this approach with two other available methods, factor-analytic modeling and bootstrapping, using a half-sib experiment that estimated G for eight cuticular hydrocarbons of Drosophila serrata. In our example, eight pheromone traits were shown to be adequately represented by only two underlying genetic dimensions by Amemiya's approach and factor-analytic modeling of the covariance structure at the sire level. In, contrast, bootstrapping identified four dimensions with significant genetic variance. A simulation study indicated that while the performance of Amemiya's method was more sensitive to power constraints, it performed as well or better than factor-analytic modeling in correctly identifying the original genetic dimensions at moderate to high levels of heritability. The bootstrap approach consistently overestimated the number of dimensions in all cases and performed less well than Amemiya's method at subspace recovery.

Measuring natural and sexual selection on breeding values of male display traits in Drosophila serrata

Fundamental to many theories of sexual selection is the expectation that sexual traits, which males use in an attempt to increase mating success, confer costs as well as benefits to individual males. Although evolution of exaggerated male traits is predicted to be halted, by costs applied by natural selection, there is a lack of empirical work devoted to quantitatively establishing whether natural selection opposes sexual selection generated by the preferences of females. In this study, we quantified natural and sexual selection gradients on breeding values for cuticular hydrocarbon (CHC) components of male contact pheromones in Drosophila serrata. As male sexual traits may often be environmentally condition dependent, breeding values were used in the selection analysis to remove the possibility of environmental correlations between the measured trait and fitness biasing estimates of selection. The direction of natural selection was found to oppose sexual selection on a subset of CHCs examined. Opposing natural and sexual selection suggests that further evolution of the male pheromone may in part be limited by costs associated with attractive male CHC blends.

The roles of natural and sexual selection during adaptation to a novel environment

The net effect of sexual selection on nonsexual fitness is controversial. On one side, elaborate display traits and preferences for them can be costly, reducing the nonsexual fitness of individuals possessing them, as well as their offspring, In contrast, sexual selection may reinforce nonsexual fitness if an individual's attractiveness and quality are genetically correlated. According to recent models, such good-genes mate choice should increase both the extent and rate of adaptation. We evolved 12 replicate populations of Drosophila serrata in a powerful two-way factorial experimental design to test the separate and combined contributions of natural and sexual selection to adaptation to a novel larval food resource. Populations evolving in the presence of natural selection had significantly higher mean nonsexual fitness when measured over three generations (13-15) during the course of experimental evolution (16-23% increase). The effect of natural selection was even more substantial when measured in a standardized, monogamous mating environment at the end of the experiment (generation 16; 52% increase). In contrast, and despite strong sexual selection on display traits, there was no evidence from any of the four replicate fitness measures that sexual selection promoted adaptation. In addition, a comparison of fitness measures conducted under different mating environments demonstrated a significant direct cost of sexual selection to females, likely arising from some form of male-induced harm. Indirect benefits of sexual selection in promoting adaptation to this novel resource environment therefore appear to be absent in this species, despite prior evidence suggesting the operation of good-genes mate choice in their ancestral environment. How novel environments affect the operation of good-genes mate choice is a fundamental question for future sexual selection research.

Field-based evaluation of semipermeable membrane devices (SPMDs) as passive air samplers of polyaromatic hydrocarbons (PAHs)

Semipermeable membrane devices (SPMDs) have been used as passive air samplers of semivolatile organic compounds in a range of studies. However, due to a lack of calibration data for polyaromatic hydrocarbons (PAHs), SPMD data have not been used to estimate air concentrations of target PAHs. In this study, SPMDs were deployed for 32 days at two sites in a major metropolitan area in Australia. High-volume active sampling systems (HiVol) were co-deployed at both sites. Using the HiVol air concentration data from one site, SPMD sampling rates were measured for 12 US EPA Priority Pollutant PAHs and then these values were used to determine air concentrations at the second site from SPMD concentrations. Air concentrations were also measured at the second site with co-deployed HiVols to validate the SPMD results. PAHs mostly associated with the vapour phase (Fluorene to Pyrene) dominated both the HiVol and passive air samples. Reproducibility between replicate passive samplers was satisfactory (CV < 20%) for the majority of compounds. Sampling rates ranged between 0.6 and 6.1 m(3) d(-1). SPMD-based air concentrations were calculated at the second site for each compound using these sampling rates and the differences between SPMD-derived air concentrations and those measured using a HiVol were, on average, within a factor of 1.5. The dominant processes for the uptake of PAHs by SPMDs were also assessed. Using the SPMD method described herein, estimates of particulate sorbed airborne PAHs with five rings or greater were within 1.8-fold of HiVol measured values. (C) 2004 Elsevier Ltd. All rights reserved.

Effects of adsorbed phase on diffusion of subcritical hydrocarbons in activated carbon at low pressures

Diffusions of free and adsorbed molecules of subcritical hydrocarbons in activated carbon were investigated to study the influence of adsorbed molecules on both diffusion processes at low pressures. A collision reflection factor, defined as the fraction of molecules undergoing collision to the solid surface over reflection from the surface, is incorporated into Knudsen diffusivity and surface diffusivity in meso/macropores. Since the porous structure of activated carbon is bimodal in nature, the diffusion of adsorbed molecules is contributed by that of weakly adsorbed molecules on the meso/macropore surfaces and that of strongly adsorbed molecules in the small confinement of micropores. The mobility of adsorbed molecules on the meso/macropore surface is characterized by the surface diffusivity D-mu 2, while that in the micropore is characterized by D-mu 1. In our study with subcritical hydrocarbons, we have found that the former increases almost linearly with pressure, while the latter exhibits a sharp increase at a very low-pressure region and then decreases beyond a critical pressure. This critical pressure is identified as a pressure at which the micropores are saturated.

Permeability of subcritical hydrocarbons in activated carbon

A new diffusion and flow model is presented to describe the behavior of hydrocarbon vapors in activated carbon. The micro/mesopore size distribution (PSD) is obtained according to Do's method which consists of two sequential processes of pore layering and pore filling. This model uses the micro/meso PSD obtained from each adsorbate equilibrium isotherm, which reflects the dynamics behavior of adsorbing molecules through the solid. The initial rise in total permeability is mainly attributed to adsorbed-phase diffusion (that is, surface diffusion), whereas the decrease over reduced pressure of about 0.9 is attributed to the reduction of pore space available for gas phase diffusion and flow. A functional form of surface diffusivity is proposed and validated with experimental data. This model predicts well the permeability of condensable hydrocarbon vapors in activated carbon. (C) 2005 American Institute of Chemical Engineers.

Nonplanar distortions and strain energies of polycyclic aromatic hydrocarbons

On the basis of HF/6-31G(d) optimized structures, the nonplanar distortions of 135 polycyclic aromatic hydrocarbons (PAHs) have been classified as splitting (S-) and arching (A-) distortions. Three bay structures are proposed as the structural origin of S-distortion. Due to the limitation of sample molecules, a set of universal motifs for molecules containing A-distortions is not available; however, a set of motifs and parameters are developed for the semiquantitative estimation of the nonplanar strain energies of PAHs containing the corannulene structure, and the differences between the E, values from quantum calculations and those from these estimations vary from -5.60 to 5.51 kcal/mol. The above results are fundamentally important for the understanding of nonplanar distortion of PAHs and fullerenes, and this method can also be employed to semiquantitatively estimate strain energies of such molecules containing hundreds of carbon atoms.

Field evaluation of passive samplers: Monitoring polycyclic aromatic hydrocarbons (PAHs) in stormwater

The aim of this study was to evaluate the feasibility of using semipermeable membrane devices (SPMDs) and polyethylene-based passive sampler devices (PSDs) for monitoring PAHs in stormwater. Firstly, SPMDs were deployed at one site and SPMD-derived water concentrations were compared with water concentration measured from grab samples. In a subsequent deployment the performance of SPMDs and PSDs was compared. Finally PSDs of multiple surface area to volume ratios were used to compare PAH concentrations at the two sites. The results obtained in this study show that SPMDs can be used to measure the water concentration of PAHs with reasonable accuracy, when compared with grab samples collected at the same site. Importantly, several PAHs which could not be detected in a 10 L grab sample could be detected in the SPMDs. PSD and SPMD samplers produced similar results when deployed at the same site, with most estimated water concentrations within a factor of 1.5. The use of PSDs in multiple surface area to volume ratios proved to be an effective means of characterizing the uptake kinetics for PAHs in situ. Overall passive water samplers proved to be an efficient technique for monitoring PAHs in stormwater.

Photodegradation of polyaromatic hydrocarbons in passive air samplers: Field testing different deployment chambers

Semi-permeable membrane devices (SPMDs) were loaded with deuterated anthracene and pyrene as performance reference compounds (PRCs) and deployed at a test site in four different chambers (open and closed box chamber, bowl chamber and cage chamber) for 29 days. The losses of PRCs and the uptake of polyaromatic hydrocarbons (PAHs) from the ambient air were quantified. UV-B levels measured in each deployment chamber indicated that SPMDs would be exposed to the most UV-B in the cage chamber and open box chamber. Significantly less PAHs were quantified in SPMDs deployed in the cage chamber and open box chamber compared to samplers from the other two chambers, suggesting that photodegradation of PAHs had occurred. The loss of PRCs confirmed these results but also showed that photodegradation was occurring in the closed box chamber. The bowl chamber appears to provide the best protection from the influence of direct photodegradation. (c) 2006 Elsevier Ltd. All rights reserved.