Garlic Revisited: Antimicrobial Activity of Allicin-Containing Garlic Extracts against Burkholderia cepacia Complex

The antimicrobial activities of garlic and other plant alliums are primarily based on allicin, a thiosulphinate present in crushed garlic bulbs. We set out to determine if pure allicin and aqueous garlic extracts (AGE) exhibit antimicrobial properties against the Burkholderia cepacia complex (Bcc), the major bacterial phytopathogen for alliums and an intrinsically multiresistant and life-threatening human pathogen. We prepared an AGE from commercial garlic bulbs and used HPLC to quantify the amount of allicin therein using an aqueous allicin standard (AAS). Initially we determined the minimum inhibitory concentrations (MICs) of the AGE against 38 Bcc isolates; these MICs ranged from 0.5 to 3% (v/v). The antimicrobial activity of pure allicin (AAS) was confirmed by MIC and minimum bactericidal concentration (MBC) assays against a smaller panel of five Bcc isolates; these included three representative strains of the most clinically important species, B. cenocepacia. Time kill assays, in the presence of ten times MIC, showed that the bactericidal activity of AGE and AAS against B. cenocepacia C6433 correlated with the concentration of allicin. We also used protein mass spectrometry analysis to begin to investigate the possible molecular mechanisms of allicin with a recombinant form of a thiol-dependent peroxiredoxin (BCP, Prx) from B. cenocepacia. This revealed that AAS and AGE modifies an essential BCP catalytic cysteine residue and suggests a role for allicin as a general electrophilic reagent that targets protein thiols. To our knowledge, we report the first evidence that allicin and allicin-containing garlic extracts possess inhibitory and bactericidal activities against the Bcc. Present therapeutic options against these life-threatening pathogens are limited; thus, allicin-containing compounds merit investigation as adjuncts to existing antibiotics.     

The evolution of phenotypes and genetic parameters under preferential mating

This article extends and adds more realism to Lande's analytical model for evolution under mate choice by using individual‐based simulations in which females sample a finite number of males and the genetic architecture of the preference and preferred trait evolves. The simulations show that the equilibrium heritabilities of the preference and preferred trait and the genetic correlation between them (r_G), depend critically on aspects of the mating system (the preference function, mode of mate choice, choosiness, and number of potential mates sampled), the presence or absence of natural selection on the preferred trait, and the initial genetic parameters. Under some parameter combinations, preferential mating increased the heritability of the preferred trait, providing a possible resolution for the lek paradox. The Kirkpatrick–Barton approximation for r_G proved to be biased downward, but the realized genetic correlations were also low, generally <0.2. Such low values of r_G indicate that coevolution of the preference and preferred trait is likely to be very slow and subject to significant stochastic variation. Lande's model accurately predicted the incidence of runaway selection in the simulations, except where preferences were relative and the preferred trait was subject to natural selection. In these cases, runaways were over‐ or underestimated, depending on the number of males sampled. We conclude that rapid coevolution of preferences and preferred traits is unlikely in natural populations, but that the parameter combinations most conducive to it are most likely to occur in lekking species.     

Sex‐specific selection and sexual size dimorphism in the waterstrider Aquarius remigis

We estimated selection on adult body size for two generations in two populations of Aquarius remigis, as part of a long‐term study of the adaptive significance of sexual size dimorphism (SSD). Net adult fitness was estimated from the following components: prereproductive survival, daily reproductive success (mating frequency or fecundity), and reproductive lifespan. Standardized selection gradients were estimated for total length and for thorax, abdomen, genital and mesofemur lengths. Although selection was generally weak and showed significant temporal and spatial heterogeneity, patterns were consistent with SSD. Prereproductive survival was strongly influenced by date of eclosion, but size (thorax and genital lengths in females; total and abdomen lengths in males) played a significant secondary role. Sexual selection favoured smaller males with longer external genitalia in one population. Net adult fitness was not significantly related to body size in females, but was negatively related to size (thorax and total length) in males.     

GENETIC CORRELATIONS AMONG TRAITS DETERMINING MIGRATORY TENDENCY IN THE SAND CRICKET,GRYLLUS FIRMUS

Migration by flight is an important component of the life cycles of most insects. The probability that a given insect will migrate by flight is influenced by many factors, most notably the presence or absence of fully-developed wings and functional flight musculature. Considerable variation has also been reported in the flight propensity of fully-winged individuals with functional flight musculature. We test the hypothesis that these components of migratory tendency are genetically correlated in a wing-dimorhic cricket, Gryllus firmus. Flight propensity and condition of the dorsal longitudinal flight muscles (DLM) are examined in fully-winged (LW) crickets from lines selected for increasing and for decreasing %LW, as well as from unselected control lines. Increased %LW is found to be associated with increased flight propensity among individuals with intact DLM, and with retention of functional DLM. The opposite is true for lines selected for decreased %LW. These results indicate both phenotypic and genetic correlations among behavioral, physiological, and morphological traits determining migratory tendency. We propose that these correlations may result from the multifunctional role of juvenile hormone, which has been reported to influence wing development, flight muscle development and degeneration, and flight propensity. Finally, we discuss the potential influence of genetic correlations for migratory traits on the evolution and maintenance of migratory polymorphisms in insects.     

SEXUAL SELECTION AND THE EVOLUTION OF SEXUAL SIZE DIMORPHISM IN THE WATER STRIDER,AQUARIUS REMIGIS

Sexual size dimorphism (SSD) is often attributed to sexual selection, particularly when males are the larger sex. However, sexual selection favoring large males is common even in taxa where females are the larger sex, and is therefore not a sufficient explanation of patterns of SSD. As part of a more extensive study of the evolution of SSD in water striders (Heteroptera, Gerridae), we examine patterns of sexual selection and SSD in 12 populations of Aquarius remigis. We calculate univariate and multivariate selection gradients from samples of mating and single males, for two sexually dimorphic traits (total length and profemoral width) and two sexually monomorphic traits (mesofemoral length and wing form). The multivariate analyses reveal strong selection favoring larger males, in spite of the female-biased SSD for this trait, and weaker selection favoring aptery and reduced mesofemoral length. Selection is weakest on the most dimorphic trait, profemoral width, and is stabilizing rather than directional. The pattern of sexual selection on morphological traits is therefore not concordant with the pattern of SSD. The univariate selection gradients reveal little net selection (direct + indirect) on any of the traits, and suggest that evolution away from the plesiomorphic pattern of SSD is constrained by antagonistic patterns of selection acting on this suite of positively correlated morphological traits. We hypothesize that SSD in A. remigis is not in equilibrium, a hypothesis that is consistent with both theoretical models of the evolution of SSD and our previous studies of allometry for SSD. A negative interpopulation correlation between the intensity of sexual selection and the operational sex ratio supports the hypothesis that, as in several other water strider species, sexual selection in A. remigis occurs through generalized female reluctance rather than active female choice. The implications of this for patterns of sexual selection are discussed.     

Body size and fecundity in the waterstrider Aquarius remigis: a test of Darwin's fecundity advantage hypothesis

The general female bias in body size of animals is usually attributed to fecundity selection. While many studies have demonstrated a positive relationship between body size and fecundity, the most common interpretation of fecundity selection is that larger females have larger abdomens and can hold more eggs, yet the relationship between abdomen size and fecundity has rarely been examined. For the waterstrider, Aquarius remigis, we find a significant relationship between body size and fecundity and demonstrate that the target of fecundity selection is abdomen size. Thus, larger females have higher fecundities because they have larger abdomens and not because of their total size per se. The rate at which fecundity increases with increasing abdomen size exceeds that which would be expected due to a simple volume constraint and suggests that other factors, such as increased ability to obtain resources, may contribute to the increase in fecundity with body size. Selection intensities estimated from our data indicate that fecundity selection could be a significant selective force on both total and abdomen lengths. Previous studies have found that abdomen size increased faster than body size and thus, larger females had relatively larger abdomens. The relationship of abdomen length and thorax length in A. remigis is hypoallometric and indicates that larger females have relatively smaller abdomens. We hypothesize that this may reflect conservation of abdomen size in females developing under poor conditions. Finally, while egg size is not directly related to body size, we find a trade-off between egg size and number when female abdomen length is held constant, suggesting that selection on egg size may influence abdomen length only indirectly through its effects on fecundity.     

Cloning of the murine homolog of the leukemia-associated PML gene

PML, a Ring-finger protein, participates in the disruption of normal myeloid differentiation when fused to the retinoic acid receptor alpha (RAR) by the translocation between Chromosomes (Chrs) 15 and 17 in acute promyelocytic leukemia (APL). As an initial step in the characterization of PML in species other than human, a murine cDNA clone of the PML gene was isolated and sequenced, and the intron/exon organization of the murine locus determined. The predicted amino acid sequence of the mouse PML protein shows 80% similarity to that of its human homolog. However, the mouse and human proteins show greater than 90% similarity in the proposed functional domains of the proteins. Despite its role in the etiology of APL, PML expression is not detectably altered during granulocytic differentiation in a murine in vitro system. Chromosomal localization of the Pml locus by somatic cell hybrids and by linkage analysis indicates that the gene maps to a region of mouse Chr 9 with known linkage homology to the region on human Chr 15q to which PML has been localized.