Selection in the absence of males does not affect male-female conflict in the parasitoid wasp Leptopilina clavipes (Hymenoptera: Figitidae)

Divergent reproductive interests of males and females can lead to sexually antagonistic coevolution (SAC). In the absence of males, adaptations evolved under SAC are released from selection and expected to deteriorate. In this study, we investigated this prediction using two populations of the parasitoid wasp Leptopilina clavipes, one arrhenotokous and one thelytokous. Thelytokous females were induced to produce sons by curing them of their Wolbachia-infection. We examined whether thelytokous males were less able to inhibit female remating than arrhenotokous males and whether thelytokous females were more susceptible to male-induced longevity reduction than arrhenotokous females. The results showed that females were monandrous, regardless of whether mated with an arrhenotokous or thelytokous male. While ongoing courtship of males reduced female life span, there was no longevity cost of mating for either arrhenotokous or thelytokous females. Our results therefore do not support the idea that adaptations evolved under SAC deteriorate under prolonged female-only selection.     

Rising temperature reduces divergence in resource use strategies in coexisting parasitoid species

Coexistence of species sharing the same resources is often possible if species are phylogenetically divergent in resource acquisition and allocation traits, decreasing competition between them. Developmental and life-history traits related to resource use are influenced by environmental conditions such as temperature, but thermal trait responses may differ among species. An increase in ambient temperature may, therefore, affect trait divergence within a community, and potentially species coexistence. Parasitoids are interesting models to test this hypothesis, because multiple species commonly attack the same host, and employ divergent larval and adult host use strategies. In particular, development mode (arrested or continued host growth following parasitism) has been recognized as a major organiser of parasitoid life histories. Here, we used a comparative trait-based approach to determine thermal responses of development time, body mass, egg load, metabolic rate and energy use of the coexisting Drosophila parasitoids Asobara tabida, Leptopilina heterotoma, Trichopria drosophilae and Spalangia erythromera. We compared trait values between species and development modes, and calculated trait divergence in response to temperature, using functional diversity indices. Parasitoids differed in their thermal response for dry mass, metabolic rate and lipid use throughout adult life, but only teneral lipid reserves and egg load were affected by developmental mode. Species-specific trait responses to temperature were probably determined by their adaptations in resource use (e.g. lipogenesis or ectoparasitism). Overall, trait values of parasitoid species converged at the higher temperature. Our results suggest that local effects of warming could affect host resource partitioning by reducing trait diversity in communities.     

The Natural Antimicrobial Carvacrol Inhibits Campylobacter jejuni Motility and Infection of Epithelial Cells

Background

Natural compounds with anti-microbial properties are attractive reagents to reduce the use of conventional antibiotics. Carvacrol, the main constituent of oregano oil, inhibits the growth of a variety of bacterial foodborne pathogens. As concentrations of carvacrol may vary in vivo or when used in animal feed, we here investigated the effect of subinhibitory concentrations of the compound on major virulence traits of the principal bacterial foodborne pathogen Campylobacter jejuni.

Methods/Principal Findings

Motility assays revealed that subinhibitory concentrations of carvacrol inhibited the motility of C. jejuni without affecting bacterial growth. Immunoblotting and electron microscopy showed that carvacrol-treated C. jejuni still expressed flagella. The loss of motility was not caused by reduced intracellular ATP levels. In vitro infection assays demonstrated that subinhibitory concentrations of carvacrol also abolished C. jejuni invasion of human epithelial cells. Bacterial uptake of invasive Escherichia coli was not blocked by carvacrol. Exposure of C. jejuni to carvacrol prior to infection also inhibited cellular infection, indicating that the inhibition of invasion was likely caused by an effect on the bacteria rather than inhibition of epithelial cell function.

Conclusions/Significance

Bacterial motility and invasion of eukaryotic cells are considered key steps in C. jejuni infection. Our results indicate that subinhibitory concentrations of carvacrol effectively block these virulence traits by interfering with flagella function without disturbing intracellular ATP levels. These results broaden the spectrum of anti-microbial activity of carvacrol and support the potential of the compound for use in novel infection prevention strategies.     

Female mating preference functions predict sexual selection against hybrids between sibling species of cichlid fish

The evolutionary outcome of interspecific hybridization, i.e. collapse of species into a hybrid swarm, persistence or even divergence with reinforcement, depends on the balance between gene flow and selection against hybrids. If female mating preferences are open-ended but sign-inversed between species, they can theoretically be a source of such selection. Cichlid fish in African lakes have sustained high rates of speciation despite evidence for widespread hybridization, and sexual selection by female choice has been proposed as important in the origin and maintenance of species boundaries. However, it had never been tested whether hybridizing species have open-ended preference rules. Here we report the first experimental test using Pundamilia pundamilia, Pundamilia nyererei and their hybrids in three-way choice experiments. Hybrid males are phenotypically intermediate. Wild-caught females of both species have strong preferences for conspecific over heterospecific males. Their responses to F1 hybrid males are intermediate, but more similar to responses to conspecifics in one species and more similar to responses to heterospecifics in the other. We suggest that their mate choice mechanism may predispose haplochromine cichlids to maintain and perhaps undergo phenotypic diversification despite hybridization, and that species differences in female preference functions may predict the potential for adaptive trait transfer between hybridizing species.     

Mechanisms of rapid sympatric speciation by sex reversal and sexual selection in cichlid fish

Mechanisms of speciation in cichlid fish were investigated by analyzing population genetic models of sexual selection on sex-determining genes associated with color polymorphisms. The models are based on a combination of laboratory experiments and field observations on the ecology, male and female mating behavior, and inheritance of sex-determination and color polymorphisms. The models explain why sex-reversal genes that change males into females tend to be X-linked and associated with novel colors, using the hypothesis of restricted recombination on the sex chromosomes, as suggested by previous theory on the evolution of recombination. The models reveal multiple pathways for rapid sympatric speciation through the origin of novel color morphs with strong assortative mating that incorporate both sex-reversal and suppressor genes. Despite the lack of geographic isolation or ecological differentiation, the new species coexists with the ancestral species either temporarily or indefinitely. These results may help to explain different patterns and rates of speciation among groups of cichlids, in particular the explosive diversification of rock-dwelling haplochromine cichlids.     

Geographical variation in encapsulation ability ofDrosophila melanogaster larvae and evidence for parasitoid-specific components

Summary The ability ofDrosophila melanogaster larvae in Europe to encapsulate the eggs of their most important parasitoids,Asobara tabida andLeptopilina boulardi, shows a large amount of geographical variation. Interestingly, encapsulation ability againstA. tabida is not correlated with encapsulation ability againstL. boulardi. This indicates that the encapsulation system ofD. melanogaster larvae has parasitoid-specific components. The variation in encapsulation ability can only partly be explained by the incidence of parasitism on the larvae. This means that factors other than the two parasitoid species must be selection pressures on the encapsulation ability ofD. melanogaster larvae.     

Competition between Gyranusoidea tebygi and Anagyrus mangicola, parasitoids of the mango mealybug, Rastrococcus invadens: interspecific host discrimination and larval competition

The competition between Gyranusoidea tebygi Noyes and Anagyrus mangicola Noyes (both Hymenoptera: Encyrtidae), exotic parasitoids of the mango mealybug, Rastrococcus invadens Williams (Homoptera: Pseudococcidae) was studied in the laboratory. No significant differences were found in the way each parasitoid species examined, attacked, stung, and oviposited into hosts, unparasitized, or previously parasitized by the other species. This suggests that neither species discriminates against each other. The total number of parasitoids of either species emerging did not significantly differ between competition experiments. When A. mangicola was the first parasitoid to attack a host, it had no significant advantage over G. tebygi. However, when A. mangicola followed G. tebygi by either 4 or 24 h, it clearly won. Overall A. mangicola won the competition in 70.9% of all cases. The level of the competition, either at the egg or larval stage, and factors responsible for the elimination of older larvae by younger ones could not be assessed in these experiments. The coexistence of the two parasitoids as complementary for the biological control of the mango mealybug is discussed.     

Sex allocation in Epidinocarsis lopezi: local mate competition

Epidinocarsis lopezi is used as a biological control agent against the cassava mealybug, Phenacoccus manihoti, a serious pest of cassava in Africa. The efficiency of parasitoid mass-rearing is maximized when maximum numbers of healthy female wasps are obtained, since only female parasitoids attack the mealybugs.Highly variable sex ratios are often found in parasitic Hymenoptera. Local mate competition (LMC) is one of the evolutionary models which provide predictions about sex allocation. In this paper we show that E. lopezi does not respond to parasitoid density with a change in sex ratio. We also show that in the field, no local mating structure exists, and that mating is random. Therefore, a shift in sex ratio in response to parasitoid density as predicted by LMC theory would not be adaptive. E. lopezi also does not change its sex allocation when ovipositing in already parasitized hosts. Hence host-size distribution and differential mortality are the only factors that can influence sex ratio in mass-rearings.

---

Résumé E. lopezi est utilisé dans la lutte biologique contre Phenacoccus manihoti, important ravageur du manioc en Afrique. Puisque seules les femelles du parasitoïde attaquent la cochenille, l'efficacité de l'élevage de masse de l'entomophage sera optimale quand le maximum de femelles saines sera obtenu.Les rapports des sexes des hyménoptères parasites varient très souvent. La compétition sexuelle locale (LMC) constitue l'un des modèles qui fournissent des prédictions de la distribution des sexes. Cette note montre que la proportion des sexes de E. lopezi n'est pas modifiée par la densité du parasitoïde. Par ailleurs, les accouplements s'effectuent au hasard dans la nature et il n'y a pas de structure locale d'accouplement. Par conséquent, le biais, prévu par la théorie du LMC, et introduit par la densité du parasitoïde dans la distribution des sexes, n'a pas de valeur adaptative. E. lopezi ne modifie pas non plus la distribution du sexe de ses descendants quant il pond dans de hôtes déjà parasités. Ainsi, la répartition en taille des hôtes et la mortalité différentielle sont les seuls facteurs qui influent sur la proportion des sexes dans les élevages de masse.

     

Antigenic sites on porin of Haemophilus influenzae type b: mapping with synthetic peptides and evaluation of structure predictions.

The major surface-located protein in the outer membrane of Haemophilus influenzae type b (Hib) is porin, molecular mass, 38 kDa, 341 amino acids. To define precisely the molecular reactivities of nine mouse monoclonal antibodies (MAbs) against Hib porin, overlapping hexapeptides corresponding to the entire sequence of porin were synthesized. The epitopes recognized by the MAbs were mapped by enzyme-linked immunosorbent assay to stretches of 6 to 11 amino acids. Antigenic sites between amino acids 112 and 126, 148 and 153, 162 and 172, and 318 and 325 were identified. The antigenic sites between amino acids 162 and 172 and between amino acids 318 and 325 were determined by flow cytometry to be on the bacterial cell surface. Four MAbs, POR.2, POR.3, POR.4, and POR.5, that react with amino acids 162 to 172 were able to discriminate among porins from the three major outer membrane protein subtypes of Hib, i.e., 1H, 2L, and 6U. A model for the topological organization of Hib porin was created by calculating the hydrophobicity, amphiphilicity, and turn propensity in its amino acid sequence. Determination of the molecular reactivities of the anti-Hib porin MAbs provided substantive evidence for the orientation of selected regions of porin in the outer membrane of Hib.