Intimate Rendezvous in a Tritrophic Context? Nothing but the Girls for Male Lysiphlebus testaceipes

In insects, mating often occurs after natal dispersal, and hence relies on a coevolved combination of sexual communication and movement allowing mate encounter. Volatile sex pheromones are widespread, generally emitted by females and triggering in‐flight orientation of conspecific males. In parasitoid wasps, unmated females can start laying unfertilized eggs via parthenogenesis so that host patches could serve as sites of rendezvous for mating. Males could therefore use cues associated with host patches to focus their search on females that have successfully found oviposition sites. We hypothesized that in parasitoids exploiting herbivorous hosts, sex pheromones, and herbivore‐induced plant volatiles (HIPV) should act in synergy, triggering male orientation toward ovipositing females. We tested this hypothesis with the aphid parasitoid Lysiphlebus testaceipes. Results from both field and laboratory experiments show that males are strongly attracted to virgin females, but that volatiles from aphid‐infested plants have no effect on male orientation, neither has a cue, nor in interaction with the female sex pheromone. The absence of synergy between sex pheromones and HIPV contrasts with results on other species and raises interesting questions on mating systems and sexual selection in parasitoid wasps.     

鳞翅目蛾类雄性昆虫的信息素

鳞翅目雄性昆虫信息素释放器官结构及分布复杂多样。释放的信息素化学成分及其功能也复杂多样 ,具有种的特异性。求偶、避免种间交配、驱避同种雄性个体和驱避捕食者可能是雄性昆虫信息素的主要功能。性选择、生殖隔离和感觉系统利用是雄性昆虫信息素起源的 3种主要假说 ,而寄主转移和建立者物种形成可能与雄性昆虫信息素消失有关。     

Local adaptation and ecological genetics of host-plant specialization in a leaf beetle

The tendency of insect species to evolve specialization to one or a few plant species is probably a major reason for the remarkable diversity of herbivorous insects. The suggested explanations for this general trend toward specialization include a range of evolutionary mechanisms, whose relative importance is debated. Here we address two potentially important mechanisms: (i) how variation in the geographic distribution of host use may lead to the evolution of local adaptation and specialization; (ii) how selection for specialization may lead to the evolution of trade‐offs in performance between different hosts. We performed a quantitative genetic experiment of larval performance in three different populations of the alpine leaf beetle Oreina elongata reared on two of its main host plants. Due to differences in host availability, each population represents a distinctly different selective regime in terms of host use including selection for specialization on one or the other host as well as selection for utilizing both hosts during the larval stage. The results suggest that selection for specialization has lead to some degree of local adaptations in host use: both single‐host population had higher larval growth rate on their respective native host plant genus, while there was no difference between plant treatments in the two‐host population. However, differences between host plant treatments within populations were generally small and the degree of local adaptation in performance traits seems to be relatively limited. Genetic correlations in performance traits between the hosts ranged from zero in the two‐host population to significantly positive in the single‐host populations. This suggests that selection for specialization in single host populations typically also increased performance on the alternative host that is not naturally encountered. Moreover, the lack of a positive genetic correlation in the two host‐population give support for the hypothesis that performance trade‐offs between two host plants may typically evolve when a population have adapted to both these plants. We conclude that although there is selection for specialization in larval performance traits it seems as if the genetic architecture of these traits have limited the divergence between populations in relative performance on the two hosts.     

Stronger convex (stabilizing) selection on homologous sexual display traits in females than in males: a multipopulation comparison in Drosophila serrata

Mutual mate choice for homologous sexual display traits has been demonstrated in several recent studies yet little attention has been given to quantitative comparison of the strength and form of mate preferences between the sexes. Such comparisons may provide important insight into the evolution of mate choice for honest signals. In particular, because females generally provide the majority of resources for initial offspring development, female displays may trade-off with fecundity, causing preference evolution to differ between the sexes. Recent theory suggests that adaptive male preferences for honest displays in females are possible under certain conditions and may result in preferences that are convex (i.e., stabilizing) in form. We compared sexual selection on a suite of contact pheromones arising from mutual mate choice using nine separate geographic populations of Drosophila serrata. We show that the convex selection is stronger on females than on males overall in these populations, and that convex selection is the predominate form of nonlinear selection on females but not males.     

Aromatized to Find Mates: α-Pinene Aroma Boosts the Mating Success of Adult Olive Fruit Flies

Background

Contrary to other Tephritidae, female but also male olive flies, Bactrocera oleae release pheromones during their sexual communication. Alpha-pinene, a common plant volatile found in high amounts in unripe olive fruit and leaves has been detected as one of the major components of the female pheromone. However, possible effects of α-pinene and that of other host volatiles on the mating behavior of the olive fly have not been investigated.

Methodology

Using wild olive flies, reared on olive fruit for 3 generations in the laboratory, we explored whether exposure of male and female olive flies to α-pinene affects their sexual performance.

Results

Exposure of sexually mature adult olive flies to the aroma of α-pinene significantly increases the mating performance over non-exposed individuals. Interestingly, exposure to α-pinene boosts the mating success of both males and female olive flies.

Conclusions

This is the first report of such an effect on the olive fly, and the first time that a single plant volatile has been reported to induce such a phenomenon on both sexes of a single species. We discuss the possible associated mechanism and provide some practical implications.     

Red Queen dancing in the lek: effects of mating skew on host–parasite interactions

The RQH (Red Queen hypothesis), which argues that hosts need to be continuously finding new ways to avoid parasites that are able to infect common host genotypes, has been at the center of discussions on the maintenance of sex. This is because diversity is favored under the host–parasite coevolution based on negative frequency‐dependent selection, and sexual reproduction is a mechanism that generates genetic diversity in the host population. Together with parasite infections, sexual organisms are usually under sexual selection, which leads to mating skew or mating success biased toward males with a particular phenotype. Thus, strong mating skew would affect genetic variance in a population and should affect the benefit of the RQH. However, most models have investigated the RQH under a random mating system and not under mating skew. In this study, I show that sexual selection and the resultant mating skew may increase parasite load in the hosts. An IBM (individual‐based model), which included host–parasite interactions and sexual selection among hosts, demonstrates that mating skew influenced parasite infection in the hosts under various conditions. Moreover, the IBM showed that the mating skew evolves easily in cases of male–male competition and female mate choice, even though it imposes an increased risk of parasite infection on the hosts. These findings indicated that whether the RQH favored sexual reproduction depended on the condition of mating skew. That is, consideration of the host mating system would provide further understanding of conditions in which the RQH favors sexual reproduction in real organisms.     

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.     

天牛成虫信息素及嗅觉感受机制研究进展

评述了天牛成虫信息素及嗅觉感受机制的研究进展。天牛雌、雄成虫均可释放性信息素,迄今已对31种天牛的性信息素进行了研究,其中完成组分鉴定的有13种。天牛性信息素包括长距离、短距离和接触性信息素3种类型。天牛性信息素存在变异现象,同种天牛分布在不同地区,其性信息素组分之间存在差异。触角是天牛感受性信息素的主要器官,也是判别成虫通讯方式的形态指标,性信息素发达的种类其触角常具显著的性二型现象。天牛利用寄主信息素（如萜烯类、醇类和酯类）寻找寄主。性信息素和寄主信息素在林间复合使用可提高诱捕率。天牛信息素还包括异种信息素、忌避信息素和产卵干扰素,能够提高天牛寄主定位效率。天牛触角嗅觉感受的神经细胞（RNs）有3类,气味信息经神经细胞群传输至中枢神经系统,神经信号按标记路线或交叉纤维样式输导。天牛气味结合蛋白（OBP）方面的研究尚未见报道。     

Artificial neural networks in models of specialization, guild evolution and sympatric speciation

Sympatric speciation can arise as a result of disruptive selection with assortative mating as a pleiotropic by-product. Studies on host choice, employing artificial neural networks as models for the host recognition system in exploiters, illustrate how disruptive selection on host choice coupled with assortative mating can arise as a consequence of selection for specialization. Our studies demonstrate that a generalist exploiter population can evolve into a guild of specialists with an 'ideal free' frequency distribution across hosts. The ideal free distribution arises from variability in host suitability and density-dependent exploiter fitness on different host species. Specialists are less subject to inter-phenotypic competition than generalists and to harmful mutations that are common in generalists exploiting multiple hosts.When host signals used as cues by exploiters coevolve with exploiter recognition systems, our studies show that evolutionary changes may be continuous and cyclic. Selection changes back and forth between specialization and generalization in the exploiters, and weak and strong mimicry in the hosts, where non-defended hosts use the host investing in defence as a model. Thus, host signals and exploiter responses are engaged in a red-queen mimicry process that is ultimately cyclic rather then directional. In one phase, evolving signals of exploitable hosts mimic those of hosts less suitable for exploitation (i.e. the model). Signals in the model hosts also evolve through selection to escape the mimic and its exploiters. Response saturation constraints in the model hosts lead to the mimic hosts finally perfecting its mimicry, after which specialization in the exploiter guild is lost. This loss of exploiter specialization provides an opportunity for the model hosts to escape their mimics. Therefore, this cycle then repeats.We suggest that a species can readily evolve sympatrically when disruptive selection for specialization on hosts is the first step. In a sexual reproduction setting, partial reproductive isolation may first evolve by mate choice being confined to individuals on the same host. Secondly, this disruptive selection will favour assortative mate choice on genotype, thereby leading to increased reproductive isolation.     

Symbiont modifies host life-history traits that affect gene flow

The evolution of herbivore-host plant specialization requires low levels of gene flow between populations on alternate plant species. Accordingly, selection for host plant specialization is most effective when genotypes have minimal exposure to, and few mating opportunities with individuals from, alternate habitats. Maternally transmitted bacterial symbionts are common in insect herbivores and can influence host fecundity under a variety of conditions. Symbiont-mediated effects on host life-history strategies, however, are largely unknown. Here, we show that the facultative bacterial symbiont Candidatus Regiella insecticola strikingly alters both dispersal and mating in the pea aphid, Acyrthosiphon pisum. Pea aphids containing Regiella produced only half the number of winged offspring in response to crowding and, for two out of three aphid lineages, altered the timing of sexual reproduction in response to conditions mimicking seasonal changes, than did aphids lacking Regiella. These symbiont-associated changes in dispersal and mating are likely to have played a key role in the initiation of genetic differentiation and in the evolution of pea aphid-host plant specialization. As symbionts are widespread in insects, symbiont-induced life history changes may have promoted specialization, and potentially speciation, in many organisms.     

叶甲科昆虫的定殖机制

在复杂的生态环境中,叶甲科昆虫利用寄主植物的挥发物作为嗅觉信号,并协同视觉信号共同作用以提高其远距离搜寻和定位寄主的效率。叶甲科昆虫也释放信息素来调节同种或者异种个体的行为反应;找到寄主植物后,叶子的形态学特性和化学组分的浓度等接触性因素就会影响叶甲科昆虫对寄主植物的最终选择。叶甲对上述这些信号物质的反应也受叶甲本身状态的影响,如生殖、滞育、饥饿、交配以及取食等。叶甲科昆虫对寄主植物的搜寻、辨识和接受、取食以及繁殖的过程受一种或多种因素协同影响。从嗅觉、视觉和触觉等方面对叶甲科昆虫的定殖机制做一综述。     

寄主植物-蚜虫-天敌三重营养关系的化学生态学研究进展

综述了寄主植物－蚜虫－天敌三重营养关系的化学生态学研究,重点阐述了3个研究热点：①植物挥发性物质在蚜虫及其天敌选择寄主行为过程中的作用;②蚜虫信息素和蜜露对蚜虫天敌寄主选择行为的影响;③植物挥发性物质对蚜虫信息系作用的影响。对寄主植物－蚜虫－天敌三重营养关系的全面了解,将为蚜虫的综合治疗提供新思维。     

Repellent function of male pheromones in the red-spotted newt

Pheromones act as attractants and sexual stimulants in most vertebrates. For example, in red-spotted newts, Notophthalmus viridescens, female pheromones attract males, and male pheromones increase female receptivity. However, no studies have determined whether male vertebrates produce a pheromone that repels competing males. Through a series of olfactory mate selection tests, we found that sexually motivated male red-spotted newts produce a pheromone that functions to repel other approaching males. Our finding is the first report of a repelling function for pheromones in male vertebrates. The pheromones may act to increase both the sender's and receiver's mating success when the operational sex ratio (OSR) is male biased.     

A failed attempt to demonstrate pheromone communication in archaic moths of the genus Sabatinca Walker (Lepidoptera, Micropterigidae)

Data on pheromones of phylogenetically archaic moths are very scant, despite being needed to understand the life history evolution and phylogeny of the basal lineages of Lepidoptera. Two New Zealand micropterigid moths, Sabatinca (Palaeomicra) chalcophanes Meyr. and Sabatinca (s.str.) demissa Philp., were investigated for pheromone communication. Consistent negative results were demonstrated by (i) behavioural observations, (ii) exposure of blends containing active components of pheromones identified in caddis-flies and archaic moths, (iii) exposure of caged males and females in sticky traps, and (iv) detection of male and female antennal responses to both male and female extracts. Since no data indicated the presence of long-distance sex pheromones in Sabatinca , we concluded that these moths use visual clues to meet sexual partners. The secondary lack of pheromone communication in Micropterigidae suggests a high degree of ecological specialization in this plylogenetically most archaic moth family.     

Parasites physically block host copulation: a potent mechanism of parasite-mediated sexual selection

Research on the role of parasites in sexual selection has focusedmainly on host mate choice favoring relatively unparasitizedmales. But parasites can also generate variance in host reproductivesuccess by influencing the ability of individual hosts to directlycompete among themselves for mates or fertilizations, a subjectarea that has received far less attention. We demonstrate experimentallythat parasitism by mites can drive sexual selection by way ofa novel mechanism involving male competition: physical inhibitionof host copulation. Mite resistance in natural populations isheritable, emphasizing the evolutionary potential of parasite-mediatedsexual selection in this system and indicating that femalesshould be receiving indirect fitness benefits as a result ofthis process. We show that parasitism by mites, Macrochelessubbadius, reduces mating success of male Drosophila nigrospiracula.Smaller males were more strongly compromised, identifying hostbody size as a tolerance trait. As parasite load increased,the rate at which males attempted to copulate but failed becauseof obstruction by mites increased. When mites were removed frominfested males, host mating success was restored. Thus, thephysical presence of the mites per se generates differentialmating success, in this case by interrupting the normal flowof mating behaviors. This study elucidates a potent mechanismof parasite-mediated sexual selection in a system wherein parasiteresistance is demonstrably heritable, and as such expands ourunderstanding of the evolutionary potential of sexual selection.     

Spider sex pheromones: emission, reception, structures, and functions

Spiders and their mating systems are useful study subjects with which to investigate questions of widespread interest about sexual selection, pre- and post-copulatory mate choice, sperm competition, mating strategies, and sexual conflict. Conclusions drawn from such studies are broadly applicable to a range of taxa, but rely on accurate understanding of spider sexual interactions. Extensive behavioural experimentation demonstrates the presence of sex pheromones in many spider species, and recent major advances in the identification of spider sex pheromones merit review. Synthesised here are the emission, transmission, structures, and functions of spider sex pheromones, with emphasis on the crucial and dynamic role of sex pheromones in female and male mating strategies generally. Techniques for behavioural, chemical and electrophysiological study are summarised, and I aim to provide guidelines for incorporating sex pheromones into future studies of spider mating. In the spiders, pheromones are generally emitted by females and received by males, but this pattern is not universal. Female spiders emit cuticular and/or silk-based sex pheromones, which can be airborne or received via contact with chemoreceptors on male pedipalps. Airborne pheromones primarily attract males or elicit male searching behaviour. Contact pheromones stimulate male courtship behaviour and provide specific information about the emitter's identity. Male spiders are generally choosy and are often most attracted to adult virgin females and juvenile females prior to their final moult. This suggests the first male to mate with a female has significant advantages, perhaps due to sperm priority patterns, or mated female disinterest. Both sexes may attempt to control female pheromone emission, and thus dictate the frequency and timing of female mating, reflecting the potentially different costs of female signalling and/or polyandry to both sexes. Spider sex pheromones are likely to be lipids or lipid soluble, may be closely related to primary metabolites, and are not necessarily species specific, although they can still assist with species recognition. Newer electrophysiological techniques coupled with chemical analyses assist with the identification of sex pheromone compounds. This provides opportunities for more targeted behavioural experimentation, perhaps with synthetic pheromones, and for theorising about the biosynthesis and evolution of chemical signals generally. Given the intriguing biology of spiders, and the critical role of chemical signals for spiders and many other animal taxa, a deeper understanding of spider sex pheromones should prove productive.     

Genomewide signatures of selection in Epichloë reveal candidate genes for host specialization

Host specialization is a key process in ecological divergence and speciation of plant‐associated fungi. The underlying determinants of host specialization are generally poorly understood, especially in endophytes, which constitute one of the most abundant components of the plant microbiome. We addressed the genetic basis of host specialization in two sympatric subspecies of grass‐endophytic fungi from the Epichloë typhina complex: subsp. typhina and clarkii. The life cycle of these fungi entails unrestricted dispersal of gametes and sexual reproduction before infection of a new host, implying that the host imposes a selective barrier on viability of the progeny. We aimed to detect genes under divergent selection between subspecies, experiencing restricted gene flow due to adaptation to different hosts. Using pooled whole‐genome sequencing data, we combined F_ST and D_XY population statistics in genome scans and detected 57 outlier genes showing strong differentiation between the two subspecies. Genomewide analyses of nucleotide diversity (π), Tajima's D and dN/dS ratios indicated that these genes have evolved under positive selection. Genes encoding secreted proteins were enriched among the genes showing evidence of positive selection, suggesting that molecular plant–fungus interactions are strong drivers of endophyte divergence. We focused on five genes encoding secreted proteins, which were further sequenced in 28 additional isolates collected across Europe to assess genetic variation in a larger sample size. Signature of positive selection in these isolates and putative identification of pathogenic function supports our findings that these genes represent strong candidates for host specialization determinants in Epichloë endophytes. Our results highlight the role of secreted proteins as key determinants of host specialization.     

Interactions among mechanisms of sexual selection on male body size and head shape in a sexually dimorphic fly

Abstract Darwin envisaged male-male and male-female interactions as mutually supporting mechanisms of sexual selection, in which the best armed males were also the most attractive to females. Although this belief continues to predominate today, it has been challenged by sexual conflict theory, which suggests that divergence in the interests of males and females may result in conflicting sexual selection. This raises the empirical question of how multiple mechanisms of sexual selection interact to shape targeted traits. We investigated sexual selection on male morphology in the sexually dimorphic fly Prochyliza xanthostoma , using indices of male performance in male-male and male-female interactions in laboratory arenas to calculate gradients of direct, linear selection on male body size and an index of head elongation. In male-male combat, the first interaction with a new opponent selected for large body size but reduced head elongation, whereas multiple interactions with the same opponent favored large body size only. In male-female interactions, females preferred males with relatively elongated heads, but male performance of the precopulatory leap favored large body size and, possibly, reduced head elongation. In addition, the amount of sperm transferred (much of which is ingested by females) was an increasing function of both body size and head elongation. Thus, whereas both male-male and male-female interactions favored large male body size, male head shape appeared to be subject to conflicting sexual selection. We argue that conflicting sexual selection may be a common result of divergence in the interests of the sexes.     

Premating isolation is determined by larval rearing substrates in cactophilic Drosophila mojavensis. X. Age‐specific dynamics of adult epicuticular hydrocarbon expression in response to different host plants

Analysis of sexual selection and sexual isolation in Drosophila mojavensis and its relatives has revealed a pervasive role of rearing substrates on adult courtship behavior when flies were reared on fermenting cactus in preadult stages. Here, we assessed expression of contact pheromones comprised of epicuticular hydrocarbons (CHCs) from eclosion to 28 days of age in adults from two populations reared on fermenting tissues of two host cacti over the entire life cycle. Flies were never exposed to laboratory food and showed significant reductions in average CHC amounts consistent with CHCs of wild‐caught flies. Overall, total hydrocarbon amounts increased from eclosion to 14–18 days, well past age at sexual maturity, and then declined in older flies. Most flies did not survive past 4 weeks. Baja California and mainland populations showed significantly different age‐specific CHC profiles where Baja adults showed far less age‐specific changes in CHC expression. Adults from populations reared on the host cactus typically used in nature expressed more CHCs than on the alternate host. MANCOVA with age as the covariate for the first six CHC principal components showed extensive differences in CHC composition due to age, population, cactus, sex, and age × population, age × sex, and age × cactus interactions. Thus, understanding variation in CHC composition as adult D. mojavensis age requires information about population and host plant differences, with potential influences on patterns of mate choice, sexual selection, and sexual isolation, and ultimately how these pheromones are expressed in natural populations. Studies of drosophilid aging in the wild are badly needed.     

Territory defense as a condition‐dependent component of male reproductive success in Drosophila serrata

Sexual selection arises from both intrasexual competition and mate choice. With respect to the evolution of male traits, there is a vast literature documenting the existence of female choice and male–male competition, and both have been shown to co‐occur in many species. Despite numerous studies of these two components of male reproductive success in isolation, few have investigated whether and how they interact to determine total sexual selection. To address this, we investigate male territoriality in Drosophila serrata, a species in which female preference for male sexual pheromones (cuticular hydrocarbons or CHCs) have been extensively studied. We demonstrate that territoriality occurs, that it involves direct male–male aggressive interactions, and that it contributes to variation in male mating success. Results from a phenotypic manipulation also indicate that territorial success is condition‐dependent, although a genetic manipulation of condition, involving three generations of full‐sib inbreeding, failed to find a significant effect. Finally, selection assays also suggest that territorial success depends on male body size but not on CHCs, whereas the opposite is true for mating success.