Host genetics and pathogen species modulate infection-induced changes in social aggregation behaviour

Identifying how infection modifies host behaviours that determine social contact networks is important for understanding heterogeneity in infectious disease dynamics. Here, we investigate whether group social behaviour is modified during bacterial infection in fruit flies (Drosophila melanogaster) according to pathogen species, infectious dose, host genetic background and sex. In one experiment, we find that systemic infection with four different bacterial species results in a reduction in the mean pairwise distance within infected female flies, and that the extent of this change depends on pathogen species. However, susceptible flies did not show any evidence of avoidance in the presence of infected flies. In a separate experiment, we observed genetic- and sex-based variation in social aggregation within infected, same-sex groups, with infected female flies aggregating more closely than infected males. In general, our results confirm that bacterial infection induces changes in fruit fly behaviour across a range of pathogen species, but also highlight that these effects vary between fly genetic backgrounds and can be sex-specific. We discuss possible explanations for sex differences in social aggregation and their consequences for individual variation in pathogen transmission.     

Cooperation between Drosophila flies in searching behavior

In Drosophila melanogaster food search behaviour, groups of flies swarm around and aggregate on patches of food. We wondered whether flies explore their environment in a cooperative way as interactions between individual flies within a population might influence the flies' ability to locate food sources. We have shown that the food search behavior in the fruit fly Drosophila is a two-step process. Firstly, 'primer' flies search the environment and randomly land on different food patches. Secondly, the remaining group of flies move to the most favorable food source and aggregate there. We call this a 'search–aggregation' cycle. Our data demonstrate that flies do not individually assess all available food resources. Rather, social interactions between flies appear to affect their choice of a specific food patch. A genetic analysis of this 'search–aggregation' behavior shows that flies carrying mutations in specific genes (for example, the dunce ( dnc ) gene which codes for a phosphodiesterase) were defective in this search–aggregation behavior when compared to normal flies. Future investigations of the neuronal signaling involved in this behavior will help us to understand the complexities of this aspect of Drosophila social behaviour.     

A New Chamber for Studying the Behavior of Drosophila

Methods available for quickly and objectively quantifying the behavioral phenotypes of the fruit fly, Drosophila melanogaster, lag behind in sophistication the tools developed for manipulating their genotypes. We have developed a simple, easy-to-replicate, general-purpose experimental chamber for studying the ground-based behaviors of fruit flies. The major innovative feature of our design is that it restricts flies to a shallow volume of space, forcing all behavioral interactions to take place within a monolayer of individuals. The design lessens the frequency that flies occlude or obscure each other, limits the variability in their appearance, and promotes a greater number of flies to move throughout the center of the chamber, thereby increasing the frequency of their interactions. The new chamber design improves the quality of data collected by digital video and was conceived and designed to complement automated machine vision methodologies for studying behavior. Novel and improved methodologies for better quantifying the complex behavioral phenotypes of Drosophila will facilitate studies related to human disease and fundamental questions of behavioral neuroscience.     

The genetic basis for fruit odor discrimination in Rhagoletis flies and its significance for sympatric host shifts

Rhagoletis pomonella (Diptera: Tephritidae) use volatile compounds emitted from the surface of ripening fruit as important chemosensory cues for recognizing and distinguishing among alternative host plants. Host choice is of evolutionary significance in Rhagoletis because these flies mate on or near the fruit of their respective host plants. Differences in host choice based on fruit odor discrimination therefore result in differential mate choice and prezygotic reproductive isolation, facilitating sympatric speciation in the absence of geographic isolation. We test for a genetic basis for host fruit odor discrimination through an analysis of F2 and backcross hybrids constructed between apple-, hawthorn-, and flowering dogwood-infesting Rhagoletis flies. We recovered a significant proportion (30-65%) of parental apple, hawthorn, and dogwood fly response phenotypes in F2 hybrids, despite the general failure of F1 hybrids to reach odor source spheres. Segregation patterns in F2 and backcross hybrids suggest that only a modest number of allelic differences at a few loci may underlie host fruit odor discrimination. In addition, a strong bias was observed for F2 and backcross flies to orient to the natal fruit blend of their maternal grandmother, implying the existence of cytonuclear gene interactions. We explore the implications of our findings for the evolutionary dynamics of sympatric host race formation and speciation.     

Circadian Dysfunction Reduces Lifespan in Drosophila melanogaster

Circadian clocks regulate physiological and behavioral processes in a wide variety of organisms, and any malfunction in these clocks can cause significant health problems. In this paper, we report the results of our study on the physiological consequences of circadian dysfunction (malfunctioning of circadian clocks) in two wild‐type populations of fruit flies (Drosophila melanogaster). We assayed locomotor activity behavior and lifespan among adult flies kept under constant dark (DD) conditions of the laboratory, wherein they were categorized as rhythmic if their activity/rest schedules followed circadian (approximately 24 h) patterns, and as arrhythmic if their activity/rest schedules did not display any pattern. The rhythmic flies from both populations lived significantly longer than the arrhythmic ones. Based on these results, we conclude that circadian dysfunction is deleterious, and proper functioning of circadian clocks is essential for the physiological well being of D. melanogaster.     

Circadian dysfunction reduces lifespan in Drosophila melanogaster

Circadian clocks regulate physiological and behavioral processes in a wide variety of organisms, and any malfunction in these clocks can cause significant health problems. In this paper, we report the results of our study on the physiological consequences of circadian dysfunction (malfunctioning of circadian clocks) in two wild-type populations of fruit flies (Drosophila melanogaster). We assayed locomotor activity behavior and lifespan among adult flies kept under constant dark (DD) conditions of the laboratory, wherein they were categorized as rhythmic if their activity/rest schedules followed circadian (approximately 24 h) patterns, and as arrhythmic if their activity/rest schedules did not display any pattern. The rhythmic flies from both populations lived significantly longer than the arrhythmic ones. Based on these results, we conclude that circadian dysfunction is deleterious, and proper functioning of circadian clocks is essential for the physiological well being of D. melanogaster.     

Evolution of mutualism between globeflowers and their pollinating flies

Plant/seed-eater pollinators mutualisms involve a plant pollinated by an insect whose larvae develop by eating a fraction of host-plant seeds. The outcome of the interaction therefore depends on the number of ovules fertilized by adult visits and the number of seeds destroyed by larvae. Among the very few cases of such mutualisms reported so far is the globeflower-globeflower flies mutualism, which is unique in that it involves several congeneric fly species (Chiastocheta genus) coexisting within a single host-plant species, Trollius europaeus. These species exhibit contrasted oviposition behaviors resulting in a more or less beneficial outcome for the plant. We designed an adaptive dynamics model to investigate how morphological traits of globeflower could affect the evolution of oviposition in its pollinating flies. Three fly traits (flower age at oviposition, clutch size and the level of avoidance of already parasitized flowers) and one plant trait (closed or open corolla) were examined. Whatever the shape of the flower, evolutionary branching occurs between early and late ovipositing flies, driven by strong competition among larvae within a fruit. Once this branching occurred, the closed shape of the corolla is likely to offer a better protection to eggs of early but not of late ovipositing flies. The difference in egg survival results in higher competition among early larvae and thus selects for decreased clutch size in early flies. This can be seen as a first step in the evolution of a mutualistic behavior. The prediction of our model fits field observations of fly behavior, giving theoretical support to the hypothesis of fly sympatric speciation within its host plant. Moreover, flower closed globe shape can be positively selected in globeflowers as it results in a reduction of parasitism strength. This last evolution therefore leads to a stable mutualism between globeflowers and globeflower flies.     

Variability in response specificity of apple, hawthorn, and flowering dogwood-infesting Rhagoletis flies to host fruit volatile blends: implications for sympatric host shifts

Rhagoletis pomonella Walsh (Diptera: Tephritidae) originating from domesticated apple (Malus pumila), hawthorn (Crataegus mollis) (Rosaceae), and flowering dogwood (Cornus florida) (Cornaceae) were tested sequentially in flight‐tunnel assays to volatile blends previously identified from the three fruit types. The majority of flies flew to odor sources containing their natal blend (68–83%). Some flies from each fruit type also flew to non‐natal fruit blends (11–39%), but of these non‐natal responders the vast majority were flies that responded to their natal blend as well. The results indicate that individual flies within R. pomonella populations infesting different host types have different degrees of specificity with respect to discriminating among fruit volatile blends, and that a moderate proportion of apple, hawthorn, and dogwood flies (10–30%) are broad responders, with the capacity to recognize and orient to more than one blend. The observed variability in response specificity could facilitate sympatric shifts to new host plants.     

中国重要检疫性实蝇的全球分布和入侵情况

实蝇是重要的蔬菜瓜果害虫。本文重点概述入侵中国实蝇的寄主植物、原产地、首次发现时间、入侵地、国内外分布和入侵扩散途径,全面整理重要检疫性实蝇的全球分布和入侵情况,同时根据全球重要检疫性实蝇的分布情况为警惕和预防实蝇入侵我国提供理论支持。本文指出,领土相邻是实蝇入侵我国的重要条件：入侵中国的实蝇原产地是中国的邻国日本、印度和泰国,最早发现地是中国的沿海和沿边地区,分别为中国台湾、广西、云南和新疆吐鲁番。寄主植物的种类数量与实蝇的分布范围正相关：橘小实蝇和瓜实蝇是多食性昆虫,分别危害305和61种植物,分别在全球83和58个国家均有发生。枣实蝇、蜜柑大实蝇和黑颜面实蝇是寡食性昆虫,只危害同属植物,仅入侵原产地周边的些许国家。随着国际瓜果贸易交流频繁,全球重要的检疫实蝇由原产地国家逐渐向周边国家扩散,其中油橄榄实蝇、桃果实蝇、埃塞尔比亚寡鬓实蝇、黑樱桃实蝇和苹果实蝇已经入侵至我国周边国家,需要警惕和预防其从沿边省份入侵我国。加强检疫和管理是防治实蝇入侵和扩散的重要手段,同时也需要中国的科研工作者进一步对世界上重大检疫实蝇的入侵风险评估、防控对策、分子鉴定和快速检测方法进行研究。     

The Value of Patch-Choice Copying in Fruit Flies

Many animals copy the choices of others but the functional and mechanistic explanations for copying are still not fully resolved. We relied on novel behavioral protocols to quantify the value of patch-choice copying in fruit flies. In a titration experiment, we quantified how much nutritional value females were willing to trade for laying eggs on patches already occupied by larvae (social patches). Females were highly sensitive to nutritional quality, which was positively associated with their offspring success. Females, however, perceived social, low-nutrition patches (33% of the nutrients) as equally valuable as non-social, high-nutrition ones (100% of the nutrients). In follow-up experiments, we could not, however, either find informational benefits from copying others or detect what females'' offspring may gain from developing with older larvae. Because patch-choice copying in fruit flies is a robust phenomenon in spite of potential costs due to competition, we suggest that it is beneficial in natural settings, where fruit flies encounter complex dynamics of microbial communities, which include, in addition to the preferred yeast species they feed on, numerous harmful fungi and bacteria. We suggest that microbial ecology underlies many cases of copying in nature.     

Genetic differentiation associated with host plants and geography among six widespread species of South American Blepharoneura fruit flies (Tephritidae)

Tropical herbivorous insects are astonishingly diverse, and many are highly host‐specific. Much evidence suggests that herbivorous insect diversity is a function of host plant diversity; yet, the diversity of some lineages exceeds the diversity of plants. Although most species of herbivorous fruit flies in the Neotropical genus Blepharoneura are strongly host‐specific (they deposit their eggs in a single host plant species and flower sex), some species are collected from multiple hosts or flowers and these may represent examples of lineages that are diversifying via changes in host use. Here, we investigate patterns of diversification within six geographically widespread Blepharoneura species that have been collected and reared from at least two host plant species or host plant parts. We use microsatellites to (1) test for evidence of local genetic differentiation associated with different sympatric hosts (different plant species or flower sexes) and (2) examine geographic patterns of genetic differentiation across multiple South American collection sites. In four of the six fly species, we find evidence of local genetic differences between flies collected from different hosts. All six species show evidence of geographic structure, with consistent differences between flies collected in the Guiana Shield and flies collected in Amazonia. Continent‐wide analyses reveal – in all but one instance – that genetically differentiated flies collected in sympatry from different host species or different sex flowers are not one another's closest relatives, indicating that genetic differences often arise in allopatry before, or at least coincident with, the evolution of novel host use.     

Robustness of Circadian Timing Systems Evolves in the Fruit Fly Drosophila melanogaster as a Correlated Response to Selection for Adult Emergence in a Narrow Window of Time

Robustness is a fundamental property of biological timing systems that is likely to ensure their efficient functioning under a wide range of environmental conditions. Here we report the findings of our study aimed at examining robustness of circadian clocks in fruit fly Drosophila melanogaster populations selected to emerge as adults within a narrow window of time. Previously, we have reported that such flies display enhanced synchrony, accuracy, and precision in their adult emergence and activity/rest rhythms. Since it is expected that accurate and precise circadian clocks may confer enhanced stability in circadian time-keeping, we decided to examine robustness in circadian rhythms of flies from the selected populations by subjecting them to a variety of environmental conditions comprising of a range of photoperiods, light intensities, ambient temperatures, and constant darkness. The results revealed that adult emergence and activity/rest rhythms of flies from the selected stocks were more robust than controls, as they displayed enhanced stability under a wide variety of environmental conditions. These results suggest that selection for adult emergence within a narrow window of time results in the evolution of robustness in circadian timing systems of the fruit fly D. melanogaster. (Author correspondence: vsharma@jncasr.ac.in or vksharmas@gmail.com)     

Phortica variegata as an intermediate host of Thelazia callipaeda under natural conditions: evidence for pathogen transmission by a male arthropod vector

Knowledge about Phortica variegata (Drosophilidae, Steganinae), the intermediate host of the eyeworm Thelazia callipaeda (Spirurida, Thelaziidae), is confined to experimental studies. To investigate the role P. variegata plays in the transmission of T. callipaeda under natural conditions, the population dynamics of these flies in the natural environment and their feeding preferences (on vegetables and/or animal lachrymal secretions) were examined. From April to November 2005, a total number of 969 (557 males and 412 females) P. variegata flies were collected weekly in a region of southern Italy with a history of canine thelaziosis. The flies were identified and dissected or subjected to a PCR assay specific for a region within the ribosomal ITS-1 DNA of T. callipaeda. The zoophilic preferences of P. variegata were assessed by collecting flies around the eyes of a person or around a fruit bait. Seven hundred and twenty flies (398 males and 322 females) were dissected under a stereomicroscope; 249 flies (158 males and 91 females) that died prior to the dissection were subjected to molecular investigation. Only P. variegata males were infected with larval T. callipaeda both at dissection (six, 0.83%) and with the specific PCR (seven, 2.81%), representing a total percentage of 1.34% flies infected. Interestingly, only males were collected around the eyes, compared with a male/female ratio of 1:4 around the fruit. This survey indicated that P. variegata males act as intermediate hosts of T. callipaeda under natural conditions in Europe. Both the zoophilic behaviour of P. variegata males on lachrymal secretions and their role as vector of T. callipaeda have been discussed as they represent a peculiarity in medical and veterinary entomology. The synchrony between the fly population dynamics and the biology of the nematode in the definitive host provides an interesting model for exploring the co-evolution of Thelazia spp. with their hosts.     

Habitat degradation and introduction of exotic plants favor persistence of invasive species and population growth of native polyphagous fruit fly pests in a Northwestern Argentinean mosaic

Expansion of agricultural land is one of the most significant human alterations to the global environment because it entails not only native habitat loss but also introduction of exotic species. These alterations affect habitat structure and arthropod dynamics, such as those among host plants, tephritid fruit flies, and their natural enemies. We compared abundance and dynamics of pest and non-pest tephritids and their natural enemies over a mosaic of habitats differing in structure, diversity and disturbance history on the Sierra de San Javier in Tucuman, Argentina. Our prediction was that conserved habitats would be more resistant to the establishment and spread of invasive tephritid species due in part to a greater abundance of natural enemies, a greater diversity of native species in the same family and trophic level, and a greater wealth of biotic interactions. We further predicted that native species with broad host ranges should be more sensitive to habitat loss yet more competitive in less disturbed habitats than generalist native and exotic species. We found that environmental degradation, and introduction and spread of exotic host plants strongly affected distribution patterns, abundance, and phenology of native and exotic tephritids. Monophagous tephritid species and several specialized parasitoids were more sensitive to habitat loss than polyphagous species and parasitoids exhibiting a wide host range. In contrast, native monophagous species and native parasitoids appeared to exclude the invasive Mediterranean fruit fly from conserved patches of native vegetation. Nevertheless, the Mediterranean fruit fly persisted in uncontested exotic host plants and thrived in highly degradeted urban landscapes.     

基于荧光标记的怒江流域桔小实蝇 (Bactrocera dorsalis)的迁移扩散

2005年7月在云南怒江流域地区,以荧光粉作为标记物,采用“标记-释放-回收”方法,对怒江流域桔小实蝇迁移扩散规律进行了研究。以释放点潞江坝为中心,东南西北4个方位设立桔小实蝇回收点,经过7d的回捕,从释放点沿潞江以北至六库沿线共回收到的标记桔小实蝇43头,最远在距释放点以北97km的地方回收到标记桔小实蝇5头。沿怒江在释放点以南,仅在小于29km的范围内回收到标记桔小实蝇17头。释放点东面和西面未能回收到标记桔小实蝇。分析释放点以北各回收点标记桔小实蝇与非标记桔小实蝇的相互关系揭示,非标记桔小实蝇与标记桔小实蝇在空间动态中具有相同的行为模式,由此推论非标记桔小实蝇与标记桔小实蝇可能来自同一种群。分析怒江流域区的自然地理发现,潞江坝桔小实蝇可借助怒江两边高大山脉形成的天然河谷通道,在适宜的气候条件下,在北上气流的携带下,实现由南向北的远距离迁移扩散;同时,由于高大山脉的阻隔,使潞江坝桔小实蝇没能向东西两个方向作远距离扩散迁移。研究首次揭示了在特定峡谷地区桔小实蝇扩散迁移现象,为桔小实蝇迁移扩散研究提供了新鲜实例,为在当地制定切实有效的桔小实蝇防治策略提供了基础信息。     

Incipient sexual isolation among cosmopolitan Drosophila melanogaster populations

Understanding the biological conditions and the genetic basis of early stages of sexual isolation and speciation is an outstanding question in evolutionary biology. It is unclear how much genetic and phenotypic variation for mating preferences and their phenotypic cues is segregating within widespread and human-commensal species in nature. A recent case of incipient sexual isolation between Zimbabwe and cosmopolitan populations of the human-commensal fruit fly Drosophila melanogaster indicates that such species may initiate the process of sexual isolation. However, it is still unknown whether other geographical populations have undergone evolution of mating preferences. In this study we present new data on multiple-choice mating tests revealing partial sexual isolation between the United States and Caribbean populations. We relate our findings to African populations, showing that Caribbean flies are partially sexually isolated from Zimbabwe flies, but mate randomly with West African flies, which also show partial sexual isolation from the United States and Zimbabwe flies. Thus, Caribbean and West African populations seem to exhibit distinct mating preferences relative to populations in the United States and in Zimbabwe. These results suggest that widespread and human-commensal species may harbor different types of mating preferences across their geographical ranges.     

Sterols as dietary markers for Drosophila melanogaster

During cold acclimation fruit flies switch their feeding from yeast to plant food, however there are no robust molecular markers to monitor this in the wild. Drosophila melanogaster is a sterol auxotroph and relies on dietary sterols to produce lipid membranes, lipoproteins and molting hormones. We employed shotgun lipidomics to quantify eight major food sterols in total lipid extracts of heads and genital tracts of adult male and female flies. We found that their sterol composition is dynamic and reflective of fly diet in an organ-specific manner. Season-dependent changes observed in the organs of wild-living flies suggested that the molar ratio between yeast (ergosterol, zymosterol) and plant (sitosterol, stigmasterol) sterols is a quantifiable, generic and unequivocal marker of their feeding behavior suitable for ecological and environmental population-based studies. The enrichment of phytosterols over yeast sterols in wild-living flies at low temperatures is consistent with switching from yeast to plant diet and corroborates the concomitantly increased unsaturation of their membrane lipids.     

黄河三角洲柽柳的开花特性及传粉生态学研究

野外定位观测了柽柳(TamarixchinensisLour.)的开花物侯、开花动态、访花者的种类、行为和访花频率,并对其繁育系统、花粉-胚珠比(P/O)、花粉活力进行了检测。结果表明,柽柳单朵花的花期仅1d,P/O为390.9±81.0,繁育系统属于自交亲和、需要传粉者的类型。花的结构和开花式样适合以食蚜蝇为主的多种昆虫传粉。自然条件下的结实率为95.23%。柽柳的果实成熟期较短(15d),整个居群有长达几个月的花期,开花数目众多,因此能产生大量的种子,在适宜条件下会形成大片的柽柳灌丛。     

Prior experience influences the fruit residence of male apple maggot flies,Rhagoletis pomonella

Male apple maggot flies spend considerable time residing on individual host fruit as territories on which they force-copulate arriving females in search of oviposition sites. Here, we present evidence from investigations in nature and the laboratory that shows the propensity of males to reside on a hawthorn or apple fruit as a territory is significantly modifiable through prior experience with fruit and, hence, involves learning. Previous studies revealed that after a female apple maggot fly, Rhagoletis pomonella, arrived on a host hawthorn or apple fruit, its propensity to accept or reject that fruit for egg-laying was similarly modifiable through prior fruit-exposure experience and also involved learning. We discuss how host fruit learning in males and females, in concert with genetic-based differences in host fruit residence and acceptance behavior between populations of flies originating from hawthorn and apple, could give rise to a reduction in gene flow between populations of flies on these two host types.     

基于荧光标记的怒江流域桔小实蝇（Bactrocera dorsalis）的迁移扩散

2005年7月在云南怒江流域地区,以荧光粉作为标记物,采用“标记-释放-回收”方法,对怒江流域桔小实蝇迁移扩散规律进行了研究。以释放点潞江坝为中心,东南西北4个方位设立桔小实蝇回收点,经过7d的回捕,从释放点沿潞江以北至六库沿线共回收到的标记桔小实蝇43头,最远在距释放点以北97 km 的地方回收到标记桔小实蝇5头。沿怒江在释放点以南,仅在小于29 km 的范围内回收到标记桔小实蝇17头。释放点东面和西面未能回收到标记桔小实蝇。分析释放点以北各回收点标记桔小实蝇与非标记桔小实蝇的相互关系揭示,非标记桔小实蝇与标记桔小实蝇在空间动态中具有相同的行为模式,由此推论非标记桔小实蝇与标记桔小实蝇可能来自同一种群。分析怒江流域区的自然地理发现,潞江坝桔小实蝇可借助怒江两边高大山脉形成的天然河谷通道,在适宜的气候条件下,在北上气流的携带下,实现由南向北的远距离迁移扩散;同时,由于高大山脉的阻隔,使潞江坝桔小实蝇没能向东西两个方向作远距离扩散迁移。研究首次揭示了在特定峡谷地区桔小实蝇扩散迁移现象,为桔小实蝇迁移扩散研究提供了新鲜实例,为在当地制定切实有效的桔小实蝇防治策略提供了基础信息。