Insect sex-pheromone signals mediated by specific combinations of olfactory receptors

We describe two male-specific olfactory receptors (ORs) in the silk moth, Bombyx mori, that are mutually exclusively expressed in a pair of adjacent pheromone-sensitive neurons of male antennae: One is specifically tuned to bombykol, the sex pheromone, and the other to bombykal, its oxidized form. Both pheromone ORs are coexpressed with an OR from the highly conserved insect OR subfamily. This coexpression promotes the functional expression of pheromone receptors and confers ligand-stimulated nonselective cation channel activity. The same effects were also observed for general ORs. Both odorant and pheromone signaling pathways are mediated by means of a common mechanism in insects.     

Combinatorial effects of odorant mixes in olfactory cortex

In mammals, each odorant is detected by a combination of different odorant receptors. Signals from different types of receptors are segregated in the nose and the olfactory bulb, but appear to be combined in individual neurons in the olfactory cortex. Here, we report that binary odorant mixes stimulate cortical neurons that are not stimulated by their individual component odorants. We propose that cortical neurons require combinations of receptor inputs for activation and that merging the receptor codes of two odorants provides novel combinations of receptor inputs that stimulate neurons beyond those activated by the single odorants. These findings may explain why odorant mixtures can elicit novel odor percepts in humans.     

Queen pheromone blocks aversive learning in young worker bees

Queen mandibular pheromone (QMP) has profound effects on dopamine signaling in the brain of young worker honey bees. As dopamine in insects has been strongly implicated in aversive learning, we examined QMP's impact on associative olfactory learning in bees. We found that QMP blocks aversive learning in young workers, but leaves appetitive learning intact. We postulate that QMP's effects on aversive learning enhance the likelihood that young workers remain in close contact with their queen by preventing them from forming an aversion to their mother's pheromone bouquet. The results provide an interesting twist to a story of success and survival.     

Learning in normal and mutant Drosophila larvae

Adult Drosophila melanogaster have previously been conditioned with shock to avoid various odors. In these experiments, larvae also sensed airborne odorants, responded to electric shock, and learned. Larval behavior paralleled adult behavior for (i) a mutant, smellblind, which failed to respond to odorants; (ii) three mutants, dunce, turnip, and cabbage, which were deficient in olfactory learning ability; and (iii) a mutant heterozygote, turnip/+, which learned but also forgot rapidly.     

A larval specific OBP able to bind the major female sex pheromone component in Spodoptera exigua(Hübner)

Odorant binding proteins(OBPs) in insects are postulated to solubilize and transport the hydrophobic odorants across the hydrophilic antennal lymph to the olfactory receptors(ORs) located on the dendrite membrane of the sensory neurons. OBPs in adult insects have been intensively reported, but those in larvae are rarely addressed. In our study, a full-length OBP c DNA, namely Sexi OBP13, was cloned by RT-PCR and RACE strategy from the heads of Spodoptera exigua larvae. The quantitative real-time PCR(q PCR) measurement indicated that Sexi OBP13 was highly expressed in larval head, but very low in other parts of larva and was not detected in any tissues of adult. The binding affinities of Sexi OBP13 to plant volatiles and female sex pheromone components were measured by competitive binding assays. Interestingly, Sexi OBP13 displayed a high binding affinity(Ki=3.82 μmol L–1) to Z9,E12–14:Ac, the major sex pheromone component of S. exigua, while low affinities to the tested host plant volatiles(Ki27 μmol L–1). The behavioral tests further confirmed that Z9,E12–14:Ac was indeed active to elicit the behavioral activity of the third instar larvae of S. exigua. Taken together, our results suggest that Sexi OBP13 may play a role in reception of female sex pheromone in S. exigua larvae. The ecological significance of the larvae preference to the adult female sex pheromone was discussed.     

绵山天幕毛虫求偶和交配行为研究

[目的]研究绵山天幕毛虫求偶和交配行为,为发展利用性信息素防控绵山天幕毛虫提供理论依据。[方法]通过室内和野外观察,研究绵山天幕毛虫成虫求偶行为的发生过程、求偶周期、不同雌雄比及种群密度对交配率的影响。[结果]自然界中绵山天幕毛虫雌雄比为1.0∶1.2,实验室饲养的绵山天幕毛虫雌雄比则为1.0∶1.8;绵山天幕毛虫的求偶高峰发生在19：00-21：00;不同比例及种群密度对雌雄蛾交配行为影响较大,且种群密度过高不利于其繁殖;绵山天幕毛虫雌、雄蛾一生均只交配1次。[结论]利用性信息素防治绵山天幕毛虫具有较好的应用前景。     

绵山天幕毛虫求偶和交配行为研究(摘要)(英文)

[目的]研究绵山天幕毛虫求偶和交配行为,为发展利用性信息素防控绵山天幕毛虫提供理论依据。[方法]通过室内和野外观察,研究绵山天幕毛虫成虫求偶行为的发生过程、求偶周期、不同雌雄比及种群密度对绵山天幕毛虫交配率的影响。[结果]虫卵越冬次年4月下旬幼虫开始孵化,5月上旬为孵化盛期,5月中旬孵化结束全部进入幼虫期,幼虫期大约70d,共6～7龄。幼虫老熟后于7月上旬开始下树,7月中下旬为化蛹盛期,蛹期约20d。7月下旬开始羽化,羽化时间一般为11:00～18:00,9月中旬产卵结束,进入滞育越冬状态。室内饲养绵山天幕毛虫成虫最早在7月中旬出现,比自然羽化时间提前,可能是由于室内平均温度较野外高。室内饲养的绵山天幕毛虫雌雄比约为1∶1.8,比野外雌雄比例有所减少,可能是由于室内的环境条件所致。自然界中绵山天幕毛虫雌雄比为1∶1.2,实验室饲养的绵山天幕毛虫雌雄比则为1∶1.8。在自然条件下,雌虫求偶最早出现在18:00,从19:00以后雌虫求偶率明显上升,19:00～21:00达到高峰,以后求偶率逐渐下降。雌虫求偶行为主要发生在羽化后的第1和第2天,第1天的求偶率达90%,第2天求偶率明显下降。不同比例及种群密度对雌雄蛾交配行为影响较大,且种群密度过高不利于其繁殖;绵山天幕毛虫雌、雄蛾一生均只交配1次。[结论]利用性信息素防治绵山天幕毛虫具有较好的应用前景。     

Population cycles in small rodents

We conclude that population fluctuations in Microtus in southern Indiana are produced by a syndrome of changes in birth and death rates similar to that found in other species of voles and lemmings. The mechanisms which cause the changes in birth and death rates are demolished by fencing the population so that no dispersal can occur. Dispersal thus seems critical for population regulation in Microtus. Because most dispersal occurs during the increase phase of the population cycle and there is little dispersal during the decline phase, dispersal is not directly related to population density. Hence the quality of dispersing animals must be important, and we have found one case of increased dispersal tendency by one genotype. The failure of population regulation of Microtus in enclosed areas requires an explanation by any hypothesis attempting to explain population cycles in small rodents. It might be suggested that the fence changed the predation pressure on the enclosed populations. However, the fence was only 2 feet (0.6 meter) high and did not stop the entrance of foxes, weasels, shrews, or avian predators. A striking feature was that the habitat in the enclosures quickly recovered from complete devastation by the start of the spring growing season. Obviously the habitat and food quality were sufficient to support Microtus populations of abnormally high densities, and recovery of the habitat was sufficiently quick that the introduction of new animals to these enclosed areas resulted in another population explosion. Finally, hypotheses of population regulation by social stress must account for the finding that Microtus can exist at densities several times greater than normal without "stress" taking an obvious toll. We hypothesize that the prevention of dispersal changes the quality of the populations in the enclosures in comparison to those outside the fence. Voles forced to remain in an overcrowded fenced population do not suffer high mortality rates and continue to reproduce at abnormally high densities until starvation overtakes them. The initial behavioral interactions associated with crowding do not seem sufficient to cause voles to die in situ. What happens to animals during the population decline? Our studies have not answered this question. The animals did not appear to disperse, but it is possible that the method we used to measure dispersal (movement into a vacant habitat) missed a large segment of dispersing voles which did not remain in the vacant area but kept on moving. Perhaps the dispersal during the increase phase of the population cycle is a colonization type of dispersal, and the animals taking part in it are likely to stay in a new habitat, while during the population decline dispersal is a pathological response to high density, and the animals are not attracted to settling even in a vacant habitat. The alternative to this suggestion is that animals are dying in situ during the decline because of physiological or genetically determined behavioral stress. Thus the fencing of a population prevents the change in rates of survival and reproduction, from high rates in the increase phase to low rates in the decline phase, and the fenced populations resemble "mouse plagues." A possible explanation is that the differential dispersal of animals during the phase of increase causes the quality of the voles remaining at peak densities in wild populations to be different from the quality of voles at much higher densities in enclosures. Increased sensitivity to density in Microtus could cause the decline of wild populations at densities lower than those reached by fenced populations in which selection through dispersal has been prevented. Fencing might also alter the social interactions among Microtus in other ways that are not understood. The analysis of colonizing species by MacArthur and Wilson (27) can be applied to our studies of dispersal in populations of Microtus. Groups of organisms with good dispersal and colonizing ability are called r strategists because they have high reproductive potential and are able to exploit a new environment rapidly. Dispersing voles seem to be r strategists. Young females in breeding condition were over-represented in dispersing female Microtus (17). The Tf(C)/Tf(E) females, which were more common among dispersers during the phase of population increase (Fig. 6), also have a slight reproductive advantage over the other Tf genotypes (19). Thus in Microtus populations the animals with the highest reproductive potential, the r strategists, are dispersing. The segment of the population which remains behind after the selection-via-dispersal are those individuals which are less influenced by increasing population densities. These are the individuals which maximize use of the habitat, the K strategists in MacArthur and Wilson's terminology, or voles selected for spacing behavior. Thus we can describe population cycles in Microtus in the same theoretical framework as colonizing species on islands. Our work on Microtus is consistent with the hypothesis of genetic and behavioral effects proposed by Chitty (6) (Fig. 7) in that it shows both behavioral differences in males during the phases of population fluctuation and periods of strong genetic selection. The greatest gaps in our knowledge are in the area of genetic-behavioral interactions which are most difficult to measure. We have no information on the heritability of aggressive behavior in voles. The pathways by which behavioral events are translated into physiological changes which affect reproduction and growth have been carefully analyzed by Christian and his associates (28) for rodents in laboratory situations, but the application of these findings to the complex field events described above remains to be done. Several experiments are suggested by our work. First, other populations of other rodent species should increase to abnormal densities if enclosed in a large fenced area (29). We need to find situations in which this prediction is not fulfilled. Island populations may be an important source of material for such an experiment (30). Second, if one-way exit doors were provided from a fenced area, normal population regulation through dispersal should occur. This experiment would provide another method by which dispersers could be identified. Third, if dispersal were prevented after a population reached peak densities, a normal decline phase should occur. This prediction is based on the assumption that dispersal during the increase phase is sufficient to ensure the decline phase 1 or 2 years later. All these experiments are concerned with the dispersal factor, and our work on Microtus can be summarized by the admonition: study dispersal.     

Temperature sensing by an olfactory neuron in a circuit controlling behavior of C. elegans

Temperature is an unavoidable environmental cue that affects the metabolism and behavior of any creature on Earth, yet how animals perceive temperature is poorly understood. The nematode Caenorhabditis elegans "memorizes" temperatures, and this stored information modifies its subsequent migration along a temperature gradient. We show that the olfactory neuron designated AWC senses temperature. Calcium imaging revealed that AWC responds to temperature changes and that response thresholds differ depending on the temperature to which the animal was previously exposed. In the mutant with impaired heterotrimeric guanine nucleotide-binding protein (G protein)-mediated signaling, AWC was hyperresponsive to temperature, whereas the AIY interneuron (which is postsynaptic to AWC) was hyporesponsive to temperature. Thus, temperature sensation exhibits a robust influence on a neural circuit controlling a memory-regulated behavior.     

Aversive learning enhances perceptual and cortical discrimination of indiscriminable odor cues

Learning to associate sensory cues with threats is critical for minimizing aversive experience. The ecological benefit of associative learning relies on accurate perception of predictive cues, but how aversive learning enhances perceptual acuity of sensory signals, particularly in humans, is unclear. We combined multivariate functional magnetic resonance imaging with olfactory psychophysics to show that initially indistinguishable odor enantiomers (mirror-image molecules) become discriminable after aversive conditioning, paralleling the spatial divergence of ensemble activity patterns in primary olfactory (piriform) cortex. Our findings indicate that aversive learning induces piriform plasticity with corresponding gains in odor enantiomer discrimination, underscoring the capacity of fear conditioning to update perceptual representation of predictive cues, over and above its well-recognized role in the acquisition of conditioned responses. That completely indiscriminable sensations can be transformed into discriminable percepts further accentuates the potency of associative learning to enhance sensory cue perception and support adaptive behavior.     

Odor-induced membrane currents in vertebrate-olfactory receptor neurons

In olfactory receptor neurons, odor molecules cause a depolarization that leads to action potential generation. Underlying the depolarization is an ionic current that is the earliest electrical event in the transduction process. In two preparations, olfactory receptor neurons were voltage-clamped and stimulated with odors and this generator current was measured. In addition, a method was developed to estimate the time course and absolute concentration of odorants delivered to the receptor sites. With this method, olfactory neurons were found to have relatively high stimulus thresholds, steep dose-response relations, long latencies, and an apparent requirement for cooperativity at one or more steps in the pathway from odorant binding to activation of the generator current.     

Adaptive phenotypic plasticity in response to climate change in a wild bird population

Rapid climate change has been implicated as a cause of evolution in poorly adapted populations. However, phenotypic plasticity provides the potential for organisms to respond rapidly and effectively to environmental change. Using a 47-year population study of the great tit (Parus major) in the United Kingdom, we show that individual adjustment of behavior in response to the environment has enabled the population to track a rapidly changing environment very closely. Individuals were markedly invariant in their response to environmental variation, suggesting that the current response may be fixed in this population. Phenotypic plasticity can thus play a central role in tracking environmental change; understanding the limits of plasticity is an important goal for future research.     

Isolation of an olfactory cDNA: similarity to retinol-binding protein suggests a role in olfaction

Molecular cloning techniques were used to isolate and characterize a protein possibly involved in the signal transducing system in olfactory tissue of the frog Rana pipiens. A complementary DNA library was constructed with messenger RNA obtained from frog olfactory neuroepithelium. A 700-base pair complementary DNA clone encoding a protein with a molecular weight of 20,300 was identified by differential hybridization analysis with polyadenylated RNA from olfactory epithelium and nonsensory respiratory epithelium. The messenger RNA corresponding to this clone was abundant in the cells of Bowman's glands in olfactory tissue but not in respiratory epithelium nor in several other tissues. The predicted sequence of this protein is homologous to members of a family of proteins that bind and transport small molecules in serum, suggesting that this protein may also bind and transport odorants in the mucus secreted by Bowman's glands.     

Pregnancy-stimulated neurogenesis in the adult female forebrain mediated by prolactin

Neurogenesis occurs in the olfactory system of the adult brain throughout life, in both invertebrates and vertebrates, but its physiological regulation is not understood. We show that the production of neuronal progenitors is stimulated in the forebrain subventricular zone of female mice during pregnancy and that this effect is mediated by the hormone prolactin. The progenitors then migrate to produce new olfactory interneurons, a process likely to be important for maternal behavior, because olfactory discrimination is critical for recognition and rearing of offspring. Neurogenesis occurs even in females that mate with sterile males. These findings imply that forebrain olfactory neurogenesis may contribute to adaptive behaviors in mating and pregnancy.     

杨干透翅蛾性信息素的研究

研究表明我国西北、华北地区危害杨树主干的透翅蛾是杨干透翅蛾Sesia siningensis(Hsu)。经室内EAG测试,林间诱蛾和活雌蛾腺体提取及化学分析,证明顺3,顺13—十八碳二烯醇是其性信息素。利用人工合成的性信息素,在山西、甘肃等省连续4年大面积应用,证明可用来检测成虫羽化期和发生量、分布范围,并可降低雌蛾交配率28.1％～98.5％,平均降低42.8％～47.6％;连续3年诱蛾后,虫口密度降低38.2％。     

Bile Acid secreted by male sea lamprey that acts as a sex pheromone

We show that reproductively mature male sea lampreys release a bile acid that acts as a potent sex pheromone, inducing preference and searching behavior in ovulated female lampreys. The secreted bile acid 7alpha,12alpha,24-trihydroxy-5alpha-cholan-3-one 24-sulfate was released in much higher amounts relative to known vertebrate steroid pheromones and may be secreted through the gills. Hence, the male of this fish species signals both its reproductive status and location to females by secreting a pheromone that can act over long distances.     

北五味子花芽分化与种植密度的相关性

采用大样本随机取样的调查和测定方法,分析了人工栽培基地内不同栽植密度区的北五味子花芽分化情况.结果表明:在花芽分化期,北五味子种群尚未达到环境最大容纳量,其总花量随种群密度的增加呈极显著增长.每棵植株雌花量可塑性大于雄花量,雌花量、总花量、雌花和总花量比与种群密度间呈极显著(P＜0.001)负相关,可以用相关程度较高的对数函数方程描述.每棵雌花量、雌花和总花量比与总花量之间呈极显著(P＜0.001)正相关关系,可以用相关程度较高的线性函数方程描述.     

Scaling of connectivity in marine populations

Defining the scale of connectivity, or exchange, among marine populations and determining the factors driving this exchange are pivotal to our understanding of the population dynamics, genetic structure, and biogeography of many coastal species. Using a high-resolution biophysical model for the Caribbean region, we report that typical larval dispersal distances of ecologically relevant magnitudes are on the scale of only 10 to 100 kilometers for a variety of reef fish species. We also show the importance of the early onset of active larval movement mediating the dispersal potential. In addition to self-recruitment, larval import from outside the local area is required to sustain most populations, although these population subsidies are very limited in particular systems. The results reveal distinct regions of population isolation based on larval dispersal that also correspond to genetic and morphological clines observed across a range of marine organisms.     

An interneuronal chemoreceptor required for olfactory imprinting in C. elegans

Animals alter their behavioral patterns in an experience-dependent manner. Olfactory imprinting is a process in which the exposure of animals to olfactory cues during specific and restricted time windows leaves a permanent memory ("olfactory imprint") that shapes the animal's behavior upon encountering the olfactory cues at later times. We found that Caenorhabditis elegans displays olfactory imprinting behavior that is mediated by a single pair of interneurons. To function in olfactory imprinting, this interneuron pair must express a G protein-coupled chemoreceptor family member encoded by the sra-11 gene. Our study provides insights into the cellular and molecular basis of olfactory imprinting and reveals a function for a chemosensory receptor family member in interneurons.     

Regulation of Drosophila life span by olfaction and food-derived odors

Smell is an ancient sensory system present in organisms from bacteria to humans. In the nematode Caenorhabditis elegans, gustatory and olfactory neurons regulate aging and longevity. Using the fruit fly, Drosophila melanogaster, we showed that exposure to nutrient-derived odorants can modulate life span and partially reverse the longevity-extending effects of dietary restriction. Furthermore, mutation of odorant receptor Or83b resulted in severe olfactory defects, altered adult metabolism, enhanced stress resistance, and extended life span. Our findings indicate that olfaction affects adult physiology and aging in Drosophila, possibly through the perceived availability of nutritional resources, and that olfactory regulation of life span is evolutionarily conserved.