Solitary Phase Research Articles

Demographic processes shaping genetic variation of the solitarious phase of the desert locust

Between plagues, the solitarious desert locust (Schistocerca gregaria) is generally thought to exist as small populations, which are particularly prone to extinction events in arid regions of Africa and Asia. Given the high genetic structuring observed in one geographical area (the Eritrean coast) by former authors, a metapopulation dynamics model involving repeated extinction and colonization events was favoured. In this study, we assessed the validity of a demographic scenario involving temporary populations of the solitarious phase of the desert locust by analysing large-scale population genetic data. We scored 24 microsatellites in 23 solitarious population samples collected over most of the species range during remission. We found very little genetic structuring and little evidence of declining genetic diversity. A Bayesian clustering method distinguished four genetically differentiated units. Three groups were largely consistent with three population samples which had undergone recent bottleneck events. Nevertheless, the last genetically homogeneous unit included all individuals from the remaining 18 population samples and did not show evidence of demographic disequilibrium. An approximate Bayesian computation treatment indicated a large population size for this main genetic group, moderately reduced between plague and remission but still containing tens of thousands of individuals. Our results diverge from the hypothesis of a classical metapopulation dynamics model. They instead support the scenario in which large populations persist in the solitarious phase of the desert locust.

MicroRNA-133 Inhibits Behavioral Aggregation by Controlling Dopamine Synthesis in Locusts

Phenotypic plasticity is ubiquitous and primarily controlled by interactions between environmental and genetic factors. The migratory locust, a worldwide pest, exhibits pronounced phenotypic plasticity, which is a population density-dependent transition that occurs between the gregarious and solitary phases. Genes involved in dopamine synthesis have been shown to regulate the phase transition of locusts. However, the function of microRNAs in this process remains unknown. In this study, we report the participation of miR-133 in dopamine production and the behavioral transition by negatively regulating two critical genes, henna and pale, in the dopamine pathway. miR-133 participated in the post-transcriptional regulation of henna and pale by binding to their coding region and 3′ untranslated region, respectively. miR-133 displayed cellular co-localization with henna/pale in the protocerebrum, and its expression in the protocerebrum was negatively correlated with henna and pale expression. Moreover, miR-133 agomir delivery suppressed henna and pale expression, which consequently decreased dopamine production, thus resulting in the behavioral shift of the locusts from the gregarious phase to the solitary phase. Increasing the dopamine content could rescue the solitary phenotype, which was induced by miR-133 agomir delivery. Conversely, miR-133 inhibition increased the expression of henna and pale, resulting in the gregarious-like behavior of solitary locusts; this gregarious phenotype could be rescued by RNA interference of henna and pale. This study shows the novel function and modulation pattern of a miRNA in phenotypic plasticity and provides insight into the underlying molecular mechanisms of the phase transition of locusts.

Predator–prey population models of migrant insects with phase change

Abstract Locusts and some noctuid moths exhibit polyphenism whereby they can change their “phase” from a solitary (“solitarious”) condition to a gregarious one. Gregarious phase insects are often migratory travelling from recession areas into larger invasion zones and, among locusts, occur in swarms. Difference equation models of the population dynamics of insects that take account of such changes between solitarious or gregarious phases in relation to predation, both with and without time delays, are described. Solutions of the models are non-linear. Chaotic solutions are obtainable under some circumstances even with very low values for the intrinsic rate of increase in the prey population, in contrast to previous conclusions from models without predation. Comparisons with the results obtained for single species with those obtained in this paper show that predation can reduce (i) the average density of the prey, (ii) durations of periods when the populations stay in the gregarious phase, and (iii) the frequency of their shifts from the solitarious state to the gregarious form. Similar results are obtained if a time delay is introduced to mimic a transient phase. With a wide range of parameter values, models including predation with or without random perturbation reveal several stable attractors for phase diagrams of the populations, which are biologically meaningful compared with empirical datasets and which were unobtainable without predation, suggesting that inclusion of predation and time delays improved the realism of the models. However, comparisons between autocorrelation analyses of locust time-series, but of swarms only, with those of model outputs suggest that inclusion of the time delay leads to less, not more, realism. The prediction of non-linearity in the dynamics of migrant insects with phase changes and its significance for forecasting to aid control is briefly discussed in relation to published data on the desert locust Schistocerca gregaria.

Neural Control of Gas Exchange Patterns in Insects: Locust Density-Dependent Phases as a Test Case

The adaptive significance of discontinuous gas exchange cycles (DGC) in insects is contentious. Based on observations of DGC occurrence in insects of typically large brain size and often socially-complex life history, and spontaneous DGC in decapitated insects, the neural hypothesis for the evolution of DGC was recently proposed. It posits that DGC is a non-adaptive consequence of adaptive down-regulation of brain activity at rest, reverting ventilatory control to pattern-generating circuits in the thoracic ganglia. In line with the predictions of this new hypothesis, we expected a higher likelihood of DGC in the gregarious phase of the desert locust (Schistocerca gregaria, Orthoptera), which is characterized by a larger brain size and increased sensory sensitivity compared with the solitary phase. Furthermore, surgical severing of the neural connections between head and thoracic ganglia was expected to increase DGC prevalence in both phases, and to eliminate phase-dependent variation in gas exchange patterns. Using flow-through respirometry, we measured metabolic rates and gas exchange patterns in locusts at 30°C. In contrast to the predictions of the neural hypothesis, we found no phase-dependent differences in DGC expression. Likewise, surgically severing the descending regulation of thoracic ventilatory control did not increase DGC prevalence in either phase. Moreover, connective-cut solitary locusts abandoned DGC altogether, and employed a typical continuous gas exchange pattern despite maintaining metabolic rate levels of controls. These results are not consistent with the predictions of the neural hypothesis for the evolution of DGC in insects, and instead suggest neural plasticity of ventilatory control.

Developmental‐ and food‐dependent foraging transcript levels in the desert locust

Drastic changes in the environment during a lifetime require developmental and physiological flexibility to ensure animal survival. Desert locusts, Schistocerca gregaria, live in an extremely changeable environment, which alternates between periods of rainfall and abundant food and periods of drought and starvation. In order to survive, locusts display an extreme form of phenotypic plasticity that allows them to rapidly cope with these changing conditions by converting from a cryptic solitarious phase to a swarming, voracious gregarious phase. To accomplish this, locusts possess different conserved mediators of phenotypic plasticity. Recently, attention has been drawn to the possible roles of protein kinases in this process. In addition to cyclic AMP-dependent protein kinase (PKA), also cyclic GMP-dependent protein kinase (PKG), which was shown to be involved in changes of food-related behavior in a variety of insects, has been associated with locust phenotypic plasticity. In this article, we study the transcript levels of the S. gregaria orthologue of the foraging gene that encodes a PKG in different food-related, developmental and crowding conditions. Transcript levels of the S. gregaria foraging orthologue are highest in different parts of the gut and differ between isolated and crowd-reared locusts. They change when the availability of food is altered, display a distinct pattern with higher levels after a moult and decrease with age during postembryonic development.

Altered Immunity in Crowded Locust Reduced Fungal (Metarhizium anisopliae) Pathogenesis

The stress of living conditions, similar to infections, alters animal immunity. High population density is empirically considered to induce prophylactic immunity to reduce the infection risk, which was challenged by a model of low connectivity between infectious and susceptible individuals in crowded animals. The migratory locust, which exhibits polyphenism through gregarious and solitary phases in response to population density and displays different resistance to fungal biopesticide (Metarhizium anisopliae), was used to observe the prophylactic immunity of crowded animals. We applied an RNA-sequencing assay to investigate differential expression in fat body samples of gregarious and solitary locusts before and after infection. Solitary locusts devoted at least twice the number of genes for combating M. anisopliae infection than gregarious locusts. The transcription of immune molecules such as pattern recognition proteins, protease inhibitors, and anti-oxidation proteins, was increased in prophylactic immunity of gregarious locusts. The differentially expressed transcripts reducing gregarious locust susceptibility to M. anisopliae were confirmed at the transcriptional and translational level. Further investigation revealed that locust GNBP3 was susceptible to proteolysis while GNBP1, induced by M. anisopliae infection, resisted proteolysis. Silencing of gnbp3 by RNAi significantly shortened the life span of gregarious locusts but not solitary locusts. By contrast, gnbp1 silencing did not affect the life span of both gregarious and solitary locusts after M. anisopliae infection. Thus, the GNBP3-dependent immune responses were involved in the phenotypic resistance of gregarious locusts to fungal infection, but were redundant in solitary locusts. Our results indicated that gregarious locusts prophylactically activated upstream modulators of immune cascades rather than downstream effectors, preferring to quarantine rather than eliminate pathogens to conserve energy meanwhile increasing the “distance” of infectious and target individuals. Our study has obvious implications for bio-pesticides management of crowded pests, and for understanding disease epidemics and adaptiveness of pathogens.

Serotonin enhances solitariness in phase transition of the migratory locust

The behavioral plasticity of locusts is a striking trait presented during the reversible phase transition between solitary and gregarious individuals. However, the results of serotonin as a neurotransmitter from the migratory locust Locusta migratoria in phase transition showed an alternative profile compared to the results from the desert locust Schistocerca gregaria. In this study, we investigated the roles of serotonin in the brain during the phase change of the migratory locust. During the isolation of gregarious nymphs, the concentration of serotonin in the brain increased significantly, whereas serotonin receptors (i.e., 5-HT1, 5-HT2, and 5-HT7) we identified here showed invariable expression patterns. Pharmacological intervention showed that serotonin injection in the brain of gregarious nymphs did not induced the behavioral change toward solitariness, but injection of this chemical in isolated gregarious nymphs accelerated the behavioral change from gregarious to solitary phase. During the crowding of solitary nymphs, the concentration of serotonin in the brain remained unchanged, whereas 5-HT2 increased after 1 h of crowding and maintained stable expression level thereafter. Activation of serotonin-5-HT2 signaling with a pharmaceutical agonist inhibited the gregariousness of solitary nymphs in crowding treatment. These results indicate that the fluctuations of serotonin content and 5-HT2 expression are results of locust phase change. Overall, this study demonstrates that serotonin enhances the solitariness of the gregarious locusts. Serotonin may regulate the withdrawal-like behavioral pattern displayed during locust phase change and this mechanism is conserved in different locust species.

Behavioral phase shift in nymphs of the desert locust, Schistocerca gregaria: Special attention to attraction/avoidance behaviors and the role of serotonin

Schistocerca gregaria exhibits a phase-specific behavior in response to crowding. Nymphs occurring at low population densities (solitarious phase) tend to avoid one another, whereas those occurring at high population densities (gregarious phase) are attracted to one another. This study examined how this attraction/avoidance behavior changed after isolation or crowding. The behavior of the test nymphs was assessed by determining their positioning with respect to a stimulus cup, which contained 12 gregarious nymphs, placed at one end of an elliptical arena and an empty cup placed at the opposite end. Gregarious (crowd-reared) nymphs were most frequently observed close to the stimulus cup, whereas solitarious (isolated-reared) nymphs tended to avoid it. This tendency was easily changed by exposing the nymphs to isolation or crowding. However, contrary to a previously reported conclusion that behavioral gregarization occurs in 4–8h of crowding, the nymphs required at least 3days to achieve a significant change in the attraction/avoidance behavior in either direction, from solitarious to gregarious or the converse. The discrepancies between the present study and previous studies appear to result from the different behaviors observed. The present study focused on the attraction/avoidance behavior that is most likely the most important element in the gregarization and solitarization processes, whereas other studies used a mixture of various activity-related behaviors. No evidence was obtained for a trans-generational accumulation in the attraction/avoidance behaviors. Serotonin, a biogenic amine that is suggested by others to be involved in behavioral phase changes in S. gregaria, had no influence on this behavior or body color when injected into the solitarious nymphs.

LIGHT AND CHEMICAL CUES TRIGGER BIBLICAL SWARMS

![Figure][1] Locusts are known for their striking demonstration of the power of epigenetics. Changes in population density cue a sudden shift in their physical form between a smaller, greener, solitary phase and a larger, darker, gregarious phase by changing the expression of their genes.

Pride Diaries: Sex, Brain Size and Sociality in the African Lion (Panthera leo) and Cougar (Puma concolor)

The purpose of this study was to examine if differences in social life histories correspond to intraspecific variation in total or regional brain volumes in the African lion (Panthera leo) and cougar (Puma concolor). African lions live in gregarious prides usually consisting of related adult females, their dependent offspring, and a coalition of immigrant males. Upon reaching maturity, male lions enter a nomadic and often, solitary phase in their lives, whereas females are mainly philopatric and highly social throughout their lives. In contrast, the social life history does not differ between male and female cougars; both are solitary. Three-dimensional virtual endocasts were created using computed tomography from the skulls of 14 adult African lions (8 male, 6 female) and 14 cougars (7 male, 7 female). Endocranial volume and basal skull length were highly correlated in African lions (r = 0.59, p < 0.05) and in cougars (r = 0.67, p < 0.01). Analyses of total endocranial volume relative to skull length revealed no sex differences in either African lions or cougars. However, relative anterior cerebrum volume comprised primarily of frontal cortex and surface area was significantly greater in female African lions than males, while relative posterior cerebrum volume and surface area was greater in males than females. These differences were specific to the neocortex and were not found in the solitary cougar, suggesting that social life history is linked to sex-specific neocortical patterns in these species. We further hypothesize that increased frontal cortical volume in female lions is related to the need for greater inhibitory control in the presence of a dominant male aggressor.

Adult female desert locusts require contact chemicals and light for progeny gregarization

Crowding causes many organisms to express phenotypic plasticity in various traits. Phase polyphenism in desert locusts represents one extreme example in which a solitary form (solitarious phase) turns into a gregarious form (gregarious phase) in response to crowding. Conspicuous differences in body size and colour occur even in hatchlings. The phase‐specific differences in hatchling characteristics are caused by the tactile stimuli perceived by the antennae of their mother. However, the nature of the tactile stimuli and the mechanism by which the perceived stimuli are processed as a gregarizing signal remain unknown. To explore this problem, the antennae of solitarious adult females of the desert locust Schistocerca gregaria are touched with the bodies of conspecific locusts at different physiological stages and those of other species. The results suggest that a cuticular chemical factor at a specific developmental stage of conspecific locusts causes the solitarious females to produce large eggs that give rise to black hatchlings characteristic of gregarious forms (progeny gregarization), and that this or a similar compound occurs in other acridids, crickets and cockroaches but not in beetles. The involvement of a chemical substance is also supported by hexane extracts of cuticular surfaces of locusts that induce the same effects. Interestingly, crowding induces such gregarizing effects only when the female receives the appropriate stimulus in the presence of light. Solitarious female S. gregaria with their head capsule coated with phosphorescent paint exhibit progeny gregarization in response to crowding and light pulses in darkness, whereas those treated in the same way without light pulses fail to do so.

Innate phase behavior in the desert locust, Schistocerca gregaria

Abstract Detailed aspects of the transition from the solitarious to the gregarious phase in the framework of locust ecology are undoubtedly most important for understanding locust phase polyphenism. Nevertheless, due to obvious difficulties in studying the solitarious phase in nature, such information is limited and mostly available from research carried out under laboratory conditions. In the current study, we examined the dispersal patterns of newly hatched locust nymphs in a laboratory setup that simulated seminatural conditions. This was carried out with no previous manipulation of the nymphs other than controlling their parental density. We comparatively tested the spatial distribution of newly hatched nymphs on perches located at different ranges within an emergence arena, and the expected Poisson (random) distribution. Hatchlings were found to disperse among the perches in a pattern significantly different from that expected by random. Irrespective of their parents’ phase, the observed distributions of all nymphs were clearly clumped, similar or close to those expected for gregarious locusts. It seems that rather than emerging with a parentally derived and predetermined phase, hatchlings have an independent default or innate behavioral state, which reflects at least tolerance if not attraction to conspecifics. The typical phase behavior may later become dominant under the appropriate environmental conditions. These results imply novel perspectives on locust phase transformation, which contribute to our understanding of the formation of locust crowds under field conditions. These should be considered in any rationale for developing a preventative management strategy of locust populations.

Mass spectral determination of phenylacetonitrile (PAN) levels in body tissues of adult desert locust, Schistocerca gregaria

Wings and legs of the gregarious desert locust, Schistocerca gregaria have been shown to be release sites of phenylacetonitrile (PAN), the major adult male-produced pheromone. However, there is limited information on the distribution of PAN within the locust. Here we show, using gas chromatography–mass spectrometry (GC–MS), that PAN occurs in nearly all body parts of both adult males and females of the locust in varying amounts. PAN was 20-fold more concentrated in males than in females. In females, PAN was concentrated more in the tarsal segments. The greatest amounts of PAN were in 2- and 3-week old female and male body parts, respectively. No trace of PAN was found in similar ages and sexes of the solitarious phase desert locust. Our results show that PAN is distributed in the body matrix of both sexes of gregarious phase locusts and suggest that no specific tissue is responsible for biosynthesis of the pheromone.

Metabolomic analysis reveals that carnitines are key regulatory metabolites in phase transition of the locusts

Phenotypic plasticity occurs prevalently and plays a vital role in adaptive evolution. However, the underlying molecular mechanisms responsible for the expression of alternate phenotypes remain unknown. Here, a density-dependent phase polyphenism of Locusta migratoria was used as the study model to identify key signaling molecules regulating the expression of phenotypic plasticity. Metabolomic analysis, using high-performance liquid chromatography and gas chromatography-mass spectrometry, showed that solitarious and gregarious locusts have distinct metabolic profiles in hemolymph. A total of 319 metabolites, many of which are involved in lipid metabolism, differed significantly in concentration between the phases. In addition, the time course of changes in the metabolic profiles of locust hemolymph that accompany phase transition was analyzed. Carnitine and its acyl derivatives, which are involved in the lipid β-oxidation process, were identified as key differential metabolites that display robust correlation with the time courses of phase transition. RNAi silencing of two key enzymes from the carnitine system, carnitine acetyltransferase and palmitoyltransferase, resulted in a behavioral transition from the gregarious to solitarious phase and the corresponding changes of metabolic profiles. In contrast, the injection of exogenous acetylcarnitine promoted the acquisition of gregarious behavior in solitarious locusts. These results suggest that carnitines mediate locust phase transition possibly through modulating lipid metabolism and influencing the nervous system of the locusts.

Field Observations of the Sheltering Behavior of the Solitarious Phase of the Desert Locust, Schistocerca gregaria, with Particular Reference to Antipredator Strategies

Solitarious phase locusts are cryptic animals and usually seek shelter in plants. This trait was thought to be a specific antipredator strategy associated with the solitarious phase. However, information on preferences for particular shelter plants and sheltering behavior remains limited. In the present study, small-scale field observations were conducted to investigate the sheltering behavior of the solitarious phase of the desert locust, Schistocerca gregaria, in relation to plant species and size. A spiny plant, Fagonia arabica, and two spineless plants, Nucularia perrini and Stipagrostis plumosa, were identified at the survey site. Although the size of F. arabica did not differ significantly from that of the two other plant species, almost all the solitarious locusts used F. arabica for shelter. Locusts were found on a majority (78%) of the individual F. arabica examined, but the number of sheltering locusts varied. The F. arabica plants with locusts were significantly larger than those without. A positive correlation was found between the total number of sheltered locusts (nymphs and adults) per individual plant and the plant size (m3). The same tendency was observed for nymphs and adults alike. The local densities (no. of sheltered locusts / plant size (m3)) remained constant over a range of plant sizes. These results might indicate that solitarious locusts selected their shelter plant based on its species and size. Because F. arabica is a spiny plant, we concluded that solitarious locusts use not only visual but also physical defense mechanisms as antipredator strategies. (Resume d'auteur)

Phase change in the desert locust: A novel computerised behavioural assay to study the effects of anaesthesia on gregarisation

Phase change in the desert locust: A novel computerised behavioural assay to study the effects of anaesthesia on gregarisation

Identification of Serotonergic neurones that show differential activity in newly and long- term gregarious Desert Locusts (Schistocerca gregaria)

Event Abstract Back to Event Identification of Serotonergic neurones that show differential activity in newly and long- term gregarious Desert Locusts (Schistocerca gregaria) Stephen Rogers1* 1 The University of Cambridge, Department of Zoology, United Kingdom Serotonin is a neurochemical that has been implicated in the regulation of wide range of behavioural processes including social interaction. In desert locusts (Schistocerca gregaria) serotonin induces a rapid behavioural change from a solitarious phase, in which locusts avoid each other, towards a more active gregarious phase in which locusts form coherent groups, which is a precursor to further profound phenotypic and behavioural changes that may ultimately culminate in swarm formation. Solitarious locusts receiving appropriate stimuli from other locusts produce a surge of serotonin in the thoracic ganglia. Once gregarization is established, however, amounts rapidly decline and fully established gregarious locusts have less serotonin in their central nervous systems than solitarious locusts. We used immunohistochemistry to compare the relative intensity of serotonin expression in each of the serotonergic neurons of the thoracic ganglia across populations of locusts receiving gregarizing stimuli and the fully established phases. In each of the thoracic ganglia neuronal somata located just ventral and lateral to the anterior connectives were relatively more intensely stained (containing more serotonin) in locusts that had received multiple gregarizing stimuli. In the pro- and meso-thoracic ganglia these occur as populations of 11-13 small somata, but in the metathoracic ganglion a single large soma occurs in a similar location. A different group of somata found across all three thoracic ganglia showed increased staining in response to exposure to the intense sight and smell of ~500 other locusts. Another distinct group of neurons in the meso- and metathoracic ganglion were less intensely stained in long-term gregarious locusts compared to long-term solitarious locusts, but were unaffected by any of the gregarizing treatments. These data suggest distinct subclasses of serotonergic neurons are responsible for the transition to gregarious behaviour from those that produce altered regulation of behaviours in the fully established phases. Keywords: Neuronal Plasticity, phase change, phenotypic plasticity Conference: Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012. Presentation Type: Poster Presentation (see alternatives below as well) Topic: Learning, Memory and Behavioral Plasticity Citation: Rogers S (2012). Identification of Serotonergic neurones that show differential activity in newly and long- term gregarious Desert Locusts (Schistocerca gregaria). Conference Abstract: Tenth International Congress of Neuroethology. doi: 10.3389/conf.fnbeh.2012.27.00448 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 04 Jul 2012; Published Online: 07 Jul 2012. * Correspondence: Dr. Stephen Rogers, The University of Cambridge, Department of Zoology, Cambridge, CB2 3EJ, United Kingdom, smr34@cam.ac.uk Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Stephen Rogers Google Stephen Rogers Google Scholar Stephen Rogers PubMed Stephen Rogers Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

The effect of climatic variation on abundance and diversity of bumblebees: a ten years survey in a mountain hotspot

Even if climates play an evident role in the bumblebees distribution, at the present time, no research has been performed to test whether climatic parameters actually affect their abundance and diversity. For more than one decade (1999–2009), we monitored the bumblebee fauna of a mountain hotspot in the Eastern Pyrenees. We sampled each year, in July, the same hayfield habitat, resulting in the sampling of 28 species. We computed the correlation of the yearly abundance of the main species with several climatic parameters concerning temperature and precipitation. We separated the parameters measured during the bumblebee solitary phase and those measured during their social phase. Bumblebee fauna composition varied significantly over years. In the 13 species considered, the abundance of 9 was correlated with at least one climatic parameter. The lowest abundance of bumblebees was correlated with hot and dry conditions during the month of August the year before sampling (the nuptial time of the founders). The highest overall abundance of bumblebees was observed during the social phase in the rainy months. Across years, climatic parameters seem to have strongly affected the composition of bumblebee fauna. Our results seem to indicate that hot and dry weather represent serious threat for most bumblebee species. The potential effects of Global Warming are discussed: they may cause a severe reduction of the mountain bumblebee diversity.

Microarray-Based Transcriptomic Analysis of Differences between Long-Term Gregarious and Solitarious Desert Locusts

Desert locusts (Schistocerca gregaria) show an extreme form of phenotypic plasticity and can transform between a cryptic solitarious phase and a swarming gregarious phase. The two phases differ extensively in behavior, morphology and physiology but very little is known about the molecular basis of these differences. We used our recently generated Expressed Sequence Tag (EST) database derived from S. gregaria central nervous system (CNS) to design oligonucleotide microarrays and compare the expression of thousands of genes in the CNS of long-term gregarious and solitarious adult desert locusts. This identified 214 differentially expressed genes, of which 40% have been annotated to date. These include genes encoding proteins that are associated with CNS development and modeling, sensory perception, stress response and resistance, and fundamental cellular processes. Our microarray analysis has identified genes whose altered expression may enable locusts of either phase to deal with the different challenges they face. Genes for heat shock proteins and proteins which confer protection from infection were upregulated in gregarious locusts, which may allow them to respond to acute physiological challenges. By contrast the longer-lived solitarious locusts appear to be more strongly protected from the slowly accumulating effects of ageing by an upregulation of genes related to anti-oxidant systems, detoxification and anabolic renewal. Gregarious locusts also had a greater abundance of transcripts for proteins involved in sensory processing and in nervous system development and plasticity. Gregarious locusts live in a more complex sensory environment than solitarious locusts and may require a greater turnover of proteins involved in sensory transduction, and possibly greater neuronal plasticity.

Parental phase status affects the cold hardiness of progeny eggs in locusts

Summary1. The capacity to adapt to low temperature is critical for the persistence of insect populations in heterogeneous environments. Locusts show remarkable phenotypic plasticity, termed ‘phase change’, in response to local population density.2. In this study, the hypothesis that population density, as a social factor, affects the cold hardiness of progeny is validated in the migratory locust, Locusta migratoria, which shows remarkable density‐dependent phase changes between gregarious and solitarious phases.3. We demonstrated that eggs of gregarious and solitarious migratory locusts significantly differ not only in size and weight, but also in cold hardiness. Eggs of solitarious locusts are more resistant to cold stress compared with those of gregarious locusts, with longer 50% lethal time at different low temperatures and under different acclimation treatments of cooling rates or cold exposure time, lower upper limit of chill injury zone, and lower sum of injurious temperature resulting from temperature–time regression. The lowest cooling rate (0·05 °C min−1) yields the highest survival of cold for eggs.4. A custom‐made microarray covering 9154 unigenes of the migratory locust demonstrated quite different gene expression profiles in the two phases in response to normal or low temperature. Under cold stress, the gregarious‐phase eggs have higher transcriptional levels of heat‐shock proteins, DOPA decarboxylases and tyrosine hydroxylase, whereas the solitarious‐phase eggs exhibit stimulated lipid metabolism and carboxylic acid transport.5. Hybridization between the two phases showed that the cold hardiness of eggs from the hybrid with solitarious females is significantly higher than that of the hybrid with gregarious females, and the cold hardiness of eggs from each reciprocal hybrid is close to their maternal origins. These results indicate that the cold hardiness of progeny is affected by the parental phase status.