Collective motion and cannibalism in locust migratory bands

Plagues of mass migrating insects such as locusts are estimated to affect the livelihood of one in ten people on the planet [1]. Identification of generalities in the mechanisms underlying these mass movements will enhance our understanding of animal migration and collective behavior while potentially contributing to pest-management efforts. We provide evidence that coordinated mass migration in juvenile desert locusts (Schistocerca gregaria) is influenced strongly by cannibalistic interactions. Individuals in marching bands tend to bite others but risk being bitten themselves. Reduction of individuals' capacity to detect the approach of others from behind through abdominal denervation (1) decreases their probability to start moving, (2) dramatically reduces the mean proportion of moving individuals in groups, and (3) significantly increases cannibalism. Similarly, occlusion of the rear visual field inhibits individuals' propensity to march. Abdomen denervation did not influence the behavior of isolated locusts. When within groups, abdominal biting and the sight of others approaching from behind triggers movement, creating an autocatalytic feedback that results in directed mass migration. This "forced march" driven by cannibalistic interactions suggests that we need to reassess our view of both the selection pressure and mechanism that can result in the coordinated motion of such large insect groups.     

Radiotelemetric analysis of the effects of prevailing wind direction on Mormon cricket migratory band movement

During outbreaks, flightless Mormon crickets [Anabrus simplex Haldeman (Orthoptera: Tettigoniidae)] form large mobile groups known as migratory bands. These bands can contain millions of individuals that march en masse across the landscape. The role of environmental cues in influencing the movement direction of migratory bands is poorly understood and has been the subject of little empirical study. We examined the effect of wind direction on Mormon cricket migratory band movement direction by monitoring the local weather conditions and daily movement patterns of individual insects traveling in bands over the same time course at three close, but spatially distinct sites. Although weather conditions were relatively homogeneous across sites, wind directions tended to be more variable across sites during the morning hours, the period during which directional movement begins. Migratory bands at different sites traveled in distinctly different directions. However, we failed to find any evidence to suggest that the observed variation in migratory band movement direction was correlated with local wind direction at any time during the day. These results support the notion that the cues mediating migratory band directionality are likely to be group specific and that a role for landscape-scale environmental cues such as wind direction is unlikely.     

Age- and density-dependent prophylaxis in the migratory, cannibalistic Mormon cricket Anabrus simplex (Orthoptera: Tettigoniidae)

As a result of the increased potential for disease transmission, insects are predicted to show an increased constitutive immunity when crowded. Cannibalistic aggressive interactions further increase the risk of wounding and pathogen transmission in crowds. Nymphal Mormon crickets Anabrus simplex Haldeman were collected in Montana and reared in the laboratory either solitarily or at densities similar to that experienced by Mormon crickets in migratory bands. As teneral adults, solitarily-reared Mormon crickets tended to have greater phenoloxidase activity than those reared in groups. Sampling enzyme activity a second time when the adults were nearing reproductive maturity, group-reared Mormon crickets had elevated levels of prophenoloxidase and encapsulated foreign objects faster than solitarily-reared insects. Rearing density did not have a significant effect on either the darkness of the cuticle or antibacterial activity. This is the first report of age-related responses of adult insect immunity to crowding.     

Radiotelemetry reveals differences in individual movement patterns between outbreak and non-outbreak Mormon cricket populations

Abstract.  1. Outbreaks of insect pest populations are common and can have devastating effects on natural communities and on agriculture. Little is known about the causes of these outbreaks or the causes of en masse migrations during outbreaks.
2. Flightless Mormon crickets ( Anabrus simplex ) were the focus of this study. They are a katydid species that forms large, dense, mobile groups (migratory bands) during outbreak periods, eating vegetation in their path.
3. Radiotelemetric methods were used to measure differences in movement rate and directionality in outbreak and non-outbreak populations, testing the hypothesis that these populations differ in their travel rate and consistency of direction.
4. Daily individual movement in outbreak populations differs substantially from non-outbreak populations that are at much lower density. In addition to large differences in distances travelled (1.6 km as compared with 1 m) and rates of travel, there is evidence for collective movement among individual Mormon crickets travelling in migratory bands.
5. These data suggest that the direction of group movement may be influenced by local environmental conditions such as wind direction and movement of nearby band members. This work forms the basis for ongoing work testing hypotheses about mass migrations in outbreak populations.     

Estimation of the composition of the cuticular wax of the Mormon cricket,Anabrus simplex Hald.

The lipid solvent extractable material from the cuticle of Anabrus simplex Hald. (Mormon cricket) has been examined in an effort to elucidate its chemical composition. Hydrocarbons, free fatty acids, esters, free cholesterol, and acidic resins are present in measurable amounts. Infra-red spectrophotometry, column chromatography, and gas chromatography have been utilized for the separation and characterization of these various components.     

The social context of well-being

Large samples of data from the World Values Survey, the US Benchmark Survey and a comparable Canadian survey are used to estimate equations designed to explore the social context of subjective evaluations of well-being, of happiness, and of health. Social capital, as measured by the strength of family, neighbourhood, religious and community ties, is found to support both physical health and subjective well-being. Our new evidence confirms that social capital is strongly linked to subjective well-being through many independent channels and in several different forms. Marriage and family, ties to friends and neighbours, workplace ties, civic engagement (both individually and collectively), trustworthiness and trust: all appear independently and robustly related to happiness and life satisfaction, both directly and through their impact on health.     

Laboratory evolution of the migratory polymorphism in the sand cricket: combining physiology with quantitative genetics

Predicting evolutionary change is the central goal of evolutionary biology because it is the primary means by which we can test evolutionary hypotheses. In this article, we analyze the pattern of evolutionary change in a laboratory population of the wing-dimorphic sand cricket Gryllus firmus resulting from relaxation of selection favoring the migratory (long-winged) morph. Based on a well-characterized trade-off between fecundity and flight capability, we predict that evolution in the laboratory environment should result in a reduction in the proportion of long-winged morphs. We also predict increased fecundity and reduced functionality and weight of the major flight muscles in long-winged females but little change in short-winged (flightless) females. Based on quantitative genetic theory, we predict that the regression equation describing the trade-off between ovary weight and weight of the major flight muscles will show a change in its intercept but not in its slope. Comparisons across generations verify all of these predictions. Further, using values of genetic parameters estimated from previous studies, we show that a quantitative genetic simulation model can account for not only the qualitative changes but also the evolutionary trajectory. These results demonstrate the power of combining quantitative genetic and physiological approaches for understanding the evolution of complex traits.     

Traveling bands of chemotactic bacteria in the context of population growth

A mathematical model for traveling bands of motile and chemotactic bacteria in the presence of cell growth and death is examined. It is found that asymptotic traveling wave solutions exist in the absence of chemotaxis, due to the balance of growth, death and random motility. Thus random motility confers the ecological advantage of population propagation through migration into nutrient-rich regions. The presence of chemotaxis amplifies this advantage by moving more cells into higher nutrient concentration regions, resulting in larger and faster bands. Therefore there seem to be two types of traveling bands that can be attained by chemotactic bacteria in the presence of growth and death: (1) these growth/death/motility bands; and (2) pure chemotactic ‘Keller-Segel'-type bands. Comparison to experimental observations by Chapman in 1973 indicate that the latter seem to be formed. The relationship between these two types of solution is at present uncertain. The growth/death/motility bands may have relevance on longer time or distance scales characteristic of microbial ecological systems.     

Personality in the context of social networks

There is great interest in environmental effects on the development and evolution of animal personality traits. An important component of an individual's environment is its social environment. However, few studies look beyond dyadic relationships and try to place the personality of individuals in the context of a social network. Social network analysis provides us with many new metrics to characterize the social fine-structure of populations and, therefore, with an opportunity to gain an understanding of the role that different personalities play in groups, communities and populations regarding information or disease transmission or in terms of cooperation and policing of social conflicts. The network position of an individual is largely a consequence of its interactive strategies. However, the network position can also shape an individual's experiences (especially in the case of juveniles) and therefore can influence the way in which it interacts with others in future. Finally, over evolutionary time, the social fine-structure of animal populations (as quantified by social network analysis) can have important consequences for the evolution of personalities-an approach that goes beyond the conventional game-theoretic analyses that assumed random mixing of individuals in populations.     

Zugunruhe of migratory and non-migratory birds in a circannual context

Recent findings in non-migratory birds have reopened questions about the interpretation and seasonal organization of Zugunruhe . I address the relationship between Zugunruhe and migration by comparing underlying circannual patterns in captive populations of migratory and non-migratory stonechats. Zugunruhe was highly variable and lacked clear periodicity, indicating its sensitivity to external cues. Patterns of Zugunruhe were similar in African residents, European short-distance migrants, and Siberian long-distance migrants, revealing no major difference in circannual organization. Moult was regulated independently of Zugunruhe and timed more rigidly, particularly in stonechats from equatorial Africa. The persistent and variable circannual patterns of Zugunruhe suggest that non-migratory and migratory stonechats have similar underlying programs but have modified the expression of actual migration. The findings, together with published observations from other species, emphasize the importance of considering programs for migration in a wide range of species, without losing sight of its environmental context.     

The influence of behavioral context and social characteristics on the physical aspects of social grooming in rhesus monkeys

The extent to which dominance status and sex can influence the physical act of grooming was examined in two groups of rhesus monkeys. Both the sex and the dominance status of the groomee, but not of the groomer, were found to affect the body sites groomed and the positions assumed by the animals during the grooming bout. Females were groomed more on the back and head and less on the tail, rump, upper leg, and lower arm than males. Females with infants tended to face away from the groomer. Higher-ranking groomees were groomed more on the tail and rump and less on the upper leg and back than lower-ranking groomees. Higher-ranking groomees spent more time lying down during grooming than lower-ranking groomees, while lower-ranking groomees faced away from the groomer more then higher-ranking groomees. The behavioral interactions just prior to and immediately after grooming were also recorded. Although the onset of grooming was preceded by social interactions between the partners, the end of grooming was followed by a complete break in interactions. Particular types of social signals displayed by the groomee just prior to grooming were highly correlated with the grooming of specific body sites. These results suggest that the groomee controls the behavior of the groomer by the social signals it displays and the positions it maintains during the grooming bout. Thus, the grooming act itself may play an important role in the social relationships between group members.     

The social context for harvestingIriartea deltoidea (Arecaceae)

Iriartea deltoidea grows abundantly from Nicaragua to Bolivia. The stem is harvested for construction, furniture making, and handicrafts. The objective of my study was to understand the potential for sustainable harvesting of this palm. Ethnographic fieldwork about market patterns and decision-making among harvesters revealed the nature of harvesting pressures near settled areas. The study also demonstrates methods for assessing social and economic influences on harvesting.     

Natural gaze signaling in a social context

Evolutionary theory, augmented by a vast literature on gaze cuing and gaze following, suggests that the unique high-contrast morphology of the human eye evolved for rapid and silent communication between conspecifics. While this theory rests on the fundamental idea that humans use their eyes to signal information, empirical studies have focused exclusively on the effects of gaze cues on human receivers. In a series of three experiments we examined the other side of the communication dynamic by investigating if, and when, humans signal gaze information to other humans in a natural, but controlled, situation involving food consumption. First, we established that there is a normative behavior to look away when someone begins to bite. Second, we found that participants were significantly more likely to look down at their food before taking a bite when they were eating with another person versus alone. Lastly, we found that in pairs where a social connection has been established, when one person looks down signaling that a bite is forthcoming, the other person tends to look away. These results demonstrate that natural gaze signaling occurs in the context of eating, and it can, dependent on the relationship between the pair, trigger a gaze response that is different from gaze following. Our study shows that natural social attention between individuals is a two-way street, where each person can signal and read gaze information, consistent with the idea that human eye morphology evolved to facilitate communication between conspecifics.     

Interactions between social factors and ovarian development in the European house cricket Acheta domesticus

Several endocrine-mediated processes in insects are influenced by environmental factors including the density and sex ratio of populations. Effects of grouping on total egg production and rate of vitellogenic ovary development were assessed in virgin Acheta domesticus (L.). Females midway through their last nymphal instar were isolated from a stock population of adults and nymphs of both sexes and maintained in groups or as isolates at 26–27°C, 70% relative humidity, on a 12L-12D photoperiod. The number of fully grown oocytes produced during the first 18 days of adult life was lower for animals in groups of 10 or 15 than for isolates, but antennectomy abolished this group effect. By contrast, terminal and penultimate oocyte length and ovary dry weight were greater in 5-day-old - pairs than in isolates. The presence of mature males during the first 21 days of adult life did not affect total egg production. Whether these group effects on cricket ovary development are mediated by the endocrine system is not yet known.

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Interaction entre les facteurs sociaux et le développement ovarien d'Acheta domesticus

Résumé L'étude a examiné les effets de groupement sur la production d'oeufs et sur la vitesse de la vitellogenèse chez les femelles vierges d'Acheta domesticus. Des femelles à la moitié de leur dernier stade larvaire, isolées d'une population adulte de base, et des nymphes des deux sexes ont été conservées en groupes ou isolées dans des récipients en plastique de 150 mm de diamètre et de 25 mm de hauteur à 26–27°C, 70% d'humidité relative et avec une photopériode de 12/12. La production totale des oeufs mûrs formés pendant les 18 premiers jours de vie imaginale était plus faible pour les animaux en groupes de 10 ou 15 que pour ceux qui étaient isolés, mais l'antennotectomie a éliminé cet effet de groupe. Au contraire, la longueur des derniers et avant-derniers ovocytes et le poids sec des ovaires étaient supérieurs pour les paires de 2 femelles de 5 jours que chez les individus isolés. La présence de mâles mûrs pendant les 21 premiers jours de vie imaginale n'a pas eu d'effet sur la production totale d'oeufs. L'hypothèse avancée est que ces effets de groupe (négatifs et positifs) sur le développement des ovaires d'Acheta domesticus ont reflété respectivement des accélérations et ralentissements de la vitellogenèse. La dépendance de l'induction de la vitellogenèse chez Acheta domesticus par les hormones juvéniles est connue (Benford, 1983) ainsi que les changements dans la quantité de produits neurosécréteurs, susceptibles d'être colorés dans la pars intercerebralis au cours du cycle reproductif (Bradley et Simpson, 1981). Nous ne savons pas si ces effets de groupement sur le développement des ovaires de grillon sont médiatisés par le système endocrine.

     

The effect of social context on dominance capacity of domestic hens

Initial paired encounters between Ss were determined. After these had extinguished, Ss were simultaneously released in a coop. Social orders were observed after 3 weeks in the flock. Subsequently, paired encounters were repeated.In one of the three flocks observed the social structure failed to stabilize. In the other two flocks the repeat peck orders corresponded highly with the social orders, but neither agreed with the original peck order.It was suggested that factors emerging from the social context produced the differences between initial encounters and the social order. On the other hand, once a pair relationship was learned in the flock it usually carried over to subsequent paired encounters.     

Connecting the dots: Stopover strategies of an intercontinental migratory songbird in the context of the annual cycle

The phases of the annual cycle for migratory species are inextricably linked. Yet, less than five percent of ecological studies examine seasonal interactions. In this study, we utilized stable hydrogen isotopes to geographically link individual black‐and‐white warblers (Mniotilta varia) captured during spring migration with breeding destinations to understand a migrant's stopover strategy in the context of other phases of the annual cycle. We found that stopover strategy is not only a function of a bird's current energetic state, but also the distance remaining to breeding destination and a bird's time‐schedule, which has previously been linked to habitat conditions experienced in the preceding phase of the annual cycle. Birds in close proximity to their breeding destination accumulate additional energy reserves prior to arrival on the breeding grounds, as reflected by higher migratory condition upon arrival, higher refueling rates measured via blood plasma metabolites, and longer stopover durations compared to birds migrating to breeding destinations farther from the stopover site. However, late birds near their breeding destination were more likely to depart on the day of arrival (i.e., transients), and among birds that stopped over at the site, the average duration of stopover was almost half the time of early conspecifics, suggesting late birds are trying to catch‐up with the overall time‐schedule of migration for optimal arrival time on the breeding grounds. In contrast, birds with long distances remaining to breeding destinations were more likely to depart on the day of arrival and primarily used stopover to rest before quickly resuming migration, adopting similar strategies regardless of a bird's time‐schedule. Our study demonstrates that migrants adjust their en route strategies in relation to their time‐schedule and distance remaining to their breeding destination, highlighting that strategies of migration should be examined in the context of other phases of the annual cycle.