The biological principles of swarm intelligence

The roots of swarm intelligence are deeply embedded in the biological study of self-organized behaviors in social insects. From the routing of traffic in telecommunication networks to the design of control algorithms for groups of autonomous robots, the collective behaviors of these animals have inspired many of the foundational works in this emerging research field. For the first issue of this journal dedicated to swarm intelligence, we review the main biological principles that underlie the organization of insects’ colonies. We begin with some reminders about the decentralized nature of such systems and we describe the underlying mechanisms of complex collective behaviors of social insects, from the concept of stigmergy to the theory of self-organization in biological systems. We emphasize in particular the role of interactions and the importance of bifurcations that appear in the collective output of the colony when some of the system’s parameters change. We then propose to categorize the collective behaviors displayed by insect colonies according to four functions that emerge at the level of the colony and that organize its global behavior. Finally, we address the role of modulations of individual behaviors by disturbances (either environmental or internal to the colony) in the overall flexibility of insect colonies. We conclude that future studies about self-organized biological behaviors should investigate such modulations to better understand how insect colonies adapt to uncertain worlds.     

Shifts in patterns and consumption of beverages between 1965 and 2002

Background: Beverage patterning may play a role in partially explaining the rising rates of obesity in the United States, yet little work on overall trends and patterns exits. Our objective was to examine trends and patterns of beverage consumption among U.S. adults. Methods: We used data from the nationally representative Nationwide Food Consumption Surveys (1965, 1977 to 1978) and the National Health and Nutrition Surveys (1988 to 1994, 1999 to 2002). To examine trends we determined percent consuming and per capita and per consumer caloric intake from all beverages. We used cluster analysis to determine year‐specific beverage patterns in 1977 and 2002. Results: The percentage of calories from beverages significantly increased between 1965 (11.8%), 1977 (14.2%), 1988 (18.5%), and 2002 (21.0%); this represents an overall increase of 222 calories per person per day from beverages, resulting largely from increased intake of calorically sweetened beverages. Beverage patterns in 2002 were more complex than in 1977 and were dominated by a greater number of beverages, reflecting the increase in alcohol, soda, and diet beverages. Conclusion: Calories from beverages increased substantially from 1965 to 2002, providing a considerable source of daily calories. Given the upward trends in calorically sweetened, nutrient‐deficient beverages and the shifts in overall beverage patterns, addressing beverage intake is a salient issue for adults.     

Overeating by young obesity-prone and lean rats caused by tastes associated with low energy foods

Objective: Childhood obesity is a prominent health problem that may involve early learning about tastes and the energy content of foods. We tested the hypothesis that food tastes predictive of low energy content cause overeating in young animals. Research Methods and Procedures: Juvenile and adolescent (4‐ and 8‐week‐old) male JCR:LA‐cp lean (+/cp or +/+) and obesity‐prone (cp/cp) rats were given sweet (saccharin) and salty (sodium chloride) gelatin cubes made with starch (high caloric) or no starch (low caloric) for 16 days of taste conditioning. After 10 hours of food deprivation, rats received pre‐meals with flavors that had been paired or unpaired with high caloric content during taste conditioning, followed immediately by measurement of chow intake at regular meals. Results: Our findings show that both lean (+/cp) and obesity‐prone (cp/cp) juvenile rats ate more regular chow after a pre‐meal with a flavor associated with low caloric value than after a similar pre‐meal with a flavor predictive of high caloric content. This effect occurred with juvenile rats but not with adolescents. Discussion: Data from our study indicate that the subversion of the relationship between taste and caloric content disrupts the normal physiological and behavioral energy balance of juvenile rats, resulting in overeating that is independent of genetic disposition for obesity.     

Birth Order Influences Reproductive Measures in Australians

We examine the relationship between birth order and reproductive behaviors in a sample of Australian residents, accounting for personality, personal achievements, and family structure. Using generalized linear models and survival analyses we build predictive models for each reproductive measure and test those models on an independent data subset. Compared with functional firstborns (middle-borns more than 5 years younger than their next older sibling), male middle-borns and last-born females had younger ages of first sexual intercourse, and middle-born females had a younger age at first pregnancy. There was no difference in females’ age at first birth. Male middle-borns tended to have an older average age at first birth. Controlling for age, both male and female middle-borns had fewer children. Overall, middle-borns differ more from functional firstborns than do last-borns. Given the significant but small effect sizes demonstrated in this study, we suggest that developmental characteristics that may facilitate middle-borns’ success within the natal family carry slight fitness costs during the reproductive years.

Equilibrium amide hydrogen exchange and protein folding kinetics

The classical Linderstrøm-Lang hydrogen exchange (HX) model is extended to describe the relationship between the HX behaviors (EX1 and EX2) and protein folding kinetics for the amide protons that can only exchange by global unfolding in a three-state system including native (N), intermediate (I), and unfolded (U) states. For these slowly exchanging amide protons, it is shown that the existence of an intermediate (I) has no effect on the HX behavior in an off-pathway three-state system (IUN). On the other hand, in an on-pathway three-state system (UIN), the existence of a stable folding intermediate has profound effect on the HX behavior. It is shown that fast refolding from the unfolded state to the stable intermediate state alone does not guarantee EX2 behavior. The rate of refolding from the intermediate state to the native state also plays a crucial role in determining whether EX1 or EX2 behavior should occur. This is mainly due to the fact that only amide protons in the native state are observed in the hydrogen exchange experiment. These new concepts suggest that caution needs to be taken if one tries to derive the kinetic events of protein folding from equilibrium hydrogen exchange experiments.     

New technique for studying reaction forces during primate behaviors on vertical substrates

Recording reaction forces from primates during behaviors on vertical substrates, such as leaping, climbing, or biting trees, typically requires the design and construction of customized recording devices or mounting commercially available force platforms in a vertical position. The technical difficulties imposed by either option have hindered in vivo research on the kinetics of primate behaviors on vertical substrates. We describe a simple, inexpensive apparatus for recording forces from primate behaviors on vertical substrates. The apparatus includes an instrumented beam fastened directly to a horizontal force platform and a surrounding vertical substrate that does not contact the instrumented beam or platform. The contact piece at the end of the instrumented beam is positioned flush with the noninstrumented vertical substrate, and reaction forces elicited on this instrumented section are directed to the force platform. Because most of the vertical substrate is not instrumented, we can isolate and record forces from a single limb or jaw during a behavior. Biewener and Full ([1992] Biomechanics Structures and Positions: A Practical Approach; New York: Oxford University press, p. 45-73) gave seven criteria to consider when designing a customized force-recording device. Where appropriate, we tested if our apparatus met their criteria. The apparatus accurately records forces in three orthogonal directions, has low cross-talk, maintains a high frequency response, exhibits a linear response up to at least 200 Newtons, and displays a uniform response to a given force across the instrumented contact piece. Our design does not easily facilitate the identification of the point of force application. Therefore, joint moments cannot be easily calculated. This limitation, however, does not affect the apparatus's ability to accurately record the magnitude and direction of a force (as shown by other tests). We developed this apparatus to measure jaw forces during tree gouging in common marmosets (Callithrix jacchus), but the general design can be readily modified to study a variety of primate behaviors on vertical substrates.     

Variables influencing the origins of diverse abnormal behaviors in a large sample of captive chimpanzees (Pan troglodytes)

The developmental origin of abnormal behaviors is generally associated with early rearing environments that lack sufficient physical and sensory stimulation. However, other factors should also be considered. A large sample of captive chimpanzees (128 males and 140 females) was surveyed for the presence or absence of 18 abnormal behaviors. Origin variables included the subject's source (zoo, pet, performer, or laboratory), rearing (mother‐ or hand‐reared), and sex. Animals were assessed while held at the Primate Foundation of Arizona, University of Texas M. D. Anderson Cancer Center, or White Sands Research Center. There was a confound among origin variables; more hand‐reared animals than expected were from laboratories. Logistic regression tested the relationship of rearing and source, with sex as a secondary predictor variable, to each of the abnormal behaviors. There was no clear association between any abnormal behavior and source. However, for coprophagy, relative to animals from the laboratory, zoo animals tended to show a higher prevalence, while performers tended to show a lower prevalence (when rearing and sex were controlled). Rocking and self‐sucking were significantly more likely in hand‐reared animals. Coprophagy and depilation of self were significantly more likely in mother‐reared animals. When rearing and source were statistically controlled, the only significant sex difference was a higher prevalence of coprophagy in females and a higher prevalence of rocking in males. In a second, smaller sample of 25 males and 33 females from Southwest Foundation for Biomedical Research, no significant sex association was found for coprophagy, urophagy, rocking, or self‐depilation. In this second sample, coprophagy was also significantly more likely in mother‐reared than hand‐reared subjects. The association of some abnormal behaviors with mother‐rearing suggests that some form of social learning may be involved in the origin of some of these behavior patterns. This indicates that some abnormal behaviors may not be always be indicative of reduced psychological well‐being in captive chimpanzees. Am. J. Primatol. 48:15–29, 1999. © 1999 Wiley‐Liss, Inc.     

Fat is sexy for females but not males: the influence of body reserves on reproduction in snakes (Vipera aspis)

Reproduction is energetically expensive for both sexes, but the magnitude of expenditure and its relationship to reproductive success differ fundamentally between males and females. Males allocate relatively little to gamete production and, thus, can reproduce successfully with only minor energy investment. In contrast, females of many species experience high fecundity-independent costs of reproduction (such as migration to nesting sites), so they need to amass substantial energy reserves before initiating reproductive activity. Thus, we expect that the relationship between energy reserves and the intensity of reproductive behavior involves a threshold effect in females, but a gradual (or no) effect in males. We tested this prediction using captive vipers (Vipera aspis), dividing both males and females into groups of high versus low body condition. Snakes from each group were placed together and observed for reproductive behavior; sex-steroid levels were also measured. As predicted, females in below-average body condition had very low estradiol levels and did not show sexual receptivity, whereas males of all body condition indices had significant testosterone levels and displayed active courtship. Testosterone levels and courtship intensity increased gradually (i.e., no step function) with body condition in males, but high estradiol levels and sexual receptivity were seen only in females with body reserves above a critical threshold.     

Cell populations and morphogenetic movements underlying formation of the avian primitive streak and organizer

The cell populations and morphogenetic movements that contribute to the formation of the avian primitive streak and organizer-Hensen's node-are poorly understood. We labeled selected groups of cells with fluorescent dyes and then followed them over time during formation and progression of the primitive streak and formation of Hensen's node. We show that (1) the primitive streak arises from a localized population of epiblast cells spanning the caudal midline of Koller's sickle, with the mid-dorsal cells of the primitive streak arising from the midline of the epiblast overlying Koller's sickle and the deeper and more lateral primitive streak cells arising more laterally within the epiblast overlying the sickle, from an arch subtending about 30 degrees; (2) convergent extension movements of cells in the epiblast overlying Koller's sickle contribute to formation of the initial primitive streak; and (3) Hensen's node is derived from a mixture of cells originating both from the epiblast just rostral to the incipient (stage 2) primitive streak and later from the epiblast just rostral to the elongating (stage 3a/b) primitive streak, as well as from the rostral tip of the progressing streak itself. Collectively, these results provide new information on the formation of the avian primitive streak and organizer, increasing our understanding of these important events of early development of amniotes.     

Influence of “protective” symbionts throughout the different steps of an aphid–parasitoid interaction

Microbial associates are widespread in insects, some conferring a protection to their hosts against natural enemies like parasitoids. These protective symbionts may affect the infection success of the parasitoid by modifying behavioral defenses of their hosts, the development success of the parasitoid by conferring a resistance against it or by altering life-history traits of the emerging parasitoids. Here, we assessed the effects of different protective bacterial symbionts on the entire sequence of the host-parasitoid interaction (i.e., from parasitoid attack to offspring emergence) between the pea aphid, Acyrthosiphon pisum, and its main parasitoid, Aphidius ervi and their impacts on the life-history traits of the emerging parasitoids. To test whether symbiont-mediated phenotypes were general or specific to particular aphid–symbiont associations, we considered several aphid lineages, each harboring a different strain of either Hamiltonella defensa or Regiella insecticola, two protective symbionts commonly found in aphids. We found that symbiont species and strains had a weak effect on the ability of aphids to defend themselves against the parasitic wasps during the attack and a strong effect on aphid resistance against parasitoid development. While parasitism resistance was mainly determined by symbionts, their effects on host defensive behaviors varied largely from one aphid–symbiont association to another. Also, the symbiotic status of the aphid individuals had no impact on the attack rate of the parasitic wasps, the parasitoid emergence rate from parasitized aphids nor the life-history traits of the emerging parasitoids. Overall, no correlations between symbiont effects on the different stages of the host–parasitoid interaction was observed, suggesting no trade-offs or positive associations between symbiont-mediated phenotypes. Our study highlights the need to consider various sequences of the host-parasitoid interaction to better assess the outcomes of protective symbioses and understand the ecological and evolutionary dynamics of insect–symbiont associations.