Tandem Recruitment and Foraging in the Ponerine Ant <Emphasis Type="Italic">Pachycondyla harpax</Emphasis> (Fabricius)

Tandem running is a common recruitment strategy in ant species with small colony sizes. During a tandem run, an informed leader guides a usually naïve nestmate to a food source or a nest site. Some species perform tandem runs only during house hunting, suggesting that tandem running does not always improve foraging success in species known to use tandem running as a recruitment strategy, but more natural history information on tandem running under natural conditions is needed to better understand the adaptive significance of tandem recruitment in foraging. Studying wild colonies in Brazil, we for the first time describe tandem running in the ponerine ant Pachycondyla harpax (Fabricius). We asked if foragers perform tandem runs to carbohydrate- (honey) and protein-rich (cheese) food items. Furthermore, we tested whether the speed and success rate of tandem runs depend on the foraging distance. Foragers performed tandem runs to both carbohydrate food sources and protein-rich food items that exceed a certain size. The probability to perform a tandem run and the travelling speed increase with increasing foraging distances, which could help colonies monopolize more distant food sources in a competitive environment. Guiding a recruit to a food source is costly for leaders as ants are ~66% faster when travelling alone. If tandem runs break up (~23% of all tandem runs), followers do not usually discover the food source on their own but return to the nest. Our results show that tandem running to food sources is common in P. harpax, but that foragers modify their behaviour according to the type of food and its distance from the nest. Competition with other ants was intense and we discuss how tandem running in P. harpax might help colonies to build-up a critical number of ants at large food items that can then defend the food source against competitors.     

Social organization of colony movement in the tropical ponerine ant,Diacamma rugosum (Le Guillou)

This work is part of a study on the social organization ofDiacamma rugosum, a large ponerine ant, which lacks a distinctive reproductive queen. This ant forms a small colony and frequently changes its nest site when the environmental conditions become unfavourable. Experiments in the laboratory showed that slight physical disturbances easily caused colony movement. The process of movement consisted of 3 successive phases: a) an exploration period, b) an movement period and c) a final movement period. The movement was organized by leader ants and 5 to 25% of all workers became leaders. These workers showed both tandem running and carrying behaviour during movement, tandem running being employed to recruit workers, whereas carrying behaviour was strictly limited to carrying eggs, larvae, pupae and males. During movement most of the tandem leader ants are those engaged in outdoor works in daily life. Potential of workers to become tandem leaders was correlated with outside works undertaken in daily life.     

Settlement in the prey termite nest by the ponerine antPachycondyla caffraria (Smith), and tandem running signal analysis for the following ant

The workers ofPachycondyla caffraria attack the nests of the termiteMicrocerotermes sp. in the laboratory. The hunter workers bore into the side of the nest, enter and catch the termites, and return to their nest with the captured prey. Later in the same day, all or part of the colony moves out and settles in the termite nest. The hunter workers use tandem running for the attack of the termite nest, the capture of termite and the removal of the colony to the nest which was raided. To analyse the relevant signals for the following ant during tandem running, we offered different dummies to followers which had been separated from their leader ants. The signals which release the following behaviour are a conbination of visual and chemical signals. Seventy percent of motivated followers reacted positively to paper with methanolic extract of the leader ant, 44% of motivated followers reacted positively to an odourless paper, and 100% reacted positively to a freshly killed leader ant. The leading effect of the body surface is lost by cleaning with solvents of different polarity.     

Leadership and Path Characteristics during Walks Are Linked to Dominance Order and Individual Traits in Dogs

Movement interactions and the underlying social structure in groups have relevance across many social-living species. Collective motion of groups could be based on an “egalitarian” decision system, but in practice it is often influenced by underlying social network structures and by individual characteristics. We investigated whether dominance rank and personality traits are linked to leader and follower roles during joint motion of family dogs. We obtained high-resolution spatio-temporal GPS trajectory data (823,148 data points) from six dogs belonging to the same household and their owner during 14 30–40 min unleashed walks. We identified several features of the dogs'' paths (e.g., running speed or distance from the owner) which are characteristic of a given dog. A directional correlation analysis quantifies interactions between pairs of dogs that run loops jointly. We found that dogs play the role of the leader about 50–85% of the time, i.e. the leader and follower roles in a given pair are dynamically interchangable. However, on a longer timescale tendencies to lead differ consistently. The network constructed from these loose leader–follower relations is hierarchical, and the dogs'' positions in the network correlates with the age, dominance rank, trainability, controllability, and aggression measures derived from personality questionnaires. We demonstrated the possibility of determining dominance rank and personality traits of an individual based only on its logged movement data. The collective motion of dogs is influenced by underlying social network structures and by characteristics such as personality differences. Our findings could pave the way for automated animal personality and human social interaction measurements.     

Coupled adult-brood transport augments relocation in the Indian queenless ant Diacamma indicum

Colony relocation is an important aspect in the lives of social insects. In ants, the process of relocation is further complicated as brood, in addition to adults, have to be transported to the new nest. Here, we have investigated brood transport in the Indian ponerine ant Diacamma indicum, which uses tandem running—a primitive mode of recruitment—for the entire colony to relocate. We have found that there were no brood transport specialists and most of the brood was transported in the mandibles of followers that were being tandem run. Therefore, in a single tandem run, one adult and one brood item was effectively transported by tandem leaders augmenting the relocation process.     

The journey of tandem running: the twists, turns and what we have learned

Tandem running, whereby one worker recruits another is utilised by many ant species. Since first being recorded, it has provided a valuable experimental tool for testing hypotheses about collective decision making, communication and even teaching. In this review I explore the journey tandem running has taken, the twists and turns in the theories surrounding it and what tandem running has taught us. This review examines the empirical research conducted on tandem running, from when it was first described, considers the theories that have arisen from that research and ultimately what has been learnt and what is still yet to be explored.     

The influence of sex,patch quality,and travel time on foraging decisions by young adult Homo sapiens L.

A series of experiments was run to examine the influence of sex, patch quality, and travel time on foraging decisions by young adult humans. Subjects were required to gather sultanas arranged at two different densities on artificial bushes. Female subjects spent less time at a bush (patch) than did males and picked sultanas at a greater rate. Female subjects increased residence time as density and travel time increased as predicted by McNair [American Naturalist 119: 511–529 (1982)]. Giving up time decreased with increasing patch quality but remained unaffected by travel time. Predictions for the habitat rate of picking were calculated assuming either residence time or giving-up time rules of thumb. A comparison of these with observed habitat rates indicated that the subjects were most likely to be using the residence time rule. Mostly, subjects employed a residence time longer than that required to produce the maximum habitat rate. The asymmetry of the reward curve may explain the overshoot.     

Homosexual tandem running as selfish herd in Reticulitermes speratus: novel antipredatory behavior in termites.

We investigated the predator avoidance mechanism of post-swarming alates of the lower subterranean termite, Reticulitermes speratus Kolbe. In some lower termites, homosexual tandem running is observed in addition to ordinary heterosexual tandem running. An experiment designed to compare the risk of predation by a termite-hunting ant, Brachyponera chinensis Emery, showed that homosexual tandem running reduced the predation risk until termites encounter the opposite sex. Since an individual ant cannot capture two dealates at once, one of the two dealates forming a tandem can escape while the ant captures its partner. Therefore, the "post-encounter risk" of individuals running in tandem was lower than that of single individuals. The "encounter risk" with predatory ants was also examined using a mathematical model considering the increased detectability of the predator due to enhanced size of the prey unit. It was suggested that tandem running reduces the predation risk of both participants, even when the enhanced encounter risk was taken into account. In males, competition for the back position was often observed, and consequently, the male at the back was always larger than the male in front. When a male-male tandem encountered a female, the back male won the female more often than the front male. This result suggested that male-male tandem running should result in selection pressure in favor of vigorous males. In conclusion, tandem running decreases the individual predation risk through the dilution effect, and it also plays a role as a mechanism of indirect sexual selection.     

Individual constancy of local search strategies in the giant tropical ant,Paraponera clavata (Hymenoptera: Formicidae)

Paraponera clavata workers engage in a period of local search after encountering a small amount of artificial nectar. Giving-up times from local search are not distributed normally; there is a strong skew to longer times. There is no statistically significant relationship between the amount of time required to collect the food and the subsequent search time. Giving-up time in response to the first reward presented to an ant is positively correlated with that ant's response to a second such reward. However, giving-up times diminish when an ant is presented with a series of rewards. Local search is a function of individual strategies, which remain relatively constant in the short term.     

The identity of Leptothorax albipennis (Curtis) (Hymenoptera: Formicidae) and its presence in Great Britain

The karyotype and external morphology of Leptothorax ( Myrafant ) ants, taken from nests at nine ' Leptothorax tuberum ' localities in England and Wales, identifies them all as L. tuberointerruptus. Their karyotype differs in chromosome number and chromosome morphology from the karyotypes of morphologically similar European Leptothorax ( Myrafant ) species including L. tuberum , but matches the karyotype shared by L. tuberointerruptus and L. rougeti. Worker propodeal spine length, and worker propodeal spine shape coupled with worker gaster banding characteristics, distinguish the nest samples from L. rougeti. The presence of L. tuberointerruptus in Britain is therefore confirmed, and the data demonstrate this ant's occurrence throughout the British range attributed to L. tuberum. In the absence of equivalent data identifying L. tuberum as a British species, it may reasonably be assumed that L. tuberointerruptus has been misrecorded as L. tuberum in Britain and that all British mainland records of L. tuberum refer to L. tuberointerruptus. An examination of the syntypes of Stenamma albipennis shows that S. albipennis and L. tuberointerruptus are synonymous, and that L. albipennis is the senior name. It follows that L. albipennis is a scarce British ant of 'Notable B' conservation status. A taxonomic synopsis for L. albipennis is given.     

Spontaneous and deferred imitation in the pigeon

Experimentally-naive pigeons were placed on one side of a clear partition. A pigeon on the other side received food for pecking a ping-pong ball, pulling a rope, or pecking a plastic disk. When given access to a similar object, each naive pigeon pecked or pulled at a low rate for several sessions and two continued to do so forseveral sessions in the absence of the leader. In a second experiment, the latter effect was demonstrated after a delay of 24 hours, even though the naive pigeons had never had access to the object in the presence of the model. A third experiment demonstrated that the effect on the follower was not due merely to the presence of or activity of another pigeon and was at least somewhat specific to the behavior of the model.     

The Use of Edges in Visual Navigation by the Ant Leptothorax albipennis

Certain navigating insects home in on their goal by moving so that currently viewed images of landmarks fall on the same retinal locations memorized during previous visits. Here we show that ants can use similar retinotopic learning to guide lengthy routes, by memorizing and walking parallel to a distinct visual edge. We induced workers of the ant Leptothorax albipennis to travel parallel to a prominent wall. When the wall's height was changed, the ants' paths consistently shifted toward a lowered wall and away from a raised wall, as would be expected if they attempt to keep the wall's image at a constant retinal position. These path shifts were smaller than would be expected if the wall was the only guide to navigation, suggesting that other cues are also important. Significantly larger shifts were seen when edge guidance was enhanced by using two walls, one on each side of the path.     

Mechanisms for synchrony and alternation in song interactions of the bushcricket <Emphasis Type="Italic">Mecopoda elongata</Emphasis> (Tettigoniidae: Orthoptera)

Males of the bushcricket Mecopoda elongata synchronise or alternate their chirps with their neighbours in an aggregation. Since synchrony is imperfect, leader and follower chirps are established in song interactions; females prefer leader chirps in phonotactic trials. Using playback experiments and simulations of song oscillator interactions, we investigate the mechanisms that result in synchrony and alternation, and the probability for the leader role in synchrony. A major predictor for the leader role of a male is its intrinsic chirp period, which varies in a population from 1.6 to 2.3 s. Faster singing males establish the leader role more often than males with longer chirp periods. The phase-response curve (PRC) of the song oscillators differs to other rhythmically calling or flashing insects, in that only the disturbed cycle is influenced in duration by a stimulus. This results in sustained leader or follower chirps of one male, when the intrinsic chirp periods of two males differ by 150 ms or more. By contrast, the individual shape of the males PRC has only little influence on the outcome of chirp interactions. The consequences of these findings for the evolution of synchrony in this species are discussed.     

Intracranial self-stimulation motivates treadmill running in rats.

Most animal running models have traditionally used aversive motivators to induce exercise tasks. This study demonstrates treadmill running motivated by reinforcement of intracranial self-stimulation (ICSS), providing an alternative model with which to study physiological responses to exercise. Twenty-nine male Sprague-Dawley rats were stereotaxically implanted with bipolar electrodes aimed at the ventral tegmental area of the brain. After 7 days of operant lever-press training for ICSS, rats that pressed at least 50 presses/min were randomly divided into three conditions: exercise-reinforcing brain stimulation (Ex-St), exercise-aversive shock (Ex-Sh), and sedentary controls (C). Ex-St and Ex-Sh ran for 30 min at 25 m/min at 5% grade for 2 wk with ICSS and electric shock as the motivator, respectively, while C did not run. At the end of 2 wk, Ex-St and Ex-Sh performed an endurance run. Results show that Ex-St ran longer than Ex-Sh [63 +/- 10 vs. 42 +/- 10 (SD) min; P less than 0.05]. HR was higher in Ex-St than in C (P less than 0.05). Rectal temperature increased similarly in both exercise groups. This model provides a highly effective method to motivate treadmill running in rats and as such can be used to characterize physiological responses to exercise without the potentially confounding influence of stress associated with an aversive shock motivator.     

Temporal variation and the evolution of a parasitoid foraging cue

This work details theory in which selection favors generalists in a more variable environment. Specifically, in a two-host-one-parasitoid model, temporal variation in host abundances alters the optimal searching strategy and leads to the evolution of more generalist parasitoid strategies. Consistent with empirical observations, parasitoids learn host/plant odors, and use them as a cue to search for oviposition sites. The amount of unsuccessful search time required before a parasitoid alters its searching cues (the "giving-up time") is modeled in order to understand the evolutionarily optimal giving-up times under a variety of conditions. When host abundances vary across time, a generalist parasitoid strategy evolves with short giving-up times as it is likely that the host initially favored by a parasitoid will now have a low abundance. In contrast, when populations reach stable dynamics across time, giving-up times typically evolve to longer times, i.e. parasitoids remain specialized longer. The effect of temporal fluctuations is consistent across variation caused by endogenous population interactions and, to some degree, by environmental stochasticity. The conclusions are robust in that there is a strong degree of concordance between the results of a stochastic, individual-based model and a deterministic, numerical model. As an extension, spatial variation in hosts that leads to unequal tradeoffs between generalist parasitoids and specialist parasitoids may also result in the evolution of reduced giving-up times.     

Multiple copies of a retroposon interrupt spliced leader RNA genes in the African trypanosome, Trypanosoma gambiense.

The 140-nucleotide spliced leader (SL) RNA, involved in mRNA maturation in the African trypanosomes and in other kinetoplastida, is encoded by a tandem array of spliced leader genes. We show that the 1.4-kb SL gene repeat unit in Trypanosoma gambiense is organized in tandem arrays confined to two large (minimum size 350-450 kb) restriction fragments. SL genes in both arrays are interrupted by a total of eight conserved insertion elements. Cleavage of genomic DNA at restriction sites present within the insertion element but not in the SL gene repeat, releases variable numbers of SL genes from the tandem array. Since the insertion element contains a terminal poly(A) track of 36 bases and because a 49-bp duplication of target DNA has occurred at the integration site, we conclude that it is a retroposon. This retropson is uniquely associated with the SL gene clusters. These retroposons presumably originated from a single insertion event after which their copy number increased, possibly through unequal sister chromatid exchange.     

Sequence specificity of 125I-labelled Hoechst 33258 damage in six closely related DNA sequences

The sequence selectivity of [125I]Hoechst 33258 in six 340 base-pair DNA sequences has been investigated. [125I]Hoechst 33258, which is a bis-benzimidazole and binds to the minor groove of B-DNA, preferentially binds to A + T-rich regions of DNA. Six out of nine strong binding sites contained four or more consecutive A.T base-pairs, while the other three strong binding sites were AAGGATT, TATAGAAA (the peak of damage was in the run of 3 A residues) and AAA. One of the six weak binding sites had five consecutive A.T base-pairs, two of the weak binding sites had three, and three did not have any. In addition to genomic 340 base-pair alpha RI-DNA (which is a tandem repeat in human cells), five 340 base-pair alpha RI-DNA clones were generated that differed from the genomic "consensus" sequence by a number of random base alterations. The effect of these base changes on the sequence specificity of [125I]Hoechst 33258 damage indicated that of the base changes that interrupted 14 binding sites, six decreased and eight did not change the extent of damage, while two sites changed position. Of the base alterations that augmented 17 binding sites, five increased, two decreased and ten did not alter the degree of cleavage, while ten sites changed position. It was concluded from the data that, while runs of consecutive A.T base-pairs was the most important parameter that determines [125I]Hoechst 33258 binding, other factors including position in the DNA sequence, nearest neighbour and long-range interactions were also important.     

Conditioned taste avoidance induced by forced and voluntary wheel running in rats

Voluntary exercise by rats running in a freely rotating wheel (free wheel) produces conditioned taste avoidance (CTA) of a flavored solution consumed before running [e.g., Lett, B.T., Grant, V.L., 1996. Wheel running induces conditioned taste aversion in rats trained while hungry and thirsty. Physiol. Behav. 59, 699-702]. Forced exercise, swimming or running, also produces CTA in rats [e.g., Masaki, T., Nakajima, S., 2006. Taste aversion induced by forced swimming, voluntary running, forced running, and lithium chloride injection treatments. Physiol. Behav. 88, 411-416]. Energy expenditure may be the critical factor in producing such CTA. If so, forced running in a motorized running wheel should produce CTA equivalent to that produced by a similar amount of voluntary running. In two experiments, we compared forced running in a motorized wheel with voluntary running in a free wheel. Mean distance run over 30 min was equated as closely as possible in the two apparatuses. Both types of exercise produced CTA relative to sedentary, locked-wheel controls. However, voluntary running produced greater CTA than forced running. We consider differences between running in the free and motorized wheels that may account for the differences in strength of CTA.     

Axon fasciculation and differences in midline kinetics between pioneer and follower axons within commissural fascicles

Early neuronal scaffold development studies suggest that initial neurons and their axons serve as guides for later neurons and their processes. Although this arrangement might aid axon navigation, the specific consequence(s) of such interactions are unknown in vivo. We follow forebrain commissure formation in living zebrafish embryos using timelapse fluorescence microscopy to examine quantitatively commissural axon kinetics at the midline: a place where axon interactions might be important. Although it is commonly accepted that commissural axons slow down at the midline, our data show this is only true for leader axons. Follower axons do not show this behavior. However, when the leading axon is ablated, follower axons change their midline kinetics and behave as leaders. Similarly, contralateral leader axons change their midline kinetics when they grow along the opposite leading axon across the midline. These data suggest a simple model where the level of growth cone exposure to midline cues and presence of other axons as a substrate shape the midline kinetics of commissural axons.