Equilibrium muscle cross-bridge behavior. Theoretical considerations.

We have developed a model for the equilibrium attachment and detachment of myosin cross-bridges to actin that takes into account the possibility that a given cross-bridge can bind to one of a number of actin monomers, as seems likely, rather than to a site on only a single actin monomer, as is often assumed. The behavior of this multiple site model in response to constant velocity, as well as instantaneous stretches, was studied and the influence of system parameters on the force response explored. It was found that in the multiple site model the detachment rate constant has considerably greater influence on the mechanical response than the attachment rate constant. It is shown that one can obtain information about the detachment rate constants either by examining the relationship between the apparent stiffness and duration of stretch for constant velocity stretches or by examining the force-decay rate constants following an instantaneous stretch. The main effect of the attachment rate constant is to scale the mechanical response by influencing the number of attached cross-bridges. The significance of the modeling for the interpretation of experimental results is discussed.     

Foraging behaviour of harvesting ants determines seed removal and dispersal

Harvesting ants can affect the regeneration of plants through at least two different processes: seed removal and seed dispersal. We analyse the role of different foraging strategies of ants on patterns of seed removal and dispersal by three Messor species with considerable differences in their foraging systems. Messor capitatus workers rarely leave the nest in well-formed columns, while the other two species form foraging trails, with M. bouvieri forming temporary trails and M. barbarus foraging on a stable system of permanent foraging trails. Overall seed intake of M. capitatus colonies is considerably less than that of the two group-foraging species. There are also differences in the size of seeds collected: M. barbarus and M. capitatus harvest similar amounts of large and small seeds, while M. bouvieri harvests small seeds more intensely than large ones, due to the smaller size of the worker caste. The three Messor species differ in the percent of seed dropping of the different seed type and in the seed dispersal distance. Moreover, M. bouvieri and M. capitatus redistributed dropped seeds preferentially in bare soil and low sparse vegetation habitats, while M. barbarus redistributed seeds mainly in the high vegetation habitat. These results show that the foraging systems of these harvesting ants determine different patterns of seed removal and dispersal and, thus, affect the abundance and redistribution of seeds in the area.     

Foraging behavior ofPachydiplax longipennis (Odonata: Libellulidae)

Food intake, prey availability, and prey capture behavior at feeding areas were quantified in the dragonflyPachydiplax longipennis by observing focal individuals on artificial perches, where they exhibited marked short-term site fidelity. Prey capture success was high and relatively constant, but the frequency and duration of feeding flights depended on the time of day and season (at least in part because of associated variation in temperature and other physical factors), study site, sex, density of other dragonflies, and prey density. Individuals rapidly responded temporally and spatially to changes in prey availability, particularly to localized prey concentrations.     

Foraging behavior of honeybees on white clover

Summary Measurements of several aspects of foraging behavior of honeybees on white clover and of factors that might influence it were made at one-to-two-week intervals during the season. Other measurements were made on intervening days. Individual blossoms yielded a mean of from 0.02 to 0.08 l of nectar containing 42 to 65% sugar during the season. On one day when the nectar averaged 65% sugar, bees with pollen on their corbiculae carried a mean of 5.2 mg of pollen and 37.3 mg of nectar; bees without pollen carried a mean of 37.9 mg of nectar. On 10 occasions each of 50 bees were timed while foraging a single blossom; the mean foraging speed differed significantly on the 10 occasions, and varied from 1.5 to 3.0 seconds per blossom. Each of 18 bees was timed during visits to 25 blossoms, and the total time required for the same bees to forage from the blossoms on 25 racemes was also measured. The mean foraging speed of these bees varied from 1.1 to 4.5 seconds per blossom; the differences were highly significant. These bees foraged 7.0 to 26.0 blossoms per minute, and there was a strong negative correlation between the mean seconds required for bees to forage blossoms and the mean number of blossoms foraged per minute. Fifty one bees observed for a total of 314.5 minutes foraged an average of 18.4 blossoms per minute and 3.4 blossoms per inflorescence. Sixty one per cent of the flights of foraging bees were made to inflorescences estimated to be less than 5 inches from the starting point.Published as Technical Contribution N^o 4244 from theTexas Agricultural Experiment Station.     

Foraging behaviour of Atta cephalotes (leaf-cutting ants): an examination of two predictions for load selection

Two mechanisms have been proposed to explain how colony-level foraging performance of leaf-cutting ants can be maximized when workers harvest leaf fragments of a size that does not maximize their individual performance. Each mechanism predicts that ants will adjust the size of leaf fragments between starting a foraging bout and establishing full traffic between the nest and foraging site, but the two models predict shifts in opposite directions. I examined fragment sizes at the start of daily foraging in five field colonies of Atta cephalotes in Costa Rica and detected an obvious shift in only one case. More shifts were detected when the small and large ends of the worker body size range were considered separately, but the direction was inconsistent among colonies. I also examined the role of returning laden workers in recruitment of nestmates by intercepting all laden workers for the first 2 h of foraging, and measuring the effect on the arrival of recruits at the foraging site. In two cases, the flow of recruits was not diminished by the interception of returning workers. The results suggest that neither mechanism correctly and consistently accounts for load size selection by leaf-cutting ants. Copyright 2000 The Association for the Study of Animal Behaviour.     

Nestmate discrimination in ants: effect of bioassay on aggressive behavior

Summary: Aggression assays are commonly used to study nestmate recognition in social insects. Methods range from detailed behavioral observations on small numbers of insects to counts of individuals fighting in group interactions. These assays vary in the equipment used and the intensity and duration of observations. We used the Argentine ant, Linepithema humile, to compare four aggression bioassays for consistency between replicates, similarity between assays, and ability to predict whole colony interactions. The assays included were 1 live – 1 dead ant interactions, live 1-1 battles, live 5-5 battles, and 1 ant introduced to a foreign colony. We tested six ant colonies in all pairwise combinations using four different assays and two to three scoring methods per assay. We also conducted a colony merging experiment to see which assays were capable of predicting this ecologically important event. We found that scoring methods within assays yielded very similar results, giving us no reason to favor observationally intense procedures, such as continuous scanning, over less observationally intense systems, such as snapshot surveys. Assays differed greatly in their consistency between replicates. No two replicates of the 1 live – 1 dead assay were significantly correlated. The live 5-5 and the colony introduction assays were the most consistent across replicates. The mean scores of the live 1-1, live 5-5 and colony introduction assays were all significantly correlated with each other; only the live 5-5 assay was significantly correlated with the 1 live – 1 dead assay. Assays that utilized the greatest number of live ants were the most likely to reveal high levels of aggression. The aggression scores of all but the 1 live – 1 dead assay were positively correlated with the number of ants that died during whole colony encounters and negatively associated with colony merging. We conclude that all live ant assays tested are useful tools for analyzing aggressive interactions between colonies, but that the pairing of a live and dead ant produced inconsistent results and generally lower levels of aggression. We found relatively low consistency between trials using the live 1-1 assay, but found that with sufficient replication its results were highly correlated with the assays using more interacting ants. We suggest that isolated aggressive acts in assays do not necessarily predict whole colony interactions: some colonies that fought in bioassays merged when the entire colonies were allowed to interact.     

Foraging ecology and patterns of diversification in dipteran parasitoids of fire ants in south Brazil

1. At least sixteen species of parasitoid flies in the genus Pseudacteon (family Phoridae) attack fire ants in the Solenopsis saevissima subcomplex in South America. Little is known of behavioural or ecological differences among Pseudacteon parasitoids of fire ants, although their coexistence in multispecies communities would suggest that important differences exist. Seven Pseudacteon species in two separate communities were studied in south-east Brazil. The way in which hosts detect and respond to the presence of parasitoids, attack rates of the parasitoids, and host location behaviour of the parasitoids were examined.
2. Reductions in fire ant recruitment were more closely related to the number of ants attacked along a foraging trail than to the amount of time that a phorid was present.
3. Pseudacteon solenopsidis differed from other phorid species by flying backwards while pursuing ants, by attacking at lower rates than other phorids, and by spending longer around fire ant foraging trails than other phorids before departing. Fire ant recruitment to food often rebounded in the continued presence of P. solenopsidis.
4. In each of the two communities, certain Pseudacteon species appeared frequently at Solenopsis foraging trails, whereas others appeared predominantly at mound disturbances. Two distinct size classes of phorids were present in each community, and the community with the larger ant host species also had a third and larger phorid species. No phorid species from the same community had similar body sizes and similar host location behaviours, although numerous species from different communities shared both of these traits.
5. Heterogeneity in host size and in the ecological circumstances under which hosts are vulnerable to attack appears to have influenced the evolution and perhaps maintenance of diverse Pseudacteon communities.     

Theoretical considerations on cell ensembles

Structure-function interdependency must apply at the supracellular level as well as at cellular and molecular levels. The overall structure and the intercellular geometry of the multicellular erythroblastic island, although strongly dependent upon molecular interactions (which determine or modulate recognition, adhesion, and the like), also carry consequences at a more general physical-chemical level. These relate to such factors as local concentrations and gradients, the nature of the forces and the phase-state of the material in the intercellular region, the generalized intercellular transport processes (diffusional, osmotic, electrokinetic, hydrodynamic, etc.), and the dynamic coupling of flows. Such "other-level" phenomena must play a significant role, and therefore must be taken into account, in formulating a comprehensive picture of the ways in which the microenvironment acts in the management and control of the processes of hematopoietic differentiation and development.     

Observations on the behavior of the Cerapachyine ants

Summary Notes on the predatory behavior of species ofCerapachys, Phyracaces, andSphinctomyrmex are given. All of the species thus far studied have proven to be myrmecophagous, feeding on the brood (and in some cases adults) of other species of ants. Raids are conducted by groups of workers and are usually of short duration. A foraging expedition ofPhyracaces cohici is described, during which the workers started out as a compact group but later dispersed into small groups and lone individuals deployed in a circular pattern around the home nest. On the basis of these observations there is suggested a hypothetical pattern of alternating foraging and raiding behavior, which is believed to result ultimately in an efficient exploitation by the ants of the surrounding territory. Notes on other phases of biology, including colony size and nest structure, are given.

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Résumé On a présenté quelques observations sur les habitudes de pillage des espècesCerapachys, Phyracases etSphinctomyrmex. Toutes les espèces étudiées jusqu'à présent sont myrmécophages; elles dévorent le couvain — et dans certains cas les adultes — d'autres espèces de Fourmis. Les incursions sont effectuées par des groupes d'ouvrières, et sont généralement de courte durée. On décrit une expédition de fourrage dePhyracaces cohici, au cours de laquelle les ouvrières, parties en troupe, se dispersèrent par petits groupes et en individus isolés déployés en cercle autour de leur fourmilière. Ces observations suggèrent l'existence d'un cycle alternatif de fourrage et de razzias, ce qui permettrait aux Fourmis l'exploitation efficace des territoires avoisinants. On décrit, de plus, quelques autres aspects de la biologie de ces espèces, notamment les dimensions et le plan de leurs fourmilières.

     

Theoretical considerations of the Tsou plot

A graphical method was proposed by Tsou in 1962 for interpreting the data obtained by chemical modification of proteins and determining the number of essential groups involved. A strict mathematical proof and the estimation of deviation probability for this method are presented here. From the well-known Chebyshev's inequality, it has been shown that the possible error which could be derived from the Tsou plot will be much smaller than the usual experimental error obtainable. Some problems related to experiment and to application of Tsou plot in oligomeric enzymes have been discussed. Some analysis of experimental data taken from the literature are presented.     

Exploratory behavior ofLasius pallitarsis ants encountering novel areas

Summary Lasius pallitarsis ants were placed in situations where they encountered unfamiliar areas and had to choose between one of two directions for further exploration. Workers advancing onto new ground apparently leave behind some chemical signature to which later ants orient. This orientation occurred under two types of experimental conditions. First, ants show a significant tendency to follow each other as they advance out from their colony into unexplored areas. The same ants transferred into an entirely novel situation, in which there is no obvious homeward direction, show similar behavior. When ants are coming from familiar ground, following tends to increase as the number of ants passing the decision point increases. However, following decreases when ants are on entirely novel ground. The results are discussed in relation to models describing foraging responses.     

Foraging among cannibals and kleptoparasites: effects of prey size on pike behavior

The northern pike (Esox lucius) is an important and selective piscivorethat chooses smaller prey than predicted from energy / timebudgets. In a laboratory experiment, we investigated pike predatorybehavior to explain this selectivity. Northern pike feedingon different prey sizes in aquaria were observed when foragingalone, when in the presence of chemical cues from similar-sizedor larger conspecifics, and when in the presence of conspecifics thatwere allowed to interact with the focal pike. The results showthat prey handling time increases with prey size and that theduration of manipulating and handling prey inflicts a risk ofexposure to cannibals and kleptoparasites on the pike. Therefore,the risk of falling victim to cannibals or kleptoparasites increaseswith prey size. Attracting and experiencing intraspecific interactorscan be regarded as major fitness costs. Chemical cues from foragingconspecifics have only minor effects on pike foraging behavior.Furthermore, the ability to strike and swallow prey head first improvespike predatory performance because failing to do so increases handlingtime. Our findings emphasize the increasing potential costswith large prey and explain previous contradictory suggestionson the underlying mechanisms of behavior, selectivity, and trophiceffects of northern pike predation.     

Theoretical considerations on myofibril stiffness.

A discrete model of the interaction between individual myofilaments was developed to study the stiffness of a sarcomere for the case in which filament compliance is not negligible. Our model retains, in the limit, the characteristics of the previously published model by Ford et al. (Ford, L. E., A. F. Huxley, and R. M. Simmons. 1981. The relation between stiffness and filament overlap in stimulated frog muscle fibres. J. Physiol. 311:219-249). In addition, the model is able to model the interaction in cases in which few cross-bridges are attached, or when the distribution of attached cross-bridges is not uniform. Our results confirm previous indications that it might be impossible to calculate the number of attached cross-bridges by using only stiffness measurements in quick-stretch (or release) experiments.     

Foraging behavior of a freshwater copepod: Frequency changes in looping behavior at high and low prey densities

Summary The foraging behavior of Mesocyclops edax in artificial patches of high and low prey density was examined. In low density patches Mesocyclops swam in an irregular curvilinear path with little or no looping behavior. In high density patches Mesocyclops exhibited extensive horizontal and vertical looping behavior. Horizontal loops were performed in the normal hop and sink swimming mode, while vertical loops were associated with predator attacks on single prey items. Previous studies on terrestrial invertebrates revealed similar looping behaviors by predatiors and have suggested such looping behavior will increase the time a predator will spend in high versus low density prey patches. When food is patchily distributed and consumers are food-limited, the adaptive significance of remaining in a high density food patch may be substantial.Supported by NSF grant DEB 78-02882 to John J. Gilbert and Peter L. Starkweather, and the Dartmouth College Cramer Fund     

Foraging behavior of the queenless ant Dinoponera quadriceps Santschi (Hymenoptera: Formicidae)

The search for and ingestion of food are essential to all animals, which spend most of their lives looking for nutritional sources, more than other activities such as mating, intra-specific disputes or escaping from predators. The present study aims to describe and quantify several aspects of foraging behavior, diet and food transport in the queenless ant Dinoponera quadriceps Santschi in a secondary Atlantic forest, Northeastern Brazil. Three colonies were randomly selected at a distance of at least 50 m from one another. On leaving the colony, worker ants were followed until their return, with no nutritional provision or interference with their activities. Activities were recorded using focal time sampling with instantaneous recording every minute for 10 consecutive minutes. Each colony was observed 1 day/week, for at least 6 h/day resulting in 53.8h of direct observation of the workers. Foraging activities, success in transporting food, type of food, cleaning and interaction among the workers were recorded. Foraging was always individual, with no occurrence of recruitment. Diet was composed mainly of arthropods, mostly insects. The collection of small fruits (Eugenia sp.) was also observed. Foraging time was greater when workers transported food to the colony, the return time being shorter than the foraging period, suggesting the use of chemical and visual cues for orientation during their foraging and food-collecting activities.