Pheromone trail decay rates on different substrates in the Pharaoh's ant, Monomorium pharaonis

Abstract. Many ants use pheromone trails to organize collective foraging. This study investigated the rate at which a well‐established Pharaoh's ant, Monomorium pharaonis (L.), trail breaks down on two substrates (polycarbonate plastic, newspaper). Workers were allowed to feed on sucrose solution from a feeder 30 cm from the nest. Between the nest and the feeder, the trail had a Y‐shaped bifurcation. Initially, while recruiting to and exploiting the feeder, workers could only deposit pheromone on the branch leading to the feeder. Once the trail was established (by approximately 60 ants per min for 20 min), the ants were not allowed to reinforce the trail and were given a choice between the marked and unmarked branches. The numbers of ants choosing each branch were counted for 30 min. Initially, most went to the side on which pheromone had been deposited (80% and 70% on the plastic and paper substrates, respectively). However, this decayed to 50% within 25 min for plastic and 8 min for paper. From these data, the half‐life times of the pheromone are estimated as approximately 9 min and 3 min on plastic and paper, respectively. The results show that, for M. pharaonis, trail decay is rapid and is affected strongly by trail substrate.     

Social enhancement and social inhibition of foraging behaviour in hatchery-reared Atlantic salmon

The results of two experiments showed that observation of a trained conspecific Atlantic salmon Salmo salar significantly increased the rate at which naïve hatchery-reared fish accepted novel, live prey items, whereas the presence of an untrained conspecific actually decreased learning rates due to social inhibition. Pre-release training involving exposure of hatchery-reared fish to live prey items in the presence of pre-trained demonstrators would result in a significant enhancement in their foraging success on release and help prevent starvation, which is thought to be one of the principal causes of post-release mortality in hatchery-reared fishes.     

Models-of-data and models-of-processes in the post-genomic era

As we are entering the post-genomic era, models-of-data, such as mining and filtering methods for gene sequences and microarrays and the clustering of co-expressed genes, must be complemented with models-of-processes that explain relationships between genomic information and phenomena at biochemical and physiological levels. Many of these models will have the structure of compartment models, whose conceptualization, identification and analysis will fundamentally benefit from the seminal work of John Jacquez. The article indicates with three vignettes that non-linear compartment models in the formulation of biochemical systems theory are viable candidates for post-genomic models-of-processes.     

Tutoring in Wild Golden Lion Tamarins

Among most nonhuman primates, juveniles must acquire most of their solid food independently. Information gleaned from adults results from efforts initiated by the juveniles. Donation of food or foraging information by adults to immatures is rare among apes and virtually unknown among monkeys. We report 3 observations in which wild adult golden lion tamarins appear to have directed their immature offspring to a location where a hidden prey item was located. According to the definition of Caro and Hauser (1992), the tamarins were tutoring their young.     

Spatial patterns, temporal variability, and the role of multi-nest colonies in a monogynous Spanish desert ant

Abstract 1. The colonies of the Spanish desert ant Cataglyphis iberica are polydomous. This study describes the temporal and spatial patterns of the polydomy in this species at two different sites, and presents analyses of its role in reducing the attacks of the queen over sexual brood, and in allowing better habitat exploitation.
2. The spatial distribution of nests was clumped while colonies were distributed randomly. Mean nearest neighbour distance ranged from 3.4 to 7.0 m for nests and from 12.3 to 14.1 m for colonies. Distance of foragers searching for food varied among nests: mean values were between 6.1 and 12.6 m.
3. At both sites, the maximum number of nests per colony occurred in summer, during the maximum activity period of the species. Colonies regrouped at the end of this period but overwintered in several nests.
4. Nest renewal in C. iberica colonies was high and showed great temporal variability: nests changed (open, close, re-open) continuously through the activity season and/or among years. The lifetime of up to 55% of nests was only 1–3 months.
5. Polydomy in C. iberica might decrease the interactions between the queen and the sexual brood. In all colonies excavated just before the mating period, the nest containing the queen did not contain any virgin female. Females were in the queenless nests of the colony.
6. The results also suggest that polydomous C. iberica colonies may enhance habitat exploitation because foraging activity per colony increases with nest number. The relationship between total prey input and foraging efficiency and number of nests per colony attains a plateau or even decreases after a certain colony size (four to six nests). This value agrees with the observed mean number of nests per colony in C. iberica .     

Effects of Hunger on Foraging Behavior of Age-0 Smallmouth Bass in a Heterogeneous Environment

We examined how hunger affected habitat use by juvenile smallmouth bass, Micropterus dolomieu, as they moved among a variety of habitat patches. Hungry and satiated fish were placed in an artificial stream that contained three types of habitat patches: pools with uniform depth and low water velocities, mazes with uniform depth and moderate water velocities, and riffle-pool complexes with varying depth and the highest water velocities. Food was only available in the riffle-pool complexes. Hungry fish spent more time in the riffle-pool complex than satiated fish did. However, hungry and satiated fish did not differ in the time it took to exit the pool they were initially placed in, the number of patches entered, or the number of times they moved among patches. Both hungry and satiated fish frequently entered other patches after foraging successfully in the riffle-pool complexes. There was wide variation in foraging behavior among individuals in both treatment groups, and we consistently observed individuals that did not alter their foraging behavior in response to the difference in food availability among patches.     

Considerations on muscle contraction

The independent force generator and the power-stroke cross-bridge model have dominated the thinking on mechanisms of muscular contraction for nearly the past five decades. Here, we review the evolution of the cross-bridge theory from its origins as a two-state model to the current thinking of a multi-state mechanical model that is tightly coupled with the hydrolysis of ATP. Finally, we emphasize the role of skeletal muscle myosin II as a molecular motor whose actions are greatly influenced by Brownian motion. We briefly consider the conceptual idea of myosin II working as a ratchet rather than a power stroke model, an idea that is explored in detail in the companion paper.