James G. Burns

The validity of three tests of temperament in guppies (Poecilia reticulata).

Differences in temperament (consistent differences among individuals in behavior) can have important effects on fitness-related activities such as dispersal and competition. However, evolutionary ecologists have put limited effort into validating their tests of temperament. This article attempts to validate three standard tests of temperament in guppies: the open-field test, emergence test, and novel-object test. Through multiple reliability trials, and comparison of results between different types of test, this study establishes the confidence that can be placed in these temperament tests. The open-field test is shown to be a good test of boldness and exploratory behavior; the open-field test was reliable when tested in multiple ways. There were problems with the emergence test and novel-object test, which leads one to conclude that the protocols used in this study should not be considered valid tests for this species.

Hastiness, brain size and predation regime affect the performance of wild guppies in a spatial memory task

The ability to return to, or avoid, specific locations is often critical to fitness-related activities. We tested for differences in spatial memory of guppies, Poecilia reticulata, from low- and high-predation populations in a maze task. We also measured the time each fish took to make a decision in the maze, because individuals can show a trade-off between the speed and the accuracy of their decisions during this kind of task. Because brain size can affect cognitive performance, we also measured brain size. There were no differences in the number of errors made or time to find the reward between predation regimes. However, high-predation guppies tended to take longer to make the decision about which maze chamber to enter than low-predation guppies; thus, low-predation guppies were more willing to make quick and potentially inaccurate decisions, a strategy we have termed ‘hastiness’. Individuals within populations also varied in hastiness and we found that hasty guppies tended to have smaller telencephalons, the brain region most responsible for spatial memory. There was no difference in brain size in relation to predation regime, although lab-reared fish had smaller brains than wild-caught fish. This study shows that the careful observation of an animals strategy for solving spatial problems may reveal subtle differences that are associated with ecology and brain size.

Impulsive bees forage better: the advantage of quick, sometimes inaccurate foraging decisions

O ne of the major challenges in conducting experiments in evolutionary ecology is selecting the currency that most closely parallels individual fitness (e.g. Crone 2001). The fitness surrogate measured must represent a currency that directly impacts individual survival or reproduction, and must not trade off with another relevant fitness currency. The fitness of a foraging nectivore should be closely linked to its rate of resource collection. Presumably, resource collection rate is higher in nectivores that can learn the difference between rewarding and unrewarding flowers, and therefore make more accurate foraging decisions. Based on this line of reasoning, accuracy (the proportion of choices that are correct) is frequently used as the variable of interest in tests of learning rate (e.g. bees: Menzel 1967; Dukas & Real 1991; Dukas & Waser 1994; Wittstock & Menzel 1994; Dukas 1995; Kunze & Gumbert 2001; Ney-Nifle et al. 2001; Cnaani et al. 2003; Paldi et al. 2003; hummingbirds: Brown & Gass 1993; Sutherland & Gass 1995; lepidopterans: Stanton 1984; Kelber 1996). Accuracy is a reasonable measure in many experimental contexts, but a danger is present when accuracy is used as a surrogate for fitness in studies of function and evolution. Although accuracy is a logical surrogate for nectar collection rate when mistakes have large time costs, it is not clear whether the time cost involved in making an accurate choice is always outweighed by the time cost of mistakes. Here I provide an example that illustrates how, when we focus on accuracy, we might be in particular danger of misconstruing the optimal behavioural strategy. Chittka et al. (2003) observed a trade-off between foraging speed and accuracy in 10 bumblebees, Bombus terrestris, discriminating between similarly, but not identically, coloured rewarding and nonrewarding artificial flowers in two experiments. Speed–accuracy trade-offs in discrimination tasks have been observed largely in humans (e.g. Phillips & Rabbitt 1995; Rival et al. 2003), but rarely in an ecological or evolutionary context (but see Franks et al. 2003; Dyer & Chittka 2004). In the first experiment, 10 bees were tested for their accuracy in choosing between flowers containing sucrose solution versus flowers containing only water. The amount of time taken between flower choices (called ‘response time’ by Chittka et al. (2003), referred to here as ‘interflower interval’) was also observed. Bees that took longer between flower visits, presumably to make judgements on the next flower to choose, made more accurate choices (interflower interval to accuracy correlation: r Z 0.963, PZ 0.00007). In a second experiment, the same 10 bees were tested for accuracy and interflower interval while foraging on rewarding flowers that contained sucrose solution and unrewarding flowers that contained a quinine hemisulphate salt solution that is aversive to bees. With this punishment for incorrect choices added, the bees increased their interflower interval and made more accurate choices (interflower interval to accuracy correlation: r Z 0.723, P Z 0.018). Of particular salience to this discussion, there was a tendency for each individual bee to be loyal to a strategy that was either fast and inaccurate or slow and accurate across the two experiments (correlation within bees between experiments 1 and 2, accuracy: r Z 0.951, P Z 0.00023, interflower interval: r Z 0.699, P Z 0.024). Here I expand upon their analysis to show that when performance is measured as nectar collection rate, the fast, inaccurate bees performed better than the slow, accurate bees. I also discuss other issues, including how consistent behavioural variation between individual bees across situations (behavioural syndromes; Sih et al. 2004a) may complicate behavioural experiments and also be selectively advantageous for social insects in natural settings. In the end, it may be that our focus on accuracy is ecologically inappropriate, because it is only an unambiguously good currency if all else (e.g. speed of making choices) is held equal. After all, an accurate but slothful bee can starve to death.

Costs of memory: lessons from ‘mini’ brains

Variation in learning and memory abilities among closely related species, or even among populations of the same species, has opened research into the relationship between cognition, ecological context and the fitness costs, and benefits of learning and memory. Such research programmes have long been dominated by vertebrate studies and by the assumption of a relationship between cognitive abilities, brain size and metabolic costs. Research on these ‘large brained’ organisms has provided important insights into the understanding of cognitive functions and their adaptive value. In the present review, we discuss some aspects of the fitness costs of learning and memory by focusing on ‘mini-brain’ studies. Research on learning and memory in insects has challenged some traditional positions and is pushing the boundaries of our understanding of the evolution of learning and memory.

A CONSIDERATION OF PATTERNS OF VIRULENCE ARISING FROM HOST-PARASITE COEVOLUTION

Abstract In this article we explore how host survival and fecundity are affected by host‐parasite coevolution. We examine a situation in which hosts upon being infected can mount a defensive response to clear the infection, but in which there is a fecundity cost to such immunological up‐regulation. We also suppose that the parasite exploits the host and thereby causes an elevated host mortality rate. We determine the coevolutionary stable strategies of the parasit—level of exploitation and the host—level of up‐regulation, and illustrate the patterns of reduced host fitness (i.e., virulence) that these produce. We find that counterintuitive patterns of virulence are often expected to arise as a result of the interaction between coevolved host and parasite strategies. In particular, despite the fact that the parasite imposes only a mortality cost on the host, coevolution by the host results in a pattern whereby infected hosts always have the same probability of death from infection, but they vary in the extent to which their fecundity is reduced. This contrasts with previous results and arises from our inclusion of two important factors absent from previous theory: costs of immunological up‐regulation and a more suitable measure of parasite‐induced mortality.

The birds, the bees, and the virtual flowers: can pollinator behavior drive ecological speciation in flowering plants?

Biologists have long assumed that pollinator behavior is an important force in angiosperm speciation, yet there is surprisingly little direct evidence that floral preferences in pollinators can drive floral divergence and the evolution of reproductive (ethological) isolation between incipient plant species. In this study, we expose computer‐generated plant populations with a wide variation in flower color to selection by live and virtual hummingbirds and bumblebees and track evolutionary changes in flower color over multiple generations. Flower color, which was derived from the known genetic architecture and phenotypic variance of naturally occurring plant species pollinated by both groups, evolved in simulations through a genetic algorithm in which pollinator preference determined changes in flower color between generations. The observed preferences of live hummingbirds and bumblebees were strong enough to cause adaptive divergence in flower color between plant populations but did not lead to ethological isolation. However, stronger preferences assigned to virtual pollinators in sympatric and allopatric scenarios rapidly produced ethological isolation. Pollinators can thus drive ecological speciation in flowering plants, but more rigorous and comprehensive behavioral studies are required to specify conditions that produce sufficient preference levels in pollinators.

Gene–environment interplay in Drosophila melanogaster: Chronic food deprivation in early life affects adult exploratory and fitness traits

Early life adversity has known impacts on adult health and behavior, yet little is known about the gene–environment interactions (GEIs) that underlie these consequences. We used the fruit fly Drosophila melanogaster to show that chronic early nutritional adversity interacts with rover and sitter allelic variants of foraging (for) to affect adult exploratory behavior, a phenotype that is critical for foraging, and reproductive fitness. Chronic nutritional adversity during adulthood did not affect rover or sitter adult exploratory behavior; however, early nutritional adversity in the larval period increased sitter but not rover adult exploratory behavior. Increasing for gene expression in the mushroom bodies, an important center of integration in the fly brain, changed the amount of exploratory behavior exhibited by sitter adults when they did not experience early nutritional adversity but had no effect in sitters that experienced early nutritional adversity. Manipulation of the larval nutritional environment also affected adult reproductive output of sitters but not rovers, indicating GEIs on fitness itself. The natural for variants are an excellent model to examine how GEIs underlie the biological embedding of early experience.

Use of Spatial Information and Search Strategies in a Water Maze Analog in Drosophila melanogaster

Learning the spatial organization of the environment is crucial to fitness in most animal species. Understanding proximate and ultimate factors underpinning spatial memory is thus a major goal in the study of animal behavior. Despite considerable interest in various aspects of its behavior and biology, the model species Drosophila melanogaster lacks a standardized apparatus to investigate spatial learning and memory. We propose here a novel apparatus, the heat maze, conceptually based on the Morris water maze used in rodents. Using the heat maze, we demonstrate that D. melanogaster flies are able to use either proximal or distal visual cues to increase their performance in navigating to a safe zone. We also show that flies are actively using the orientation of distal visual cues when relevant in targeting the safe zone, i.e., Drosophila display spatial learning. Parameter-based classification of search strategies demonstrated the progressive use of spatially precise search strategies during learning. We discuss the opportunity to unravel the mechanistic and evolutionary bases of spatial learning in Drosophila using the heat maze.

Social Environment Influences Performance in a Cognitive Task in Natural Variants of the Foraging Gene

In Drosophila melanogaster, natural genetic variation in the foraging gene affects the foraging behaviour of larval and adult flies, larval reward learning, adult visual learning, and adult aversive training tasks. Sitters (for s) are more sedentary and aggregate within food patches whereas rovers (forR) have greater movement within and between food patches, suggesting that these natural variants are likely to experience different social environments. We hypothesized that social context would differentially influence rover and sitter behaviour in a cognitive task. We measured adult rover and sitter performance in a classical olfactory training test in groups and alone. All flies were reared in groups, but fly training and testing were done alone and in groups. Sitters trained and tested in a group had significantly higher learning performances compared to sitters trained and tested alone. Rovers performed similarly when trained and tested alone and in a group. In other words, rovers learning ability is independent of group training and testing. This suggests that sitters may be more sensitive to the social context than rovers. These differences in learning performance can be altered by pharmacological manipulations of PKG activity levels, the foraging (for) genes gene product. Learning and memory is also affected by the type of social interaction (being in a group of the same strain or in a group of a different strain) in rovers, but not in sitters. These results suggest that for mediates social learning and memory in D. melanogaster.

RELATIONSHIP OF CALIDRIS SANDPIPER WING SHAPE WITH RELATIVE FUEL LOAD AND TOTAL MIGRATION DISTANCE

Abstract It has proven difficult to support the classic prediction of aerodynamic theory that highly migratory birds should have more pointed wings than less migratory birds. This study extends the search by testing for correlations between wing shape of Calidris sandpipers and a traditional migratory variable (total migration distance) as well as a novel variable (relative fuel load). Using phylogentically independent contrasts, it was determined that relative fuel load is a better predictor of wing shape than total migration distance.