Optimal memory: Toward an evolutionary ecology of animal cognition?

Individual variation in foraging behavior reveals a trade-off between flexibility and performance of a top predator

There is increasing evidence that behavioral flexibility is associated with the ability to adaptively respond to environmental change. Flexibility can be advantageous in some contexts such as exploiting novel resources, but it may come at a cost of accuracy or performance in ecologically relevant tasks, such as foraging. Such trade-offs may, in part, explain why individuals within a species are not equally flexible. Here, we conducted a reversal learning task and predation experiment on a top fish predator, the Northern pike (Esox lucius), to examine individual variation in flexibility and test the hypothesis that an individual's behavioral flexibility is negatively related with its foraging performance. Pikes were trained to receive a food reward from either a red or blue cup and then the color of the rewarded cup was reversed. We found that pike improved over time in how quickly they oriented to the rewarded cup, but there was a bias toward the color red. Moreover, there was substantial variation among individuals in their ability to overcome this red bias and switch from an unrewarded red cup to the rewarded blue cup, which we interpret as consistent variation among individuals in behavioral flexibility. Furthermore, individual differences in behavioral flexibility were negatively associated with foraging performance on ecologically relevant stickleback prey. Our data indicate that individuals cannot be both behaviorally flexible and efficient predators, suggesting a trade-off between these two traits.

On function, cause, and being Jerry Hogan's student

Jerry Hogan has forcefully maintained that cause and function are distinct questions, and that attempts to integrate them are conceptually muddled. I dissent from his view, maintaining that causal analysis is conducted in the shadow of premises about function, and that bringing functional ideas out of the shadows facilitates the generation of fruitful causal hypotheses. This is not to suggest, however, that cause-function muddles are non-existent; I agree with Hogan that they are both common and mischievous. This article is part of a Special Issue entitled: In Honor of Jerry Hogan.

Temporal dynamics of information use in learning and retention of predator-related information in tadpoles

Due to the high variability in predation risk through space and time, prey have to continuously update information about the risk level posed by predators. Despite numerous studies focusing on temporal risk assessment, we know very little about how individuals deal with information regarding changes in risk level of a given predator through time. In this study, we conditioned tadpoles to recognize a predator as a high or low risk twice 2 weeks apart, in a 2 × 2 design. We tested the responses of the tadpoles 1 and 11 days after each conditioning event. Prey showed responses to the predator 1 day after the first conditioning, but the low-risk group failed to respond to the predator after 11 days. However, we found that information learned during the first conditioning affected the response to the predator after the second conditioning, indicating that prey do not 'forget' old information, but simply ignore it. Moreover, tadpoles were able to assess their change in vulnerability over the 2-week period and further extrapolate the risk level of the predator through time to display adaptive threat-sensitive antipredator responses. Our study highlights the complex decision-making that prey use to assess temporal fluctuation in predation risk.

Laterality enhances cognition in Australian parrots

Cerebral lateralization refers to the division of information processing in either hemisphere of the brain and is a ubiquitous trait among vertebrates and invertebrates. Given its widespread occurrence, it is likely that cerebral lateralization confers a fitness advantage. It has been hypothesized that this advantage takes the form of enhanced cognitive function, potentially via a dual processing mechanism whereby each hemisphere can be used to process specific types of information without contralateral interference. Here, we examined the influence of lateralization on problem solving by Australian parrots. The first task, a pebble-seed discrimination test, was designed for small parrot species that feed predominately on small seeds, which do not require any significant manipulation with the foot prior to ingestion. The second task, a string-pull problem, was designed for larger bodied species that regularly use their feet to manipulate food objects. In both cases, strongly lateralized individuals (those showing significant foot and eye biases) outperformed less strongly lateralized individuals, and this relationship was substantially stronger in the more demanding task. These results suggest that cerebral lateralization is a ubiquitous trait among Australian parrots and conveys a significant foraging advantage. Our results provide strong support for the enhanced cognitive function hypothesis.

Associative learning in wild Anastrepha obliqua females (Diptera, Tephritidae) related to a protein source

The aim of the present study was to determine whether wild adult Anastrepha obliqua (Macquart, 1835) females are able to associate a compound (quinine sulphate - QS) not related to their habitual diet with a protein-enriched food. Females were first fed on diets based on brewer yeast and sucrose containing or not QS. The groups were then allowed to choose between their original diets and a diet with or without QS, depending on the previous treatment, and between a diet based on agar and a diet containing agar and QS. When the nutritional value of the diets was adequate, the females did not show any preference for the diet with or without QS. With respect to the agar diet and the agar + QS diet, females previously fed on a nutritive diet containing QS preferred the diet containing QS, indicating an association between the compound and the nutritional value of the diet. The importance of this behavioral strategy is discussed.

Algorithmic behaviour and spatial memory are used by two intertidal fish species to solve the radial maze

We used an eight-arm radial maze to assess the relative contributions of learned patterns of movement (algorithmic behaviour) and spatial memory to the foraging efficiency of two sympatric rocky-shore fish, fifteen-spined stickleback, Spinachia spinachia, and corkwing wrasse, Crenilabrus melops, exploiting nonrenewable food sources. To forage efficiently, subjects had to avoid arms already depleted within a trial. In the absence of spatial cues, sticklebacks and wrasse improved their foraging efficiency by developing the algorithm of visiting every third arm. In the presence of spatial cues (coloured tiles) algorithmic behaviour was largely subsumed by the use of spatial memory. Imposition of a delay within trials reset the behavioural algorithm, so depressing foraging efficiency in the absence of cues, but not in their presence when memory could be used to guide behaviour. Memory retention for previous choices (working memory) lay within the range 0.5-5.0 min, consistent with the characteristic timescale expected for habitats where prey distribution changes rapidly during the tidal cycle. We considered two hypotheses on the type of information memorized: the cue list hypothesis and the spatial configuration hypothesis. The cue list hypothesis predicts that neither random repositioning nor fixed rotation of spatial cues should impair foraging efficiency, whereas the spatial configuration hypothesis predicts that efficiency should be impaired by random repositioning of cues but not by rotation. Data supported the spatial configuration hypothesis. Copyright 1999 The Association for the Study of Animal Behaviour.

The Effects of a Limited Memory Capacity on Foraging Behavior

We introduce a simple mathematical model to describe the behavior of a forager with a limited memory capacity in the presence of two prey types that differ in their energetic values. The model is used to analyze the effect of memory capacity on foraging behavior and on foraging energetics and it contrasts with classic optimal foraging theory, which implicitly assumes that the forager has an infinite memory capacity. Classic optimal foraging theory dictates that the low value prey type should be invariably excluded from the diet when the high value type exceeds some critical relative frequency and invariably consumed otherwise. Our model forager behaves similarly except that, as its memory capacity declines, it is increasingly predisposed to consume the low value prey when it is suboptimal to do so. Nevertheless, our analysis indicates that the energetic efficiency of a forager with an infinite memory capacity can be approximated by a forager with a memory of modest capacity, perhaps one that contains information about 5-20 previously consumed prey items. In our model, memory constraints necessarily result in so-called "partial preferences" being exercised towards the low value prey type. Thus, limited memory capacity offers a possible explanation for observed violations of the "zero-one" rule of optimal diet composition. We also find a resemblance to a sigmoidal shape in the relationship between the representation of each prey type in the diet and its relative frequency. Thus, the memory-constrained forager exhibits behavior that resembles the type III functional response. Therefore, it is possible that memory constraints such as we envisage can contribute to the explanation of both partial preferences and functional responses. Copyright 1997 Academic Press

Effects of experience on crab foraging in a mobile and a sedentary species

The effects of experience on prey and prey-patch choice were compared between two species of marine predatory crabs. The blue crab, Callinectes sapidus Rathbun, is highly mobile and forages in a variety of estuarine and lagoonal habitats. The Atlantic mud crab, Panopeus herbstii H. Milne-Edwards, is smaller and less mobile and is found mostly in oyster reefs and on shelly bottoms. In the laboratory, crabs were offered a choice between two prey types (juvenile hard clams, Mercenaria mercenaria Linne, and juvenile oysters, Crassostrea virginica Gmelin) following a preliminary phase in which crabs were trained to feed on clams only, oysters only or a mixture of the two prey types. In field enclosures, crabs were offered a choice between patches of juvenile hard clams located in an inter-tidal salt marsh and in an adjacent unvegetated inter-tidal flat after they were trained to feed in either one of the two habitat types. Both in the laboratory prey-choice and the field prey-patch choice experiments, blue crabs modified their foraging behaviour depending on previous experience. The effect of experience on their foraging behaviour did not diminish after 24 hours. Experience had no significant effects on the foraging behaviour of mud crabs. Differences in the ecological contexts (e.g. in the variability of prey quality and availability) in which the two species forage may explain the greater effect of experience on the blue crab foraging behaviour, although alternative explanations cannot be ruled out.