Costs of memory: lessons from ‘mini’ brains

Abstract

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.

Maternal predator-exposure has lifelong consequences for offspring learning in threespined sticklebacks

“…Importantly, we found that offspring of both maternal treatments successfully learned the colour association but differed in their speed at obtaining the food. The maternal effect seen here could well be adaptive if predator-exposed mothers are 'preparing' their offspring for a high-predation environment where the induced costs of learning and memory outweigh the benefits of having enhanced learning performance [3], or where increased vigilance and caution is favoured at the expense of obtaining a learned food source quickly [15]. Examining how learning performance and behaviour in a variety of learning paradigms affect overall fitness would provide insight into the adaptive nature of this maternal effect.…”

“…However, the ability to learn might not always be favoured owing to potential costs [3]. While there is evidence that learning performance might be heritable, it can also be influenced by the environment [1,2].…”

Investment in higher order central processing regions is not constrained by brain size in social insects

“…Small brains and body sizes may confer computational or metabolic advantages to miniaturized taxa (for example, by reducing the transmission distance between neurons [10]), and tiny animals with highly miniaturized cells (such as Drosophila) can have many more neurons-and thus potentially more computational power-than larger animals (such as Aplysia). Nevertheless, theory suggests that energetic and architectural costs of increasing nervous system miniaturization should eventually outweigh any benefits, limiting the information processing and behavioural capabilities of very small animals [10,12]. Yet, the behavioural complexity of small-bodied arthropods is often surprisingly similar in quality to that of vastly larger vertebrates [6,12].…”

“…However, the degree to which the sensory processing and integrative abilities of brains are constrained by absolute size remains unclear, despite intensive recent analysis [6][7][8][9][10][11][12][13]. Small brains and body sizes may confer computational or metabolic advantages to miniaturized taxa (for example, by reducing the transmission distance between neurons [10]), and tiny animals with highly miniaturized cells (such as Drosophila) can have many more neurons-and thus potentially more computational power-than larger animals (such as Aplysia).…”

“…Nevertheless, theory suggests that energetic and architectural costs of increasing nervous system miniaturization should eventually outweigh any benefits, limiting the information processing and behavioural capabilities of very small animals [10,12]. Yet, the behavioural complexity of small-bodied arthropods is often surprisingly similar in quality to that of vastly larger vertebrates [6,12]. In fact, extremely small arthropods that have brains smaller than some single-celled protists [9,13] are capable of behaviours similar in sophistication to those performed by larger bodied relatives [8].…”