Should dispersers be fast learners? Modeling the role of cognition in dispersal syndromes.

Both cognitive abilities and dispersal tendencies can vary strongly between individuals. Since cognitive abilities may help dealing with unknown circumstances, it is conceivable that dispersers may rely more heavily on learning abilities than residents. However, cognitive abilities are costly and leaving a familiar place might result in losing the advantage of having learned to deal with local conditions. Thus, individuals which invested in learning to cope with local conditions may be better off staying at their natal place. In order to disentangle the complex relationship between dispersal and learning abilities, we implemented individual-based simulations. By allowing for developmental plasticity, individuals could either become a 'resident' or 'dispersal' cognitive phenotype. The model showed that in general residents have higher learning abilities than dispersers. Dispersers evolve higher learning ability than residents when dispersers have long life spans and when dispersal occurs either early or late in life, thereby maximizing the time in one habitat patch. Time is crucial here, because the longer an individual resides in a location where it can use its learned knowledge or behavior, the more often it profits from it and thus eventually obtains a net benefit from its investment into learning. Both, longevity and the timing of dispersal within lifecycles determine the time individuals have to recoup that investment and thus crucially influence this correlation. We therefore suggest that species' life history will strongly impact the expected cognitive abilities of dispersers, relative to their resident conspecifics, and that cognitive abilities might be an integral part of dispersal syndromes.

Exploratory behaviour is not related to associative learning ability in the carabid beetle Nebria brevicollis.

Recently, it has been hypothesised that as learning performance and animal personality vary along a common axis of fast and slow types, natural selection may act on both in parallel leading to a correlation between learning and personality traits. We examined the relationship between risk-taking, exploratory behaviour and associative learning ability in carabid beetle Nebria brevicollis females by quantifying the number of trials individuals required to reach criterion during an associative learning task ('learning performance'). The associative learning task required the females to associate odour and direction with refugia from light and heat in a T-maze. Further, we assessed learning performance in a reversal task by quantifying the number of correct trials when the reinforcement was switched to previously unrewarding stimuli. We found that N. brevicollis females can associate conditional stimuli with a reward. No female was able to reverse the learned association within the number of trials given, however individuals differed in the number of correct trials in the reversal phase. Contrary to previous predictions neither exploratory behaviour, which was repeatable, nor risk-taking were correlated with learning performance. Our results suggest that the relationship between learning and personality may not take a common form across species.

Modelling the evolution of cognitive styles.

BACKGROUND: Individuals consistently differ in behaviour, exhibiting so-called personalities. In many species, individuals differ also in their cognitive abilities. When personalities and cognitive abilities occur in distinct combinations, they can be described as 'cognitive styles'. Both empirical and theoretical investigations produced contradicting or mixed results regarding the complex interplay between cognitive styles and environmental conditions. RESULTS: Here we use individual-based simulations to show that, under just slightly different environmental conditions, different cognitive styles exist and under a variety of conditions, can also co-exist. Co-existences are based on individual specialization on different resources, or, more generally speaking, on individuals adopting different niches or microhabitats. CONCLUSIONS: The results presented here suggest that in many species, individuals of the same population may adopt different cognitive styles. Thereby the present study may help to explain the variety of styles described in previous studies and why different, sometimes contradicting, results have been found under similar conditions.

Need for speed: Short lifespan selects for increased learning ability.

It is generally assumed that an investment into cognitive abilities and their associated cost is particularly beneficial for long-lived species, as a prolonged lifespan allows to recoup the initial investment. However, ephemeral organisms possess astonishing cognitive abilities too. Invertebrates, for example, are capable of simple associative learning, reversal learning, and planning. How can this discrepancy between theory and evidence be explained? Using a simulation, we show that short lives can actually select for an increase in learning abilities. The rationale behind this is that when learning is needed to exploit otherwise inaccessible resources, one needs to learn fast in order to utilize the resources when constrained by short lifespans. And thus, increased cognitive abilities may evolve, not despite short lifespan, but because of it.

The synganglion of the jumping spider Marpissa muscosa (Arachnida: Salticidae): Insights from histology, immunohistochemistry and microCT analysis.

Jumping spiders are known for their extraordinary cognitive abilities. The underlying nervous system structures, however, are largely unknown. Here, we explore and describe the anatomy of the brain in the jumping spider Marpissa muscosa (Clerck, 1757) by means of paraffin histology, X-ray microCT analysis and immunohistochemistry as well as three-dimensional reconstruction. In the prosoma, the CNS is a clearly demarcated mass that surrounds the esophagus. The anteriormost neuromere, the protocerebrum, comprises nine bilaterally paired neuropils, including the mushroom bodies and one unpaired midline neuropil, the arcuate body. Further ventrally, the synganglion comprises the cheliceral (deutocerebrum) and pedipalpal neuropils (tritocerebrum). Synapsin-immunoreactivity in all neuropils is generally strong, while allatostatin-immunoreactivity is mostly present in association with the arcuate body and the stomodeal bridge. The most prominent neuropils in the spider brain, the mushroom bodies and the arcuate body, were suggested to be higher integrating centers of the arthropod brain. The mushroom body in M. muscosa is connected to first and second order visual neuropils of the lateral eyes, and the arcuate body to the second order neuropils of the anterior median eyes (primary eyes) through a visual tract. The connection of both, visual neuropils and eyes and arcuate body, as well as their large size corroborates the hypothesis that these neuropils play an important role in cognition and locomotion control of jumping spiders. In addition, we show that the architecture of the brain of M. muscosa and some previously investigated salticids differs significantly from that of the wandering spider Cupiennius salei, especially with regard to structure and arrangement of visual neuropils and mushroom body. Thus, we need to explore the anatomical conformities and specificities of the brains of different spider taxa in order to understand evolutionary transformations of the arthropod brain.

Association and reversal learning abilities in a jumping spider.

The ability to learn and overwrite learned associations allows animals to respond adaptively to changes in their environment. However, such behavioural plasticity is presumed to be costly and the question arises to which extent animals with restricted neuronal capacity are capable of such flexible behaviour. In this study, we investigated the learning and reversal learning abilities of a jumping spider (Marpissa muscosa). In two discrimination tasks spiders had to associate colour in the first task and colour or location in the second task as a predictor of a food reward. Results show that spiders were able to quickly form and reverse associations. Individuals show differences in their learning success and in their preference of which cues they used (colour vs. location) as a reward's predictor. These results highlight the potential for flexible behaviour in species with small neuronal capacities and short life spans.

When should cuckolded males care for extra-pair offspring?

In socially monogamous species with bi-parental care, males suffer reduced reproductive success if their mate engages in extra-pair copulations (EPCs). One might therefore expect that males should refuse to care for a brood if they can detect that an EPC has occurred. Here, we use a game-theory model to study male brood care in the face of EPCs in a cooperatively breeding species in which offspring help to raise their (half-) siblings in their parents' next breeding attempt. We show that under certain conditions males are selected to care even for broods completely unrelated to themselves. This counterintuitive result arises through a form of pseudo-reciprocity, whereby surviving extra-pair offspring, when helping to rear their younger half-siblings, can more than compensate for the cost incurred by the male that raised them. We argue that similar effects may not be limited to cooperative breeders, but may arise in various contexts in which cooperation between (half-) siblings occurs.

Big brains are not enough: performance of three parrot species in the trap-tube paradigm.

The trap-tube task has become a benchmark test for investigating physical causality in vertebrates. In this task, subjects have to retrieve food out of a horizontal tube using a tool and avoiding a trap hole in the tube. Great apes and corvids succeeded in this task. Parrots with relative brain volumes comparable to those of corvids and primates also demonstrate high cognitive abilities. We therefore tested macaws, a cockatoo, and keas on the trap-tube paradigm. All nine parrots failed to solve the task. In a simplified task, trap tubes with a slot inserted along the top were offered. The slot allowed the birds to move the reward directly with their bills. All but one individual solved this task by lifting the food over the trap. However, the parrots failed again when they were prevented from lifting the reward, although they anticipated that food will be lost when moved into the trap. We do not think that the demanding use of an external object is the main reason for the parrots' failure. Moreover, we suppose these parrots fail to consider the trap's position in the beginning of a trial and were not able to stop their behaviour and move the reward in the trap's opposite direction.