Towards a unified vision on animal navigation.

The study of animal navigation is a complex and fertile field of research: Several questions regarding how animals relate to external stimuli, integrating them to perform their everyday movement routine, have been or are being addressed in different organisms and taxa, both from the behavioural and the neuronal activity point of view. Several invertebrate model organisms are the object of studies aimed at unravelling how they navigate and their ability to precisely return to a starting point and also how navigational information is communicated to conspecifics when precise social structures are present. Also, vertebrates are studied because of the interest in their orientation abilities while migrating, homing over impressive distances and studying exploration, orientation and space recognition. Last, research on the navigation capabilities of humans pursues a better understanding of the neural architecture involved in these processes in the remarkable effort to find answers and possible solutions to impairments, lesions and diseases. However, an 'all-inclusive' vision of navigation still appears to be in its embryonic state: A better perspective could (and should) shift from a paradigm where single research teams are centred on studying navigation in a single genus or species towards a more comprehensive evolutionary-centred view, searching systematically for behavioural analogies, and possibly for homologies in neural architecture between different taxa. In this review, we introduce examples of relevant topics in animal navigation from distinct animal groups, highlighting the similar approaches of those studies, and why, in our opinion, this research field could profit from a 'new' perspective.

Lifespan and ROS levels in different Drosophila melanogaster strains after 24†h hypoxia exposure.

During recent decades, model organisms such as Drosophila melanogaster have made it possible to study the effects of different environmental oxygen conditions on lifespan and oxidative stress. However, many studies have often yielded controversial results usually assigned to variations in Drosophila genetic background and differences in study design. In this study, we compared longevity and ROS levels in young, unmated males of three laboratory wild-type lines (Canton-S, Oregon-R and Berlin-K) and one mutant line (Sod1n1) as a positive control of redox imbalance, under both normoxic and hypoxic (2% oxygen for 24 h) conditions. Lifespan was used to detect the effects of hypoxic treatment and differences were analysed by means of Kaplan-Meier survival curves and log-rank tests. Electron paramagnetic resonance spectroscopy was used to measure ROS levels and analysis of variance was used to estimate the effects of hypoxic treatment and to assess ROS differences between strains. We observed that the genetic background is a relevant factor involved in D. melanogaster longevity and ROS levels. Indeed, as expected, in normoxia Sod1n1 are the shortest-lived, while the wild-type strains, despite a longer lifespan, show some differences, with the Canton-S line displaying the lowest mortality rate. After hypoxic stress these variances are amplified, with Berlin-K flies showing the highest mortality rate and most evident reduction of lifespan. Moreover, our analysis highlighted differential effects of hypoxia on redox balance/unbalance. Canton-S flies had the lowest increase of ROS level compared to all the other strains, confirming it to be the less sensitive to hypoxic stress. Sod1n1 flies displayed the highest ROS levels in normoxia and after hypoxia. These results should be used to further standardize future Drosophila research models designed to investigate genes and pathways that may be involved in lifespan and/or ROS, as well as comparative studies on specific mutant strains.

A heuristic underlies the search for relief in Drosophila melanogaster.

Humans rely on multiple types of sensory information to make decisions, and strategies that shorten decision-making time by taking into account fewer but essential elements of information are preferred to strategies that require complex analyses. Such shortcuts to decision making are known as heuristics. The identification of heuristic principles in species phylogenetically distant to humans would shed light on the evolutionary origin of speed-accuracy trade-offs and offer the possibility for investigating the brain representations of such trade-offs, urgency and uncertainty. By performing experiments on spatial learning in the invertebrate Drosophila melanogaster, we show that the fly's search strategies conform to a spatial heuristic-the nearest neighbor rule-to avoid bitter taste (a negative stimulation). That is, Drosophila visits a salient location closest to its current position to stop the negative stimulation; only if this strategy proves unsuccessful does the fly use other learned associations to avoid bitter taste. Characterizing a heuristic in D. melanogaster supports the view that invertebrates can, when making choices, operate on economic principles, as well as the conclusion that heuristic decision making dates to at least 600 million years ago.