Abstract
Disoriented humans and animals are able to reorient themselves using environmental geometry (“metric properties” and “sense”) and local features, also relating geometric to non-geometric information. Here we investigated the presence of these reorientation spatial skills in two species of blind cavefish (Astyanax mexicanus and Phreatichthys andruzzii), in order to understand the possible role of extra-visual senses in similar spatial tasks. In a rectangular apparatus, with all homogeneous walls (geometric condition) or in presence of a tactilely different wall (feature condition), cavefish were required to reorient themselves after passive disorientation. We provided the first evidence that blind cavefish, using extra-visual systems, were able i) to use geometric cues, provided by the shape of the tank, in order to recognize two geometric equivalent corners on the diagonal, and ii) to integrate the geometric information with the salient cue (wall with a different surface structure), in order to recover a specific corner. These findings suggest the ecological salience of the environmental geometry for spatial orientation in animals and, despite the different niches of adaptation, a potential shared background for spatial navigation. The geometric spatial encoding seems to constitute a common cognitive tool needed when the environment poses similar requirements to living organisms.
Highlights
Disoriented animals are able to reorient themselves in an environment with a distinctive geometry, sometimes ignoring featural cues as odours, colours, 2D patterns and objects[1], but more often integrating geometric and non-geometric information[2,3,4]
Our work aimed to investigate if blind cavefish (P. andruzzii and A. mexicanus) were able to reorient themselves by using only geometric cues, such as the shape of a rectangular arena (Experiment 1), or through the integration of geometric and non-geometric information (Experiment 2)
The ability to reorientation through the use of geometric information have been extensively studied in many animal species[1,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,21,22,24,25]
Summary
Disoriented animals are able to reorient themselves in an environment with a distinctive geometry (i.e., a rectangular enclosure, that has “metric properties” – longer, shorter - and “sense” – left, right), sometimes ignoring featural cues as odours, colours, 2D patterns and objects[1], but more often integrating geometric and non-geometric information[2,3,4]. The Somalian blind cavefish Phreatichthys andruzzii are able to use them as reference points to guide the swimming activities: trained to locate the food near to an object with a particular shape, they were able to recognize and store the presence/ absence of that object, to discriminate different shapes, using them as cues for orientation[55]. These results show that cues of different shapes can act as reference points, supporting the hypothesis of the existence of a non-visual orientation mechanism, which may operate in habitats with constant and total absence of light[55]. They observed that Somalian cavefish, trained from the beginning only with stimuli controlled for continuous quantities, proved able to learn the discrimination of quantities based on the sole numerical information, with a numerical acuity lower than that of other visual teleost fish
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