Vera Schluessel

University of Bonn | Uni Bonn · Institute of Zoology

Using the expression of the immediate early gene (IEG) egr-1 as a neuronal activity marker, brain regions potentially involved in learning and long-term memory functions in the grey bamboo shark were assessed with respect to selected visual discrimination abilities. Immunocytochemistry revealed a significant up-regulation of egr-1 expression levels...

Previous studies have shown that marine stingrays have the anatomical and physiological basis for colour vision, with cone spectral sensitivities in the blue to green range of the visible spectrum. Behavioural studies on Glaucostegus typus also showed that blue and grey can be perceived and discriminated. The present study is the first to assess vi...

The numerical understanding of cichlids and stingrays was examined regarding addition and subtraction abilities within the number space of one to five. Experiments were conducted as two alternative forced-choice experiments, using a delayed matching to sample technique. On each trial, fish had to perform either an addition or subtraction, based on...

450 million years of evolution have given chondrichthyans (sharks, rays and allies) ample time to adapt perfectly to their respective everyday life challenges and cognitive abilities have played an important part in that process. The diversity of niches that sharks and rays occupy corresponds to matching diversity in brains and behaviour, but we ha...

Two species of fish were tested in a serial reversal learning task using two dimensional objects varying in colour and/or form. After reaching the learning criterion (LC) in the original discrimination task, individuals reversed for up to ten times, i.e., stimulus association was switched and animals rewarded for choosing the stimulus that had not...

Dopamine is present in all vertebrates and the functional roles of the subsystems are assumed to be similar. Whereas the effect of dopaminergic modulation is well investigated in different target systems, less is known about the factors that are causing the modulation of dopaminergic cells. Using the zebra mbuna, Pseudotropheus zebra, a cichlid fis...

The neural correlates of most cognitive functions in fish are unknown. This project aimed to identify brain regions involved in visual learning in the cichlid fish Pseudotropheus zebra. The expression of the protein pS6 was measured in 19 brain areas and compared between groups of individuals subjected to four different behavioral contexts (control...

Behavioral situations consist of different sets of sensory, cognitive and motor components. This study assessed the neural substrates involved in four behavioral contexts in the cichlid fish Pseudotropheus zebra. In particular, brain areas implicated in cognitive information processing in regards to a visual learning task were targeted. The level o...

Cognitive abilities of sharks are well developed and comparable to teleosts and other vertebrates. Most studies exploring elasmobranch cognitive abilities have used visual stimuli, assessing a wide range of discrimination tasks, memory retention and spatial learning abilities. Some studies using acoustic stimuli in a cognitive context have been con...

Over the last decade, studies examining the cognitive abilities of fish have increased, using a broad range of approaches. One of the foci has been to test the ability of fish to discriminate quantities of items and to determine whether fish can solve tasks solely on the basis of numerical information. This study is the first to investigate this ab...

Over the last few decades, it has been shown that fish, comprising the largest group of vertebrates and in many respects one of the least well studied, possess many cognitive abilities comparable to those of birds and mammals. Despite a plethora of behavioural studies assessing cognition abilities and an abundance of neuroanatomical studies, only f...

Potamotrygon motoro has been shown to use vision to orient in a laboratory setting and has been successfully trained in cognitive behavioral studies using visual stimuli. This study explores P. motoro's visual discrimination abilities in the context of two-alternative forced-choice experiments, with a focus on shape and contrast, stimulus orientati...

Serial reversal learning is considered a reliable approach for the testing of behavioral flexibility, and animals that inhabit fluctuating habitats and different environments are expected to possess behavioral and cognitive flexibility. The ocellate river stingray (Potamotrygon motoro) is one such species. Comprising the first serial reversal learn...

Synopsis Fishes can detect the geomagnetic field as well as artificial magnetic fields of much higher magnitude. They can be trained to discriminate and associate certain field strengths with particular tasks or rewards. It is highly likely that many fish species, whether migratory or not, use the geomagnetic field for orientation and navigation an...

Background: Previous studies have shown that stingrays can exploit a variety of spatial learning strategies, including directional, landmark, and place learning. In these studies, allocentric and global strategies were preferred over egocentric information and local strategies. Elasmobranchs represent the oldest extant vertebrate group. Considering...

Sorting objects and events into categories and concepts is an important cognitive prerequisite that spares an individual the learning of every object or situation encountered in its daily life. Accordingly, specific items are classified in general groups that allow fast responses to novel situations. The present study assessed whether bamboo sharks...

Fish rival birds and mammals in many of their cognitive skills, and have been shown to successfully discriminate between a range of stationary and moving objects. The present study tested the ability of Pseudotropheus zebra to recognize unique movement patterns shown in the form of a single moving dot, point displays (PDs), point-light displays (PL...

Metacognition is thinking about thoughts and/or feelings. It is the ability to reflect upon the own knowledge [1, 2], as has been shown for dolphins or monkeys [3, 4]. Mirror-self recognition on the other hand is interpreting information in a mirror as oneself, as in dolphins, elephants or magpies [5, 6, 7]. Aim of this study was to find the most s...

The aim of the present study was to test juvenile grey bamboo sharks (Chiloscyllium griseum) for their ability to perceive and discriminate simple and complex motion patterns. Experiments were carried out as two-alternative forced choice experiments; choosing the designated positive stimulus was rewarded with food. Individuals were first trained to...

This is the first study to comparatively assess the perception of the Ebbinghaus-Titchener circles and variations of the Delboeuf illusion in four juvenile bamboo sharks (Chiloscyllium griseum) and five damselfish (Chromis chromis) using identical training paradigms. We aimed to investigate whether these two species show similarities in the percept...

Freshwater stingrays (Potamotrygon motoro) have been shown to use a variety of spatial learning strategies including directional, landmark and place learning. In the present study, the significance of landmarks and geometric cues was investigated in a hole-board task. The aim was to determine cue preferences and collect additional information on th...

Vision is of primary importance for many fish species, as is the recognition of movement. With the exception of one study, assessing the influence of conspecific movement on shoaling behaviour, the perception of biological motion in fish had not been studied in a cognitive context. The aim of the present study was therefore to assess the discrimina...

Litter size and details of the reproductive biology of female brown guitarfish Rhinobatos schlegelii from the Penghu Islands, Taiwan, are provided for the first time. Litter size ranged 1–14 (mean 8.5), with an embryonic sex ratio of 1:1. Vitellogenesis proceeded in parallel with gestation.

This study investigated memory retention capabilities of juvenile gray bamboo sharks (Chiloscyllium griseum) using two-alternative forced-choice experiments. The sharks had previously been trained in a range of visual discrimination tasks, such as distinguishing between squares, triangles and lines, and their corresponding optical illusions (i.e.,...

Object categorization is an important cognitive adaptation, quickly providing an animal with relevant and potentially life-saving information. It can be defined as the process whereby objects that are not the same, are nonetheless grouped together according to some defining feature(s) and responded to as if they were the same. In this way, knowledg...

Adaptation of brain structures, function and higher cognitive abilities most likely have contributed significantly to the evolutionary success of elasmobranchs, but these traits remain poorly studied when compared to other vertebrates, specifically mammals. While the pallium of non-mammalian vertebrates lacks the mammalian neocortical organization...

This study assessed spatial memory and orientation strategies in Chiloscyllium griseum. In the presence of visual landmarks, six sharks were trained in a fixed turn response. Group 1 started from two possible compartments approaching two goal locations, while group 2 started from and approached only one location, respectively. The learning criterio...

Despite convincing data collected by microspectrophotometry and molecular biology, rendering sharks colourblind cone monochromats, the question of whether sharks can perceive colour had not been finally resolved in the absence of any behavioural experiments compensating for the confounding factor of brightness. The present study tested the ability...

Fish move in a three-dimensional environment in which it is important to discriminate between stimuli varying in colour, size, and shape. It is also advantageous to be able to recognize the same structures or individuals when presented from different angles, such as back to front or front to side. This study assessed visual discrimination abilities...

Several species have been shown to perceive symmetry as a measure of superior genetic quality, useful for assessing potential mates or mediating other visual activities such as the selection of food sources. The current study assessed whether Pseudotropheus sp. and Chiloscyllium griseum, two fish species from distantly related groups, possess symme...

Bamboo sharks (Chiloscyllium griseum) were tested for their ability to perceive subjective and illusionary contours as well as line length illusions. Individuals were first trained to differentiate between squares, triangles, and rhomboids in a series of two alternative forced-choice experiments. Transfer tests then elucidated whether Kanizsa squar...

This study assessed visual discrimination abilities in bamboo sharks (Chiloscyllium griseum). In a visual discrimination task using two-dimensional (2D) geometric stimuli, sharks learned to distinguish between a square, being the positive (rewarded) stimulus, and several negative stimuli, such as two differently sized triangles, a circle, a rhomboi...

This study assessed complex spatial learning and memory in two species of shark, the grey bamboo shark (Chiloscyllium griseum) and the coral cat shark (Atelomycterus marmoratus). It was hypothesized that sharks can learn and apply an allocentric orientation strategy. Eight out of ten sharks successfully completed the initial training phase (by loca...

Animals face different threats; to survive, they have to anticipate how to react or how to avoid these. It has already been shown in teleosts that selected regions in the telencephalon, i.e., the medial pallium, are involved in avoidance learning strategies. No such study exists for any chondrichthyan. In nature, an avoidance reaction may vary, ran...

The ability to recognize and distinguish between visual stimuli is fundamental for everyday survival of many species. While diverse aspects of cognition, including complex visual discrimination tasks were previously successfully assessed in fish, it remains unknown if fish can learn a matching-to-sample concept using geometrical shapes and discrimi...

Object categorization is an important function of the visual system, quickly providing an animal with relevant information about its surrounding and current situation, as for example during predator detection. While the ability to categorize objects has already been observed in several vertebrate and even invertebrate species, no attempt has previo...

Aetobatus narinari, a circumglobal batoid, is subjected to increasing fishing pressures, especially throughout South-east Asia. However, its management and protection is complicated by the lack of relevant life history information. It appears to be a late-maturing, long-lived stingray with a size-at-maturity of ,130 and4150 cm in ventral disc width...

The white-spotted eagle ray Aetobatus narinari is a species complex that occurs circumglobally throughout warm-temperate waters. Aetobatus narinari is semi-pelagic and large (up to 300 cm disc width), suggesting high dispersal capabilities and gene flow on a wide spatial scale. Sequence data from two mitochondrial genes, cytochrome b (cytb) and NAD...

Seven elasmobranch species, a group known for their highly-developed sense of smell, were examined for developmental changes in the number of olfactory lamellae, the size of the surface area of the sensory olfactory epithelium and the mass of both the olfactory rosettes (primary input to the CNS), and the olfactory bulbs. Within each species, juven...

This study investigated the relationship between olfactory morphology, habitat occupancy, and lifestyle in 21 elasmobranch species in a phylogenetic context. Four measures of olfactory capability, that is, the number of olfactory lamellae, the surface area of the olfactory epithelium, the mass of the olfactory bulb, and the mass of the olfactory ro...

Vera Schluessel, PhD Thesis, The Universty of Queensland The white spotted eagle ray, Aetobatus narinari is a graceful animal, which greatly contributes to the beauty of coral reefs and other marine environments around the world. Unfortunately, increases in fishing pressure, habitat destruction, urbanization, pollution and climate change have cont...

We investigated whether juvenile freshwater stingrays (Potamotrygon motoro) can solve spatial tasks by constructing a cognitive map of their environment. Two experimental conditions were run: allocentric and ego-allocentric. Rays were trained to locate food within a four-arm maze placed in a room with visual spatial cues. The feeding location (goal...

1.Over the past two decades the number of fisheries targeting shark resources has increased dramatically. A combination of factors, including relatively slow growth rate, low fecundity and late age of maturity, result in low recovery rates from exploitation for most shark species. This, in turn, is reflected in the poor record of sustainability of...

We compared growth rates of the lemon shark, Negaprion brevirostris, from Bimini, Bahamas and the Marquesas Keys (MK), Florida using data obtained in a multi-year annual census. We marked new neonate and juvenile sharks with unique electronic identity tags in Bimini and in the MK we tagged neonate and juvenile sharks. Sharks were tagged with tiny,...

The aim of this study was to investigate, whether cartilaginous fish construct and use cognitive maps of their environment (cognitive mapping strategy) to master various navigational tasks, in contrast to just using a single direct visual cue for orientation (guidance strategy) or performing a body referenced turn (orientation strategy). Freshwater...