Aktuelle Forschung
Research
Behavioural topics (sharks, rays and cichlids) include (among others) visual discriminations and categorizations of 2D and 3D structures, matching-to-sample and same-from-oddity tasks, perception of illusionary contours and amodal completion, symmetry perception and categorization, form constancy, (serial-) reversal learning, memory retention capabilities, avoidance behavior, the perception of movement (including biological motion) and color, assessment of numerical abilities as well as experiments on visual resolution thresholds. Several extensive and ongoing experimental series deal with spatial orientation, spatial memory and numerical abilities in elasmobranchs as well as abstract concept learning. There is large inter- and intraspecific variation regarding performance of fish, with some reoccurring trends (e.g. in general sharks are better at abstract concept learning while cichlids are better at movement perception) which may be related to different ecologies and lifestyles. Other studies in my lab have included experiments on sex differences in regards to solving cognitive tasks in sharks and stingrays.
Biological motion, i.e. point light displays were used in three studies (Schluesset et al. 2015, 2018 and Fuss et al. 2017) to assess whether fish can recognize familiar organisms based on movement itself and to determine what information is contained within biological motion patterns and accessed through the perception of movement by fish. Several follow up studies are in progress looking at the importance of facial features, and the effect of potentially threatening motion displays (e.g. by predators), or by potentially emotionally charged movements (as for example produced by injured fish).
We have also been looking at acoustic discrimination abilities in bamboo sharks. Sharks were trained to differentiate between two low frequency sounds in the presence or absence of a secondary reinforcer (light). Transfer tests elucidated that in situations where both cues are available, vision is more important than sound; however, in the absence of visual cues, acoustic cues are sufficient to solve a task. Frequencies close to training frequencies elicit similar responses as these, while unfamiliar frequencies lead to random swimming behavior. Current projects investigate acoustic discrimination abilities using a variety of methods other than two-alternative-forced choice procedures. I am also currently looking at the retention capabilities of acoustic information.
To complement behavioral work, I am also looking at the neural substrates involved in the processing of cognitive information. One of the most striking differences in brain morphology between different groups of vertebrates is the lack of the typical mammalian neocortex organization in fish, amphibians and sauropsids (Wullimann 1997). Higher cognitive abilities of mammals are dependent on cortical circuits; a mammal whose cortex has been ablated, can no longer perform higher cognitive tasks (Kaas 1987). It follows that in the absence of a mammalian cortex cognitive abilities in fish must be localized in other neural substrates (such as the pallium). However, only very few studies have identified some of these structures, with our studies being the only ones available for elasmobranchs. We used selective lesion experiments (telencephalon ablation) to successfully identify relevant neural substrates for some aspects of spatial orientation (Fuss, Bleckmann, Schluessel 2014a,b) and avoidance learning (Schwarze, Bleckmann, Schluessel 2013) in bamboo sharks. Additionally, a three-year pilot study using immediate early genes (egr-1, c-fos) to identify neural substrates relevant to visual discrimination learning in elasmobranchs was successfully conducted (Fuss and Schluessel 2018). Future studies include further IEG studies on sharks and cichlids as well as lesion experiments involving telencephalic, diencephalic and mesencephalic nuclei.
Dissections Carribean reef sharks
(Bahamas)
