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High-speed decision-making in Archerfish [Elektronische Ressource] = (Hochgeschwindigkeits-Entscheidungsfindung bei Schützenfischen) / vorgelegt von Thomas Schlegel

124 pages
High-speed Decision-making in Archerfish (Hochgeschwindigkeits-Entscheidungsfindung bei Schützenfischen) Der Naturwissenschaftlichen Fakultät der Friedrich-Alexander-Universität Erlangen-Nürnberg zur Erlangung des Doktorgrades Dr. rer. nat. vorgelegt von Thomas Schlegel aus Nürnberg Als Dissertation genehmigt von der Naturwissenschaftlichen Fakultät der Friedrich-Alexander-Universität Erlangen-Nürnberg Tag der mündlichen Prüfung: 08. Juni 2010 Vorsitzender der Promotionskommission: Prof. Dr. Eberhard Bänsch Erstberichterstatter: Prof. Dr. Stefan Schuster Zweitberichterstatter: Prof. Dr. Helmut Brandstätter High-speed Decision-making in Archerfish Abstract 1. Abstract Archerfish are famous for their ability to dislodge insects (such as flies) by spitting precisely aimed jets of water at them. Once fish manage to dislodge a prey of interest, they carefully monitor the initial movement of the prey item, precisely extracting several critical parameters of movement (such as speed and direction of prey movement, the distance to and height of prey), promptly predicting its future impact position, reacting with a swift and accurate turn. Finally fish accelerate towards that position, snatching their reward as it hits the water surface.
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High-speed Decision-making in Archerfish
(Hochgeschwindigkeits-Entscheidungsfindung bei
Schützenfischen)




Der Naturwissenschaftlichen Fakultät
der Friedrich-Alexander-Universität Erlangen-Nürnberg
zur
Erlangung des Doktorgrades Dr. rer. nat.



vorgelegt von
Thomas Schlegel

aus Nürnberg









Als Dissertation genehmigt von der
Naturwissenschaftlichen Fakultät der Friedrich-Alexander-
Universität Erlangen-Nürnberg









Tag der mündlichen Prüfung: 08. Juni 2010

Vorsitzender der
Promotionskommission: Prof. Dr. Eberhard Bänsch

Erstberichterstatter: Prof. Dr. Stefan Schuster
Zweitberichterstatter: Prof. Dr. Helmut Brandstätter






High-speed Decision-making in Archerfish

























Abstract
1. Abstract
Archerfish are famous for their ability to dislodge insects (such as flies) by
spitting precisely aimed jets of water at them. Once fish manage to dislodge a
prey of interest, they carefully monitor the initial movement of the prey item,
precisely extracting several critical parameters of movement (such as speed
and direction of prey movement, the distance to and height of prey), promptly
predicting its future impact position, reacting with a swift and accurate turn.
Finally fish accelerate towards that position, snatching their reward as it hits
the water surface. The experiments of this thesis extensively engaged in the
manipulation of the visual input cues, e.g. via changes in contrast levels,
displaying two prey objects simultaneously or depriving the available visual
input of moving prey spatially and temporally. The method of choice was the
study of archerfish behaviour subsequent to the onset of prey movement as
an amalgamation of the whole system!s signal extraction, information
processing, decision-making and overall performing abilities.
In the process, I discovered that the archerfish!s predictive turning behaviour
can be elicited via prey movement alone – no preceding shooting is
necessary (enabling all subsequent experimentation in the first place). The
predictive behaviour is all the more remarkable, since it features the ability to
instantly decide for one of two simultaneously appearing flies, applying a
spatial representation of the outside world in the process. Furthermore fish
keep up their turning accuracy even if prey motion will appear with a spatial
offset to the fish!s point of gaze. The latency of the fish!s responses depends
e.g. on the contrast levels between fly and background. The entire processing
in between the onset of prey movement and the triggering of the fish!s turn
can be delivered within a time frame of 40 milliseconds, severely restricting
the number of underlying neurons. Subsequent experiments revealed a visual
input of less than 300 activated photoreceptors (equivalent to a retinal area of
roughly 0.01 mm) completely suffices to elicit a precise predictive reaction.
The accumulated results prove Archerfish to be a vertebrate system, shaped
for top speed, in which a complex and plastic decision is performed by
surprisingly small circuitry.
4 Tables
2. Tables
2.1 Table of contents
1. Abstract .................................................................................................... 4
2. Tables ....................................................................................................... 5
2.1 Table of contents .................................................................................. 5
2.2 Table of figures ..................................................................................... 7
2.3 Table of supplemental tables ................................................................ 8
3.Introduction ............................................................................................... 9
4. General methods.................................................................................... 16
4.1 Animals and their keeping................................................................... 17
4.2 Recording and managing behavioural data......................................... 19
4.3 Statistics ............................................................................................. 20
4.4 Characterising the fish!s performance................................................. 21
4.4.1 Latency ........................................................................................ 21
4.4.2 Precision and Error....................................................................... 22
4.5 Seven criteria separating the analysable from the discarded reactions 24
5. The experiments .................................................................................... 25
5.1 Depriving the fish of shooting-related information ............................... 26
5.1.1 Objectives and Experimental Approach........................................ 26
5.1.2 Results ......................................................................................... 27
5.1.3 Discussion.................................................................................... 30
5.2 Spatial attention .................................................................................. 34
5.2.1 Objectives and Experimental Approach........................................ 34
5.2.2 Results ......................................................................................... 35
5.2.3 Discussion.................................................................................... 37
5.3 Deciding for one of two flies ................................................................ 38
5.3.1 Objectives and Experimental Approach........................................ 38
5.3.2 Results ......................................................................................... 39
5 Table of contents
5.3.3 Discussion.................................................................................... 42
5.4 Contrast dependency.......................................................................... 44
5.4.1 Objectives and Experimental Approach........................................ 44
5.4.2 Results ......................................................................................... 46
5.4.3 Discussion.................................................................................... 48
5.5 Do the fish need a priori information on target height.......................... 50
5.5.1 Objectives and Experimental Approach........................................ 50
5.5.2 Results ......................................................................................... 52
5.5.3 Discussion.................................................................................... 57
5.6 Finding the minimal integration interval............................................... 59
5.6.1 Objectives and Experimental Approach........................................ 59
5.6.2 Results ......................................................................................... 64
5.6.3 Discussion.................................................................................... 78
5.7 Breeding Archerfish ............................................................................ 81
5.7.1 Objectives and Experimental Approach........................................ 81
5.7.2 Results ......................................................................................... 82
5.7.3 Discussion.................................................................................... 83
6. Discussion.............................................................................................. 87
6.1 A conception of archerfish: from visual input to motor output .............. 88
6.2 Some closing remarks on cognition .................................................... 94
7. References ............................................................................................. 96
9. Supplemental ....................................................................................... 107
10. Acknowledgements ........................................................................... 121
11. Zusammenfassung auf Deutsch ....................................................... 123






6 Table of figures
2.2 Table of figures
Figure 1: Distribution of participating fish species......................................... 17
Figure 2: Exemplary experimental setup ...................................................... 20
Figure 3: Sequence, visualising latency determination ................................. 21
Figure 4: Sequence, visualising determination of precision .......................... 22
Figure 5: Sign conventions applied in error measurements .......................... 23
Figure 6: Experimental differences in deprived versus natural setup ............ 27
Figure 7: Reactions to natural and deprived conditions are alike .................. 29
Figure 8: Matching fly movement in natural and deprived conditions............ 30
Figure 9: Using several platforms to test spatial attention............................. 35
Figure 10: Behavioural reactions to horizontal offsets .................................. 36
Figure 11: Two flies simultaneously.............................................................. 39
Figure 12: Providing two flies simultaneously ............................................... 40
Figure 13: Parameters of fly movement........................................................ 41
Figure 14: Experimental setups applied to test for several visual contrasts .. 45
Figure 15: No correlation between latency and the fly!s velocity................... 46
Figure 16: Changing contrast conditions affects latency but not precision .... 47
Figure 17: Testing ten different contrast levels on two groups of fish............ 48
Figure 18: Experimental setup, testing behaviour to vertical offsets ............. 51
Figure 19: Applicability of method for fish of group B.................................... 52
Figure 20: Responses according to attentional presetting and height........... 54
Figure 21: The fish do not need a priori information on object height............ 55
Figure 22: Comparability of the applied conditions ....................................... 56
Figure 23: Setup for temporally restricting the available visual input............. 62
Figure 24: Display of the black coating of the depriving pipes ...................... 63
Figure 25: Applied accuracy to measure the fly!s velocity............................. 65
Figure 26: In time reactions depend on input duration .................................. 67
Figure 27: Projecting the flies! movement onto the fish!s retina .................... 68
Figure 28: Control data for reactions to fully available visual input................ 69
Figure 29: Latency of the reactions .............................................................. 70
Figure 30: Bearing errors with respect to both of the fish!s turns .................. 71
Figure 31: Duration and size of the fish!s first and second turns................... 73
7 Table of figures
Figure 32: First turns of reactions classified as too late ................................ 75
Figure 33: Combining two intervals leads to longer latencies ....................... 77
Figure 34: Injecting procedure...................................................................... 82
Figure 35: Exemplary images of fertilised eggs and fish larvae .................... 83
Figure 36: Visualisation of processes that lead to a predictive turn............... 93


2.3 Table of supplemental tables
Table 1: Supporting data for figures 7, 8 and 10......................................... 107
Table 2: Supporting data for figures 12, 13 and 16..................................... 108
Table 3: Supporting data for figure 17. ....................................................... 109
Table 4: Supporting data for figures 19, 20, 21 and 22. .............................. 110
Table 5: Supporting data for figures 25 and 26........................................... 111
Table 6: Supporting data for figures 26 and 27 A. ...................................... 112
Table 7: Supporting data for figures 27 B and 28. ...................................... 113
Table 8: Supporting data for figure 29. ....................................................... 114
Table 9: Supporting data for figure 30 A. .................................................... 115
Table 10: Supporting data for figure 30 B. .................................................. 116
Table 11: Supporting data for figure 31 A. .................................................. 117
Table 12: Supporting data for figure 31 B. .................................................. 118
Table 13: Supporting data for figure 32. ..................................................... 119
Table 14: Supporting data for figure 33. ..................................................... 120









8





3.Introduction





















9 Introduction
During the last couple of years, archerfish proved to feature a diversity of
sophisticated behaviours in addition to their shooting ability. It became
increasingly conceivable that this species features astonishingly fast visual
processing and may provide more than understanding of its shooting
mechanism. However, completely and properly characterising the archerfish!s
behavioural repertoire in the first place is not just bearing an inherent
fascination by itself; it is also fundamentally necessary to provide a decent
basis for further neurobiological studies. Knowledge of as many constraints of
the natural behaviour as possible, will guide the dissection of its function.
This dissection could start with multi-electrode recordings [1, 2] for instance,
or a histological approach – or a combination of both [3]. Concepts about the
"where! and "when! of signal computation within the fish!s brain may be
generated, using functional magnetic resonance imaging [4-9]. The shape and
activity of single cells can be visualised with single-unit recordings with
subsequent cell staining [10-13], even using multi-photon laser scanning
nowadays [14-19]. With such an abundance of neurobiological methods
available, what is the benefit of behavioural studies?

The clear benefit of behavioural studies originates within the chance to study
animals as a whole and entirely intact system, flexibly moving in familiar
territory. In such a system, the single components are precisely co-operating
to perform the sound symphony of animal behaviour. Harmony within that
symphony is the ultimate verification that the system is operating properly, as
a whole. But at the same time – having to cope with a whole symphony can
become a tough challenge. Unless we have the possibility to identify the
functional role of each single unit ("how does a viola sound, compared to a
violin!), the whole issue can become fairly puzzling. But at the same time,
exactly distinguishing each single instrument will probably prevent us from
having a satisfactory musical enjoyment. The same applies for a certain
behavioural pattern – watching animals behave will not inevitably result in
better understanding of the underlying neuronal circuits. Such an
understanding requires plausible concepts about the number and nature of
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