2. Behavioral Biology TALKS - Deutsche Zoologische Gesellschaft

����16 Philipp Krupczynski
Archerfish and the changing world: temperature affects latency but not accuracy of
the predictive start
Authors: Philipp Krupczynski 1 , Stefan Schuster 1
Affiliation: 1 Department of Animal Physiology, University of Bayreuth
Archerfish are not only renowned for shooting down aerial insects with powerful jets
of water but also for their ability of predicting their prey's later point of impact.
Shortly after the prey is dislodged the fish initiate a quick C-shaped turn towards
where the prey will later land and move on a straight line towards that position.
Archerfish live in mangrove areas from Southeast Asia to Australia. This complex
biotope enforces the fish to cover considerable distances in their search for hunting
grounds. Thereby the fish may face dramatic and rapid changes in light conditions,
salinity and temperature over the course of a few hours. Here we show that the time
needed from the onset of prey movement to initiating the C-start (latency) increases
strongly with decreasing temperature. However, the precision of their predictive
start is not affected by temperature at all. This is surprising, because all underlying
circuitry involved in monitoring prey motion, selecting and carrying out the
appropriate motor pattern is strongly dependent on temperature. Given the high
competition, but also the predation risk of starting archerfish, mechanisms must be
at work to ensure that starts are only released when they are appropriately aimed.
����17 Etienne Campione
Brightness discrimination in the hunting spider Cupiennius salei
Authors: Etienne Campione 1 , Axel Schmid 1
Affiliation: 1 Department für Neurobiologie - Universität Wien, Austria
Cupiennius salei is a nocturnal spider with eight eyes, divided in two principal and six
secondary eyes, which differ morphologically and functionally. They are extremely
sensitive (< 0.001 lux) and the spectral sensitivy of the spider range from 365 nm to
675 nm, due to three different types of photoreceptors. In behavioural experiments,
however, the animals are shown to be colour blind. On the other hand, the three
photoreceptors might be used to provide a good brightness discrimination ability,
necessary in the dim habitat of Cupiennius salei to discriminate preys and predators.
We tested this hypothesis by presenting the spiders square-shaped flickering stimuli
on a stationary background, both with variable brightness. The principal eyes have
two muscles each whose activity increases when the spider detects a visual stimulus.
Thus, when the spider perceives a visible contrast between the stimulus and the
background, its principal eye muscle activiy should increase. This activity could be
recorded in vivo through a special telemetric device. Our results show that
Cupiennius salei has a quite good ability in brightness discrimination, a contrast of
0.25 is sufficient to elicit a significant response, except with very dark stimuli, where
the minimal contrast needs to be higher. We were also able to calculate the Weber’s
fraction in order to compare the brightness discrimination ability of Cupiennius salei
with others animals.
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