Interactive effects of fish kairomone and light on Daphnia escape behavior |
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Authors: | Brewer M; Dawidowicz P; Dodson S |
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Institution: | Center for Great Lakes Studies, University of Wisconsin-Milwaukee, 600 E. Greenfield Avenue, Milwaukee, WI 53204, USA; Department of Hydrobiology, University of Warsaw, Nowy Swiat 67, 00-046 Warsaw, Poland; University of Wisconsin-Madison, Department of Zoology, 430 Lincoln Drive, Madison, WI 53706, USA; Corresponding author/address |
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Abstract: | We investigated the effects of fish kairomone and light intensity on the
inducibility and effectiveness of escape behavior in four clones of the
water flea Daphnia from different habitats. To
characterize and determine the effectiveness of their escape responses,
individuals were observed: (i) escaping from the hydrodynamic disturbances
of a simulated predator (a small sphere dropped from above); (ii) being
preyed upon by small fish (Poecelia reticulata); (iii)
responding to encounters with conspecifics in crowded conditions. The
simulated predation experiments revealed that when exposed to fish
kairomone for 48 h, two Daphnia pulicaria clones, but
not two hybrid clones, became about twice as sensitive to fluid
disturbances when tested in the light, relative to no-kairomone and dark
treatments. When tested in the dark, kairomone had no effect on sensitivity
in any clone. All four clones had an all-or-none escape response, in which
the strength of the response, as measured by escape distance and speed, was
constant regardless of treatment. In the guppy predation trials,
kairomone-treated D.pulicaria escaped significantly
more often from guppies, in both bright- and dim-light conditions. In dim
light, similar to natural lighting conditions, regardless of kairomone, all
but the most weakly escaping clone were able to elude attacking guppies in
a significant proportion of attacks. Finally, kairomone had no effect on
the number of escapes performed by crowded individuals in response to the
comparatively weak, non-threatening signals created by other
Daphnia, indicating that the kairomone-induced
alertness in the D.pulicaria clones did not make them
'excessively' sensitive. The results suggest that
Daphnia escape behavior is under complex and efficient
environmental regulation, and may play a significant role in aquatic
trophic relationships.
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