First published online May 30, 2008
Journal of Experimental Biology 211, 1868-1873 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.018036
Nest-mark orientation versus vector navigation in desert ants
Patrick Bregy*,
Stefan Sommer and
Rüdiger Wehner
Institute of Zoology, University of Zürich, Winterthurerstrasse 190,
CH-8057 Zürich, Switzerland
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Fig. 1. Experimental paradigm. (A) Training setup. Ants were trained to a food
source (open square) at 15 m due south. The nest entrance (black dot) was
marked by a black cylinder, hitherto referred to as the `landmark' (open
circle). N indicates north. Ants, which had been caught at the feeder, were
released on a distant field (indicated by the broken arrow between A and B).
(B) Test field. Ants were released (black square) in the test field, which was
marked out as a rectangular grid of white lines with a mesh width of 1 m.
Coloured circles indicate alternative positions of the landmark, which was
identical to the beacon presented at the nest entrance during training. In one
series of experiments (the `negative control') the landmark was removed from
the test field. The open and the shaded squares indicate the areas selected to
assess the ants' nest-search densities at the positions indicated by the home
vector and the nest mark, respectively. In the example shown here the beacon
is assumed to be set up at 5 m to the north and 3 m to the west of the point
of release.
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Fig. 2. Test runs. Shown are the ants' trajectories from the point of release to
the first turn (black dots). The beacon (open circle) was positioned along
(A), to the left (B) or to the right (C) of the ants' home-vector course. In
series A1 the beacon was removed during tests. The orange square marks the
position of the fictive nest entrance as indicated by the ants' home vector.
Numbers in parentheses represent sample sizes. For illustrative purposes
landmarks are slightly enlarged. Scale bar, 5 m.
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Fig. 3. Effects of the displaced nest-defining landmark on the ants' running
direction. (A) Ants of series B2 (data mirrored) and C2 (see
Fig. 2) experienced the beacon
(open orange circle) to one side after having run off their home vector for 5
m. (B) Ants of series B1 and C1 were tested with the landmark (open green
circle) at 3 m to the west (data mirrored) or to the east of the point of
release (black dot), respectively. (C) The landmark (open blue circle) was
positioned at the fictive position of the nest, that is, at 15 m due north
(0°; series A4). Coloured dots and bars depict the ants' mean homing
directions and the 95% confidence intervals, respectively. N indicates
north.
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Fig. 5. Nest-search densities. (A) Conceptual scheme used for the evaluation of the
ants' spatial search preferences. The open and the shaded squares indicate the
areas selected to assess the search densities at the positions indicated by
the ants' home vector (open arrow) and the beacon (open circle), respectively.
In the example shown the landmark is assumed to be set up 5 m beyond the
position of the nest entrance as indicated by the ants' home vector (at
position +5). The black square marks the point of release. (B) Mean search
densities with upper 95% confidence limits of the test series with the
landmark positioned in the direction of the ants' home vector. Red and white
bars are the search densities in the vicinity of the landmark and at the tip
of the home vector, respectively. In the `positive control' experiment
(landmark position 0), the two squares coincide and the white bar is omitted.
In the `negative control' experiment (no landmark), the beacon was removed
during tests. (C) Results of the experiments with the landmark positioned to
one side of the ants' home vector. Data sets for the corresponding left and
right series are pooled. Blue bars are the search densities in the vicinity of
the landmark (white bars as above).
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© The Company of Biologists Ltd 2008
(in degrees) and distance d to
the landmark (open green circle) were evaluated at distinct distances (in the
example shown here at a 9 m distance) from the start of the ant's homeward run
(see concentric circles in Fig.
3). The black and red squares depict the point of release and the
fictive position of the nest, respectively. The black dot marks the ant's
first turn (i.e. the onset of the ant's nest search behaviour). (B)