First published online June 29, 2006
Journal of Experimental Biology 209, 2739-2748 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02297
Behavioral responses of Drosophila to biogenic levels of carbon dioxide depend on life-stage, sex and olfactory context
Cécile Faucher1,2,
Manfred Forstreuter3,
Monika Hilker2 and
Marien de Bruyne1,*
1 Freie Universität Berlin, Neurobiologie, Königin-Luise-Strasse
28-30, D-14195 Berlin, Germany
2 Freie Universität Berlin, Angewandte Zoologie, Haderslebener Strasse
9, D-12163 Berlin, Germany
3 Technische Universität Berlin, Ökologie,
Königin-Luise-Strasse 22, D-14195 Berlin, Germany
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Fig. 1. Drosophila flies are attracted to apple cider vinegar but avoid
CO2. Time spent by flies in each of the fields in a four-field
olfactometer during a 600 s experiment. (A) Control situation when only air is
delivered from the four corners (N=57). (B) Apple cider vinegar odor
(N=39) is added to the air in one field (grey bar). (C)
CO2 of different concentrations (N0.02%=38;
N0.1%=42; N1%=35) is added to the air
in one field (black bars). The orientation of the fields is indicated relative
to the field laced with the test odor: L, left, O, opposite, R, right. Insets
show examples of 10 min tracks of single flies for control, vinegar, and 1%
CO2 respectively. The broken line at 150 s indicates an equal
amount of time in all fields. Deviations from equal distribution were tested
with a Friedman-ANOVA (P<0.001; ns, no significant difference).
Fields with different letters above the bars are significantly different from
each other (Wilcoxon-Wilcox test; P<0.05 for 0.1% CO2,
P<0.001 for 1% CO2 and vinegar). Values are means
± s.e.m.
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Fig. 2. Apple cider vinegar makes females more sensitive to CO2.
Distributions of time spent in four fields of the olfactometer as in
Fig. 1. (A) 0.02%
CO2 (black hatched bars) added to apple cider vinegar (vin.; grey
bars; N=53, Friedman-ANOVA: P<0.001; Wilcoxon-Wilcox:
P<0.001) is as attractive as apple cider vinegar alone (same data
as in Fig. 1B; ns, no
significant difference, Mann-Whitney U-test). (B) When all fields
contain apple cider vinegar odor (grey bars) as background, a field laced with
0.02% CO2 (hatched bars) is avoided, but only by females
(Nfemales=29, Nmales=17,
Friedman-ANOVA, P<0.001; Wilcoxon-Wilcox: P<0.001).
Values are means ± s.e.m.
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Fig. 3. Effects of vinegar and CO2 backgrounds on walking activity of
male and female flies. Percentage of time walking is indicated for males and
females when all four fields contain air only (Air), apple cider vinegar
(Vin.) or 0.1% CO2. For females, Nair=30;
Nvinegar=22; NCO2=21; for males,
Nair=27; Nvinegar=20;
NCO2=20. *Significant difference compared to
air (Mann-Whitney U-test, P<0.01 for vinegar,
P<0.05 for CO2); ns, no significant difference. Values
are means ± s.e.m.
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Fig. 4. Bananas and flies emit carbon dioxide. (A) Mean CO2 emission for
a single banana (N=5) over a period of 21 days. (B) Decrease in fresh
mass of the bananas is linear over the same period. Values are means ±
s.d. (C) CO2 emission from three groups of 20 flies. The horizontal
bar indicates 1 min of shaking, which induces a sharp rise in CO2
emission. The three curves are normalized to their mean at a point before
shaking. The dots indicate the absolute values for the three curves at that
time. Note the differences in scale of both axes compared to A. The delay
observed between the start of the stimulation and the increase in emission is
caused by the design of the system.
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Fig. 5. Drosophila larvae avoid CO2 and prefer vinegar. (A)
Mean distribution of groups of 10 larvae after 10 min when air is delivered in
the four fields (N=18). (B) Mean distributions after 10 min when
CO2 is added to one field (black) at two concentrations
(N0.1%=24; N1%=25). (C) Mean
distribution at four time points when one field (gray) is laced with vinegar
odor (N=17). Abbreviations and statistics are as in
Fig. 1. The broken line at 25%
indicates an equal distribution in all fields. In contrast to the results in
Figs 1 and
2 the test field is not
significantly different from all control fields (Friedman-ANOVA,
P<0.01 for CO2, P<0.001 for vinegar;
Wilcoxon-Wilcox: P<0.05); ns, no significant difference. Values
are means ± s.e.m.
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Fig. 6. The Gr21a-expressing neuron mediates CO2 detection in
larvae. (A) Confocal image of the anterior of a third instar larva expressing
membrane-bound UAS-mCD8::GFP (green) driven by a Gr21a-Gal4
construct. Dotted line indicates the position of the dome of the dorsal organ
in the transmission image; arrows point to the terminal organs. (B,C)
Distributions of larvae in the four-field olfactometer as in
Fig. 5. (B) Responses to 1%
CO2 by larvae lacking the Gr21a-expressing neurons due to
Gr21a-driven expression of the apoptotic gene reaper
(rpr) (Gr21a-rpr, N=22), compared to their genetic controls
carrying only the driver construct (Gr21a, N=20) or the
reaper construct (rpr, N=17). Significant avoidance is only
seen in the controls. (C) Response to apple cider vinegar of larvae lacking
the Gr21a-expressing neuron (Gr21a-rpr, N=18) is
normal when compared to wild-type larvae (CS, same data as in
Fig. 5C at 10:00 min; ns, no
significant difference, Mann-Whitney U-test). Abbreviations and
statistics are as in Fig. 1.
The broken line at 25% indicates an equal distribution in all fields. In
contrast to Figs 1 and
2 the test field is not
significantly different from all control fields (Friedman-ANOVA,
P<0.05 for CO2, P<0.001 for vinegar;
Wilcoxon-Wilcox: P<0.05); ns, no significant difference. Values
are means ± s.e.m.
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© The Company of Biologists Ltd 2006
