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First published online February 12, 2007
Journal of Experimental Biology 210, 897-905 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02706
Structural complexity of chemical recognition cues affects the perception of group membership in the ants Linephithema humile and Aphaenogaster cockerelli
1 Department of Biology, University of Colorado at Denver and Health
Sciences Center, Campus Box 171, PO Box 173364, Denver, CO 80217-3364
USA
2 Department of Biological Sciences, 371 Serra Mall, Stanford University,
Stanford, CA 94305-5020 USA
* Author for correspondence (e-mail: michael.greene{at}cudenver.edu)
Accepted 4 January 2007
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Summary |
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Key words: cuticular hydrocarbons, social recognition, colony recognition, species recognition
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Introduction |
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).
Cuticular hydrocarbon profiles, detected by ants through antennal contact, are
thought to be compared to a template that defines group membership
(LeMoli et al., 1983;
Vander Meer and Morel, 1998).
Differences from the template can lead to a behavioural recognition response
such as aggression. Template-label matching may involve neural mechanisms in
the brain and has been shown to occur in sensilla peripheral to the central
nervous system (Obin and Vander Meer,
1989; Ozaki et al.,
2005; Vander Meer and Morel,
1998).
Cuticular hydrocarbon-based cues mediate the species recognition response
in termites and ants of the genus Pachycondyla
(Bagnères et al., 1991;
Howard and Blomquist, 1982;
Lucas et al., 2005;
Vauchot et al., 1996).
Nestmate recognition, identifying which conspecifics belong to the same
colony, is mediated by hydrocarbons in paper wasps Polistes dominulus
(Dani et al., 2001), the
European hornet Vespa crabro
(Ruther et al., 2002), honey
bees Apis mellifera (Breed,
1998), and several species of ants
(Lahav et al., 1999;
Liang et al., 2001;
Thomas et al., 1999;
Wagner et al., 2000). Within
colonies, harvester ant (Pogonomyrmex barbatus) workers recognize
task-specific hydrocarbon profiles, which provide information used in task
allocation (Greene and Gordon,
2003). Workers of the primitive ant Myrmecia gulosa
discriminate among queens, fertile workers and non-fertile workers using
variation in cuticular hydrocarbons
(Dietemann et al., 2003).
Hydrocarbons are the most abundant class of chemicals coating the cuticle
of social insects (Nelson and Blomquist,
1995). Their primary functions are to prevent water loss across
and abrasion to the cuticle, and to protect against infection
(Lockey, 1988). Cuticular
hydrocarbons generally range in size from about 21 to over 40 carbons in
chain-length, with three known structural classes: n-alkanes,
n-alkenes and methyl-branched alkanes
(Nelson and Blomquist, 1995).
Cuticular hydrocarbon profiles can differ among groups in the presence or
absence of compounds and in the relative abundance of shared compounds
(Bagnères et al., 1991;
Haverty et al., 2000;
Singer, 1998;
Vauchot et al., 1996). Within
a species, individual colonies generally share the same hydrocarbon
components, but the relative abundance of each compound varies
(Bonavita-Courgourdan et al.,
1987; Howard,
1993; Singer,
1998; Vander Meer and Morel,
1998). The hydrocarbon profile of a colony can change over time
and season (Haverty et al.,
1996; Liu et al.,
2001; Nielsen et al.,
1999; Vander Meer et al.,
1989). Within a colony, workers performing different tasks can
vary in the relative abundance of hydrocarbon compounds
(Haverty et al., 1996;
Kaib et al., 2000;
Wagner et al., 1998).
Patriline differences in hydrocarbon profiles have been shown in the ant
Formica truncorum (Boomsma et al.,
2003).
Although considerable evidence shows that cuticular hydrocarbons are used
as recognition cues, we know little about what information in these
multi-component cues denotes nestmate, species, or task group status and how
social insects perceive such information. Are certain components of the
cuticular hydrocarbon profile more important than others? Is the relevant
information present in the entire hydrocarbon profile, parts of the profile,
or only in specific molecules? The recognition response may depend upon
complex cues that vary subtly among species
(Bagnères et al., 1991).
It has been suggested that certain hydrocarbon components, such as
n-alkenes and methyl-alkanes, have evolved signal function while
other compounds, such as n-alkanes, serve little role in
communication (Bonavita-Courgourdan et al.,
1987; Dani et al.,
2001; Dani et al.,
2005; Espelie et al.,
1994; Lucas et al.,
2005).
In this study, we examined the role of structural complexity of hydrocarbon
cues in the recognition of species and conspecifics. We considered two ant
species, the Argentine ant (Linepithema humile) and the ant
Aphaenogaster cockerelli. We investigated species recognition in
both, and the recognition of conspecifics in L. humile. L. humile
(subfamily Dolichoderinae) is a worldwide invader of Mediterranean-type
habitats (Human and Gordon,
1999; Sanders et al.,
2003). The ants are polygynous and polydomous, forming diffuse
colonies composed of connected nests that reproduce by budding
(Markin, 1968;
Giraud et al., 2002). The ants
exhibit little intraspecific aggression over large geographic areas
(Heller et al., 2006). L.
humile can acquire hydrocarbons from prey that elicit aggressive
responses from conspecifics (Liang et al.,
2001), and it interacts aggressively with other species including
the ant Formica moki (Human and
Gordon, 1996). A. cockerelli (subfamily Myrmicinae) is a
monogynous, desert-dwelling ant native to the Southwestern USA. This ant
competes for seed resources with other ants including the red harvester ant
Pogonomyrmex barbatus (Barton et al., 2004).
In this study, recognition responses were elicited by presenting cuticular hydrocarbons in bioassays that measured aggression. We tested whether the ants respond with aggression to any mixture of hydrocarbons that differs from their own, or if their response depends on the structural complexity of the hydrocarbon cue.
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). Hydrocarbons were separated from polar surface lipids by
running samples through a solid phase of 2 cm of silica gel in a Pasteur
pipette and eluting hydrocarbons with 2 ml 100% pentane
(Nelson and Blomquist, 1995).
Samples were stored at –20°C.
For experiment 2, heterospecific hydrocarbons were taken from the ant
Formica moki, a species with which the L. humile were
observed to fight (M.J.G., personal observation)
(Human and Gordon, 1997;
Human and Gordon, 1999). For
experiment 3, heterospecific hydrocarbons were taken from the red harvester
ant (Pogonomyrmex barbatus), a species with which A.
cockerelli competes for seed resources
(Barton et al., 2002).
Separation of cuticular hydrocarbon structural classes
Saturated and unsaturated hydrocarbons were separated by adding purified
hydrocarbons to a silica gel column impregnated with 20% silver nitrate with 2
cm of solid phase (Nelson and Blomquist,
1995). Saturated hydrocarbons were eluted with 2.5 ml of 100%
pentane. Unsaturated hydrocarbons were eluted into a separate tube with 2.5 ml
of 10% ethyl ether in pentane. Straight chain n-alkane hydrocarbons
were absorbed by 5 Å molecular sieves (Sigma Chemical Co., St Louis, MO
USA) in iso-octane at 75°C for 12 h
(Nelson and Blomquist, 1995).
The molecular sieves were prepared by baking at 250°C for 12 h prior to
adding the samples. As the n-alkanes were lost in the pockets of the
molecular sieves, 4 µg of an n-alkane mixture
(C21–C31, C33: n-tricosane,
n-tetracosane, n-pentacosane, n-hexaconsane,
n-heptacosane, n-octacosane, n-nonacosane,
n-triacontane, and n-tritriacontane; Sigma Aldrich) was used
as the n-alkane structural class.
Experiment 1: the role of hydrocarbon structural complexity in the recognition of conspecifics by L. humile
This experiment tested whether (1) differences in relative abundance in
conspecific hydrocarbons elicit a recognition response and (2) if a single
structural class of hydrocarbons, n-alkanes, can elicit aggression
from the ants. A mixture of synthetic saturated n-alkane hydrocarbons
was added to L. humile lipid extracts. The surface lipid extracts
supplemented with n-alkane standards were tested in a bioassay that
measured aggressive behaviour from L. humile.
Linepithema humile (Mayr) were collected from focal ant trails the day before the experiment and killed by freezing. As a simple method to normalize the amount of surface lipid extracted, a 1 ml volume of thawed L. humile was extracted for each stimulus. Extraction of 1 ml (average of 212 ants, N=3 samples) of L. humile yields on average 900 µg purified hydrocarbon. Thus, one ant-equivalent of L. humile hydrocarbon is equivalent to approximately 4.2 µg purified hydrocarbon.
The surface lipid extract was then divided into two aliquots, each of the same volume and therefore containing equal amounts of lipids. The first aliquot was left untreated and used as a control. The second aliquot was supplemented with 100 µg of a synthetic n-alkane mixture. The n-alkane mixture was composed of n-alkane hydrocarbons ranging from C23–C30 and C33 (n-tricosane, n-tetracosane, n-pentacosane, n-hexaconsane, n-heptacosane, n-octacosane, n-nonacosane, n-triacontane, and n-tritriacontane; Sigma Aldrich). Another stimulus was created by coating cotton with 100 micrograms of the synthetic n-alkane mixture alone. The blank control was created by soaking cotton in 100% pentane for 10 min and allowing the solvent to evaporate for at least 3 h until dry.
Both aliquots were then added to approximately 1 cm3 of pentane washed cotton; the amount of cotton used for each sample was equal to the volume of ants that were extracted. The cotton was loosely packed into a screw-top tube to the same level as the ants in the extraction screw-top tube. The sample in pentane was then added so that cotton was submerged and the cotton was soaked through. The solvent was allowed to evaporate for at least 3 h so that the cotton was completely dry. Thus, each piece of cotton was treated with one ant-equivalent of hydrocarbon per volume unit area of cotton. This method ensured that all pieces of cotton used in the bioassays were treated approximately the same amount of extracted material.
All of the hydrocarbons in the n-alkane standard mixture are
present on the cuticle of L. humile
(Brophy et al., 1983;
Cavill and Houghton, 1973;
Liang et al., 2001), although
only n-pentacosane (C25), n-octacosane (C28) and
n-nonacosane (C29) have been reported to have average relative
abundances of greater than 1.0% (Liang et
al., 2001). Thus, the constituents of the n-alkane
mixture differed in relative abundance, i.e. quantitatively but not
qualitatively, from L. humile hydrocarbon profiles. Confirmation of
samples using gas chromatography was performed using a DB-1 fused silica
capillary column (30 m, 0.25 i.d., 0.25 µm film thickness; J&W
Scientific, Folsom, CA, USA). During injection the oven temperature was held
at 170°C for 5 min. Oven temperature was then raised to 220°C at
25°C min–1 and then to 310°C at a rate of 3°C
min–1 with a 5 min hold. Peak areas of each chromatogram were
measured and the relative abundance of each peak was calculated (peak area
divided by total area of all peaks). Peaks were identified by comparing
elution patterns to those reported elsewhere
(Liang et al., 2001). The
relative abundance of n-alkanes changed from 0.214 of total
hydrocarbon abundance without the addition of hydrocarbon standard mixture to
a relative abundance of 0.876 when the standard mixture was added to cuticular
hydrocarbons. Thus, the supplemented levels of n-alkanes were not
`physiological doses', being much greater than levels of n-alkane
abundance normally found on the cuticle of L. humile
(Liang et al., 2001). However,
the goal of this experiment was not to mimic natural conditions, but to
determine if the ants responded differently to the n-alkane mixture
when presented alone than to a mixture of cuticular hydrocarbons and
n-alkane standards.
We used a behavioural bioassay that measured the ants' aggression towards
stimuli presented on pieces of cotton. Treatments were: (1) whole surface
lipid extract, including cuticular hydrocarbons, (2) surface lipid extract
supplemented with synthetic n-alkane mixture, (3) synthetic
n-alkane mixture alone, and (4) a blank control (solvent only). In
all tests, surface lipid samples were collected from the nest being tested to
avoid nestmate recognition responses. A response was considered aggressive if
the ants bit or pulled the cotton fibres. Biting and pulling is displayed
during encounters between L. humile and other ants (M.J.G., personal
observation) (Roulston et al.,
2003). In each trial, we placed treated pieces of cotton
approximately 2 cm away from trails of foraging L. humile. The pieces
of cotton used in the bioassay were pulled from the larger piece of cotton
onto which surface lipids were added. These smaller pieces were approximately
3 mmx3 mm and were meant to approximate the size and amount of
hydrocarbon of a live ant. Replicates within each experiment were conducted
along trails leading to different nest entrances that were separated by at
least 10 m. Stimuli were tested in a random order by an observer blind to the
treatment order. We conducted the study at eight colonies at three sites in
northern California, USA, all within 20 km of Stanford University: (1) on the
campus of Stanford University, (2) in a suburban area of Redwood City,
California, and (3) at Stanford University's Jasper Ridge Biological Preserve
in Palo Alto, California. The number of ants biting or pulling the cotton and
the number of ants in contact with the cotton but not aggressive towards it
were counted every minute for a total of 10 min.
Experiment 2: the role of hydrocarbon structural complexity in the L. humile species recognition response
Bioassay 1
This experiment tested whether species recognition in L. humile is
a response to entire hydrocarbon profiles or only to specific parts of the
profile. Surface hydrocarbons from 20 Formica moki were separated
into three structural classes: n-alkanes, methyl-alkanes and alkenes,
according to the methods outlined above. Samples in pentane were added to 1
cm2 pieces of cotton so that each piece of cotton was treated with
a total of two-ant-equivalents of hydrocarbon extract or hydrocarbon class.
For example, one half the amount, as determined by volume, of methyl-alkenes
was added to the methyl-alkane and n-alkene mixture as compared to
the methyl-alkane class alone. The solvent was allowed to completely dry,
usually overnight, until used in the bioassay.
In each trial, the following stimuli were tested in a sequential, random order along eight replicate L. humile foraging trails using the bioassay described above for experiment 1: (1) solvent-treated cotton (blank control), (2) n-alkane fraction alone, (3) methyl-branched alkane fraction alone, (4) n-alkene fraction alone, (5) a mixture of n-alkanes and methyl-branched alkanes, (6) a mixture of n-alkanes and n-alkenes, (7) a mixture of methyl-branched alkanes and n-alkenes, (8) a mixture of n-alkanes, methyl-branched alkanes, and n-alkenes and (9) hydrocarbon extract from F. moki.
We were not able to identify F. moki cuticular hydrocarbons, so as
a surrogate we confirmed the separation methods by running P.
barbatus hydrocarbons, which had been structurally identified and
reported in the literature (Wagner et al.,
1998), through the same protocols and analysing the results using
gas chromatography (Varian 3900 gas chromatograph; DB-1 fused silica column,
30 m, 0.25 ID, 0.25 µm film thickness; J&W Scientific) using the
temperature program described above for experiment 1. Peak areas of each
chromatogram were measured and the relative abundance of each peak was
calculated (peak area divided by total area of all peaks). Peaks were
identified by comparing elution patterns to those of Wagner et al.
(Wagner et al., 1998). The
n-alkane structural class, created from synthetic standards, was
composed of 100% n-alkanes. Analysis showed clear separation of
structural classes; the methyl-alkane structural class was composed of a
relative abundance of 1.0 for methyl-alkane hydrocarbons and the
n-alkene structural class was composed of a relative abundance of 1.0
for n-alkenes.
In the bioassay, which was performed as described for experiment 1, we presented approximately 3 mmx3 mm treated pieces of cotton to ants about 2 cm away from active L. humile foraging trails. There were 10 min breaks between the presentation of stimuli during each trial, the stimuli were presented in a random order and the observer was blind to stimulus order. We conducted the study at eight colonies on the campus of Stanford University that were separated by at least 10 m. We measured the number of ants in contact with the stimuli and the number of ants pulling or biting the stimuli every minute for 10 min.
Bioassay 2
This experiment tested if the number of hydrocarbon compounds in each class
contributed to a species-recognition response. This experiment replicated
bioassay 1 but, since we were not able to identify structurally the
constituents of F. moki cuticular hydrocarbon profiles, we used neat
hydrocarbon standards to confirm the results.
We followed the methods outlined for bioassay 1, but synthesized hydrocarbon standards, rather than F. moki hydrocarbons, were used to make hydrocarbon structural classes. Two hydrocarbon compounds were used in each structural class: (1) n-tricosane (C23) and n-pentacosane (C25) for n-alkanes, (2) 5-methylpentacosane and 11-methylpentacosane for methyl-alkanes (Sigma Chemical Co.) and (3) 1-hexadecene and 1-octadecene for n-alkenes (Ultra Scientific, North Kingstown, RI, USA). 1 mg of each compound was added to stock solutions. Pieces of cotton (1 cm2) were treated with stock solutions so that the cotton was soaked through. After treatment, the pieces of cotton were allowed to completely dry, and then treated with a total of 1 mg of hydrocarbon so that all stimuli had the same total amount of hydrocarbon on them. For example, the n-alkane class received 1 mg of the n-alkane standard while the mixture of n-alkanes and methyl-alkanes received 0.5 mg of n-alkane stock solution and 0.5 mg of methyl-alkane stock solution.
At eight active L. humile trails on the Stanford University campus, we presented approximately 3 mmx3 mm treated pieces of cotton to ants about 2 cm away from foraging trails. There were 10 min breaks between the presentation of stimuli during each trial and the stimuli were presented in a random order. The observer was blind to stimulus order. As in the other experiments, we measured the number of ants in contact with the stimuli and the number of ants pulling or biting the stimuli every minute for 10 min. Data were normalized by dividing the number of ants displaying agonistic behaviour by the total number of ants in contact with the cotton during 10 min observation periods.
Experiment 3: the role of hydrocarbon structural complexity in the A. cockerelli species recognition response
In another ant species from a different subfamily, Aphaenogaster
cockerelli (André) we tested whether species recognition depends
on the structural complexity of cuticular hydrocarbon cues. The following
stimuli were tested in each trial, in a sequential, random order, at 11 A.
cockerelli nests: (1) solvent-treated blank control, (2) nestmate
hydrocarbons from the focal colony, (3) n-alkane fraction alone, (4)
methyl-branched alkane fraction alone, (5) n-alkene fraction alone,
(6) a mixture of n-alkanes and methyl-branched alkanes, (7) a mixture
of n-alkanes and n-alkenes, (8) a mixture of methyl-branched
alkanes and n-alkenes, (9) a mixture of n-alkanes,
methyl-branched alkanes, and n-alkenes, (10) hydrocarbon extract from
P. barbatus. The observer was blind to the order of stimuli
presentation.
To perform the bioassay, treated 5 mm diameter glass beads (Fisher
Scientific, Pittsburgh, PA, USA) were placed on A. cockerelli nest
mounds 5–10 cm from the nest entrance. We measured the number of ants
displaying aggressive behaviour and the total number of ants in contact with
the cotton every 30 s for 5 min, with 5 min intervals between tests. Ants were
considered aggressive if they flared their mandibles or bit the glass bead.
These behaviours were observed during interactions with Pogonomyrmex
barbatus in the field (M.J.G., personal observation). These trials were
conducted at a field site near Rodeo, NM, USA (Barton et al., 2004;
Sanders and Gordon, 2004).
Structural class samples were created using hydrocarbons extracted from 20
P. barbatus foragers. Glass beads were added to each extract and
hydrocarbon fraction in pentane in screw-top vials. The pentane was allowed to
evaporate completely, coating the beads with hydrocarbons. Each bead was
coated with a total of one-ant-equivalent of hydrocarbon extract or
hydrocarbon structural class. One-ant-equivalent of P. barbatus
hydrocarbon was estimated to be equivalent to a mass of 9 µg
hydrocarbon.
Confirmation of hydrocarbon structural class separations was performed by
analyzing structural class samples created for this experiment using P.
barbatus worker hydrocarbons using a Varian 3900 gas chromatograph
(Varian, Inc.) with a DB-1 fused silica capillary column (30 m, 0.25 ID, 0.25
µm film thickness; J&W Scientific) and using the same temperature
program as detailed above. Peak areas of each chromatogram were measured and
the relative abundance of each peak was calculated (peak area divided by total
area of all peaks). Peaks were identified by comparing elution patterns to
those of Wagner et al. (Wagner et al.,
1998). The n-alkane structural class, created from
synthetic standards, was composed of 100% n-alkanes. Analysis showed
that the methyl-alkane structural class was composed of 100% methyl-alkane
hydrocarbons and that the n-alkene structural class was composed of
100% n-alkenes.
Data analysis
For all experiments, we calculated for each trial the sum of the number of
ants aggressive towards the stimuli and the sum of the number of ants in
contact with the stimuli without displaying aggression. To normalize for
colony differences in the number of ants, data were converted to proportions,
calculated as the total number of ants that were aggressive toward a stimulus
in a given trial divided by the total number of ants in contact with a
stimulus. To help meet the assumptions of normality for analysis of variance
(ANOVA), the data were transformed using an angular transformation (arcsine of
the square root of the proportion). ANOVA was used to test for statistical
differences among treatments.
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Experiment 3: the role of hydrocarbon structural complexity in the A. cockerelli species recognition response
The response of A. cockerelli to the surface hydrocarbons of
P. barbatus also depended upon having a mixture of structural classes
in the stimulus (F9,100=9.38, P<0.0001;
Fig. 3). Mixtures of
hydrocarbon structural classes elicited a significantly higher proportion of
aggressive ants than did the single structural classes, nestmate hydrocarbons,
or the blank control (LSD, P<0.05 for all comparison). The
proportion of A. cockerelli that showed aggression toward the blank
control did not differ from the response to the single structural classes of
hydrocarbons or nestmate hydrocarbons (LSD, P>0.05).
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A high proportion of L. humile responded aggressively toward
conspecific hydrocarbons that had been supplemented with n-alkane
standards. A low proportion of ants displayed aggression toward the
n-alkane standards when presented alone in the bioassay, despite the
fact that the hydrocarbons in this mixture differed in relative abundance from
those found on the cuticle of the ants. Thus a recognition response can be
elicited by changes to the relative abundances of n-alkane compounds
in the colony hydrocarbon profile, but only as part of a structurally complex
mixture of cuticular hydrocarbons. Previous work
(Liang et al., 2001) showed
that changes to L. humile cuticular hydrocarbons in the relative
abundance of long chain methyl-branched hydrocarbons over 35 carbons in length
elicited aggression towards conspecifics
(Liang et al., 2001). The
n-alkane standard mixture used in our study contained molecules of
shorter chain-length, ranging in size from 21 carbons to 31 carbons in length,
but also elicited aggression. Thus, changes in the relative abundances of both
n-alkanes and long chain methyl-alkanes play a role in aggression
towards conspecifics in this species.
Species recognition in L. humile and A. cockerelli occurs
through the detection of recognition cues present in heterospecific
hydrocarbon profiles. The relevant cues are in the mixture of structural
classes within hydrocarbon profiles rather in particular components of the
profile. Despite many differences in their social structure and responses to
other species of ants (Human and Gordon,
1996; Giraud et al.,
2002; Sanders et al.,
2003; Markin,
1968), both L. humile and A. cockerelli
exhibited very similar responses to the stimuli. For both species, fewer ants
responded with aggression toward the blank control and pure structural classes
than to any of the hydrocarbon class mixtures. The proportion of ants
aggressive toward mixtures of structural classes was similar to those elicited
by heterospecific hydrocarbons. No single hydrocarbon structural class
elicited more aggression than the others. Hydrocarbon molecules of all three
structural classes appear to provide information about species membership.
The number of compounds in a hydrocarbon profile does not appear to provide additional information to L. humile in its species recognition response. There were no significant differences between the proportion of aggressive ants toward the F. moki hydrocarbon extract and toward the combination of two or three synthetic hydrocarbon classes. At least two hydrocarbon structural classes, containing only four compounds, were sufficient to elicit aggression from a high proportion of L. humile. This response is similar to the proportion of ants displaying aggression towards F. moki cuticular hydrocarbons, which contain more than a dozen compounds (M.J.G., personal observation). Thus, even a simple hydrocarbon profile, as long as it contains a mixture of structural classes, can elicit a recognition response from L. humile.
In the species recognition responses of L. humile and A.
cockerelli, all structural classes were equally effective in eliciting an
aggressive response. Other work indicates that some hydrocarbon structures may
be more important than others in eliciting recognition responses
(Boomsma et al., 2003;
Breed, 1998;
Dani et al., 2001;
Espelie et al., 1994;
Lucas et al., 2005;
Singer, 1998). For example,
ants of the genus Pachycondyla displayed greater levels of aggression
toward branched methyl-alkanes than toward n-alkanes and alkenes;
however, mixtures of hydrocarbon classes were not tested in this study
(Lucas et al., 2005). In paper
wasps (Polistes dominulus), methyl-alkanes elicited significantly
more aggression from nestmates than n-alkanes and n-alkenes
(Dani et al., 2001).
Methyl-alkanes, n-alkanes, and n-alkenes have been
implicated in honey bee (Apis mellifera) nestmate recognition, along
with various fatty acids and esters in chemical derived mostly from comb wax
(Breed, 1998;
Dani et al., 2005). Also, the
addition of synthetic (Z)-9-tricosene to the cuticle of the ant Campanotus
vagus, was perceived by nestmates
(Meskali et al., 1995).
European hornets responded aggressively toward nestmates treated with a single
n-alkane, heneicosane, or with a mixture of heneicosane, tricosane
and (Z)-9-tricosene (Ruther et al.,
2002) and honey bees recognize changes in the relative abundance
of hexadecane and octadecane on nestmates
(Breed, 1998). Our data support
the suggestion (Breed, 1998)
that any compound on the surface of a social insect could potentially play a
role in the recognition cue.
Since cuticular hydrocarbons serve a primary function in prevention of water across the cuticle, variation in the relative abundance of compounds in order to facilitate communicative functions may be constrained. Structural complexity may provide the correct chemical context necessary to allow ants to discriminate group membership accurately. Recognition appears to be based upon subtle differences in many components of hydrocarbon profiles, not on larger differences in only a few hydrocarbon constituents. Mistakes in the recognition of group membership could lead to aggressive interactions among colony members, disrupting the social structure of the colony.
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Acknowledgments |
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References |
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