Arthropod-Plant Interactions
DOI 10.1007/s11829-017-9559-8
ORIGINAL PAPER
Variation in the composition and activity of ants on defense of host
plant Turnera subulata (Turneraceae): strong response
to simulated herbivore attacks and to herbivore’s baits
Nayara G. Cruz1 • Paulo F. Cristaldo2,3 • Leandro Bacci3 • Camilla S. Almeida1
Gabriela P. Camacho4 • Alisson S. Santana3 • Efrem J. M. Ribeiro2 •
Alexandre P. Oliveira3 • Abraão A. Santos3 • Ana P. A. Araújo2
•
Received: 7 July 2016 / Accepted: 19 August 2017
Springer Science+Business Media B.V. 2017
Abstract Plants with extrafloral nectaries attract a variety
of ant species, in associations commonly considered
mutualistic. However, the results of such interactions can
be context dependent. Turnera subulata is a shrub widely
distributed among disturbed areas which has extrafloral
nectaries at the base of leaves. Here, we evaluated whether
the ants associated with T. subulata (i) vary in space and/or
time; (ii) respond to simulated herbivory, and (iii) reduce
herbivory rates. For this, we quantified the abundance and
species richness of ants associated with T. subulata
throughout the day in six different sites and the defensive
capability of these ants under simulated herbivory in the
leaves and stems of T. subulata plants (N = 60). We also
checked the proportion of the lost leaf area and quantified
leaf damage by chewing herbivores in the host plant. We
found that a total of 21 ant species associated with the host
plant. Species composition showed significant variation
across the sampled sites and throughout the day. Visitation
Handling Editor: Jouni Sorvari.
Electronic supplementary material The online version of this
article (doi:10.1007/s11829-017-9559-8) contains supplementary
material, which is available to authorized users.
& Ana P. A. Araújo
anatermes@gmail.com
1
Programa de Pós-Graduação em Ecologia e Conservação,
Universidade Federal de Sergipe, São Cristovão, SE, Brazil
2
Laboratório de Interações Ecológicas, Departamento de
Ecologia, Universidade Federal de Sergipe, São Cristovão,
SE, Brazil
3
Clı́nica Fitossanitária, Departamento de Engenharia
Agronômica, Universidade Federal de Sergipe,
São Cristovão, SE, Brazil
4
Universidade Federal do Paraná, Curitiba, PR, Brazil
rates and predation by ants were higher in plant stems than
in leaves. In general, herbivory rates were not correlated
with ant association or activity, with the exception of the
proportion of leaf area consumed; there was a significant
lower herbivory rate on plants in which ants defended the
leaves. Our results suggest that the benefits of association
may depend on the ecological context. This context
dependence may mask the correlation between the defense
of ants and herbivory rates.
Keywords Extrafloral nectary Herbivory Indirect
defense Protection
Introduction
Plants express a wide variety of direct and indirect defense
mechanisms known to minimize herbivory (Strauss and
Zangerl 2002). Indirect mechanisms are represented by the
emission of herbivory-induced plant volatiles that attract
natural enemies of herbivores (Dicke et al. 1990) or by
defense provided by natural enemies (e.g., predators and
parasitoids) that are attracted to resources offered by the
host plant (Moreira and Del-Claro 2005; Byk and DelClaro 2011; Heil 2011). Some plant species, for example,
produce extrafloral nectaries (EFNs), which provide
attractive resource for potential defenders (Moreira and
Del-Claro 2005).
Ants are among the most abundant and diverse
macroarthropods in tropical terrestrial environments (Wilson 1971), and are the most frequent visitors to plant EFNs
(Oliveira and Brandão 1991). Such associations can benefit
the host plant directly (through effective predation) or
indirectly (by their presence or patrolling, which may repel
potential herbivores). Ant–plant associations are
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N. G. Cruz et al.
commonly considered mutualistic. However, the results of
these interactions can be context dependent when there are
low specificity between the species involved (Heil 2008;
Bronstein 2009). The resources offered by plants may also
attract individuals that do not offset the energy investment
of the host, resulting in low contribution to increasing plant
fitness. In some cases, ants may also harm other positive
associations for the host plant (e.g., pollinator, predator,
and parasitoid visitors) (Ness 2006; Assunção et al. 2014).
Some studies have suggested that the effectiveness of
defense depends on the species identity (Stanton and Palmer 2011) and quantity of ants associated with host plants
(Rico-Gray and Oliveira 2007). In the shrub Turnera
ulmifolia, for example, studies have reported a total of 25
species of associated ants (Cuautle et al. 2005) and found
that their relationships with the host plant are not always
mutualistic (Torres-Hernández et al. 2000; Cuautle et al.
2005; Salazar-Rojas et al. 2012).
The genus Turnera L. (Turneraceae) consists of shrub
species occurring in a range of countries in the Latin
America (Piacente et al. 2002). Turnera subulata is a
widely distributed ruderal plant that is abundant in different
Brazilian biomes (Arbo 2005). It occurs in natural environments, but is more frequently found in disturbed areas.
In this species, the petiole of each leaf has a pair of EFNs
which are typically associated with ants (Arbo 2013).
However, the nature of these ant–plant associations has not
been studied.
Here, we evaluated whether T. subulata ant assemblages
(i) vary across sampled sites and/or throughout the day; (ii)
respond to simulated herbivory and the damage to different
structures of the host plant (stem and leaf); and (iii) reduce
herbivory rates (for sucking and chewing insects) via
defense of the host plant.
Methods
Study area
The study was conducted at the campus of the Federal
University of Sergipe (UFS) (10550 3500 S, 3760 1400 W),
located in São Cristóvão, Sergipe, Brazil. The climate is
classified as tropical wet and dry (Aw) according to the
Köppen system, with an average temperature of 25.3 C
and an average annual rainfall of 1,372 mm. The experiments were conducted from March to April, 2015 (‘‘dry
season’’).
Associated ant assembly
To assess whether there is temporal and spatial variations
in the composition of plant-associated ants, these insects
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were collected from 60 plants (10 plants from each sampled site) containing at least five main branches. The plants
were randomly selected in six different areas (e.g., ‘‘sampled sites’’), with a minimum distance of 80 m from each
other (designed to test for variation across sampled sites).
Ants were collected using the beating tray technique—a
white tray placed beneath tree branches to catch falling
insects after three vigorous hits (Herms et al. 1990; Prado
et al. 2016)—over three periods of the day: 10:00–12:00
a.m.; 1:00–3:00 p.m., and 4:00–6:00 p.m. (to test variation
throughout the day). Specimens were collected with forceps, placed in vials with 80% alcohol, and identified using
published identification keys (Bolton 2003; Baroni-Urbani
and Andrade 2007). Specimens were compared to those at
the Padre Jesus Moure Entomological Collection at the
Federal University of Paraná, Brazil. Ants were later
classified into feeding guilds according to Brown Jr (2000).
Ant responses to T. subulata-simulated herbivory
and plant damage
Experiments were conducted to test the indirect defense of
plants by ants, via (i) recognition mechanisms and
aggressiveness against potential herbivores (i.e., herbivore
cues) and (ii) perception and response to odors emitted by
damaged plant tissue (i.e., simulated herbivory cues). To
isolate these responses, two separate experiments were
performed.
The first experiment measured ant responses to immobilized herbivores (i.e., without plant damage), and the
second experiment measured responses to simulated herbivory cues (i.e., plant tissue damage) in the absence of
herbivores. Treatments were applied to arbitrarily selected
plant branches for both experiments, and ants were allowed
to choose between cues from the stems or leaves (see
Fig. 1). Treatments were applied 15 cm from the apical
end of the branches. In all cases, the behavioral experiments were conducted between 7:00 and 10:00 a.m. in the
absence of rain.
For the first experiment, Nasutitermes macrocephalus
worker termites were fixed to host plants as proposed by
Oliveira et al. (1987). A single live termite ‘bait’ was
adhered to the leaf or stem of each plant using a 1-cm strip
of double-sided tape. We randomly selected three branches
of each plant, in which the leaf and the stem on the same
branch were always subjected to the same treatment
(Fig. 1). The treatments were as follows: (i) taped termite
‘‘herbivore bait’’ (termite ? double-sided tape); (ii) control
(only tape) (double-sided tape controls); or (iii) control
(no-treatments) (Fig. 1a). Observations were carried out for
all treatments during ten consecutive minutes simultaneously by two researchers. During the observation period,
we measured the following: (i) time spent for the first ant
Variation in the composition and activity of ants on defense of host plant Turnera subulata…
A
B
Fig. 1 Scheme of behavioral bioassays simulating the presence of
herbivores and Turnera subulata structural damage. a Tests with
herbivorous simulation: b1 = branch containing treatments with
tape ? termite (taped termite ‘‘herbivore bait’’); b2 = branch with
tape-only control [control (only tape)]; b3 = branch with no-
treatment controls [control (only stem or leaf)]. b Test with damage
simulation: b4 = branch with injury located on the stem or leaf;
b5 = no-damage branch (control: only stem or leaf). In all cases, ants
were allowed to choose between treatments located on the stem or
leaf. Each plant represented a true repetition of each treatment
arrival in each one of treatments and (ii) time spent for the
first ant to attack the baits (in treatment with the presence
of herbivore). At the end of each test, the tape and termites
were carefully removed without causing damage or disruption to the plants.
Thirty minutes after the plant defense tests by ants, we
evaluated ant responses to simulated plant herbivory cues.
We selected randomly two branches that were different
from those used in predation test, and inflicted the damage
on the leaf and stem of each branch by cutting a 1-cm-long
incision using a utility knife (probe). The treatments consisted of (i) mechanical injury and (ii) no-treatment controls (Fig. 1b). Leaves and stems on the same branch were
always subjected to the same treatment. Observations were
carried out in each one of the plants simultaneously for
both treatments (mechanical injury and no-treatment controls) during 10 consecutive minutes. During the observation period, we measured the time spent for the first ant
arrival in each one of treatments. For all bioassays, each
plant was considered as a true repetition (N = 60), totalizing 1.200 min of observations.
Herbivory rates in T. subulata
After bioassays and quantification of the associated ant
assembly, 50 plants were randomly selected to quantify
herbivory rates (over the entire development of the plant
until the sampling time). Shoots were removed and kept in
a freezer to quantify the total number of leaves versus the
number of leaves with injuries (punctures) caused by
sucking insects. Subsequently, all leaves were removed
from plants and photographed in order to estimate the total
leaf area and the area lost to chewing insects. The images
were processed using Image J (Wayne Rasband, National
Institutes of Health, USA).
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N. G. Cruz et al.
Statistical analyses
All analyses were performed using R software (R Development Core Team 2011) via generalized linear models
(GLMs), followed by residual analysis to verify the suitability of distributions and the tested models.
The effect of variation across sampled sites and
throughout the day, and the interaction between these
factors on the composition of ants associated with T. subulata were tested by permutation multivariate analysis of
variance (PERMANOVA). PERMANOVA was performed
using the Jaccard dissimilarity index and multiple-paired
comparisons with 999 permutations in the routine of the
‘vegan’ package. The terms ‘‘sampled sites’’ and ‘‘time
periods’’ were included in the model as fixed explanatory
factors, and the identity of each plant was included in the
model as a random block effect. A similar model was used
to evaluate whether there were differences in the assemblage of ant species that attacked the termite baits on plant
stems and leaves.
The time spent for the visit and predation by ants in
different treatments were analyzed using survival analysis
with Weibull distribution (‘survival’ package). The censored values in the survival analysis were the time for ant
arrival to treatments, or the time for the ant to attack termite baits. In all cases, each plant was considered a true
repetition. Thus, the analysis provided the average time
spent for 50% of the analyzed plants to be visited or for
termite baits to be attacked by ants.
In order to check whether herbivory rates are correlated
with the defense effectiveness of ants in the stem, the leaf,
or both (stem ? leaf), we conducted tests on independent
models. The response variables were set as the proportion
of area leaf consumed by chewing herbivores (leaf area
consumed 9 100/total leaf area); and the proportion of
leaves with sucking insect damage (number of leaves with
damage 9 100/number of total leaves). The explanatory
variables were the occurrence of predation on the stem,
leaf, or both (stem ? leaf; total predation) (ANODEV);
and the total abundance and richness of associated ants
(linear regression analysis). Data were analyzed under
Negative Binomial.
Results
Change in species composition of associated ants
We collected 21 ant species associated with T. subulata
belonging to 11 genera and four subfamilies (Table 1). The
most frequent species and morphospecies considering all
times of the day and all the sampled sites were Solenopsis
invicta (occurring in 96.5% of plants), Dorymyrmex sp.1
123
(93%), and Brachymyrmex sp.1 (70%) (Table 1). All of the
most common species considering occurrence on plants,
time of day, and across sampled sites, belonged to the
generalist guild (Table 1).
Ant assembly composition differed significantly across
sampled sites and throughout the day (PERMANOVA,
P \ 0.001; Table SM01), and there were significant
interactions between these factors (PERMANOVA,
P = 0.005; Table SM01). The Monte Carlo test indicated
that Camponotus atriceps and Ca. melanoticus were
responsible for changes in the composition throughout the
day (Table 2), while Ca. leydigi, Cephalotes clypeatus, Ce.
pusillus, Crematogaster obscurata, Paratrechina longicornis, Pseudomyrmex schuppi, Solenopsis invicta, and
Wasmannia auropunctata were responsible for changes in
composition across sites (Table 2).
Ant responses to T. subulata-simulated herbivory
and plant damage
Ants visited both stems and leaves on all plants. The proportion of visits by ants increased over the observation time
(Fig. 2a–b). The percentage of visits by ants to stems were
higher in the treatment containing the termite ‘‘herbivore
bait’’ than for controls (v2 = 22.32, df = 180, P \ 0.0001;
Fig. 2a). For leaves, a higher proportion of ants visited those
with termite baits (v2 = 7.92, df = 180, P \ 0.019); however, there were no significant differences between the two
control treatments (‘tape only’ and ‘no-treatment’)
(v2 = 0.58, df = 179, P = 0.580; Fig. 2b). In general,
visits to stem baits were more frequent and faster than those
for leaf baits (v2 = 44.93, df = 120, P \ 0.0001; Fig. 2c).
We observed ant attacks on a total of 59 termite baits, in
which 74.6% of termite attacks by ants occurred on stems,
and 25.4% occurred on leaves. The highest attack rates
were observed in the ‘generalist’ ant guild (94.8%).
Solenopsis invicta was the most common species, and also
defended the plants most frequently. Termite baits were
attacked by S. invicta in 35.6% of all studied plants
(Table 1). Among plants with associated S. invicta, 70%
had termite baits attacked. Dorymyrmex sp.1 attacked termite baits in 13.3% of the total plants and 50% of plants
with which it was associated, while Brachymyrmex sp. did
not attack termites. The proportion of attacked baits
increased throughout the observation time. Ants attacked
termite baits significantly more on stems than on leaves
(v2 = 34.26, df = 118, P \ 0.0001; Fig. 3). The species
composition of ants that attacked termite baits also differed
significantly between the stems and the leaves of host
plants (PERMANOVA, pseudo F = 3.3227; P = 0.002).
Ants also responded to signals from plant stems after
mechanical injury (Fig. 4). The proportion of visits by
ants to damaged plants increased over time, and it was
Variation in the composition and activity of ants on defense of host plant Turnera subulata…
Table 1 Ant species and morphospecies, and their respective guilds
in association with Turnera subulata, including occurrence throughout the day, occurrence (=number of plants found, N = 60) and the
Species/morphospecies
Guild
number of times that defense activity was observed in different host
plant structures (for details see ‘‘Methods’’)
Occurrence
Total occurrence
10–12 h
13–15 h
16–18 h
15
16
25
3
2
11
16
Number of defense activity
Leaf
Stem
Total
56
2
6
8
2
7
0
2
2
15
42
0
0
0
Dolichoderinae
Dorymyrmex
Dorymyrmex sp.1
Generalist
Ectatomminae
Ectatomma
Ectatomma brunneum
Predador and nectarivorous
Formicinae
Brachymyrmex
Brachymyrmex sp.1
Generalist
Camponotus
Camponotus atriceps
Generalist
3
13
1
17
1
1
2
Camponotus blandus
Generalist
14
3
13
30
1
9
10
Camponotus crassus
Generalist
3
0
3
6
1
1
2
Camponotus leydigi
Generalist
4
2
3
9
0
1
1
Camponotus melanoticus
Camponotus sp.1
Generalist
Generalist
1
1
8
0
0
0
9
1
0
0
0
0
0
0
Generalist
2
4
5
11
0
1
1
Predador
5
1
5
11
0
1
1
Cephalotes clypeatus
Pollen-feeding
1
0
1
2
0
0
0
Cephalotes pellans
Pollen-feeding
0
1
0
1
0
0
0
Cephalotes pusillus
Pollen-feeding
5
1
3
9
0
1
1
Crematogaster evallans
Generalist
1
1
1
3
0
0
0
Crematogaster obscurata
Generalist
7
8
6
21
1
5
6
Generalist
18
23
17
58
7
14
21
Paratrechina
P. longicornis
Myrmicinae
Cardiocondyla
Cardiocondyla emeryi
Cephalotes
Crematogaster
Solenopsis
Solenopsis invicta
Pseudomyrmex
Pseudomyrmex schuppi
Predador and nectarivorous
2
0
0
2
0
0
0
Pseudomyrmex simplex
Predador and nectarivorous
3
0
1
4
0
0
0
Pseudomyrmex termitarius
Predador and nectarivorous
0
0
1
1
0
0
0
Generalist
2
2
2
6
2
2
4
15
45
60
Wasmannia
Wasmannia auropunctata
Total 21
São Cristóvão, Sergipe, Brazil. 2015
higher for stems than for leaves (v2 = 1974.59, df = 237,
P = 0.001). Damaged stems had more visits than stems
without injuries (v2 = 6.98, df = 118, P = 0.008).
However, ant visited leaves with and without mechanical
damage at a similar rate (v2 = 2.96, df = 118,
P = 0.084; Fig. 4).
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N. G. Cruz et al.
Herbivory rates in T. subulata and ant defenses
The average percentage loss of leaf area was 3.37 ± 0.05%
(mean ± SE), while the percentage of leaves damaged by
sucking insect was on average 15.06 ± 2.61%
(mean ± SE). No signs of stem herbivory were found on T.
subulata.
The proportion of leaf area consumed and the ratio of
leaves damaged by sucking insect did not correlate with ant
protection of stems, leaves, or both (Table 3). The only
exception was the proportion of leaf area consumed, which
Table 2 Ant species with a significant observed indicator value (IV),
which is a measure of species occurrence (across sampled sites and
throughout the day) from different samples according to the Monte
Carlo test
Indicator value (IV)
Discussion
Our results showed that species composition of ants associated with T. subulata varied across sampled sites and
throughout the day, and that visitation and attack rates
depended on the plant structure (Figs. 2, 3, 4) and the
species composition of ants associated with host plant.
Herbivory rates did not correlate with timely defense by
P value
Across sampled sites
Camponotus leydigi
0.2029
0.002
Cephalotes clypeatus
0.1111
0.014
Cephalotes pusillus
0.1355
0.022
Crematogaster obscurata
0.1440
0.026
Paratrechina longicornis
0.1855
0.006
Pseudomyrme schuppi
0.1111
0.025
Solenopsis invicta
0.2093
0.008
Wasmannia auropunctata
0.1538
0.010
Camponotus atriceps
0.1657
0.002
Camponotus melanoticus
0.1185
0.005
Proportion of baits predated
by ants
Species
was significantly reduced on plants where ants defended
the leaves (Table 3; Fig. 5).
Similarly, the proportion of leaf area consumed and the
proportion of leaves damaged by sucking insects were not
significantly correlated with the abundance and species
richness of ants (Table 4).
stem
leaf
Throughout the day
Time (s)
B
termite
"herbivore baits"
Control
(only tape + leaf)
termite
"herbivore baits"
Control (only tape)
Control (stem)
Fig. 2 Ant visits in Turnera subulata throughout the day. A Ratio of
ant visits to the stem; and B ratio of ant visits to the leaves. Stems and
leaves had the following treatments: taped termite ‘‘herbivore baits’’,
123
Proportion of baits visited by ants
Proportion of ant visits
A
Fig. 3 Predation by ants throughout the day on Turnera subulata
stems and leaves
C
stem
leaf
control (only double-sided tape), and plant structure only (control:
only stem or leaf). C Proportion of termite-baited stems and leaves
visited by ants
Proportion of leaf area consumed
Proportion of ant visits
Variation in the composition and activity of ants on defense of host plant Turnera subulata…
stem: w/ damage
stem: w/o damage
leaf: w + w/o damage
Time (s)
Fig. 4 Responses of ants over time to mechanical damage on
Turnera subulata steams and leaves
ants (Table 3); however, a series of results observed here
suggest that the presence of ants may have a positive effect
on their host plants, since (i) most associated ants are
considered potential predators; (ii) most ants carried out
patrolling and defense (Table 1); and (iii) the proportion of
leaf area consumed by chewing insects was lower on leaves
defended by ants (Fig. 5).
In facultative mutualism interactions, the lack of shelter
offered by host plants tends to produce rapid changes in the
abundance and the composition of associated ants over the
time (Heil and Mckey 2003). Such variation in ant
assemblies have been reported to promote context dependency in these associations (Bronstein 1994; Di Gusto et al.
2001; Chamberland and Holland 2009). In the present
study, the association of T. subulata with ants that depended on the resources offered by the plant was rare (13.6%)
(e.g., predator and nectarivore guilds; Table 1), which
suggests low fidelity of ant species to these plants. Our
Table 3 Summary of the
effects of ant defenses on stems,
leaves, and both (stem ? leaf;
‘total predation’) on herbivory
rates, under the proportion of
leaf area consumed and the
proportion of leaves damaged
by sucking insects
Term
No defended
Defended
Ants responses
Fig. 5 Variation in proportion of leaf area consumed in Turnera
subulata depending on ant responses
results seem to support this assumption, since the species
compositions associated with the host plant varied across
sampled sites and throughout the day (Table 2). Furthermore, not all species associated with T. subulata are efficient predators (Table 1). This apparent low associative
fidelity may create temporal or spatial opportunities for
attacking herbivores, resulting in an apparent lack of correlation between ant defense and herbivore damage noted
here (Table 3).
On the other hand, we must consider that associations
with ants may provide other benefits to the plants in
addition to reducing herbivory. Studies on T. ulmifolia
demonstrated that its association with 25 different species
of ants brings benefits to the host plant through seed
df
Deviance
Resid. df
Resid. dev.
F
P
1.3724
0.241
5.1399
0.021
0.8292
0.362
1.7767
0.186
1.1578
0.284
1.7715
0.183
y = Percentage of leaf area consumed
Null model
Predation on stem
1
1.372
Null model
Predation on leaf
1
5.319
Null model
Total predation (stem ? leaf)
1
10.496
48
47
52.014
50.641
48
55.021
47
49.701
48
605.37
47
594.88
y = Percentage of leaves with sucking damage
Null model
Predation on stem
48
11.372
1
0.435
47
10.936
48
11.372
1
0.288
47
11.084
Null model
Predation on leaf
Null model
Total predation (stem ? leaf)
1
0.059
48
1.6461
47
1.5863
Each model was conducted separately
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N. G. Cruz et al.
Table 4 Summary of the
effects of the abundance and
species richness of ants
associated with T. subulata on
herbivory rates, under the
proportion of leaf area
consumed and the proportion of
leaves damaged by sucking
insects
Term
d.f.
Deviance
Resid. d.f.
48
53.274
3.001
47
50.266
48
52.252
47
50.526
F
P
3.001
0.082
1.7257
0.189
0.1831
0.668
1.4189
0.233
Percentage of leaf area consumed
Null model
Ants abundance
1
Null model
Number of ants species
1
1.725
Percentage of leaves with sucking damage
Null model
Ants abundance
1
0.183
Null model
Number of ants species
1
dispersal (Cuautle et al. 2005). However, most ants associated with T. subulata (86.4%) belong to the potential
predator guild, and two of the most common species were
also more effective predators, highlighting the favorable
role of ant defense for the host plant.
Ants associated with T. subulata visited faster and
attacked intruders more on stems than those on leaves
(Figs. 2, 3), which may explain the lack of herbivorous
damage to the stems. Differences in ant activity between
plant structures may be due to the location of EFNs; these
structures are positioned on the leaf petiole base and to
access them, it is not necessary for ants to walk on the leaf
surfaces. In addition, ants seem to modulate their responses
differently to the released signals (e.g., vibration, visual,
and olfactory cues) between host plant structures. Ants
responded differently to signals from the control treatments
only in the stem (e.g., no-treatment and tape-only controls),
while on the leaf, ants only perceived the presence of termite ‘‘herbivores baits.’’ This suggests that vibration or
kairomones released by herbivores—the only cues that
were unique to the treatment-simulating herbivory—are the
primary stimuli promoting leaf patrolling by ants. That is,
although not actively patrolling the leaf, the ants are still
able to perceive the presence of herbivores and initiate the
defense. This assumption is supported by the significant
reduction in the proportion of leaf area consumed by
chewing insects on plant leaves defended by ants (Fig. 5).
Indeed, it is widely recognized that the localization of prey
by predators is facilitated by a number of cues, including
those from chewing and moving herbivorous insects (i.e.,
vibratory stimuli) (Pfannenstiel et al. 1995; Cocroft and
Rodrigues 2005). This capability has been documented in
Azteca ants, which increase patrolling with leaf vibration
caused by insect intruders (Dejean et al. 2009).
Similarly, ants responded to damage signals only on the
stem (Fig. 4). Several mechanisms acting alone or in
combination could be responsible, including (i) the
importance of the structure (stem) to the ants themselves
(e.g., access to EFNs) or (ii) due to the differential
123
Resid. dev.
0.418
48
28.204
47
28.021
48
28.204
47
26.785
responses of ant species regarding volatiles emitted by the
plant. It is widely recognized that damaged plants can
release volatiles as a means of indirect defense (Paré and
Tumlinson 1997), as they can, for example, attract natural
enemies of herbivores (Turlings et al. 1995; Kessler and
Baldwin 2001). Despite the mechanisms involved, our
results suggest that even though responses were stronger to
stem cues, ants seem to be able to defend the leaf when
herbivores are present (Fig. 2b). Future studies focusing on
the mechanisms responsible for this difference in allocation
of defense by plant structure may contribute to our
understanding of the patterns observed here.
This is the first study describing the T. subulata associated ant fauna and their defensive roles for the host plant.
Manipulative studies that control the presence of ants along
host plant phenology may enhance our understanding of
the interactions between these organisms. As mutualistic
interactions can exert strong influence on communities
(Rico-Gray and Oliveira 2007; Geange et al. 2011), such
studies may elucidate evolutionary aspects and the communities structure under the influence of facultative ant–
plant interactions.
Acknowledgements The authors thank the colleagues of the Clı́nica
Fitossanitária (UFS) for their help in the field, and the two anonymous
referees for their valuable contributions. CNPq funded this research
granting aid to LB and APAA (PQ 306923/2012-2 and 484823/20132, respectively). PFC received a postdoctoral scholarship (CNPq/
FAPITEC-SE 302 246/2014-2). NGC and CSA received master’s
scholarships (CAPES).
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