Open access journal: http://periodicos.uefs.br/ojs/index.php/sociobiology
ISSN: 0361-6525

DOI: 10.13102/sociobiology.v65i2.2162Sociobiology 65(2): 337-339 (June, 2018)

Simarouba versicolor (Simaroubaceae) Dispersal by the Leaf-Cutter Ant Atta sexdens

Simarouba versicolor is a semi-deciduous tree 
belonging to the family Simaroubaceae, which is a heliophite 
and a selective xerophytic pioneer, and occurs in Cerrado 
and Caatinga biomes, preferably in open areas and well-
drained soils. In Brazil, it is found from the Northeast region 
to the state of São Paulo and in some parts of the states of 
Pará and Mato Grosso do Sul (Lorenzi & Flora, 2002). 
Rapid growth, efficient germination, and survival, in direct 
seeding in the field, are characteristics that make it important 
in forest restoration (Filho & Sartorelli, 2015). Its dispersal 
is zoocorical, since its drupe-type fruits serve as food for 
birds, fishes, and bats. So far, there have been no reports of 
myrmecochory, i.e., ants aiding its dispersal.

Ants can play an important role as secondary seed 
dispersers (Gallegos et al., 2014). Besides dispersal, ants also 
are able to deposit seeds in sites favorable to their germination 
and development (Culver & Beattie, 1983; Oliveira & Koptur, 
2017), which helps to avoid seed consumption by predators 
(Heithaus, 1981; Tanaka et al., 2015), decrease interspecific and 
intraspecific competition between seedlings under the mother 

Abstract 
The importance of Simarouba versicolor St. Hil. fruit dispersal by the leaf-
cutting ant Atta sexdens (L.) was studied in the Cerrado, Tocantins, Brazil. 
The trees and nests were located between a forest area and a Brachiaria 
decumbens Stapf pasture. Seeds were collected in October 2015 along 
foraging trails and on the anthill of an A. sexdens colony. Germination of 
three groups of seeds was tested: (1) seeds with the tegument removed 
by the ants; (2) seeds without tegument, cleaned manually, and (3) 
seeds with tegument. The germination rates for the three treatments 
were similar; however, it was verified that the seeds cleaned by ants 
germinated faster. In addition, it was verified that the ants dispersed the 
seeds by at least 20 meters in the study area. Simarouba versicolor is a 
plant studied for its insecticidal properties, and this is the first study to 
our knowledge reporting its dispersal by ants.

Sociobiology
An international journal on social insects

DRS lopes, RC Tavares, KOM Batista, PB Souza, MO Nascimento, DJ Souza

Article History

Edited by
Evandro Nascimento Silva, UEFS, Brazil
Received                         13 October 2017
Initial acceptance                   12 February 2018
Final acceptance                12 February 2018
Publication date                     09 July 2018

Keywords 
Myrmecochory, Cerrado, Forest Fragmentation. 

Corresponding author
Danival José de Souza
Federal University of Tocantins (UFT)
Campus of Gurupi 
Rua Badejós, Lote 7, Chácaras 69/72, Caixa 
postal 66, CEP 77402-970, Gurupi-TO, Brasil.
E-Mail: danival@uft.edu.br

plant (Leal et al., 2015; Giliomee 1986), and protect seeds from 
fire (Bond & Slingsby, 1984; Leal et al., 2015; New, 2014).

The objective of the present study was to evaluate S. 
versicolor fruit dispersal by the leaf-cutter ant Atta sexdens, 
and its potential benefits to the plant at the edges of a Cerrado-
type forest remnant, in the southern state of Tocantins.

The study was carried out near the urban area of the 
municipality of Gurupi - TO (11°44'42.4"S - 49°00'53.1"W) 
in a Cerrado area near a pasture composed primarily of 
Brachiaria decumbens. The climate of the region is classified 
as tropical humid (Aw) according to Köppen’s climate 
classification (Alvares et al., 2013), with rainy summers and 
dry winters, and an average temperature of 25 °C. Annual 
precipitation varies from 1,327 to 1,798 mm (Marcuzzo 
et al., 2012). In September 2015, seeds of S. versicolor, 
clean and with tegument, were observed along A. sexdens 
trails at the edges of the forest. Simarouba versicolor has a 
fleshy drupe-type fruit with a single seed, which can only be 
mechanically separated. Some fruits dry in the plant, whereas 
those that fall may be transported to ant nests where they are 

 Federal University of Tocantins (UFT), Campus of Gurupi, Tocantins, Brazil

SHORT  NOTE



DRS lopes et al. – Simarouba versicolor seed dispersal338

cleaned and removed. Seeds collected for the germination 
tests came from an individual S. versicolor located 21 m 
from the A. sexdens nest. The seeds of S. versicolor were 
collected from the soil, along the trail, under the plant and 
in the deposit formed near the anthill. More seeds cleaned 
by the ants (drupes in which the tegument and pulp were 
removed) were collected near the anthill than along the trail, 
whereas non-cleaned seeds (dried drupe still containing the 
pericarp) were found scattered under the mother tree and 
along the ant-foraging trail.

Germination tests were performed on 9 cm diameter 
Petri dishes, properly sterilized and lined with two sheets of 
filter paper, moistened with 5 ml of distilled water. Seeds 
that presented physical damage, such as perforations, were 
excluded from the germination tests. The treatments consisted 
of eight replicates (plates) containing eight seeds, with a total 
of 64 seeds for each of the three treatments: (T1) seeds cleaned 
by ants, (T2) seeds cleaned manually, and (T3) non-cleaned 
seeds. The seeds were incubated in a germination chamber at 
25 °C and photoperiod of 12 h, and were observed every 2 
d in the morning for a maximum period of 36 d. Seeds were 
considered germinated when they had a root length ≥ 3 mm. 
Based on these results, the average germination percentage 
and germination speed index were obtained at 36 d after 
sowing. The germination percentage was calculated by the 
following formula: G = (N/100) x 100, where: N = number 
of seeds germinated at the end of the test. The germination 
speed index (GSI) was calculated based on the methodology 
proposed by Maguire (1962) using the formula:

GSI = Σ (ni /ti), where: ni = number of seeds 
germinating at time ‘i’; ti = time after test installation; i = 1 → 
36 days. Unit: dimensionless.

The data of germination percentage and speed index did 
not present a normal distribution. Therefore, the values were 
transformed using the following formulas: for the average 
germination percentage (2 × arc sine √ (y/100) + 0.5)) and 
for the germination rate (Logarithm (y) +1). Subsequently, 
they were submitted to analysis of variance using the F-test 
and compared by Tukey’s test at 5% significance level. All 
analyses were performed using the software Statistica 7.0.

Regarding the average germination percentage of S. 
versicolor at the end of the 36 d of observation, it was verified 
that there was no significant difference between the treatments 
(ANOVA, F2.21 = 1.36, p = 0.28), i.e., the leaf-cutting ant 
cleaning did not change the chances of germination. The 
treatments showed the following germination rates (G): G = 
37.5% for T1 (seeds cleaned by ants), G = 25% for T2 (seeds 
cleaned manually), and G = 29.7% for T3 (non-cleaned seeds). 
A significant difference was observed in the germination rate 
between the three treatments F2.21 = 7.24, p = .004, and the 
seeds cleaned by the ants had a higher average GSI than those 
in the other two treatments (Fig 1, Tukey’s test, α = 5%).

The ants did not reduce the germination rate of the seeds 
by consuming the fruit pulp, which characterizes the positive 

effects of dispersion by the ants. In the study site, fruit dispersal 
was observed for distances up to 21 m from the mother plant. 
It should also be noted that the foraging distance of A. sexdens 
workers may exceed this distance by many meters depending 
on several factors, such as the size of the colony and availability 
of plant resources (Della Lucia, 2011).

After a period of drought, which may begin in May, 
the first rains appear at the beginning of October in the 
southern Tocantins. Therefore, the fruits of S. versicolor and 
other species, although occasional, are important items in 
the survival of the leaf-cutter ant, particularly in regions and 
periods in which dry conditions prevail. At the same time that 
we observed the interaction of A. sexdens with S. versicolor, 
we also observed seeds of the following forest species: 
Hirtella glandulosa (Chrysobalanaceae), Diospyros hispida 
(Ebenaceae), and Copaifera langsdorffii (Fabaceae) in the 
trails and anthills. Germination tests were not performed 
because of the small amount of seeds collected; however, 
these observations reinforce the importance of these fruits to 
leaf-cutting ants at this time of year.

Fig 1. Germination speed index of T1, T2, and T3 treatments, where 
T1: seeds cleaned by ants (free of the pericarp, without pulp, and 
endocarp); T2: aryl-free seeds, cleaned manually; and T3: seeds with 
aryl. Means followed by the same letters between columns do not 
differ from each other based on the Tukey’s test at 5%.

Regarding the differences in speed germination, the 
myrmecochory may be an important ecological advantage 
for S. versicolor in the study area, since the rainy period, 
favorable for the development of the plants, is more restricted 
than that of other regions, and the presence of grasses and 
other common invasive species at this edge of the forest may 
inhibit the development of native species (Machado et al., 
2013). In this situation, the seedlings would have a longer 
time to develop and settle before the dry season.

In the present study, it was possible to observe that 
some cleaned and non-cleaned seeds of S. versicolor remained 
on the foraging trail. The seed cleaning process occurred along 
the trail, but most seeds were cleaned inside the nests and 



Sociobiology 65(2): 337-339 (June, 2018) 339

then removed and deposited at the anthills. Thus, the colony 
did not suffer from the toxic effects of substances present in 
the seeds, including insecticides and fungicides (Alves et al., 
2014), and seeds maintained their chances of germination, 
since no physical damage was observed.

Therefore, it is concluded that S. versicolor seed cleaning 
by A. sexdens ants does not alter the germination percentage, 
but increases the germination speed. The role of ants is 
important in the dispersal of this arboreal species. 

Acknowledgments

We thank the anonymous reviewers for their careful 
reading of our manuscript and their many insightful comments 
and suggestions. This work was supported by grants of 
CNPq (Project 403708-2013-3) and research funds of Federal 
University of Tocantins for DJ Souza.

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