CONTENT - International Society of Zoological Sciences

ICZ2008 – Abstracts S16
How many nestmates ? A key issue in ants’ social
organization
Claire Detrain and Jean-Louis Deneubourg
Unit of Social Ecology, Université Libre de Bruxelles, 50 Avenur F.
Roosevelt, B-1050 Brussels, Belgium
Social insects have evolved means of sharing information about
many aspects of their everyday life. Each ant behave or make
decisions based on its own experience but also integrate grouplevel
information provided directly or indirectly by nestmates. Cues
are the keystones of this socially acquired information: they are
namely used by ants as “statistical” tools to assess the occupancy
level of a location and hence to determine the potential for
amplification processes and emergence of cooperative behaviour
(1,2). Cues about nestmate density can be acquired by a direct
sampling of the others, through antennal contacts and/or food
exchanges. These direct cues are most useful for work
organization by providing ants with a precise- albeit local and
punctual- information about the origin, status or recent activities of
encountered ants (3). Another efficient way for ants to assess their
social environment is through indirect cues – through the
perception of chemical cues passively laid by conspecifics (4).
Unlike direct encounters, such area marking provides to the
receiver ant an estimate of average ant density without necessarily
requiring a time-consuming sampling effort. It is an integrative cue
resulting from the summation through time of tracks left by
nesmtates and hence reflecting their activity level in the nest
surroundings. Furthermore, it appears as a unique way for ants to
“smell the past” since compounds ratios and concentrations vary
depending on how intensively and for how long one area has been
foraged by nestmates.
(1) Detrain, C. & Deneubourg, J.L (in press). Social cues and
adaptive foraging strategies in ants. In: Food Exploitation by Social
Insects: An Ecological, Behavioral, and Theoretical Approach
(Jarau S. & Hrncir M. eds)
(2) Detrain C. & Deneubourg J.L. 2006. Self-organization in a
superorganism: do ants behave like molecules? Physics of life
Reviews 3:162-187.
(3) Gordon D.M. & Mehdiabadi N. 1999. Encounter rate and task
allocation in harvester ants. Behav. Ecol. Sociobiol. 45: 370-377.
(4) Devigne C., Renon A. & Detrain C. 2004. Out of sight but not
out of mind: modulation of recruitment according to home range
marking in ants. Anim. Behav. 67: 1023-1029.
Using social insects for seed dispersal: the case of
myrmecochory
Claire Detrain and Pablo Servigne
Unit of Social Ecology, Université Libre de Bruxelles, 50 Avenue F.
Roosevelt, B-1050 Brussels, Belgium
Ants are one of the rare invertebrate groups that participate into
seed dispersal. In the first phase of this myrmecochory process,
ants removed seeds from the parent plant, behave as centralplace
foragers and bring them back to the nest. We show that this
centripetal movement of seeds towards the ant nest follows a
species-specific dynamics. For the two tested plant species
(Chelidonium majus, Viola odorata, the insectivorous Myrmica
rubra ants remove seed items in larger number and at higher
speed than the aphid-tending Lasius niger workers what supports
the hypothesis of a convergence between odours of elaiosomes
and insect preys. Within the nest, seed nutritive bodies (i.e.
elaiosomes) are discarded and eaten by ants or larvae. Then
begins the second phase of myrmecochory, during which the still
viable seeds do not interest ants anymore: they are removed from
the nest and dispersed to outside final locations. We demonstrate
that this centrifugal movement is also highly specific with Myrmica
ants rejecting seeds from the nest at quicker rates than Lasius
workers. Such a difference may be due to the higher propensity of
insectivorous species to remove waste items due to higher
sanitary constraints on their nest-confined social life. This raises
questions on how plant seeds may have evolved ways to be
attractive to ant species that are the most likely to promote their
dispersal.
- 53 -
How individual foraging behaviour is affected by social
environment in ants
Renée Fénéron 1 , Marie-Claire Malherbe 1 , Vincent Fourcassié 2 and
Stéphane Chameron 1
1 Laboratoire d’Ethologie Expérimentale et Comparée (CNRS UMR
7153), Université Paris-Nord, Villetaneuse, France
2 Centre de Recherche en Cognition Animale (CNRS UMR 5169),
Université Paul Sabatier, Toulouse, France
Division of labour amongst eusocial animals implies that most
individuals contribute energy, time or work capacity rather than
direct reproduction to their group. In insect societies, workers
benefit the colony fitness through the altruistic behaviours they
perform. Among the worker's behavioural tasks, foraging is of
utmost importance because adult survival and larvae growth
entirely depend on food provisioning and colony energetic
reserves. As foragers support a high mortality risk, theories predict
that colony-level selection should regulate foraging behaviour most
strictly in social contexts where the loss of foragers is costly. It is
especially the case when colonies are small and food demands
high. We then investigated how individual foraging behaviour is
affected by social environment, namely the numbers of workers
and larvae, in the ant Ectatomma tuberculatum (Formicidae,
Ectatomminae). We analysed the behaviour and foraging paths of
individual foragers in experimental groups varying in worker and
larvae composition. Rate of foraging was more important in large
groups but individual foraging effort higher in small ones. Trip
duration decreased with the amount of larvae, independently of the
colony size; both the decrease in walking distance, stop numbers
and feeding duration were responsible for shorter trips. Our results
complement the numerous studies on optimal foraging,
demonstrating that foragers through their behaviour and
movement patterns continue to be influenced by the social
environment they have temporarily left. Discussion focuses on the
ants' ability to assess colony needs and the regulation
mechanisms of task allocation on the basis of threshold models.
Path efficiency of ants foraging in tunnel networks with
different branching geometries
Vincent Fourcassié, Simon Garnier, Aurélie Guérécheau, Christian
Jost, Grégory Gerbier, Maud Combe and Guy Theraulaz
Centre de Recherches sur la Cognition Animale, CNRS UMR 5169,
Université de Toulouse, 118 route de Narbonne, F-31062
Toulouse Cedex 4, France
Some species of ants forming large colonies use a system of mass
chemical recruitment to explore collectively novel areas. Workers
lay a trail more or less permanently and this quickly leads through
a process of self-organization to the emergence of a network of
interconnected trails 1 . When a food source is discovered a
recruitment trail is established over existing exploratory trails and
the question arises as to whether ants are able to establish this
trail along the shortest possible path going from their nest to the
food source. To answer this question we investigated in the
Argentine ant Linepithema humile the collective performance of
workers moving in artificial networks of tunnels in which several
interconnected paths can be used to reach a single food source.
We used two networks of same length but differing in the geometry
of their branching (symmetrical, i.e. in which the angles between
tunnels is the same, or asymmetrical). For both networks most
experiments ended with the establishment of the trail along one of
the shortest path 2 , which shows that ants did not orient randomly in
the network. Moreover, the traffic was more concentrated along
the shortest paths in asymmetrical than in symmetrical networks.
Experiments conducted at the individual level show that ants
reaching an asymmetrical bifurcation prefer to orient on the branch
that deviates less from their initial direction. This bias could partly
explain the results observed at the collective level in the path
chosen by ants for the establishment of a recruitment trail.
1 Edelstein-Keshet, L., Watmough, J. & Ermentrout, G. B. 1995.
Behav Ecol Sociobiol, 36, 119-133.
2 Vittori, K., Talbot, G., Gautrais, J., Fourcassie, V., Araujo, A. F. R.
& Theraulaz, G. 2006. J Theoret Biol, 239, 507-515.