Behavioral Ecology
doi:10.1093/beheco/arp070
Advance Access publication 19 May 2009
Larger colonies do not have more specialized
workers in the ant Temnothorax albipennis
Anna Dornhaus,a,b Jo-Anne Holley,a,c and Nigel R. Franksb
Department of Ecology and Evolutionary Biology, University of Arizona, 1041 East Lowell Street,
Tucson, AZ 85721, USA, bUniversity of Bristol, School of Biological Sciences, Woodland Road, Bristol
BS8 1UG, UK, and cUniversity of Illinois at Urbana-Champaign, School of Integrative Biology, 505 South
Goodwin Avenue, Urbana, IL 61801, USA
a
Social insects are distinguished by their extraordinary degree of cooperation and the complexity of their group organization.
However, a high proportion of individuals (often .50% at any one time) in a social insect colony tend to be inactive. It has been
hypothesized that larger colonies can afford such inactivity because of efficiencies gained through stronger division of labor. We
quantify the degree to which colonies of different sizes exhibit division of labor, and what proportion tends to be inactive, in the
ant Temnothorax albipennis. Colony size neither influenced individual specialization nor overall division of labor in this species and
larger colonies did not show a higher proportion of inactive workers. Interestingly, small colonies seemed to rely more on a small
number of high-performance workers: the proportion of work performed by the single most active worker is significantly higher
in smaller colonies for several tasks. More research is needed to resolve when and how colony size affects collective organization
and division of labor in insect colonies. Key words: colony size, division of labor, scaling, self-organization, social insects, specialization, task allocation. [Behav Ecol 20:922–929 (2009)]
he study of how an organism’s body size affects both physiological and ecological parameters has recently generated
a lot of interest (e.g., Kaspari and Weiser 1999; West et al.
1999; Banavar et al. 2003; Enquist et al. 2003; Jetz et al.
2004; Woodward et al. 2005; Chown et al. 2007). Body size is
thought to predict everything from chewing frequency (Gerstner
and Gerstein 2008) to life span (Blueweiss et al. 1978;
Lindstedt and Calder 1981) and from home range size
(Swihart et al. 1988; Jetz et al. 2004) to ecosystem characteristics (Makarieva et al. 2005; Woodward et al. 2005). These
relationships are generally described by scaling laws. In many
cases, scaling laws are thought to be the result of strict physical
constraints, whether volume/area relationships or flow rates
in a fractal network (West et al. 1999; Enquist et al. 2003). If
such is the case, one would predict that in many cases, similar
scaling laws should apply to entities at other levels of organization: for example, groups (Yip et al. 2008) or ‘‘superorganisms’’ (Karsai and Wenzel 1998; Jun and Pepper 2003). Social
insect colonies have been termed superorganisms because of
their high levels of integration (Emerson 1939). Strong reproductive skew (only 1 or a few members of the colony reproduce, others are essentially sterile ‘‘workers’’) leads to the
evolution of traits that optimize colony-level success, similar to
selection at the level of the whole individual in multicellular
organisms (Hölldobler and Wilson 1990; Seeley 1995). Should
we therefore expect that many traits of social insect colonies
can be predicted from their colony size? Some authors have
argued this (Oster and Wilson 1978; Beckers et al. 1989;
Bourke 1999; Anderson and McShea 2001). However, empirical studies are still scarce (e.g., Murakami et al. 2000; London
and Jeanne 2003; Thomas and Elgar 2003; Beekman 2004;
Dornhaus and Franks 2006; others discussed in detail below).
T
Address correspondence to A. Dornhaus. E-mail: dornhaus@email.
arizona.edu.
Received 15 December 2008; revised 17 April 2009; accepted 20
April 2009.
The Author 2009. Published by Oxford University Press on behalf of
the International Society for Behavioral Ecology. All rights reserved.
For permissions, please e-mail: [email protected]
Social insect colonies do vary in population size by several
orders of magnitude, both within and between species (Hölldobler and Wilson 1990; Karsai and Wenzel 1998). This has
been predicted to affect collective behaviors, such as communication strategies (Beckers et al. 1989; Karsai and Wenzel
1998; Anderson and Ratnieks 1999; Anderson and McShea
2001), specifically because larger group size may lead to higher rates of information flow and more frequent interactions
(Burkhardt 1998; Karsai and Wenzel 1998; Gordon and Mehdiabadi 1999). Large colony size may also allow more effective
exploration behavior (Dornhaus and Franks 2006) and reduce risk aversion (Herbers 1981). Colony size may affect
specific behaviors: large colonies, for example, seem to invest
more in territory defense, both across and within species (e.g.,
Spradbery 1973; Gordon and Kulig 1996, reviewed in London
and Jeanne 2003), and colony size may have nonlinear effects
on the structure of nests built (Tschinkel 1999; Jeanne and
Bouwma 2002; Buhl et al. 2004; Tschinkel 2004). Recent work
has also shown that there may be interesting patterns of metabolic scaling, that is, changes in energy used per body weight,
with colony density (Cao and Dornhaus 2008), thus possibly
also with colony size if nest space is limited. Finally, colony size
may affect individual traits, such as life span (which was reported to be longer in larger colonies, O’Donnell and Jeanne
1992).
However, there are several examples where colony size effects are not consistent across species and thus do not seem
amenable to the establishment of general scaling laws. For example, results on productivity and its relationship with colony
size are mixed (reviewed in Bouwma et al. 2006; Dornhaus
et al. 2008). Similarly, previous studies on communication
did not agree whether foraging success with recruitment increases (Beckers et al. 1989; Beekman et al. 2001; Mailleux
et al. 2003), decreases (Jun and Pepper 2003), or stays constant (Dornhaus et al. 2006) with colony size. In the latter
case, the differences can be easily explained by the idiosyncrasies of the different communication systems; in particular,
if the audience for each recruitment signal increases with
colony size (such as with pheromone trails), colony size has
Dornhaus et al.
•
Division of labor and colony size in ants
a strong effect on the number of recruits, but if it stays constant (such as in the bee waggle dance, where 1 dancer can
only communicate with 1–5 recruits, independent of total
colony size), then no effects of colony size are to be expected.
In this paper, we focus on the effects of colony size on division of
labor. We test empirically the idea that in larger colonies, individuals should show a higher degree of specialization, and thus,
larger colonies should display a greater division of labor than
smaller ones. Complexity of collective behavior in general, and
division of labor in particular, have been predicted to be affected
by (Pacala et al. 1996; O’Donnell and Bulova 2007) or specifically
to increase with colony size (in conceptual papers: Bourke 1999;
Anderson and McShea 2001; and in specific modeling studies:
Oster and Wilson 1978; Gautrais et al. 2002). There is also evidence from empirical (Thomas and Elgar 2003; Jeanson et al.
2007) and comparative studies (Bourke 1999) that larger colony
size correlates with increased levels of division of labor. Particularly, ‘‘task partitioning’’ is thought to be affected by group size
(theory: Anderson and Ratnieks 1999; Ratnieks and Anderson
1999; empirical or comparative data: Jeanne 1986; Karsai and
Wenzel 1998). Task partitioning implies that material is passed
along an assembly or processing line, which may require high
interaction rates for a smooth flow. However, task partitioning
has only been shown in very few species and only for specific tasks,
such as nest building in wasps (where wood pulp is processed with
water and integrated into the nest structure). Most tasks that
social insect workers specialize in may not require such precise
coordination of worker groups. Perhaps because of this, other
comparative studies have found no evidence of increasing division of labor with colony size (Fjerdingstad and Crozier 2006) or
found more complex effects, such as a difference in the mechanism of task allocation with colony size (Murakami et al. 2000).
There is also no agreement in the literature on whether colony
size has a consistent effect on individual workload (reviewed in
Dornhaus et al. 2008).
We used the ant Temnothorax albipennis as a model system.
These ants have small colonies (up to about 200–400 workers)
and monomorphic workers, both traits typical of most species
of ants. They usually have a single queen and are functionally
monogynous and monandrous (Pearson et al. 1995, 1997).
Although some ants studied in the context of division of labor
have much larger colonies (such as leaf-cutting ants or army
ants), many social insect species have similarly small colonies
of less than 500 workers (Wilson 1971; Hölldobler and Wilson
1990; Kaspari and Vargo 1995; Goulson 2003). Ants of the
genus Temnothorax are easy to maintain in the laboratory
and long lived (individual workers can live .5 years, SendovaFranks AB, personal communication) and have frequently
been used as model systems to study self-organized processes,
including effects of colony size on collective decision making
(Franks et al. 1992, 2003, 2005; Dornhaus et al. 2004; SendovaFranks et al. 2004; Dornhaus and Franks 2006; Franks,
Dornhaus, Best, and Jones 2006; Franks, Dornhaus, Metherell,
et al. 2006; Franks, Dornhaus, et al. 2007; Franks, Hooper,
et al. 2007; Aleksiev et al. 2008). Recent studies have begun
to investigate individual behavior, in particular learning
(Langridge et al. 2004, 2008a, 2008b); but they have also been
model organisms in the study of division of labor (SendovaFranks and Franks 1993, 1994, 1995a, 1995b, 1999; Backen
et al. 2000; Sendova-Franks et al. 2002; Dornhaus 2008;
Dornhaus et al. 2008; Dornhaus A, Holley J-A, Franks NR, in
preparation). Temnothorax ants live in preexisting cavities,
often cracks in rock or hollow twigs or acorns; colony density
may be limited by the abundance of such nest sites (Herbers
1983; Foitzik et al. 2004).
We quantify the work performed by .1100 individually
marked ants from 11 colonies in 7 separate tasks in the contexts
of foraging, nest building, and colony emigrations. We
923
compare the number of inactive workers, the contribution
of the most active workers, and the overall division of labor
as measured by the ‘‘division of labor index’’ (DOL) (Gorelick
et al. 2004) between small and large colonies.
MATERIALS AND METHODS
Colony collection and housing
More than 100 colonies of T. albipennis were collected in
October 2004 in Dorset, southern United Kingdom. For this
study, we used 4 of the largest colonies and 7 of the smallest
ones collected to cover the maximum colony size range in this
species. For information on the overall distribution of colony
sizes, see Dornhaus and Franks (2006) and Franks, Dornhaus,
Best, and Jones (2006). All workers in the colonies were individually marked with paint spots, 1 on the head, 1 on the
thorax, and 2 on the gaster (Sendova-Franks and Franks
1993). Each colony contained at least 1 queen (2 colonies
contained more: 2 and 4 queens, respectively) and brood of
different stages. After marking, large colonies contained a median of 175 workers (quartiles 160–197) and 358 brood items
(quartiles 318–390). Small colonies contained a median of 57
workers (quartiles 43–71) and 180 brood items (quartiles 105–
205). Adults were counted from photographs of the nest. The
number of brood items was determined as the number of
brood transports during the emigration, as small brood items
are hard to distinguish on a photograph (this means that the
number of eggs and small larvae were somewhat underestimated, as these are often transported in clumps). The colonies were housed in nests made of a piece of cardboard from
which a cavity had been cut and sandwiched between 2 glass
slides. Internal dimensions of the cavity were 33 3 25 3 1 mm
(width 3 depth 3 height), with a 3-mm wide entrance. All
ants could thus be observed through the transparent roof of
the nest. This method of housing Temnothorax colonies is well
established (Franks et al. 2003, 2005; Dornhaus et al. 2004;
Dornhaus and Franks 2006; Franks, Dornhaus, Best, and
Jones 2006; Franks, Dornhaus, Metherell, et al. 2006; Franks,
Dornhaus, et al. 2007; Franks, Hooper, et al. 2007), and the
same colonies were also used in other studies (Dornhaus
2008; Dornhaus et al. 2008; Dornhaus A, Holley J-A, Franks
NR, in preparation). For improved color discrimination,
a light brown paper was placed underneath the nest to provide a light brown background to videos of the colony interior. Nests were placed in large square petri dishes (220 3
220 mm). Ants were fed with honey solution and dead
Drosophila flies weekly.
Recording individual activity in different tasks
A total of 731 individually marked ants from large colonies and
412 marked ants from small colonies were observed in 3 contexts: colony emigrations, foraging, and wall building. A digital
video camera with high color resolution (Panasonic NV-MX500
3CCD) was set up above the new nests in the emigration and
building manipulations and the original nest during the foraging period. Individual activity in 7 different tasks was recorded:
1) scouting, 2) brood transports, and 3) adult transports during emigrations; 4) collection of flies and 5) collection of
honey solution during the foraging experiment; and 6) collection of ‘‘stones’’ (sand grains) and 7) movement of stones inside the nest during wall building. Definitions of these tasks
and procedures to induce them are detailed below. After
the videos were analyzed, all records (163 h of video; 5739 task
performances) were double-checked by a second person to
ensure accurate recordings of ant identity across experiments.
Behavioral Ecology
924
Colony emigrations
To induce an emigration of the colony, the top glass slide of the
nest was removed and both this glass slide and the rest of the
nest were placed in a new, clean petri dish. Any remaining
workers were also moved from the old to the new petri dish
with a fine brush. At the same time, a new, identical nest
was placed with its entrance 10 cm from the entrance of the
old nest. The new nest was filmed until the last brood item
had been carried there. The median duration from the start
of the experiment to the last brood transport was 176 min; this
total duration does not depend on colony size (Dornhaus and
Franks 2006). The videos were then analyzed to identify which
ants entered the nest scouting for a new nest location and
which ants entered the nest carrying a brood item or another
adult ant.
Foraging
Foraging behavior was observed after a 2-week period of starvation during which the ants only had access to water. A dish of
1:10 honey solution and small pile of freeze-killed Drosophila
(ca., 15) were placed in the foraging arena, both 10 cm from
the nest entrance and each other. Filming began 30 min before food was laid in the arena and ceased after 180 min. From
the videos, we identified which ants entered the nest with fly
parts; those entering and not carrying flies were tracked for
10 min to observe whether trophallaxis with nestmates occurred.
The ants that returned from a trip outside but did not carry or
regurgitate food were considered ‘‘unsuccessful foragers.’’
Wall building
Building by workers was stimulated by initially causing the ants
to emigrate to a new nest (as above). The new nest lacked
a cardboard wall in the front of the cavity, leaving a 33-mm
gap rather than a 3-mm entrance. Colonies were provided with
a pile of blue-dyed sand grains with which to construct a perimeter wall (Aleksiev et al. 2008). Filming started with the addition of the manipulated nest and removal of the glass cover of
the original nest. Colonies were filmed for at least 360 min.
Video analysis identified which ants brought sand grains
(henceforth called stones) into the nest cavity and which
workers repositioned the stones (i.e., picked up a stone inside
the nest and moved it).
Figure 1
Proportion of workers active in each task (median percent across
colonies). In any given task in each colony, less than 50% of workers
were recorded as active. Overall, a high proportion of workers was
never recorded as performing any of the 7 tasks examined here
(‘‘inactive ants’’). The proportions differ between small and large
colonies only for 2 tasks, protein foraging and stone collection
(Mann–Whitney U tests, N1 ¼ 4, N2 ¼ 7: scouting, P ¼ 0.85; brood
transport, P ¼ 0.92; adult transport, P ¼ 0.21; honey foraging,
P ¼ 0.39; fly foraging, P ¼ 0.03; stone collection, P ¼ 0.046; stone
rearranging, P ¼ 0.09; unsuccessful foraging, P ¼ 0.046; inactive ants,
P ¼ 1.0). Whiskers show interquartile range.
performed by a restricted set of workers (DOLtask ¼ I[indiv,
task]/H[indiv]). For a more detailed discussion of how this
index is derived, see Gorelick et al. (2004) and Gorelick and
Bertram (2007); however, note that the definitions of the indices DOLindiv and DOLtask are mistakenly inverted in
Gorelick et al. (2004). As individual workers perform 1 task
to the exclusion of others, the DOLindiv increases, approaching
1.0 (whereas equal performance of all tasks by workers results
in DOLindiv ¼ 0.0). If tasks are performed by nonoverlapping
discrete worker subsets, DOLtask approaches 1.0, whereas this
index declines as worker subsets overlap among tasks.
All statistical analyses were performed using Minitab 14.
Nonparametric analyses were used throughout.
RESULTS
Division of labor indices
Individual and colony task performance
‘‘Division of labor’’ implies first that individuals tend to restrict
their labor to a subset of available tasks (this is called specialization) and second that each task tends to be performed by
only a subset of the individuals. The first does not necessarily
imply the second; all workers may perform more foraging than
nest building, for example, thus creating apparent specialization on foraging. However, division of labor implies that
workers differ in their preference distribution. In terms used
in information theory, if division of labor occurs, then knowing
the individual predicts the task and knowing the task predicts
the individual that performed it. The degree to which task and
individual are linked can be quantified in a single number,
called the DOL (Gorelick et al. 2004). This index is calculated
from a matrix giving the number of times each task was performed by each worker. In addition to the overall measure of
division of labor, 2 other indices can be used to assess separately 1) the degree to which individuals have a restricted task
repertoire using the mutual entropy of individuals (I[indiv,
task]) and the marginal entropy of tasks (H[task]): DOLindiv ¼
I(indiv, task)/H(task) and 2) the degree to which tasks were
In each colony, each of the 7 tasks monitored was performed by
some workers (scouting, brood transports, adult transports,
foraging for honey and protein, and collection and rearrangement of sand grains), but the number of workers engaging in
any given task never exceeded 50% (Figure 1) and was usually
less than 25% (Figure 2). A high proportion of workers did
not perform any of these tasks during our observations (a
median of 44% in small and 46% in large colonies; ‘‘inactive
workers’’ in Figure 1). The workers that were active, however,
usually performed the same task repeatedly; at the extreme, 1
individual worker in a small colony transported 143 sand
grains to the wall around its nest within the recorded period
(Figure 2).
Division of labor indices
The median value for the DOL (Gorelick et al. 2004) across all
colonies was 0.38 (with DOLindiv ¼ 0.50 and DOLtask ¼ 0.25).
Because these indices are normalized for number of tasks and
number of individuals, they can be directly compared with
Dornhaus et al.
•
Division of labor and colony size in ants
925
Figure 2
Frequency distribution of individual workload across all tasks
(a) and for each of the 7 tasks
(b–h). For any given task, most
workers do not participate,
and a small number of individuals assumes a high workload
(perform the task many
times). Please note that the x
axis scale is not linear to show
the number of worker performing each task just once.
Bars are medians and whiskers
show interquartile range.
other systems (Gorelick et al. 2004). The DOL values recorded
here are higher than those reported for solitary and communal
halictine bees (about 0.08–0.21; Jeanson et al. 2007) or our
own measurements on Bombus impatiens (0.15–0.30; Jandt J,
Dornhaus A, in preparation) or the ant Camponotus festinatus
(0.15–0.25; Dornhaus A, Duffy K, unpublished data).
Colony size and division of labor
The degree to which the set of workers performing each task
was restricted and the overall measure of division of labor did
not change with colony size (Spearman rank correlations with
colony size—DOLtotal: P ¼ 0.71, R2 ¼ 0.00; DOLtask: P ¼ 0.21,
R2 ¼ 0.08). However, only our measure of worker specialization (DOLindiv) is predicted to be invariant to sample size
(number of workers observed). Any change in this measure
would therefore indicate a true difference in the degree to
which workers specialize among colonies. In our study, there
is no such significant difference, that is, worker specialization
was not significantly predicted by colony size (P ¼ 0.051,
R2 ¼ 0.29), although there is some trend toward this being
higher in larger colonies (Figure 3).
In total, more trips were performed by larger colonies across
all tasks (Spearman rank correlation: P ¼ 0.004, R2 ¼ 0.58;
Figure 4). Because there is no significant effect of colony size
on the absolute amount of work done by the 1 hardest working individual (P ¼ 0.25, R2 ¼ 0.05; Figure 4), these individuals therefore do a greater proportion of the overall work in
small colonies (P ¼ 0.004, R2 ¼ 0.57). This is also true for
most tasks if tasks are analyzed separately (Figure 5). The
proportion of inactive workers is not affected by colony size
(Spearman rank correlation: P ¼ 0.37, R2 ¼ 0.00; Figure 1).
Small colonies may thus be said to rely more on a few ‘‘key
individuals,’’ as has been shown previously for colony emigrations (Dornhaus and Franks 2006; Dornhaus et al. 2008).
DISCUSSION
We showed that in T. albipennis, larger colonies do not seem to
divide labor more than smaller ones or at least that this effect
926
Figure 3
Division of labor indices (DOLs; Gorelick et al. 2004) of all 11
colonies. There is no significant increase in degree of division of
labor or specialization as measured with these indices (see text); the
crucial index for detecting colony size effects is DOLindiv.
must be very weak. Nor do larger colonies have more inactive
ants (possible ‘‘reserve workers’’). Although our overall measure of division of labor in the colony was not affected by
colony size, we did find that in small colonies, the single most
active worker played a proportionately larger role (this is consistent with previous results, Dornhaus et al. 2008). However,
the absolute number of task performances of the most active
individual was invariant with colony size, suggesting that there
was a limit to how much a single worker can do. This constant
amount was, however, a relatively larger contribution in a small
colony with an overall smaller work amount. We also found
that in all colonies, in any given context, a large majority of
individuals did not take part in the activity observed (.75%).
This may be explained by the fact that we only focused on 1
task at a time: for example, we did not record brood care or
Figure 4
The number of task performances recorded overall for each colony
and for the individual ant that made the highest contribution. Larger
colonies perform more trips (in foraging, brood transport, and wall
building), but the workload of the most active individual does not
correlate significantly with colony size (see text for statistics). This
has the effect that a single worker contributes a much higher
proportion to the total work in smaller colonies.
Behavioral Ecology
nest cleaning or defense. However, high levels of inactivity
have been reported previously in a related ant species (Cole
1986); they may be the result of selfish behavior by workers
(who can lay male eggs, Cole 1986) or possibly reflect low
levels of collective optimization in this species (Dornhaus
2008).
This is contrary to theoretical predictions of increased division of labor with increasing colony size (Anderson and
McShea 2001; Gautrais et al. 2002) and previous comparative
(Karsai and Wenzel 1998; Bourke 1999) and empirical
(Jeanne 1986; Thomas and Elgar 2003; Jeanson et al. 2007)
studies. Some of these studies have concentrated on systems
that involve task partitioning, particularly in wasps and honey
bees. In task partitioning, a single process is divided up into
multiple steps. This often requires that workers directly interact with workers in the processing steps immediately preceding or following their own in an assembly-line fashion. For
example, in the nest-building behavior of wasps, water and
pulp need to be collected, processed, and integrated into
the nest structure; because none of these materials can be
stored, workers bringing water must immediately encounter
a processing worker to work efficiently (Jeanne 1986). Such
a system is predicted to require a large group size to ensure a
smooth operation (Anderson and Ratnieks 1999). However,
the ant species studied here, T. albipennis, is not known to
employ task partitioning, even though individuals clearly specialize on particular tasks. Future comparative studies showing
whether task partitioning is widespread or rare among social
insect species would be desirable.
It is possible that the range in colony sizes studied here is
not sufficient to expose any effects of colony size. However,
most ant species and many stingless bee and bumble bee species have colonies that stay within the size range tested here
across their entire ontogeny (Hölldobler and Wilson 1990;
Kaspari and Byrne 1995; Kaspari and Vargo 1995; Huang and
Dornhaus 2008). Also, at least 1 previous study found effects
of colony size on division of labor across a similar, or slightly
larger, size range (Thomas and Elgar 2003). It thus seems that
there is no universal relationship between division of labor
and colony size, as is the case for many other behaviors (see
in the introduction). Alternatively, the advantages of specialization at larger colony sizes may only be realized between
species and not within species (although see Thomas and
Elgar 2003). Finally, we studied colonies under conditions of
unusually high workloads (during colony emigrations, new
nest-building activity, or after starvation periods). It is possible, indeed likely, that even fewer workers take part in tasks
when workloads are low overall, and this may affect the degree
of specialization. Of course, this begs the question why so
many workers are inactive even under conditions of high
workload; that question, common to many social insects, has
not been answered (Cole 1986; Dornhaus 2008; Dornhaus
et al. 2008).
Higher specialization in larger societies is also a pattern observed in humans and studied by anthropologists (Keeley 1988;
Bird and O’Connell 2006). Similarly, economic division of
labor is thought to depend on the size of the market or the
society (Smith 1776). However, in both of these cases, the
causal relationship may be reversed (Young 1928; Panter-Brick
2002; Bird and O’Connell 2006): for example, higher population densities may intensify competition and therefore social
structure, followed by division of labor—it is thus not clear
whether the link between group size and division of labor
is adaptive or a result of intragroup conflict (Bird and
O’Connell 2006). Social insect biology, as well as anthropology and economics, may benefit from mutually understanding
how specialization emerges in their different complex systems
and how and why it may be linked with system size.
Dornhaus et al.
•
Division of labor and colony size in ants
927
Finding general ‘‘laws’’ to explain variation in natural systems
is satisfying because it usually implies that we have understood
the mechanics of the properties in question. Unfortunately, biological systems often display many idiosyncrasies, specific behaviors, or constraints that make it difficult to discern the
general rules among the exceptions. Are social insect workers
in larger groups more specialized? A comparative analysis, controlling for phylogeny and lifestyle, using an objectively quantifiable trait (such as the DOL index), and a larger species set, will
be essential for answering this question.
FUNDING
Ecology and Evolutionary Biology Department at the University
of Arizona; Biotechnology and Biological Sciences Research
Council (UK) (grant number E19832).
We thank the undergraduate students who helped with the video analysis. N.R.F. wishes to thank the Biotechnology and Biological Sciences
Research Council (UK) for supporting this research.
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Figure 5
The percentage of colony workload done by the worker most active
for each task. Emigration tasks are shown in (a), foraging tasks in (b),
and building tasks in (c). Spearman rank correlations show
a decrease in relative contribution of the most active worker with
colony size in all emigration and foraging tasks, but not in building
tasks (scouting, P ¼ 0.004, R2 ¼ 0.58; brood transport, P ¼ 0.009,
R2 ¼ 0.50; adult transport, P ¼ 0.017, R2 ¼ 0.43; honey foraging,
P ¼ 0.010, R2 ¼ 0.49; fly foraging, P , 0.001, R2 ¼ 0.76; stone
collection, P ¼ 0.396; stone rearranging, P ¼ 0.496).
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