Aggressive Transition between Alternative Male Social Tactics in a Long-Lived Australian Dragon (Physignathus lesueurii) Living at High Density
ABSTRACT Theory predicts the evolution of alternative male social tactics when intense competition coupled with the superior competitive ability of some individuals limits access to reproductive opportunities by others. How selection has shaped alternative social tactics may be especially interesting in long-lived species where size among sexually mature males varies markedly. We conducted experimental studies on long-lived eastern Australian water dragons living where competition was intense to test the hypotheses that mature males adopt alternative social tactics that are plastic, and that large size and body condition determine resource-holding potential. Approximately one-half of mature males (N = 14) defended territories using high rates of patrol and advertisement display, whereas 16 smaller mature males having lower body condition indices utilized non-territorial social tactics. Although territorial males were larger in absolute size and head dimensions, their heads were not allometrically larger. Territorial males advertised very frequently using displays involving stereotypical movements of the head and dewlap. More aggressive displays were given infrequently during baseline social conditions, but increased during periods of social instability. Female home ranges overlapped those of several territorial and non-territorial males, but females interacted more frequently with territorial males. The extreme plasticity of social tactics in this species that are dependent on body size was confirmed by two instances when relatively large non-territorial males spontaneously evicted territory owners, and by marked shifts in tactics by non-territorial males in response to temporary experimental removals of territory owners, followed (usually) by their expulsion when original owners were reinstated. The high level of social plasticity in this population where same-sex competitors are densely concentrated in preferred habitat suggests that chronic high energetic costs of defense may select for males to cycle between territorial and non-territorial social tactics depending upon their changing energetic status and their current capacity for competition with rivals.
- SourceAvailable from: Troy A. Baird[Show abstract] [Hide abstract]
ABSTRACT: Water dragons (Intellegama [Physignathus] lesueurii) are large (to > 1 m) agamid lizards from eastern Australia. Males are fiercely combative; holding a territory requires incessant displays and aggression against other males. If a dominant male is absent, injured or fatigued, another male soon takes over his territory. Our sampling of blood from free-ranging adult males showed that baseline levels of both testosterone and corticosterone were not related to a male’s social tactic (territorial versus non-territorial), or his frequency of advertisement display, aggression, or courtship behavior. Even when we elicited intense aggression by non-territorial males (by temporarily removing territory owners), testosterone did not increase with the higher levels of aggression that ensued. Indeed, testosterone levels decreased in males that won contests. In contrast, male corticosterone levels increased with the heightened aggression during unsettled conditions, and were higher in males that won contests. High chronic male-male competition in this dense population may favor high testosterone levels in all adult males to facilitate advertisement and patrol activities required for territory maintenance (by dominant animals), and to maintain readiness for territory take-overs (in non-territorial animals). Corticosterone levels increased in response to intense aggression during socially unstable conditions, and were higher in contest winners than losers. A positive correlation between the two hormones during socially unstable conditions, suggests that the high stress of contests decreased androgen production. The persistent intense competition in this population appears to exact a high physiological cost, which together with our observation that males sometimes lose their territories to challengers, may indicate cycling between these two tactics to manage long-term energetic costs.Hormones and Behavior 01/2014; · 4.51 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Understanding the ways individuals socialize with each other and how they differ temporally, spatially and phylogenetically is key to unravelling the evolutionary processes that shape social evolution. Our current knowledge of social evolution in vertebrates, however, has primarily come from bird and mammalian studies. Despite being largely understudied, reptiles remain an important piece of the puzzle in our study of social evolution; they represent a major class of vertebrates and, similar to mammals and birds, many are gregarious. Increasing our understanding of sociality in reptiles is important given that it would allow for comparisons across phylogenetically distinct vertebrate classes. In this study, we investigated the social structure of the eastern water dragon, Intellagama lesueurii, and found that males and females showed both preference and avoidance for members of either sex. Furthermore, we found sex differences in the extent of individual sociability: females generally formed stronger associations with one another than any other sex class (e.g. male–male, male–female). Although association patterns correlated to some extent with home range overlap, we found no evidence of a correlation with kinship. Overall, our study presents additional evidence that sociality can evolve outside the realm of kin selection.Animal Behaviour 11/2014; 97:53–61. · 3.07 Impact Factor
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ABSTRACT: Water dragons (Intellegama [Physignathus] lesueurii) are large (to>1m) agamid lizards from eastern Australia. Males are fiercely combative; holding a territory requires incessant displays and aggression against other males. If a dominant male is absent, injured or fatigued, another male soon takes over his territory. Our sampling of blood from free-ranging adult males showed that baseline levels of both testosterone and corticosterone were not related to a male's social tactic (territorial versus non-territorial), or his frequency of advertisement display, aggression, or courtship behavior. Even when we elicited intense aggression by non-territorial males (by temporarily removing territory owners), testosterone did not increase with the higher levels of aggression that ensued. Indeed, testosterone levels decreased in males that won contests. In contrast, male corticosterone levels increased with the heightened aggression during unsettled conditions, and were higher in males that won contests. High chronic male-male competition in this dense population may favor high testosterone levels in all adult males to facilitate advertisement and patrol activities required for territory maintenance (by dominant animals), and to maintain readiness for territory take-overs (in non-territorial animals). Corticosterone levels increased in response to intense aggression during socially unstable conditions, and were higher in contest winners than losers. A positive correlation between the two hormones during socially unstable conditions, suggests that the high stress of contests decreased androgen production. The persistent intense competition in this population appears to exact a high physiological cost, which together with our observation that males sometimes lose their territories to challengers, may indicate cycling between these two tactics to manage long-term energetic costs.Hormones and Behavior 06/2014; · 4.51 Impact Factor
Aggressive Transition between Alternative Male Social
Tactics in a Long-Lived Australian Dragon (Physignathus
lesueurii) Living at High Density
Troy A. Baird1*, Teresa D. Baird1, Richard Shine2
1Department of Biology, University of Central Oklahoma, Edmond, Oklahoma, United States of America, 2School of Biological Sciences, University of Sydney, Sydney,
New South Wales, Australia
Theory predicts the evolution of alternative male social tactics when intense competition coupled with the superior
competitive ability of some individuals limits access to reproductive opportunities by others. How selection has shaped
alternative social tactics may be especially interesting in long-lived species where size among sexually mature males varies
markedly. We conducted experimental studies on long-lived eastern Australian water dragons living where competition was
intense to test the hypotheses that mature males adopt alternative social tactics that are plastic, and that large size and
body condition determine resource-holding potential. Approximately one-half of mature males (N=14) defended territories
using high rates of patrol and advertisement display, whereas 16 smaller mature males having lower body condition indices
utilized non-territorial social tactics. Although territorial males were larger in absolute size and head dimensions, their heads
were not allometrically larger. Territorial males advertised very frequently using displays involving stereotypical movements
of the head and dewlap. More aggressive displays were given infrequently during baseline social conditions, but increased
during periods of social instability. Female home ranges overlapped those of several territorial and non-territorial males, but
females interacted more frequently with territorial males. The extreme plasticity of social tactics in this species that are
dependent on body size was confirmed by two instances when relatively large non-territorial males spontaneously evicted
territory owners, and by marked shifts in tactics by non-territorial males in response to temporary experimental removals of
territory owners, followed (usually) by their expulsion when original owners were reinstated. The high level of social
plasticity in this population where same-sex competitors are densely concentrated in preferred habitat suggests that
chronic high energetic costs of defense may select for males to cycle between territorial and non-territorial social tactics
depending upon their changing energetic status and their current capacity for competition with rivals.
Citation: Baird TA, Baird TD, Shine R (2012) Aggressive Transition between Alternative Male Social Tactics in a Long-Lived Australian Dragon (Physignathus
lesueurii) Living at High Density. PLoS ONE 7(8): e41819. doi:10.1371/journal.pone.0041819
Editor: Henry Harpending, University of Utah, United States of America
Received April 16, 2012; Accepted June 26, 2012; Published August 8, 2012
Copyright: ? 2012 Baird et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: Australian Research Council Grant FF056365 to Richard Shine. The funders had no role in sudy design, data collection and analysis, descision to publish,
or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
* E-mail: email@example.com
Male vertebrates under strong sexual selection sometimes evolve
alternative reproductive tactics (ART) characterized by distinctive
behavior patterns, and/or morphological differences that are
associated with resource holding potential (=RHP). Alternative
male tactics may be either genetically fixed, or ontogenetically
plastic. When alternative tactics are fixed, males utilize one tactic
throughout their lives [1–3]. In other cases, males switch between/
among two or more alternative tactics [4,5]. The usual case is for
males to adopt socially dominant behavioral tactics, often defense
of reproductive territories, when they obtain high RHP. High
male RHP has been associated with large overall body size [6–9],
allometric enlargement of particular body structures [9–11],
conspicuous coloration [12,13], secretion of certain chemical
signals , and other traits that enhance performance in contests
. Males that are not able to acquire and defend territories may
adopt subordinate tactics characterized by sneaking copulations
when they can do so without being detected by socially-dominant
males [16,17], or by mimicking females . Ascension to
dominant social status by subordinate males often occurs through
passive inheritance when socially dominant individuals die [5,19].
However, especially in long-lived philopatric species, subordinate
males may acquire territories by aggressive eviction of current
territory owners [20,21].
Diurnal lizards are among the best studied vertebrate examples
of both fixed and conditional alternative male social tactics
[4,5,18,22]. Most research has involved lizard clades occurring in
the New World and Europe, even though agamid lizards are
conspicuous, diurnally active members of many habitats through-
out Australia, Africa, and Asia. Moreover, some agamids are long
lived, which likely increases the potential for the evolution of
alternative tactics. Regardless of taxon, relatively few studies of
lizards characterized by alternative male tactics have used
experimental manipulations in the field to examine the mecha-
nisms by which males switch from subordinate to dominant social
The eastern water dragon (Physignathus lesueurii), is common and
conspicuous in riparian habitats throughout eastern Australia.
Nonetheless, only two studies have addressed this species’ social
PLoS ONE | www.plosone.org1August 2012 | Volume 7 | Issue 8 | e41819
ecology despite several observations suggesting that sexual
selection may play a role in its social structure. Water dragons
occur at high density along freshwater shorelines and individuals
remain in relatively small areas . This species shows male-
biased sexual dimorphism in body size, head dimensions, and
ventral coloration; red in mature males, brown/tan in females
. Moreover, because P. lesueurii is relatively large (up to 1 kg), it
is probably long-lived . Long-lived male iguanids typically
display alternative reproductive tactics because individuals become
reproductively mature before they acquire sufficient RHP to
acquire and maintain dominant social status [18,25,26]. The large
size and long life span of water dragons coupled with previous
studies showing male-biased sexual dimorphism suggest strong
potential for intense competition among males, and perhaps the
evolution of alternative social tactics. We conducted experimental
field studies to test two predictions related to male-male
competition: 1) male water dragons will display alternative social
tactics, and 2) social tactics will be conditional depending on
resource holding potential related to overall body-size/dimensions
and body condition. We report evidence to support both
hypotheses. Because we documented spontaneous aggressive
takeover of territories during our study (see below) and we
prompted these experimentally, we also describe the behavioral
dynamics of aggression during this process.
This research was conducted with the permission of the New
South Wales National Parks and Wildlife Service (permit #
S12905) and the Animal Ethics Committee, University of Sydney
Study Population and General Methods
Physignathus lesueurii is a large (up to 1 kg, 304 mm snout-to-vent
length=SVL) semiaquatic, diurnal agamid that occurs in riparian
habitat throughout eastern New South Wales and southern
Queensland [23,27]. Adults are at least four years of age .
Water dragons are strong swimmers, and enter the water routinely
to escape predators, and at night . They feed primarily on
terrestrial insects , but we also observed them eating aquatic
crustacean and small lizards (Scincidae).
We conducted this study on the grounds of the Flynn’s Beach
Resort in Port Macquarie, NSW (31u 269 S latitude, 152u 559 E
longitude) from 12 Sept –30 Nov, 2009, during the Austral spring
when eastern water dragons are reproductively active [23,24,29].
Water dragons occur throughout the resort grounds (8980 m2),
but are highly concentrated along 0.2 km of Wright’s Creek which
bisects this site. Microhabitat used by water dragons consisted of
naturally vegetated riparian areas as well as lawns, plant beds,
sidewalks, and even tiled swimming pool decks. Here, lizards were
habituated enough to humans that they tolerated approach to
within 2 m, but retreated when approached more closely. We
captured 111 adult lizards by noose from 15–30 Sept, 2009, and
then recaptured some of them once or twice. This number of
lizards per 0.2 km of creek length extrapolates to an even higher
estimate of density (555 lizards/km) than previously reported
(138–215 lizards/km of shoreline) . Lizards were marked by
painting numbers on each side of the dorsal torso using white
water proof nail polish. Worn numbers were retouched during
recaptures, but none of the lizards lost their numbers through
We determined the sex of individuals by 1) everting hemipenes,
2) palpating the abdomen for enlarging ovarian follicles, 3)
inspecting head dimensions (larger in males), and 4) recording
ventral coloration (more red-orange, red-black in males) . We
marked 36 females (SVL=146–223 mm) in which we palpated
enlarging ovarian follicles. We marked 38 males (SVL=200–
271 mm) with hemipenes that were secreting seminal fluid. Eight
of these males were not observed on the study site after marking,
but three of them moved a short distance onto property adjacent
to the resort grounds. The remaining 30 males (SVL=238–
271 mm) were present throughout the study. We also marked 12
lizards (SVL=192–214 mm) that lacked enlarging follicles, or
eversible hemipenes, and had no more than 10 ventral scales that
were light orange. We classified these lizards as immature,
although they could have been mature females that did not
produce eggs during the 2009 season . There were also
numerous (100–200) smaller lizards (60–160 mm SVL) through-
out that we did not capture or mark. Previous estimates 
indicate that water dragons of this size are juveniles up to 4 years
old. Therefore, the larger, reproductively active adults that we
focused on were considerably older.
Social and Spatial Behavior
We mapped the study site to scale by recording distance and
compass measurements among prominent, permanent landmarks
(sidewalks, fence and light posts, trees, creek shore-line). The
location of each mapping marker was determined using measure-
ments among a minimum of five adjacent markers to yield a
composite map accurate to the nearest 2 m. To determine use of
space by mature females and males, we recorded at least one
census of the entire study site each day from 24 Sept–26 Nov
(N=58 total censuses), except for 10 d when inclement weather
prevented lizard activity. Censuses involved walking a routine path
through the entire site and recording the location of all marked
adults on maps. Daily census sightings were combined with the
beginning and ending points of focal observations (described
below) to determine the home ranges of individual lizards using
the minimum convex polygon method [30–32]. The mean
number of sightings used to map home ranges/territories was
28.8 (62.0) for females, 87.1 for territorial males (63.2), and 32.9
(63.6) for non-territorial males (social status defined below). We
used a planimeter (Planix 2000) to measure the areas and spatial
overlap of home ranges/territories, and the linear interface of
these with Wright’s Creek.
One of us (TAB) also recorded the behavior of lizards during
focal observations . Focal observations involved recording all
of the displays and aggressive encounters with conspecifics of both
sexes initiated by subject lizards . Although lizards at this site
were not overtly affected by human presence, we recorded focal
observations when human disturbance was minimal. Each
observation session lasted 20 min, except for a few (,5%) that
were ended 1–5 min earlier because focal lizards were lost from
view under thick vegetation. We recorded a minimum of five focal
observations during baseline social conditions on separate days on
30 mature males, and one focal observation on each of 17 mature
females. We used principal components analysis (PCA) with
Variamax rotation of rate of patrol (m/h), total displays/min,
aggressive encounters initiated with rival males/min, and percent
intrasexual encounters won or tied to further examine behavioral
variation among these 30 mature males.
We recorded nine morphometrics that have been associated
with success and performance in agonistic contests in other lizard
species [6,34,35]. These were: SVL - the tip of the snout to the
vent along the ventral midline, tail-length – posterior tip of the
Alternative Social Tactics in Male Water Dragons
PLoS ONE | www.plosone.org2August 2012 | Volume 7 | Issue 8 | e41819
tail to the vent (both 61 mm), total body mass (65 g), three
head dimensions 60.1 mm (width - at the jaw articulation where
it is widest, length - from the tip of the upper jaw to the anterior
edge of the tympanum, depth - from the top to the bottom
behind the eyes where greatest with the jaws held closed), length
of the hind- and front legs - both on the right side from the
anterior insertion on the torso to the distal end of the longest
digit when the limb was held at a right angle, and the cumulative
length of the three longest dorsal crests on the head. We also
recorded the number of scars. The residuals of a regression of log
SVL on log total body mass (F1,29=22.08, P,0.0001, r2=0.44)
was used as an index of body condition.
We first summarized variation among mature males in their
absolute size and body dimensions by calculating principal
components analysis on nine measurements not corrected for
body size. Because behavioral data indicated that mature males
adopted two distinct social tactics (territorial and non-territorial;
see Results below), we used non-paired t-tests to compare
morphometric factor scores on the nine non-size-corrected
measurements of males in these two social categories. All body
dimensions were positively correlated with SVL (r- values=0.382–
0.864, P values=0.0372,0.0001) except tail length (r=0.012,
P=0.948). Therefore, to examine the possibility that territorial
and non-territorial males showed allometric variation, we correct-
ed for variation in body size by regressing eight log-transformed
body dimensions on log-transformed SVL and calculating the
residuals . We then calculated PCA on the residuals of these
eight variables, and compared the factor scores for the size-
corrected measurements of territorial and non-territorial males.
Spontaneous Territory Takeovers and Removal
Before we could perform removal experiments (see below) to
test whether alternative behavioral tactics displayed by water
dragon males are fixed or plastic, we observed two spontaneous
takeovers of territories where a previously non-territorial male
challenged, defeated, and evicted a male territory owner for which
we had previously recorded baseline observations for both males,
and recorded observations during and following the eviction. We
then partially mimicked these instances by conducting 11 trials
where we removed a territorial male (a different individual in each
trial) at 1400–1600 h and kept him off site for 2 d. Removed males
were maintained in damp, low light conditions to mimic cool,
cloudy, rainy field conditions when water dragons are inactive.
From 0730–1500 h during the 2 d removal, we recorded at least
three, 20-min focal observations on all of the mature males
adjacent to the territory of the removed male. After nightfall on
the second removal day (2000–2100 h), we returned the removed
male to his original territory. On the following day (0900–1500 h)
we recorded at least three, 20-min focal observations on the males
that had been present during the removal, plus focal observations
on the reinstated territorial male. We used repeated-measures
analysis of variance (ANOVA) to test for behavioral differences
during the three phases (pre-removal, during removal, reinstate-
ment) of our removal experiments.
Male Social Behavior and Alternative Tactics
During baseline social conditions, 98% of displays given by
males were stereotypical movements of the head alone. Head
raises involved lifting the head abruptly to a 45u angle, which was
almost always followed by bobbing it (=head bobs) vertically as
many as eleven times in succession . Much less often, males
raised the head gradually at first but then abruptly jerked it
upward to its highest angle. Dorsal crests on the head were usually
erected during head displays. Males also occasionally displayed by
rolling their tails vertically from the tip to base in a smooth motion,
or by lateral movements of the slightly raised tail.
More aggressive displays were infrequent during baseline
conditions, but became more common during escalated social
encounters that characterized unstable social conditions (described
below). Males sometimes began escalated encounters by charging
an opponent while running on only the hind legs and flailing their
front limbs (bipedal charges). More usually, encounters began with
‘‘full shows’’ which involved tilting the head upward at a 30–40u
angle while holding the mouth open partially, extending the
dewlap, slowly elevating on all four legs and compressing the torso
laterally and then lowering. Males sometimes performed only one
full show which they held for a few seconds before lowering, but
other times they elevated and lowered as many as four times in
succession. When rival males approached more closely (#5 body
lengths), opponent males elevated and laterally compressed their
torso while running sideways toward their rivals (3–15 steps) using
a stiffened gait and with the dewlap extended (=display runs).
Under baseline social conditions, 14 of the mature males were
sighted on all (100%) censuses, which was statistically more
frequent (F=2,62=113.6, P,0.0001) than the mean (x=56.9%,
SE=3.6) for the other 16 mature males. A significant (P,0.0001)
PCA on the frequency of social behavior patterns revealed two
factors that together explained 83.7% of the total variance in
male behavior. Rate of patrol, total displays/minute, and percent
encounters won or tied loaded together on Factor 1 (58.8% of
total variance), whereas only intrasexual encounters initiated/min
loaded on Factor 2 (24.9% of variance) (Table 1). The mean
score for Factor 1 was higher (t1,28=8.29, P,0.0001) for the 14
males that were sighted on all censuses, whereas the means for
Factor 2 (frequency of intrasexual aggression) were not different (t
1,28=0.79, P=0.438) in these two groups of males. Based upon
these marked differences in Factor 1 scores and differences in
sighting frequencies on censuses, both of which we interpret as
indications of the extent to which males were advertising
ownership to rivals, we classified males as territorial (N=14)
and non-territorial (N=16) for subsequent analysis.
Comparison of individual behavioral variables revealed that
average rate of patrol by territorial males was twice (U1,28=183,
P=0.0003) that of non-territorial males (Table 2). Rates of head-
raise and head bob displays, were each 6.7 times those of non-
territorial males (U1,28- values=216.0, 210.5, respectively, both
P–values ,0.0001), and the frequency of all displays pooled by
territorial males was also higher (U
Territorial males usually either repelled non-territorial rivals, or
Table 1. Principal component factor loadings for social
behavioral variables during baseline conditions.
Aggresssive encounters Initiated/min
% contests won or tied0.912 0.120
Parenthetical numbers are the percent of total variance explained by each
factor. High loading factors are in boldface.
Alternative Social Tactics in Male Water Dragons
PLoS ONE | www.plosone.org3August 2012 | Volume 7 | Issue 8 | e41819
tied in contests with neighboring territory owners on shared
borders (Table 2). By contrast, non-territorial males lost almost all
encounters with territorial males (except during spontaneous
takeovers described below), but prevailed in encounters with
smaller juvenile males.
We anecdotally witnessed only five instances of short chases
between females. However, neither aggression nor advertisement
displays by females were observed during focal observations, even
though they routinely basked within 5 m of at least one consexual.
A significant (P,0.0001) PCA on nine non-size-corrected
measurements revealed three factors that together explained
80.7% of the morphometric variation among mature males
(Table 3). SVL, all three head dimensions, front leg length, body
mass, and the cumulative length of the three longest dorsal crests
all loaded highest on Factor 1, which explained 54.9% of the total
variance. Hind leg length and tail length each loaded highest on
Factors 2 and 3 (Table 3) and explained 13.7 and 12.2% of the
total variance, respectively. The mean score for Factor 1 was
higher (t1,29=2.29, P=0.030) in territorial males (x=0.42,
SE=0.15) than non-territorial males (x=20.37, SE=0.29),
whereas the two groups of males had similar mean scores for
Factor 2 (t1,29=0.47, P=0.65) and Factor 3 (t1,29=1.68,
P=0.104). Estimates of body condition were higher (t1,29=2.50,
P=0.019) in territorial (x residual score 61.0 SE=0.4660.29)
than non-territorial males (20.4260.21).
A significant (P,0.008) PCA analysis on eight size-corrected
measurements also revealed three factors that together explained
66.4% of the total morphometric variation among males. All three
head dimensions, the cumulative length of the three longest dorsal
crests loaded highest on Factor 1 which explained 34.3% of the
total variance (Table 3). Hind leg length alone loaded highest on
Factor 2 explaining 17.2% of variance, and tail length and front
leg length loaded on Factor 3 which explained 14.8% of the
variance (Table 3). There were no significant differences in any of
the factor scores (t’s=0.52–1.29, P’s=0.21–0.61) between territo-
rial versus non-territorial males.
Use of Space and Intersexual Interactions
Areas occupied by all mature males included some shoreline of
Wright’s Creek, but the relative amount of shoreline was higher
(F2,62=8.26, P=0.0007) in non-territorial males than both
territorial males and females (Table 4). Male social tactics and
sex influenced the amount of area used by water dragons
(F2,62=16.5, P,0.0001). Non-territorial males used 1.7 and 4.2
times more space than territorial males (P=0.015) and females
respectively (P,0.0001; Table 4). Male territories were larger
(P=0.014) than female home ranges. Home ranges of females
partially overlapped with as many as eight other female home
ranges, resulting in very little home range area exclusive of other
females (Table 4). Territorial males had 2–6 territorial neighbors,
but they controlled exclusive use of more than 75% of their
territory from these neighboring rivals. By contrast, portions of the
home ranges used by non-territorial males were overlapped by 2–
13 other non-territorial males as well as 2–7 territorial males, such
that none of the area used was exclusive of space used by same-sex
rivals (Table 4).
Home ranges of 17 (of 36) females were overlapped by one
territorial male, whereas nine, seven, and three females were
overlapped by two, three, and four territorial males respectively.
Similarly, 2–8 non-territorial males partially overlapped the home
ranges of all 36 females. The cumulative result was that at least
90% of all of the area occupied by females was overlapped by
several mature males. Despite extensive spatial overlap by both
classes of males (see below), females interacted much more
frequently (t1,28=4.18, P=0.0003) with territorial males (x
encounters/hour 61.0 SE=1.1560.13) than non-territorial males
(0.3260.15). The most common type (98%) of interaction between
the sexes involved males approaching a female to within one body
length and the female lowering her head, arching both her back
and proximal tail dorsally while holding the distal end of the tail
stiffly on the ground. Females gave this display either when they
remained in place or when walking slowly forward as the male
approached. Males usually only made brief contact with displaying
females and then moved past them. During focal observations, we
observed one attempted copulation and three instances when a
male and female sat for several minutes with one lizard partially
superimposed over the other. During censuses, we observed 22
other instances of intersexual physical contact, and all of these
involved territorial males.
Spontaneous Takeover of Territories
We recorded two spontaneous takeovers of territories by males
that were not territorial at the beginning of our study. In both
instances, the non-territorial males engaged a territory owner and
defeated him during one highly aggressive encounter involving
prolonged (up to 1 h) full shows, display runs, bipedal chases
(described above), and especially, intensely physical fights charac-
terized by bites that produced injury (described below). As a
consequence of these single decisive fights, winners increased rates
of patrol, and head displays 1.0–2.8– fold respectively, whereas
these behavior patterns decreased 2.3–4.3-fold in the losers. In
both instances, the non-territorial males that took-over territories
were larger in snout-to-vent length and mass, and both males held
their usurped territory for the remainder of the study (35 and
51 d). The expelled males remained in these same areas, but
adopted socially subordinate behavior at least until the end of our
Male Removal Experiments
In 10 of 11 removal trials, one overlapping non-territorial male
exhibited marked shifts in social tactics. Two non-territorial males
responded similarly in the other trial. These initial responses began
within 2 h of first sunlight on the first removal day. Responses
involved marked increases (Table 5) in rates of display (repeated-
(F1,11=12.85, P=0.0002). The single respondent in ten trials
quickly prevailed using mostly displays and bipedal charges in
Table 2. Behavior of male water dragons during baseline
Patrol (m/h) 13.3 (1.8)*26.4 (3.2)
Aggressive encounters/min0.021 (0.004)0.033 (0.009)
Head-up displays/min0.03 (0.01)*0.18 (0.02)
Head-bob displays/min0.13 (0.04)*0.81 (0.10)
Total displays/min0.16 (0.05)*1.01 (0.46)
% wins + draws7.2 (2.9)*90.4 (4.9)
Data are means 61.0 standard error. Asterisks indicate statistically significant
differences (P – values=0.05–0.0001) between territorial and non-territorial
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encounters with other non-territorial males, and increased
(F1,11=14.21, P,0.0001) the frequency of encounters that they
won or fought to a tie to establish occupancy of the territory by
1200 h of the first removal day (Table 5). In the other trial, two
non-territorial males (snout-to-vent lengths=237 and 256 mm)
fought intermittently from 1330–1530 h of the first removal day
before the larger male prevailed and the smaller male withdrew.
On the second removal day, all of the newly established males
continued their higher rates of display and patrol, and winning or
at least fighting to a draw with all rivals.
Nine different non-territorial males responded during the 11
removal experiments. Two of these were animals that had very
large home ranges that partially overlapped the territories of
several males, and each responded in two and three removal trials
respectively. They contested one another in the trial where two
males responded (described above). Seven different non-territorial
males responded in the other trials. There were nine additional
mature non-territorial males that also overlapped the territories of
removed males, but these immediately fled in all 18 interactions
with respondent males, and their very low rates of prior display (x
displays/min 61.0 SE=0.0960.02), did not change (t1,14=0.92,
P=0.38) during removals (x=0.1260.04). These non-responding,
non-territorial males were smaller in SVL (t1,14=2.36, P=0.03),
total mass (t1,14=4.43, P=0.004), all three head dimensions
(t’s1,14=3.09–3.86, P’s=0.001–0.007), and had lower body
condition indices (t1,14=5.05, P=0.001), than responding non-
territorial males. They did not differ significantly (t’s1,14=0.13–
1.51, P’s=0.15–0.9) in mean tail length, length of the front- and
hind-limbs, and the cumulative length of the longest three dorsal
Reinstatement of original territory owners elicited the highest
intensity contests that we observed. Aggression began as soon as
original owners first confronted new owners when removal sites
became sunlit (0730–0800 h). Contests began with males ap-
proaching opponents giving head displays, full shows, display runs,
and/or bipedal charges (described above). Aggression escalated
with males confronting one another, snout-to-snout within one
head length, and then butting the sides of their heads against that
of their rival. In this position, each male pushed forcefully in
opposite directions using the torso, limbs, and tail to gain leverage
and traction (Figure 1). Both males were sometimes able to bite
and clamp on their rival’s head or front limbs, and/or forcefully
twist their opponent and even hold him underwater when fights
occurred along the shoreline. Fighting males separated intermit-
tently (one body length or less) during which they breathed rapidly
and deeply before re-engaging. Most such contests lasted 30–
40 min, but the fight between two rival non-territorial males on
day 1 of one trial (described above) continued intermittently for
2 h, and the most intense contest that ensued following
reinstatement of an original owner continued uninterrupted for
160 min. Although these intense fights were the consequence of
removal/reinstatement experiments, a higher number of scars
(F1,62=19.04, P,0.0001) in both territorial (x number of scars
61.0 SE=6.861.2) and non-territorial males (x=4.761.1) than
females (x=0.660.4) indicates that fights among males that
produce injuries are common in this population.
Upon their reinstatement, in 9 of 11 trials the original territory
owners defeated and repelled the males that changed to using
territorial tactics, causing rates of patrol and display by male losers
to decrease (P=0.01 for both tests, Table 5). In two trials, the
Table 3. Principal component factor loadings for male water dragon morphometric variables.
Snout-to-vent length 0.9150.0950.087–––
Head width 0.891
Head length0.936 0.041
Cumulative dorsal crest length 0.7920.114
Hind leg length0.3500.7830.384
Front leg length0.6960.2560.343
Parenthetical values are the percent variance explained by each factor. High loading factor scores are in boldface.
Table 4. Use of space by territorial and non-territorial male, and female water dragons.
Spatial Variable Non-Territorial Males (N=16)Territorial Males (N=14) Females (N=36)
Area (m2)731.9 (154.1) *434.9 (40.9)+
% area exclusive from consexuals0(0.0) 78.5 (5.1)15.2 (3.8)
Ratio of home range shoreline to
*0.34 (0.46)*0.31 (0.22)
Data are means 61.0 SE. Asterisks indicate statistically significant differences (P,0.05) between adjacent columns. The single plus sign indicates a significant difference
between territorial males and females, double plus sign indicates a statistical difference between non-territorial males and females.
Alternative Social Tactics in Male Water Dragons
PLoS ONE | www.plosone.org5August 2012 | Volume 7 | Issue 8 | e41819
newly established owners defeated and repelled the original
owners, and continued to occupy their territories for at least the
remainder of the study (only 5 and 11 d because these trials were
conducted toward the end of our study). In one of these instances,
the removed male’s lower jaw was fractured at the mandibular
symphysis and the surrounding soft tissue was infected. This male
did not vigorously contest the new owner when we reinstated him.
In the other trial, the contesting males were identical in SVL (both
248 mm) but the newly victorious male was 10 g heavier. The
contest that ensued during the reinstatement phase of this trial was
the longest (160 min) bout of aggression that we observed.
Theory addressing habitat settlement in territorial species often
assumes that individuals gain territories by either inheriting them
following mortality of previous owners, or by colonizing vacant
areas [20,36,37]. Examples of mortality-induced territory inher-
itance are well documented in a variety of vertebrate taxa (e.g.,
birds [38–41], fish , lizards ). Territory acquisition by
forcible eviction of current territory owners, like that observed
twice during only a short study on water dragons, is much more
rare but has also been documented in insects [42–45], fish ,
birds [20,21,46], mammals , and at least one lizard .
Together, our observations of spontaneous evictions of territory
owners, rapid territory takeovers in response to experimental
removals, high baseline rates of advertisement display by territory
owners, as well as prominent scars on large males all indicate that
intrasexual male competition is intense in this high density
population of water dragons, which likely makes the costs of
territory maintenance very high.
Marked variation in the baseline behavior of mature males
clearly supports the hypothesis that sexually mature water dragon
males utilize two social tactics (territory defense and non-territorial
satellite behavior). Moreover, territory takeovers by aggression,
both spontaneously and in response to removals, show that
alternative male tactics are plastic. A significant role of absolute
size in RHP is indicated by the larger snout-to-vent length and
head dimensions of territory owners under baseline conditions as
well as the outcome of contests provoked by removals in relation to
size. There was no indication that the head dimensions of territory
owners were allometrically larger than those of non-territorial
males; resource-holding potential simply increases as males grow
isometrically. Reacquisition of territories by original owners in
most trials may also be promoted by prior residency advantages
[49,50]. Future analyses of the behavioral dynamics during the
prolonged interactions that we recorded will evaluate the extent to
which asymmetries in male size and prior residency may explain
contest resolution in water dragon males in relation to the
predictions of game-theory models (TA Baird, TD Baird, & R
Shine unpublished data).
Although field studies on agamid social behavior are still sparse,
there is growing evidence of the evolution of alternative male
tactics in this clade. Male defense of territories has been reported
in several species [51–54]. In at least two species where some
males defend territories, alternative tactics are suggested by the
observation that other individuals adopt subordinate behavior
patterns when they are near to defended areas [52,55]. Male-
biased sexual dimorphism in body dimensions [56,57] and
coloration  are also consistent with a role for sexual selection
in the social systems of still other agamids. Moreover, advertise-
ment displays involving stereotypical head movements, dewlap
extension, lateral compression and vertical elevation of the torso,
as observed in water dragons and other agamids, are similar to
those described for many new world sexually-selected iguanids
[59–61], and suggest intense sexual selection and the evolution of
male ART. Despite these general similarities, water dragons differ
from other agamids in the relative frequency that they use various
types of advertisement displays. The most frequent displays by
male water dragons involved head movements, whereas tail
displays (infrequent in Physignathus), are prominent in both jacky
dragons [62,63] and frillneck lizards . Interspecific variation in
display use may be a consequence of factors that influence signal
transmission and reception in the particular habitats occupied by
The primary benefit for males of defending territories during
the breeding season is access to receptive females . Consistent
with this prediction, territorial male water dragons interacted
more frequently with females that they overlapped than did non-
territorial males. Nonetheless, social dominance and interactions
do not necessarily equate with exclusive reproductive access in
squamate reptiles, including agamid lizards . For example, in a
population of ornate dragons, in which both males and females
defended territories, 25% of female clutches were fertilized by
multiple males, 65% of clutches were partially sired by males other
than the overlapping territorial male, and 35% of clutches were
partially fertilized by males having no observed spatial overlap
with females that they sired offspring with . Given the
extensive overlap of female water dragon home ranges by mature
territorial and non-territorial males, the distribution of reproduc-
tive success among males of this species in relation to their social
tactics remains an open question.
High chronic costs of territory defense in our population are
indicated by the frequent (,1 per min) advertisement displays,
intense contests that produce injuries, and spontaneous territory
Table 5. Responses by non-territorial water dragon males to
temporary removal and reinstatement of individual territorial
0.27 (0.07)* 1.81 (0.14)* 0.52 (0.17)
Patrol (m/h)15.5 (3.4)* 61.8 (7.5)*29.7 (9.3)
% wins + draws + 17.8 (7.2)* 79.4 (9.3)* 16.7 (11.2)
Data are means 61.0 standard errors. Plus signs indicate statistically significant
effects (Repeated measures ANOVA, P,0.001) of experimental phase. Asterisks
indicate statistically significant differences (P,0.05) between adjacent columns.
Figure 1. Male water dragons engaged in a prolonged
Alternative Social Tactics in Male Water Dragons
PLoS ONE | www.plosone.org6August 2012 | Volume 7 | Issue 8 | e41819
takeovers. When costs of territory maintenance are chronically
high, selection may favor mechanisms to reduce them [50,66,67].
One possibility is that high chronic defensive costs may select for
the evolution of signals requiring a range of energetic expenditure
and graded content (iguanians [16,68]; chameleonids ;
varanids ; other agamids [62,63]. Consistent with this
hypothesis, the most frequent displays by water dragon males
involved movements of the head, which likely require only low
expenditure of energy. More aggressive behavior patterns that
almost certainly require higher energy expenditure were given
only infrequently when social conditions were stable, but these
increased when social encounters intensified into highly aggressive
disputes over territory ownership.
The high density of water dragon males in relation to
preferred habitat (creek shoreline) appears to result in chronic
intense competition that probably exacts a high cumulative
energetic cost. On our site, competition among sexually-mature
males was intense enough to prevent several large individuals
from controlling territories having preferred shoreline. Instead,
these males adopted subordinate satellite tactics to remain
within this high-quality habitat, but remained poised to compete
aggressively for territories when opportunities arose. Territory
acquisition tactics included spontaneous aggressive challenges
which were sometimes successful in evicting territory owners,
perhaps because these territorial males had been weakened by
the high chronic costs of advertisement and defense imposed by
the intense level of chronic competition in this population.
Because water dragon males are long-lived, and both large size
and high body condition are correlated with their social status,
the chronic high energetic demands necessary to both sustain
peak physical condition and advertise/defend territory occupan-
cy may require males to cycle between aggressive (territorial)
and less aggressive (non-territorial) social tactics to manage their
life-time energetic costs. The most similar situation reported for
other lizards appears to be the density-induced shifts among
three conditional social tactics in male marine iguanas ,
which are also long lived and occupy habitats where high-
quality territories are limited [71,72]. Usurpation of territories
by evicting owners and cycling between alternative social tactics
also occurs in dense populations of long-lived birds. For
example, loons engage in intense, costly territorial contests,
and eviction of territory owners is common . Territory
acquisition by eviction is also common in song-sparrows that
survive several seasons and live at high density on islands from
which they do not migrate . Hence, shifting between low
aggression - low cost, and more aggressive - higher cost social
tactics may be an optimal strategy for long-lived sedentary
males where the demands of defending territories is chronically
high owing to the ever present large number of intrasexual
We thank M. Elphick, M. Greenles, A. Haythornwaite, S. Lafave, D. Pike,
T. Shine, and W. Unsell for valuable logistical support. We are very
grateful to the entire staff of the Flynn’s Beach Resort and Blue Water Bar
and Restaurant for access to the study site. Special thanks to A. Greenway
and P. Kemsley whose enthusiasm and keen appreciation of water dragons
contributed greatly to this project.
Conceived and designed the experiments: TAB TDB RS. Performed the
experiments: TAB TDB RS. Analyzed the data: TAB TDB RS.
Contributed reagents/materials/analysis tools: TAB TDB RS. Wrote the
paper: TAB TDB RS.
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