This allowed us to compare across cages differing in total number. While this lacks some sensitivity regarding the animals just above the lowest rank or below the highest rank, this would be sensitive to a large group effect size. After 4 days each animal had an average rank score. This experiment followed the same protocol as the within cage tube test. Between E2 and E3 the home cage was cleaned, animals were moved to a new cage and all bedding was replaced to remove any odors identifying the previously dominant animal in the group.
E3 and E4 were carried out 1 and 24 h, respectively, after cage change. Specifically, if an animal had a rank of 3 before the bedding change and 4 after, this was recorded at 1.
If an animal had a rank of 4 before the bedding change and 4 after, this was recorded as 0. Each encounter consisted of one animal and a cage-mate placed on either side of the wire mesh, through which they could receive visual, auditory and olfactory information, but could not physically interact. The experiment was carried out under dim lighting conditions and each encounter lasted 1 h. Each individual animal met each of its cage-mates in such an encounter, with no animal having more than one encounter per day.
Scent marks made on absorbent filter paper were visualized under ultraviolet light and outlined by pencil. Analysis was modified from Arakawa et al. Marks greater than 4 squares in size were excluded in order to differentiate general urine pools from specific scent marks.
The dominant animal in the encounter was designated as the animal that scent marked more than its opponent. During the experiment animals had restricted access to water see above and were individually trained to locate and consume freely available water, provided though a metal drinking spout in a s session in a Phenotyper arena Noldus Information Technology.
Within three daily training sessions all animals had successfully learnt that water was available as indexed by visual confirmation of initiation of water consumption within 30 s of drinking spout presentation.
Following training, a test session was performed in which all animals from a given cage group were placed in the Phenotyper arena and the same time and drinking spout was introduced. The duration each animal spent drinking was then scored manually offline. Each animal was assigned a rank depending on the duration of water access obtained in the first s and the full s. One individual died between scent marking and competition for water access tasks. Two separate tests of olfactory function were used, one using social odors and another using non-social odors.
Animals were then returned to the arena, with the odor in place. Arena set up as above with the addition of 2 cm of clean sawdust on base of arena.
A cookie was submerged under sawdust. Animals were placed in the opposite quadrant to the cookie and the quadrant was changed for each successive animal. In addition, latency to find and begin eating the cookie was recorded manually. Trials ended once animal began to eat cookie. All statistical analysis was carried out using SPSS Group housed male mice establish a linear, transitive Williamson et al. Strikingly, given our previous findings McNamara et al. Cdkn1c over expression does not affect dominance behaviors within the home cage group.
These results are not caused by an inability to perform the tasks, as a clear transitive hierarchy was apparent in each measure of social dominance. For instance, a linear, transitive, hierarchy was apparent for an average of 3.
A clear hierarchy was also apparent in Specifically, tube test vs. Fisher r-to-z transformations confirmed these group differences, as the correlation coefficients seen in groups of Cdkn1c BACx1 and their WT cage-mates were significantly different from the correlation coefficients between in groups of Cdkn1c BACLacZ animals and their WT cage-mates Tube test vs. Presence of a Cdkn1c BACx1 male destabilizes the established social hierarchy. In groups containing Cdkn1c BACx1 males and their wild-type WT cage-mates there was no correlation between rank in the tube test and rank in the water access task in the first s A , nor rank in the scent marking task is correlated with rank in the water access task in s B.
Additionally, rank in the scent-marking task correlated with rank in the water access task in s D. We hypothesized that the loss of stability between different measures of social dominance may be as a consequence of a greater propensity of Cdkn1c BACx1 animals to challenge the established hierarchy.
Therefore, we would expect these animals to have a more variable rank in the cage hierarchy across time. Dominancy relationships, while generally stable, can change under pressurizing circumstances Cohn et al.
One such circumstance is when the odor cues are removed e. In groups of Cdkn1c BACLacZ and WT animals, rank fluctuation did not differ when olfactory cues indicating the dominant animal were removed A , left nor when the environment remained stable A , right. This was not the case when the environment remained stable B , right. This indicates that in the absence of odor communicants indicating the dominant animal Cdkn1c BACx1 animals are more likely to change rank.
The maintenance of social status within a specific territory is an important aspect of social behavior. Both wild-caught and laboratory mice establish territories Anderson and Hill, ; Hurst, ; Fuxjager et al.
This scent marking behavior positively influences male reproductive success Thonhauser et al. A more detailed examination of these data revealed that WT animals increased scent marking toward i. This indicates that the presence of Cdkn1c BACx1 animals may elicit a differential territorial behavior response in WT cage-mates. Olfactory response to social and non-social odors is normal in Cdkn1c BACx1 mice.
There was no difference in time spent exploring a social odor A. Latency to detect a non-social odor was similar between all groups B.
A stable social hierarchy normally benefits group-housed animals Ebbesen et al. The correct expression of imprinted genes is critical for a number of aspects of physiology Cleaton et al. Although our previous work indicated that male Cdkn1c BACx1 mice were more dominant as measured by tube test encounters with unfamiliar WT males McNamara et al.
However, we find that presence of Cdkn1c BACx1 animals within a group leads to instability of the normal social hierarchy, as indicated by greater variability in social rank within the group over time and an increase in territorial behavior in WT cage-mates. These abnormal behaviors led to an increased incidence of fighting, and suggest that normal expression of Cdkn1c is required for maintaining stability of the social group.
In contrast to our previous finding that Cdkn1c BACx1 mice were more successful in the tube test when paired with unfamiliar mice McNamara et al.
Two additional tests of social dominance behavior, competition for resource and a test of scent marking, confirmed this finding showing that Cdkn1c BACx1 animals were no more likely occupy the top rank position in the cage hierarchy than WT cage-mates. These three separate tests did reveal that groups containing one or more Cdkn1c BACx1 had a much less stable dominance hierarchy. Specifically that the rank of an individual changed between test-days, as indicated by an absence of correlation between the three different measures.
In contrast, and as is expected Wang et al. Importantly, the lack of a correlation between measures in cage of Cdkn1c BACx1 and WT cage mates was not caused by an inability to perform the tasks, as a clear transitive hierarchy was apparent in each measure of social dominance. To test whether the stability of dominancy in a social group is disrupted by the presence of mice over-expressing Cdkn1c , we carried out a further manipulation.
In contrast, Cdkn1c BACx1 animals were significantly more likely to change rank after an environment change. This was not statistically significant and repetition with a larger cohort size may provide further insight. It not possible, using these experiments to conclude definitively the origin of the disruption of the social hierarchy, and this deficit may not necessarily manifest exclusively in social behavior.
Nonetheless, these direct, and indirect, actions of elevated Cdkn1c expression on territorial behaviors and social stability may underlie the observed increased incidence of signs of in-cage fighting. Group living is enriched in both frequency of observation and complexity in Eutherian mammals in comparison to monotremes and marsupials Muller and Thalmann, This has occurred in conjunction with an expansion in neocortical neuron number Cheung et al.
A comparison of marsupials, rodents and primates found that a larger brain size was associated with social play prevalence, across taxa Iwaniuk et al. Concurrent with this expansion of neocortical complexity and social play is the emergence of genomic imprinting, and a potentially function role for imprinted genes and the change in neocortical organization has been posited Keverne et al.
Monoallelic expression of Cdkn1c and the differential methylation of the CpG island encompassing its imprinting control region also emerge at this time Suzuki et al. This suggests a functional role for acquisition of monoallelic expression of Cdkn1c in neocortical expansion and group living, in Eutherian mammals.
Social behaviors have long been a suggested site at which genomic imprinting may exert influence Haig, ; Brandvain et al. This study provides further clear evidence in support of this idea generally but indicates that, at least for Cdkn1c , this is not due to effects on social dominance per se.
Instead the findings presented here indicate a role for Cdkn1c in the maintenance of a cohesive social unit. Moreover, whilst further work is required, when coupled with the previous findings for Grb10 Garfield et al.
GMN performed the experiments and analyzed the data. RJ provided the materials. GMN and AI wrote the manuscript. GMN declared her affiliation with Frontiers, and the handling Editor states that the process nevertheless met the standards of a fair and objective review. The other authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
We thank Simon J. Tunster for his help in developing and maintaining the transgenic lines. There were significantly more signs of severe in-cage fighting fresh cuts along flanks or in ano-genital region observed on at least one occasion in cages containing animals over-expressing Cdkn1c and their wild-type cage-mates compared to cages of Cdkn1c BAClacZ animals and their wild-type cage-mates.
Whenever possible, we selected categories on the basis of their predominance in terms of behavior, or their prevalence across the global range of a species. In variable or wide-ranging species, we ensured that predictors and response variables were drawn from the same or geographically closest population. Because communal signaling and the underlying degree of cooperation among individuals may be influenced by latitude and climatic conditions Rubenstein and Lovette, ; Jetz and Rubenstein, ; Odom et al.
Species lacking adequate data were excluded for the relevant analyses, leaving a sample of species for nested taxonomic models. After further excluding species for which no published genetic data yet exist, we retained a sample of species for phylogenetic mixed models. For further details of hypotheses and data collection methods, see Appendix A in Supplementary Material; for a complete list of species and sources of information, see Appendices B, C in Supplementary Material.
In this study, we provide the first global assessment of communal signaling, territoriality, and social bond duration across the world's birds. The scale of this assessment raises a number of challenges, not least because a large proportion of bird species remain poorly known.
Nonetheless, we argue that sufficient information is now available to assign almost all species to a useful classification system.
To achieve this goal, we used multiple strands of evidence, including direct observations and extensive unpublished information from sound archives and expert field ornithologists. Given the rapid pace of recent ornithological exploration in remote regions, most bird species—aside from a handful of extreme rarities—are now familiar to fieldworkers or birding guides at particular localities where information gathered on repeated visits can provide insight into territorial and social behavior through time.
This influx of information is not readily available in published literature, but allows many species previously considered data deficient to be categorized with greater confidence. For example, Cacicus koepckeae is excluded from previous literature-based analyses of communal signaling Odom et al. Where evidence was inconclusive, classifications were inferred partly from information relating to multiple close relatives, following standard procedures Wilman et al.
For communal signals, this type of inference was only used when there were strong grounds for doing so—for instance, when behavior was consistent across close relatives, backed up by circumstantial evidence such as field reports, sound recordings or videos. A similar approach was taken for life history attributes, with estimates of the duration of territory defense or social bonds often representing a best-guess when sufficient evidence was available from field observations, literature, and related species see Appendix A in Supplementary Material for full details and rationale.
Inferences were never drawn on the basis of phylogenetic relationships alone. Nonetheless, given the scale of our dataset, some lineages are almost certainly misclassified. A detailed summary of possible sources of error is provided in Appendix A of Supplementary Material.
To provide more information about variation in uncertainty, we assigned classifications of all species to four categories of data quality: A, high quality data based on published sources or strongly supported evidence from direct observations; B, medium quality data, including cases where the classification is very likely correct but largely based on field observations and reports; C, low quality data based on few observations, or unsubstantiated literature reports; D, absence of direct evidence.
Henceforth, we refer to A as the conservative dataset, B as the medium quality dataset, and C and D together as poor quality data. The degree of inference from congeners is reflected in these categories, from very low inference in A, and minor, supporting inference in B, to larger levels of inference in C. Classifications of data-deficient species D were entirely based on inference. Where we found a strong consensus from all strands of evidence, we scored data quality higher than where evidence was in conflict.
For example, golden whistlers Pachycephala pectoralis are reported to duet in captivity Brown and Brown, , but this behavior has not been detected in the field. Although this report may use a different definition of duetting to that employed in this study, it nonetheless increases the level of doubt about the lack of duetting observed in congeners, and thus we score most other Pachycephala species with an increased level of uncertainty.
Finally, because levels of uncertainty often differ for information on communal signaling and general ecology, we scored data quality for both signaling and ecological data separately. Inclusion of species in analyses depended on both signaling and ecological data meeting minimum standards.
Like all datasets of global scale, ours will undoubtedly benefit from further quality control and curation, and we hope to facilitate this process by archiving all data online in association with this article. Our analyses included a range of categorical behavior and life history variables, and continuous climatic variables extracted from geographical ranges. We assessed the effects of these factors on the occurrence and evolution of communal signaling using Bayesian binary-response mixed-effect models with logit link, implemented in the R package, MCMCglmm Hadfield, ; Hadfield and Nakagawa, To account for the potential effects of phylogenetic inertia, we adopted two complementary modeling approaches: 1 Bayesian taxonomic mixed models BTMM in which Order, Family and Genus were entered as nested random factors for all species, and 2 Bayesian phylogenetic mixed models BPMM , in which phylogenetic relationships were entered as a random factor, assuming a Brownian model of evolution.
We then re-ran the same models including significant predictors i. Only interactions with strong effects were included, following Gelman and Hill, see electronic Supplementary Material, Table S3. We ran three independent runs of MCMCglmm for all models models, each run for 1. After discarding a burn-in of 10 6 and a thinning of , the remaining samples constituted our posterior distribution for each chain.
Regression analysis such as BTMM or BPMM are informative about the ecological and social conditions favoring the evolution of communal signaling, but not about the direction of causality. To address this question, we used Pagel's Discrete algorithm implemented in BayesTraits Pagel and Meade, to test whether and how key traits have evolved in tandem across the same phylogenetic tree described above. The BayesTraits method uses a likelihood ratio test to compare a model in which the traits evolve independently independent model with one in which they evolve in tandem dependent model.
It also estimates the likelihood of evolutionary transitions among traits, assuming correlated evolution. These transition rates provide information about the relative stability of communal signaling with or without a particular life-history trait and vice versa. We used this approach to model how communal signaling was associated with territoriality, social bonds and mating system independent and dependent models in each case, 6 models in total. As the method can only be applied to binary traits, we dichotomized variables initially classified into three categories see Table S1.
We grouped traits in this way for two main reasons. First, it produces the most balanced sampling in a dichotomous framework because relatively few species are non-territorial or lack social bonds Figure 3. Second, this division most closely reflects existing hypotheses for communal signaling, which point to the importance of year-round territoriality Benedict, and social stability Logue and Hall, We ran each BayesTraits model for 1.
We ran two independent chains on each tree in the sample and combined samples resulting from all the runs, which constituted our posterior distributions for all parameter estimates. The trees were scaled by 0. This places the transition rates on a more usable scale and does not alter their relative values. For each chain, the marginal likelihood was calculated using a stepping stone sampler Xie et al. Figure 1. Data are aggregated from species within bird families and plotted at the tips of a maximum clade credibility phylogenetic tree.
Species with high uncertainty were removed prior to calculating family totals; data presented are therefore the same as our main analyses medium certainty ; patterns based on more conservative data are very similar see Figure S1. Our data confirmed that the geographical distribution of communal signaling is uneven, with greatest prevalence in western Amazonia, western and central Africa, Indo-Malaya, and northern Australia Figure 2A.
This distribution remains essentially unchanged when focusing on duetting species Figure 2B and conservative data Figure S2. In general, more duetting and chorusing species occur in the tropics Figures 2 , 3A. However, this pattern is largely driven by greater species richness in the tropics, and after correcting for the gradient in overall diversity we find that communal signaling peaks in the southern hemisphere Figure 3A.
Across the world's terrestrial biomes Olson et al. Figure 2. Global patterns in the distribution of communal signaling. Legend gives lower and upper values for each color. Figure 3. Spatial and environmental correlates of communal signaling in birds. We found that there is a strong phylogenetic signal in the occurrence of duetting and chorusing Figure 1 , with evolutionary history a dominant predictor of these traits in our combined full Table S2 , and final models Table S3.
This result is not surprising given that communal signaling is widespread in some clades e. However, the strength of phylogenetic signal may be inflated because we sometimes inferred shared character states among close relatives.
We note that 1 even a much weaker phylogenetic signal supports our assumption of a Brownian motion model of evolution in subsequent analyses, and 2 inference of shared character states among relatives does not affect our main results because we use both taxonomic BTMM and phylogenetic BPMM models to correct for phylogenetic non-independence when testing for associations with communal signaling. We found that territoriality, social bonds, cooperative breeding, latitude, and temperature range were all significant predictors of communal signaling in BTMMs Tables S2, S3.
No such association was found between habitat density or migration and communal signaling. However, the results of this hierarchical model should be treated with some caution because the BTMM contains only basic evolutionary information and may therefore fail to account adequately for phylogenetic non-independence pseudoreplication. Table S4 When we re-analyzed our data using BPMM, thus controlling for phylogeny, we found that communal signaling was significantly associated with territoriality and social bond stability, and that cooperative breeding was the only other significant but weaker correlate.
We note that territoriality and cooperative breeding are strongly correlated: a model predicting cooperative breeding as a function of territoriality has an overall estimated R 2 of 0.
In contrast, we found no evidence that latitude, habitat density, migration, or climatic variability were associated with communal signaling Tables S2, S3. Thus, although species with duets and choruses appear to be more prevalent in relatively stable tropical habitats Figure 2A with low annual variation in temperature Figure 3B and rainfall Figure 3C , these associations disappeared when we accounted for evolutionary relationships and life-history traits. Running BPMMs on conservative data produced very similar results, except that the relationship between cooperative breeding and communal signaling then becomes non-significant Table S2.
The fact that year-round territoriality and long-term social stability emerge as the most important predictors of communal signaling seems to make sense because many duetting or chorusing species share both these life history traits Figure 4. We also detected a significant interaction between territoriality and sociality Table S3. Specifically, our results suggest that having one or other of year-round territoriality or social stability has a very large effect on the probability of communal signaling, particularly in the case of year-round territoriality, but that it's less important to have both Table S3.
Figure 4. Associations between communal signaling and the stability of territoriality and social bonds. When we used BayesTraits analyses to examine evolutionary transitions between states, we again found strong evidence that communal signaling evolved together with year-round territoriality average log Bayes Factor A log Bayes Factor above two can be viewed as significant Kass and Raftery, Re-running these analyses on conservative data produced similar results Tables S4, S6.
The associations were slightly weaker although still very strong between communal signaling and both year-round territoriality average log Bayes Factor However, the significant association between communal signaling and cooperative breeding in the conservative dataset was much lower average log Bayes Factor 6. Figure 5 illustrates the flow between evolutionary states detected in BayesTraits analyses.
The arrows depicting this flow provide information about the stability of evolutionary states, with a low transition rate toward and a high transition rate away from a particular state indicating low stability of that state. For example, in C State 3 communal signals and weak social bonds is highly unstable, readily transitioning to State 1 solo signals and weak social bonds or State 4 communal signals and strong social bonds.
Similarly, the co-occurrence of communal signaling with cooperative breeding is unstable, readily transitioning to state 3, where breeding is non-cooperative but signaling is communal Figure 5D. Conversely, in B , State 4 communal signals and strong territoriality is stable, with balanced transitions to and from State 2 solo signals and strong territoriality , and State 3 communal signals and weak territoriality. The key points to take from Figure 5 are that q24 evolving communal signals with territoriality occurs 20 times faster than q13 evolving communal signals without territoriality; Figure 5B , and that q34 evolving communal signals with social bonds occurs 23 times faster than q12 evolving social bonds without communal signals; Figure 5C ; Table S5.
Figure 5. The co-evolution of communal signaling with life-history traits in birds. A Model illustrating four possible evolutionary states 1—4 between two traits and eight possible transition paths q. B—D Results of BayesTraits analyses testing the relative stability of communal signaling in relation to three other life-history traits: B territoriality, C social bonds, and D cooperative breeding. Actual values are provided in Table S5.
Our comparative analyses reveal that avian duets and choruses are significantly linked to both year-round territory defense and long-term social bonds, and only weakly associated with cooperative breeding. Furthermore, once we accounted for these relationships, as well as for shared ancestry, we found no evidence that latitude, climatic variability, habitat, or migration predicted the occurrence of communal signals.
These findings are corroborated by patterns of co-evolution among key life-history traits, which indicate that the presence of duets and choruses is most stable in association with territoriality and sociality. Thus, our results suggest that social factors predominate over environmental factors in driving communal signal evolution, and that the intensity and duration of ecological resource defense coupled with social stability provides the most general explanation for communal signal evolution.
The advantage of our broad-scale approach is that it offers sufficient statistical power to compare the effects of multiple factors. Our results shift the emphasis away from previously identified correlations with latitude, habitat density, migration, and climatic variability, perhaps because earlier studies were based on relatively restricted datasets sampled inconsistently across latitudes, climates, or major clades e.
This patchy sampling may generate different outcomes because associations vary across clades and contexts. For instance, while it is clear that for some species duets function partly in maintaining contact between pair members in dense habitats Mennill and Vehrencamp, , many duetting species occur in open environments, implying that habitat density does not provide a general explanation for communal signaling.
By sampling across the full span of environmental and life history variation in the world's birds, we have shown that correlations between communal signaling and environmental extrinsic factors are consistently subordinate to correlations with life-history intrinsic factors.
The importance of species ecology over environmental conditions in promoting communal signaling has not previously been reported, but fits the observation that duets are well known in temperate zone species with year-round territoriality e.
Rather than latitude or climate explaining patterns in signaling behavior, our results suggest that the uneven geographical distribution of communal signaling shown in Figure 2 arises simply because extended forms of territoriality and sociality are biased toward the tropics and southern hemisphere.
Indeed, this effect has been reported within evolutionary lineages: in the house wren Troglodytes aedon complex, for example, communal signals are common in the tropics where territories are defended year-round, but rare in the temperate zone where territoriality is seasonal Stutchbury and Morton, Selection is likely to favor long-term territoriality and social bonds at low and southern latitudes for a number of reasons Jankowski et al.
First, the climate is generally more stable than in the northern temperate zone Ghalambor et al. Second, the year-round availability of many ecological resources Huston and Wolverton, means that the territories of land-birds are worth defending over longer time-periods. Third, avian populations in the tropics often approach carrying capacity owing to reduced mortality and increased longevity Wiersma et al. Together, these factors place a high premium on the collaborative defense of ecological resources and group membership in the tropics, as territory or group vacancies are theoretically scarce and difficult to regain if lost.
In this context, individuals may signal communally to protect their positions in long-term coalitions, which in turn cooperate over signal production to deter rival pairs or groups. Disentangling the role of territoriality and sociality is challenging because communal signaling frequently occurs in conjunction with both year-round territoriality and long-term social bonds, which often occur together Figure 4.
This connection between long-term territoriality and social cohesion suggests that competition for ecological resources increases in parallel with competition over membership of partnerships or coalitions of individuals, perhaps helping to explain why avian duets appear to mediate both cooperation i. Nonetheless, phylogenetic mixed models revealed that the effect of territoriality was more than twice as strong as that of social bonds Tables S2, S3 , whereas cooperative breeding was only weakly associated, with an effect approximately one quarter that of social bonds.
Similarly, the evidence from evolutionary transitions suggests that the combination of year-round territoriality and communal signaling is a more stable state, and far more likely to co-evolve, than long-term social bonds coupled with communal signaling Figure 5 , Table S5. Furthermore, the BayesTraits analyses provide a clue that territoriality may be crucially important as a precursor to communal signaling, whereas long-term social bonds in pairs or groups may actually arise after communal signaling evolves—that is, pair and group bonds may result from selection for defending resources as a coalition, rather than vice versa.
Although the pattern of evolutionary transitions in our dataset is most consistent with this interpretation, we do not specifically reconstruct ancestral states, and so the question of evolutionary pathways to and from communal signaling requires further investigation. Many cooperatively breeding birds appear to signal as a group, and thus our finding that cooperative breeding is only weakly associated with communal signaling is perhaps surprising.
The reason for this outcome becomes clearer when considering the correlation between cooperative breeding and territoriality, which is both strong and largely explained by phylogeny. Of these two associated variables, our results indicate that cooperative breeding is a much weaker predictor of communal signaling, and thus when territoriality is accounted for in phylogenetic models, cooperative breeding has very little additional explanatory power.
This is particularly evident in our conservative analyses, where the association between cooperative breeding and communal signaling is removed altogether. Cooperative breeding is only one form of cooperation in birds, and almost all avian duets and choruses function at least partly in cooperative contexts Dahlin and Benedict, , suggesting that global patterns of communal signaling can shed light on the evolution of cooperation Logue and Hall, In highlighting the importance of long-term social bonds, our findings echo those of previous studies on duetting Benedict, ; Logue and Hall, Previous explanations for this effect are mainly based around the concepts of trust, reciprocity or kin selection Heide and Miner, Causes and Consequences of Biodiversity Declines.
Disease Ecology. Animal Migration. Sexual Selection. Territoriality and Aggression. The Development of Birdsong. Citation: Briffa, M. Nature Education Knowledge 3 10 Conflict is ubiquitous in the animal kingdom. In some cases it results in direct violence, injuries, and death. But in many examples conflicts are resolved through posturing, displays, and trials of strength. If natural selection produces individuals that behave selfishly, how could aggression without injuries evolve?
This article explains how the Hawk-Dove game and other models predict the evolution of aggressive displays. Aa Aa Aa. References and Recommended Reading Briffa, M. Hamilton, W. Extraordinary sex ratios. Science , Article History Close. Share Cancel. Revoke Cancel. Keywords Keywords for this Article.
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