Early Comers Become Owners: Effect of Residency Experience on Territorial Contest Dynamics in a Lycaenid Butterfly

A positive relationship between ownership and contest success is widespread among territorial butterflies. We tested the hypothesis that owners win simply because they have a longer experience occupying a given territory than do intruders in territorial butterflies. Using the lycaenid butterfly Chrysozephyrus smaragdinus , we staged contests between two males that had experienced different residency periods at the same contested territory, similar to owners and intruders in natural contests. We found that males that had occupied the contested territory for a longer period (a day) always defeated the shorter occupancy males (15 min). Therefore, residency period plays a key role in settling territorial contests. As residency confers advantages in a time-dependent manner, the mechanism of owner dominance could be an increase in motivation to fight as local familiarity increases. Moreover, this result predicts a population-level territorial dynamics. If residency period per se confers advantages in each contest, males arriving at a territory early in their adult season should acquire territorial dominance because they can remain there for a certain period with only a few rivals; late-appearing males do not have this advantage. As predicted, we found that males appearing at territory sites early in the season were more likely to hold their territories. This finding provides new evidence for the evolution of protandry in butterflies.     

Contest outcome in a territorial butterfly: the role of motivation

In many butterfly species, males compete over areas advantageous for encountering females. Rules for contest settlement are, however, largely unknown and neither morphological nor physiological traits can reliably predict the contest outcome. Here, we test the hypothesis that contests are settled in accordance with a motivation asymmetry. We staged contests between males of Pararge aegeria and after removing the resident, the non-resident was allowed (i) either to interact with a non-receptive female for 30 min (n = 30) or (ii) to spend 30 min alone in the cage (n = 30), after which the initial resident was reintroduced. The results show that males that had interacted with a female had a higher probability of becoming dominant and reversing contest outcome. Moreover, males that were faster to take over a vacant territory when the resident was removed were more likely to become dominant. Here, we show for the first time, to our knowledge, that frequent encounters with a mated female can increase male motivation to persist in a territorial contest in a butterfly. Further, we suggest that variation in intrinsic motivation reflects male eagerness to take over vacant territory. This study indicates that variation in resource value and motivational asymmetries are important for settling contests in butterflies.     

Agonistic display or courtship behavior? A review of contests over mating opportunity in butterflies

Male butterflies compete over mating opportunities. Two types of contest behavior are reported. Males of various butterfly species compete over a mating territory via aerial interactions until one of the two contestants retreats. Males of other butterfly species fly around larval food plants to find receptive females. Males of some species among the latter type can find a conspecific pupa, and they gather around it without expelling their rivals. Scramble competition over mating occurs when a female emerges from the pupa. Many studies have been performed on territorial species, and their contest resolution has often been understood from the point of view of contest models based on game theory. However, these models cannot explain why these butterflies perform contest displays despite the fact that they do not have the ability to attack their opponent. A recent study based on Lloyd Morgan’s Canon showed that territorial contests of male butterflies are better understood as erroneous courtship between sexually active males. In this paper, I review research on contests over mating opportunity in butterflies, and show that the erroneous courtship framework can explain not only territorial contests of butterflies but also why males do not determine the owner of a conspecific pupa.     

Territory Availability at Different Spatial Scales does not Affect Fighting Investment in Males of the Lycaenid Butterfly Strymon mulucha

In territorial species, rivals investment in fights over territories may increase when the availability of suitable areas for defense is low. This should occur because low territory availability may increase the costs to maintain and acquire territories. Although such process occurs in small spatial scales (local scale), territory availability in larger scales (regional scale) may also affect fighting investment, as losers should incur additional dispersing costs to find new territories. In this study, we used males of the hilltopping butterfly Strymon mulucha to evaluate the hypothesis that males should invest more in territorial fights when the costs to find new territories are higher (both at local and at regional scale). We timed male–male contests for territories located in 12 hilltops and measured male density per territory in each hilltop (local scale). We also quantified the distance between hilltops containing suitable areas for territories (regional scale). Male–male contests lasted 21 s on average, and copulations did not occur during the observations. The duration of contests was unrelated to the male density per territory or to the distance among hilltops, indicating that the investment in fights was unaffected by the availability of territorial sites, independent of the spatial scale. As male–male contests in S. mulucha are longer than the mean contest duration in other butterfly species and mating is extremely rare, we suggest that the value of each territory may be high enough to favor males that always invest as much as possible in contests.     

Sexual selection constrained by life history in a butterfly

Trait evolution via sexual selection has traditionally been viewed as isolated from life-history constraints. Recent theoretical treatments, however, predict that costly sexually selected characters should be mediated by the same allocational trade-offs that apply to more conventional aspects of reproductive investment. Participation in risky competitive behaviours, for example male-male combat, should therefore increase as the opportunity for future reproduction declines. However, the demonstration of such trade-offs has proven to be elusive due to concomitant age-based variation in the physical determinants of fighting 'ability'. Here, I exploit the unique nature of a butterfly contest system to provide compelling evidence for lifetime partitioning of risky and aggressive sexually selected behaviours. I show that male Hypolimnas bolina become more willing to persist in contests over mating territories, and more generally accepting of injury risks, as they age. Contest persistence in this species is not mediated simply by physical condition, and I experimentally isolate the effect of ageing per se from resource ownership and previous contest experience. These results demonstrate how sexually selected behaviours can be ultimately mediated by a shifting trade-off between contemporary reproductive effort and future opportunities.     

Contest Duration and Dynamics are Affected by Body Size in a Potentially Subsocial Crayfish (Crustacea: Decapoda)

Fighting is a costly behavior, consuming both time and energy. As a result, the benefits of acquiring resources must outweigh these costs. Resource value will thus influence willingness to invest in a contest through its objective (the intrinsic properties of the resource) and subjective value (context/state dependent). In burrowing crayfish, subjective resource value may vary with life stage: adults, subadults, and juveniles differ in their ability to obtain resources. As juveniles cannot dig their own burrows, we hypothesize that earlier life stages will exhibit lower aggression than later life stages. To test this, we evaluated contests between paired individuals according to their cephalothorax length (CL), encompassing different life stages of Parastacus brasiliensis. To quantify aggression levels, we recorded contest duration, the frequency of low and highly aggressive behaviors, the time to escalate to highly aggressive behaviors, the probability of initiating contests with highly aggressive behaviors, and the latency to initiate a contest. We examined the relationship between these dependent variables and CL (independent variable) using GLMs to test how aggressive behaviors develop. Contest duration increased with pair mean, winner's and loser's CL. Frequency of low aggressive behaviors increased with CL, whereas highly aggressive behaviors, latency, and time to reach highly aggressive behaviors were unrelated to CL. Smaller individuals had a higher probability of initiating contests with highly aggressive behaviors. Self‐assessment explains the contest dynamics of P. brasiliensis, with smaller individuals giving up sooner, probably due to lower energy and time budgets.     

Residency effects in animal contests

The question of why territorial residents usually win asymmetrical owner-intruder contests is critical to our understanding of animal contest evolution. Game theory suggests that, under certain conditions, residency could be used as an arbitrary means of contest settlement in a manner analogous to tossing a coin. Key empirical support for this idea is provided by a study on the speckled wood butterfly (Pararge aegeria); however, this result has proven controversial. We show conclusively that residency does not serve as an arbitrary cue for contest settlement in this species. By means of a series of manipulative experiments, conducted on two phenotypically divergent populations of P. aegeria, we also rule out the recently presented alternative that contests are settled due to resource-correlated asymmetries in thoracic temperature. Our results instead suggest that more intrinsically aggressive males accumulate as residents and continue to win due to the self-reinforcing effect of prior winning experience. Truly arbitrary contest settlement may be rare or non-existent in the wild.     

Influence of previous residency and body mass in the territorial contests of the butterfly Hermeuptychia fallax (Lepidoptera: Satyrinae)

Although many studies have evaluated the possible rules used by males to settle territorial contests, few have simultaneously considered the possibility of mutual or self-assessment of fighting ability and the effect of prior residence on the chances of winning. Here, we experimentally investigated the influence of previous residency on the development and outcome of contests between males of the butterfly Hermeuptychia fallax. By comparing the frequency of resident victories in nonmanipulated disputes versus interactions in which both rivals were induced to behave as residents, we showed that prior residency may interact with body mass in contest resolution. In nonmanipulated disputes, resident males showed high winning probabilities, although they were similar to losers in body mass. However, when both males behaved as residents, the disputes were longer and were settled in favor of the heavier male. This indicates that, although residency is an important component of male willingness to fight, it is not the only factor influencing conflict resolution. Despite the correlation between body mass and territorial success, the weight of neither winners nor losers correlated with fighting duration. We conclude that residence asymmetry may sometimes conceal male traits important to contest resolution and that it may obscure the identification of the assessment strategy used in contests.     

Body temperature and territory selection by males of the speckled wood butterfly (Pararge aegeria): what makes a forest sunlit patch a rendezvous site?

1. Insects locate mobile resources like prey items or mates using either sit‐and‐wait (‘perching’) or active (‘patrolling’) searching strategies. The sit‐and‐wait strategy can be accompanied by defending and monopolising a site through territorial behaviour. 2. The present study focuses on the territorial perching behaviour in males of the speckled wood butterfly (Pararge aegeria L.). Recent studies suggested that the selection of territories (i.e. sunlit patches on the forest floor) is driven by structural characteristics of the site that affect male visual detection. However, given that adult butterflies are heliothermic organisms and that forests provide a diverse array of light environments, it seems likely that thermal aspects may also be used for territory selection. 3. We tested whether used and unused sunlit patches differed in thermal profile under field conditions in a Belgian woodland. We also used dummy butterflies to quantify variation in operative thoracic temperature and to calculate heating rates within (i.e. different vegetation structures) and between patches. 4. Sunlit patches occupied by a territorial male were larger, and were more frequently characterised by low vegetation structures compared with empty sunlit patches. It took longer to reach optimal thorax temperature (starting from a fixed suboptimal body temperature) in small patches compared with large patches. 5. We suggest that aspects of visual detection need to be combined with thermal aspects to fully understand territory selection in the speckled wood butterfly, as synergetic and/or trade‐off effects of ambient temperature, solar radiation, and canopy/vegetation structure may be involved.     

Prior Residence Influences Contest Outcome in Flocks of Non-Breeding Birds

We sought to determine whether early arrival was a determinant of contest outcome in loosely organized, non‐breeding flocks of birds. In White‐throated Sparrows (Zonotrichia albicollis) arrival date during autumn migration, i.e. within‐year prior residence, was a significant determinant of contest outcome for those birds that were not present on the study site in previous years. To determine whether the advantage of early arrival was due to prior residence per se, as opposed to some correlate of arrival date (e.g. condition), we experimentally delayed the arrival of 60 migrants. We found a significant effect of the delay: the outcome of contests between naturally arriving (control) birds and experimentally delayed birds was significantly related to the difference between the control bird's natural arrival date and the experimental bird's delayed arrival date. Thus, prior residence per se, and not some correlate of arrival date, had a significant effect on a naïve individual's ability to win contests. Interestingly, arrival date had no effect on contest outcome among birds that had wintered on the site in previous years. Because a prior residence advantage accumulates in a time‐dependent manner, our results suggest that fighting ability or perceived resource value increases with site familiarity. Thus, there may be selection on arrival date and site‐faithfulness as behavioral strategies to increase access to resources.     

Prior residence effect determines success of male–male territorial competition in a color polymorphic poison frog

Male–male competition shapes resource distributions and reproductive success among individuals, and can drive trait evolution when phenotypes differ in competitive abilities and/or strategies. Divergence of populations, regardless of the cause, is often accompanied by divergence in male competitive ability, and such asymmetries can play an important role in mediating the interactions and evolutionary trajectory of the nascent lineages. Here, we designed a field experiment to examine the importance of color, a divergent trait, in determining territorial contest outcomes in the poison frog Oophaga pumilio. Males of different O. pumilio color morphs differ in aggression level, suggesting a potential dominance hierarchy between these divergent phenotypes. In a contact zone between red and blue-color morphs, we first removed territorial males from their calling sites, and examined whether certain color morph(s) were better at establishing in these now-vacant territories. We then staged a territorial contest by simultaneously releasing the original and the new occupant to their point of capture. Surprisingly, we found no significant effect of color on acquiring territories or winning staged contests. However, the original occupants won against the new occupant in 84% of the staged contests, revealing a strong prior residence effect. This suggests that asymmetries that stem from prior residency override coloration in predicting contest outcomes of male–male territorial contests in wild O. pumilio. Thus, contradicting our hypothesis, male–male territorial competition alone seems unlikely to exert selection on coloration in this contact zone.     

Post-contest behaviour in black-capped chickadees (<Emphasis Type="Italic">Poecile atricapillus</Emphasis>): loser displays,not victory displays,follow asymmetrical countersinging exchanges

Victory displays are behaviours that occur after the conclusion of a signaling contest, performed solely by the contest winner. Victory displays may reinforce the dominance of the winner either to the loser or to other conspecifics within signaling range. Victory displays are poorly studied despite the significant consequences that post-conflict behaviour may have on the individuals involved. We examined the period immediately following 50 territorial countersinging contests between males in 10 neighbourhoods of black-capped chickadees (Poecile atricapillus) of known dominance rank. We characterized the post-contest singing behaviour of chickadees and evaluated whether post-contest behaviour is consistent with victory displays. Using a 16-microphone acoustic location system to simultaneously record entire neighbourhoods of breeding chickadees, we isolated 50 dyadic countersinging contests and measured the vocal behaviour of the contestants in the minutes following each interaction. Eighty-six percent of contests were followed by a period of solo singing by one of the contestants, while 14% were followed by silence. The post-contest singer was most often the contestant who held a subordinate dominance position in the previous winter’s dominance hierarchy; dominant males performed post-contest song bouts significantly less often. Asymmetry in overlapping between contestants did not predict which bird sang a post-contest bout. However, in a significant majority of cases, the post-contest singer was pitch-matched by his opponent during the contest more than he pitch-matched his opponent. Our results indicate that male chickadees do not perform acoustic victory displays after countersinging contests. In contrast, the post-contest behaviour of territorial chickadees is more consistent with a “loser display”.     

Effect of larval food stress on male adult behaviour, morphology and reproductive investment in the butterfly Pararge aegeria

Males of several animals increase their reproductive success by territorial behaviour. In butterflies, males may defend a territory (i.e., territorial perching tactic), but this is assumed to be an energetically costly way to locate mates. Limitations of the energy budget may affect fight performance, and may, consequently, force males to adopt an alternative non-territorial searching behaviour (i.e., patrolling tactic) to maximize reproductive success. In this study, we tested to what extent behavioural tactics adopted by adult males of the butterfly Pararge aegeria (L.) were affected by the nutritional conditions during the larval stage. We compared the occurrence of territorial versus patrolling behaviour, lipid mass, flight muscle ratio, metabolic rate and spermatophore production of low quality males that were reared as a larva on drought-stressed host plants and control, high quality males. Low quality males were less likely to adopt the territorial perching tactic and emerged as adults with lower lipid mass than high quality males, but they were able to restore their lipid mass through adult feeding (and perhaps the breakdown of flight muscles). Host plant quality also affected spermatophore size. Independent of the larval food treatment, territorial perching males metabolised more lipids than non-territorial males, produced larger spermatophores and copulated for longer than males adopting non-territorial behaviour. We discuss the results relative to the co-existence of the behavioural tactics (perching and patrolling).     

Size,sex and social experience: Experimental tests of multiple factors mediating contest behaviour in a rockpool fish

Aggressive contests amongst conspecifics are important to understand from an ecological and evolutionary perspective as contest dynamics can directly influence individual fitness. For some species, individual attributes such as relative body size closely predict the outcome, intensity and duration of contests, whereas for others, prior social experiences play a key role. However, disentangling the relative effects of individual attributes and social experiences is challenging from an experimental perspective, and because of this, few studies have investigated relative effects of multiple factors. Rockpool fishes have been well studied in terms of factors governing abundance, distribution and community structure, but much less so in terms of contest behaviour. This is surprising because contest dynamics are likely to directly affect the distribution of fishes along the rocky shore, and hence indirectly govern population and community composition. Here, we explored multiple factors potentially influencing contest behaviour in a numerically dominant, resident intertidal fish species, Bathygobius cocosensis (Gobiidae). Using a series of staged pairwise contest trials, we investigated the effect of size, sex and social experiences (namely prior residency and winner–loser experiences) on contest dynamics. We found no evidence that prior residency influenced contest outcome, suggesting social experiences play a minor role in contest dynamics. Previous winner/loser experience also did not influence contest outcome, although this is likely a product of low sample size. In addition, the likelihood of winning was unrelated to contestant sex, and the combination of sexes in paired contests did not influence contest intensity or duration. Instead, body size was related to contest outcome, intensity and duration in the majority of experimental trials. These results suggest that body size rather than sex or social experiences is the key determinant of contest dynamics in this species. We suggest that the dynamic biotic and abiotic environment inhabited by intertidal fish may reduce the influence of prior social experiences in modulating contest dynamics.     

Matter of Size or Matter of Residency Experience? Territorial Contest in a Green Hairstreak,Chrysozephyrus smaragdinus (Lepidoptera: Lycaenidae)

Territorial residents usually win asymmetrical owner‐intruder contests and a variety of hypotheses have been proposed to explain this phenomenon. In the butterfly Chrysozephyrus smaragdinus (Lepidoptera: Lycaenidae), male territorial residents defended their territories against intruders during numerous contests and kept them for many successive days. Field observations and experiments were conducted to examine the factors related to this superiority of residents. Forewing length did not differ between residents and intruders, suggesting that body size is not correlated with resource holding potential. Removal–replacement experiments demonstrated that residency did not serve as an arbitrary means for contest settlement, and did not support the recently presented alternative hypothesis that males with higher body temperature are more likely to win. New residents fought longer in defense of the territory as their residence duration in the territory increased. I discuss these results in light of game theory and suggest that the superiority of residents in C. smaragdinus may be based on the asymmetry of resource (territory) value for residents and intruders.     

Individual plasticity drives boldness senescence in a territorial butterfly

Most behavioural traits show plastic responses to changes in internal or external conditions. Similarly, animal personality is not necessarily fixed during an individual's lifetime, leading to age-related changes. Both individual plasticity (i.e., within-individual effect) and non-random selective (dis)appearance of behavioural types (i.e., between-individual effect) may contribute to age-related changes observed at the population level. Here, we investigated how boldness changes with age in a woodland population of the Speckled wood butterfly (Pararge aegeria L.) using a capture–mark–recapture approach. We used wing wear as an index for age and we show that fresh individuals are bolder than worn individuals. Using the subsample of recaptured butterflies, we found that this pattern is most likely driven by individual plasticity. Our design also allowed us to explore some aspects of the species' spatial ecology and how it relates to personality. We found no relationship between boldness and net displacement between successive captures, a finding which we discuss within a movement ecology framework.     

Contests with deadly weapons: telson sparring in mantis shrimp (Stomatopoda)

Mantis shrimp strike with extreme impact forces that are deadly to prey. They also strike conspecifics during territorial contests, yet theoretical and empirical findings in aggressive behaviour research suggest competitors should resolve conflicts using signals before escalating to dangerous combat. We tested how Neogonodactylus bredini uses two ritualized behaviours to resolve size-matched contests: meral spread visual displays and telson (tailplate) strikes. We predicted that (i) most contests would be resolved by meral spreads, (ii) meral spreads would reliably signal strike force and (iii) strike force would predict contest success. The results were unexpected for each prediction. Contests were not resolved by meral spreads, instead escalating to striking in 33 of 34 experiments. The size of meral spread components did not strongly correlate with strike force. Strike force did not predict contest success; instead, winners delivered more strikes. Size-matched N. bredini avoid deadly combat not by visual displays, but by ritualistically and repeatedly striking each other''s telsons until the loser retreats. We term this behaviour ‘telson sparring'', analogous to sparring in other weapon systems. We present an alternative framework for mantis shrimp contests in which the fight itself is the signal, serving as a non-lethal indicator of aggressive persistence or endurance.     

Body Mass and not Wing Length Predicts Territorial Success in a Tropical Satyrine Butterfly

The males of numerous butterfly species fight with conspecific rivals to possess mating territories. Although there is little consensus on the nature of fight costs or on what traits favor victory, a recent analysis suggests that size may be of minor importance. However, data are inconsistent, and wing length, the metric that has been most widely used for expressing size in butterfly field studies, may not provide a reliable index of muscle mass or other traits that determine resource holding potential. Here we investigate the influence of wing length, body mass and wing wear on the territorial success of a neotropical satryine butterfly, Paryphthimoides phronius. In a removal experiment, original residents were heavier than replacement males that took over territories in the following minutes. Winners of naturally occurring contests were also heavier than losers after correcting for weight loss since weighing. Although wing length correlated significantly with body mass and body mass decreased with age, neither wing length nor wing wear (a surrogate for age and body condition) contributed to explaining territorial success. As body mass may be related to traits such as muscle mass, fat stores, and age, no conclusion is possible on how mass translates into success in disputes. However, because wing length is unrelated to residency status in P. phronius, whereas mass is both a reliable predictor and performs significantly better than wing length, our results may help explain the frequent failure of wing length to predict territorial success in butterfly field studies.     

Lifetime resource utilization,flight physiology,and the evolution of contest competition in territorial insects

Adaptationist analyses of animal contests have contributed much to our understanding of behavioral evolution. One class of contest, however, the war of attrition, has proven difficult to interpret. In wars of attrition involving aerial displays, there is evidence that asymmetries in performance parameters such as flight energetics may be important determinants of contest resolution. This paradigm is not universal, however, and we presently lack a framework for understanding why certain biophysical parameters are important only in some cases. One possibility is that the relevance of these parameters is determined by evolutionarily conserved life-history-scale patterns of resource allocation and acquisition. We evaluated this hypothesis by investigating the correlates of competitive success in two territorial insects that exemplify markedly different lifetime patterns of resource utilization. We found that in the bot fly Cuterebra austeni, an extreme capital breeding species that depends entirely on energy acquired during its immature stages, territorial residency was most strongly correlated with a size-independent measure of energetic availability. In contrast, residency in the tarantula hawk wasp Hemipepsis ustulata was best predicted by variation in body size per se. Adult H. ustulata are able to supplement their larval-derived nutrient capital in the manner of an income breeder, and fuel reserves were independent of age and actually correlated negatively with residency in this species. These results underscore how the study of sexually selected phenomena may be enriched by an explicit consideration of life-history principles.