Does prior residency interact with loss? A study of male–male contests in the hermit crab Pagurus minutus

Residency is an important predictor of success in contests with ownership asymmetries. Residency often can interact with a winning experience. However, given that some residents lose a contest even when showing an ownership advantage and that the process leading to loss often determines the loser's subsequent success, prior ownership might also interact with a loss. Here, we staged experimental contests between males of the hermit crab Pagurus minutus with a similar-sized weapon (i.e., cheliped) to examine this possibility. Male–male contests in this species occur between a solitary intruder and an owner guarding a mature female. We evaluated (a) whether resource ownership and female value affect the contest outcome and (b) whether the probability of winning after losing differs depending on the initial role of the loser (i.e., owner or intruder) by using precopulatory guarding pairs of P. minutus collected from the field. In the first fighting trial, we found an ownership advantage and increasing owner success as the body size of his partner increased. Although some owners lost the fight, in contrast to our prediction, the frequency of losing in the second fighting trial did not differ between prior owners and prior intruders. Because losers from the first fighting trial of male–male contests have no female regardless of their initial role, this shared solitary status might be related to the lack of difference in success in the second fighting trial. Moreover, unlike in other animals, resident status might not always assure greater fighting ability in P. minutus males because guarding Pagurus males can avoid male–male contests by climbing up objects in the field. Losers in the first trial, therefore, may have been weaker contestants based on traits other than size, regardless of whether they were owners or intruders.     

Patch Defence in the Parasitoid Wasp Trissolcus basalis (Insecta: Scelionidae): The Time Structure of Pairwise Contests,and the ‘Waiting Game’

Aggressive defence of host patches has been reported in many parasitoid wasps, but rarely examined in quantitative detail. One aspect of interest is that foraging female parasitoids do not simply consume resource patches, they invest offspring in them. Therefore, patch defence in parasitoids can involve not only resource defence prior to oviposition, but also postoviposition defence of offspring (maternal care). In this paper, the time-structure and sequence of pairwise agonistic contests between females of the parasitoid Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae) are analysed. Three main periods were evident in contests. In the first period, both females exploited the patch with no aggression. After the initiation of fighting, they entered a ‘contest period’, during which resident and intruder roles became clearly resolved. The resident then usually guarded the patch for up to several hours before leaving. This signalled the beginning of the third period, in which the intruder returned to superparasitise the patch. During the contest period, resident behaviour initially reflected the trade-off between exploiting fresh hosts, and defending those it had already parasitised from the intruder, which persistently returned to the patch to try and oviposit, with some success. However, when the patch became fully parasitised, both resident and intruder switched to a ‘waiting game’, in which they sat motionless for extended periods, the resident on the patch and the intruder at a distance. These stand-offs were punctuated by occasional aggressive patrolling by the resident, and cryptic returns to the palch by the intruder. This waiting game appears to be an informational war of attrition, suggesting a conceptual basis for modelling patch-leaving decisions using evolutionary game theory.     

A conflicting-tendency model of spider agonistic behaviour: Hybrid-pure population line comparisons

Contests over web-sites in the spider, Agelenopsis aperta, have been simulated by a model in which the next act of a spider is determined by the value of two ‘drives’ or ‘tendencies’, to attack and to flee. Such a model can explain the fact that F₁ hybrids between two geographical races of A. aperta are not intermediate between their parents, but are more aggressive than either. The model also accounts for the following features of the observed contests: (1) contests consist of a series of bouts, during which the spiders perform increasingly aggressive acts; (2) contests are usually won by the larger spider; (3) if sizes are equal, contests are usually won by the owner; (4) contests over excellent-quality sites are more costly than over poor-quality sites; and (5) transition probabilities for de-escalation, matching and escalation with respect to prior acts show site quality and weight bias trends. It is argued that a two-tendency model is the simplest that would account for these observations. The model also accurately simulates spider behaviour in agonistic contexts not used in its development (i.e. round-robin contests involving opponents from different populations, and a group of contests involving unequally-matched hybrid opponents).The main discrepancy between the model and observed encounters is that the model predicts that, if the owner is larger, the cost of a contest will not vary with the value of the disputed site. This is because the smaller intruder, having no knowledge of site quality (Riechert 1984) is expected to withdraw early in the contest, regardless of site quality. In the actual contests over excellent sites, estimated costs are higher even when the owner is larger and the intruder loses. The change in intruder behaviour associated with site value occurs following the first series of actions, but within the first bout of the interactions: our analyses indicate that any information conveyed by the owner concerning site value is not through overt behaviour (i.e. through the frequencies with which specific acts are performed).     

Trophic position and growth stages of Caddisfly (Stenopsyche marmorata Navas) larvae in the Echi River, Japan

We investigated the trophic position of the larval filter-feeding caddisfly species—Stenopsyche marmorata Navas in the Echi River (Japan) using δ¹³C and δ¹⁵N measurements by instar growth stage. We also analyzed δ¹³C and δ¹⁵N of food sources (periphyton and suspended and benthic POM) along the course of the river. The larvae showed some degree of spatial variation in δ¹³C and δ¹⁵N values with a downstream increase in δ¹³C and δ¹⁵N values. Our results demonstrate that the trophic structure of S. marmorata of different larval stages were spatially varying, depending on food sources. Small-sized instars displayed a higher trophic position than larger instars, confirming that their non-selective feeding behavior leads to consumption of items with high δ¹⁵N values according to the spatial distribution of food sources in the riverine system.     

All by myself? Meta‐analysis of animal contests shows stronger support for self than for mutual assessment models

Since the 1970's, models based on evolutionary game theory, such as war of attrition (WOA), energetic war of attrition (E‐WOA), cumulative assessment model (CAM) and sequential assessment model (SAM), have been widely applied to understand how animals settle contests. Despite the important theoretical advances provided by these models, empirical evidence indicates that rules adopted by animals to settle contests vary among species. This stimulated recent discussions about the generality and applicability of models of contest. A meta‐analysis may be helpful to answer questions such as: (i) is there a common contest rule to settle contests; (ii) do contest characteristics, such as the occurrence of physical contact during the fight, influence the use of specific contest rules; and (iii) is there a phylogenetic signal behind contest rules? To answer these questions, we gathered information on the relationship between contest duration and traits linked to contestants' resource holding potential (RHP) for randomly paired rivals and RHP‐matched rivals. We also gathered behavioural data about contest escalation and RHP asymmetry. In contests between randomly paired rivals, we found a positive relationship between contest duration and loser RHP but did not find any pattern for winners. We also found a low phylogenetic signal and a similar response for species that fight with and without physical contact. In RHP‐matched rivals, we found a positive relationship between contest duration and the mean RHP of the pair. Finally, we found a negative relation between contest escalation and RHP asymmetry, even though it was more variable than the other results. Our results thus indicate that rivals settle contests following the rules predicted by WOA and E‐WOA in most species. However, we also found inconsistencies between the behaviours exhibited during contests and the assumptions of WOA models in most species. We discuss additional (and relatively untested) theoretical possibilities that may be explored to resolve the existing inconsistencies.     

Effect of Population Density and Female Body Size on Number and Size of Offspring in a Species with Size‐Dependent Contests over Resources

When size‐dependent contests over resources influence reproductive success, the trade‐off between number and size of offspring depends on the frequency of contests. Under these circumstances, clutch size should decrease and offspring size should increase as contests become more frequent. We tested these predictions with the burying beetle Nicrophorus pustulatus through manipulation of rearing densities. Burying beetles reproduce on small vertebrate carcasses, a rare but high quality food source for the larvae. Large beetles are more likely to win contests over carcasses and gain exclusive access to a carcass. The winner of a contest kills eggs and larvae already present on a carcass. As a result of the rarity of carcasses, burying beetles are unlikely to breed more than once. As predicted, brood size of N. pustulatus decreased with increasing rearing density. Despite a negative correlation between brood size and larval mass, larval mass did not increase with increasing rearing density. This may be due to the special biology of N. pustulatus which can use snake eggs for reproduction. Potentially larger supply of resources and generally small population densities of N. pustulatus may weaken selection on body size and thus the correlation between brood size and larval mass. As size‐dependent constraints can limit reproductive phenotypes, we examined whether female size influenced reproductive phenotype. Small females produced larger broods with smaller, but more variable, offspring than large females. Mechanical constraints of egg size seem an unlikely explanation for the differences because burying beetles can compensate for small egg size through parental care. Energetic constraints may impact small females because body mass and brood size of small females decreased with increasing density. Yet, at all density levels small females produced larger, not smaller, broods than large females. The larger and more variable broods of small females seem to be in agreement with a bet‐hedging strategy.     

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.     

Pure Self‐Assessment of Size During Male–Male Contests in the Parasitoid Wasp Nasonia vitripennis

During contest competition, a competitor may persist in a given contest based on information regarding its own fighting ability (resource‐holding potential, RHP), or that of its opponent. Although a number of models formalize the ways in which competitors are hypothesized to use RHP‐related information to determine their persistence in contests, we focused on pure self‐assessment and mutual assessment models in this study. According to pure self‐assessment models, a competitor uses only information regarding its own RHP to determine its persistence in a contest. In contrast, according to mutual assessment models, persistence is based on information regarding a competitor's RHP relative to that of its opponent and therefore requires assessment between competitors. In this study, using size as a proxy for RHP, we tested whether the parasitoid wasp Nasonia vitripennis utilizes pure self‐assessment or mutual assessment during pairwise, male–male contests. When we examined competitors of varied sizes, we found that the losing male's size was positively related to contest duration, but the winning male's size was uncorrelated with contest duration. When we examined contests in which competitors were size‐matched, we found that the mean size of paired competitors was positively related to contest duration. These results suggest that male N. vitripennis engage in pure self‐assessment during contests.     

Agonistic interactions between nymphs of Lycorma delicatula (Hemiptera: Fulgoridae)

The nymphs of Lycorma delicatula typically aggregate on tree branches for feeding. We studied agonistic interactions between nymphs in the field and investigated the effects of prior residence and body size on contest outcome. Resident nymphs maintained positions on tree branches and engaged in feeding, whereas intruding nymphs moved along tree branches. When an intruder approached, the resident typically raised its front legs as a threat posture. The intruder would either move away or palpate the resident, and the resident often lowered its body when palpated. The intruder would then attempt to shake the resident back and forth, with the number of attempts varying from one to several. The resident either maintained its position or fled. After a contest, the winner was determined to be the one occupying the contested position on the branch. The resident nymphs won 84.2% of the agonistic encounters, and the nymphs with larger body size won 63.2% of the agonistic encounters. Logistic regression analysis revealed that prior residence was a significant factor for the contest outcome, but body size was not. We discuss the hypotheses for the dominance of the residents in agonistic interactions between nymphs of L. delicatula.     

Nesting biology of Asian paper wasps Polistes chinensis antennalis Pérez,and Australian paper wasps P. humilis (Fab.) (Hymenoptera: Vespidae) in northern New Zealand

Abstract

We recorded the numbers of cells, and where possible distinguished between cells containing pupating larvae and vacated cells, from 585 paper wasp nests from the northern North Island, New Zealand, plus nest site characteristics of 540 of these nests. Nests of Polistes chinensis antennalis and P. humilis developed at similar rates in early summer. P. c. antennalis nests were larger at the Post‐emergence stage than those of P. humilis, and contained more vacated cells but less capped cells. All of the P. c. antennalis nests had reached the Post‐emergence stage by February in Northland, but not in the other regions. P. c. antennalis nests in the Post‐emergence stage were larger in Northland than further south, and contained the most capped or vacated cells. Nests of both species were usually found in northern‐facing sites. Substrate did not affect nest size. Differences between the species in nest sites included greater use of manmade structures by P. c. antennalis; the use of leaves by P. humilis only; and a higher average nest site height in P. humilis. These differences in nest site selection may reduce competition between the species.     

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.     

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.     

Asymmetrical Resource Ownership Increases Owners’ and Reduces Non‐Owners’ Motivation to Fight in the Mangrove Rivulus,Kryptolebias marmoratus

Resource ownership often increases an individual's aggressiveness and its probability of defeating a competitor. Individuals contesting resource owners could therefore incur higher costs, making individuals reluctant to compete with owners. We tested the hypothesis that animals use asymmetry in resource ownership as a cue for contest costs and adjust contest decisions accordingly. Using a mangrove rivulus fish (Kryptolebias marmoratus), we staged (1) contests with a randomly assigned asymmetry in resource ownership (one fish was provided with a shelter) and (2) contests in which neither fish had a shelter. Owners that were in their shelters at the contest start showed a greater tendency to fight and won more contests than their intruder opponents; those outside the shelter at the start did not. Compared with fish in contests with no shelters at stake, shelter owners had a higher tendency to fight whether or not they were in their shelters at the start; intruders, however, had a lower tendency to fight only against owners that were inside the shelter at the start. These results demonstrate (1) that ownership status influences both owners’ and intruders’ contest decisions (and in opposite directions), producing a detectable ownership advantage and (2) that intruders required confirmation of their opponents’ ownership status before retreating without challenging them. Ownership status per se is therefore important to the fish's contest decisions.     

Secondary seed dispersal by ants in Neotropical cerrado savanna: species‐specific effects on seeds and seedlings of Siparuna guianensis (Siparunaceae)

1. Most woody plant species in tropical habitats are primarily vertebrate‐dispersed, but interactions between ants and fallen seeds and fruits are frequent. This study assesses the species‐specific services provided by ants to fallen arillate seeds of Siparuna guianensis, a primarily bird‐dispersed tree in cerrado savanna. The questions of which species interact with fallen seeds, their relative contribution (versus vertebrates) to seed removal, and the potential effects on seedling establishment are investigated. 2. Seeds are removed in similar quantities in caged and control treatments, suggesting that ants are the main dispersers on the ground. Five ant species attended seeds. Pheidole megacephala (≈0.4 cm) cooperatively transported seeds, whereas the smaller Pheidole sp. removed the seed aril on spot. Large (> 1.0 cm) Odontomachus chelifer, Pachycondyla striata, and Ectatomma edentatum individually carried seeds up to 4 m. Bits of aril are fed to larvae and intact seeds are discarded near the nest entrance. 3. Overall, greater numbers of seedlings were recorded near ant nests than in control plots without nests. This effect, however, was only detected near P. megacephala and P. striata nests, where soil penetrability was greater compared with controls. Soil nutrients did not differ between paired plots. 4. This study confirms the prevalence of ant–seed interactions in cerrado and shows that ant‐derived benefits are species‐specific. Ant services range from seed cleaning on the spot to seed displacement promoting non‐random spatial seedling recruitment. Although seed dispersal distances by ants are likely to be shorter than those by birds, our study of S. guianensis shows that fine‐scale ant‐induced seed movements may ultimately enhance plant regeneration in cerrado.     

Contest dynamics for food and reproductive resources are defined by health condition in a dung beetle

Male dung beetles compete to obtain food and females, and early resource recognition and appropriation increase the probability of mating. The outcome of such encounters is expected to be defined by self‐ and the opponent’s health condition. In this study, we analyzed the effect of body condition and immune defense on the contest dynamics between males that rolled a food ball with a partner female (owner males) and intruder males of dung beetle Canthon cyanellus. Body condition was measured as body size, body dry mass, lipid mass, and muscle mass; immune defense was estimated via phenoloxidase activity. Owner males with higher lipid mass contacted the food ball significantly earlier than owner males with lower lipid mass. Individuals with lower phenoloxidase activity started to roll food balls earlier than individuals with higher phenoloxidase activity. Owner males that had higher body dry mass, compared to female partners, began to roll the food ball significantly earlier than male–female pairs with lower differences in dry mass. Heavier males won significantly more contests than lighter males. Our results suggest that the health condition is a key factor related to the dynamics and outcome of male–male contests for resources and females in C. cyanellus. Consequently, differences in individual condition are main determinants of contest outcomes in dung beetles.     

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.     

Nest density and distribution of subterranean ants in an evergreen broadleaf forest in Japan with special reference to Amblyopone silvestrii

The density and distributions of nests of the subterranean ants were studied by excavation of thirty 1‐m² quadrats in an evergreen broadleaf forest in central Japan. A total of 20 ant species were collected and the densities of Amblyopone silvestrii and Paratrechina flavipes were highest (both 0.83 nests/m²). The distribution patterns were analyzed by the Standardized Morisita Index (I_p) for the five species that had mean densities of more than 0.5 nests/m². Of them, A. silvestrii and Hypoponera sauteri showed random distributions, while nests of Paratrechina flavipes were significantly overdispersed and those of Carebara yamatonis and Myrmecina nipponica were weakly clumped. These distributional patterns were discussed in connection with the ecology of the ants. In particular, the social organization of A. silvestrii was investigated based on the distributional pattern and the composition of collected colonies.     

The Association Between Male Offspring Aggression and Paternal and Maternal Behavior of Peromyscus Mice

Parents influence offspring aggression through genetic and non‐genetic mechanisms, although the latter are less well understood. To examine potential non‐genetic effects of parents on offspring, we cross‐fostered the highly aggressive and biparental California mouse (Peromyscus californicus) and the less aggressive, less parental white‐footed mouse (Peromyscus leucopus). In‐fostered animals within each species were used as controls. We examined associations between the foster parents’ behavior and aggression of the fostered male offspring in resident–intruder (R–I) and neutral arena aggression tests. When both species and fostering groups were combined, R–I aggression of offspring was positively associated with paternal time spent retrieving pups. In contrast, aggression in a neutral arena was negatively associated with a composite score of maternal behavior. We discuss how our findings regarding paternal retrievals may explain previously reported effects of cross‐fostering on male aggression.     

The true identity of Obama (Platyhelminthes: Geoplanidae) flatworm spreading across Europe

Since 2008 there have been many records in Europe (British Isles, Spain, France, Italy) of a large terrestrial planarian morphologically very similar to the Brazilian species Obama marmorata. Sequences of mitochondrial (Cox1) and nuclear (18S, 28S, ITS‐1 and EF) genes from European specimens and some from Brazil indicate that they belong to a species different from that of other specimens also collected in Brazil. Moreover, the phylogenetic results show that they are not sister‐species. Histological sections of both Brazilian and European specimens reveal subtle morphological differences between the two species. Obama marmorata is confined to Brazil, and the second, herein described new species, O bama nungara sp. nov. , is found in Brazil and Europe. These cryptic species may be syntopic in areas in Brazil. The new species occurs in human‐modified environments both in Brazil and in Europe. We also conclude that the specimens from Spain and Argentina identified previously as Obama marmorata belong to the new species.