Enrique García-Muñoz, Francisco Ceacero, Miguel A. Carretero, Luis Pedrajas-Pulido, Gema Parra, Francisco Guerrero, Optimizing protection efforts for amphibian conservation in Mediterranean landscapes, Acta Oecologica, Volume 49, May 2013, Pages 45-52, ISSN 1146-609X, 10.1016/j.actao.2013.02.013.
Amphibians epitomize the modern biodiversity crisis, and attract great attention from the scientific community since a complex puzzle of factors has influence on their disappearance. However, these factors are multiple and spatially variable, and declining in each locality is due to a particular combination of causes. This study shows a suitable statistical procedure to determine threats to amphibian species in medium size administrative areas. For our study case, ten biological and ecological variables feasible to affect the survival of 15 amphibian species were categorized and reduced through Principal Component Analysis. The principal components extracted were related to ecological plasticity, reproductive potential, and specificity of breeding habitats. Finally, the factor scores of species were joined in a presence-absence matrix that gives us information to identify where and why conservation management are requires. In summary, this methodology provides the necessary information to maximize benefits of conservation measures in small areas by identifying which ecological factors need management efforts and where should we focus them on.
Jessyca Michele Citadini, Carlos Arturo Navas, Inter-individual variation and temperature-dependent antipredator behavior in the snake Tomodon dorsatus (Dipsadidae), Behavioural Processes, Available online 31 March 2013, ISSN 0376-6357, 10.1016/j.beproc.2013.03.008.
Although many studies assessed the influence of temperature on the behavior of ectotermic vertebrates, little attention has been given to interindividual variation in the defensive responses of reptiles. In the present study we investigated the defensive behavior of the snake Tomodon dorsatus, in order to test the hypotheses that (1) individuals differ in their antipredator behavior consistently with the concept of behavioral syndromes, (2) temperature influences the defensive behavior, and (3) these two factors interact with each other. There was significant interindividual variation in defensive behavior, as well as consistently aggressive, passive or evasive behaviors. Temperature influenced aggressiveness, which was slightly higher when body temperature was lower, but this trend was only evident in animals with aggressive disposition. Our results corroborate the hypothesis of interaction between individuality of behavior and temperature-dependent defensive behavior in T. dorsatus. These results, together with results from previous studies, suggest that the evolution of temperature-dependent defensive behavior differs among lineages of ectothermic tetrapods.
Re-description of Arapaima agassizii (Valenciennes), a Rare Fish from Brazil (Osteoglossomorpha: Osteoglossidae)
Donald J. Stewart
Copeia 2013(1):38-51. 2013, http://dx.doi.org/10.1643/CI-12-013
The bony-tongue fish genus Arapaima Müller has been considered monotypic since 1868, with A. gigas being the only recognized species. Review of species-level taxonomy of Arapaima has revealed that Arapaima agassizii Valenciennes (in Cuvier and Valenciennes, 1847) should be considered a valid species. The holotype was destroyed in World War II, but the species can be recognized based on the original description, which included detailed osteological illustrations. At least nine characters distinguish it from all other Arapaima: 1) dentary teeth 44 (counted on one ramus only, vs. 21–37 in other Arapaima); 2) maxillary teeth 43 (vs. 21–38 in other Arapaima); 3) orbit diameter 1.5% standard length (SL, vs. 1.5–2.8, relatively larger in all other Arapaima at similar SL); 4) interorbital width 4.1% SL (vs. 5.3–6.5 in other Arapaima); 5) parietals with pronounced posterior projections that are pointed and curve slightly toward midline (vs. absent in other Arapaima); 6) caudal fin widely separated from dorsal and anal fins by long caudal peduncle, 9.7% SL (vs. much shorter peduncle, 3.2–5.5 in others); 7) anal fin with only 26 rays (vs. 30–40 in others), with distinctly shorter basal length than dorsal-fin base; 8) dorsal and anal fins extremely low in profile; dorsal-fin base divided by longest dorsal ray about 7 (vs. 3.1–5.5 in others); and 9) first pectoral-fin ray with proximal tip similar in form to subsequent pectoral-fin rays (vs. first pectoral-fin ray noticeably enlarged relative to subsequent rays). Arapaima agassizii still is known only from the holotype, which was collected in 1817–20 somewhere in lowlands of the Brazilian Amazon. It thus is important to locate this taxon to determine its distribution and conservation status.
Capoccioni, F., Lin, D.-y., Iizuka, Y., Tzeng, W.-N. and Ciccotti, E. (2013), Phenotypic plasticity in habitat use and growth of the European eel (Anguilla anguilla) in transitional waters in the Mediterranean area. Ecology of Freshwater Fish. doi: 10.1111/eff.12049
Lagoons and estuaries are transitional waters (TW), saline in character but substantially influenced by freshwater (FW) flows and the most productive habitat after upwelling areas. The European eel, Anguilla anguilla, is a typical inhabitant of these habitats and a target of important lagoon fisheries since ancient times. Notwithstanding this, in the Mediterranean region, where the numerous coastal lagoons are the most eligible habitat for this species, eel habitat use and growth, which display a high inter-individual variability, are poorly studied. To gain knowledge about the migratory behaviour and the relative growth history of this species in TW in the Mediterranean area, the otolith Sr/Ca ratios of 56 individuals were analysed. The study sampling sites were two typical coastal lagoon environments, Caprolace lagoon and Lesina lagoon, located, respectively on the Tyrrhenian and the Adriatic coast of Italy, and the Tiber River (TR) estuary, in Central Italy. Otolith Sr/Ca profiles revealed that in all the sites, the resident contingent is substantial, while the proportion of nomad eels, or habitat inter-shifter, was different among sites. Mean annual grow rate of resident eels is higher in productive environments (TR and lagoon of Lesina), while in Caprolace lagoon, an oligotrophic lagoon, resident eels grow slower. The observed patterns of habitat use and growth seem linked to local ecological conditions: facultative movements of eels with a nomadic behaviour seem affected by food availability rather than by the salinity gradient. This consideration supports the hypothesis that the facultative catadromous migration of European eel in Mediterranean TW, and the trophic shifts that this species exhibits, depend primarily on the productivity of the environment rather than on its salinity gradient.
Implication of the presence of Megathericulus (Xenarthra: Tardigrada: Megatheriidae) in the Laventan of Peruvian Amazonia
François Pujos, Rodolfo Salas-Gismondi, Guillaume Baby, Patrice Baby, Cyrille Goillot, Julia Tejada, Pierre-Oliver Antoine
Journal of Systematic Palaeontology
Middle Miocene remains of giant megatheriine ground sloths (Tardigrada: Megatherioidea) are scarce and generally located in southern South America. The discovery of a well-preserved edentulous dentary of Megathericulus sp. from the Middle Miocene (Laventan South American Land Mammal Age – SALMA; 13.5–11.8 Ma) of the Amazonian Peru increases our knowledge of this genus, which had previously been recognized in Argentina. A preliminary revision of the earliest Megatheriinae allowed clustering the four middle Miocene species within the genus Megathericulus Ameghino: M. patagonicus Ameghino, M. primaevus Cabrera, M. andinum (Kraglievich), and M. cabrerai (Kraglievich). This small-sized genus is mainly characterized by a lateral depression that borders m1, a posterior external opening of the mandibular canal anterior to the base of the ascending ramus that opens anteriorly or anterodorsally, the base of the symphysis located anteriorly to the m1, important anteroposterior compression of the teeth, elongation of the region of the maxilla anterior to the M1, humerus elongated and gracile, patellar trochlea of femur contiguous with medial and lateral articular facets for tibia, strongly developed odontoid tuberosity, and astragalus with prominent odontoid process. The genus Eomegatherium Kraglievich is therefore restricted to the Huayquerian SALMA of Argentina and represented by a single species, E. nanum Burmeister. Megatheriinae constitute the first clade of Tardigrada in which the caniniform tooth has been secondarily modified into a molariform tooth. Three molariform patterns can be observed during megatheriine evolution in relation to tooth compression and loph or lophid orientation. Middle Miocene Megatheriinae occur only in the westernmost part of South America. These giant ground sloths might have dispersed latitudinally from Colombia/Patagonian Argentina before colonizing eastern areas of Andean South America (Bolivia, Venezuela, north, and east of Argentina) during the late Miocene and early Pliocene.
Postcranial axial skeleton of Europasaurus holgeri (Dinosauria, Sauropoda) from the Upper Jurassic of Germany: implications for sauropod ontogeny and phylogenetic relationships of basal Macronaria
José L. Carballido, P. Martin Sander
Journal of Systematic Palaeontology
Neosauropods are well represented in the Late Jurassic fossil record, both in Laurasia and Gondwana. Among Macronaria, Europasaurus represents one of the most basal forms of this group. In addition to its systematic importance, Europasaurus is also the first unequivocal dwarf sauropod from which adult and juvenile material is available. Despite the abundance of sauropods in the fossil record, early juvenile specimens are rare, limiting knowledge about sauropod ontogeny. Therefore, the great amount of material of Europasaurus provides an excellent opportunity to improve our knowledge on the early evolution of Macronaria, as well as to shed light on some morphological changes through ontogeny. The postcranial axial skeleton of sauropods is extremely modified with respect to the anatomy observed in its ancestors, the ‘prosauropods’, proving to be one of the most informative regions of the body. Here we provide a detailed description of the axial skeleton of Europasaurus, including adult and juvenile elements, discussing its systematic and ontogenetic importance. We also analyse the phylogenetic position of Europasaurus through a cladistic analysis using TNT, which retrieves this taxon in a basal position among Camarasauromorpha. Additionally, the presence/absence of discrete characters and the comparison of juvenile elements with adult specimens allowed us to recognize different morphological ontogenetic stages (MOS). Whereas early stages lack derived characters (e.g. spinodiapophyseal lamina and prespinal lamina on dorsal vertebrae), all derived characters (including autapomorphies) are present in late immature specimens. Therefore, while late immature specimens provide the same phylogenetic signal as adult specimens of Europasaurus, more immature stages are recovered in a basal position among sauropods. Finally, we apply the MOS to other maturity criteria (e.g. neurocentral closure, sexual maturity) in a search for a wider definition of maturity.
A new genus of Rhinocerotidae (Mammalia, Perissodactyla) from the Oligocene of Europe
Damien Becker, Pierre-Olivier Antoine, Olivier Maridet
Journal of Systematic Palaeontology
A newly discovered, well-preserved skull and associated fragment of a juvenile mandible from the Early Oligocene locality of Poillat (Canton Jura, NW Switzerland), bearing close affinities with the rhinocerotid Protaceratherium albigense (Roman, 1912), are attributed to a new small-sized representative of early diverging Rhinocerotinae, Molassitherium delemontense gen. et sp. nov. Other specimens from Western Europe, formerly questionably referred to Epiaceratherium Abel, 1910, are assigned to this new genus. Comparison with the previously described Protaceratherium Abel, 1910 (including type material) and a phylogenetic analysis highlight the mismatch of Protaceratherium minutum (Cuvier, 1822) and Protaceratherium albigense (Roman, 1912). Given the topology of the most parsimonious tree, a basal split within Rhinocerotidae coincides with the well-supported divergence of the Elasmotheriinae and Rhinocerotinae clades. Relationships within Rhinocerotinae are [Epiaceratherium bolcense Abel, 1910 [Epiaceratherium magnum Uhlig, 1999 [Molassitherium gen. nov. [Mesaceratherium Heissig, 1969 [Pleuroceros Roger, 1898 [Protaceratherium minutum (Cuvier, 1822) [Plesiaceratherium mirallesi (Crusafont, Villalta and Truyols, 1955) [Aceratheriini, Rhinocerotini]]]]]]]]. The only paraphyletic genus in the analysis is Epiaceratherium, with the earliest Oligocene Epiaceratherium bolcense Abel, 1910 being sister taxon to an [Epiaceratherium magnum Uhlig, 1999, Rhinocerotinae] clade. In the single most parsimonious tree, Molassitherium gen. nov., included within the early diverging Rhinocerotinae, forms a clade encompassing Molassitherium delemontense gen. et sp. nov. and the type species Molassitherium albigense comb. nov. The range of Molassitherium delemontense gen. et sp. nov. is so far restricted to the late Early–early Late Oligocene interval in Western Europe (Germany, Switzerland, France; ‘late MP22’–MP25).
The petrosal of the earliest elephant-shrew Chambius (Macroscelidea: Afrotheria) from the Eocene of Djebel Chambi (Tunisia) and the evolution of middle and inner ear of elephant-shrews
Julien Benoit, Maeva Orliac, Rodolphe Tabuce
Journal of Systematic Palaeontology
Macroscelidea (elephant-shrews or sengis) are small insectivorous mammals restricted to Africa; they belong to the super-cohort Afrotheria along with other insectivorans (aardvarks, tenrecs and golden moles) and ungulates (elephants, sea cows and hyraxes). Though their fossil record extends back to the Eocene, cranial remains of Palaeogene elephant-shrews, including the middle and inner ear structure, remain unknown. Two macroscelid isolated petrosal bones are described from the late Early–early Middle Eocene Djebel Chambi locality in Tunisia. Chambius kasserinensis is the only macroscelid represented in this locality. A cladistic analysis based on petrosal and inner ear characters highlights the crucial interest of the petrosal and inner ear morphology for understanding the evolution of Macroscelididae. It confirms the attribution of these isolated petrosals to C. kasserinensis. This hypothesis is supported by a common pattern of circulatory system, the morphology of the rostral and caudal tympanic processes, and the shape of the cochlea. In addition, Chambius appears to be the basal-most taxon among the macroscelid sample; this position is supported by the lack of some specializations of the middle ear such as inflated ossicular bones and pneumatized bulla. The presence of a secondary common crus in Chambius suggests a convergent loss of this structure, at least in Macroscelidea and Tenrecoidea. The petrosal and inner ear characters support the clade Afroinsectivora, which gathers macroscelids with other endemic African insectivorans (tenrecs and golden moles), reinforcing the hypothesis of an African origin of macroscelids. The petrosal bone and inner ear characters provide further morphological support for the debated clade (Petrodromus, Elephantulus rozeti, Macroscelides). New data underlines the fact that the cranial arterial pattern of the Eocene macroscelid Chambius was already similar to that of modern macroscelid species. It also suggests that early elephant-shrews were probably not as capable of hearing low frequencies as their extant representatives.
New craniodental remains of the barbourofelid Albanosmilus jourdani (Filhol, 1883) from the Miocene of the Vallès-Penedès Basin (NE Iberian Peninsula) and the phylogeny of the Barbourofelini
Josep M. Robles, David M. Alba, Josep Fortuny, Soledad De Esteban-Trivigno, Cheyenn Rotgers, Jordi Balaguer, Raül Carmona, Jordi Galindo, Sergio Almécija, Juan V. Bertó, Salvador Moyà-Solà
Journal of Systematic Palaeontology
Available remains of the barbourofelin Albanosmilus jourdani from the Middle to Late Miocene of the Vallès-Penedès Basin (NE Iberian Peninsula) are described. In addition to the dentognathic remains described by previous authors, the new material includes a complete cranium, a calvarium and several mandibles from Abocador de Can Mata, Creu Conill 20 and Hostalets Superior. It is concluded that Albanosmilus, previously considered a subjective junior synonym of Sansanosmilus, must be resurrected as a polytypic genus including A. jourdani (= A. vallesiensis). The most plesiomorphic North American barbourofelin, previously included in Barbourofelis, is also transferred into Albanosmilus as A. whitfordi. An emended diagnosis of Albanosmilus is provided. The results of a cladistic analysis support the monophyly of the family Barbourofelidae and the tribe Barbourofelini, further indicating that amongst the latter, Sansanosmilus occupies the basalmost position. The two Albanosmilus species are more derived, although the analysis fails to resolve conclusively whether A. whitfordi is more closely related to A. jourdani or Barbourofelis s.s. From a palaeobiogeographical viewpoint, our results suggest that: (1) barbourofelins originated in Eurasia during the early Middle Miocene; (2) Barbourofelis originated in North America during the late Middle Miocene, following the dispersal of Eurasian Albanosmilus into that continent; and (3) the presence of Barbourofelis in Turkey during the Late Miocene may represent a later independent dispersal event from North America back into Eurasia.
Janicke Nordgreen, Mette Helen Bjørge, Andrew M. Janczak, Trygve Poppe, Erling Olaf Koppang, Birgit Ranheim, Tor Einar Horsberg, The effect of morphine on changes in behaviour and physiology in intraperitoneally vaccinated Atlantic salmon (Salmo salar), Applied Animal Behaviour Science, Available online 1 April 2013, ISSN 0168-1591, 10.1016/j.applanim.2013.03.002
Granulomatous peritonitis is often induced by intraperitoneal vaccination in fish. Peritonitis is a very painful condition in mammals, but little is known about how fish experience this condition. In a previous experiment we found increased latency to eat and a tendency to decreased swimming during feeding in vaccinated salmon housed in groups of three. These changes in behaviour correlated with the severity of the peritonitis. However, dominance relationships may influence the degree of pain-related changes in behaviour and physiology shown by group-housed fish, and we therefore conducted the present study using singly-housed fish. The aim was to describe changes in latency to eat, hiding, swimming and bottom behaviour after vaccination, to test whether morphine would alleviate changes in behaviour, and finally to test whether vaccination and/or morphine would influence the response of the fish in the novel object test. In addition, we looked for microscopic changes of peritonitis two days after vaccination to test whether we would be able to detect inflammation at an early stage. Four treatment groups were used: VS (injected with vaccine intraperitoneally (ip) and saline intramuscularly (im)), VM (injected with vaccine ip and 300mgkg−1 morphine im), SS (saline ip, saline im) and SM (saline ip, morphine 300mgkg−1 im). Swimming during feeding decreased in the VS fish 2 days after treatment, both compared to baseline (p =0.031) and to the SS group (p =0.023). The latency to eat differed significantly between groups at 6.5h after treatment (p =0.027), and showed a tendency towards a difference 2 days after treatment (p =0.092). The VS group showed significantly higher latency to eat compared with the saline group 6.5h and 2 days after treatment (p =0.024 and 0.043, respectively). Contrary to predictions, we did not find an increase in bottom behaviour after vaccination. We could not detect any microscopic signs of peritonitis 48h after vaccination. Morphine did not seem to have an analgesic effect in that there were no differences between the VM and VS groups. However, the SM fish spent significantly more time in the open during the novel object test compared with the SS fish (χ 2 =6.97, df=1, p =0.0083) one day after injection, indicating an anxiolytic effect of morphine at that time-point. It is important that the lack of analgesic effect is not taken to indicate lack of pain perception in salmon. Inter species differences in analgesic efficacy is well known in veterinary medicine, and the results from this paper indicate that we need to look at alternatives to morphine to find effective analgesics for Atlantic salmon.
Asa, C. S., Bauman, K. L., Devery, S., Zordan, M., Camilo, G. R., Boutelle, S. and Moresco, A. (2013), Factors Associated With Uterine Endometrial Hyperplasia and Pyometra in Wild Canids: Implications for Fertility. Zoo Biol.. doi: 10.1002/zoo.21069
The ability to safely and effectively manage reproduction is central to the success of AZA captive-breeding programs. Although the AZA Wildlife Contraception Center routinely monitors contraceptive safety, there have been no studies that compare the effects of contraceptive use to separation of males from females, the other option for preventing reproduction. We used retrospective medical records and pathology reports submitted by AZA and related facilities for the seven AZA-managed canid species to assess rates of uterine pathology relative to female reproductive life histories. Our results showed that the prevalence of both pyometra and endometrial hyperplasia (EH) was associated not only with treatment with the two most common contraceptives (Suprelorin® and MGA implants) but also with the number of years barren (i.e., not producing a litter and not contracepted). Rates of pyometra and EH were especially high in African painted dogs and red wolves, but lowest in swift and fennec foxes. The number of years producing a litter had a low association, suggesting it could be protective against uterine pathology. A more recently developed Suprelorin® protocol using Ovaban® to prevent the initial stimulation phase, followed by implant removal when reversal is desired, may be a safer contraceptive option. These results concerning the relationship between reproductive management and uterine health have important implications for AZA-managed programs, since the unsustainability of many captive populations may be due at least in part to infertility. Managing a female’s reproductive lifespan to optimize or maintain fertility will require a reconsideration of how breeding recommendations are formulated.
Zootaxa 3635 (5): 557–568 (2 Apr. 2013)
A survey of the internal oral morphology in larvae of the genus Hylodes Fitzinger, 1826 (Amphibia, Anura, Hylodidae)
LUIZ NORBERTO WEBER & ULISSES CARAMASCHI
From the 24 species allocated in the genus Hylodes, 16 have their tadpoles described, which five have information on the oral anatomy. Herein, the internal oral morphology of the tadpoles of H. dactylocinus, H. heyeri, H. aff. lateristrigatus, H. magalhaesi, H. meridionalis, H. phyllodes, H. sazimai, and H. uai is described, along with comparisons among all species in the genus with previously known oral morphology.
Souza ASMC, Del Lama SN, Miño CI. 2013. Conspecific brood parasitism in the white-faced ibis Plegadis chihi (Aves: Pelecaniformes) revealed by microsatellites‘ based kinship-reconstruction. J. Exp. Zool. 9999:1–8.
The white-faced ibis Plegadis chihi Vieillot, 1817 (Pelecaniformes: Threskiornithidae) is a socially monogamous colonially breeding bird in which behavioral and ecological observations suggest the occurrence of conspecific brood parasitism (CBP). We inferred aspects of the genetic mating system of P. chihi in nature, using a genetic approach in the absence of parental information. We used five heterologous microsatellite loci and a multiple-step methodological approach to infer kinship patterns among 104 pairs of nestlings sampled inside 80 nests in a breeding colony from southern Brazil. The estimated effective population size was 69 white-faced ibises (95% CI: 50–98), enough to ensure long-term population survival. Kinship patterns were identified for 38% of the analyzed pairs: 60% of the diagnosed pairs were identified as full-siblings, 2.5% as half-siblings and 37.5% as unrelated individuals. CBP could explain the presence of unrelated nestlings within broods, in agreement with available non-genetic evidence. The presence of half-siblings within broods could indicate extra-pair paternity. Results suggest that a non-strictly monogamous genetic mating system may be present in the white-faced ibis. This study is the first molecular approach to better characterize the reproductive behavior of P. chihi in the wild. Our findings set the stage for further research to investigate the possible causes and consequences of alternative reproductive strategies in this species.
Guimarães M., Gaiarsa M.P. and Cavalheri H.B. 2013. Morphological adaptations to arboreal habitats and heart position in species of the neotropical whipsnakes genus Chironius. —Acta Zoologica 00: 000–000.
The evolution of arboreality in snakes is accompanied by modifications that are remarkably similar across species. Gravity is one of the most important selective agents, and arboreal snakes present adaptations to circumvent the gradient of pressure, including modifications on heart position (HP) and body slenderness (BS). However, the degree to which different life-history traits influence the cardiovascular system of snakes remains unclear. Here, we used an ecological and a phylogenetic approach to explore the relationship between habitat, HP, BS, and heart size (HS) in five species of the neotropical whipsnakes genus Chironius that occupy terrestrial, semiarboreal, and arboreal habits. Our ecological comparison indicated that the arboreal species have the most posterior-positioned heart, the most slender body, and the smallest HS, whereas the terrestrial representative of the group exhibited the most anterior heart, the less flattened body, and the largest HS. After removing the phylogenetic effect, we found no difference in HP and BS between terrestrial and arboreal species. Habitat only differed when contrasting with HS. Body slenderness and HS were correlated with HP. Our results suggest that different restrictions, such as anatomical constraints, behavior, and phylogenetic inertia, may be important for the studied species.
Peter G. Judge, Katherine A. Bachmann, Witnessing reconciliation reduces arousal of bystanders in a baboon group (Papio hamadryas hamadryas), Animal Behaviour, Available online 2 April 2013, ISSN 0003-3472, 10.1016/j.anbehav.2013.02.011.
Reconciliation is the occurrence of friendly behaviour between opponents shortly after an aggressive conflict. In primate groups, reconciliation reduces aggression and postconflict arousal. Aggression within a group can also increase arousal of bystanders (e.g. increase bystanders’ rates of self-directed behaviour). Since reconciliation reduces aggression between opponents, we tested whether it also reduces self-directed behaviour in bystanders. Following aggression in a captive group of hamadryas baboons, one observer conducted a focal sample on one of the combatants to document reconciliation and a second observer simultaneously conducted a focal sample on a randomly selected bystander. Matched control observations were then collected on the same individuals in a nonaggressive context to obtain baseline levels of behaviour. The self-directed behaviour of bystanders was elevated after witnessing a fight compared to baseline levels. If combatants reconciled aggression, bystander rates of self-directed behaviour significantly decreased. If combatants did not reconcile aggression, bystander rates of self-directed behaviour remained at elevated levels, significantly higher than after reconciliation. If combatants affiliated with partners other than their original opponent, bystander rates of self-directed behaviour did not decrease. The rate of bystander self-directed behaviour after a combatant affiliated with its opponent was significantly lower than the rate after a combatant affiliated with other animals. Witnessing aggression increased arousal in bystanders, and reconciliation between the combatants was accompanied by reduced bystander arousal. The reduction was specific to contexts in which former opponents interacted. We suggest that bystanders recognized the functional significance of this conflict-resolution mechanism when it occurred in their group.