Unusual intra-specific aggression in striped hyena

Unicoloniality emerges as a feature that characterizes successful invasive species. Its underlying mechanism is reduced intraspecific aggression while keeping interspecific competitiveness. To that effect, we present here a comparative behavioural and chemical study of the invasive ant Wasmannia auropunctata in parts of its native and introduced ranges. We tested the hypothesis that introduced populations (New Caledonia archipelago) have reduced intraspecific aggression relative to native populations (e.g., Ilhéus area, Brazil) and that this correlates with reduced variability in cuticular hydrocarbons (CHCs). As predicted, there was high intraspecific aggression in the Brazilian populations, but no intraspecific aggression among the New Caledonian populations. However, New Caledonian worker W. auropunctata remained highly aggressive towards ants of other invasive species. The chemical data corresponded with the behaviour. While CHCs of ants from the regions of Brazil diverged, the profiles of ants from various localities in New Caledonia showed high uniformity. We suggest that in New Caledonia W. auropunctata appears to behave as a single supercolony, whereas in its native range it acts as a multicolonial species. The uniformity of recognition cues in the New Caledonia ants may reflect a process whereby recognition alleles became fixed in the population, but may also be the consequence of a single introduction event and subsequent aggressive invasion of the ecosystem. Chemical uniformity coupled with low intraspecific but high interspecific aggression, lend credence to the latter hypothesis.

Intraspecific aggressiveness can be affected by multiple environmental pressures. In several cases, aggressiveness can grade into full-scale cannibalism, particularly when resources are scarce. However, limited information exists on how intraspecific aggressiveness varies among populations experiencing different environmental pressures, and on the role intraspecific predation plays for the exploitation of harsh habitats. The fire salamander, Salamandra salamandra, is an excellent model species to study factors affecting intraspecific aggressiveness, because of its ability to breed in habitats with contrasting food resources and predation pressure. Here, we evaluated the influence of predation risk and habitat of origin on aggressive interactions. To this extent, we reared larvae from cave (scarce resources; nearly-absent predators) and surface (abundant resources and predators) populations under different risk conditions and measured aggressive behavior towards conspecifics. During behavioral trials, larvae were exposed to different combinations of predator and wounded conspecific chemical cues. Intraspecific aggressiveness increased in large and late-development larvae. Larvae from all the populations significantly reduced aggressiveness under both typologies of risk experienced during rearing (constant presence of predator; pulses of high predation risk), and also when stimulated by predator cues. However, larvae from cave populations exhibited a more pronounced aggressiveness, especially when exposed to wounded conspecific cues. Intraspecific aggressiveness can be modulated by the complex interaction between multiple variables, and both behavioral plasticity and local adaptations can determine its variation across populations. Our findings reveal that aggressive interactions are favored in cave environment, suggesting intraspecific predation can play a key role in the exploitation of resource-depleted habitats. In this study, we investigated how intraspecific aggressiveness of salamander larvae is shaped under predation risk in populations originating from contrasting environments, such as cave and surface habitats. Larvae experiencing predator presence during their development or exposed to predator cues significantly reduced their aggressive interactions, both in cave and surface populations. Interestingly, cave-originating individuals reacted to wounded conspecific cues by increasing the frequency of their aggressive displays, suggesting cannibalistic behavior is locally enhanced in populations from resource-depleted habitats. The present study offers new insights on the importance of intraspecific aggressiveness for the adaptation to harsh environments.

We examined the changes in the intensity of intra-specific aggression (ISA) in a kestrel (Falco tinnunculus canariensis) population throughout the breeding season, in order to evaluate the main hypotheses regarding ISA (defence of parentage, food, nest-site and offspring). Each pair was presented with a live caged adult male or female as a conspecific intruder. The intensity of ISA did not vary significantly during the breeding season, and nor did it correlate with offspring value, or food availability. Our island-dwelling kestrel population showed low fluctuation in ISA during the breeding season, and similar levels of aggression in both members of the pair towards male or female intruders. These findings support the nest-site defence hypothesis. Pairs with more exposed nest-sites showed increased ISA, unexplained by offspring value. We suggest that this behaviour is related with nest-site conspicuousness and vulnerability. The pairs displaying greater ISA also showed greater aggression towards humans, the main local predator. This may indicate that defensive behaviour evolved in the past when it was advantageous against predators, and became a trait. Compared with the non-island reference population, we only found differences in ISA during the pre-laying phase: lower intensity of aggressive behaviour between males, and higher between females.

Infanticide has been widely documented throughout the animal kingdom, and has generally been viewed as an evolved, or adaptive behavior for the perpetrators. Infanticide motivated by increased sexual access to females with calves, or the elimination of potential genetic competition in the form of calf-directed aggression or infanticide, has been proposed for delphinids including killer whales, Indo-Pacific humpback dolphins, Guiana dolphins, and bottlenose dolphins. However, reports of intraspecific aggression towards bottlenose dolphin calves are relatively infrequent, and accounts of confirmed infanticide are rarer still. Reporting instances of intraspecific calf-directed aggression aids researchers to better understand the socio-behavioral context of these aggressive interactions. Here, we report an incident of conspecific aggression towards a calf in a small group of common bottlenose dolphins near Sabine Lake, northwestern Gulf of Mexico. We discuss the behavioral context, and surveyed other researchers to attempt to gauge the prevalence of perceived aggressive interactions among the bottlenose dolphin groups they study in the northern Gulf of Mexico.

A novel semi-automated apparatus for measurement of aggressive biting behavior in mice

Understanding the rates and causes of mortality in wild chimpanzee populations has important implications for a variety of fields, including wildlife conservation and human evolution. Because chimpanzees are long-lived, accurate mortality data requires very long-term studies. Here, we analyze 47 years of data on the Kasekela community in Gombe National Park. Community size fluctuated between 38 and 60, containing 60 individuals in 2006. From records on 220 chimpanzees and 130 deaths, we found that the most important cause of mortality in the Kasekela community was illness (58% of deaths with known cause), followed by intraspecific aggression (20% of deaths with known cause). Previous studies at other sites also found that illness was the primary cause of mortality and that some epidemic disease could be traced to humans. As at other study sites, most deaths due to illness occurred during epidemics, and the most common category of disease was respiratory. Intraspecific lethal aggression occurred within the community, including the killing of infants by both males and females, and among adult males during the course of dominance-related aggression. Aggression between communities resulted in the deaths of at least five adult males and two adult females in the Kasekela and Kahama communities. The frequency of intercommunity violence appears to vary considerably among sites and over time. Intercommunity lethal aggression involving the Kasekela community was observed most frequently during two periods. Other less common causes of death included injury, loss of mother, maternal disability, and poaching.

Acts of aggression by Roseate Tern (Sterna dougallii) adults on conspecific chicks were examined on Aride Island, Seychelles, from 13 June-10 July 1998. Data were used to examine two hypotheses to explain adult aggression towards chicks: (1) the adoption avoidance hypothesis, and (2) the feeding unfamiliar chicks hypothesis. Throughout the entire nestling development, adults pecked mostly unattended chicks (96%). The intensity of pecking was higher on b-chicks than on a-chicks and 72% of the pecking acts were on chicks that were on their own nests. During each pecking act, young chicks (0-6 days) were pecked by a greater number of adults than were old chicks (>6 days). When pecked, young chicks moved significantly greater distances away from nests than did old chicks (1.41 ± 1.92 m vs. 0.18 ± 0.42 m). Of the 23 chicks killed by adults, 11 were a-chicks, representing 8.5% of the a–chicks in the study area. Parents sometimes rescued a-chicks, but did not attempt to rescue b-chicks from adult attacks. Chicks that died had moved significantly greater distances away from nests than chicks that survived (2.8 ± 2.5 m vs. 0.3 ± 0.67 m). This study presents evidence that both hypotheses may be important in explaining intraspecific adult aggression by Roseate Terns on chicks. In particular, the feeding unfamiliar chicks hypothesis may be invoked to explain the significant negative correlation between daily intensity of adult aggression and the amount of food delivered to chicks. The adoption avoidance hypothesis may explain why b-chicks were disproportionately involved in pecking in relation to a-chicks. Adult aggression is an additive factor of chick mortality, operating mostly on days of food shortage.

We examined intraspecific colonial aggressiveness in Wasmannia auropunctata (Roger), a tramp species originating from the neotropics. By observing the results of one-on-one confrontations, we compared the behavioral responses of workers originating from six New Caledonian locations (introduced range) and four Brazilian cocoa plantations (original range). We recorded interindividual “aggressive” behavior on four levels ranging from physical contact, with no aggressive response, to prolonged aggressiveness, including stinging by one or both ants. In Brazil, we often observed high intraspecific aggressiveness between populations originating from distant locations, indicating that W. auropunctata may behave as a multicolonial species in its native range. In New Caledonia, paired encounters resulted in low agonistic behavior, as shown by the absence of “full attacks” (which include stinging by one or both opponents). Our results suggest that W. auropunctata behaves as a single supercolony throughout New Caledonia and that the scale of its unicoloniality (widespread colonies with interconnected nests without aggressiveness between workers originating from distant areas) is different in introduced and native populations. According to the present study, it seems likely that differences in intraspecific aggressiveness between native and introduced populations of W. auropunctata contribute to its invasive success.

SummaryBody size often varies among insular populations relative to continental conspecifics – the ‘island rule’ – and functional, context‐dependent morphological differences tend to track this body size variation on islands.Two hypotheses are often proposed as potential drivers of insular population differences in morphology: one relating to diet and the other involving intraspecific competition and aggression. We directly tested whether differences in morphology and maximum bite capacity were explained by interisland changes in hardness of both available and consumed prey, and levels of lizard‐to‐lizard aggression among small‐island populations.Our study included 11 islands in the Greek Cyclades and made use of a gradient in island area spanning five orders of magnitude. We focused on the widespread lizardPodarcis erhardii.We found that on smaller islands,P. erhardiibody size was larger, head height was larger relative to body size, and maximum bite capacity became proportionally stronger.This pattern in morphology and performance was not related to differences in diet, but was highly correlated with proxies of intraspecific aggression – bite scars and missing toes.Our findings suggest that critical functional traits such as body size and bite force inP. erhardiifollow the predictions of the island rule and are changing in response to changes in the competitive landscape across islands of different sizes.

Since 1985 a resident community of Atlantic spotted dolphins (Stenella frontalis), and bottlenose dolphins (Tursiops truncatus), have been studied underwater in the Bahamas. Over 200 individuals of both species have been identified and observed over the years. Basic correlations with sound patterns and behavior such as whistles during contact/reunions and squawks during aggression have been reported. This paper describes a small subset of their vocal repertoire that involves synchronous/rhythmic sound production. Dolphin behavior was recorded underwater using underwater video cameras with hydrophone input. Vocalizations were correlated with basic underwater behavioral activity and analyzed using Raven 1.3. Spotted dolphins were observed using two types of synchronized vocalizations including synchronized squawks (burst pulsed vocalizations) and screams- (overlapping FM whistles) during intraspecific and interspecific aggression. Bottlenose dolphins used three types of synchronized vocalizations; whistles/buzz bouts, bray/buzz bouts, and buzz bouts during intraspecific aggression. Body postures were synchronous with physical movements and often mirrored the rhythm of the vocalizations. The intervals between highly synchronized vocalizations had small variance and created a rhythmic quality and cadence to the acoustic sequences. Three types of vocalizations had similar ratios of sound duration to the spacing between sounds (Screams, whistle/buzz bouts, and bray/buzz bouts). Temporal aspects of sequences of sound and postures may be important aspects of individual and group coordination and behavior in delphinids.

Sexual dimorphism and intraspecific aggression, and their relationship to sex ratios in Caprella gorgonia Laubitz & Lewbel (Crustacea: Amphipoda: Caprellidae)

An influential period in avian life‐cycles is the annual breeding season, when competition over suitable nesting sites and territories is a key factor that can determine fitness and distribution, especially for species that are highly selective in their nesting habitats. We analysed nest‐site characteristics, breeding success and competitive interactions between two apex predator populations. Whereas the Short‐toed Eagle Circaetus gallicus has nested in the Judean Foothills (Israel) for a long time, the Long‐legged Buzzard Buteo rufinus has only invaded the nesting habitat of the Short‐toed Eagle during their breeding season in the last two decades. These two recently sympatric species have similar nesting ecology and frequently use the same nests. They are therefore expected to compete over nesting sites and territories. We analysed interspecific interactions between these two species by combining information from comprehensive observational, experimental, GIS analysis and remote sensing data, deriving 65 variables to characterize the nest‐sites used and the breeding success in 381 breeding attempts over four consecutive breeding seasons. To assess interspecific and intraspecific territorial behaviour and aggressiveness, stuffed Long‐legged Buzzards and Short‐toed Eagles were presented close to nests. Nest‐site characteristics overlapped substantially between species, and Long‐legged Buzzards occupied 21% of all Short‐toed Eagle nests. Intraspecific aggression rates among Long‐legged Buzzards were higher than their interspecific aggression rates with Short‐toed Eagles and also higher than intraspecific aggression among Short‐toed Eagles. Long‐legged Buzzard and Short‐toed Eagle breeding densities (1.59 ± 0.11 and 2.96 ± 0.11 pairs per 10 km2, respectively) are likely to be the highest across their respective breeding distributions, with a maximum productivity of 0.96 ± 0.01 and 0.56 ± 0.05 (young fledged/breeding pair) for Long‐legged Buzzard and Short‐toed Eagle, respectively. Intraspecific interactions among both species play an important role in determining their breeding success and the spatial distribution of nesting sites. Our results suggest that interspecific competition over nesting sites and territories between both species, and the potential dominance of Long‐legged Buzzard, has both direct and indirect impacts on the spatial and demographic distribution of Short‐toed Eagles due to the recent establishment of Long‐legged Buzzard territories in the Judean breeding area.

Intraspecific competition plays an important role for territory acquisition and occupancy, in turn affecting individual fitness. Thus, understanding the drivers of intraspecific aggression can increase our understanding of population dynamics. Here, we investigated intraspecific aggression in Eurasian (Castor fiber) and North American (Castor canadensis) beavers that are both monogamous, territorial mammals. Combined, we examined tail scars from >1,000 beavers (>2,000 capture events) as part of two long‐term studies in Norway and the USA. We investigated the influence of landscape structure, population density, sex, age, and (for Eurasian beavers only) social status and group size on the number of tail scars caused by conspecifics. The number of tail scars was affected by population density in well‐connected landscape types (large lakes and rivers), but not in more isolated areas (ponds), where individuals generally had fewer tail scars. Further, the relationship of population density was not linear. In the North American beaver population occurring in large lakes, intraspecific aggression increased with population density. Conversely, in the saturated Eurasian beaver population, intraspecific aggression was in a negative relationship with population density (except at the highest densities), likely due to inverse density‐dependent intruder pressure via dispersers. Our findings emphasize that population density can affect intraspecific aggression depending on landscape structure, which might have important consequences for local patterns of dispersal, mate change, and territory occupancy, all of which can affect population dynamics.

Shared and unshared parental investment in the precocial goldeneye (Aves: Anatidae)

Ground-nesting seabirds are vulnerable to human intrusion which can potentially impair their breeding success. We examined whether tourist traffic on a boardwalk through a Silver Gull Larus novaehollandiae breeding colony affected the birds' behaviour sufficiently to potentially decrease reproductive success. Nest density was positively correlated with distance from the boardwalk. Gulls nesting ≤5 m from the boardwalk were more vigilant towards a stationary investigator than those further away. Tourists walking past breeding gulls stimulated a large increase in intra-specific aggression; stopping alongside parents with mobile chicks increased their intra-specific aggression even more. Larger tourist groups (≥3) stimulated more intra-specific aggression than smaller ones. An investigator walking past breeding gulls similarly stimulated an increase in intra-specific aggression, but the investigator's clothing colour, noise emission level and walking speed had no effect on the birds. An ambulatory investigat...