Pair-housing of male and female rats during chronic stress exposure results in gender-specific behavioral responses

Social support has a positive influence on the course of a depression and social housing of rats could provide an animal model for studying the neurobiological mechanisms of social support. Male and female rats were subjected to chronic footshock stress for 3 weeks and pair-housing of rats was used to mimic social support. Rats were isolated or housed with a partner of the opposite sex. A plastic tube was placed in each cage and subsequently used as a 'safe' area in an open field test. Time spent in the tube was used as a measurement of anxiety levels. Chronic stress increased adrenal weights in all groups, except for isolated females who showed adrenal hypertrophy in control conditions. In isolated males, chronic stress resulted in an increase in the time the animals spent in the tube. While stress did not affect this parameter in socially housed males, males with a stressed partner showed a similar response as isolated stressed males. Even though adrenal weights showed that isolated females were more affected by stress, after chronic stress exposure, they spent less time in the tube than socially housed females. Socially housed stressed females spent less time in the 'safe' tube compared to control counterparts, indicating that stress has a gender-specific behavioral effect. In conclusion: pair-housing had a stress-reducing effect on behavior in males. Isolation of females was stressful by itself. Pair housing of females was not able to prevent stress-induced behavioral changes completely, but appeared to reduce the effects of chronic stress.     

Breeding biology and social behaviour of Magellanic Woodpeckers (<Emphasis Type="Italic">Campephilus magellanicus</Emphasis>) in Argentine Patagonia

The Magellanic Woodpecker (Campephilus magellanicus) is a poorly known species endemic of the Austral Temperate Forests of South America, where it is a potential keystone habitat modifier. Here, I summarize data on the social and breeding biology of this woodpecker, based on 22 active nests located from 1998–2002 in forests from northwestern Argentine Patagonia. Woodpeckers normally traveled in pairs or family parties. In late Austral winter, one to three cavities were selected for completion at each territory. Breeding occurred between mid- to late spring and early to mid-summer, and took about 65 days. Monogamous parents shared duties in nest excavation, incubation and young rearing. Egg length (±SD) measured 34.13±0.79 mm and egg breadth 23.91±0.67 mm, and incubation took roughly 20 days. Nestlings were altricial and remained at the nest for about 45 days. Clutch size was one, occasionally two eggs, and one nestling was produced at all successful nests. Young remained with their family group for up to 2 years or more, and were fed by adults, who normally bred every second year. Nest re-use, nest predation and helpers at the nest were not recorded. Holes were placed (±SD) 8.84±3.71 m high and were 32.3±5.32 cm deep. Entrances (±SD) were 8.92±0.46 cm wide and 15.59±2.54 cm high and mostly oval in shape. Peculiarities of the breeding biology and social behaviour of this species are discussed in the light of patterns common to picids, especially Campephilus spp.     

Underwater observations of piranhas in western Brazil

Synopsis The behaviour of three piranha species,Serrasalmus marginatus, S. spilopleura, andPygocentrus nattereri, and their prey fishes was studied underwater in the Pantanal region, Mato Grosso, Brazil. General habits, predatory tactics, feeding behaviour, and social interactions while foraging, as well as defensive tactics of prey fishes were observed.S. marginatus is solitary whereas the other two species live in shoals; their agonistic behaviour varies accordingly, the simplest being displayed by the solitary species. Predatory tactics and feeding behaviour also vary:S. spilopleura shows the most varied diet and highly opportunistic feeding strategy, which includes aggressive mimicry. The solitaryS. marginatus, besides fin and scale-eating, occasionally cleans larger individuals ofP. nattereri. Several cichlid species display defensive tactics clearly related to piranha attacks: tail protecting, watching, and confronting the predator are the most commonly observed behaviours. Piranhas seem to strongly influence use of habitat, social structure, and foraging mode of the fish communities.     

Spatial effects in social dilemmas

Social dilemmas and the evolutionary conundrum of cooperation are traditionally studied through various kinds of game theoretical models such as the prisoner's dilemma, public goods games, snowdrift games or by-product mutualism. All of them exemplify situations which are characterized by different degrees of conflicting interests between the individuals and the community. In groups of interacting individuals, cooperators produce a common good benefitting the entire group at some cost to themselves, whereas defectors attempt to exploit the resource by avoiding the costly contributions. Based on synergistic or discounted accumulation of cooperative benefits a unifying theoretical framework was recently introduced that encompasses all games that have traditionally been studied separately (Hauert, Michor, Nowak, Doebeli, 2005. Synergy and discounting of cooperation in social dilemmas. J. Theor. Biol., in press.). Within this framework we investigate the effects of spatial structure with limited local interactions on the evolutionary fate of cooperators and defectors. The quantitative effects of space turn out to be quite sensitive to the underlying microscopic update mechanisms but, more general, we demonstrate that in prisoner's dilemma type interactions spatial structure benefits cooperation-although the parameter range is quite limited-whereas in snowdrift type interactions spatial structure may be beneficial too, but often turns out to be detrimental to cooperation.     

Group differences in captive gorillas’ reaction to large crowds

The impact of visitor crowd size on captive animal behaviour can be difficult to interpret in many institutions due to the lack of variation in crowd size over short periods of time. In attempts to compare greater variation in crowd size, animal behaviour is often compared over conditions that create additional confounds, such as day of week or season. Fluctuations in attendance over the holiday season at Disney's Animal Kingdom^® Theme Park provided an opportunity to examine the impact of variation in crowd size on gorilla behaviour without the confounds found in many other studies. Ten western lowland gorillas (Gorilla g. gorilla) in a bachelor group (n = 4) and a family group (n = 6) were observed over a period of 8 weeks in late 2005. Observations were classified into Large Crowd and Small Crowd days and a repeated-measures ANOVA procedure was conducted to determine the effects of crowd size and social group on gorilla behaviour patterns. Few overall differences were found in behaviour during the Large Crowd and Small Crowd conditions. However, similar to previous research, gorillas were less visible during the Large Crowd condition (F_1,8 = 14.15, P = 0.01). There was also an interaction of crowd size and group (F_1,8 = 7.58, P = 0.01), indicating the bachelor group of gorillas was more aggressive during the Large Crowd condition, whereas the family group showed no increase in aggression with large crowds. These results indicate the importance of providing complex enclosures with visual barriers to allow animals to move away from large crowds if they choose. Future research should focus on the individual characteristics of animals and enclosures that may contribute to behavioural differences in visitor–animal interaction research, as well as the proximate cues associated with behaviour change when exposed to large crowds.     

Scale-dependent interactions and community structure on cobble beaches

Recent theory suggests that scale-dependent interaction between facilitation and competition can generate spatial structure in ecological communities. The application of this hypothesis, however, has been limited to systems with little underlying heterogeneity. We evaluated this prediction in a plant community along an intertidal stress gradient on cobble beaches in Rhode Island, USA. Prior studies have shown that Spartina alterniflora facilitates a forb-dominated community higher in the intertidal by modifying the shoreline environment. We tested the hypothesis that, at a smaller scale, Spartina competitively excludes forb species, explaining their marked absence within the lower Spartina zone. Transplant experiments showed forb species grow significantly better in the Spartina zone when neighbours were removed. Removal of the Spartina canopy led to a massive emergence of annual forbs, showing that competition limits local occupation. These findings indicate that interaction of large-scale facilitation and small-scale competition drives plant zonation on cobble beaches. This study is the first to provide empirical evidence of scale-dependent interactions between facilitation and competition spatially structuring communities in heterogeneous environments.     

Plant–Plant and Plant–Topography Interactions on a Rock Outcrop at High Altitude in Southeastern Brazil1

Plant establishment and growth on rocky outcrops in the Itatiaia massif (2400 m a.s.l.), southeastern Brazil, are limited by lack of soil and by freezing temperatures in winter nights. Mat‐forming species of different sizes and shapes on bare rock provide substrate for other plants to establish. The habitat preference of two geophytes, Stevia camporum (Asteraceae) and Alstroemeria foliosa (Alstroemeriaceae), was compared with regard to their association with the type of mat species and distinct rock topographies. The habitat preference of the mat species in regard to topography was also assessed. We found 1706 ramets of S. camporum and 1317 of A. foliosa in 253 vegetation islands ranging in size from 0.005 to 18.097 m². Mat species in these islands were Fernseea itatiaiae, Vriesea itatiaiae (both Bromeliaceae), Pleurostima gounelleana (Velloziaceae) and/or Campylopus pilifer (Dicranaceae) and other mosses. Mat species were segregated by topography. Geophytes were similarly distributed across types of topography but showed negative interspecific association. S. camporum occurred mostly on the moss‐dominated islands, whereas A. foliosa was more common in P. gounelleana islands. We found geophyte co‐occurrence in larger vegetation islands containing both P. gounelleana and mosses as mat species. Thus, the effect of topography on geophyte segregation was indirect, since topography affects mat species distribution, and the geophyte preference for distinct mat species as substrate resulted in their segregation.     

Peripheral administration of oxytocin increases social affiliation in the naked mole-rat (Heterocephalus glaber)

The neuropeptide oxytocin regulates a wide variety of social behaviors across diverse species. However, the types of behaviors that are influenced by this hormone are constrained by the species in question and the social organization that a particular species exhibits. Therefore, the present experiments investigated behaviors regulated by oxytocin in a eusocial mammalian species by using the naked mole-rat (Heterocephalus glaber). In Experiment 1, adult non-breeding mole-rats were given intraperitoneal injections of either oxytocin (1 mg/kg or 10 mg/kg) or saline on alternate days. Animals were then returned to their colony and behavior was recorded for minutes 15–30 post-injection. Both doses of oxytocin increased huddling behavior during this time period. In Experiment 2, animals received intraperitoneal injections of either oxytocin (1 mg/kg), an oxytocin-receptor antagonist (0.1 mg/kg), a cocktail of oxytocin and the antagonist, or saline across 4 testing days in a counterbalanced design. Animals were placed in either a 2-chamber arena with a familiar conspecific or in a small chamber with 1 week old pups from their home colony and behaviors were recorded for minutes 15–30 post-injection. Oxytocin increased investigation of, and time spent in close proximity to, a familiar conspecific; these effects were blocked by the oxytocin antagonist. No effects were seen on pup-directed behavior. These data suggest that oxytocin is capable of modulating affiliative-like behavior in this eusocial species.