Maternal behaviour in sows of different social rank

The maternal behaviour of domestic sows in intensive husbandry has been studied in relation to their social rank during the second half of pregnancy when they were kept in groups. The sows dominant during pregnancy were more active immediately before farrowing but not after it. The low-ranking sows showed much more restlessness from the early days after farrowing and many stereotyped/redirected patterns. Those sows voluntarily interrupted nursing in the early days of lactation more often, while the dominant sows were more likely to allow piglets to suckle freely.     

Cow traffic in relation to social rank and motivation of cows in an automatic milking system with control gates and an open waiting area

Cow traffic in automatic milking (AM) systems can be controlled with gates at the entrances to feeding areas, where cows are either let through (gate opens) or redirected (gate remains closed) to an open waiting area in front of the milking unit (MU). The motivation of a cow to enter the MU after a redirection is assumed to be reflected in redirection time, which is the elapsed time from a redirection in a control gate (CG) until the next registration in the MU (i.e. CG → milking in MU/passage through MU). In order to study the possibility of guiding cows in this kind of system and to increase the understanding for the emergence of redirection time, a behavior study was performed at the Swedish University of Agricultural Sciences, Uppsala, Sweden. Two groups of 12 cows each (high and low social rank, respectively) in an AM-system with control gates and an open waiting area were used as focal cows. After a redirection in a CG, the location of each focal cow was continuously observed until entrance in the MU or during a maximum observation time of 1 h. This was repeated five times for each focal cow, generating 120 observations in total. The social rank of the cows was established from registered visits to roughage stations. Cows of high social rank spent, on an average, 13 min in the waiting area during the observation period, compared to 20 min for cows of low social rank. In 22% of all observations, the cows entered cubicles in a resting area during the 1 h observation period and when they did, they, on an average, spent 41 min of the 1 h long observation time in the cubicles. Both time since last feeding and time since last milking were in negative relationship to redirection time. The number of cows in the waiting area significantly prolonged the redirection time. Redirection time was influenced by individual characteristics, such as social rank and by situation-specific factors, such as time since last feeding, time since last milking and the number of cows in the waiting area.     

Anabolic androgenic steroid affects social aggression and fear-related behaviors in male pair-housed rats

This study examines the effect of chronic administration of the anabolic androgenic steroid nandrolone decanoate (ND) on dominant and subordinate male rats in a pair-housed condition. Pair-housed rats were assessed for dominance status based on their behavior and alterations in body weights. Throughout the study the rats were allowed limited social interactions on a daily basis. At all other times, a Plexiglas divider kept the rats separated, allowing olfactory and visual contact between the cage mates while preventing significant physical contact. One week into the study all subjects were subcutaneously implanted with a pellet that continuously infused either ND (15 mg/kg/day) or placebo for 21 days. Following the pellet implant, behavioral tests including reassessment for dominance status, and a conditioned fear test were conducted over a period of approximately 2 months to investigate possible long-term changes. The main finding is that during the allowed social interactions, the dominant ND-pretreated rats spent more time on highly aggressive behaviors than the dominant placebo-treated rats. In addition, the probability for highly aggressive behaviors was maintained for the ND-treated rats throughout the study, whereas it was decreased for the placebo-treated rats. The ND-treated subordinate rats showed less fear in a potential threatening situation compared to placebo-treated controls. These findings support the relatively long-term behavioral changes that have been seen in humans after abuse of ND and other anabolic androgenic steroid compounds.     

Diurnal rhythm of bar-biting in relation to other behaviour in pregnant sows

Instantaneous observations of behaviour were made with video once every sixth minute around the clock (in 20-s recordings at each interval) during the first 3 days following the introduction of pregnant sows into one of the following three environments: (1) loose housing in groups of five with a common lying area, a dunging area and individual feeding stalls (20 sows); (2) semiconfinement in groups of four in individual feeding stalls with access to a common dunging area (16 sows); (3) confinement in individual stalls (16 sows). In addition, direct observations of straw-directed behaviour after feeding were made. Bar-biting was most frequent in confinement and least in loose housing (22.5% of observations when the sows were active in confinement, 7.5% in semi-confinement and 3% in loose housing). Bar-biting was mainly performed during ∼2 h following feeding. At the time when confined and semi-confined sows performed most bar-biting, the loose-housed sows moved a lot and performed complex straw-directed activities, including several of the normal nest-building behaviours. It was concluded that the differences in frequencies of stereotypies cannot be explained only by frustration at feeding, but depend on the housing system of the sows. Many of the movements in the stereotyped sequences of the confined sows resembled elements in the nesting sequences of loose-housed sows, supporting the hypothesis that a thwarted movement pattern can develop into a stereotypy, which then may bear resemblance to the normal movements.     

Oviductal isthmic motility in relation to ovulation and endocrine changes in unrestrained sows

This study was designed to characterize changes in the motility of the oviductal isthmus in relation to endocrine changes around ovulation in unrestrained sows in their normal environment. Oviductal isthmic motility was monitored on Polyview from 11 h prior to and up to 36 h after ovulation in 13 unrestrained multiparous sows during their second estrus after weaning, using a pressure microtransducer implanted 3 cm into the isthmus. Both the maximum, minimum and mean pressures and the frequency of phasic pressure fluctuations were high prior to ovulation but declined significantly (P<0.05) at 9 to 12 h, 13 to 16 h, 13 to 16 h and 5 to 8 h after ovulation, respectively. Plasma estradiol-17beta and prostaglandin F2alpha metabolite levels declined significantly (P<0.05) at 4 to 7 h prior to ovulation while progesterone levels increased significantly (P<0.01) at 5 to 8 h after ovulation. The decrease in the plasma estradiol-17beta levels was correlated to the decrease in maximum and mean pressures and the frequency of phasic pressure fluctuations (n=113; r=0.30, 0.25, 0.25, respectively; P<0.01) but not to the decrease in minimum pressure (n=113; r=0.17, P>0.05). Similarly, the decrease in PGF2alpha metabolite levels was correlated to the decrease in minimum, maximum and mean pressures and the frequency of phasic pressure fluctuations (n=112; r=0.43, 0.35, 0.38, 0.32, respectively; P<0.001). Conversely, the increase in plasma progesterone levels was correlated to the decrease in minimum, maximum and mean pressures and the frequency of phasic pressure fluctuations (n=113; r=-0.56, -0.70, -0.68, -0.60, respectively; P<0.001). Therefore, the pressure parameters seem to be influenced by changes in the levels of estradiol-17beta, prostaglandin F2alpha and progesterone with respect to ovulation.     

Sexual dimorphism in relation to current selection in the house finch

Abstract.— Sexual dimorphism is thought to have evolved in response to selection pressures that differ between males and females. Our aim in this study was to determine the role of current net selection in shaping and maintaining contemporary sexual dimorphism in a recently established population of the house finch ( Carpodacus mexicanus ) in Montana. We found strong differences between sexes in direction of selection on sexually dimorphic traits, significant heritabilities of these traits, and a close congruence between current selection and observed sexual dimorphism in Montana house finches. Strong directional selection on sexually dimorphic traits and similar intensities of selection in each sex suggested that sexual dimorphism arises from adaptive responses in males and females, with both sexes being far from their local fitness optimum. This pattern is expected when a recently established population experiences continuous immigration from ecologically distinct areas of a species range or as a result of widely fluctuating selection pressures, as found in our study. Strong and sexually dimorphic selection pressures on heritable morphological traits, in combination with low phenotypic and genetic covariation among these traits during growth, may have accounted for close congruence between current selection and observed sexual dimorphism in the house finch. This conclusion is consistent with the profound adaptive population divergence in sexual dimorphism that accompanied very successful colonization of most of the North America by the house finch over the last 50 years.     

Dynamics and mechanics of social rank reversal

Stable social relationships are rearranged over time as resources such as favored territorial positions change. We test the hypotheses that social rank relationships are relatively stable, and although social signals influence aggression and rank, they are not as important as memory of an opponent. In addition, we hypothesize that eyespots, aggression and corticosterone influence serotonin and N-methyl-D-aspartate (NMDA) systems in limbic structures involved in learning and memory. In stable adult dominant-subordinate relationships in the lizard Anolis carolinensis, social rank can be reversed by pharmacological elevation of limbic serotonergic activity. Any pair of specific experiences: behaving aggressively, viewing aggression or perceiving sign stimuli indicative of dominant rank also elevate serotonergic activity. Differences in the extent of serotonergic activation may be a discriminating and consolidating factor in attaining superior rank. For instance, socially aggressive encounters lead to increases in plasma corticosterone that stimulate both serotonergic activity and expression of the NMDA receptor subunit 2B (NR_2B) within the CA₃ region of the lizard hippocampus. Integration of these systems will regulate opponent recognition and memory, motivation to attack or retreat, and behavioral and physiological reactions to stressful social interactions. Contextually appropriate social responses provide a modifiable basis for coping with the flexibility of social relationships.     

Glucocorticoids of bison bulls in relation to social status

A primary response to stress is an increase in circulating adrenal glucocorticoids (GC) such as cortisol. Two hypotheses propose differential stress responses to agonistic and aggressive interactions in social groups. If subordinate animals are subjected to social and psychological stressors leading to chronic GC elevation, the 'stress of subordination' hypothesis predicts that GCs will be higher in subordinates than dominants. Alternatively, if dominant animals are subject to physiological stressors (e.g., fight at higher rates than subordinates) or hierarchies are unstable, the 'stress of domination' hypothesis predicts higher GCs in dominant individuals. Both models predict that GC levels will peak during the breeding season. We tested these predictions in bison bulls (Bison bison) using fecal steroid analysis to characterize GC concentration and behavioral observations to determine dominance rank, copulatory success, and tending status of bulls. Fecal samples were collected during 2003 from adult bison bulls during pre-rut (June), rut (July-August), and post-rut (September). Matched sample data indicated that mean GC levels (ng/g feces) of bulls strongly peaked during the 4-week rut, doubling from pre-rut to rut and then declining again during post-rut. High ranked dominant bulls maintained higher GC levels than lower ranked subordinate bulls. Dominance rank was positively correlated with copulatory success and age, and dominant bulls were more likely to tend (guard) cows as they approached estrus. There was a positive correlation between GC level and copulatory success, with prime-aged bulls (> or =7 years) obtaining the most copulations. GC levels were positively correlated with bull androgen levels determined in a previous study. These results support the 'stress of domination' hypothesis, indicating that dominant bison bulls pay a significant physiological price for high social status and the opportunity to mate.     

Sexual incentive motivation in male rats requires both androgens and estrogens

In Experiment 1 castrated male rats were implanted with a Silastic capsule containing either E or cholesterol (CHOL) 35 days after castration. They were then tested for sexual incentive motivation and copulatory behaviors every 5th day for 3 weeks. None of the treatments affected sexual incentive motivation. After the last test, all subjects were implanted with DHT-containing Silastic capsules, and tests continued for another 3 weeks. While E + DHT enhanced sexual incentive motivation and copulatory behavior, DHT alone failed to do so. In Experiment 2 the aromatase inhibitor fadrozole (F) was combined with testosterone (T). T restored all behaviors to the level seen in intact rats, and F significantly reduced these effects. In fact, T + F was not different from DHT. T and DHT restored the weight of the prostate and seminal vesicles to levels close to those of intact rats. In Experiment 3 a lower dose of E was employed. Also this dose of E failed to affect sexual incentive motivation while E + DHT restored it to the level of intact animals. Castration enhanced the serum concentrations of LH and FSH. E alone caused a marked reduction, and E + DHT brought both gonadotropins back to the level of intact animals. It was concluded that the doses of E and DHT employed in these experiments were within or close to the physiological range, and that such doses of E completely fail to enhance sexual incentive motivation in castrated animals. DHT has small or no effects. It appears that sexual incentive motivation and copulation require simultaneous stimulation of androgen and estrogen receptors.     

Stress, social rank and leukocyte telomere length

Blood leukocytes are a heterogeneous mixture of cell types whose telomere lengths differ greatly, reflecting variation in stem cell turnover and recruitment, expansion and replacement of more mature cell types as well as variable telomere loss and telomere repair. These differences in cell and telomere length dynamics, together with the evidence that telomere length is influenced strongly by genetic polymorphisms, greatly complicate the interpretation of claims that socio-economic status modulates the rate of telomere attrition.     

Influence of social rank on defecating behaviors in feral cats

Feral cats,Felis catus, showed 2 different defecating behaviors: they buried feces or left then exposed on the ground. We studied the relationship between the spatial distribution of buried/exposed feces and body weight of the producers, using the bait-marking method. Disproportionally small numbers of feces were found in the core areas of home ranges. The proportion of exposed feces in the core area was not different from that outside the core area, either and was not correlated with body weight in either sex. Heavier male cats buried feces at higher frequencies at sites closer to the centers. Such relationships were not found for females. These results suggest that social rank influences defecating behaviors in male feral cats. alphabetical order     

Reproductive success in relation to dominance rank in the absence of prime-age males in Barbary macaques

In some primate species dominance rank of males is correlated with reproductive success, whereas in other species this relationship is inconsistent. Barbary macaques (Macaca sylvanus) live in a promiscuous mating system in which males are ranked in a dominance hierarchy that influences their access to females. High-ranking males usually monopolize fertile females during their estrous period and show increased mating activities. Subadult males generally rank below adult males. For Barbary macaque females in the Gibraltar colony, there was no correlation between dominance status and reproductive success. Paternity data for 31 offspring collected over four consecutive breeding seasons were used to test whether male social rank was associated with reproductive success and whether reproductive success was mainly confined to a small number of males. Genetic variation was assessed using 14 microsatellite markers for a dataset of 127 individuals sampled in all five social groups of the Gibraltar colony. Paternity analysis was conducted for offspring in one social group only, where all in-group males were sampled. Eighty-three percent of the offspring could be assigned to an in-group candidate father; none of the extra-group males appeared to have sired an infant. Male dominance rank was not found to contribute to the observed variation in male reproductive output. Fifty-nine percent of the offspring was sired by two low-ranking males, whereas the two top-ranking males sired one-fifth. A highly significant correlation was found for male age and dominance rank. Reproductive success of subadult males might be explained by the gap in the age distribution of male group members. These missing prime males are usually regarded as serious competitors for older males. Subadult males may have gained easier access to females in their absence. In addition, the presence of inbreeding avoidance mechanisms, which might also have overpowered possible rank effects, cannot be excluded.     

Rapid adjustments of sperm characteristics in relation to social status

Sperm competition models predict that males typically mating in disfavoured roles should be selected to compensate for their disadvantage by investing more into sperm. We studied the effect of rapid changes in social status on ejaculate investments during experimental trials with an externally fertilizing teleost--the Arctic charr (Salvelinus alpinus). We document that males becoming dominant produce less sperm with lower velocity, but have higher sex steroid concentrations than subordinate males. These differences in sperm characteristics seem mainly to result from a decreased investment in sperm among fish that become dominant compared to pre-trial levels. Moreover, these adjustments of sperm production and sperm velocity seem not to be traded against sperm longevity. Our results support theoretical models of sperm competition, as males forced to mate in disfavoured roles seem to invest more into ejaculate quality than males in favoured roles. Additionally, we are the first to report that males, in a species with status-dependent shifts in reproductive tactics, have evolved rapid tactic specific adjustments of sperm production and sperm velocity corresponding to what could be predicted from their reproductive roles.     

Sexual dimorphism in relation to big-game hunting and economy in modern human populations

Postcranial skeletal data from two recent Eskimo populations are used to test David Frayer's model of sexual dimorphism reduction in Europe between the Upper Paleolithic and Mesolithic. Frayer argued that a change from big-game hunting and adoption of new technology in the Mesolithic reduced selection for large body size in males and led to a reduction in skeletal sexual dimorphism. Though aspects of Frayer's work have been criticized in the literature, the association of big-game hunting and high sexual dimorphism is untested. This study employs univariate and multivariate analysis to test that association by examining sexual dimorphism of cranial and postcranial bones of two recent Alaskan Eskimo populations, one being big-game (whale and other large marine mammal) hunting people, and the second being salmon fishing, riverine people. While big-game hunting influences skeletal robusticity, it cannot be said to lead to greater sexual dimorphism generally. The two populations had different relative sexual dimorphism levels for different parts of the body. Notably, the big-game hunting (whaling) Eskimos had the lower multivariate dimorphism in the humerus, which could be expected to be the structure under greatest exertion by such hunting in males. While the exertions of the whale hunting economic activities led to high skeletal robusticity, as predicted by Frayer's model, this was true of the females as well as the males, resulting in low sexual dimorphism in some features. Females are half the sexual dimorphism equation, and they cannot be seen as constants in any model of economic behavior. © 1993 Wiley-Liss, Inc.     

Sexual size dimorphism and reproductive ecology in relation to mating system in waders

The relationship between sexual size dimorphism, body-weight and different reproductive traits (e.g. clutch size, egg weight and incubation period) in relation to mating system and forms of parental care was studied in waders. Two hypotheses were examined. (1) Sexual size dimorphism is correlated with the intensity of sexual selection. (2) The degree of sexual size dimorphism is the result of an interrelationship between the reproductive strategy of the female and her body size. In the polygynous species the male was significantly larger than the female. This is consistent with the sexual selection hypothesis. However, among waders, a positive correlation exists between egg weight, clutch mass and body-weight. Selection for small eggs or a short incubation period may therefore have an influence on female body-weight. If the lack of paternal care reduces the female's possibility for producing large eggs or incubating a large clutch mass, we would expect a selection pressure for small female size among polygynous species. Thus, large sexual size dimorphism among polygynous waders may be a result of selection for small female size to lack of paternal care, or selection for large male size due to intramale competition or a female preference for large-sized males. In multiple-clutch species (viz. species in which the female regularly lays more than one clutch during the season) egg weight was low both for a given female and male body-weight. The low egg weight of multiple-clutch species is assumed to be a result of the constraints placed on the female from producing several clutches during a single breeding season.