Sex-reversed correlation between stress levels and dominance rank in a captive non-breeder flock of crows

Social niche shapes social behavior and cortisol concentrations during adolescence in female guinea pigs

Individualized social niches arise in social groups, resulting in divergent social behavior profiles among group members. During sensitive life phases, the individualized social niche can profoundly impact the development of social behavior and associated phenotypes such as hormone (e.g. cortisol) concentrations. Focusing on adolescence, we investigated the relationship between the individualized social niche, social behavior, and cortisol concentrations (baseline and responsiveness) in female guinea pigs. Females were pair-housed in early adolescence (initial social pair formation), and a social niche transition was induced after six weeks by replacing the partner with either a larger or smaller female. Regarding social behavior, dominance status was associated with aggression in both the initial social pairs and after the social niche transition, and the results suggest that aggression was rapidly and completely reshaped after the social niche transition. Meanwhile, submissive behavior was rapidly reshaped after the social niche transition, but this was incomplete. The dominance status attained in the initial social pair affected the extent of submissive behavior after the social niche transition, and this effect was still detected three weeks after the social niche transition. Regarding cortisol concentrations, higher baseline cortisol concentrations were measured in dominant females in the initial social pairs. After the social niche transition, cortisol responsiveness significantly increased for the females paired with a larger, older female relative to those paired with a smaller, younger female. These findings demonstrate that the social niche during adolescence plays a significant role in shaping behavior and hormone concentrations in females.

Salivary corticosterone measurement in large-billed crows by enzyme-linked immunosorbent assay

Salivary corticosteroid measurement, as a surrogate for plasma corticosteroid levels to evaluate an animal's stress or metabolic state, commonly used in mammals. However, the validity of salivary corticosterone (CORT) measurements in birds has not yet been reported. We aimed to measure salivary CORT in crows using a commercially available CORT enzyme-linked immunosorbent assay kit. An adrenocorticotropic hormone (ACTH) challenge experiment using synthetic cosyntropin, an ACTH analogue, was conducted to compare CORT level elevations between the serum and the saliva in a 10-60 min range. Both salivary and blood CORT was significantly elevated 10 min after injecting synthetic cosyntropin. The results supported the validation of salivary CORT as a surrogate for a blood CORT in crows.

Social encounters produce different autonomic response between dominants and subordinates in crows

Recent studies of behavioural physiology on animals have suggested the crucial role of peripherally physiological signals in eliciting arousal and emotion. Heart rate (HR) is one of the useful and critical signals to measure autonomic regulation as a physiological basis for arousal and emotion in response to biologically significant stimuli such as social encounter with conspecific individuals. However, our understanding of peripherally physiological response such as HRs and autonomic activities under social contexts of non-human animals is still limited, particularly in birds. Here, we examined the autonomic activity of behaving crows exposed to a dominant and a subordinate conspecific by using non-invasive electrocardiogram recording. We found different patterns of autonomic responses dependent on the relative dominance position: dominant crows encountering subordinates showed the elevation of sympathetic activity, whereas subordinates encountering dominants showed decreased HR with elevated parasympathetic activity. This is the first study in birds to report different autonomic responses dependent on relative dominance positions during dyadic social encounters. The present study advances our understanding of the role of the peripheral autonomic system, as an interactive system with the brain, in eliciting emotion/arousal associated with socially challenging environments from an evolutionary perspective.

Circulating hormones and dominance status predict female behavior during courtship in a lekking species

Female competitive behaviors during courtship can have substantial fitness consequences yet we know little about the physiological and social mechanisms underlying these behaviors - particularly for females of polygynous lek mating species. We explored the hormonal and social drivers of female intersexual and intrasexual behavior during courtship by males in a captive population of Indian peafowl. We investigated whether (1) female non-stress induced circulating estradiol (E2) and corticosterone (CORT) levels or (2) female dominance status in a dyad predict female solicitation behavior. We also tested whether female circulating E2 and CORT predict dominant females' aggressive behaviors toward subordinate females in the courtship context. Our findings demonstrate that females with higher levels of circulating E2 as well as higher levels of circulating CORT solicit more courtships from males. Dominant females also solicit more courtships from males than subordinate females. Female intrasexual aggressive behaviors during courtship, however, were not associated with circulating levels of E2 or CORT. Overall, we conclude that circulating steroid hormones in conjunction with social dominance might play a role in mediating female behaviors associated with competition for mates. Experimental manipulation and measures of hormonal flexibility throughout the breeding season in relation to competitive and sexual behaviors will be necessary to further examine the link between hormonal mechanisms and female behavior in polygynous lekking systems.

Basal cortisol concentrations related to maternal behavior during puppy development predict post-growth resilience in dogs

A prolonged stress hyporesponsive period (SHRP) due to the mother's presence may delay the timing of glucocorticoid (GC) elevation in infants, thereby reducing the excessive stress response that would affect post-growth temperament. In dogs, the SHRP has been suggested to persist until postnatal week (PW) 4; therefore, PW 5, which SHRP may be prolonged by the mother dog, may be a critical point in the developmental stage of dogs to establish stress responsiveness. We conducted a long-term survey on the development of dogs to investigate i) whether the degree of the stress response at PW 5 is determined by maternal behavior and ii) whether it can predict post-growth stress responses and temperament in dogs. As a result, the offspring of mother dogs who had more delivery experience and exhibited more maternal behavior showed higher basal cortisol concentrations at PW 5. These offspring may have acquired less fear response as an individual trait and had relatively quick adaptability, albeit with high cortisol concentrations during exposure to novel environments post-growth, suggesting that high cortisol concentrations at PW 5 are linked to resilience post-growth. Basal cortisol concentrations at PW 7 were not affected by maternal variables and were not associated with cortisol response to novel environments post-growth. GCs are essential hormones that increase the probability of survival. Therefore, the high hypothalamic pituitary adrenal activities of the mother dogs and their offspring in this study may not immediately indicate negative states, and these results prompt a reconsideration of the role of GC in organisms.

The association of social rank with paternity efficiency in competitive mating flocks of Zi goose ganders (Anser cygnoides L.)

The purpose of this study was to investigate the influence of social rank (SR) on paternity efficiency (PE) in competitive mating flocks of geese. Thirty ganders and 150 geese (Zi geese, Anser cygnoides L.) aged approximately one, were divided into 3 groups. Flock 1 included 10 ganders and 50 female geese, flock 2 included 11 ganders and 55 female geese, and flock 3 included 9 ganders and 45 female geese. The frequency of the agonistic behavioral interactions (ABI) of the ganders and mating activity (MA) were video recorded in each flock. The SR of each gander was determined by the frequency of ABI with a score of 1 to 3 (1 being the dominant and 3 the most subordinate). To clarify the difference between being dominant and submissive, we collapsed rank 2 and rank 3 into a “subordinate” category. In total, 280 eggs were collected, and 219 goslings were hatched. Parent–offspring relationships among 399 individuals from the 2 generations were identified via 20 microsatellite markers, and the PE of each gander was calculated. There was no significant difference in individual body weight and semen quality factor among the different SR groups (dominant and subordinate), and the SR of the ganders was significantly correlated to PE for the 3 flocks. Goslings of high-ranking ganders contributed 48.68% in flock 1, 37.50% in flock 2, and 47.62% in flock 3. Approximately 45% of all goslings were sired by the 7 dominant ganders of the 30 total ganders across the 3 flocks. As SR has been shown to be heritable in geese, the selection of high-ranking ganders might be an effective way to improve reproductive efficiency in commercial geese flocks.

Sex-specific effects of cooperative breeding and colonial nesting on prosociality in corvids

The investigation of prosocial behavior is of particular interest from an evolutionary perspective. Comparisons of prosociality across non-human animal species have, however, so far largely focused on primates, and their interpretation is hampered by the diversity of paradigms and procedures used. Here, we present the first systematic comparison of prosocial behavior across multiple species in a taxonomic group outside the primate order, namely the bird family Corvidae. We measured prosociality in eight corvid species, which vary in the expression of cooperative breeding and colonial nesting. We show that cooperative breeding is positively associated with prosocial behavior across species. Also, colonial nesting is associated with a stronger propensity for prosocial behavior, but only in males. The combined results of our study strongly suggest that both cooperative breeding and colonial nesting, which may both rely on heightened social tolerance at the nest, are likely evolutionary pathways to prosocial behavior in corvids.

STRESS INFLUENCE ON PLASMA PROTEIN ELECTROPHORESIS IN THE RED-BREASTED GOOSE (BRANTA RUFICOLLIS) AND HAWAIIAN GOOSE (BRANTA SANDVICENSIS)

The objective of this study was to evaluate the effects of stress (as measured by total heterophil + eosinophil counts [THECs] and plasma corticosterone [PC] levels) on plasma protein electrophoresis (PPE) in two Anseriform species. Ten red-breasted geese ( Branta ruficollis ) and eight Hawaiian geese (Branta sandvicensis) were received into quarantine at Beauval Zoo and housed together with other Anseriformes. Two days later, all were examined as part of routine quarantine procedures, and blood was collected. THECs were performed using a Malassez hemocytometer after a 1 : 200 dilution with an eosinophil dilution liquid containing phloxine B. PPE, as well as total protein and PC assays, was performed on lithium heparin plasma. Twenty days after arrival, all birds were similarly restrained, examined, and sampled. Pododermatitis lesions were identified on four geese that were excluded from statistical analysis. For each goose, THECs and PC values were sorted by value (lower or higher) independently from the day of sampling. A Wilcoxon signed rank test showed no significant differences between lower and higher values of THECs for any of the PPE fractions. Higher values of corticosterone were associated with higher values of prealbumin, but none of the other fractions were significantly different. A Spearman rank correlation coefficient showed that THECs and PC were not correlated; this suggested differences in kinetics between these stress markers. Results did not show significant alterations of electrophoresis patterns associated with stress as measured with THECs and PC. The results also highlight the complexity of precisely assessing acute and chronic stress in avian species.

Reconciliation and third-party affiliation in pair-bond budgerigars (Melopsittacus undulatus)

Some group-living animals show conciliatory tendencies towards specific group members after conflicts, referred to as post-conflict affiliation (PC-affiliation). PC-affiliation with a former opponent and a third-party bystander is classified as ‘reconciliation’ and ‘third-party affiliation’, respectively. PC-affiliation is assumed to be mediated by high-quality social relationships between individuals. Recently, studies assessing lifelong monogamous birds, such as corvids, have found PC-affiliation as a case of convergent evolution with regard to primates. Nevertheless, PC-affiliation divergence in birds is still poorly understood. Here, we report that pair-bonds of budgerigars, a lifelong-monogamous small parrot, engage in both reconciliation and third-party affiliation. We also found that males initiated both types of PC-affiliation more often than females. However, during reconciliation, this skewed affiliation pattern was unlikely specific to the PC-context but could also stem from sex differences in basic social-behavioural features (i.e., female dominance over males and males’ primary role in initiating affiliation with females), which are common outside the PC-context. Conversely, the third-party PC-affiliation pattern was significantly different from the basic affiliation pattern: affiliations were initiated more often by combatant winners, by bystander males toward defeated females, and less often by defeated males. These results suggest specific signal and stress reduction functions related to PC-affiliation among budgerigar pair-bonds. The present study supports the view that PC-affiliations, based on high-quality relationships, did not only evolve in mammals but also in birds, with species-specific forms associated with social behavioural tendencies.