Seasonal body mass changes in Eurasian Golden Plovers Pluvialis apricaria staging in the Netherlands: decline in late autumn mass peak correlates with increase in raptor numbers

Eurasian Golden Plovers Pluvialis apricaria staging in the Netherlands during the non-breeding season show strikingly constant seasonal changes in body mass with a first mass peak in late November and December and a second peak in late April and May. Despite huge sample sizes, variations in this pattern over successive years in the 1990s and among age classes were minuscule. However, in contrast to the body mass levels at other times of the year, there was a marked decline in the winter peak mass of Golden Plovers from the 1970s/early 1980s to 1989–2000. The decrease, by an average of 29 g, was about half the extra mass previously stored in autumn. This additional mass is known to consist of fat and may be interpreted as an energy store − insurance − for sudden cold spells when a negative energy balance forces the birds to move south and stay in front of the frostline. As the rate of the mass increase in September–October showed no change from the 1980s to the 1990s, changes in food availability are unlikely to explain the long-term mass decline. Also, there were no differences in two factors known to influence energy expenditure and feeding rate, air temperature and rainfall. The one striking environmental change relevant to plovers was the steep increase in the occurrence of raptors in the northern Netherlands in the 1980s, notably Peregrine Falcons Falco peregrinus and Goshawks Accipter gentilis. We argue that the halving of the winter mass peak over a decade is consistent with the hypothesis that under increased risk of predation, birds lower their body mass in order to reduce individual vulnerability, a reduction that may be traded off against an increased risk of starvation.

Effect of different agonistic experiences on behavioural seizures in fully amygdala kindled rats

Fully amygdala kindled rats were exposed to two different inter-male agonistic experiences in order to study the interaction between epilepsy and acute social stress. Victory experience did not influence the severity of seizure behaviour, whereas a single acute defeat modified both ictal and postictal seizure manifestations. Defeat resulted in less severe and shorter lasting motor seizures, and the accompanied postictal inhibition or behavioural depression was of shorter duration in comparison with pre-stress values. The ability of acute defeat to trigger anticonvulsant activity as implied by the weakened convulsive response is discussed.

The Corticomedial Amygdala and Learning in an Agonistic Situation in the Rat

Social agonistic behaviour of intact male rats is strongly reduced by the experience of defeat by a dominant male conspecific. Small electrolytic lesions in the corticomedial amygdala strongly affected this behavioural change due to defeat. No effects of the lesions were observed before and during the defeat. Some learning is still possible in corticomedial amygdala lesioned animals. A comparison of the effects of lesions made before the defeat with lesions made after the defeat revealed that the lesions primarily produce a retention deficit in social learning.

Individual strategies of aggressive and non-aggressive male mice in encounters with trained aggressive residents

To determine whether individual differences in offensive behaviour are related to differences in defensive behaviour, the responses of male wild house mice, Mus domesticus, of an aggressive and a non-aggressive line to defeat by physically stronger residents were analysed. Individuals of the aggressive line engaged in more flight behaviour, whereas the males of the non-aggressive line predominantly showed immobility. The higher flight tendency of the aggressive intruders provoked more attacks by the resident, resulting in more fighting between the resident and an aggressive male than between the resident and a non-aggressive intruder. However, if offered an opportunity to escape from the home-cage of the resident, aggressive males more readily made use of it than non-aggressive intruders. Differences between aggressive and non-aggressive male mice are interpreted in terms of fundamentally different behavioural strategies adopted in response to social interaction. The response of aggressive males can be characterized as an active behavioural strategy by which they tend to determine actively their social situation. In contrast, the prevailing lack of overt attempts to manipulate the situation by the non-aggressive mice points to passive confrontation, in an offensive as well as in a defensive context.

INDIVIDUAL COPING STRATEGIES AND VULNERABILITY TO STRESS PATHOLOGY

Psychosocial factors are implicated in the individual development, course and recovery from disease. Studies with animal models using social interactions show that the magnitude and direction of changes in the immune-, neuroendocrine-, and cardiovascular system are highly correlated with the social position of the animal. This relationship appears to depend on the animalxs coping strategy both in terms of behaviour and neuroendocrinology, and hence in immunology as well. It is argued that disease processes should be considered as a function of the baseline behavioural, neuroendocrine, and immunological state

Vasopressin Prolongs Behavioral and Cardiac Responses to Mild Stress in Young But Not in Aged Rats

In young male Wistar rats sudden silence superimposed on low intensity background noise evokes a relative decrease in heart rate. This bradycardia is accompanied by immobility behavior. In the present study, involving young (3 month), late-adult (14 month), aged (20 month), and senescent (25 month) rats the magnitude of the stress-induced bradycardia shows an age-related reduction while the behavioral immobility response remained unchanged during the process of aging. Arginine-8-vasopressin (AVP, 6 µg/kg SC) administered 60 min prior to the experiment led to a prolonged behavioral and cardiac stress response in young and late-adult rats, but not in aged and senescent animals. The peripheral and central mechanisms possibly involved in the failure of systemically applied AVP to improve bradycardiac stress responses in aged rats are discussed.

Behavioral Profiles of Genetically Selected Aggressive and Nonaggressive Male Wild House Mice in Two Anxiety Tests

Artificially selected aggressive (SAL) and non-aggressive (LAL) male house mice were tested in a hexagonal tunnel maze and light–dark preference (LD) box to determine if the bidirectional selection for aggressive behavior leads to a coselection for different levels of trait anxiety. The tunnel maze consists of an open, brightly lit central arena surrounded by a complex system of interconnecting tunnels. As in the LD box, animals which spend less time and are less active in the brightly illuminated section of the maze are considered to have higher anxiety levels. In the tunnel maze, the LAL mice showed more exploration and spent more time in the central arena than the SAL animals, but only during the final 2 min of the 6-min test. This reduced preference for the central arena was not due to general inactivity or a failure of the SAL to find the central arena and indicates a higher level of state anxiety in the aggressive animals. In contrast, no “anxiety-like” differences were found in the LD box, either for the percentage of time spent in the light compartment or for the number of crossings. SAL males actually showed higher levels of moving and rearing, and lower levels of freezing, than did LAL males.

Mytilus galloprovincialis-type foot-protein-1 alleles occur at low frequency among mussels in the Dutch Wadden Sea

The presence of M. galloprovincialis-type genes among the population of mussels in the Dutch Wadden Sea, historically described as M. edulis, was assessed. We applied the molecular technique in which a fragment of the gene coding for an adhesive protein of the byssus of mussels is amplified by PCR and assayed for length using electrophoresis. Among 321 individual mussels collected in August–October 2001 at 14 sites (5 intertidal, 9 subtidal) widely dispersed over the Dutch Wadden Sea, 6 specimens (collected at 5 sites) were found that showed a heterozygote genotype with both the M. edulis- and the M. galloprovincialis-type alleles being amplified; all others were identified as homozygotes for the M. edulis-type allele. Differentiation in frequencies of heterozygotes among sites was not detected. The ofact that the M. galloprovincialis-type allele was present at low frequency (0.0093) may be attributed to one of three possible, and not mutually exclusive, causes: incomplete diagnosticity of this marker, an historically stable introgression zone in the Wadden Sea, or a recent invasion.