Number Of Aggressive Encounters Research Articles

Repeatability of combat rate across different group compositions in male house finches

Abstract Studies of animal contests have focused on the probability of winning an encounter, because it directly affects the benefits of competition. However, the costs (e.g., physiological stress) and benefits of competition should also depend on the number of aggressive encounters per unit time (combat rate, hereafter) in which the focal individual is involved. Using colourful and drab male house finches (Haemorhous mexicanus) from urban and rural sites, we showed that combat rate was repeatable across the same and different group sizes for birds who won competitions. In addition, colourful urban males exhibited the lowest propensity for frequent aggression (and hence low combat rate). However, male bill size (another trait we previously found to correlate with male competitiveness in this species) was not related to aggressive propensity. Combat rate can be predicted by male identity and some, but not all, predictors of male competitiveness.

Ganho de peso de porcas gestantes associado ao comportamento em baias e à uniformidade da leitegada

O objetivo deste trabalho foi avaliar a associação do comportamento de fêmeas suínas mantidas em baias coletivas, durante a alimentação, com o ganho de peso no último mês de gestação, e determinar se a uniformidade de peso das leitegadas é influenciada pelo ganho de peso das fêmeas. As fêmeas (n = 699) foram separadas em três grupos de ordem de parto (OP): 2, 3-5 e 6-9. Cada grupo de OP foi dividido em três subgrupos com percentual de ganho de peso: baixo, médio e alto. Fêmeas de OP 6-9 tiveram mais leitões com peso menor que 1.200 g e maior coeficiente de variação desse peso, em comparação às de OP 2. O menor peso de leitões e o maior número de leitões com peso<1.200 g foram observados no subgrupo de peso baixo. Houve correlação do percentual de ganho de peso na gestação com o número de vezes que a fêmea esteve em pé no cocho (r = 0,669) e com o número de vezes que a fêmea agrediu outras fêmeas (r = 0,451). A variação do ganho de peso das fêmeas, durante o último mês de gestação, em baias coletivas é influenciada pela competição durante a alimentação, e o menor ganho de peso no último mês de gestação reduz o peso dos leitões ao nascimento.

Reduced resource defence in an uncertain world: an experimental test using captive nutmeg mannikins

Recent models of economic defence in a group-foraging context predict that the frequency of aggressive interactions should decline as resource density increases, but empirical studies have provided only equivocal support for this prediction. We suggest that whether or not foragers have information concerning the location of patches will influence both the intensity of aggressive encounters and the effect that changes in food density will have on aggression. The intensity of aggression should be greatest when patch locations are known to all, making resources spatially predictable and the availability of alternatives more certain. When food is hidden, increasing the density of patches should have little effect on aggression levels, mostly as a result of the greater uncertainty about the availability of replacement food patches. To test these predictions, we investigated the effect of patch density on the use of aggressive behaviour in nutmeg mannikins, Lonchura punctulata, when food patches were either visible (signalled patch location) or hidden (unsignalled patch location) to all foragers. As predicted, we found that the intensity of aggressive encounters was higher when patch location was signalled than when it was not. Moreover, the effect of patch density on aggression depended on whether patch location was signalled or not. When patch location was unknown, the number of aggressive encounters was unaffected by changes in patch density, but when food location was signalled, increasing patch density resulted in the expected decline in the frequency of aggression.

Milt quality, parasites, and immune function in dominant and subordinate Arctic charr

Within a species, different males may display different mating strategies. For example, some males may be selected to invest in attractiveness and mate guarding, whereas others are selected for increased sperm production and sneaky breeding. In systems with a hierarchical structure, dominant males are expected to adopt mate-guarding behaviour and subordinate males sneaky-breeding behaviour. In this study, we kept wild-caught and sexually ripe male Arctic charr (Salvelinus alpinus) in size-matched pairs and determined social rank from the number of aggressive encounters. After 4 days, subordinate males showed symptoms of stress, with higher blood glucose and erythrocyte levels than dominant males. There were no differences between dominant and subordinate males in parasite intensities or immune activity, measured as levels of granulocytes and lymphocytes in blood. Although subordinate males had smaller testes than dominant males, they still had a higher density of sperm cells and higher sperm numbers relative to the size of their testes. These results can be explained as indicating adaptation of subordinate males for reproduction in an unfavourable role, always exposed to sperm competition and out of synchrony with females' egg release. Our results suggest that rapid changes in social rank may affect ejaculate production.

The relative costs and benefits of territorial defense and the two conditional male mating tactics in the Comanche Springs pupfish ( Cyprinodon elegans )

We examined the aggressive costs and reproductive benefits of territorial defense and its alternatives in a population of the Comanche Springs pupfish (Cyprinodon elegans). The breeding system was characterized by three different male mating tactics: territorial defense, satellite positioning, and sneak spawning. The mating tactic adopted by males reflected the males' sizes. Territorial residents were the largest, satellites were medium-sized, and sneakers were the smallest adult males observed. Consistent with the hypothesis that primary mating tactics are relatively high-cost, high-benefit strategies, we found that territorial males engaged in a number of aggressive encounters but had higher reproductive successes than any other males. However, our observations did not support the premise that conditionally breeding males engage in relatively low-benefit, low-cost tactics. Medium satellites and small sneakers acquired fewer spawns than did territorial males, but both satellites and sneakers were involved in as much aggression as territorials. That is, the data supported the prediction that satellite or sneaker males with the inability to compete for territories would attempt to accrue some reproductive opportunities in the presence of territorial males despite the high costs of spending time on the breeding grounds. Adopting conditional tactics appeared to allow satellites and sneakers to make the best of a bad situation. During a subsequent breeding season, large males were absent from the population, and medium-sized males established territories. The aggressive behavior exhibited by medium residents was similar to the previous year, but these males did not acquire higher reproductive successes than medium satellites had. The implications of switching tactics and the influence of operational sex ratios on the costs and benefits of the male tactics are briefly addressed.

Parental investment of male two-spotted goby, Gobiusculus flavescens (Fabricius).

The trade-off between parental care and feeding was studied in the male two-spotted goby (Gobiusculus flavescens F.). Two temperatures, 8.5 degrees C and 13.0 degrees C, were used, with five replicates at each temperature, in order to determine whether temperature influenced parental behaviour. In each replicate, two males and four females were introduced to an aquarium, where the males chose between two nests and courted the females. In each replicate, one male spawned. After spawning, the males guarded the eggs until hatching. The guarding males' behaviour was recorded with a video camera twice a day (15 min each time), once before and once after they were fed. The male's condition (c-factor) was calculated at the start of the experiment and after egg hatching. The eggs were spawned in an artificial nest (half of a PVC tube), and attached to the nest in a single layer. The areas with eggs (representing brood size) were marked after spawning and the fry counted after hatching (which was used to calculate area hatched). Numbers of prey eaten (plankton) and number of aggressive encounters between the guarding male and the other fishes were recorded. Time spent in the nest and time used on fertilisation, fanning and cleaning were estimated and related to egg age, brood size, hatching success, temperature and food availability (no food or food).The results showed that feeding (expected to influence future reproduction) decreased and parental expenditure (current reproduction) increased, as the eggs developed (became closer to independence). Parental expenditure was significantly higher at 13.0 degrees C than at 8.5 degrees C, presumably due to higher oxygen demands by the eggs, and a greater risk of egg-infections. The c-factor of the males guarding eggs decreased over time, in contrast to the non-guarding males' c-factor. Guarding males' aggressiveness decreased as the eggs got older, but increased just before hatching. A possible explanation for this could be the decreasing intrusion by the non-guarding male and females caused by high aggressive behaviour by the guarding male early in the brood cycle. The exploitation of the nest (percentage of total nest area covered by eggs) seemed to determine the amount of parental expenditure and loss of condition, while brood size (area of eggs) had no effect.

Do leks limit the frequency of aggressive encounters in fallow deer? Linking local male density and lek occurrence

We suggest here that the formation of leks in ungulates is a mating tactic that aims at decreasing the number of aggressive encounters in which dominant males are involved when the local male density becomes too high. Using a simulation model, we show that the spatial stability of territories in leks should limit the number of aggressive encounters between males, despite a high number of males locally present. Data on the frequencies of aggressive interactions recorded in both lekking and nonlekking fallow deer (Dama dama) populations under different local male densities support our hypothesis.

Do leks limit the frequency of aggressive encounters in fallow deer? Linking local male density and lek occurrence

We suggest here that the formation of leks in ungulates is a mating tactic that aims at decreasing the number of aggressive encounters in which dominant males are involved when the local male density becomes too high. Using a simulation model, we show that the spatial stability of territories in leks should limit the number of aggressive encounters between males, despite a high number of males locally present. Data on the frequencies of aggressive interactions recorded in both lekking and nonlekking fallow deer (Dama dama) populations under different local male densities support our hypothesis.

Intraspecific density effects in Nereis (Neanthes) arenaceodentata Moore (Polychaeta: Nereidae)

Effects of intraspecific density on Neanthes arenaceodentata Moore were examined under laboratory conditions by rearing animals for 28 days, in the presence of sediment, at densities of 230, 575, 1150, and 1730 worms/m 2. The lowest density examined in this study was similar to the mean reported field density for N. arenaceodentata. Food was allocated to each beaker on a per worm basis to focus the experiment on competition for space. Individual worm growth increased with increasing density. This result contrasts with other studies of intraspecific density effects in this species conducted in the absence of sediment where negative effects on growth were observed. Estimated individual dry weight and ash free dry weight of worms in the highest density treatment were significantly greater (13 and 18%, respectively) than worms in the lowest density treatment at the end of 28 days of growth. This increase in growth was associated with a decrease in the number of ovigerous females, suggesting a delay in reproductive development, and an increase in the number of worms regenerating posterior segments, suggesting an increase in the number of aggressive encounters. At the end of the 28 day growth experiment, mated pairs were established in separate beakers. Intraspecific density did not have a lasting effect on time to egg deposition and juvenile emergence or fecundity. The benefits of larger body size at higher densities may include the fact that larger worms are more successful at defending territories and finding mates. The results of this study emphasize the importance of sediment as a structuring agent in soft substratum habitats and the potential for complex density dependent effects.

Social behaviour of roe deer at winter feeding stations

The behaviour of roe deer ( Capreolus capreolus) at winter feeding stations was studied during the three winters of 1971 to 1973. Four groups were studied, three of which were kept in a 14-ha enclosure, while the fourth group consisted of free-ranging animals. The animals were fed a special wildlife feed and hay was also available to the enclosed deer. Special emphasis was laid upon the occurrence and type of hierarchies, the relationships between social rank and utilization of supplemental food, activity patterns at the feeding stations and types and frequencies of aggressive encounters. The study indicates that winter groups of roe deer are socially organized according to a hierarchical system of an almost linear type. The number of aggressive encounters was reduced and the feeding time increased when the roe deer had access to two or three sources of preferred food instead of one. The study did not reveal any relationship between the animals' social status and their utilization of supplemental food.

Effect of Shelters on the Resistance of Dominant and Submissive Blue gills (Lepomis macrochirus) to a Lethal Concentration of Zinc

When pairs of bluegills (Lepomis macrochirus Rafinesque) were kept in bare, 10-gal compartments for 5 days, dominant–submissive relations developed, and the dominant fish survived a subsequent exposure to 32 mg/liter zinc longer than submissive fish. A flowerpot shelter in each compartment reduced the number of aggressive encounters between fish and removed the response difference. These results indicate that dominant–submissive relations may be a source of variability in the results of bioassays that use fish.

Alterations of social behavior in rats and hamsters following lesions of the septal forebrain

Septal lesions alter the nature of social behavior in rats and hamsters. Rats were hyperemotional and more gregarious (contact time) in the open field following septal lesions. Hamsters were neither hyperemotional nor more gregarious after septal lesions. A marked increase in number of aggressive encounters was observed between hamsters.