Resource holding potential, subjective resource value, and game theoretical models of aggressiveness signalling

Empirical evidence suggests that aggressiveness (willingness to enter into, or escalate an aggressive interaction) may be more important than the ability to win fights in some species. Both empirical and theoretical traditions treat aggressiveness as a distinct property from the ability (RHP) or motivation (subjective resource value) to win a fight. I examine how these three traits are clearly distinct when modelled using a simple strategic model of escalation. I then examine game theoretical models of agonistic communication and demonstrate that models in which aggressiveness is signalled require: (1) a trait, aggressiveness, which is neither a correlate, nor consequence of RHP or motivation, (2) a handicap which negates any benefit to be gained through the use of a particular signal, and (3) the absence of any other asymmetry which could be used to assign roles to players. I conclude that it is unlikely that these assumptions are ever met, and that empirical examples of "aggressiveness" are far more likely to represent long-term differences in subjective resource value.     

Sources of (co)variation in alternative siring routes available to male great tits (Parus major)

Males of socially monogamous species can increase their siring success via within‐pair and extra‐pair fertilizations. In this study, we focused on the different sources of (co)variation between these siring routes, and asked how each contributes to total siring success. We quantified the fertilization routes to siring success, as well as behaviors that have been hypothesized to affect siring success, over a five‐year period for a wild population of great tits Parus major. We considered siring success and its fertilization routes as “interactive phenotypes” arising from phenotypic contributions of both members of the social pair. We show that siring success is strongly affected by the fecundity of the social (female) partner. We also demonstrate that a strong positive correlation between extra‐pair fertilization success and paternity loss likely constrains the evolution of these two routes. Moreover, we show that more explorative and aggressive males had less extra‐pair fertilizations, whereas more explorative females laid larger clutches. This study thus demonstrates that (co)variation in siring routes is caused by multiple factors not necessarily related to characteristics of males. We thereby highlight the importance of acknowledging the multilevel structure of male fertilization routes when studying the evolution of male mating strategies.     

Social environment affects testosterone level in captive male blue-black grassquits

The challenge hypothesis proposes that testosterone (T) elevation above what is needed for breeding is associated with social factors, and males possibly modulate their hormonal response to variations in population density and sex ratio. We investigated the role of social environment in altering testosterone levels and aggression in a tropical, seasonally breeding grassquit (Volatinia jacarina). We exposed males to three social conditions during 1 year: all-males treatment (six males), mixed treatment (three males-three females), and paired treatment (one male-one female). We quantified aggressiveness among males and T plasma concentration for each individual in each treatment monthly. We found that more aggressive interactions occurred in the all-males treatment than in the mixed treatment. The data also revealed that, coincident with these behavioral changes, the patterns of T variation through time in each treatment were markedly different. The all-males treatment exhibited an early increase in T concentration, which was sustained for a lengthy period with two distinctive peaks, and subsequently declined sharply. The mixed treatment presented an intermediate pattern, with more gradual increase and decrease in T levels. At the other extreme, the paired treatment presented a later rise in T concentration. We conclude that the more competitive environment, with higher density of males, caused the early and higher elevation in T level, thus the presence of competitors may influence the decision of how much a male should invest in reproduction. We suggest that the male's perception of his social environment ultimately mediates hormonal production and alters his reproductive strategy.     

Evaluation of the clinical efficacy of Gonazon implants in the treatment of reproductive pathologies, behavioral problems, and suppression of reproductive function in the male dog

Efficacy of a slow-release gonadotropin-releasing hormone (GnRH)-agonist implant (Gonazon) was assessed in 53 male dogs presented with benign prostatic hyperplasia (BPH), hypersexuality, aggressive behavior (either alone or in combination), excessive micturition, or to suppress fertility. Changes in testosterone (T) and estradiol (E2) concentrations and size of testes and prostate were monitored on Weeks 0, +8, and +26 after implantation. Additional measurements during and after this period were performed in 35 dogs. Clinical signs were assessed by the owners. All implants except one were retained throughout the study. Full downregulation of testicular function (T < 0.35 nmol/L) was achieved in 46 dogs, five dogs showed partial downregulation (T = 0.36 to 0.47 nmol/L), one dog did not respond, and another one displayed a transient downregulation on Week +18. On Week +8, mean T and E2 levels were reduced by 96% and 62%, respectively, and did not further decrease. Full downregulation (T < 0.35 nmol/L) lasted between 6 to >22 mo in most dogs except two. Compared with pretreatment values, mean testicular and prostatic size was reduced (P < 0.00001) by 54% and 52%, respectively, on Week +8 and by 68% and 64%, respectively, on Week +26. Relative reduction of prostatic size was more marked in dogs with BPH than in healthy ones on Week +8 (P < 0.05) and Week +26 (P < 0.02), and clinical signs of BPH disappeared rapidly after implantation. Dogs affected with BPH were significantly older (P < 0.001) than nonaffected ones (9.7 vs. 2.5 yr). Hypersexuality was more common in dogs < 3 yr of age, and treatment clearly improved clinical signs. Age significantly affected the response to treatment in aggressive dogs; 75% of the cases responded with an improvement. The only minor and possibly treatment-related events observed were a short-lasting exacerbation of clinical signs of BPH (two dogs), increased weight gain (three dogs), and anxiety (three dogs) with one of these dogs developing a blunt coat. These results demonstrate the clinical efficacy and overall safety of the Gonazon implants.     

Coexistence between Cyphomyrmex ants and dominant populations of Wasmannia auropunctata

The little fire ant Wasmannia auropunctata is able to develop highly dominant populations in disturbed areas of its native range, with a resulting negative impact on ant diversity. We report here on the tolerance of such populations towards several fungus-growing ants of the genus Cyphomyrmex (rimosus complex) in French Guiana. This tolerance is surprising given the usually high interspecific aggressiveness of W. auropunctata when dominant. In order to understand the mechanisms behind such proximity, aggressiveness tests were performed between workers of the different species. These behavioural assays revealed a great passivity in Cyphomyrmex workers during confrontations with W. auropunctata workers. We also found that the aggressiveness between W. auropunctata and two Cyphomyrmex species was more intense between distant nests than between adjacent ones. This dear-enemy phenomenon may result from a process of habituation contributing to the ants' ability to coexist over the long term.     

迁地保育林麝的侵犯性、等级序位及相互关系

侵犯性是动物个性的重要维度之一,体现了其主动挑衅和攻击其他个体的倾向。动物的侵犯性与其社会结构及等级序位存在紧密关系。本研究于2018年6月1日至7月31日对四川马尔康林麝繁育场的圈养林麝(Moschus berezovskii)进行了行为取样,计算林麝个体的侵犯性个性(侵犯性指数)和等级序位指数,分析圈养林麝的侵犯性和等级序位格局、影响因素及相互关系。结果表明,圈养林麝的侵犯性在性别间存在显著差异,雄性林麝的侵犯性(0.45±0.09,n=22)显著高于雌性(0.22±0.06,n=30)(P <0.05),年龄和驯养密度对其侵犯性的效应均不显著(P> 0.05),说明林麝侵犯性的刚性较强;圈养林麝等级序位的性别间差异不显著(P> 0.05),亚成体麝与成体麝的等级序位差异也未达显著水平(P> 0.05),原因在于麝场的建群未区分年龄组;圈养林麝个体的侵犯性与其等级序位显著正相关,林麝个体的侵犯性越大,其等级序位越高(r=0.73,P <0.05),推测这与社群的序位等级构建和资源竞争有关。     

Substance P and behavior: opposite effects of N-terminal and C-terminal fragments

Most of the biological actions of substance P (SP) have been thought to be mediated by the carboxy-terminal portion of the peptide. Some of the behavioral effects produced by exogenous SP exhibit a strikingly different structure-activity relationship. The N-terminal heptapeptide fragment of SP, SP(1-7), inhibits nociceptive, aggressive and grooming behaviors and stimulates investigative motor behavior, but the C-terminal hexapeptide fragment analog pyroglutamyl-SP(7-11) exerts opposite effects. While the C-terminal fragment mimics the effects of administered intact SP on motor behaviors, the N-terminal fragment mimics the effects of intact SP on aggressive and nociceptive behaviors. The significant behavioral effects of SP(1-7) and the consistently opposite behavioral effects of N- and C-terminal fragments are important new findings.     

雄性川金丝猴睾酮分泌与其社群环境变化的关系

采用化学免疫发光法,跟踪测定了上海野生动物园一个半放养川金丝猴群中3只先后参与交配繁殖活动的成年雄猴一年中尿中睾酮含量,并结合行为学记录对其性激素和性行为间的相互影响关系进行了初步研究。发现成年雄猴睾酮分泌峰的出现更多的是由其社会因素的变化引起的,而且,睾酮分泌峰出现的时期并不与雌性受孕高峰期相重叠,提示雄性繁殖具非季节性特点。睾酮分泌峰的出现,一方面说明此时社群的社会关系处于不稳定状态,另一方面发现睾酮水平的提高对雄猴攻击能力的增强起促进作用。由此,本研究认为川金丝猴雌雄性个体在繁殖中采用了不尽相同的繁殖策略[动物学报49(3)：325—33l,2003]。     

Are male rhesus monkeys more aggressive than females?

The justification for the “generalization that primate males are more aggressive than females” (Fedigan & Baxter, 1984) was tested in a troop of 24 captive rhesus monkeys. Males (N=9) were more dominant than females (N=15), i.e., they had more subordinate partners ( _m=17.0 vs. _f=6.6;p<0.01); hence, their aggression rate was higher ( _m=77.6 vs. _m=38.1;p<0.05). However, adjusting the rate of aggression according to the number of subordinate targets revealed no gender difference and males directed numbers of aggressive acts against individual subordinate partners that were not higher than those of females ( _m=4.4 vs. _f=5.4;p>0.1). It was concluded that aggressiveness is an individual attribute that is (1) independent of dominance status, and (2) independent of sex.     

Rainfall triggered dynamics of Aedes mosquito aggressiveness

Inspired by Davidson method of estimating daily survivals of a structureless population of mosquitoes, we present a model which describes the behavior of floodwater mosquitoes in terms of emergence functions following a rainfall event, blood feeding frequency and parous stages, and survival at various stages. As a generalization of the Davidson formula, we have developed an approach for dealing with the dynamics of structured population of mosquitoes, and derived various formulas allowing assessment of demographic parameters like durations of gonotrophic cycles and (apparent) daily survivals. The method was subsequently applied to field data of floodwater mosquitoes Aedes vexans arabiensis, potential vectors of Rift Valley fever in West Africa, collected during the 2003 rainy season in Barkedji, Senegal. We found that mosquitoes emerged about 3 to 4 days following an efficient rainfall, and mosquito emergences, described by a bell shaped function, lasted for about 2 days. The mean duration of the gonotrophic cycle was 3 days and the apparent daily survival about 0.87.