Sexual Interference in the Sword-tailed Newt,Cynops ensicauda popei (Amphibia: Salamandridae)

This paper describes competitive interaction between males of the salamandrid Cynops ensicauda popei. The sexual behaviour of the male is influenced by the presence of a second, rival, male. Competition for access to the female and other male interactions continuously interrupt ongoing courtships. Spermatophore pick-up success is lower than in encounters involving single pairs. During triad encounters, fewer spermatophores were deposited than in dyad encounters, due to interference during the creep stage of courtship. Two basic forms of male sexual interference were distinguished: ‘lure away’ during the creeping stage, from a position that is different from the direction of creep; and ‘female mimicry’, during which the male presses his snout alternately against the courting male's tail and the female's snout. In both forms, a rival male may shove one of the courting individuals away. The repertoire of sexual behaviour patterns of Cynops ensicauda popei appears to be less complex and varied than that of most Triturus species. The courtship of Cynops places less emphasis on display behaviour with tail and body, and a stronger emphasis on the creeping stage, where the male carefully leads the responsive female over a series of spermatophores, but during which rival males may interfere in a variety of ways.     

Why do curly tail lizards (genus Leiocephalus) curl their tails? An assessment of displays toward conspecifics and predators

Animal display behaviors are used to convey specific messages to other animals, including potential mates, rivals, and predators. However, because these different types of interactions can be mediated by a single behavioral display, or conversely, multiple signals can be used to convey one specific message, interpretation of any particular behavioral display can be difficult. Leiocephalus lizards (i.e., curly tails) provide an excellent opportunity to study the use of display behaviors across multiple contexts. Previous research has demonstrated that the use of tail curling in these lizards is associated with predation risk, but less is known regarding the use of this behavior in social interactions with conspecifics. The goal of this study was to determine the extent to which tail curling display behavior is used to mediate both social and predatory interactions in two species, Leiocephalus barahonensis and L. carinatus. We found that in lizards of both species, tail curling was used in interactions with both conspecifics and potential (human) predators. However, tail curl intensity did not differ between lizards involved in social encounters and solitary lizards, although L. barahonensis lizards performed more headbobs during social than non‐social observations. Further, L. carinatus lizards exhibited greater intensity of tail curling upon fleeing from a human predator than during observations in which individuals interacted with conspecifics, and lizards that exhibited tighter tail curls fled from predators for a longer distance. Finally, tail curl intensity was not correlated with headbob displays in either species, suggesting that these two components of display communicate different information. Our results suggest that tail curling displays, while consistently a component of interactions with potential predators, are not a necessary component of social interactions. These data contribute to a more complete understanding of how and why visual signals evolve for use in communication across multiple contexts.     

Repeated Recent Aggressive Encounters Do Not Affect Behavioral Consistency in Male Siamese Fighting Fish

Consistent individual differences in behavior suggest that individuals respond in a predictable and repeatable manner in a specific situation while differing from other individuals. Male Siamese fighting fish exhibit consistent individual differences in decision‐making strategies when they encounter a receptive female and a rival male simultaneously. However, whether these differences are altered by recent experience is unknown. We examined the influence of repeated aggressive encounters on behavioral consistency and decision‐making. Males were presented with paired female–male dummies prior to any aggressive experiences to obtain a baseline measure. Next, males either won or lost three consecutive contests against rivals and then received the paired female–male dummies after each of these encounters. Overall levels of highly aggressive behaviors were affected by contest outcome, while levels of female‐directed were not. Not surprisingly, winning a fight led to an increase in male‐directed bites, an overtly aggressive behavior that only occurs after fights have escalated. Fighting a male before encountering the dummies caused males to perform more tail beats to the dummy male, perhaps as a result of increased motivation. Males exhibited similar levels of repeatability and used the same strategies when faced with conflicting stimuli regardless of fighting experience. Thus, while winning or losing a fight impacts overall aggression, it does not influence behavioral consistency. This study demonstrates that consistent individual differences and decision‐making strategies may be resistant to recent aggressive experiences, even over a period of days.     

Effect of type of opponent on aggression in male mice with particular reference to studies with antihormones

The potential influence of the type of opponent used in intermale aggression encounters to assess the actions of drugs was examined. Two experiments were carried out, one with the antiandrogen Cyproterone Acetate and the other with the antioestrogen CI-680 (both administered every three days over 25 days). In both experiments the antihormone-treated subjects encountered different opponents, namely: a) an antihormone-treated male, b) a non aggressive anosmic male or c) a vehicle-treated male. Vehicle-treated subjects also confronted a vehicle-treated or an anosmic opponent. The behaviour displayed by antihormone-treated subjects varied according to the characteristics of the partner, suggesting that the effects of drugs might be interpreted differently depending on the type of animal employed as an adversary. In fact, some of the apparently contradictory results reported in the literature seem to be consequences of the utilisation of different kinds of opponents. It is concluded that the choice of the opponent is of paramount importance in the study of drug actions on intermale aggression tests and that using more than one type of opponent can provide more complete information about the actions of particular drugs.     

Encounters between adult spined assassin bugs,Sinea diadema (F.) (Hemiptera: Reduviidae): The occurrence and consequences of stridulation

The sequence of events leading to the resolution of agonistic interactions between adult femaleSinea diadema (F.) (Hemiptera: Reduviidae) is described. Contact between these predatory bugs resulted in a series of defensive and offensive actions, including stereotypical posturing and striking movements of the forelegs. Although these encounters usually escalated in intensity and frequency of contact, they rarely resulted in injury or cannibalism. Instead, one individual retreated from the perch. The original resident on the perch retreated in 70% of the encounters. Stridulation was observed during 33% of the encounters. Stridulating individuals retreated more often than their nonstridulating opponents, indicating that stridulation may be a startle mechanism employed by temporarily disadvantaged individuals to escape from encounters. These encounters were conflicts in which the participants are both potential predators and possible prey. The combinations of posturing, striking, and stridulation that occurred during encounters may have provided each bug with information concerning the identity and relative fitness of its opponent. If an individual is fit, it may be advantageous for it to probe the defensive capabilities of its opponent, since its own risk is low, and a less fit opponent could be killed and eaten.     

Winning fights elevates testosterone levels in California mice and enhances future ability to win fights

The 'winner effect' has been studied in a variety of species, but only rarely in mammals. We compared effects of winning three, two, one, or zero resident-intruder encounters on the likelihood of winning a subsequent aggressive encounter in the California mouse (Peromyscus californicus). During the training phase, we ensured that resident males won all encounters by staging contests with mildly sedated, smaller intruders. During the test phase, the resident male encountered an unfamiliar, more evenly matched intruder that had experience winning an encounter and was larger than the resident. Testosterone (T) plasma levels significantly increased after the final test when they had experienced two prior winning encounters, and the probability of winning a future encounter increased significantly after three prior wins independent of intrinsic fighting ability. We hypothesize a 'winner-challenge' effect in which increased T levels serve to reinforce the winner effect in male California mice.     

The pairbond in the titi monkey (Callicebus moloch): intrinsic versus extrinsic contributions of the pairmates

Aspects of a monogamous relationship can be inferred by observing reactions of mated individuals to unfamiliar conspecifics. The present study examined the behaviours shown by male and female titi monkeys (Callicebus moloch) toward an opposite-sex stranger, and the effect of their pairmate's absence or presence on these encounters. Behaviours within unfamiliar heterosexual pairs showed superficial similarities to behaviours of mated pairs. Although there were few affiliative behaviours between unfamiliar individuals, animals were often in spatial proximity and even performed sexual behaviour. The visual presence of a pairmate clearly affected encounters between unfamiliar heterosexual pairs in several respects. The presence of a male pairmate had a much stronger influence on all behavioural measures compared to the presence of a female pairmate. Possible functional aspects of these results are discussed.     

"Necking" behaviour in the giraffe

Previous references to "necking" behaviour, and the main features of the study area are briefly outlined.
"Necking" behaviour in giraffe takes place only in all male herds. When the animals are in a head to head posture the intensity is either high or low, but when animals take up a head to tail posture the actions are always of high intensity and appear to have greater sexual significance.
The significance of "necking" is discussed, and it is suggested that these ritualized actions form an important sexuo-social bonding mechanism whereby a hierarchy is created amongst the males, and movement between strictly bachelor and mixed herds helps to maintain contact between the sexes in this polygamous mammal.     

"Necking" behaviour in the giraffe

Previous references to "necking" behaviour, and the main features of the study area are briefly outlined.
"Necking" behaviour in giraffe takes place only in all male herds. When the animals are in a head to head posture the intensity is either high or low, but when animals take up a head to tail posture the actions are always of high intensity and appear to have greater sexual significance.
The significance of "necking" is discussed, and it is suggested that these ritualized actions form an important sexuo-social bonding mechanism whereby a hierarchy is created amongst the males,and movement between strictly bachelor and mixed herds helps to maintain contact between the sexesin this polygamous mammal.     

Intergroup encounters in wild white-faced capuchins (Cebus capucinus)

Wrangham (1980) hypothesized that knowledge of the nature of intergroup encounters is crucial to understanding primate social relationships and social organization. I studied a single social group of wild white-faced capuchins over a period of 26 months and observed 44 encounters between social groups during 3703 hr of observation. All intergroup encounters consisted of predominantly hostile social interactions. However, nonaggressive interactions between males of different social groups occurred in a few cases. Adult males were the sole participants in 39 encounters and the primary participants in all 44 encounters. The alpha male was the most frequent participant. High-ranking females participated aggressively in five encounters, and low-ranking females never participated. There was no stable intergroup dominance hierarchy. I hypothesize that the need for male-male cooperation in intergroup aggression is an important factor influencing the quality of intragroup male-male relationships. Behavior during intergroup encounters is consistent with the idea that intergroup behavior is related to male reproductive strategies, but inconsistent with the idea that intergroup aggression is related to female defense of resources. The possibility that males are “hired guns” (Wrangham, 1980) cannot be ruled out.     

Who's Watching Me: Female Siamese Fighting Fish Alter Their Interactions in Response to an Audience

It is well established that interactions between conspecifics are often influenced by the presence of passive bystanders. Individuals have been found to alter their behavior in a variety of contexts, from foraging to aggression, based on the presence, sex, or identity of an audience. This audience effect may influence not only the nature of a signaling event but also the evolution of signal structure as signals may have to convey information across a distance. Additionally, audience individuals may use information obtained by watching in later encounters with these individuals, which may act as a selection pressure on communication. Communication networks in Siamese fighting fish, Betta splendens, are particularly well studied, with audience effects influencing both male–male interactions and male–female interactions. However, the effects of an audience on female–female interactions have not been examined in this species or any other. This study examined the interactions of pairs of females in three different audience conditions (male, female, and no audience). The results suggest that female–female interactions are affected by the presence of an audience as interactant‐directed gill flaring, the most commonly performed behavior, was performed more with an audience present. Additionally, the sex of the audience seemed to be influential, reflected by a difference in the frequency of interactant‐directed behaviors when a female vs. a male audience was present. This study is one of the first to demonstrate that females modify their behavior as a result of being watched and stresses the importance of examining audience effects in a variety of social contexts.     

Residency and size affect fight duration and outcome in the fiddler crab Uca annulipes

We performed a field experiment to investigate the effect of carapace width, major cheliped length and burrow ownership on the righting success of male fiddler crabs (Uca annulipes) . We removed males from their burrows and released them back into the colony ( n = 82). Released males tended to initiate encounters with burrow owners slightly smaller than themselves. Several general predictions of Sequential Assessment Game models of contest behaviour were supported: (1) residents won more encounters; (2) intruders were more likely to win when larger than residents. When body size (carapace width) was controlled for, intruders with relatively large claws for their body size were more likely to win contests; (3) the duration of encounters was related to the size difference between males; (4) encounters won by the larger male were of shorter duration than those won by the smaller male; (5) encounters won by the resident tended to be of shorter duration than those won by intruders ( P = 0.07); (6) on average, encounter duration was longer when the intruder was larger than the resident. However, the encounters we documented began with seemingly costly behaviour such as pushing and the inter-locking of claws and did not unambiguously escalate from initial low cost behaviours. Sequential assessment of relative fighting ability may therefore not have been occurring. Prior visual assessment of opponents' fighting ability, followed by 'all-out fights' during physical encounters may also provide a plausible explanation for our results.     

Dominance, Status Signals and Coloration in Male Mandrills (Mandrillus sphinx)

Where individuals contest access to a resource, escalated physical fighting presents a risk to all involved. The requirement for mechanisms of conflict management has led to the evolution of a variety of decision rules and signals that act to reduce the frequency of aggression during competitive encounters. We examined strategies of conflict management in male mandrills (Mandrillus sphinx) living in two semi‐free‐ranging groups in Gabon. Adult male mandrills are large (31 kg), with long canines, making the costs of conflict potentially very high. We found that males formed dominance hierarchies, but that male–male relationships were characterized by avoidance, appeasement and ignoring. Fights were rare, but could result in death. Examination of the relationship between dominance and signaling showed that males use facial and gestural signals to communicate dominance and subordinance, avoiding escalated conflict. Male mandrills also possess rank‐dependent red coloration on the face, rump and genitalia, and we examined the hypothesis that this coloration acts as a ‘badge of status’, communicating male fighting ability to other males. If this is the case, then similarity in color should lead to higher dyadic rates of aggression, while males that differ markedly should resolve encounters quickly, with the paler individual retreating. Indeed, appeasement (the ‘grin’ display), threats, fights and tense ‘stand‐off’ encounters were significantly more frequent between similarly colored males, while clear submission was more frequent where color differences were large. We conclude that male mandrills employ both formal behavioral indicators of dominance and of subordination, and may also use relative brightness of red coloration to facilitate the assessment of individual differences in fighting ability, thereby regulating the degree of costly, escalated conflict between well‐armed males.     

Impact of aggressive encounters on reproductive behaviour in the Indian desert gerbil,Meriones hurrianae (Jerdon)

The gerbils were exposed to daily I min aggressive encounters for 30 days, to study the effect of social stress on reproduction. The encounters were induced by introduction of an adult male or female gerbil into the cage of a male retired breeder living in isolation. In the male gerbils the encounters decreased (P < 0.001) gonadal weight and sperm counts. The accessory sex organs responded variedly to the encounters. The surface areas of abdominal scent glands decreased (P < 0.001). The results suggest that exposure to aggressive encounters had a negative influence on male reproduction in the gerbil. Contrary to the results in male gerbils, encounters with males had a positive influence on reproduction in females. This was evidenced by data on ovarian and uterine weights, follicular kinetics and the estrous cycle. The ovarian and uterine weights increased (P < 0.001) in gerbils exposed to the encounters. The number of estruses increased (P < 0.001) whereas the diestruses decreased. Study of follicular kinetics revealed an increase in the number of growing follicles and a decrease in the number of regressive follicles. The mechanism(s) by which the encounters influence reproduction is not known. Adrenal gland weights increased (P < 0.001) in both male and female gerbils exposed to the encounters. The pinealocyte cell and nuclear diameters decreased (P < 0.01) in males and increased (P < 0.001) in female gerbils after the encounters. Presumably the adrenal and pineal glands may play an important role mediating the effects of the encounters.     

Female choice, male interference, and sperm precedence in the red-spotted newt

Darwin first identified female choice and male—male competitionas forms of sexual selection resulting in the evolution of conspicuoussexual dimorphism, but it has proven challenging to separatetheir effects. Their effects on sexual selection become evenmore complicated when sperm competition occurs because spermprecedence may be either a form of cryptic female choice ora form of male—male competition. We examined the effectsof tail height on male—male competition and female choiceusing the sexually dimorphic red-spotted newt (Notophthalmusviridescens viridescens). Experiment 1 examined whether maletail height influenced male mating success. Males with deeptails were more successful at mating with females than thosewith shallow tails. Successful, deep-tailed males also were bigger(snout-vent length; SVL) than unsuccessful, shallow-tailed males,but they did not vary in tail length or body condition. Of these,only tail height and tail length are sexually dimorphic traits.Experiment 2 tested the hypothesis that the differential successof males with deeper tails was due to female choice by examiningboth simultaneous female preference for association and sequentialfemale choice. We found no evidence of female choice. When maleswere not competing to mate with females, tail height did notinfluence male mating success. Successful males did not havedifferent SVL and tail lengths than unsuccessful males. Thus,tail height in male red-spotted newts appears to be an intrasexuallyselected secondary sexual characteristic. Experiment 3 usedpaternity exclusion analyses based on molecular genetic markersto examine the effect of sperm precedence on sperm competitionin doubly-mated females. Sperm precedence likely does not havea pervasive and consistent effect on fertilization success becausewe found evidence of first, last, and mixed sperm usage.     

Female Goldeneye Ducks (Bucephala clangula) Do Not Discriminate among Male Precopulatory Display Patterns

Female goldeneyes remain motionless on the surface of the water while single males circle them performing a series of highly stereotyped displays. After performing between eight and 90 of these displays the male either copulates or attempts to copulate with the female. However, females allow only 58% of males to mount them, while rejecting 42%. We have examined 804 of these precopulatory sequences containing 11,841 actions in an effort to determine why females find some display sequences of males unsuitable, while others are accepted. Males have an extraordinarily varied sequence of actions, and sequence variation leading to successful and unsuccessful copulation attempts was similar. Most surprising was the tendency of males to eliminate one of the five actions, whether in successful or unsuccessful attempts. As unlikely as we think it might be as the result of natural selection, the only statistically significant difference we found between successful and unsuccessful attempts was the reduction in the frequency of expression of one or more of the behaviors in successful attempts. These observations, coupled with the large variation seen in most sequences, suggest that there is not a correct sequence, or even a correct set of actions leading to copulation. The male must, however, perform goldeneye species-specific precopulatory behavior as performed by adult males, although it apparently can be performed in a wide variety of patterns.     

BEHAVIORAL OBSERVATIONS OF SEXUAL ISOLATION AMONG ALLOPATRIC POPULATIONS OF THE MOUNTAIN DUSKY SALAMANDER,DESMOGNATHUS OCHROPHAEUS

The behavioral basis of sexual isolation was investigated in 11 crosses staged between individuals from nine allopatric populations of the Appalachian mountain dusky salamander, Desmognathus ochrophaeus. Scan-sampled observations of within-population (homotypic) and between-population (heterotypic) heterosexual encounters yielded the following results. 1) Fewer heterotypic encounters than homotypic encounters resulted in insemination of females. Indices of the strength of sexual isolation based on insemination data ranged from 0.26 (lowest) to 0.82 (highest), indicating that mechanisms that confer sexual isolation may evolve during allopatric differentiation. 2) Heterotypic encounters that progressed as far as the stage of courtship during which the male stimulates the female to mate did so at the same time as homotypic encounters, although the number of the former reaching this stage was lower. 3) The time interval from courtship initiation to insemination was longer in heterotypic encounters than homotypic encounters. In some crosses, males did not attempt to initiate heterotypic encounters, indicating that this sex is responsible for sexual isolation in these instances. We use our results to formulate specific hypotheses concerning the behavioral basis of sexual isolation in these salamanders, and some possible experimental approaches are suggested.     

DIFFERENTIAL COSTS OF A SECONDARY SEXUAL CHARACTER: AN EXPERIMENTAL TEST OF THE HANDICAP PRINCIPLE

The evolution of reliable signaling can be explained by the handicap principle, which assumes that (1) the cost of a signal guarantees its reliability, and (2) cheating is prevented because the cost of a unit of display is greater for low-quality than for high-quality individuals. A test of these two assumptions was performed using manipulations of the length of the outermost tail feathers of male barn swallows Hirundo rustica, a trait currently subject to a directional female mate preference. We found that survival decreased with tail elongation and increased with tail shortening of males, supporting the assumption that the secondary sexual character is costly. Naturally long-tailed males were better able to survive with an elongated tail, whereas naturally short-tailed males improved their survival following tail shortening. This observation supports the second assumption of a differential cost of a signal. One mechanism imposing differential costs on sexually signaling barn swallows is foraging. Males with elongated tails captured smaller, less profitable Diptera, whereas males with shortened tails captured large, profitable prey items. The conditions for reliable sexual signaling by the tail ornament of male barn swallows are thus fulfilled.     

Theoretical aspects of sexual selection: A generalized model of mating behaviour

A model of mate selection is described in which females mate preferentially according to their probability of encounter with the males they prefer. In this model, different thresholds of response to the courtship of different male phenotypes determine the female mating preferences. Females with a lower threshold toward particular males require fewer encounters before mating with these males and more encounters before mating with any of the others. Such females mate preferentially if they encounter a male they prefer before they have been stimulated to the level of the higher threshold. At the higher threshold they mate at random. The number of the extra encounters required to raise the females' level of stimulation from the lower to the higher threshold is a parameter of the model. The frequency of the preferred males then determines the probability that a female encounters and mates with one of them before she has been sufficiently stimulated to mate at random. Sexual selection by differences in male courtship can also be described in terms of this model.The preferred characters may be determined either by dominant and recessive alleles or by each different genotype. When only one extra encounter is required before the females mate at random, the preferred males only gain a slight frequency-dependent advantage: Stable polymorphisms can only be maintained if the heterozygotes have the greater preference in their favor. When more than one extra encounter is required before random mating, the males gain a negative frequency-dependent advantage: Stable polymorphisms are generally maintained.The models are fitted to published data on the mating success of male Drosophila at varying frequencies and provide an explanation of the “rare male” effect in which less common males gain a mating advantage.     

旅游干扰下水质对大鲵繁殖行为与繁殖力的影响

通过控制大鲵仿生态繁育池进水量模拟旅游干扰下的水质溶解氧特征,采用红外数字监控系统研究大鲵繁殖行为(产卵与护卵)及繁殖力(相对产卵量、受精率与孵化率)特点,分析它们与水质的关系,探讨旅游干扰导致的水质变化对大鲵繁殖行为及繁殖力的影响。结果表明: 与对照组相比,旅游干扰下大鲵的产卵行为与繁殖力未受到显著影响,但雄鲵护卵行为中的扇尾与搅动时间显著延长,以提高水中溶解氧浓度,满足大鲵胚胎发育需求;此外,旅游干扰下受精卵的孵化时间显著延长,但孵化率未受到显著影响。雄鲵护卵行为变化与受精卵孵化时间延长可能是大鲵对旅游干扰导致的水质变化的一种主动响应。