Male Aggressive Behavior Research Articles

Aggressive behavior in the antennectomized male cricket Gryllus bimaculatus

Male crickets (Gryllus bimaculatus) exhibit intensively defensive aggressive behavior towards attacking males most often culminating in fighting. After the fight, the loser no longer exhibits aggressiveness in a second, separate encounter with another male; rather, the defeated male exhibits avoidance behavior. Here, we investigated the role of sensory input from the antennae in male defensive aggressive behavior. When we removed antennae from males (antennectomized males), we found that they showed little aggressiveness towards each other whereas they continued to exhibit typical fighting behavior towards an intact male. In addition, in a second encounter, antennectomized losers showed significantly higher aggressiveness towards another male than did intact losers. We further found that antennectomized crickets do not utilize visual or palpal sensory input to elicit aggressive behavior. In contrast, intact males showed aspects of aggressive behavior to male cuticular substances before and after winning a fight, and if they lost a fight they showed avoidance behavior. It thus appears that antennal sensory information is crucial in the mediation of aggressive and avoidance behaviors. However, sensory inputs from the antennae are not necessary to elicit defensive aggressive behavior but are necessary to discriminate conspecific males and initiate attacks against them.

Apparent Forced Mating and Female Control in Saltmarsh Sparrows

Saltmarsh Sparrows (Ammodramus caudacutus) are non-territorial, lack pair-bonds, and practice promiscuous mating behavior and obligate maternal care of young. Behavioral details of mating behavior and associated intermale aggressive behavior are poorly understood in the species. We report the results of an observational study of mating and agonistic behavior of individually marked breeding birds in New York. We witnessed 1,265 sexual and agonistic interactions within and among males and females from 1977 through 1985. We found no evidence of male mating aggregations, and male aggressive behavior was prevalent only in male-initiated sexual interactions. Females solicit matings from males during nest-building, but the behavior is inconspicuous and not associated with male aggression. Males spend the morning patrolling their home ranges, and chase or approach females they encounter anywhere in their breeding habitat. Males often concentrate patrol activity in the vicinity of nests under construction, but we found little evidence they know the location of most nest sites. Some males seek to forcibly mount females on the ground at any breeding stage, despite female resistance. Females thwart forced mountings in 57% of cases either by fighting with the males, or by uttering an aggressive call. When a more persistent male suppresses a female's resistance, she then crouches passively as he assumes a copulatory position on her back. We discuss this behavior in terms of female control of forced mountings, female choice of mates, and forced mating as a tactic of males that appear not to know the fertility status of females. Males have a large cloacal protuberance, which suggests sperm competition is strongly developed in the species. We caution that evolution of the unusual mating behavior in Saltmarsh Sparrows must be understood in relation to the different sexual behaviors of its closest relatives.

Testosterone elevation and response to gonadotropin-releasing hormone challenge by male Northern Cardinals (Cardinalis cardinalis) following aggressive behavior

There is much discrepancy about the relationship between testosterone (T) and male aggressive behavior. For example, in birds, males of many species significantly elevate T levels during inter-male conflict. However, this is not universal, and in species where males typically do not elevate T during aggressive interactions, concentrations of the hormone are often assumed to be circulating at maximum levels. We examined if male northern cardinals (Cardinalis cardinalis) significantly elevated T during simulated territorial intrusions (STIs). We also examined if individuals had the capacity to further elevate T levels in response to gonadotropin-releasing hormone (GnRH) injections immediately after an aggressive encounter. Our results indicate that male cardinals do not significantly elevate T levels in response to STIs, but have the physiological capacity to significantly elevate T in response to GnRH injections following aggressive interactions. This implies that T levels of individuals captured during STIs were not at maximum concentrations. However, additional findings in this study also suggest the possibility that prolonged social instability could elicit significant elevations in T in males of this species, warranting further investigation.

Mechanisms of Speciation

Mechanisms of Speciation

Territoriality, Reproductive Behavior, and Parental Care in Gray Triggerfish, Balistes capriscus, from the Northern Gulf of Mexico

We documented spawning behaviors in gray triggerfish, Balistes capriscus (Gmelin, 1789), in June and July 2004-2007 on artificial reefs in the northern Gulf of Mexico, including territoriality, nest building, harem spawning, and parental care. Males were significantly larger than females and could be distinguished from females by size and dark charcoal coloration during the spawning season. Pre-fertilization dominant males were observed building and maintaining one to 13 demersal nests at particular reef sites, aggressively defending the immediate area surrounding the nests against other male gray triggerfish and other fishes, while attracting one to five females to spawn. Pre-fertilization females were observed frequently visiting and inspecting the newly constructed nest. Post-fertilization females stayed continuously on the nest guarding the eggs, and displayed a contrasting white and black color pattern, while fanning and blowing the eggs. Post-fertilization males continued to defend a territory immediately around the nest, visiting the female on the nest, and chasing other fish away. Actual spawning behavior was observed where a male and female tightly circled each other within the nest, with fertilized eggs produced immediately after this circling. Active nests with a guarding female and male were observed 28 times on 18 different reef sites. Mean number of eggs per spawning event was 772,415 from 13 active nests each with a guarding female. Observations of aggressive male behavior and sex ratios of single dominant male and up to five spawning-condition females indicate that gray triggerfish display harem spawning behavior.

As clear as mud: Turbidity induces behavioral changes in the African cichlid Pseudocrenilabrus multicolor

Abstract Aquatic biodiversity is being lost at an unprecedented rate. One factor driving this loss is increased turbidity, an environmental stressor that can impose behavioral, morphological, and/or physiological costs on fishes. Here we describe the behavioral response of a widespread African cichlid, Pseudocrenilabrus multicolor victoriae, to turbidity. We used a split-brood rearing design to test if F1 offspring reared in turbid water, originating from river (turbid) and swamp (clear) populations, behave differently than full-sibs reared in clear water. We examined two facets of behavior: (1) behaviors of fish in full sib groups, including activity level and social dynamics collected during the rearing period; and (2) male aggressive behavior directed at potential male competitors after fish had reached maturity; this was done in an experimental set-up independent of the rearing aquaria. Regardless of population of origin, fish reared in turbid water were marginally less active and performed fewer social behaviors than those reared in clear water. On the other hand, when tested against a competitor in turbid water, males performed more aggressive behaviors, regardless of population of origin or rearing environment. Our results suggest a plastic behavioral response to turbidity that may allow P. multicolor to persist over a range of turbidity levels in nature by decreasing activity and general social behaviors and intensifying reproductive behaviors to ensure reproductive success.

Stereotypes and Self-Perceptions of Physical Education Pre-Service Teachers

Stereotypes and self-perceptions are important in understanding how people develop their self-knowledge and social identity, become members of groups, and view groups and their members. While we have some understanding of the stereotypical view of the physical education teacher, we currently have little knowledge of how physical education pre-service teachers (students studying a physical education degree) are stereotyped, and also if there is any relationship between these stereotypes and how physical education pre-service teachers perceive themselves. The purpose of this study was to examine the stereotypes and self-perceptions of physical education pre-service teachers. The aims were to describe how physical education pre-service teachers stereotype and perceive themselves, examine if there are differences in the stereotypes and self-perceptions between males and females, and to explore if there were relationships between what the physical education pre-service teachers believed stereotyped them and how they perceived themselves. Participants were 250 students (n=120 males, n=130 female) studying a 4-year Bachelor of Education (Physical Education) degree at a university who completed a questionnaire which contained 10 items about how they viewed physical education pre-service teachers (stereotypes), and 26 items on how they viewed male physical education pre-service teachers and female pre-service teachers (stereotypes) and 26 items on how they view themselves (self-perceptions). Factor analysis revealed 2 stereotype factors, which were labelled as Sociable (e.g., socialise, partying, drinking, loud and outgoing) and Health and Lifestyle (e.g., fit, playing sport and not smoking). The stereotype of the male physical education pre-service teacher, comprised two factors: physical, assertive and aggressive behaviour (e.g., aggressive, dominant, self-confident, and competitive) and physical and self-presentation factors (muscular, athletic, physically fit, physically coordinated, and attractive). The stereotype of female physical education pre-service teachers comprised three factors: physical appearance and ability (e.g., physically fit, athletic, able-bodied, attractive, thin, and physically coordinated), aggressive and assertive behavioural style (e.g., intimidating, unapproachable, and aggressive), and masculine behavioural style (e.g., aggressive, masculine, feminine, muscular and dominant). The self-perception of male physical education pre-service teachers comprised three factors: perceived appearance and ability (e.g., athletic, physical fit, thin, attractive, muscular and pleased with their body), aggressive and confident behaviour (e.g., intimidating, dominant, show off and aggressive) and independence and intellect (e.g., independent, ambitious, self confident and intelligent). The self-perception of female physical education pre-service teachers comprised three factors: strong willed behaviour (e.g., ambitious, and dominant), presentation and appearance (e.g., pleased with their body, attractive, thin and self confident), and aggressive and dominant behaviour (e.g., aggressive, intimidating, masculine and show off). There were significant relationships between the male physical and self-presentation stereotype factor stereotype and perceived appearance and ability self-perception factor and between the male physical, assertive and aggressive behaviour stereotype factor and the male aggressive and confident behaviours self-perception factor. For females, the aggressive and dominant behaviour stereotype was related to both the aggressive and assertive behavioural style self-perception factor and the masculine behavioural style self-perception factor. It is suggested that future studies investigate the stereotypes and self-perceptions of students in schools during the recruitment phase of socialisation, and the possible influence of the physical education teacher education programme, faculty leaders, and significant others on the physical education pre-service teachers’ self-perceptions, stereotypes and socialisation into physical education.

Four-Week Fluoxetine (SSRI) Exposure Diminishes Aggressive Behaviour of Male Siamese Fighting Fish (<i>Betta splendens</i>)

Aggression, especially territorial is a serious problem in farmed and ornamental fish. Especially the tropical species like Siamese fighting fish Betta splendens or marine species like blu head Thalassoma bifasciatum. Also farmed species of Salmoniformes (Coho salmon Oncorhynchus kisutch, rainbow trout Oncorhynchus mykiss) exhibit territorial aggression which is correlated with growth rate of the fish. In these species native territorial aggression occurs, and in ethology it is called stereotypical agonistic behaviour or conspecific aggression. In this type modulation of aggression serotonin (5-HT) plays a main role. A decrease of 5-HT in brain intensifies these type of aggression and in opposite an increase of 5-HT reduces it. The purpose of this study was to examine the effects of different doses of fluoxetine on male aggressive behaviors of Betta splendens fish. It was concluded that fluoxetine added to aquarium water in the doses of 4, 40 and/or 100 μg·ga–1 BW during 14 - 28 days increased synaptic levels of 5-HT what in turn resulted in the reduction of the specific aggressive behaviors. Fluoxetine caused periodic, and sometimes even total weakening of male-male type fight, which is a standard trial applied in ethological research on Siamese fighting fish. In current study, the most effective was the dose of 40 μg·g–1 BW. The mechanism of this antiaggressivity depended on an increase of serotonergic system activity in animal brain (especially, in raphe nuclei), however synaptic levels of 5-HT in brain were not measured in this experiment. Thus, the hypothesis that exposure from day 1 - 21 would reduce aggression was rejected; as was the hypothesis that exposure on fluoxetine from day 10 (16) - 14 - 28 would rapidly reduce aggression in teleost fishes. The results obtained suggests that a complex role of serotonin in the expression of aggression in teleost fish because acute treatment with 5-HT1A receptor agonist WAY-100635 did not increase aggression in fish [1]. We emphasize the physiological concepts that can be addressed with this experiment, including the role of the serotonergic system in regulation of aggression, and the interplay of environmental contaminants and physiology in regulating the expression of behavior of fishes.

Roles for Oestrogen Receptor β in Adult Brain Function

Oestradiol exerts a profound influence upon multiple brain circuits. For the most part, these effects are mediated by oestrogen receptor (ER)α. We review here the roles of ERβ, the other ER isoform, in mediating rodent oestradiol-regulated anxiety, aggressive and sexual behaviours, the control of gonadotrophin secretion, and adult neurogenesis. Evidence exists for: (i) ERβ located in the paraventricular nucleus underpinning the suppressive influence of oestradiol on the stress axis and anxiety-like behaviour; (ii) ERβ expressed in gonadotrophin-releasing hormone neurones contributing to oestrogen negative-feedback control of gonadotrophin secretion; (iii) ERβ controlling the offset of lordosis behaviour; (iv) ERβ suppressing aggressive behaviour in males; (v) ERβ modulating responses to social stimuli; and (vi) ERβ in controlling adult neurogenesis. This review highlights two major themes; first, ERβ and ERα are usually tightly inter-related in the oestradiol-dependent control of a particular brain function. For example, even though oestradiol feedback to control reproduction occurs principally through ERα-dependent mechanisms, modulatory roles for ERβ also exist. Second, the roles of ERα and ERβ within a particular neural network may be synergistic or antagonistic. Examples of the latter include the role of ERα to enhance, and ERβ to suppress, anxiety-like and aggressive behaviours. Splice variants such as ERβ2, acting as dominant negative receptors, are of further particular interest because their expression levels may reflect preceeding oestradiol exposure of relevance to oestradiol replacement therapy. Together, this review highlights the predominant modulatory, but nonetheless important, roles of ERβ in mediating the many effects of oestradiol upon adult brain function.

Size-mediated dominance and aggressive behavior of male Japanese fluvial sculpin Cottus pollux (Pisces: Cottidae) reduce nest-site abundance and mating success of conspecific rivals

Despite growing evidence for plasticity in the mating patterns of nest-holding animals in relation to the changes in nest abundance, the effects of aggressive interaction by dominant males on nest availability for conspecific rivals remains unclear. To quantify the effects of male–male competition on nest-site choice and mating success of the male Japanese fluvial sculpin Cottus pollux, we conducted experiments on 5 males from different 5 size classes under both sufficient and shortage nest-abundance conditions. Nest-choice experiments showed that both male size class and nest-abundance condition had significant effects on the nesting rates of males. Following the nest-choice experiments, 10 gravid females were added in the experimental tanks. Mating experiments revealed that male size, nesting rate before addition of females, and the number of courtship attempts on females were valid variables of male mating success, regardless of nest-abundance conditions. After achieving initial mating success, the largest nesting male exhibited more frequent aggressive interaction with other conspecific males than he did before obtaining eggs in his nest. Our results suggest that size-mediated dominance and aggressive behavior of males may disrupt nest acquisition of other conspecific males, and may consequently result in extreme variation in mating success among males even under sufficient nest-abundance conditions.

Divergent evolution of male aggressive behaviour: another reproductive isolation barrier in extremophile poeciliid fishes?

Reproductive isolation among locally adapted populations may arise when immigrants from foreign habitats are selected against via natural or (inter-)sexual selection (female mate choice). We asked whether also intrasexual selection through male-male competition could promote reproductive isolation among populations of poeciliid fishes that are locally adapted to extreme environmental conditions [i.e., darkness in caves and/or toxic hydrogen sulphide (H2S)]. We found strongly reduced aggressiveness in extremophile P. oecilia mexicana, and darkness was the best predictor for the evolutionary reduction of aggressiveness, especially when combined with presence of H2S. We demonstrate that reduced aggression directly translates into migrant males being inferior when paired with males from non-sulphidic surface habitats. By contrast, the phylogenetically old sulphur endemic P. sulphuraria from another sulphide spring area showed no overall reduced aggressiveness, possibly indicating evolved mechanisms to better cope with H2S.

Functionally similar acoustic signals in the corncrake (Crex crex) transmit information about different states of the sender during aggressive interactions

We combined playback experiments with hormonal manipulations to study the information content of acoustic signals during aggressive interactions between male corncrakes. During territorial conflicts, fights are uncommon, but the intensity of signaling usually increases. Such signals can be temporally and contextually associated with many aggressive behaviors and most likely function as threats or as indicators of the sender's quality or motivation. However, such correlational data are unsatisfactory for the proper interpretation of the function and information content of signals. Experimental tests are required to determine whether signals and aggressive behaviors are controlled by common or independent mechanisms. In our experiment, we assigned subjects to four groups: testosterone-implanted birds, flutamide-implanted birds, birds with empty implants, and non-captured control birds. Males produced two types of calls (quiet soft calls and loud broadcast calls), both of which are known to be reliable predictors of aggressive escalation. When testosterone action was blocked with flutamide, males significantly limited the amount of time spent close to the playback speaker and stopped responding to playback with soft calls. Broadcast calling was unaffected by the blockage of testosterone. Conversely, increased levels of testosterone neither affected calling nor the time spent near the speaker, indicating a permissive, rather than a graded effect of androgens. We concluded that, despite the seemingly similar function, both signals may transmit information about different states of the sender; soft calls seem to imply a threat of force, while broadcast calls appear to be more similar to an announcement, which is only indirectly associated with a male's aggressive behavior.

Early life stress disrupts peripubertal development of aggression in male mice

To investigate the effects of early life stress on the development of social behaviors in male mice, we examined behavioral responses toward same sex stimulus mice in the social investigation test and aggressive behaviors in peripubertal male mice exposed to maternal separation (MS) during the first 2 weeks of life. MS suppressed aggressive behaviors from 5-9 weeks of age, but had no effect on social investigative behaviors in the social investigation test. Investigation of neuroendocrine bases of behavioral effects of MS showed that MS reduced plasma testosterone levels and decreased arginine vasopressin and increased oxytocin immunoreactivity in the paraventricular nucleus of peripubertal males. These results collectively suggest that early life stress disrupts the development of male aggressive behaviors and associated neuroendocrine systems.

Gender-specific impairments on cognitive and behavioral development in mice exposed to fenvalerate during puberty

In human and rodent models, endocrine disrupting chemicals (EDCs) interfere with the development of cognition and behaviors. Fenvalerate is a potential EDC. The purpose of this study was to examine whether pubertal fenvalerate exposure altered behavioral development. Mice were orally administered with either vehicle or fenvalerate (7.5 or 30 mg/kg/day) from postnatal day (PND) 28 to PND56. Learning and memory were assessed by Morris Water Maze. Aggressive performance was evaluated by aggressive behavior test. Anxiety-related activities were detected by three tests: open-field, plus-maze and black-white alley. Sensorimotor function was analyzed using beam walking and tightrope. Results found that the impairment for spatial learning and memory was more severe in fenvalerate-exposed female mice than in male mice. In addition, pubertal fenvalerate exposure inhibited aggressive behavior in males. Moreover, pubertal fenvalerate exposure increased anxiety activities in females. Altogether, these results suggest that pubertal fenvalerate exposure impairs spatial cognition and behavioral development in a gender-dependent manner. These findings identify fenvalerate as candidate environmental risk factors for cognitive and behavioral development, especially in the critical period of development.

Social instigation and aggression in postpartum female rats: role of 5-Ht1A and 5-Ht1B receptors in the dorsal raphé nucleus and prefrontal cortex

5-HT(1A) and 5-HT(1B) receptor agonists effectively reduce aggressive behavior in males that has been escalated by social instigation. Important sites of action for these drugs are the receptors in dorsal raphé nuclei (DRN) and the ventral-orbital prefrontal cortex (VO PFC). DRN and VO PFC areas are particularly relevant in the inhibitory control of escalated aggressive and impulsive behavior. The objectives of this study are to assess the anti-aggressive effects of 5-HT(1A) (8-OH-DPAT) and 5-HT(1B) (CP-93,129) receptor agonists microinjected into DRN and VO PFC, respectively, and to study the aggressive behavior in postpartum female Wistar rats using the social instigation protocol to increase aggression. 8-OH-DPAT (0.56 μg) in the DRN increased aggressive behavior in postpartum female rats. By contrast, CP-93,129 (1.0 μg) microinjected into VO PFC decreased the number of attack bites and lateral threats. 5-HT(1A) and 5-HT(1B) receptor agonists differed in their effects on non-aggressive activities, the former decreasing rearing and grooming and the latter increasing these acts. When 8-OH-DPAT was microinjected into DRN and CP-93,129 was microinjected into VO PFC in female rats at the same time, maternal aggression decreased. Specific participation of 5-HT(1B) receptors was verified by reversal of the anti-aggressive effects using the selective antagonist SB-224,289 (1.0 μg). The decrease in maternal aggressive behavior after microinjections of 5-HT(1B) receptor agonists into the VO PFC and DRN of female postpartum rats that were instigated socially supports the hypothesis that activation of these receptors modulates high levels of aggression in a behaviorally specific manner, due to activation of 5-HT(1B) receptors at the soma and terminals.

A lover, not a fighter: mating causes male crickets to lose fights

Both resource-holding potential (RHP) and experience in aggressive contests are known to affect future aggressive behaviour. However, few studies have examined the effects of mating experience on agonistic behaviour, despite the fact that dominant males usually acquire more matings. We investigated the effect of mating experience on male aggressive behaviour including the relationship between RHP and fighting success in the fall field cricket, Gryllus pennsylvanicus. We formed pairs of size- and age-matched males that varied in RHP (relative weapon size) and conducted two experiments. In the first, we varied male mating experience by allowing one male in a pair to either be (a) ‘mated’: court, be mounted and copulate with a virgin female or (b) ‘experienced’: court, be mounted, but prevented from copulating. The second experiment varied postcopulatory experience where the male was allowed (‘contact’) or prevented from (‘no-contact’) continued contact with his recent mate. Following treatment, experimental males engaged in an aggressive contest with the naive size- and age-matched male. In our first experiment, we found that mated and experienced males were equally likely to escalate contests to combat with a naive opponent, but mated males were less likely than experienced males to win. There was no effect of mating on the relationship between RHP and fighting success. In our second experiment, we found no effect of maintaining contact with the female on the tendency to escalate or the probability of winning. As in the first experiment, males with relatively larger heads again won more fights and this relationship was unaffected by male experience. These results suggest that mating is itself detrimental to male success in aggressive contests, but that this effect is not sufficient to eliminate the effect of RHP on fighting success.

Inter-male Spacing and Aggression in African Painted Reed Frogs, Hyperolius marmoratus

Inter-male spacing and the role of aggression in the maintenance of spatial organization was examined in choruses of Hyperolius marmoratus males housed in a semi-natural enclosure. The effects of chorus size on spacing patterns, nearest neighbour distances and male aggressive behaviour were examined. Males were found to reduce nearest neighbour distances as chorus size increased. This was accompanied by a shift in spacing pattern from even in small choruses (5–9 males) to random in choruses of 10 to 13 males. In choruses of 14, spacing patterns were once again even. The reason for these shifts is unclear but may reflect a sudden, rather than gradual increased tolerance by individuals to high neighbour call intensity as space to call from becomes more limited. The level of male aggression was influenced by chorus size and the time of night. In general, more aggressive interactions occurred in high density choruses. However, this did not translate into higher levels of individual male aggression as density increased. Individual male aggression was high in early evening choruses and declined to a minimum at peak chorusing time. High levels of aggression during early evening may reflect the establishment of calling sites by males, while the drop in aggression at peak chorusing time may occur in response to the presence of females in the chorus at this time or as a consequence of masking of neighbours calls.

Adverse health effects of anabolic–androgenic steroids

Anabolic–androgenic steroids (AAS) are synthetic drugs derived from testosterone. Illegally, these drugs are regularly self-administered by body builders and power lifters to enhance their sportive performance. Adverse side effects of AAS include sexual dysfunction, alterations of the cardiovascular system, psyche and behavior, and liver toxicity. However, severe side effects appear only following prolonged use of AAS at high dose and their occurrence is limited. Occasionally, AAS abuse may be linked to certain social and psychological traits of the user, like low self-esteem, low self-confidence, suffered hostility, childhood conduct disorder, and tendency to high-risk behavior. The overwhelming stereotype about AAS is that these compounds cause aggressive behavior in males. However, the underlying personality traits of a specific subgroup of the AAS abusers, who show aggression and hostility, may be relevant, as well. Use of AAS in combination with alcohol largely increases the risk of violence and aggression. The dependence liability of AAS is very low, and withdrawal effects are relatively mild. Based on the scores for acute and chronic adverse health effects, the prevalence of use, social harm and criminality, AAS were ranked among 19 illicit drugs as a group of drugs with a relatively low harm.

Photoperiodic modulation of reproductive physiology and behaviour in the cichlid fish Cichlasoma dimerus

Timing of breeding to an optimal season is a requirement for a successful reproductive outcome in seasonally breeding species. Photoperiodic signals are capable of modifying the reproductive behaviour and reproductive systems in several vertebrate species. The cichlid fish Cichlasoma dimerus shows highly organized breeding activities and different social status. The aim of this study is to test whether C. dimerus reproductive behaviour (male aggressive behaviour and female choice) and reproductive physiology (GnRH3 morphometric parameters, pituitary hormones content and organ-somatic indexes) are modulated by photoperiod. Before spawning, dominant pairs were isolated and kept in opposite tanks of 20 l for one week, so they could see each other but not physically interact. Afterwards, a group was exposed for four weeks to a short photoperiod (8 h light:16 h dark) (short photoperiod exposed animals: SP) while another group was exposed to a long photoperiod (14 h light:10 h dark) (long photoperiod exposed animals: LP). Temperature was maintained constant. Behavioural experiments showed that male aggression related to territory selection and its defence is reduced in SP males. Further, SP females were never chosen. At the brain level we demonstrated that GnRH3 neuronal optical density of staining was reduced. Finally, at the pituitary level we showed that SP males showed low levels of β-LH, PRL and GH in the pituitary, and that SP females showed no significant differences in the pituitary content of any hormone. Taken all together these results suggest that in C. dimerus the photoperiod is a relevant environmental cue related to reproductive behaviour and physiology.

Large Male Advantage: Phenotypic and Genetic Correlates of Territoriality in Tuatara

In reptiles, phenotypic measures such as body size usually predict a male’s success in territorial interactions. Recent evidence from fish, birds, and mammals has shown that genetic heterozygosity also has a strong influence on competitive ability and territory quality. Here, we provide a comprehensive assessment of the social structure and factors affecting male territory quality and aggressive behavior in a dense population of Tuatara, a long-lived reptile that maintains long-term territories, on Stephens Island, New Zealand. The only significant predictor of female access and competitive ability was male body size, and there was no relationship between male body size or condition and individual genetic heterozygosity. Body size, body condition, and heterozygosity did not predict territory size. Also, heterozygosity, body condition, and territory size had no relationship with the number of females to which a male had access. Large males were more effective at (1) monopolizing areas where females were most dense and (2) guarding females by consistently winning aggressive encounters with other males. Our finding of no relationship between territoriality and heterozygosity probably reflects the genetic background of this large, outbred population or that behavioral attributes or neutral heterozygosity are not appropriate individual fitness correlates for these long-lived reptiles.