Female Aggressive Behavior Research Articles

Arginine-Vasotocin Neuronal System in Steindachneridion parahybae (Siluriformes: Pimelodidae) and Its Influence on Artificially Induced Spawning in Captivity

This study summarizes new data on induced spawning of Steindachneridion parahybae, focusing on the aggressive behavior of females. This study characterizes the vasotocinergic system using immunohistochemistry, highlighting the potential influence of arginine-vasotocin (AVT) on reproductive physiology. Two experimental groups were proposed: (A) control, with one female in the aquarium, and (B) experimental, with two females in the same aquarium. Dominant (D) females presented a more aggressive behavior and did not show any injury. They apparently had a length and body mass higher than injured nondominant (ND) females. The analysis identified positive AVT immunoreactive (ir) neurons exclusively within the preoptic area, including parvocellular, magnocellular, and gigantocellular subpopulations, containing fibers-ir extending into the pituitary gland. Cellular and nuclear areas were greater in D compared to ND in the magnocellular subpopulation. There were no differences between parvocellular and gigantocellular subpopulations. There was a difference on the steroid plasma profile of cortisol (more in ND than in D) and 17α,20β-dihydroxy-4-pregnen-3-one (more in D than in ND). Furthermore, control and D females presented higher optical densities for AVT-ir, gonadotropin-releasing hormone-ir, and luteinizing hormone-ir than ND. In general, there were no differences in the results of female (control group) with D females. The AVT system is highly complex, possibly counting multiple sites of action during artificial reproduction and acting directly and/or indirectly associated with behavioral and physiological changes in S. parahybae females when induced to spawning.

Influence of Immune System Activation in Early Ontogenesis on Aggressiveness and Sexual Motivationi Adult Wistar Rats

Stresses in early ontogenesis can influence anxiety-depressive, defensive and social behavior, as well as the immune and hormonal reactivity of adult animals. The model of early proinflammatory stress assumes activation of the immune system by the introduction of bacterial lipopolysaccharide (LPS) in early ontogenesis. Whether neonatal LPS stress impacts aggressive behavior or sexual motivation is still unknown. Pathological aggressiveness and disorders in sexual behavior are characteristic of many neuropsychiatric diseases, therefore, the study of the prerequisites for their occurrence is highly relevant. On the 3rd and 5th day after birth, the rats were injected with either LPS at a dose of 50 mcg/kg (LPS group) or saline solution (SAL group, control). The aggressive behavior of adult rats in the resident-intruder test after a week of social isolation was analyzed, as well as the sexual preference of males or females in a three-chamber test. The behavior of rats was compared with baseline levels of corticosterone and interleukin-1beta in blood serum. The males of the LPS group compared with the control had more attacks on the intruder in the resident-intruder test, and the number of attacks did not decrease by the end of the experiment. The males of the LPS group had an increased interaction time with the female at the diestrus stage in the social preference test of males and females. There were no changes in aggressive behavior in females after the administration of LPS in early ontogenesis. The baseline level of interleukin-1beta was higher in males, and corticosterone was higher in females, there were no differences between the LPS and PHYS groups in biochemical parameters. The results obtained indicate an increase in aggressiveness provoked by social isolation, as well as sexual motivation in adult males after early pro-inflammatory stress, i.e., a change in the motivational and emotional component in social behavior.

Montelukast induces beneficial behavioral outcomes and reduces inflammation in male and female rats.

BackgroundAccumulative data links inflammation and immune dysregulation to the pathophysiology of mental disorders; little is known regarding leukotrienes’ (LTs) involvement in this process. Circumstantial evidence suggests that treatment with leukotriene modifying agents (LTMAs) such as montelukast (MTK) may induce adverse neuropsychiatric events. Further methodic evaluation is warranted.ObjectiveThis study aims to examine behavioral effects, as well as inflammatory mediator levels of chronic MTK treatment in male and female rats.MethodsDepression-like phenotypes were induced by exposing male and female rats to a chronic unpredictable mild stress (CUMS) protocol for four weeks. Thereafter, rats were treated (intraperitoneally) once daily, for two weeks, with either vehicle (dimethyl sulfoxide 0.2 ml/rat) or 20 mg/kg MTK. Following treatment protocols, behavioral tests were conducted and brain regions were evaluated for inflammatory mediators including tumor necrosis factor (TNF)-α, interleukin (IL)-6 and prostaglandin (PG) E2.ResultsOverall, MTK did not invoke negative behavioral phenotypes (except for an aggression-inducing effect in males). Numerous positive behavioral outcomes were observed, including reduction in aggressive behavior in females and reduced manic/hyperactive-like behavior and increased sucrose consumption (suggestive of antidepressant-like effect) in males. Furthermore, in control males, MTK increased IL-6 levels in the hypothalamus and TNF-α in the frontal cortex, while in control females it generated a robust anti-inflammatory effect. In females that were subjected to CUMS, MTK caused a prominent reduction in TNF-α and IL-6 in brain regions, whereas in CUMS-subjected males its effects were inconsistent.ConclusionContrary to prior postulations, MTK may be associated with select beneficial behavioral outcomes. Additionally, MTK differentially affects male vs. female rats in respect to brain inflammatory mediators, plausibly explaining the dissimilar behavioral phenotypes of sexes under MTK treatment.

The doublesex gene regulates dimorphic sexual and aggressive behaviors in Drosophila

Most animal species display dimorphic sexual behaviors and male-biased aggressiveness. Current models have focused on the male-specific product from the fruitless (fruM) gene, which controls male courtship and male-specific aggression patterns in fruit flies, and describe a male-specific mechanism underlying sexually dimorphic behaviors. Here we show that the doublesex (dsx) gene, which expresses male-specific DsxM and female-specific DsxF transcription factors, functions in the nervous system to control both male and female sexual and aggressive behaviors. We find that Dsx is not only required in central brain neurons for male and female sexual behaviors, but also functions in approximately eight pairs of male-specific neurons to promote male aggressiveness and approximately two pairs of female-specific neurons to inhibit female aggressiveness. DsxF knockdown females fight more frequently, even with males. Our findings reveal crucial roles of dsx, which is broadly conserved from worms to humans, in a small number of neurons in both sexes to establish dimorphic sexual and aggressive behaviors.

Neuroendocrine regulation of female aggression.

Classically the neurobiology of aggression has been studied exclusively in males. Thus, females have been considered mildly aggressive except during lactation. Interestingly, recent studies in rodents and humans have revealed that non-lactating females can show exacerbated and pathological aggression similarly to males. This review provides an overview of recent findings on the neuroendocrine mechanisms regulating aggressive behavior in females. In particular, the focus will be on novel rodent models of exaggerated aggression established in non-lactating females. Among the neuromodulatory systems influencing female aggression, special attention has been given to sex-steroids and sex-steroid-sensitive neuronal populations (i.e., the core nuclei of the neural pathway of aggression) as well as to the neuropeptides oxytocin and vasopressin which are major players in the regulation of social behaviors.

Circulating Hormones and Dominance Status Predict Female Behavior during Courtship in a Lekking Species.

Female competitive behaviors during courtship can have substantial fitness consequences, yet we know little about the physiological and social mechanisms underlying these behaviors-particularly for females of polygynous lek mating species. We explored the hormonal and social drivers of female intersexual and intrasexual behavior during courtship by males in a captive population of Indian peafowl. We investigated whether (1) female non-stress induced circulating estradiol (E2) and corticosterone (CORT) levels or (2) female dominance status in a dyad predicts female solicitation behavior. We also tested whether female circulating E2 and CORT predict dominant females' aggressive behaviors toward subordinate females in the courtship context. Our findings demonstrate that females with higher levels of circulating E2 as well as higher levels of circulating CORT solicit more courtships from males. Dominant females also solicit more courtships from males than subordinate females. Female intrasexual aggressive behaviors during courtship, however, were not associated with circulating levels of E2 or CORT. Overall, we conclude that circulating steroid hormones in conjunction with social dominance might play a role in mediating female behaviors associated with competition for mates. Experimental manipulation and measures of hormonal flexibility throughout the breeding season in relation to competitive and sexual behaviors will be necessary to further examine the link between hormonal mechanisms and female behavior in polygynous lekking systems.

Influence of female coalitionary aggressive behavior on the success of male introductions to female groups of rhesus macaques (Macaca Mulatta)

Migration patterns of wild rhesus macaque males are often mimicked in captivity by introducing unfamiliar males to female groups every few years. This strategy prevents inbreeding and has been shown to encourage group stability once males are fully integrated. The current study focused on female coalitionary aggressive behavior directed toward males during introductions to describe factors that predict its frequency and any relationship with introduction success. Observational data (755 h) were collected during eight introductions of male cohorts (3–7 individuals) to established female groups (14–39 breeding-age females). Female coalitionary aggression (FCA), defined as four or more females simultaneously attacking an individual male, was recorded 114 times and occurred during all introductions. Data showed that male groups with alpha males who aggressed females during the coalitionary events were more likely to be successfully integrated than those with alpha males who did not retaliate against females. Stepwise multiple regression analyses of individual females (N = 183) revealed that females from larger groups and older females were more likely to be involved in coalitionary aggression, while rank, family size and number of matrilines in the group did not play a role. A rating system of the severity of FCA events revealed male groups receiving more severe FCA were less likely to be successfully introduced, and larger male groups received more severe FCA than did smaller groups of males. Based on these data, it is recommended that colony managers expect FCA to occur during introductions, especially with older females and larger groups. Colony managers should monitor the alpha male’s response to FCA, as well as the severity of the FCA since those factors may predict introduction success.

Language and Aggressive Behaviors in Male and Female Youth with Autism Spectrum Disorder.

Aggressive behaviors are common among youth with autism spectrum disorder (ASD) and correlate with pervasive social-emotional difficulties. Communication skill is an important correlate of disruptive behavior in typical development, and clarification of links between communication and aggression in ASD may inform intervention methods. We investigate child/family factors and communication in relation to aggression among 145 individuals with ASD (65 female; ages 8-17years). Overall, more severe aggression was associated with younger age, lower family income, and difficulties with communication skills. However, this pattern of results was driven by males, and aggression was unrelated to child or family characteristics for females. Future work should incorporate these predictors in conjunction with broader contextual factors to understand aggressive behavior in females with ASD.

A circuit logic for sexually shared and dimorphic aggressive behaviors in Drosophila

Aggression involves both sexually monomorphic and dimorphic actions. How the brain implements these two types of actions is poorly understood. We have identified three cell types that regulate aggression in Drosophila: one type is sexually shared, and the other two are sex specific. Shared common aggression-promoting (CAP) neurons mediate aggressive approach in both sexes, whereas functionally downstream dimorphic but homologous cell types, called male-specific aggression-promoting (MAP) neurons in males and fpC1 in females, control dimorphic attack. These symmetric circuits underlie the divergence of male and female aggressive behaviors, from their monomorphic appetitive/motivational to their dimorphic consummatory phases. The strength of the monomorphic → dimorphic functional connection is increased by social isolation in both sexes, suggesting that it may be a locus for isolation-dependent enhancement of aggression. Together, these findings reveal a circuit logic for the neural control of behaviors that include both sexually monomorphic and dimorphic actions, which may generalize to other organisms.

Omega-3 supplementation, child antisocial behavior, and psychopathic personality: a randomized, double-blind, placebo-controlled, stratified, parallel group trial.

While some RCTs have observed efficacy for omega-3 supplementation in reducing antisocial behavior, the role of psychopathic personality and gender in moderating treatment outcome has not been examined. This study examines whether omega-3 supplementation reduces antisocial behavior, and whether any treatment effects are a function of gender and psychopathy. Three hundred and twenty-four schoolchildren with a mean age of 11.9years were randomized into 3 groups: omega-3 (N = 108), placebo (N = 110), and no-treatment controls (N = 106). Parent and child reports of child antisocial and aggressive behavior and psychopathic-like personality were collected at 0months (baseline), 6months (end of treatment), and 12months (6months post-treatment). A group × time × gender interaction (p = .016) indicated that only females in the omega-3 group showed a significant reduction in antisocial behavior 6months post-treatment compared to baseline (d = .35), whereas the females in the two control groups showed no change over time. A group x time x psychopathy interaction (p < .006) was also observed, with psychopathic personality levels moderating treatment outcome. Children in the omega-3 group with high (but not low) psychopathic-like personality showed significant improvements in child-reported antisocial behavior at the end of treatment (d = .19) Results suggest that omega-3 supplementation may be helpful in reducing childhood antisocial and aggressive behavior in females, and those with psychopathic-like personalities.

Pay attention to the ladies: female aggressive behavior and weapon allometry provide clues for sexual selection in freshwater anomurans (Decapoda: Aeglidae)

Contesting scarce resources can trigger the evolution of specialized morphological structures (i.e., animal weapons). While most research focus on male weapons, females might also bear weapons, although generally smaller and less conspicuous than male weapons. Social selection is evoked to explain female weaponry in which females fight for nonsexual resources such as food and shelter. Males might fight for similar resources but are expected to have proportionally larger weapons due to additional inputs from sexual selection. We tested whether males have proportionally larger weapons than females in two species of Aegla crabs. Interestingly, only males of one species had proportionally larger claws than females. Given that these larger weapons typically correlate to increased aggression, we expected males to fight more intensely than females. Thus, we compared intrasexual contests of males and females of the same species. Females fought similarly to males: latency, contest duration, and frequency of highly aggressive acts were similar between the sexes. Therefore, despite males having proportionally larger weapons in one species (as predicted by sexual selection), they fought similarly to females. Our results hint that fighting might not necessarily be the source of selection for sexual dimorphism we typically expect. Other sources, such as the frequency of fighting and predation pressure, might be selecting larger claws in males despite the similar fights, while fecundity costs might downsize female claws. We highlight that comparing female with male weapons and the associated fighting behavior shows that selection on weapons is not as straightforward as we might think. We show that studying the highly neglected female weapon allometry and usage allows us to infer on the selective process acting on animal weapons. We show here that males of one species have proportionally larger weapons, and, despite that, males fight similarly to females in every aspect analyzed. Therefore, fighting per se might not be the sole source of selection to explain sexual dimorphism. Other sources, such as frequency of fighting, and how expensive it is to produce gametes might be additional sources of selection.

Artificial selection for male winners in the Siamese fighting fish Betta splendens correlates with high female aggression

In Southeast Asia, males of the Siamese fighting fish Betta splendens have been selected across centuries for paired-staged fights. During the selection process, matched for size males fight in a small tank until the contest is resolved. Breeders discard losing batches and reproduce winner batches with the aim of increasing fight performance. We assessed the results of this long-term selection process by comparing under standard laboratory conditions male and female aggressive behaviour of one strain selected for staged fights (“fighters”) and one strain of wild-types. The aggressive response of adult fish was tested against their mirror image or a size-matched conspecific. Fighter males were more aggressive than wild-type males for all measured behaviours. Differences were not only quantitative but the pattern of fight display was also divergent. Fighter males had an overall higher swimming activity, performing frequent fast strikes in the direction of the intruder and displaying from a distance. Wild-type males were less active and exhibited aggressive displays mostly in close proximity to the stimuli. Females of the fighter strain, which are not used for fights, were also more aggressive than wild-type females. Aggressive behaviours were correlated across male and female fighter siblings, suggesting common genetic and physiological mechanisms to male and female aggression in this species. The study further shows that results were largely independent of the stimulus type, with the mirror test inducing similar and less variable responses than the live conspecific presentation. These results suggest that selection for male winners co-selected for high-frequency and metabolic demanding aggressive display in males and also enhanced female aggression, opening a wide range of testable hypothesis about the ultimate and proximate mechanisms of male and female aggression in B. splendens.

The driving forces behind female-female aggression and its fitness consequence in an Asian agamid lizard

Female-female aggression and its effect on fitness are poorly understood compared to male-male aggression. We quantified female-female aggression in the viviparous toad-headed agama, Phrynocephalus vlangalii, and tested the mate limitation and resource competition hypotheses, to explain the driving forces behind heightened female-female aggression. We established populations in outdoor enclosures and separately manipulated mate and food availability while quantifying aggressive interactions between known females. Female mass and offspring quantity and quality were monitored for 2 years and used as an index of female fitness. Interestingly, female-female aggression was highest outside the mating season, when females were pregnant. Also, male availability did not significantly influence female-female aggression. Consequently, we found no evidence in support of the mate limitation hypothesis. Female-female aggression, however, was greatest during periods of low-food availability. Greater food availability did have positive fitness consequence for females: high-food treatment females were more likely to gain mass and give birth than females from the low-food treatment, and offspring from high-food treatment females were more likely to survive the first winter. However, we did have an effect of year: female mass was negatively associated with female-female aggression in year 1 but positively associated in year 2, although the association was not significant. The same pattern appeared in the association between offspring sprint speed and female-female aggression: higher levels of female-female aggression in year 1 were associated with slower offspring, while in year 2, higher female-female aggression was associated with faster offspring. Overall, our results demonstrate a link between female-female aggression and competition for resource (food) and highlight the potential importance of female aggressive behavior as a mechanism that influences female fitness. Male-male contest competition has been a cornerstone of sexual selection theory for decades because dominant males can control more space and access to females. Conversely, female aggression is poorly understood and sometimes considered a paradox, especially in species lacking parental care. We tested whether female-female aggression in the viviparous lizard P. vlangalii is best explained by competition for males (mate limitation hypothesis) or competition over food (food limitation hypothesis). Interestingly, female aggression peaks after mating, while females are still pregnant. Heightened aggression at this time supports the food limitation hypothesis because any advantage females have in terms of access to resources will benefit offspring born into her home range. Likewise, access to additional food resources may improve female survival and future reproductive investment through greater energy storage.

Seasonal variation in sexual behavior and web aggregation in a little-known long-jawed spider (Tetragnatha straminea) (Araneae: Tetragnathidae)

General insights in sexual selection can be enhanced by the addition of data from under-studied species. Understanding the natural history of these species is acritical first step. Here, we report detailed field observations of Tetragnatha straminea Emerton, 1884, a long-jawed orb weaver common in riparian meadows. Relatively little is known about this spider, in which the elongate chelicerae of males lock with those of females during copulation. We assessed courtship, mate-guarding, intrasexual competition and predictors of female receptivity to mating. As inter-sexual fang-lock is critical to successful mating, we also examined male and female cheliceral allometry. Finally, we observed patterns of aggregative clustering during peak-mating periods, as this may indicate elevated levels of intra-sexual aggression. Overall, females were polyandrous, and it was not possible to predict female receptivity based on the number of males present or female aggressive behavior towards males. Courtship was not evident prior to mating attempts, although some males remained in close proximity to females for extended periods. Towards the middle-to-end of the mating season, multiple females would aggregate in clusters, where elevated intra-sexual aggression and frequent copulations occurred. Our observations suggested that fang-lock clasping may be important in intra-sexual agonistic interactions as well as mating, particularly during mid-season web aggregations. Consistent with this, morphological data suggest a trend towards larger chelicerae in males rather than females. Tetragnatha straminea may be ideal for testing hypotheses regarding effects of seasonal variation in sexual selection, and the evolution of structures that serve more than one sexually-selected function.

Exogenous testosterone does not modulate aggression in sex-role-reversed female Barred Buttonquails, Turnix suscitator

In sex-role-reversed species, females are typically the more competitive sex, defending territories and access to mates, while males take care of the young, often without any help from the female. In males of species with traditional sex roles, testosterone levels generally rise during the breeding season and modulate territorial and aggressive behaviour. Similarly, testosterone may modulate aggressive behaviour in females of sex-role-reversed species. To test this idea, we experimentally increased testosterone levels in sex-role-reversed polyandrous female Barred Buttonquails (Turnix suscitator) by implanting them with testosterone pellets and testing their behavioural responses during a simulated territorial challenge. Contrary to expectations, the testosterone treatment did not elicit a stronger aggressive response towards a simulated intruder than in control females. Furthermore, testosterone levels of control females were not elevated during the challenge, and were actually lower after the challenge than before it. Our study did not find any evidence that exogenous testosterone increases aggression in female Barred Buttonquails.

Fifty shades of silk: sexual behavior and bridal veil deposition in the spider Ctenus longipes

Males of some spider species lay silk threads on the female’s body during courtship and/or copulation. There are several hypotheses trying to explain the function of this behavior, known as bridal veil deposition. One of them proposes that bridal veils could occur to immobilize females and prevent sexual cannibalism when females are larger than males, or that they could inhibit female aggressive behavior. Ctenus longipes is a wandering and nocturnal spider that inhabits ravine forests in South America. The aim of this work was to describe in detail courtship and copulatory behaviors in C. longipes and confirm the occurrence of a bridal veil, discussing its possible functions in this species. For that purpose, we exposed 13 virgin male-female pairs at laboratory conditions and recorded courtship, copulation, and post-copulation behaviors. We also measured body and leg size of all individuals to estimate sexual size dimorphism. In all the cases, the male deposited silk on top of the female’s body in the form of a bridal veil, covering the anterior carapace and forelegs. The data did not support the hypothesis that bridal veil deposition is related to sexual cannibalism avoidance because females were not immobilized during mating, larger females did not present longer silk bindings, and we did not observe aggressions in any case. Future studies where males are prevented from producing silk will allow a better understanding of whether or not the veil is involved in avoiding cannibalism in C. longipes.

Sperm and sex peptide stimulate aggression in female Drosophila.

Introductory paragraphFemale aggression towards other females is associated with reproduction in many taxa, and traditionally thought to be related to the protection or provisioning of offspring, such as through increased resource acquisition. However, the underlying reproductive factors causing aggressive behaviour in females remain unknown. Here we show that female aggression in the fruit fly Drosophila melanogaster is strongly stimulated by the receipt of sperm at mating, and in part by an associated seminal fluid protein, the sex peptide. We further show that the post-mating increase in female aggression is decoupled from the costs of egg production and from post-mating decreases in sexual receptivity. Our results suggest that male ejaculates can have a surprisingly direct influence on aggression in recipient females. Male ejaculate traits thus influence the female social competitive environment with potentially far-reaching ecological and evolutionary consequences.

Maternal defensive behaviors of Uloborus sp. (Araneae, Uloboridae): behavioral repertoire and influence of clutch size and female size on female aggressiveness

Maternal care in spiders often involves behaviors associated with the protection of eggs and spiderlings against parasitoids and predators (including conspecifics). The females of several species have been documented to move their egg sacs away from natural enemies or to invest in active defense behaviors against web invaders, such as parasitoid wasps or araneophagic spider species, to protect their brood. In this study, we present observations of protective behavior by Uloborus sp. females carrying egg sacs. We also investigated whether brood size and female size influence female aggressive behaviors and response time against an artificial source of disturbance. Females carrying egg sacs almost immediately perceived and reacted aggressively against the artificial stimulus, whereas females without egg sacs moved away or ran to the web margins, avoiding the source of disturbance. The aggressive response was independent of clutch size and female body size, indicating that all females will risk interacting with potential agents of egg mortality. This systematic response by all females with egg sacs may be important for reducing the incidence of attack by the egg predator wasp Bathyzonus sp. (Ichneumonidae).

Testosterone might not be necessary to support female aggression in incubating northern cardinals

Testosterone's (T) influence on male aggression has been well established in many vertebrate species, but the impact of T on female aggressive behaviour is poorly understood. Among birds, a link between T and female aggression is plausible, as females of many species exhibit a seasonal peak in T concentrations at the onset of breeding when social instability is greatest and they may have circulating T through much of the breeding season. However, investigations examining the relationship between T and female aggression are few and have yielded conflicting results, with experimentally or endogenously elevated T supporting aggressive behaviour in females of some species but not others, and T elevating with aggression at some points of the reproductive cycle but not others. We examined the relationship between endogenous levels of T and female aggression in the northern cardinal, Cardinalis cardinalis, a resident temperate species in which pairs exhibit prolonged territoriality and females have measurable levels of T year-round, including all stages of reproduction (incubation, nestling feeding, etc.). Using simulated nest intrusions, we assessed aggressive responses of incubating females to intrasexual ‘intruders’ at the nest and quantified T levels after each aggressive encounter. Displays of aggression towards ‘intruders’ varied among females; yet, individuals showing greater levels of aggression did not demonstrate higher levels of T. These results imply that T might not support maternal aggression in this species.

The influence of androgenic steroid hormones on female aggression in ‘atypical’ mammals

Dimorphism on dominance and agonistic behaviour in mammals tends to be strongly biased toward males. In this review, we focus on a select few species of mammals in which females are as or more aggressive than males, and/or are dominant to males, and explore the role of androgenic hormones in mediating this important difference. While the data are not as clear-cut as those published on traditional laboratory mammals, our review highlights important endocrine substrates for both organizational and activational influences of steroids on female aggressive behaviour. We highlight areas in which further observations and experiments are crucial, especially the potential facilitative effects of androgens on female aggression. Finally, new and innovative techniques, including molecular genetics and receptor pharmacology, portend important insights into the ways in which androgenic hormones regulate aggressive behaviour in 'atypical' female mammals.