Learning about sex: Conditioning of partner preference: Theoretical comment on Coria-Avila et al. (2005).

Sexual partner preference in female rats has been difficult to establish experimentally because the vaginocervical stimulation the female receives during the preference test can be rewarding or aversive depending on the context. G. A. Coria-Avila, A. J. Ouimet, P. Pacheco, J. Manzo, and J. G. Pfaus (2005) (see record 2005-06959-008) reported that female rats can be conditioned to show partner preference for a male that is scented with a sexually neutral odor if they are mated repeatedly with that male in a paced mating test. These results suggest that establishment of a partner preference depends on rewarding characteristics of the vaginocervical stimulation the female receives during an initial mating and that selection of a sexual partner can be determined by olfactory stimuli associated with that stimulation. These results are discussed within the context of the appetitive-consummatory construct of sexual behavior and the evolutionary significance of conditioned partner preference. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sexual experience increases nitric oxide synthase in the medial preoptic area of male rats.

Nitric oxide in the medial preoptic area (MPOA) is important for the expression and sensitization of male sexual behavior. In this article, the authors report that repeated sexual experience (mating for 2 hr on each of 3 days) increased levels of nitric oxide synthase (NOS) in the MPOA of male rats, regardless of whether they mated on the day they were given an overdose of sodium phenobarbital. This effect resulted from the previous experience and not acute mating, as NOS was not increased 2 hr after the first mating in previously naive males. Experience-induced increases in NOS in the MPOA may be one mechanism through which sexual experience facilitates sexual behavior in male rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mating activates NMDA receptors in the medial preoptic area of male rats.

Studies have emphasized the role of the medial preoptic area (MPOA) as an important site for the regulation of male sexual behavior. Indeed, ablations of the MPOA impair sexual behavior, whereas stimulation of the MPOA enhances behavior. Furthermore, neural activity in the MPOA increases with mating. The current study tested the hypothesis that activation of N-methyl-D-aspartate (NMDA) receptors occurs in MPOA neurons and is essential for the expression of male sexual behavior in rats. Results indicate that nearly all MPOA neurons that expressed Fos following mating also contained the NR1 subunit of NMDA receptors. Furthermore, mating increased phosphorylation, thus activation, of NR1 in the MPOA. Additionally, blocking NMDA receptors significantly decreased mating-induced Fos expression and mating-induced phosphorylation of NMDA receptors and impaired male sexual behavior. These results provide evidence that mating activates NMDA receptors in the MPOA and that this activation is important for the expression of male sexual behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Activation of POMC neurons during general arousal but not sexual behavior in male rats.

Exogenous opioids influence male rat sexual behavior, suggesting that endogenous opioid peptides are released during mating. Supporting this hypothesis, the authors recently showed that mating induced activation of mu opioid receptors. However, it is unknown which ligand(s) is acting on these receptors during mating. The current set of experiments tested the hypothesis that beta-endorphin-producing neurons, that is, proopiomelanocortin (POMC) neurons, are activated during sexual behavior. Mating-induced activation of POMC neurons was investigated during either the dark phase or the light phase, following different components of male rat sexual behavior or following control manipulations that resulted in general arousal. Results show activation of POMC neurons in the mediobasal hypothalamus following general arousal but not specifically related to sexual behavior per se. In addition, mating did not activate the subpopulation of POMC neurons that project to the medial preoptic nucleus. These results suggest that it is unlikely that POMC neurons contribute to the action of endogenous opioids in the brain area during sexual behavior but instead may contribute to the change in arousal state essential for the expression of sexual behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Naloxone blocks place preference conditioning after paced mating in female rats.

Sexual behavior in male rats induces a positive affect as evaluated by conditioned place preference (CPP). In addition, when females control or "pace" the rate of sexual interaction, a clear CPP is also observed. The reward state induced by mating in male rats is blocked by the injection of the opioid antagonist naloxone. In the present experiment, a dose of 4 mg/kg of naloxone completely blocked the CPP induced in females by paced mating. It appears that a common opioid system is involved in the positive affect induced by sexual behavior in both male and female rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of ibotenic acid lesions of the nucleus accumbens on paced mating behavior in the female rat.

The present study investigated the role of the nucleus accumbens (NAcc) in paced mating behavior in female rats. A sexually receptive female rat will approach and withdraw from a sexually active male, thereby controlling the timing of the receipt of sexual stimulation (e.g., mounts, intromissions, ejaculations). In this study, ibotenic acid lesions in the NAcc core increased the likelihood that a female rat would withdraw from a male rat after a mount but did not affect contact return latency or sexual receptivity. lbotenic acid lesions in the NAcc shell did not affect paced mating behavior or sexual receptivity. The results suggest that the NAcc core plays a role in suppressing withdrawal behavior in response to less intense mating stimulation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

What is so special about male adolescent sexual offending? A review and test of explanations through meta-analysis.

We tested special and general explanations of male adolescent sexual offending by conducting a meta-analysis of 59 independent studies comparing male adolescent sex offenders (n = 3,855) with male adolescent non-sex offenders (n = 13,393) on theoretically derived variables reflecting general delinquency risk factors (antisocial tendencies), childhood abuse, exposure to violence, family problems, interpersonal problems, sexuality, psychopathology, and cognitive abilities. The results did not support the notion that adolescent sexual offending can be parsimoniously explained as a simple manifestation of general antisocial tendencies. Adolescent sex offenders had much less extensive criminal histories, fewer antisocial peers, and fewer substance use problems compared with non-sex offenders. Special explanations suggesting a role for sexual abuse history, exposure to sexual violence, other abuse or neglect, social isolation, early exposure to sex or pornography, atypical sexual interests, anxiety, and low self-esteem received support. Explanations focusing on attitudes and beliefs about women or sexual offending, family communication problems or poor parent–child attachment, exposure to nonsexual violence, social incompetence, conventional sexual experience, and low intelligence were not supported. Ranked by effect size, the largest group difference was obtained for atypical sexual interests, followed by sexual abuse history, and, in turn, criminal history, antisocial associations, and substance abuse. We discuss the implications of the findings for theory development, as well as for the assessment, treatment, and prevention of adolescent sexual offending. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The development of reproductive strategy in females: Early maternal harshness → earlier menarche → increased sexual risk taking.

To test a proposition central to J. Belsky, L. Steinberg, and P. Draper’s (1991) evolutionary theory of socialization—that pubertal maturation plays a role in linking early rearing experience with adolescent sexual risk taking (i.e., frequency of sexual behavior) and, perhaps, other risk taking (e.g., alcohol, drugs, delinquency)—the authors subjected longitudinal data on 433 White, 62 Black, and 31 Hispanic females to path analysis. Results showed (a) that greater maternal harshness at 54 months predicted earlier age of menarche; (b) that earlier age of menarche predicted greater sexual (but not other) risk taking; and (c) that maternal harshness exerted a significant indirect effect, via earlier menarche, on sexual risk taking (i.e., greater harshness → earlier menarche → greater sexual risk taking) but only a direct effect on other risk taking. Results are discussed in terms of evolutionary perspectives on human development and reproductive strategy, and future directions for research are outlined. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Parental investment, reproductive success and polygyny in the lapwing, Vanellus vanellus

We studied the consequences of monogamy and polygyny for male and female lapwings at a site in northern England between 1993 and 1995. Males and females differed in breeding behaviour, and thus the pattern of reproductive investment: males contributed less time than females to the care of their offspring and more time to mating behaviour. We argue that this has resulted from sexual selection. Reproductive behaviour was similar in monogamous and polygynous individuals of both sexes. Male mating success was related to territory size, with males on the largest territories gaining more females. Polygynous male lapwings reared on average between 58 and 100% more chicks each year than monogamous males because of fewer complete breeding failures; between-year return rates of males to the area were similar. This would result in a strong advantage in terms of lifetime reproductive success for polygynous male lapwings. The seasonal breeding success of polygynous females was marginally, but not significantly, lower than that of monogamous females. Between-year return rates of monogamous and polygynous females were similar. Copyright 1998 The Association for the Study of Animal Behaviour.     

Is sexual motivational state linked to dopamine release in the medial preoptic area?

The medial preoptic area (mPOA) is a key site for the dopaminergic enhancement of male sexual behavior. Dopamine release increases in the rat mPOA with mating, supporting the critical stimulatory role played by preoptic dopamine on male sexual behavior. However, it has been questioned whether dopamine is specifically related to the occurrence of male sexual behavior and not simply involved in general arousal. To address this question, we asked whether dopamine release in the mPOA is linked to the production of male sexual behavior in Japanese quail (Coturnix japonica), a species that exhibits a much shorter temporal pattern of copulation than rats and does not have an intromittent organ, resulting in a very different topography of their sexual response. Extracellular samples from the mPOA of adult sexually experienced male quail were collected every 6 min before, during, and after exposure to a female using in vivo microdialysis and analyzed using high-performance liquid chromatography with electrochemical detection. Extracellular dopamine significantly increased in the presence of a female and returned to baseline after removal of the female. However, quail that failed to copulate did not display this increased release. These findings indicate that it is not solely the presence of a female that drives dopamine release in males, but how a male responds to her. Furthermore, in quail that copulated, dopamine release did not change in samples collected during periods of no copulation. Together, these findings support the hypothesis that dopamine action in the mPOA is specifically linked to sexual motivation and not only to copulatory behavior or physical arousal. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A meta-analytic review of research on gender differences in sexuality, 1993–2007.

In 1993 Oliver and Hyde conducted a meta-analysis on gender differences in sexuality. The current study updated that analysis with current research and methods. Evolutionary psychology, cognitive social learning theory, social structural theory, and the gender similarities hypothesis provided predictions about gender differences in sexuality. We analyzed gender differences in 30 reported sexual behaviors and attitudes for 834 individual samples uncovered in literature searches and 7 large national data sets. In support of evolutionary psychology, results from both the individual studies and the large data sets indicated that men reported slightly more sexual experience and more permissive attitudes than women for most of the variables. However, as predicted by the gender similarities hypothesis, most gender differences in sexual attitudes and behaviors were small. Exceptions were masturbation incidence, pornography use, casual sex, and attitudes toward casual sex, which all yielded medium effect sizes in which male participants reported more sexual behavior or permissive attitudes than female participants. Most effect sizes reported in the current study were comparable to those reported in Oliver and Hyde’s study. In support of cognitive social learning theory, year of publication moderated the magnitude of effect sizes, with gender differences for some aspects of sexuality increasing over time and others decreasing. As predicted by social structural theory, nations and ethnic groups with greater gender equity had smaller gender differences for some reported sexual behaviors than nations and ethnic groups with less gender equity. Gender differences decreased with age of the sample for some sexual behaviors and attitudes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sexual conflict and speciation

We review the significance of two forms of sexual conflict (different evolutionary interests of the two sexes) for genetic differentiation of populations and the evolution of reproductive isolation. Conflicting selection on the alleles at a single locus can occur in males and females if the sexes have different optima for a trait, and there are pleiotropic genetic correlations between the sexes for it. There will then be selection for sex limitation and hence sexual dimorphism. This sex limitation could break down in hybrids and reduce their fitness. Pleiotropic genetic correlations between the sexes could also affect the likelihood of mating in interpopulation encounters. Conflict can also occur between (sex-limited) loci that determine behaviour in males and those that determine behaviour in females. Reproductive isolation may occur by rapid coevolution of male trait and female mating preference. This would tend to generate assortative mating on secondary contact, hence promoting speciation. Sexual conflict resulting from sensory exploitation, polyspermy and the cost of mating could result in high levels of interpopulation mating. If females evolve resistance to make pre- and postmating manipulation, males from one population could be more successful with females from the other, because females would have evolved resistance to their own (but not to the allopatric) males. Between-locus sexual conflict could also occur as a result of conflict between males and females of different populations over the production of unfit hybrids. We develop models which show that females are in general selected to resist such matings and males to persist, and this could have a bearing on both the initial level of interpopulation matings and the likelihood that reinforcement will occur. In effect, selection on males usually acts to promote gene flow and to restrict premating isolation, whereas selection on females usually acts in the reverse direction. We review theoretical models relevant to resolution of this conflict. The winning role depends on a balance between the 'value of winning' and 'power' (relating to contest or armament costs): the winning role is likely to correlate with high value of winning and low costs. Sperm-ovum (or sperm-female tract) conflicts (and their plant parallels) are likely to obey the same principles. Males may typically have higher values of winning, but it is difficult to quantify 'power', and females may often be able to resist mating more cheaply than males can force it. We tentatively predict that sexual conflict will typically result in a higher rate of speciation in 'female-win' clades, that females will be responsible for premating isolation through reinforcement, and that 'female-win' populations will be less genetically diverse.     

Dopamine: Helping males copulate for at least 200 million years: Theoretical comment on Kleitz-Nelson et al. (2010).

Brain dopamine (DA) systems are implicated in a variety of behavioral responses and clinical syndromes, including sex, drug addiction, feeding, satiety, sleep, wakefulness, arousal, attention, reward, decision-making, depression, anxiety, psychosis, and movement disorders. The paper in this issue (see record 2010-24688-004) by Kleitz-Nelson, Dominguez, and Ball (2010) shows how DA release in the medial preoptic area of male quail are activated in an androgen-dependent manner during appetitive and consummatory phases of sexual behavior, similar to that reported previously in male rats. Those data suggest that the steroid-dependent role of hypothalamic DA in male sexual behavior has been conserved through evolutionary time. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Romantic involvement often reduces men's testosterone levels--but not always: The moderating role of extrapair sexual interest.

Testosterone (T) appears to facilitate what biologists refer to as mating effort--the investment of time and energy into same-sex competition and mate-seeking behavior. Multiple studies show that men who are romantically involved (i.e., are paired) have lower T than single men, which may be due to a facultative adjustment by men of T levels in response to lower demands for mating effort. The authors proceeded on the basis of the idea that men who retain interests in sexual opportunities with women other than a primary partner continue to dedicate more time and energy to mating effort when romantically paired, and so they predicted that the association between relationship status and T depends on men's extrapair sexual interests. Study 1 used the Sociosexual Orientation Inventory to measure extrapair sexual interests, whereas Study 2 used a broader measure to examine this interaction. Both studies found support for it. These results have implications for an understanding of the biosocial regulation of men's behavior in romantic relationships. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sex differences in parasite infections: patterns and processes

Sex differences in parasite infection rates, intensities, or population patterns are common in a wide range of taxa. These differences are usually attributed to 1 of 2 causes: (1) ecological (sociological in humans); and (2) physiological, usually hormonal in origin. Examples of the first cause include differential exposure to pathogens because of sex-specific behavior or morphology. The second cause may stem from the well-documented association between testosterone and the immune system; sexually mature male vertebrates are often more susceptible to infection and carry higher parasite burdens in the field. Although many researchers favor one explanation over the other, the requisite controlled experiments to rule out confounding variables are often neglected. We suggest that sex differences in disease have evolved just as sex differences in morphology and behavior, and are the result of selection acting differently on males and females. Research has often focused on proximate mechanistic explanations for the sex difference in infection rates, but it is equally important to understand the generality of the patterns in an evolutionary context. Because males potentially gain more than females by taking risks and engaging in competition, sexual selection pressure has shaped male behavior and appearance to maximize competitive ability and attractiveness. Many of the classic male attributes such as antlers on deer are testosterone-dependent, putting males in what appears to be a cruel bind: become vulnerable to disease by developing an attractive secondary sexual ornament, or risk lowered mating success by reducing it. A variety of hypotheses have been put forward to explain why males have not circumvented this dilemma. The mating system of the host species will influence the likelihood of sex differences in parasite infection, because males in monogamous species are subject to weaker sexual selection than males in polygynous species. Whether these evolutionary generalizations apply to invertebrates, which lack testosterone, remains to be seen.     

The great struggles of life: Darwin and the emergence of evolutionary psychology.

Darwin envisioned a scientific revolution for psychology. His theories of natural and sexual selection identified two classes of struggles--the struggle for existence and the struggle for mates. The emergence of evolutionary psychology and related disciplines signals the fulfillment of Darwin's vision. Natural selection theory guides scientists to discover adaptations for survival. Sexual selection theory illuminates the sexual struggle, highlighting mate choice and same-sex competition adaptations. Theoretical developments since publication of On the Origin of Species identify important struggles unknown to Darwin, notably, within-families conflicts and conflict between the sexes. Evolutionary psychology synthesizes modern evolutionary biology and psychology to penetrate some of life's deep mysteries: Why do many struggles center around sex? Why is social conflict pervasive? And what are the mechanisms of mind that define human nature? (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sex differences in social behavior: Are the social role and evolutionary explanations compatible?

Examines the competing claims of 2 explanations of sex differences in social behavior: social role theory, and evolutionary psychology. The origin and scope of research on sex differences in social behavior are outlined, and the application of social role theory is discussed. Research that is based on modern sexual selection theory is described, and whether its findings can be explained by social role theory is considered. Findings associated with social role theory are weighted against evolutionary explanations. It is concluded that evolutionary theory accounts much better for the overall pattern of sex differences and for their origins. A coevolutionary approach is proposed to explain cross-cultural consistency in socialization patterns. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Individual variation in male vocal traits and female mating preferences in Bufo americanus

We investigated the amount of variation in mating behaviour between and within individual male and female American toads, because both sources of trait variation can influence the course of sexual selection. Males varied in all four call parameters investigated (dominant call frequency, pulse rate, call rate and call duration). Individual males lowered the dominant frequency of their call when they interacted vocally with nearby males. Dominant call frequency was more highly correlated with body size in vocally interacting males than in non-interacting males. Pulse rate of calls primarily varied with water temperature. Call rate and call duration showed the most variation of the four call properties, but this variation was unrelated to male morphology or social interactions. Females varied in three aspects of mating behaviour: two measures of pair formation and their preference for dominant frequency of male calls. The body size of paired males varied between females both in pairings initiated by either sex and in pairings initiated only by females. Males chosen by females were usually larger than average, although age and prior breeding experience of females did not affect mate choice. Playback experiments indicated that female preference for calls of low dominant frequency depended on the temporal patterning of alternative calls presented. Each of the four male vocal properties showed significant repeatability, but only one of the three aspects of female mating behaviour was repeatable. We discuss how different degrees of repeatability in sexual traits of males and females may influence the action and detection of sexual selection in this and other species. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.     

A comparative approach to the study of dopamine and male sexual behavior: What can Japanese quail teach us? A reply to Pfaus (2010).

One of the most robust findings about dopamine (DA) is that the stimulation of dopaminergic systems promotes the activation of male sexual behavior. The commentary by Pfaus (see record 2010-24688-009) included a thorough review of studies of DA and male sexual behavior. We agree with him that the release of DA in the preoptic region in male quail in response to females and in association with the exhibition of male sexual behavior appears to be highly conserved and that it seems to have evolved very early in the evolutionary history of the vertebrate brain. However, additional data have been collected indicating that there may be significant species differences in the dopaminergic regulation of male behavior in quail compared with rats. In this response, we take the opportunity to make a few broader points about DA and male sexual behavior in light of other studies that have been conducted in birds and introduce some interesting taxonomic variation that is still not well understood. (PsycINFO Database Record (c) 2010 APA, all rights reserved)