Receptive Females Research Articles

Finding love: fruit fly males evolving under higher sexual selection are inherently better at finding receptive females

Courtship is an important component of male reproductive behaviour that enables males to learn about the suitability of their mating partners. Experimental evidence suggests that Drosophila melanogaster males can learn to modify their courtship behaviour based on their prior experience with unreceptive females. This courtship learning is expected to provide a fitness advantage to males and could therefore evolve given suitable heritable variation. We investigated the role of sexual selection in the evolution of courtship learning ability of males, using populations of D. melanogaster evolving under high and low levels of sexual selection for over 170 generations. We exposed males from both types of population to unreceptive females and then tested their ability to discriminate between receptive and unreceptive females in a complex mating environment. After being exposed to unreceptive females, males from both types of population (1) courted females less (both receptive and unreceptive), (2) took longer to initiate courtship, but took less time to start mating after initiating courtship and (3) increased the proportion of courtship directed towards receptive females, indicating the ability of both types of males to learn from previous experience. We did not find any difference in the courtship learning ability of males from the two types of populations. However, males from populations with higher levels of sexual selection were better at recognizing and courting receptive females, even when they were not previously exposed to unreceptive females. Taken together, these results show that sexual selection may not result in improved learning abilities but can lead to the evolution of an improved innate ability of males to assess the receptivity of females. • Selectively courting receptive females can greatly affect the fitness of males. • Courtship learning enables males to assess the receptivity of females. • History of sexual selection does not affect the males' courtship learning ability. • Males evolving under higher sexual selection recognize receptive females better. • Courtship learning affected courtship and mating latency and courtship intensity.

Intersexual Differences in Behaviour and Resource Use of Specialist Phengaris teleius Butterflies.

Simple SummaryIn this study, we compared intersexual differences in behaviour and resource use of well-known Scarce Large Blue butterflies. The results indicated that females take short, but exceptionally regular flights, exploring available resources for oviposition. Males took longer, less regular flights, characterised by frequent interactions in search for receptive females. Interestingly, interactions between conspecific butterflies of the investigated species lasted significantly longer than with other species, especially when different sexes were involved. This suggests that individuals were able to quickly and efficiently recognise potential mating partners. Finally, the focal species showed strong association with its larval host plant while resting and nectaring, and less so with other plants with similarly coloured and shaped flowers. Females were particularly strongly restricted to the larval host plant, which provides some evidence that their sensory system shows neural limitation towards this valuable resource.Although the behaviour of the Large Blue butterflies of the genus Phengaris (= Maculinea) is relatively well studied, most empirical data come from investigations of their dispersal and oviposition. Here, we assessed overall intersexual differences in resource use by tracking Phengaris teleius (Bergsträsser, 1779) individuals and recording the duration of their behaviours. Females were characterised by frequent, short flights, and devoted more time to resting and oviposition. Males engaged in numerous, but usually short interactions, and spent most of the time in flight exploring their surroundings for receptive females. Their average flight time was significantly longer compared to females. Average feeding time did not differ between the sexes but was shorter when butterflies were feeding on Sanguisorba officinalis L. Intraspecific interactions within P. teleius were three times longer than those with other insect species, and interactions between sexes were particularly long lasting. Significantly shorter interspecific interactions imply that butterflies can easily recognise conspecifics and differentiate between sexes, which offers obvious fitness benefits. Both sexes, but especially females, showed strong association with their larval host plant, and less so with other flowers of similar colour and shape. Females predominantly used their host plant for feeding, which possibly indicates neuro-sensory constraints towards this resource.

Seminal fluid gene expression and reproductive fitness in Drosophila melanogaster

BackgroundThe rapid evolution of seminal fluid proteins (SFPs) has been suggested to be driven by adaptations to postcopulatory sexual selection (e.g. sperm competition). However, we have recently shown that most SFPs evolve rapidly under relaxed selective pressures. Given the role of SFPs in competition for fertilization phenotypes, like the ability to transfer and store sperm and the modulation of female receptivity and ovulation, the prevalence of selectively relaxed SFPs appears as a conundrum. One possible explanation is that selection on SFPs might be relaxed in terms of protein amino acid content, but adjustments of expression are essential for post-mating function. Interestingly, there is a general lack of systematic implementation of gene expression perturbation assays to monitor their effect on phenotypes related to sperm competition.ResultsWe successfully manipulated the expression of 16 SFP encoding genes using tissue-specific knockdowns (KDs) and determined the effect of these genes’ perturbation on three important post-mating phenotypes: female refractoriness to remating, defensive (P1), and offensive (P2) sperm competitive abilities in Drosophila melanogaster. Our analyses show that KDs of tested SFP genes do not affect female refractoriness to remating and P2, however, most gene KDs significantly decreased P1. Moreover, KDs of SFP genes that are selectively constrained in terms of protein-coding sequence evolution have lower P1 than KDs of genes evolving under relaxed selection.ConclusionsOur results suggest a more predominant role, than previously acknowledged, of variation in gene expression than coding sequence changes on sperm competitive ability in D. melanogaster.

Very short mountings are enough for sperm transfer inLittorina saxatilis

ABSTRACTConflict over reproduction between females and males exists because of anisogamy and promiscuity. Together they generate differences in fitness optima between the sexes and result in antagonistic coevolution of female and male reproductive traits. Mounting duration is likely to be a compromise between male and female interests whose outcome depends on the intensity of sexual selection. The timing of sperm transfer during mounting is critical. For example, mountings may be interrupted before sperm is transferred as a consequence of female or male choice, or they may be prolonged to function as mate guarding. In the highly promiscuous intertidal snail Littorina saxatilis, mountings vary substantially in duration, from less than a minute to more than an hour, and it has been assumed that mountings of a few minutes do not result in any sperm being transferred. Here, we examined the timing of sperm transfer, a reproductive trait that is likely affected by sexual conflict. We performed time-controlled mounting trials using L. saxatilis males and virgin females, aiming to examine indirectly when the transfer of sperm starts. We observed the relationship between mounting duration and the proportion of developing embryos out of all eggs and embryos in the brood pouch. Developing embryos were observed in similar proportions in all treatments (i.e. 1, 5 and 10 or more minutes at which mountings were artificially interrupted), suggesting that sperm transfer begins rapidly (within 1 min) in L. saxatilis and very short matings do not result in sperm shortage in the females. We discuss how the observed pattern can be influenced by predation risk, population density, and female status and receptivity.

Physical, behavioral, and hormonal changes in the resumption of sexual receptivity during postpartum infertility in female bonobos at Wamba

The operational sex ratio (OSR) is used as a predictor for the intensity of mating competition. While many factors affect the OSR, there tends to be a high male bias in primate species with long interbirth intervals and non-seasonal breeding, such as hominid apes. However, the OSR of bonobos (Pan paniscus) is lower than that of chimpanzees (Pan troglodytes), which is thought to reduce competitive and aggressive male behaviors. The low OSR of bonobos is considered to result from the early resumption of female sexual receptivity during postpartum infertility and the receptivity that they continue to show until the late stage of pregnancy. In this study, we aimed to examine the early resumption of sexual receptivity by providing quantitative data on the resumption of maximal swelling (MS) in sexual skin and copulation, and changes in urinary estrone conjugate (E1C) concentrations during postpartum infertility in wild bonobos at Wamba in the Luo Scientific Reserve, Democratic Republic of the Congo. An analysis of 9 years of data revealed that females showed the first MS at 225.4 ± 132.7 days after parturition and performed the first copulation at 186.8 ± 137.5 days after parturition, both of which were in the early stage of postpartum infertility. The proportion of days with MS and the frequency of copulation steadily increased subsequently; however, the rate of increase gradually slowed approximately 42–48 months after parturition. There was a significant correlation between the proportion of days with MS and the frequency of copulation in each period for each female. We confirmed that E1C concentrations were significantly higher during the MS phase than during the non-MS phase. Data collected over 15 months on the E1C concentration during MS showed that it increased linearly from the early stage of lactation to the next conception. These results suggest that, although female bonobos do not usually conceive until 49.7 months after parturition, they resume MS and receptivity at a low level of E1C concentration during an early stage of postpartum infertility. This study of female bonobo receptivity and sex hormone changes during the postpartum non-fertile period provides important insights for examining the evolution of low OSR, which has been considered to contribute to peaceful social relationships among bonobos.

First report of male–male combat in free-ranging Amazonian Common Lanceheads (Bothrops atrox)

In many snakes, males engage in agonistic interactions (male–male combat) apparently to establish dominant–subordinate relationships to gain priority access to reproductive females. In the Neotropical genus Bothrops Wagler, 1824 (∼45 species), male–male combat has been recorded only in three species of the monophyletic Bothrops atrox group. However, most male combats recorded in this clade occurred in captivity, an environment that facilitates the emergence of agonistic interactions. Here, we provide the first record of male–male combat in free-ranging Amazonian Common Lanceheads (Bothrops atrox (Linnaeus, 1758)) and discuss the implications of this observation for the species mating system. During fieldwork, we found one immature female and five active adult males, two of them fighting. These observations suggest that reproductive male B. atrox actively search and compete for widely dispersed and scarce receptive females.

Cumulative effects of sex pheromone components in mate recognition of Muscidifurax raptorellus

AbstractIn insects, chemical information is often crucial for mate recognition. The chemical signal may be perceived already from a distance or only at close range, depending on the volatility of the sex pheromone compounds. In many species, close‐range mate recognition is mediated by compounds of low volatility that originate from the insects’ cuticular lipid layer. The most prominent constituents are usually non‐polar hydrocarbons, but other, more polar compounds can be present as well. Upon detection, these lipids can elicit courtship behaviour. We studied mate recognition in the parasitoid wasp Muscidifurax raptorellus Kogan & Legner (Hymenoptera: Pteromalidae). In this species, courtship behaviour starts with bouts of wing fanning (high frequency wing beats while standing or walking). Once the male has mounted the female, he shows stereotypical antennal movements (antennal courtship) that lead to female receptivity signalling and copulation. We investigated the role of chemical compounds for mate recognition by evaluating the reaction of male M. raptorellus towards live conspecifics and dummies treated with whole‐body extracts or with extract fractions (non‐polar, intermediately polar, and polar compounds) in bioassays. Our results indicate that despite the sex specificity of cuticular hydrocarbon profiles, these compounds alone are not sufficient for mate recognition. Rather, we found that cuticular lipids of all three fractions seem to constitute the mate recognition signal, with a ternary mixture eliciting wing fanning significantly more often than single fractions. Overall, our results suggest that the three lipid fractions contribute cumulatively to the mate recognition signal.

Silencing Doublesex expression triggers three-level pheromonal feminization in Nasonia vitripennis males.

Doublesex (Dsx) has a conserved function in controlling sexual morphological differences in insects, but our knowledge of its role in regulating sexual behaviour is primarily limited to Drosophila. Here, we show with the parasitoid wasp Nasonia vitripennis that males whose Dsx gene had been silenced (NvDsx-i) underwent a three-level pheromonal feminization: (i) NvDsx-i males were no longer able to attract females from a distance, owing to drastically reduced titres of the long-range sex pheromone; (ii) NvDsx-i males were courted by wild-type males as though they were females, which correlated with a lower abundance of alkenes in their cuticular hydrocarbon (CHC) profiles. Supplementation with realistic amounts of synthetic (Z)-9-hentriacontene (Z9C31), the most significantly reduced alkene in NvDsx-i males, to NvDsx-i males interrupted courtship by wild-type conspecific males. Supplementation of female CHC profiles with Z9C31 reduced courtship and mating attempts by wild-type males. These results prove that Z9C31 is crucial for sex discrimination in N. vitripennis; and (iii) Nvdsx-i males were hampered in eliciting female receptivity and thus experienced severely reduced mating success, suggesting that they are unable to produce the to-date unidentified oral aphrodisiac pheromone reported in N. vitripennis males. We conclude that Dsx is a multi-level key regulator of pheromone-mediated sexual communication in N. vitripennis.

Influence of operational sex ratio and male age on mating competition intensity in reindeer (Rangifer tarandus)

The operational sex ratio (OSR), the ratio of sexually active males to sexually receptive females, is one of the main measures used to predict the intensity and direction of mating competition, influencing the opportunity for sexual selection. Here, we conducted the first experimental study to investigate how OSR and male age impacts the intensity of mating competition in reindeer (Rangifer tarandus), under semi-natural conditions during the rut. We manipulated OSR on two levels in two enclosures, a female biased treatment (3♂:6♀ = OSR 0.5) and a sex balanced treatment (3♂:3♀ = OSR 1), over 2 years with males from two age groups, and with females of various ages. We found some support for prevailing OSR theory, notably with female intrasexual competition occurring at lower frequencies in OSR 1 than OSR 0.5, and male intrasexual competition occurring at higher frequencies in the older male age group. Courtship behaviour was found to occur at higher frequencies in OSR 1 than OSR 0.5; however, there was no effect of male age. To successfully pass on genes to the next generation, one needs access to mates and winning a competitive bout is not always indicative of successfully accomplishing gene flow. Studies on OSR have the potential to help us understand the drivers behind sexual competition and how best to predict breeding outcomes during a rut.

Male chimpanzee sexual coercion and mating success at Ngogo.

Chimpanzees (Pan troglodytes) have a complex mating system in which both sexes use multiple tactics. Most copulations occur in group contexts, and high-ranking males can gain high mating and reproductive success, but females typically mate with multiple males and the potential for sperm competition is high. Also, male-female dyads sometimes form temporary exclusive mating associations (consortships). Male aggression to receptive females is common. Several studies have supported the hypothesis that this is sexual coercion, but debate exists regarding the importance of coercion relative to that of female choice. The number of adult males in a community can influence the balance between these processes. In the large Ngogo community, male dominance ranks and rates of aggression to fully-swollen females were positively related to mating success as estimated by copulation rates and by proportions of copulations achieved. Aggression rates were higher than at other sites, overall and per male, especially during periovulatory periods, and increased with the number of males associating with a female. Aggression impaired female foraging efficiency. Males initiated most copulations and females rarely refused mating attempts. Male-to-female grooming was positively associated with male mating success and with the proportion of copulations that females initiated, but the amount of grooming was typically small and whether grooming-for-mating trading occurs is uncertain. These results are consistent with the hypothesis that sexual coercion is an important component of male chimpanzee mating strategies in many sociodemographic circumstances, but also show that male tactics vary both in response to and independently of those circumstances.

To harass or to respect: the economy of male persistence despite female refusal in a damselfly with scramble mate competition

In sexual conflict, males are often thought to gain fitness benefits from harassing females over mating. Yet when harassment itself incurs costs to males and if alternative, receptive females are available in a local population, theory predicts that when confronted with a female refusal, a male’s choice of persisting or retreating is determined in part by the likelihood of achieving a mating. We tested that prediction in the damselfly Enallagma hageni, whose males compete by intense scramble competition, resulting in widespread mating harassment toward females, which have a high level of control over mating. Using captive individuals of E. hageni in outdoor insectaries, we quantified male persistence in mating after refusals by pre- and post-oviposition focal females whose egg content we quantified after observations. We documented a novel, context-dependent head-turning refusal signal of sexual non-receptivity, most often displayed in tandem pairs by post-oviposition females that typically carried few mature eggs for males to fertilize. Male persistence was less likely to result in mating with post-oviposition females compared with pre-oviposition females carrying a clutch of mature eggs. Accordingly, males were less likely to persist following refusal signals given by post-oviposition females, supporting the theoretical prediction. Compared with a refusal signal known as wing spread, head-turning was significantly more effective in deterring harassing males. Our results suggest that despite on-going sexual conflict over mating, cooperation benefits both sexes when females use the honest signal of non-receptivity because they carry few mature eggs that males could fertilize.

Out on a limb: female chameleons (Bradypodion pumilum) position themselves to minimise detection, whereas males maximise mating opportunity

ABSTRACT Although reproductive strategies are poorly documented in chameleons, sperm storage has been confirmed among some species for which male reproductive success may be maximised by increasing the number of females inseminated and/or preventing subsequent female copulation with rival males. Behaviour, such as mate searching, may enable males to maximise the number of mating opportunities with different partners and mate guarding may increase the likelihood that a male will sire offspring with a particular female. In this study, we investigated behavioural differences in movement (distance travelled) and perch choice between sexes of the Cape Dwarf Chameleon, Bradypodion pumilum, to offer data for a better understanding of mate searching and mate guarding behaviours. Wild chameleons were radio-tracked in 2010 (n = 8) and 2014 (n = 5) for approximately two weeks. The geographic location and perch height above ground were recorded multiple times per day to capture both the scale of movement and their perch use. Linear mixed effect models were used to assess differences between sexes. Our results indicated that females perched lower than males and moved shorter distances, offering support of a mate searching strategy in males. Ad hoc field observations revealed behaviours consistent with mate guarding by some males, and mate avoidance by some unreceptive females. Our results could indicate that males increase their reproductive fitness by using higher perches in both a mate guarding and mate searching context and moving further distances in search of receptive females.

Designing illustrative social media stories to promote adolescent peer support and healthy sexual behaviors.

ObjectiveAdolescent females in the United States continue to have unmet sexual and reproductive healthcare needs. Research shows that interventions incorporating peer support can augment perceived self-efficacy and reinforce healthy behaviors. Yet, few user-centered digital sexual health interventions incorporate peer support, and aim to change perceptions of peer norms and model social skills. The objective of this study was to design and demonstrate the receptivity of adolescent females to illustrated digital social media stories that promote healthy sexual behaviors and peer social support.MethodsWe conducted a three-phase study approved by our Institutional Review Board. In Phase 1, we presented sexually active adolescent female emergency department patients aged 14–19 with eight sexual health scenarios via a survey study. Participants wrote three text messages addressed to the protagonist of each scenario which motivated and encouraged her to consider the use of contraceptives. Messages were scored based on the construct of peer support (emotional, tangible, informational, and belonging). In Phase 2, we worked with a professional artist and screenwriter to design digital sexual health comics using the gathered messages. In Phase 3, we gathered feedback on the comics from adolescent female emergency department patients.ResultsFemales (n = 22) provided 352 messages. Using top rated messages, we designed five digital visualizations in a running story called Mari tells it like it is. Each story incorporated 5–12 peer-authored quotes. We inserted the final images into Instagram®. Additional females (n = 39) found the images “relatable,” “super-realistic,” and “educational.”ConclusionCollecting peer-authored texts from our local adolescent community led to the creation of well-received sexual health visualizations. This novel method of design incorporated adolescent voices to promote peer support and healthy behaviors.

Choosing the Optimal Rat Stock as a Model for Research into Pharmacological Correction of Male Sexual Dysfunction.

The aim of the study is to identify the mechanisms mediating differences in sexual behavior between Sprague Dawley and Wistar rats, in order to choose the optimal stock for research into pharmacological correction of male sexual dysfunction.Materials and MethodsThe experiments were carried out on sexually mature male rats of two stocks (Sprague Dawley and Wistar) weighing 350–450 g and aged 3 to 6 months. The comparative study of animal behavior was performed using standard tests for social interaction, locomotor activity, and anxiety level, as well as male mating behavior patterns. In order to determine the role of hypothalamic glycine receptors in the male sexual behavior, pharmacological manipulations of glycine receptor activity during mating with receptive females were conducted via bilateral intracerebral microcannulas implanted in the medial preoptic area (mPOA) of the male rat anterior hypothalamus.ResultsThe obtained results revealed statistically significant inter-stock differences in sexual behavior at the final consummatory stage of both intact animals and those after pharmacological activation of glycine receptors in the mPOA. The number of anxiety-related grooming patterns in the Open Field test significantly differed between the stocks for both intact animals and those after pharmacological activation of glycine receptors; the observed differences disappeared after the mPOA glycine receptors were blocked. In the Crowley test of social interaction, no significant difference was found between the stocks.Thus, the revealed difference in sexual behavior between Sprague Dawley and Wistar male rats is likely due to the difference in the level of anxiety, which, in turn, may be associated with difference in the mechanisms of glycinergic neurotransmission in the hypothalamic mPOAs of these rats.ConclusionTo study the relationship between the level of anxiety and sexual behavior, the choice of the Wistar rat stock is optimal since the male sexual behavior in this stock is more sensitive to stress than that in Sprague Dawley rats. However, to model male sexual dysfunction not associated with anxiety, the use of Sprague Dawley male rats should be preferred as these animals show more stable sexual behavior, which is less dependent on the level of anxiety.

Influence of operational sex ratio and male age on mating competition intensity in reindeer (Rangifer tarandus)

The operational sex ratio (OSR), the ratio of sexually active males to sexually receptive females, is one of the main measures used to predict the intensity and direction of mating competition, influencing the opportunity for sexual selection. Here, we conducted the first experimental study to investigate how OSR and male age impacts the intensity of mating competition in reindeer (Rangifer tarandus), under semi-natural conditions during the rut. We manipulated OSR on two levels in two enclosures, a female biased treatment (3♂:6♀ = OSR 0.5) and a sex balanced treatment (3♂:3♀ = OSR 1), over 2 years with males from two age groups, and with females of various ages. We found some support for prevailing OSR theory, notably with female intrasexual competition occurring at lower frequencies in OSR 1 than OSR 0.5, and male intrasexual competition occurring at higher frequencies in the older male age group. Courtship behaviour was found to occur at higher frequencies in OSR 1 than OSR 0.5; however, there was no effect of male age. To successfully pass on genes to the next generation, one needs access to mates and winning a competitive bout is not always indicative of successfully accomplishing gene flow. Studies on OSR have the potential to help us understand the drivers behind sexual competition and how best to predict breeding outcomes during a rut.

Modestly increasing systemic interleukin-6 perinatally disturbs secondary germinal zone neurogenesis and gliogenesis and produces sociability deficits

Epidemiologic studies have demonstrated that infections during pregnancy increase the risk of offspring developing Schizophrenia, Autism, Depression and Bipolar Disorder and have implicated interleukin-6 (IL-6) as a causal agent. However, other cytokines have been associated with the developmental origins of psychiatric disorders; therefore, it remains to be established whether elevating IL-6 is sufficient to alter the trajectory of neural development. Furthermore, most rodent studies have manipulated the maternal immune system at mid-gestation, which affects the stem cells and progenitors in both the primary and secondary germinal matrices. Therefore, a question that remains to be addressed is whether elevating IL-6 when the secondary germinal matrices are most active will affect brain development. Here, we have increased IL-6 from postnatal days 3–6 when the secondary germinal matrices are rapidly expanding. Using Nestin-CreERT2 fate mapping we show that this transient increase in IL-6 decreased neurogenesis in the dentate gyrus of the dorsal hippocampus, reduced astrogliogenesis in the amygdala and decreased oligodendrogenesis in the body and splenium of the corpus callosum all by ∼ 50%. Moreover, the IL-6 treatment elicited behavioral changes classically associated with neurodevelopmental disorders. As adults, IL-6 injected male mice lost social preference in the social approach test, spent ∼ 30% less time socially engaging with sexually receptive females and produced ∼ 50% fewer ultrasonic vocalizations during mating. They also engaged ∼ 50% more time in self-grooming behavior and had an increase in inhibitory avoidance. Altogether, these data provide new insights into the biological mechanisms linking perinatal immune activation to complex neurodevelopmental brain disorders.

Effect of Oral Estradiol Valerate versus Vaginal Sildenafil on Endometrial Receptivity in Clomiphene-Induced Cycle Infertile Females

Effect of Oral Estradiol Valerate versus Vaginal Sildenafil on Endometrial Receptivity in Clomiphene-Induced Cycle Infertile Females

Consort partner preference in male Tibetan macaques: How to choose when females conceal their ovulation?

Growing evidence suggested that males suffer energetic costs from sexual behavior, males should discriminate among receptive females due to their reproductive quality, and deservedly, they would prefer females during the fertile phase. However, in species with females concealing their ovulation, males cannot identify the females’ fertile phase, and then what are the criteria for males to select their female partners? To answer this question, we collected behavioral data spanning two consecutive years (from February 2017 to January 2019) to investigate the effects of female individual, social and sexual traits on male consort partner choice in Tibetan macaques ( Macaca thibetana ), a species characterized by distinct seasonal breeding and female concealed ovulation, at Mt. Huangshan, China. Results showed that, in terms of individual traits, males prefer to consort with young/middle-aged, but not old or high-fecundity females; in terms of social traits, males did not engage in more consortship with high-ranking females or their previous non-sexual “friends”; in terms of sexual traits, males were more likely to consort with lower-polyandry females (the level of diversity of the female sexual solicitation). Besides, our results also showed that, compared to other males, alpha males consort more with higher-ranking and lower-polyandry females. Our study suggested that males selected their consort partner based on female sexual traits rather than individual and social traits. Contrary to the previous insights of sexual selection that emphasized female choice and male-male competition, the current study focused on male consort partner choice to provide new insights into the co-evolution of female concealed ovulation and male mating decisions.

Enhanced D2 Agonism Induces Conditioned Appetitive Sexual Responses Toward Non-reproductive Conspecifics.

Brain mechanisms of sexual attraction toward reproductive partners develop from a systematic interrelationship between biology (nature) and learning (nurture). However, the causes of attraction toward non-reproductive partners are poorly understood. Here, we explored the role of Pavlovian learning under dopaminergic agonism on the development of sexual preference and brain activation for young male rats. During conditioning, adult sexually naïve males received either Saline (Saline-Paired) or the D2-receptor agonist quinpirole (QNP-Paired) and cohabited in contingency, or out of contingency (QNP-Unpaired) during 24 h with an almond-scented prepubertal juvenile male (PD25). Conditioning occurred every 4days for three trials. Social and sexual responses were assessed four days after the last conditioning trial in a drug-free test, and males chose freely between a scented young male (PD37) and a novel receptive female. Four days later, males were exposed to the conditioned odor only and brain Fos-IR and serum testosterone were analyzed. Saline-Paired and QNP-Unpaired males displayed more non-contact erections (NCEs) and genital investigations for females, whereas QNP-Paired males expressed more NCEs and genital investigations for young males. In the QNP-Paired group, exposure to the young male-paired odor evoked more Fos-IR in limbic, hypothalamic and cortical areas, but no differences in serum testosterone were observed. Cohabitation with juvenile males during enhanced D2 agonism results in atypical appetitive sexual responses and a higher pattern of brain response for the young male-paired odor, with no changes in serum testosterone. We discuss the potential implications for the development of pedophilic disorder and perhaps other paraphilias.

Attractiveness of female sexual signaling predicts differences in female grouping patterns between bonobos and chimpanzees

Here we show that sexual signaling affects patterns of female spatial association differently in chimpanzees and bonobos, indicating its relevance in shaping the respective social systems. Generally, spatial association between females often mirrors patterns and strength of social relationships and cooperation within groups. While testing for proposed differences in female-female associations underlying female coalition formation in the species of the genus Pan, we find only limited evidence for a higher female-female gregariousness in bonobos. While bonobo females exhibited a slightly higher average number of females in their parties, there is neither a species difference in the time females spent alone, nor in the number of female party members in the absence of sexually attractive females. We find that the more frequent presence of maximally tumescent females in bonobos is associated with a significantly stronger increase in the number of female party members, independent of variation in a behavioural proxy for food abundance. This indicates the need to look beyond ecology when explaining species differences in female sociality as it refutes the idea that the higher gregariousness among bonobo females is driven by ecological factors alone and highlights that the temporal distribution of female sexual receptivity is an important factor to consider when studying mammalian sociality.