Male-female Conflict Research Articles

Gender norm conflict and marital outcomes

AbstractWe investigate the impact of male–female conflict over gender norms on marital outcomes. As marriage requires mutual agreement regarding the role of husband and wife, we hypothesize that a person who is less likely to encounter a potential mate with similar gender norms will face a lower chance of marrying. Even if two parties marry despite a difference in gender norms, their marriage may be more vulnerable to external shocks, making divorce more likely relative to their counterparts without gender norm conflict. Finally, we predict that in the presence of gender norm conflict, high-skilled individuals may be less likely to get or stay married relative to low-skilled individuals, as the former group faces better outside options. Estimates from an analysis of U.S. marriage markets differentiated by birth cohort, state, race, and skill level support our theoretical predictions. Additional extensions explore heterogeneous effects and additional outcomes such as the presence of children in the household.

Demonstrating sexual selection by cryptic female choice on male genitalia: What is enough?

Rapid divergence in external genital structures occurs in nearly all animal groups that practice internal insemination; explaining this pattern is a major challenge in evolutionary biology. The hypothesis that species-specific differences in male genitalia evolved under sexual selection as courtship devices to influence cryptic female choice (CFC) has been slow to be accepted. Doubts may stem from its radical departure from previous ideas, observational difficulties because crucial events occur hidden within the female's body, and alternative hypotheses involving biologically important phenomena such as speciation, sperm competition, and male-female conflicts of interest. We assess the current status of the CFC hypothesis by reviewing data from two groups in which crucial predictions have been especially well-tested, Glossina tsetse flies and Roeseliana (formerly Metrioptera) roeselii bushcrickets. Eighteen CFC predictions have been confirmed in Glossina and 19 in Roeseliana. We found data justifying rejection of alternative hypotheses, but none that contradicted CFC predictions. The number and extent of tests confirming predictions of the CFC hypothesis in these species is greater than that for other generally accepted hypotheses regarding the functions of nongenital structures. By this criterion, it is reasonable to conclude that some genital structures in both groups likely involved sexual selection by CFC.

Males, Outcrossing, and Sexual Selection in Caenorhabditis Nematodes.

Males of Caenorhabditis elegans provide a crucial practical tool in the laboratory, but, as the rarer and more finicky sex, have not enjoyed the same depth of research attention as hermaphrodites. Males, however, have attracted the attention of evolutionary biologists who are exploiting the C. elegans system to test longstanding hypotheses about sexual selection, sexual conflict, transitions in reproductive mode, and genome evolution, as well as to make new discoveries about Caenorhabditis organismal biology. Here, we review the evolutionary concepts and data informed by study of males of C. elegans and other Caenorhabditis We give special attention to the important role of sperm cells as a mediator of inter-male competition and male-female conflict that has led to drastic trait divergence across species, despite exceptional phenotypic conservation in many other morphological features. We discuss the evolutionary forces important in the origins of reproductive mode transitions from males being common (gonochorism: females and males) to rare (androdioecy: hermaphrodites and males) and the factors that modulate male frequency in extant androdioecious populations, including the potential influence of selective interference, host-pathogen coevolution, and mutation accumulation. Further, we summarize the consequences of males being common vs rare for adaptation and for trait divergence, trait degradation, and trait dimorphism between the sexes, as well as for molecular evolution of the genome, at both micro-evolutionary and macro-evolutionary timescales. We conclude that C. elegans male biology remains underexploited and that future studies leveraging its extensive experimental resources are poised to discover novel biology and to inform profound questions about animal function and evolution.

Size Matters: Understanding the Conflict Faced by Large Flowers in Mediterranean Environments

Flower size is a key trait in the reproductive ecology of animal-pollinated plants. However, pollinator-mediated selection does not always modulate this trait and environmental conditions and/or antagonist interactions may favor smaller flowers. We evaluate the occurrence of a large-flowered family in a hot and dry Mediterranean environment, mediated by a cost-benefit balance and a male–female conflict. Large flowers have sizeable benefits in terms of pollination and reproductive success and pollinators mediate selection through male function, but female fitness is context-dependent. High floral production and maintenance costs and florivore incidence in large flowers limit female function, which counteracts pollinator-mediated selection. Large flowers are highly costly in the Mediterranean and flower size is mediated by a sexual conflict between the benefits of male function and the costs of the female one. However, a short floral longevity, occasional pollen limitation and selection through maleness keep the existence of large flowers in these environments.

We do not select, nor are we choosy: reproductive biology of Strepsiptera (Insecta)

The cryptic entomophagous parasitoids in the order Strepsiptera exhibit specific adaptations to each of the 34 families that they parasitize, offering rich opportunities for the study of male–female conflict. We address the compelling question as to how the diversity of Strepsiptera (where cryptic speciation is common) arose. Studying 13 strepsipteran families, including fossil taxa, we explore the genitalic structures of males, the free-living females of the Mengenillidia (suborder), and the endoparasitic females of the Stylopidia (suborder). Inferring from similarity between aedeagi of males either between congeners, heterogeners, or between species within the same taxonomic family, the same of which is true of the cephalothoraces of females, we predict that male–female conflict and a co-evolutionary morphological arms race between sexes is not likely to exist in most species of Strepsiptera. We then review the non-genitalic structures that play a role during sexual communication, and present details of copulatory behaviour. We conclude that Strepsiptera fall within the synchronous sensory exploitation model where short-lived males take advantage of a pre-existing sensory system involving pheromone signals emitted by females. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 00, 000–000.

Female resistance behaviour and progeny sex ratio in two Bradysia species (Diptera: Sciaridae) with paternal genome elimination

The relationship between female mating preferences and sex allocation has received considerable theoretical and empirical support. Typically, choosier females adjust their progeny sex ratio towards sons, who inherit the attractive traits of their father. However, in species with paternal genome elimination, where male sperm do not contain the paternal genome, predictions for the direction of progeny sex ratio biases and their relationship with female choosiness are atypical. Paternal genome elimination also creates a potential for male-female conflict over sex allocation, and any influence of female mate choice on sex ratio outcomes have interesting implications for sexually antagonistic coevolution. Within the Sciaridae (Diptera) are species that produce single-sex progeny (monogenic species) and others in which progeny comprise both sexes (digenic species). Paternal genome elimination occurs in both species. We explore female mate resistance behaviour in a monogenic and digenic species of mushroom gnat from the genus Bradysia. Our experiments confirmed our theoretical predictions, revealing that in the monogenic and digenic species, females producing female-biased progeny were more likely to have resisted at least one mating attempt.

The Limitations of Law as a Tool for Responding to Violence Against Women

In their article, Hudson, Bowen, and Nielsen (2011) argue that inequities in family law codify an evolutionary legacy of male control over female reproduction that correlates with increased rates of violence against women. Their general argument is comprised of three fundamental premises. First, the authors provide empirical evidence indicating a relationship between inequities in family law, defined as “state regulation of marriage, parenthood, dissolution of marriage, custody of children, and transmission of goods across generations” (454), and levels of physical violence against women in particular societies. Second, the authors anchor their general argument in a feminist evolutionary analytic approach (FEAA). They contend that evolutionary forces are an ultimate cause of patriarchy and violence against women, even as they acknowledge the importance of more proximate causes of specific forms of violence against women. According to the authors, an FEAA approach can help explain “persistent patterns of patriarchy throughout human history” (464) and “…tells us that there is a strong evolutionary component to violence, and that its origin is male-female conflict over reproduction, and that these influences will be mirrored in human systems of family law” (468). Finally, the authors draw upon the two previous premises to build the third and most critical premise of their argument. Because the authors believe that evidence showing a correlation between inequities in family law and levels of physical violence are ultimately rooted in evolutionary dynamics, they conclude that “[s]ocieties that persist in safeguarding inequitable family law are societies built upon evolutionary male reproductive strategies of structural control and higher levels of coercion of women by men” (470).

Female Mate-Guarding in Lawrence’s “Wintry Peacock”: An Evolutionary Perspective

D. H. Lawrence’s 1921 story “Wintry Peacock” presents a vivid example of female mate-guarding behavior, along with the male counter-strategies it provokes. Employing an elaborate yet subtle allusion to a tale from classical mythology, Lawrence underlines the archetypal—and, indirectly, the Adaptationist—significance of the male-female conflict he depicts. The allusion explains the otherwise puzzling presence of the title peacock, moreover, a non-human character who serves as a magnet for the fierce emotions of the battling husband and wife. Conflict between the sexes is inevitable, the story indicates: men and women are caught up in a contest neither sex can win definitively. Evolutionary theory helps to identify the causes of this conflict, which is rooted in innate biological differences. Deeply ingrained in evolved adaptations, male and female behavioral tactics are bound to collide, creating mutual frustration. Instead of demanding sympathy for either the male or female point of view, Lawrence’s story encourages readers to view the vicissitudes of intersexual competition with detachment.

The Study of Sex Differences

The rise of research in behavior genetics, endocrinology, neurotransmitter systems, brain imaging, and evolutionary psychology bears witness to psychology’s increasingly biological stance. This approach has been fiercely opposed by some academic feminists. This paper examines and responds to three of their key objections: determinism (the brain as an evolved organ is unresponsive to its environment), politics (the demonstration of sex differences obstructs the goal of gender equality), and epistemology (notions of cause and effect should be replaced by the study of the social construction of gender). The second part of the paper suggests some areas of convergence between the interests of feminists and biologically minded researchers. These include the role of neuropeptides in modulating sex differences; male-female conflict at a genetic and behavioral level; the functions and social impact of peer group sex segregation; the evolution and contemporary effects of cultural transmission and the role of higher-order cognitive systems in modulating the expression of evolved emotional adaptations.

Cooperation and Stability through Periodic Impulses

Basic games, where each individual chooses between two strategies, illustrate several issues that immediately emerge from the standard approach that applies strategic reasoning, based on rational decisions, to predict population behavior where no rationality is assumed. These include how mutual cooperation (which corresponds to the best outcome from the population perspective) can evolve when the only individually rational choice is to defect, illustrated by the Prisoner's Dilemma (PD) game, and how individuals can randomize between two strategies when neither is individually rational, illustrated by the Battle of the Sexes (BS) game that models male-female conflict over parental investment in offspring. We examine these questions from an evolutionary perspective where the evolutionary dynamics includes an impulsive effect that models sudden changes in collective population behavior. For the PD game, we show analytically that cooperation can either coexist with defection or completely take over the population, depending on the strength of the impulse. By extending these results for the PD game, we also show that males and females each evolve to a single strategy in the BS game when the impulsive effect is strong and that weak impulses stabilize the randomized strategies of this game.

Reconciliation in captive cotton‐top tamarins (Saguinus oedipus), a cooperative breeding primate

Reconciliation has been demonstrated in all primate species in which the phenomenon has been studied. However, reconciliation has been studied in only two species of callitrichids, and conclusions remain controversial. The first aim of this study has been to find out whether captive cotton-top tamarins (Saguinus oedipus) reconcile, since this is the first such study on this species. We examined 227 conflicts in three family groups (N=19). Instances in which individuals remained together in t=0 (29; 12.8%) were not analyzed. The cotton-top tamarins showed heightened affiliation between opponents in the postconflict periods (PC) compared with matched control (MC) periods (39.88+/-5.12% and 3.18+/-1.27%, respectively), with a corrected conciliatory tendency of 37.17+/-5.37%, and a "time window" that included the first 180 sec of the PC period. Former opponents were the most likely recipient of affiliative behaviors during the PC periods: 39.83+/-4.26% vs. 11.36+/-5.33% during MC periods. The proportion of attracted pairs (47.13+/-6.25%) was significantly higher than those of dispersed pairs for male-male conflicts (3.79+/-1.79), but not for male-female conflicts (27.31+/-9.32 and 4.82+/-2.9, respectively). In cooperative-breeding species, specific sex-class dyads might differ in how they resolve conflicts.

Diversité morphologique et fonctionnelle des spermatozoïdes chez les drosophiles

Unlike mammals, where the males produce huge quantities of tiny spermatozoa, insects, and Drosophila in particular, exhibit a wide range of reproductive strategies. Sperm gigantism in Drosophila deviates from the rules that normally govern anisogamy, i.e. differences in the size and quantity of male and female gametes. Sperm gigantism has driven anatomical, physiological and cytological adaptations that affect the correlated evolution of the male and female reproductive systems, and has led to the evolution of a new structure, the roller, located between the testis and the seminal vesicle, and to sperm coiling to form pellets. The diversification of sperm strategy is investigated in the light of sexual selection processes that occur in the female genital tract after copulation. These processes, which bias paternity, result from interactions either between spermatozoa from different males, or between the spermatozoa and the environment within the female reproductive tract. In Drosophila, increased sperm size does not confer any reproductive advantage on the male. The evolution of sperm gigantism does not seem to be attributable to competition between spermatozoa from different males, as has been shown to occur in some vertebrate species. Alternative mechanisms, such as interactions between spermatozoa and the female reproductive system, are therefore currently viewed as being more likely explanations. In particular, the impact of sperm size on female reproductive physiology is being investigated to find out whether having large spermatozoa increases the likelihood of male reproductive success. Correlated adaptations of the spermatozoa and female storage organs also seem to be a major factor in determining sperm success, and their role in male-female conflicts is discussed briefly.

Selection in the absence of males does not affect male–female conflict in the parasitoid wasp Leptopilina clavipes (Hymenoptera: Figitidae)

Divergent reproductive interests of males and females can lead to sexually antagonistic coevolution (SAC). In the absence of males, adaptations evolved under SAC are released from selection and expected to deteriorate. In this study, we investigated this prediction using two populations of the parasitoid wasp Leptopilina clavipes, one arrhenotokous and one thelytokous. Thelytokous females were induced to produce sons by curing them of their Wolbachia-infection. We examined whether thelytokous males were less able to inhibit female remating than arrhenotokous males and whether thelytokous females were more susceptible to male-induced longevity reduction than arrhenotokous females. The results showed that females were monandrous, regardless of whether mated with an arrhenotokous or thelytokous male. While ongoing courtship of males reduced female life span, there was no longevity cost of mating for either arrhenotokous or thelytokous females. Our results therefore do not support the idea that adaptations evolved under SAC deteriorate under prolonged female-only selection.

Appearances deceive: female “resistance” behaviour in a sepsid fly is not a test of male ability to hold on

Female rejections of males are crucial events in sexual selection by female choice and sexually antagonistic coevolution, but there are few detailed studies of the process of rejection. Female struggles when mounted by males are often assumed to function to dislodge the male. But this study, in which female receptivity was manipulated by using females of different ages, showed that this “dislodgement” males. Mounts in Archisepsis diversiformis often failed, but males were nevertheless seldom thrown off; instead, they almost always dismounted while the female was quiet. Males also showed signs of being in control of dismounts, as they dismounted more quickly if the female had recently been mounted by another male. Predictions from two other hypotheses for the function of female resistance behaviour also either failed or were not consistently supported: (1) females resist in order to filter males with respect to their ability to hold on to the female or outlast her resistance, or to court while mounted (“male endurance/female exhaustion” hypothesis); (2) females resist in order to sense the male's grip on her wings and thus filter males with respect to their species-specific clamps or to elicit other male courtship (“male screening” hypothesis). Several predictions of a further possibility, that (3) females resist in order to communicate their lack of receptivity to the male, and to induce him to leave (“communication” hypothesis), hypothesis is incorrect in a group (sepsid flies) in which energetic female shaking behaviour was previously interpreted as female attempts to dislodge were confirmed. Although one type of data did not fit easily with the communication hypothesis, overall it was the most likely explanation for female shaking behaviour. Our results call into question conclusions from previous studies regarding male-female conflict in this and other groups, and suggest testable alternative hypotheses. A survey of behaviour in other flies (which are presumably indicative of other animals in this respect) indicates that female “resistance” behaviour probably has a variety of functions. In sum, facile interpretations of a forceful resistance function should not be accepted without careful analyses.

The Portrayal of Interpersonal Conflict Management in Popular G and PG-Rated Animated Films

Researchers have focused on the portrayal of violence in G-rated animated films and the possible effects on the viewers. These studies largely disregard the total communicative behaviours of characters when in situations of conflict. This study analyses the verbal and non verbal conflict management strategies used by characters experiencing interpersonal conflict through a quantitative content analysis of sixteen of the most popular animated films to date. It also seeks to extend its attention to both G and PG Rated animated films. The latter of which are largely under researched, yet they are continually growing in popularity among viewers both young and old. As a result of the noted differences between male's and female's conflict management styles (Sheldon, 1993; Tannen, 1991); particular attention has also been paid to the portrayal of the two sexes when engaged in interpersonal conflict. This extended abstract reports on the preliminary findings based on a pilot study conducted on two purposively selected animated films.

Sexually antagonistic coevolution in insects is associated with only limited morphological diversity

Morphological traits involved in male-female sexual interactions, such as male genitalia, often show rapid divergent evolution. This widespread evolutionary pattern could result from sustained sexually antagonistic coevolution, or from other types of selection such as female choice or selection for species isolation. I reviewed the extensive but under-utilized taxonomic literature on a selected subset of insects, in which male-female conflict has apparently resulted in antagonistic coevolution in males and females. I checked the sexual morphology of groups comprising 500-1000 species in six orders for three evolutionary trends predicted by the sexually antagonistic coevolution hypothesis: males with species-specific differences and elaborate morphology in structures that grasp or perforate females in sexual contexts; corresponding female structures with apparently coevolved species-specific morphology; and potentially defensive designs of female morphology. The expectation was that the predictions were especially likely to be fulfilled in these groups. A largely qualitative overview revealed several surprising patterns: sexually antagonistic coevolution is associated with frequent, relatively weak species-specific differences in males, but male designs are usually relatively simple and conservative (in contrast to the diverse and elaborate designs common in male structures specialized to contact and hold females in other species, and also in weapons such as horns and pincers used in intra-specific battles); coevolutionary divergence of females is not common; and defensive female divergence is very uncommon. No cases were found of female defensive devices that can be facultatively deployed. Coevolutionary morphological races may have occurred between males and females of some bugs with traumatic insemination, but apparently as a result of female attempts to control fertilization, rather than to reduce the physical damage and infections resulting from insertion of the male's hypodermic genitalia. In sum, the sexually antagonistic coevolution that probably occurs in these groups has generally not resulted in rapid, sustained evolutionary divergence in male and female external sexual morphology. Several limitations of this study, and directions for further analyses are discussed.

Functional Morphology of the Male Genitalia of Four Species of <I>Drosophila</I>: Failure to Confirm Both Lock and Key and Male-Female Conflict Predictions

Several hypotheses attempt to explain why male genitalia typically diverge rapidly over evolutionary time. Predictions of the lock and key and the sexually antagonistic coevolution hypotheses were tested by studying the functional morphology of several male genitalic traits by freezing copulating pairs of four species of Drosophila: saltans, willistoni, melanogaster, and malerkotliana. Contrary to the predictions of the hypotheses, there were no species-specific differences in female morphology that corresponded to interspecific differences in the morphology of the male surstylus (which pressed and perhaps spread the distal tip of the oviscape), the epandrium (which grasped the external surface of the extended oviscape), and the aedeagus and paraphyses (which, in willistoni, clamped the oviscape). Antagonistic coevolution could possibly explain the diverse male genitalic morphology if female resistance behavior rather than morphology has coevolved with male morphology, but there are reasons doubt this explanation.

Male-female conflict and genitalia: failure to confirm predictions in insects and spiders.

Some recent models suggest a new role for evolutionary arms races between males and females in sexual selection. Female resistance to males is proposed to be driven by the direct advantage to the female of avoiding male-imposed reductions in the number of offspring she can produce, rather than by the indirect advantage of selecting among possible sires for her offspring, as in some traditional models of sexual selection by female choice. This article uses the massive but hitherto under-utilized taxonomic literature on genitalic evolution to test, in a two-step process, whether such new models of arms races between males and females have been responsible for rapid divergent evolution of male genitalia. The test revolves around the prediction that 'new arms races' are less likely to occur in species in which females are largely or completely protected from unwanted sexual attentions from males (e.g. species which mate in leks or in male swarms, in which males attract females from a distance, or in which females initiate contact by attracting males from a distance). The multiple possible mechanical functions of male genitalia are summarized, and functions of male genitalic structures in 43 species in 21 families of Diptera are compiled. Functions associated with intromission and insemination (e.g. seizing and positioning the female appropriately, pushing past possible barriers within the female, orienting within the female to achieve sperm transfer), which are unlikely to be involved in new arms races when females are protected, are shown to be common (> 50 % of documented cases). This information is then used to generate the new arms race prediction: differences in genitalic form among congeneric species in which females are protected should be less common than differences among congeneric species in which females are vulnerable to harassment by males. This prediction was tested using a sample of 361 genera of insects and spiders. The prediction clearly failed, even when the data were adjusted to take into account several possible biases. Comparative analyses within particular taxonomic groups also failed to show the predicted trends, as did less extensive data on other non-genitalic male display traits. Arms races, as defined in some recent models, seem to have been less important in male-female coevolution of genitalic structures than has been suggested. By elimination, alternative interpretations, such as traditional female choice, which do not predict associations between female protection from harassment and rapid divergent evolution, are strengthened.

RAPID DIVERGENT EVOLUTION OF SEXUAL MORPHOLOGY: COMPARATIVE TESTS OF ANTAGONISTIC COEVOLUTION AND TRADITIONAL FEMALE CHOICE

Male structures specialized to contact females during sexual interactions often diverge relatively rapidly over evolutionary time. Previous explanations for this pattern invoked sexual selection by female choice, but new ideas emphasize possible sexually antagonistic coevolution resulting from male-female conflict over control of fertilization. The two types of selection have often not been carefully distinguished. They do not theoretically exclude one another, but they have not necessarily had equally important roles in producing rapid evolutionary divergence. To date, most recent empirical studies of antagonistic coevolution have emphasized only a few taxa. This study uses the abundant but little-used data in the taxonomic literature on morphology to evaluate the roles of antagonistic coevolution and traditional female choice over a wide taxonomic spectrum (61 families of arthropods, mostly insects and spiders). Groups with species-specific male structures that contact females were checked for coevolution of species-specific female structures that are contacted by the male and that have mechanical properties that could potentially defend her against the male. Facultatively deployable, species-specific female defensive structures, a design that would seem likely to evolve frequently under the sexually antagonistic coevolution hypothesis, were completely absent (0% of 106 structures in 84 taxonomic groups). Although likely cases of sexually antagonistic coevolution exist, using conservative criteria, 79.2% of the 106 structures lacked even potentially defensive female coevolution. A common pattern (53.8% of 106) was a nearly complete absence of female change in areas contacted by species-specific male structures. Post-hoc arguments invoking possible coevolution of defensive female behavior instead of morphology, or of female sensitivities and responses to male sensory traps, could enable the sexually antagonistic coevolution hypothesis to explain these data. No case of such coevolution of female behavior or sensitivities has been demonstrated, and there are additional reasons to doubt that they are general explanations for the data presented here. Detailed studies of female resistance behavior could help illuminate several issues. The possibility of a greater role for antagonistic coevolution in reproductive physiology than in morphology and the possibility that female choice and sexually antagonistic coevolution have both been important in some lineages are discussed.

Female choice of sexually antagonistic male adaptations: a critical review of some current research.

We contrast some recent uses of the concept of male-female conflict, with the type of conflict that is inherent in traditional Darwinian female choice. Females in apparent conflict situations with males may suffer reduced lifetime reproduction, but nevertheless benefit because they obtain sons with superior manipulative abilities. Female defences against male manipulations may not be 'imperfect' because of inability to keep pace with male evolution, but in order to screen males and favour those that are especially good manipulators. We examine the consequences of these ideas, and of the difficulties of obtaining biologically realistic measures of female costs, for some recent theoretical and empirical presentations of male-female conflict ideas, and find that male-female conflict in the new sense is less certain than has been commonly supposed. Disentangling previous sexual selection ideas and the new conflict of interest models will probably often be difficult, because the two types of payoffs are not mutually exclusive.