'Concealed ovulation' and sexual signals in primates.

The absence of conspicuous sexual signals in some primates, particularly humans and vervets, has been interpreted as evidence that females of these species are 'concealing' ovulation from males. This conclusion is unjustified: the null hypothesis of no adaptation, that the absence of conspicuous sexual signals has resulted from the absence of selective pressures maintaining such adaptations, is both more parsimonious and better fits the facts. The related suggestion that there has been adaptation among females to conceal ovulation from their own consciousness is also unjustified. What, then, maintains sexual signals in those species that do have them? Many proposed hypotheses for the function of sexual signals do not account for their most puzzling feature: their conspicuousness. According to current theory on the evolution of communication, two explanations seem most plausible: conspicuous sexual signals function to communicate to distant receivers and/or to convince reluctant receivers. There is some empirical support for both hypotheses, but not overwhelming support for either.     

Migration and the evolution of sexual dichromatism: evolutionary loss of female coloration with migration among wood-warblers

The mechanisms underlying evolutionary changes in sexual dimorphism have long been of interest to biologists. A striking gradient in sexual dichromatism exists among songbirds in North America, including the wood-warblers (Parulidae): males are generally more colourful than females at northern latitudes, while the sexes are similarly ornamented at lower latitudes. We use phylogenetically controlled comparative analysis to test three non-mutually exclusive hypotheses for the evolution of sexual dichromatism among wood-warblers. The first two hypotheses focus on the loss of female coloration with the evolution of migration, either owing to the costs imposed by visual predators during migration, or owing to the relaxation of selection for female social signalling at higher latitudes. The third hypothesis focuses on whether sexual dichromatism evolved owing to changes in male ornamentation as the strength of sexual selection increases with breeding latitude. To test these hypotheses, we compared sexual dichromatism to three variables: the presence of migration, migration distance, and breeding latitude. We found that the presence of migration and migration distance were both positively correlated with sexual dichromatism, but models including breeding latitude alone were not strongly supported. Ancestral state reconstruction supports the hypothesis that the ancestral wood-warblers were monochromatic, with both colourful males and females. Combined, these results are consistent with the hypotheses that the evolution of migration is associated with the relaxation of selection for social signalling among females and that there are increased predatory costs along longer migratory routes for colourful females. These results suggest that loss of female ornamentation can be a driver of sexual dichromatism and that social or natural selection may be a stronger contributor to variation in dichromatism than sexual selection.     

Sexual dimorphism, extrapair fertilizations, and operational sex ratio in great frigatebirds (Fregata minor)

Across taxa, the presence of sexual ornaments in one sex isusually correlated with disproportionately great parental effortby the other. Frigatebirds (Fregatidae) are sexually dimorphic,with males exhibiting morphological and behavioral ornaments,but males and females share in all aspects of parental effort.All other taxa in a clade of 237 species exhibit biparentalcare, but only frigatebirds exhibit pronounced sexual dimorphism. We tested for the presence of two factors that could contributeto the evolution of male ornaments in great frigatebirds: ahigh frequency of extrapair fertilizations and a male-biasedoperational sex ratio. In 92 families sampled over two breedingseasons, there was only one extrapair fertilization. However,in both seasons, there were more males than females availablefor mating, and the sex ratio among individuals actively engagedin mate-acquisition behavior was strongly male biased, withtypically five or six males available per female. Our resultssuggest that extrapair fertilizations are not responsible forthe exaggeration of sexual ornaments in male frigatebirds,and that operational sex ratio may be related to sexual dimorphismin this species. Further work is needed to determine whetherthe male-biased operational sex ratio creates the variancein male reproductive success that would be needed to drivethe evolution of male ornaments.     

The Effects of Experimentally Induced Polyandry on Female Reproduction in a Monandrous Mating System

Females of most insect species maximize their fitness by mating more than once. Yet, some taxa are monandrous and there are two distinct scenarios for the maintenance of monandry. While males should always benefit from inducing permanent non‐receptivity to further mating in their mate, this is not necessarily true for females. Since females benefit from remating in many species, cases of monandry may reflect successful male manipulation of female remating (i.e. sexual conflict). Alternatively, monandry may favor both mates, if females maximize their fitness by mating only once in their life. These two hypotheses for the maintenance of monandry make contrasting predictions with regards to the effects of remating on female fitness. Here, we present an experimental test of the above hypotheses, using the monandrous housefly (Musca domestica) as a model system. Our results showed that accessory seminal fluid substances that males transfer to females during copulation have a dual effect: they trigger female non‐receptivity but also seem to have a nutritional effect that could potentially enhance female fitness. These results suggest that monandry is maintained in house flies despite potential benefits that females would gain by mating multiply.     

THE EVOLUTION OF REVERSED SEXUAL DIMORPHISM IN SIZE IN MONOGAMOUS SPECIES OF BIRDS

Reversed sexual dimorphism in size (RSD) occurs in most species of several taxonomic groups of birds. The hypotheses proposed to explain this phenomenon are examined theoretically, using inequalities to state selection in the most rigorous possible terms. The most pertinent empirical evidence is also examined critically. Proponents of hypotheses on the evolution of RSD have failed to consider the genetic constraints on the evolution of dimorphism. Selection for dimorphism can act on only that small portion of the genetic determination of body size that is sex limited. In general, selection for body size is much more likely to lead to a similar change (e.g. larger) in both sexes than to dimorphism. The most popular hypotheses involve selection for size-related differences in foraging ability. It is unlikely that there is variation in size-related foraging differences available for selection in a monomorphic, ancestral population. Foraging differences between the sexes cannot lead to the evolution of RSD; evolution of large and small morphs of both sexes is a more likely outcome. Selection for sex-role differentiation factors (e.g. large females lay larger eggs, small males are more agile in flight) can lead to the evolution of RSD, but only if the magnitudes of opposing selection for small males and for large females are equal. Combining selection for size-related foraging differences with selection for sex-role differentiation factors hinders the evolution of RSD until the sexes differ in size by 3 s.d . Empirical evidence supports this assertion: statistically significant differences between the sexes in the size of prey taken are found only in highly dimorphic species. The sex-role differentiation factors that have been proposed appear unlikely to provide the equal selection necessary for the evolution of RSD. Several authors have proposed that small size in males is selected for foraging ability and large size in females for some sex-role differentiation factor. Males cannot be more efficient foragers without females being less efficient and efficiency cannot be a factor only when the male is feeding his family. RSD cannot evolve in monogamous species if large females survive less well than small males. RSD might evolve as the result of sexual selection for small size in males and constraints on the reduction of size in females because of some factor associated with reproduction. Examination of seven studies indicating a relationship between female size and reproductive success shows very little unequivocal evidence for small size in females allowing breeding earlier in the season. Large size in females allows females to breed at a younger age in the sparrowhawk and pairs to form more rapidly in three species of sandpipers. Both of these may be the result of sexual selection. There are fewer theoretical problems with sexual selection as a cause for the evolution of RSD than with the other hypotheses. Empirical evidence for sexual selection is scarce but better than that for the other hypotheses. Evidence is contradictory for the selection of small size in males for agility in aerial displays for courtship or defence of territory. Large size in females does not appear to be the result of selection for competitive ability to obtain mates. Facilitation of female dominance and hence of the formation and maintenance of a pair bond is the most viable explanation of the evolution of RSD. It is most likely that all dimorphism (normal or reversed) is the result of sexual selection. RSD is correlated with birds in the diet in the Falconiformes and this is a central theme in the foraging hypotheses. This correlation may be because birds are abundant and available in a continuum of sizes, thus permitting but not causing the evolution of RSD or because species that prey upon birds are better equipped physically (and perhaps more likely behaviourally) to inflict damaging attacks on conspecifics and the greater RSD increases female dominance and the ease of pair formation.     

Male red coloration,female mate preference,and sperm longevity in the cyprinid fish Puntius titteya

In recent decades, the link between the exaggeration of male sexual ornaments and ejaculate quality has received much attention. When males with conspicuous sexual ornaments have high-quality ejaculate, females are believed to obtain benefits, such as high fertilization success and offspring with good genes, by choosing mates on the basis of male ornamentation. In this study, we examined the relationships among male body coloration, female mate preference, and sperm longevity in the sexually dichromatic fish Puntius titteya. Males of this species assume a bright red coloration over the entire body, and neither sex invests in the parental care of eggs. In the female preference test, females preferred males with redder body coloration over their counterpart males with duller coloration. In addition, the sperm longevity test indicated that redder males had sperm with greater longevity. These results suggest that the red coloration of males in this species may signal sperm longevity and that females can mate with males with higher quality sperm by choosing redder males.     

Why are female color polymorphisms rare in territorial damselflies?

In nonterritorial damselflies, females often come in multiple color morphs, perhaps because females with rare colors experience reduced sexual harassment, and thus have a frequency‐dependent fitness advantage, compared to females of the most common color morph, but such polymorphisms are rare in territorial species. We consider three hypotheses to explain the rarity of female color polymorphisms in territorial species: (a) misdirected male aggression, (b) poor male mate recognition, and (c) low mating harassment rates. The first hypothesis has some empirical support, and can account for the absence of andromorphs (i.e., females that resemble males), but does not explain the absence of multiple heteromorphs. We tested the second hypothesis by presenting females of two novel color morphs (green‐ or red‐banded abdomens) to territorial male Hetaerina capitalis. Females of both novel color morphs elicited fewer sexual responses than control females, and the red morph occasionally elicited aggressive responses. These results indicate that novel female color morphs would experience reduced mating harassment in this species, contradicting the hypothesis that male mate recognition is too poorly developed to reduce harassment of novel female morphs. By process of elimination, the third hypothesis, that harassment rates are too low in territorial species to provide rare female morphs a fitness advantage, is favored, but remains untested. Our findings also suggest that the common practice of color‐marking odonates for behavioral research is likely to interfere with mate choice, as has long been known to be the case in birds.     

Sexual size dimorphism in seabirds: sexual selection, fecundity selection and differential niche-utilisation

Seabirds exhibit a range of sexual size dimorphism (SSD) that includes both male-biased (males>females) and female-biased SSD (males相似文献   

Evolution of reversed sex roles, sexual size dimorphism, and mating system in coucals (Centropodidae, Aves)

The evolution of greater male than female parental care remains poorly understood. In birds it is thought to be related to precocial chicks and small clutch size. This review shows, however, that such role reversal has also evolved in a family with altricial young and relatively large clutch size: coucals (Centropodidae, Cuculiformes). Males perform most nest building, incubation, and feeding of young. As predicted by sexual selection theory, coucals have also reversed sexual size dimorphism, females being larger than males in all 12 species for which size data are available. Most coucals that have been studied are monogamous, but the black coucal Centropus grillii appears to be polyandrous, and males perform almost all parental care, whereas females show more active advertisement behaviour. In this species, females are about 50% heavier than males. Polyandry in the black coucal seems to be associated with a shift to a habitat with seasonally rich food resources. Difficulties for female coucals of gathering enough resources for producing several clutches of relatively large eggs may favour mainly male parental care. Female sexual competition and resource storage, and male foraging economy, may explain why females are larger. Additional field studies are needed to test these hypotheses; the coucals are of great interest to sexual selection and mating systems theory.     

The costs of choice in sexual selection

In Fisher's model of sexual selection female mating preferences are not subject to direct selection but evolve purely because they are genetically correlated with the favoured male trait. But when female choice is costly relative to random mating, for example in energy, time or predation risks, the evolution of female mating preference is subject also to direct selection. With costly female choice the set or line of equilibria found in models of Fisher's process no longer exists. On the line the male trait is under zero net selection, and there is no advantage for a female choosing a male with a more exaggerated character. Therefore any cost to choice causes choosiness to decline. In turn this lowers the strength of sexual selection and the male trait declines as well. So when Fisher's process is the sole force of sexual selection and female choice is costly, only transitory increases in female choice and the preferred male trait are possible. It has often been claimed that exaggerated male characters act as markers or revealers of the genetic quality of potential mates. If females choose their mates using traits that correlate with heritable viability differences then stable exaggeration of both female choice and the preferred male character is possible, even when female choice is costly. The offspring of choosy females have not only a Fisherian reproductive advantage but also greater viability. This suggests that in species with exaggerated male ornamentation, in which female choice is costly, it is likely that female mate choice will be for traits that correlate with male genetic quality.     

Male genotype influences female reproductive investment in Drosophila melanogaster

In many species, males can influence the amount of resources their mates invest in reproduction. Two favoured hypotheses for this observation are that females assess male quality during courtship or copulation and alter their investment in offspring accordingly, or that males manipulate females to invest heavily in offspring produced soon after mating. Here, we examined whether there is genetic variation for males to influence female short-term reproductive investment in Drosophila melanogaster, a species with strong sexual selection and substantial sexual conflict. We measured the fecundity and egg size of females mated to males from multiple isofemale lines collected from populations around the globe. Although these traits were not strongly influenced by the male's population of origin, we found that 22 per cent of the variation in female short-term reproductive investment was attributable to the genotype of her mate. This is the first direct evidence that male D. melanogaster vary genetically in their proximate influence on female fecundity, egg size and overall reproductive investment.     

Sexual conflict and antagonistic coevolution across water strider populations

Microevolutionary studies have demonstrated sexually antagonistic selection on sexual traits, and existing evidence supports a macroevolutionary pattern of sexually antagonistic coevolution. Two current questions are how antagonistic selection within-populations scales to divergence among populations, and to what extent intraspecific divergence matches species-level patterns. To address these questions, we conducted an intraspecific comparative study of sexual armaments and mating behaviors in a water strider (Gerris incognitus) in which male genitals grasp resistant females and female abdominal structures help ward off males. The degree of exaggeration of these armaments coevolves across species. We found a similar strong pattern of antagonistic coevolution among populations, suggesting that sexual conflict drives population differentiation in morphology. Furthermore, relative exaggeration in armaments was closely related to mating outcomes in a common environment. Interestingly, the effect of armaments on mating was mediated by population sexual size dimorphism. When females had a large size advantage, mating activity was low and independent of armaments, but when males had a relative size advantage, mating activity depended on which sex had relatively exaggerated armaments. Thus, a strong signal of sexually antagonistic coevolution is apparent even among populations. These results open opportunities to understand links between sexual arms races, ecological variation, and reproductive isolation.     

Sexual selection in hermit crabs: a review and outlines of future research

The information currently available on sexual selection in hermit crabs is reviewed to identify the role of males and females before, during and after mating. According to this information, possible mechanisms of male–male competition, female choice and/or sexual conflict are suggested. Important male components that may affect mating success include dragging the female shell, rotations of the female's shell and male cheliped palpations, and male size and/or shell characteristics (species and size). Possible female determinants of male mating/fertilization success include size (as an indicator of egg production capacity), signalling of sexual receptivity to males, delay from mate guarding to copulation and mating duration. Avenues for deeper exploration in males include the role of the number and morphometry of male sexual tubes during sperm transfer, and whether ejaculate size and sperm number can be adjusted with variable situations of sperm competition intensity and risk. In females it would be interesting to investigate the chemical and behavioural mechanisms affecting spermatophore breakage for sperm release and the variable duration from sperm transfer to spawning. Given these possibilities, and that sperm is externally deposited on the female's body but inside her shell (except for those species that do not use shells, e.g. Birgus , or species where shells are rather small and do not cover the body totally, e.g. Parapagurus ), we conclude that hermit crabs are unique subjects for separating male and female effects, particularly with respect to the applicability of current ideas in sexual selection such as female choice and sexual conflict. Some practical ideas are provided to disentangle both hypotheses using these animals.     

Behavioural processes in social context: female abductions, male herding and female grooming in hamadryas baboons

The formation of bonds between strangers is an event that occurs routinely in many social animals, including humans, and, as social bonds in general, they affect the individuals' welfare and biological fitness. The present study was motivated by an interest in the behavioural processes that drive bond formation in a social context of hostility, in which the incumbent partners vary greatly in physical power and reproductive interests, a situation in which individuals of many group-living species find themselves often throughout their lives. We focused on the quantitative analysis of female abductions via male aggressive herding in a nonhuman primate, the hamadryas baboon, in which intersexual bonds are known to be strong. We tested three hypotheses informed by sexual conflict/sexual coercion theory (male herding-as-conditioning and female grooming-as-appeasement) and by socioecological theory (unit size and female competition). The results supported the predictions: males resorted to coercive tactics (aggressive herding) with abducted females, and abducted females elevated the amount of grooming directed at their new unit males; in fact, they escaped from the otherwise negative effect of unit size on female-to-male grooming. These findings reveal that conflicts of interest are natural ingredients underpinning social bonds and that resorting to coercive aggression may be an option especially when partners differ greatly in their physical power.     

Do exaggerated chelicerae function as weapons or genitalia in a long‐jawed spider? Functional allometric analysis yields an answer

From the elongated neck of the giraffe to the elaborate train of the peacock, extreme traits can result from natural or sexual selection (or both). The extreme chelicerae of the long‐jawed spiders (Tetragnatha) present a puzzle: do these exaggerated chelicerae function as weapons or genitalia? Bristowe first proposed that Tetragnatha chelicerae function as a holdfast because these spiders embrace chelicerae during mating. This hypothesis has remained untested until now. Here, we use functional allometry to examine how extreme chelicerae develop and perform in the long‐jawed spider Tetragnatha elongata. Similar to other Tetragnatha species, chelicerae were longer in adult males than in adult females. Overall, we confirm Bristowe's hypothesis: elongation only occurred in the adult stage. However, we propose that chelicerae function as more than a holdfast in T. elongata. Male chelicerae exhibited positive allometry, which suggests scaling as weapons rather than genitalia. However, fieldwork revealed that the operational sex ratio is female‐biased and both adult male–male competition and sexual cannibalism were rarely observed. Consequently, we propose that the positive allometry of male chelicerae may result from sexual selection to mechanically mesh with larger and more fecund females. Evidence for mechanical mesh includes multiple traits ranging from apophyses and grooves to guide teeth on the basal portion of the chelicerae. In contrast, we propose that chelicerae of females are analogous to the female peacock's tail: shortened by natural selection limiting the exaggeration of sexually selected traits. Indeed, females had increased foraging efficiency compared to males and exhibited negative cheliceral allometry. We discuss the implications for the evolution of elongated chelicerae in Tetragnatha.     

Primate sexual swellings as coevolved signal systems

Many female catarrhine primates possess visually conspicuous organs that apparently function to increase the sexual interest of adult male conspecifics around the time the female is ovulating—i.e. sexual swellings. The hypothesized functional benefits for both sexes of these sexual swellings are reviewed (honest signaling; paternity confusion; paternity confidence and paternal investment; protection; incitement of precopulatory male-male competition; and postcopulatory sexual selection), as well as an additional hypothesis that has not yet been applied to this problem (sensory exploitation). Currently available evidence is presented that supports or fails to support each of these hypotheses. Predictions associated with broad groupings of these hypotheses, which could be tested in noninvasive field studies, are then presented. Ecological circumstances are discussed that could have led to differential mating success among female primates, and hence to sexual selection on females and directional evolution of sexual swellings. It is concluded that the available evidence does not support the paternity confidence-paternal investment hypothesis; that the paternity confusion hypothesis lacks empirical support, but could still be viable; and that insufficient data exists at present to rigorously test the other hypotheses. The ecological factors that may have led to differential reproductive success among females as a function of mating frequency or mate choice likewise require further empirical investigation.     

Do female garter snakes evade males to avoid harassment or to enhance mate quality?

Females of many species behave in ways that make it difficult for males to locate, court, and inseminate them. Two hypotheses have been advanced to explain such behavior: either a female thereby minimizes costs of harassment (sexual conflict model) or by playing "hard to get" she discourages inferior suitors (indirect mate choice model). Our studies of garter snakes (Thamnophis sirtalis parietalis) at a communal den in Manitoba support an interpretation of sexual conflict rather than indirect mate choice. Female snakes dispersed rapidly from the den through areas with relatively few males rather than waiting for additional courtship. Many females dispersed without mating. Experimental (pheromonal) manipulation of the intensity of courtship accelerated rates of female dispersal rather than delaying dispersal, as would be predicted if females wait to obtain matings. The behaviors of females escaping from courting groups were maximally effective in losing their suitors regardless of the number of courting males or whether or not the female was capable of mating (recently mated females cannot mate again because of a mating plug). In total, our data are most consistent with the hypothesis that female garter snakes at communal dens evade males to escape harassment rather than to enhance mate quality.     

Evolution of the structure of tail feathers: implications for the theory of sexual selection

Bird tails are extraordinarily variable in length and functionality. In some species, males have evolved exaggeratedly long tails as a result of sexual selection. Changes in tail length should be associated with changes in feather structure. The study of the evolution of feather structure in bird tails could give insight to understand the causes and means of evolution in relation to processes of sexual selection. In theory, three possible means of tail length evolution in relation to structural components might be expected: (1) a positive relationship between the increase in length and size of structural components maintaining the mechanical properties of the feather; (2) no relationship; that is, enlarging feather length without changes in the structural components; and (3) a negative relationship; that is, enlarging feather length by reducing structural components. These hypotheses were tested using phylogenetic analyses to examine changes in both degree of exaggeration in tail length and structural characteristics of tail feathers (rachis width and density of barbs) in 36 species, including those dimorphic and nondimorphic in tail length. The degree of sexual dimorphism in tail length was negatively correlated with both rachis width and density of barbs in males but not in females. Reinforcing this result, we found that dimorphism in tail length was negatively associated with dimorphism in tail feather structure (rachis width and density of barbs). These results support the third hypothesis, in which the evolution of long feathers occurs at the expense of making them simpler and therefore less costly to produce. However, we do not know the effects of enfeeblement on the costs of bearing. If the total costs increased, the enfeeblement of feathers could be explained as a reinforcement of the honesty of the signal. Alternatively, if total costs were reduced, the strategy could be explained by cheating processes. The study of female preferences for fragile tail feathers is essential to test these two hypotheses. Preferences for fragile tails would support the evolution of reinforcement of honesty, whereas female indifference would indicate the existence of cheating in certain stages of the evolutionary process.     

Sexual swelling in mandrills (Mandrillus sphinx): a test of the reliable indicator hypothesis

Various hypotheses have been proposed to account for the functionof sexual swellings in female primates, but few empirical dataexist to test predictions arising from these hypotheses. Controversyhas recently arisen over a field study that appeared to supportthe predictions of the reliable indicator hypothesis. This hypothesisproposes that females compete for males or matings, that differencesin swelling size between females reliably advertise female quality,and that males use swelling characteristics to differentiallyallocate mating effort to females with certain swelling characteristics,hence to females of higher quality. To provide an independenttest of this hypothesis, we collected data concerning the sizeand coloration of 40 sexual swellings for 29 semi-free-rangingfemale mandrills, varying in age and parity, along with dataconcerning the behavior of males toward the females, and comparedthese with the long-term reproductive history of the females.We examined the following predictions: (1) swelling characteristicsare consistent across subsequent cycles for individual females,(2) swelling characteristics indicate aspects of female reproductivequality, and (3) males prefer to mate with females that showparticular swelling characteristics. Our results support prediction1; we found little change in swelling characteristics acrossswellings for individual females. However, we found no significantrelationships between female reproductive history and swellingcharacteristics and, thus, no support for prediction 2. Finally,we found only limited support for prediction 3; females withlarger (wider) sexual swellings were more likely to have a spermplug when maximally swollen. However, male mate-guarding wasnot significantly related to female swelling characteristics.Furthermore, in situations in which more than one female wasmaximally swollen, the alpha male (who has "free" choice) didnot show the most interest in the female with the largest swelling.We conclude that the reliable indicator hypothesis does notexplain variation in sexual swellings in female mandrills.     

Evolution of female remating behaviour following experimental removal of sexual selection

The relatively small number of ova produced by a female can be fertilized by a single ejaculate in most species. Why females of many species mate with multiple males is therefore enigmatic, especially given that costs associated with remating have been well documented. Recently, it has been argued that females may remate at a maladaptive rate as an outcome of sexually antagonistic coevolution: the evolutionary tug-of-war between manipulation by one sex and resistance to being manipulated by the other sex. We tested this hypothesis experimentally for the evolution of the female remating interval in a naturally promiscuous species, Drosophila melanogaster. In two replicate populations, sexual selection was removed through enforced monogamous mating with random mate assignment, or retained in polyandrous controls. Monogamy constrains the reproductive success of mates to be identical, thereby converting prior conflicts between mates into opportunities for mutualism. Under these experimental conditions, the sexually antagonistic coevolution hypothesis generates explicit predictions regarding the direction of evolutionary change in female remating behaviour. These predictions are contingent upon the mechanism of male manipulation, which may be mediated biochemically by seminal fluids or behaviourally by courtship. Levels of divergence in female remating interval across lines, and in male ejaculatory and courtship effects on female remating, were quantified after 84 generations of selection. Data refute the hypothesis that the evolutionary change in female remating behaviour was due to sexually antagonistic coevolution of courtship signal and receiver traits. The data were, however, consistent with a hypothesis of sexual conflict mediated through ejaculate manipulation. Monogamy-line males evolved ejaculates that were less effective in inducing female non-receptivity and monogamy-line females evolved to remate less frequently, symptomatic of lowered resistance to ejaculate manipulation. The consistency of the results with alternative hypotheses to explain female promiscuity are discussed.