Acute pulmonary embolism: assessment of helical CT for diagnosis

Male pigeons, Columba livia, employ intense mate guarding and frequent copulation apparently as strategies to ensure their paternity. The aim of this study was to investigate the benefits to females of mate guarding by males and frequent copulation. Field observations showed that females initiated the majority of copulations and females that solicited copulations more frequently were guarded more closely by their partner. Experimental removal of guarding male partners showed that: (1) unguarded, fertile females suffered increased harassment from extrapair males which reduced their foraging efficiency; and (2) unguarded, fertile females did not seek copulations with extrapair males. Various explanations for frequent pair copulation initiated by females are discussed and we conclude that female pigeons trade pair copulations for protection (mate guarding) against sexual harassment from other males. Copyright 1998 The Association for the Study of Animal Behaviour.     

Development of approximate formula for LDL-chol, LDL-apo B and LDL-chol/LDL-apo B as indices of hyperapobetalipoproteinemia and small dense LDL

The adaptive significance of repeated withinpair copulations is not well understood. We analysed the copulatory behaviour of 16 pairs of solitary-nesting American kestrels, Falco sparverius, in southern Quebec (Canada), and the achieved reproductive success (paternity) of 21 kestrel families determined by DNA fingerprinting, in terms of four hypotheses. (1) The paternity assurance hypothesis, which suggests that males copulate frequently to avoid being cuckolded, was rejected because there were few extrapair copulation attempts (<1% of all copulations observed), withinpair copulations were not timed during the fertile period and mate attendance did not increase as the fertile period approached. (2) The immediate material benefits hypothesis, which suggests that females trade copulations for food, was refuted because copulations most often occurred without food transfers, especially outside the fertile period. (3) The female mate guarding of males hypothesis, which suggests that females distract their mates from other mating opportunities by copulating frequently, was rejected because extrapair copulation attempts were infrequent, male and female solicitation frequencies were similar and females did not differ in the timing or frequency of solicitations. (4) The mate assessment hypothesis, which suggests that assessment of mate quality is mediated via copulation, most closely predicted the behaviour observed since withinpair copulations were frequent outside the fertile period and at pair formation, males and females solicited similar numbers of copulations and pairs did not differ significantly in solicitation or copulation frequency. In line with this hypothesis we found that only one brood was extrapair, probably the result of mate replacement.Copyright 1998 The Association for the Study of Animal Behaviour     

Certainty of paternity and paternal investment in eastern bluebirds and tree swallows

Extra-pair paternity is common in many socially monogamous passerine birds with biparental care. Thus, males often invest in offspring to which they are not related. Models of optimal parental investment predict that, under certain assumptions, males should lower their investment in response to reduced certainty of paternity. We attempted to reduce certainty of paternity experimentally in two species, the eastern bluebird, Sialia sialis, and the tree swallow, Tachycineta bicolor, by temporarily removing fertile females on two mornings during egg laying. In both species, experimental males usually attempted to copulate with the female immediately after her reappearance, suggesting that they experienced the absence of their mate as a threat to their paternity. Experimental males copulated at a significantly higher rate than control males. However, contrary to the prediction of the model, experimental males did not invest less than control males in their offspring. There was no difference between experimental and control nests in the proportion of male feeds, male and female feeding rates, nestling growth and nestling condition and size at age 14 days. We argue that females might have restored the males' confidence in paternity after the experiment by soliciting or accepting copulations. Alternatively, males may not reduce their effort, because the fitness costs to their own offspring may outweigh the benefits for the males, at least in populations where females cannot fully compensate for reduced male investment. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.     

Female multiple mating behaviour in the common shrew as a strategy to reduce inbreeding

Three hypotheses concerning potential genetic benefits of female multiple mating behaviour are evaluated for the common shrew. In a high-density population, many successful copulations took place between individuals estimated to be close relatives (e.g. full or half siblings). Juveniles resulting from such matings tended to be relatively small at weaning, and were generally less likely to survive to sexual maturity than more outbred individuals. Multiple paternity was discovered in eight of nine litters examined. The incidence of matings between close relatives, the cost of inbreeding, and the high incidence of multiple paternity presented are each consistent with the hypothesis that female multiple mating is a strategy to reduce inbreeding. That is, if females cannot always distinguish close kin, then they may copulate with several different males and so reduce the risk that all their offspring will be sired by a close relative.     

Density-dependent selection on horn phenotype in Soay sheep

In the naturally regulated population of Soay sheep (Ovis aries L.) on Hirta (St Kilda), 12% of males and 24% of females have scurred horns. This trait reduces the competitive ability of males in the mating season but is associated with higher overwinter survival rates in both sexes (Moorcroft et al. 1996). In this paper, we show that scurred females also show higher conception rates and weaning rates than non-scurred ones, and that these differences are associated with heavier maternal body weight as well as higher birth weights of offspring. Selection pressures favouring scurredness in females vary with population density and are generally more pronounced among younger animals than adults. We discuss these results with reference to recent suggestions that temporal fluctuation in selection pressures may help to maintain genetic diversity within populations. We suggest that selection against scurredness operating through male mating success is opposed by selection favouring this trait, operating through the breeding success of females and the survival of both sexes.     

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

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

Sex differences in parasite infections: patterns and processes

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

Size and pairing success in Gammarus duebeni: can females be too big?

The crustacean Gammarus duebeni exhibits precopula mate guarding and size-assortative pairing, in which larger males tend to pair with larger females. Size-assortative pairing may result from sexual selection or natural selection (mechanical or loading constraints limiting the size of female that can be carried by the male). If loading constraints are important, large females should have lower pairing success than females of intermediate size as they will be less likely to encounter sufficiently large males capable of carrying them in precopula. We tested this hypothesis in a laboratory study. Female pairing success was dependent on size; however, the relationship was curvilinear: pairing success increased with size up to a point, but larger females suffered decreased pairing success. This supports the hypothesis that loading constraints play a part in structuring size-assortative pairing in this species. We found no evidence for size-related female resistance in structuring the pattern of pairing. We considered size-related pairing success with regard to environmental sex determination and parasitic sex-ratio distortion in G. duebeni1997 The Association for the Study of Animal BehaviourCopyright 1997 The Association for the Study of Animal Behaviour1997The Association for the Study of Animal Behaviour     

Sexual behavior patterns of male chacma baboons (Papio ursinus) under laboratory conditions with opportunity for repeated ejaculation.

Eight adult male chacma baboons received pair-mating tests with 8 stimulus females that had received a high or low percentage of copulations to ejaculation with several male partners during 15 previous testings. Males showed a higher number of ejaculations during their tests with the high-preference females. However, males did not differentiate between the 2 classes of females in terms of their numbers of contacts, mounts, or intromissions. Latency measures also failed to demonstrate a difference between the 2 classes of partners, and thrust parameters were nearly identical for both. Repeated ejaculation resulted in increases in the postejaculatory interval but no other mating parameter changes. Results are consistent with the view that an arousal mechanism had been affected by the experimental manipulations. Discussion focuses on the appropriate categorization of the chacma as either a single or multiple intromission to ejaculation species. (50 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Multiple sexual partners among U.S. adolescents and young adults

CONTEXT: Because many teenagers and young adults fail to use condoms correctly and consistently, the number of sexual partners they have is an important risk factor for sexually transmitted diseases, including HIV. Identifying factors that are associated with having multiple partners can help in the design of disease interventions. METHODS: Data on 8,450 males and females aged 14-22 who participated in the 1992 Youth Risk Behavior Survey were used to examine the prevalence of and factors associated with young people's having multiple partners. RESULTS: In all, 63% of female respondents and 64% of males were sexually experienced. Among those who had had sex during the three months before the survey, 15% and 35%, respectively, had had two or more partners during that period. At each age, the majority of sexually experienced respondents had had more than one lifetime partner; between ages 14 and 21, the proportion who had had six or more rose from 8% to 31% among females and from 14% to 45% among males. In logistic regression analyses, alcohol use, illicit drug use and young age at first coitus were associated with increased odds that females had had two or more partners in the previous three months, and being married lowered the odds; black or Hispanic race or ethnicity, alcohol use and young age at first coitus increased the odds for males, and being married reduced the odds. As the number of reported alcohol-related behaviors increased, the adjusted proportion of respondents who had recently had multiple partners rose from 8% to 48% among females and from 23% to 61% among men. CONCLUSIONS: The strong association between alcohol use and having multiple sexual partners underscores the need to educate young people about the effects of alcohol on partner choice and the risk of infection with sexually transmitted diseases.     

Sexual selection by male choice in monogamous and polygynous human populations

The theoretical possibility of coevolution of a viability-reducing female physical trait and a male mating preference for that trait by Fisherian sexual selection in monogamous and polygynous populations is demonstrated using two-locus haploid models. It is assumed that there is dichotomous variation in male resources, resource-rich males have a wider choice among females than resource-poor males, and a female has greater reproductive success when mated with a resource-rich male than a resource-poor one. Under these assumptions, we find that sexual selection operates effectively when female reproductive success is strongly dependent on male resource, the proportion of females that mate with resource-rich males is neither small nor large, the degree of polygyny is low, and resources are inherited from father to son. We suggest that some human female physical traits may have evolved by sexual selection through male choice. The evolution of skin color by sexual selection is discussed as an example.     

Sex ratio adjustment in relation to paternal attractiveness in a wild bird population

When the relative fitness of sons and daughters differs, sex-allocation theory predicts that it would be adaptive for individuals to adjust their investment in different sexes of offspring. Sex ratio adjustment by females in response to the sexual attractiveness of their mate would be an example of this. In vertebrates the existence of this form of sex ratio adjustment is controversial and may be confounded with sex-biased mortality, particularly in sexually size-dimorphic species. Here we use PCR amplification of a conserved W-chromosome-linked gene to show that the sex ratio within broods of a natural population of sexually size-monomorphic collared flycatchers Ficedula albicollis is related to the size of their father's forehead patch, a heritable secondary sexual character implicated in female choice. Experimental manipulations of paternal investment, which influence the size of his character in future breeding attempts, result in corresponding changes in the sex ratio of offspring born to males in those breeding attempts. In contrast, manipulations of maternal investment have no effect on future sex ratios, and there is no relationship between variables predicting the reproductive value of the brood and nestling sex ratio. Analysis of recruitment of offspring reveals similar patterns of sex ratio bias. The results suggest that female collared flycatchers be able to adjust the sex ratio of eggs ovulated in response to the phenotype of their mate. This finding is most consistent with "genetic quality" models of sexual selection.     

Parentage and kinship studies in an obligate brood parasitic bird, the brown-headed cowbird (Molothrus ater), using microsatellite DNA markers

Recent studies suggest that single-locus microsatellite DNA markers have the potential to unambiguously resolve parentage among individuals in natural populations where maternity is known. However, their power for determining parentage when neither parent is known is unclear. Here we investigate the usefulness of microsatellite DNA markers to determine parentage in a brood parasitic bird, the brown-headed cowbird (Molothrus ater), where, for a given offspring, no a priori knowledge of either parent is available. Seven polymorphic microsatellite DNA markers isolated from brown-headed cowbirds and yellow warblers (Dendroica petechia) were used to genetically characterize an individually marked breeding population of male and female cowbirds at Delta Marsh, Manitoba. Forty-four males, 21 females, and 61 cowbird chicks were genotyped at seven loci using DNA amplified from blood and tissue samples. The mean exclusion probabilities pooled across all seven loci were 0.9964 for males and 0.9948 for females. Two null (non-amplifying) alleles at one locus were discovered and accounted for by constructing alternate nonoverlapping primer sets. Exclusion analyses performed using all individuals determined both paternity and maternity for 43 chicks and paternity only for 4 chicks. Another microsatellite locus was then used to determine paternity for three additional chicks. Relatedness analyses placed 12 of the 18 remaining chicks not assigned both maternity and paternity into four unique full sibling groups. Overall, 90.16% (55 of 61) of all offspring examined were placed into distinct parent/sibling groups, demonstrating that this marker set is extremely useful for parentage studies in this species.     

Copulatory behavior of voles (Microtus montanus and M. ochrogaster) in multiple-female test situations.

12 male prairie voles and 12 male mountain voles were given test of copulatory behavior with 1, 2, or 4 mating partners. Changes in the number of available partners produced minimal changes in the parameters of copulatory behavior in males of the 2 species. Male montane voles generally copulated with more of the females, showed a lesser tendency to concentrate copulations on a single female, and changed females more often than did prairie voles. These differences are consistent with differences in social structure reported in field studies and may reflect processes underlying species differences in social organization. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dominance and heterosexual attraction.

Four experiments examined the relation between behavioral expressions of dominance and the heterosexual attractiveness of males and females. Predictions concerning the relation between dominance and heterosexual attraction were derived from a consideration of sex role norms and from the comparative biological literature. All four experiments indicated an interaction between dominance and sex of target. Dominance behavior increased the attractiveness of males, but had no effect on the attractiveness of females. The third study indicated that the effect did not depend on the sex of the rater or on the sex of those with whom the dominant target interacted. The fourth study showed that the effect was specific to dominance as an independent variable and did not occur for related constructs (aggressive or domineering). This study also found that manipulated dominance enhanced only a male's sexual attractiveness and not his general likability. The results were discussed in terms of potential biological and cultural causal mechanisms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sexual behavior in young adulthood: A population-based twin study.

Objective: With behavior genetic analyses of data from young adult twins, we evaluated theoretical perspectives that differentially emphasize biological dispositions, social/cultural factors, or universal pathways to explain individual differences in sexual behaviors. Design: We fit biometric sex limitation models to three aspects of sexual behavior reported by 4,925 Finnish twins ages 23-27. Main Outcome Measure: From a postal questionnaire, we obtained self-report information on initiation/abstinence of sexual intercourse, onset age, and number of sexual partners. Results: Genetic and non-shared environmental influences were significant for all three measures. There were trends for common environmental influences on initiation and, in females, age at first intercourse. Some differential effects in males and females were found. Results comparing onset age and number of partners among experienced twins from pairs concordant and discordant for initiation found genetic and environmental influences on initiation/abstinence overlapped those found for the other aspects of sexual behavior. Conclusions: These results document genetic variation in individual differences in sexual behavior of young adults. Incorporating genetic dispositions into integrated models of sexual behavior will facilitate more effective health promotion and risk taking intervention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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

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

Endogenous formaldehyde as a potential factor of vulnerability of atherosclerosis: involvement of semicarbazide-sensitive amine oxidase-mediated methylamine turnover

Several adaptive explanations regarding the function of lengthy copulations in insects have been proposed. They may represent a form of mate guarding, where the male physically prevents the female from copulating with rival males. Alternatively, they may function to ensure full insemination of the male's sperm when copulation duration covaries with the amount of sperm transferred and male fertilization success. Finally, lengthy copulations may serve to allow males to assess female quality in terms of mating status and body weight. In this study I examine these hypotheses for the function of lengthy copulations in the Australian bushcricket Coptaspis sp. 2 (Orthoptera: Tettigoniidae). Unlike most other bushcrickets, males of this species do not produce a large spermatophylax that the female feeds on during insemination, but remain attached to the female's genitals up to 6 h after spermatophore attachment. Experimental manipulation of the duration of spermatophore attachment showed it to be related to the amount of sperm transferred. This suggests that the main function of copulation duration is to ensure complete transfer of the male's ejaculate. Males also discriminated between females, and provided mated females with more sperm which resulted in longer copulations than with virgin females. It is possible that possession of a large spermatophylax has been lost evolutionarily in this species, with males themselves acting as a sperm protection device during insemination.Copyright 1998 The Association for the Study of Animal Behaviour     

Sexual conflict and speciation

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

Sexual selection as a side-effect of sexual conflict in the seaweed fly, Coelopa ursina (Diptera: Coelopidae)

The mating system of the seaweed fly involves a premating struggle. When mounted, females violently try to remove the male. In this study 48% of premating struggles resulted in successful rejection of the male, 46% in copulation and 6% were terminated by the male. Large males had a mating advantage. However, contrary to what would be predicted if this sexual selection occurred as a result of active female mate choice, we found a positive association between the duration of premating struggles and male size. A positive association was also found between the duration of premating struggles and male mating success, suggesting that large males may benefit through their superior ability to withstand female rejection. Large females rejected males more easily than small females, suggesting that the premating struggle has not evolved to allow mate assessment by females. We conclude that sexual selection is occurring as a side-effect of the female rejection response, which has probably evolved in order to avoid costs associated with copulation. Nevertheless, a sexual size dimorphism has evolved with males being larger and much more variable in size than females. (c) 1998 The Association for the Study of Animal Behaviour.