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PubMed1992

The external genitalia of female gibbons, Hylobates (H.) lar.

The external genitalia of one perimenarcheal and five adult female white handed-gibbons (Hylobates (H.) lar) were examined to clarify their gross anatomy. It was found that the vulval structures were complex and exhibited inter-individual variation in arrangement. This complexity appears to result from an ontogenetic process by which the tissues of the vaginal rim (the labia minora) bud-off and extrude extensions toward the vagina immediately prior and subsequent to menarche. Two of these lobular structures surround the urethral meatus and constitute a urethral eminence. The tissues of the vulva, excluding the clitoris with associated prepuce and frenulum and vestigial labia majora, undergo cycles of tumescence and detumescence during intermenstrual intervals. The complex form of the external genitalia and the presence of a swelling cycle are unusual for a monogamous species, are contrary to current applications of sexual selection theory, and raise questions about the significance of mate choice in hominoid evolution.

Animals↗

PubMed1992

Call patterns and basilar papilla tuning in cricket frogs. II. Intrapopulation variation and allometry.

We determined the influence of body size on the male advertisement call's dominant frequency and basilar papilla's (BP) tuning in male and female cricket frogs (Acris crepitans) in two Texas populations (Wimberley and Stengel Ranch). In both populations, call and tuning characters correlated negatively with body size; females were larger than males and their BPs were tuned to a lower frequency. Analysis of covariance showed that neither the sex difference in tuning nor the population differences in calls or tuning were due to the difference in body size alone, but instead represented differences in the allometric relationships of each character with body size. The analysis implied that differences between sexes or populations were due more to shifts in the Y-intercept rather than the slope of the relationship with body size. This suggests a developmental model in which sexes or populations possess resonant structures in the ear or larynx with similar growth rates but different starting points or initial growth phases, resulting in different frequency characteristics as adults. The examination of the relationship between female BP tuning and male call dominant frequency predicts potentially different patterns of sexual selection in the two populations, with the Wimberley population males subject to much greater directional selection for low frequency calls.

Animals↗

PubMed2006

Highly variable sperm precedence in the stalk-eyed fly, Teleopsis dalmanni.

BACKGROUND: When females mate with different males, competition for fertilizations occurs after insemination. Such sperm competition is usually summarized at the level of the population or species by the parameter, P2, defined as the proportion of offspring sired by the second male in double mating trials. However, considerable variation in P2 may occur within populations, and such variation limits the utility of population-wide or species P2 estimates as descriptors of sperm usage. To fully understand the causes and consequences of sperm competition requires estimates of not only mean P2, but also intra-specific variation in P2. Here we investigate within-population quantitative variation in P2 using a controlled mating experiment and microsatellite profiling of progeny in the multiply mating stalk-eyed fly, Teleopsis dalmanni. RESULTS: We genotyped 381 offspring from 22 dam-sire pair families at four microsatellite loci. The mean population-wide P2 value of 0.40 was not significantly different from that expected under random sperm mixing (i.e. P2 = 0.5). However, patterns of paternity were highly variable between individual families; almost half of families displayed extreme second male biases resulting in zero or complete paternity, whereas only about one third of families had P2 values of 0.5, the remainder had significant, but moderate, paternity skew. CONCLUSION: Our data suggest that all modes of ejaculate competition, from extreme sperm precedence to complete sperm mixing, occur in T. dalmanni. Thus the population mean P2 value does not reflect the high underlying variance in familial P2. We discuss some of the potential causes and consequences of post-copulatory sexual selection in this important model species.

Animals↗

PubMed1998

Ethical and cultural concerns in sexual function assessment.

The ethical and cultural issues accompanying sex research methods are rarely discussed. The present remarks briefly examine three previously described ethical principles--respect for people, beneficence and justice--as they might relate to sexual dysfunction assessment in clinical trials. Given the fact that sexuality is a social behavior and the outcome measures are reliant on some form of self report, there are specific pressures on investigators to conduct research assessment that respects ethical principles and cultural values. Examples with respect to screening criteria and participant selection are discussed. Recommendations include: (a) excluding participants with selected sexual and non-sexual diagnoses, psychosocial behaviors and habits; (b) including proportional ethnic groups as well as non-heterosexual participants; and (c) considering the couple, rather than just an individual, as study subjects who each require medical and psychosocial screening, assessment, and informed consent.

Culture↗

PubMed2004

Chicken W: a genetically uniform chromosome in a highly variable genome.

The Y chromosome of organisms with male heterogamety is expected to show reduced levels of genetic diversity, because the effective population size is one-fourth that of autosomes. However, studies in mammals, flies, and plants show that Y chromosome diversity is lower than expected even when differences in effective population size are taken into account. This may be explained by skewed reproductive success among males, leading to low male effective population size, or by a strong role of selection in shaping levels of nucleotide diversity in nonrecombining chromosomes. We tested these hypotheses in a system with female heterogamety by estimating nucleotide diversity in the female-specific W chromosome of the domestic chicken by resequencing of 7,643 base pairs in 47 birds from 10 highly divergent breeds. The screening revealed only one single segregating site, which is in sharp contrast to our previous observation, using a similar panel of birds of, on average, one segregating site every 39 base pairs in autosomal sequence. When taking sex-specific mutation rates and differences in effective population size into account, the observed degree of W chromosome polymorphism is 28-fold lower than expected for the frequency of segregating sites and 13-fold lower than expected for estimates of nucleotide diversity (autosomes, 6.5 x 10(-3); W, 7.0 x 10(-5)). We note that selection is the only factor that can explain the reduced diversity in the sex-limited chromosome irrespective of mode of reproduction or whether there is male or female heterogamety. Reduced variability in female-specific W chromosomes is not easily explained by sexual selection.

Animals↗

PubMed2002

Mate choice and imprinting in birds studied by cross-fostering in the wild.

Sexual-selection theories generally assume that mating preferences are heritable traits. However, there is substantial evidence that the rearing environment may be important for the development of mating preferences, indicating that they may be learnt, or modified by experience. The relative importance of such sexual imprinting across species remains largely unexplored. Here, we report results of a large-scale cross-fostering experiment in the wild in which nestling birds were raised by parents of a different species. We show that resulting sexual imprinting may have a negative effect on pairing success in one species (the great tit, Parus major), but not in two other species (the blue tit, P. caeruleus and the pied flycatcher, Ficedula hypoleuca). A remarkable variation thus seems to exist, even between species that are congeneric and have similar breeding ecologies. The cross-fostering resulted in heterospecific pairings between the two tit species (female blue tit breeding with male great tit), which has never, to our knowledge, been previously documented. However, the chicks fledging from these nests were all blue tit.

Animals↗

PubMed1995

A Darwinian approach to the origins of psychosis.

BACKGROUND: The onset of psychotic illness in the reproductive phase of life with a decrease in fecundity (and approximately constant incidence across populations) requires an evolutionary explanation. What is the survival value of the predisposing gene or genes? METHOD: Evolutionary theories, including the author's, are reviewed and critically compared. RESULTS: Some theories (e.g. Huxley et al, 1964) postulate an advantage outside the nervous system: such theories fail to explain either the characteristic age distribution or constant incidence. More plausible are theories that relate the advantage to diversity of personality structure or social ability, or even to general intelligence, i.e. to the areas of function in which the phenomena of psychosis arise. CONCLUSIONS: It is argued that psychosis arises as the boundary of a distribution of variation in cerebral structure generated in the course of hominid evolution. Language played a central role, with the critical changes taking place on the basis of a mutation that allowed the two cerebral hemispheres to develop with a degree of independence. Sexual selection (differing criteria in females and males in choosing a mate) acting on this genetic innovation has generated a dimension of competence in social interaction in relation to which there has been a progressive increase in cerebral size by delayed maturation (neoteny). A sexual dimorphism in cerebral asymmetry and the sex difference in age of onset of psychosis can be parsimoniously explained if a gene regulating the relative growth of the two hemispheres is X-Y homologous.

Biological Evolution↗

PubMed2005

Patterns of male sterility in a grasshopper hybrid zone imply accumulation of hybrid incompatibilities without selection.

It is now widely accepted that post-zygotic reproductive isolation is the result of negative epistatic interactions between derived alleles fixed independently at different loci in diverging populations (the Dobzhansky-Muller model). What is less clear is the nature of the loci involved and whether the derived alleles increase in frequency through genetic drift, or as a result of natural or sexual selection. If incompatible alleles are fixed by selection, transient polymorphisms will be rare and clines for these alleles will be steep where divergent populations meet. If they evolve by drift, populations are expected to harbour substantial genetic variation in compatibility and alleles will introgress across hybrid zones once they recombine onto a genetic background with which they are compatible. Here we show that variation in male sterility in a naturally occurring Chorthippus parallelus grasshopper hybrid zone conforms to the neutral expectations. Asymmetrical clines for male sterility have long tails of introgression and populations distant from the zone centre show significant genetic variation for compatibility. Our data contrast with recent observations on 'speciation genes' that have diverged as a result of strong natural selection.

Animals↗

PubMedDate not supplied

Reproductive health/family planning and the health of infants, girls and women.

The 1994 International Conference on Population and Development developed international consensus amongst health providers, policy makers, and group representing the whole of civil society regarding the concept of reproductive health and its definition. In line with this definition, reproductive health care is defined as the constellation of methods, techniques and services that contribute to reproductive health and well-being by preventing and solving reproductive health problems. Reproductive health care saves lives and prevents significant levels of morbidity through family planning programmes, antenatal, delivery and post-natal services, prevention and management programmes for reproductive tract infections (including sexually transmitted diseases and HIV/AIDS), prevention of abortion and management of its complications, cancers of the reproductive system, and harmful practices that impact on reproductive function. Reproductive health care needs are evident at all stages of the life cycle and account for a greater proportion of disability adjusted life years (DALYS) in girls and women than in boys and men. Reproductive health protects infant health by enabling birth spacing and birth limitation to be practiced through family planning. The prevention and early detection of reproductive tract infections, including sexually transmitted diseases and HIV, through the integration of preventive measures in family planning service delivery not only improves the quality of care provided but is also directly responsible for improvement in survival and health of infants. Addressing harmful practices such as son preference, sex selection, sexual violence and female genital mutilation complements the positive impact of planned and spaced children through family planning services on infant mortality and the reproductive health of young girls and women. They are also in addition to prenatal, delivery and postnatal services, positive determinants of low maternal mortality and morbidity and are integral to the promotion of reproductive health in women of child bearing age. Reproductive tract infections, including sexually transmitted diseases and HIV contribute to significant level of ill-health in women of reproductive age and continue to pose a threat through the menopause which in turn brings with it increasing risk of cancers of the reproductive system.

Adolescent↗

PubMed1998

The major histocompatibility complex and mate choice: inbreeding avoidance and selection of good genes.

It has been known for decades that MHC genes play a critical role in the cellular immune response, but only recent research has provided a better understanding of how these molecules might affect mate choice. Original studies in inbred mouse strains revealed that mate choice was influenced by MHC dissimilarity. Detection of MHC differences between individuals in these experiments was related to olfactory cues, primarily in urine. Recent studies in humans have shown an analogous picture of MHC-based mating. Taken together, these findings could support either the hypothesis of MHC-based inbreeding avoidance or the hypothesis of MHC-related avoidance of reproductive failure, since studies in mice, humans and pigtailed macaques have shown that parental sharing of certain MHC alleles correlates with frequent spontaneous abortion or prolonged intergestational intervals. Data from many mammalian species clearly demonstrate that reproductive failure occurs as a result of inbreeding. Therefore, MHC similarity might serve as an indicator of genome-wide relatedness. In contrast, increased fitness due to the presence of individual MHC alleles in a pathogenic environment could explain MHC-based selection of currently good genes. Specifically, the physical condition of long-living animals depends on the ability to respond to immunological challenge and an individual's MHC alleles determine the response, since, unlike the T cell receptors, MHC alleles are not somatically recombined. Therefore, sexual selection of condition-dependent traits during mate choice could be used to select successful MHC alleles, thereby providing offspring with a higher relative immunity in their pathogenic environment.

Animals↗

PubMed1979

The adaptive role of maladaptive neurosis.

A hypothesis is proposed which postulates that repeated failure in social competition may lead to a "neurotic" maladaptive vicious cycle. It is proposed that by magnifying genetically transmitted differences in fitness, this mechanism emphasizes the superiority of the better endowed, both in mate choice and in fitness of offspring. Species displaying high plasticity and flexibility, the concomitants of high intellectual ability, may be more susceptible to neurosis, hence may be more likely to be influenced by the vicious cycle mechanism operating at the ontogenetic level. Such species would display an accelerated rate of adaptation and intelligence. Some of the implications of the hypothesis for sexual selection, change in status, and preventive mental health are discussed.

Adaptation, Psychological↗

PubMed2002

Behavioural determinants of gene flow in malaria vector populations: Anopheles gambiae males select large females as mates.

BACKGROUND: Plasmodium-refractory mosquitoes are being rapidly developed for malaria control but will only succeed if they can successfully compete for mates when released into the wild. Pre-copulatory behavioural traits maintain genetic population structure in wild mosquito populations and mating barriers have foiled previous attempts to control malaria vectors through sterile male release. METHODS: Varying numbers of virgin male and female Anopheles gambiae Giles, from two strains of different innate sizes, were allowed to mate under standardized conditions in laboratory cages, following which, the insemination status, oviposition success and egg batch size of each female was assessed. The influence of male and female numbers, strain combination and female size were determined using logistic regression, correlation analysis and a simple mechanistic model of male competition for females. RESULTS: Male An. gambiae select females on the basis of size because of much greater fecundity among large females. Even under conditions where large numbers of males must compete for a smaller number of females, the largest females are more likely to become inseminated, to successfully oviposit and to produce large egg batches. CONCLUSIONS: Sexual selection, on the basis of size, could either promote or limit the spread of malaria-refractory genes into wild populations and needs to be considered in the continued development and eventual release of transgenic vectors. Fundamental studies of behavioural ecology in malaria vectors such as An. gambiae can have important implications for malaria control and should be prioritised for more extensive investigation in the future.

Animals↗

PubMed1999

Mating system of Microcebus murinus.

Microcebus murinus, a small nocturnal lemur from Madagascar, has retained features of ancient primates. Based on these ancestral traits, its social organization has often been used as a model for early primate social systems. In captivity it breeds polygynously, i.e., one male mates with several females, while females usually copulate only with the dominant male. The present project tested whether or not sexual size dimorphism, spatial distribution, and relative testis size of M. murinus correspond with predictions of the sexual selection theory concerning polygynous mating systems. The study was combined with a mark-recapture study and radio tracking of 12 animals in 1993 in a dry deciduous forest of western Madagascar at the end of the dry season. Large overlapping home ranges in males, lack of sexual size dimorphism, and relatively large testes suggest a multi-male mating system, i.e., one that is promiscuous rather than polygynous.

Adaptation, Biological↗

PubMed2000

Muscles or testes? Comparative evidence for sexual competition among dioecious blood parasites (Schistosomatidae) of vertebrates.

Schistosomes, which live as parasitic adults in the blood vessels of mammals, birds and crocodiles, are unique among trematodes because they have separate sexes. Several studies have shown that the sex ratio is often biased towards males. Sexual dimorphism can be very important in several genera (Schistosoma, Heterobilharzia, Schistosomatium), as larger males grip smaller females in a gynecophoric canal. But not all schistomatid species have developed a gynecophoric canal. It is also striking that the number of testes varies widely, from a small number of testes reported (2-7) to a very high number (> 500). We tested the hypothesis of trade-off investment by males: muscle (as estimated by the length of the gynecophoric canal) in order to sequester one or a few females, or testes in order to inseminate numerous females. We used recent comparative methods, which need phylogenetic information of the analysed species. We employed a morphological cladistic analysis of the Schistosomatidae and a construction of a phylogenetic supertree of Schistosoma based on available molecular information. Our phylogenetic analysis supports previous hypotheses on the origin and diversification of the schistosomes. The family seems to have originated as parasites of crocodiles (or possibly other related poikilotherms) and to have secondarily evolved within the Aves and then mammals. Our phylogenetic analyses show that (1) the possession of a gynecophoric canal is a plesiomorphic character, and several reductions of this character have occurred during the diversification of the Schistosomatidae; (2) a small number of testes is a plesiomorphic stage, and an increase of testes number has occurred several times. Finally, our comparative analysis suggests that there is a trade-off between investment in muscle or in number of testes (other variables being controlled for). Male competition for access to females seems to follow two ways: investment in testes in order to fertilize a high number of females or investment in muscle in order to hold and sequester one (Schistosoma) or a few females (Heterobilharzia). We show the existence of the trade-off between muscles and testes in connection with a male biased sex ratio. The development of dioecy cannot explain the trade-off between muscles and testes, which instead appears to be a result of sexual selection possibly driven by the male biased sex ratio.

Alligators and Crocodiles↗

PubMed2005

Dual functions of a melanin-based ornament in the common yellowthroat.

Melanin-based ornaments often function as signals in male-male competition, whereas carotenoid-based ornaments appear to be important in female mate choice. This difference in function is thought to occur because carotenoid pigments are more costly to produce than melanins and are thus more reliable indicators of male quality. We examined the role of melanin- and carotenoid-based ornaments in male-male competition and female choice in the common yellowthroat Geothlypis trichas, a sexually dichromatic passerine. Males display a black facial mask produced by melanin pigmentation and a bright yellow bib (throat, breast and belly) produced by carotenoid pigmentation. In controlled aviary experiments, mask size was the best predictor of both male-male competition and female mate choice, and, therefore, mask size may be regarded as an ornament of dual function. These dual functions may help to maintain the reliability of mask size as an indicator of male quality, despite the potentially low cost of production. The size of the bib was unrelated to male-male competition or female choice, but there was a tendency for females to prefer males with more colourful bibs. We propose that the black mask is important in competition for territories with other males and for attracting females. Our results highlight the need for more studies of the mechanisms of sexual selection in species with ornaments composed of different pigment types.

Animal Communication↗

PubMed2007

Biology of the bed bugs (Cimicidae).

The cimicids, or bed bugs, belong to a highly specialized hematophagous taxon that parasitizes primarily humans, birds, and bats. Their best-known member is the bed bug, Cimex lectularius. This group demonstrates some bizarre but evolutionarily important biology. All members of the family Cimicidae show traumatic insemination and a suite of female adaptations to this male trait. Cimicids therefore constitute an ideal model system for examining the extreme causes and consequences of sexual selection. Our dual goal in re-examining the extensive literature on this group is to identify issues relevant to pest control, such as dispersal ecology and the recent global spread, and to understand the selective forces that have shaped the unique aspects of this insect's biology.

Animals↗

PubMed2000

Developments of the Price equation and natural selection under uncertainty.

Many approaches to the study of adaptation, following Darwin, centre on the number of offspring of individuals. Population genetics theory makes clear that predicting gene frequency changes requires more detailed knowledge, for example of linkage and linkage disequilibrium and mating systems. Because gene frequency changes underlie adaptation, this can lead to a suspicion that approaches ignoring these sophistications are approximate or tentative or wrong. Stochastic environments and sexual selection are two topics in which there are widespread views that focusing on number of offspring of individuals is not enough, and that proper treatments require the introduction of further details, namely variability in offspring number and linkage disequilibrium, respectively. However, the bulk of empirical research on adaptation and a great deal of theoretical work continue to employ these approaches. Here, a new theoretical development arising from the Price equation provides a formal justification in very general circumstances for focusing on the arithmetic average of the relative number of offspring of individuals.

Adaptation, Biological↗

PubMed2004

Plant-like mating in an animal: sexual compatibility and allocation trade-offs in a simultaneous hermaphrodite with remote transfer of sperm.

The importance of sexual compatibility between mates has only recently been realized in zoological research into sexual selection, yet its study has been central to botanical research for many decades. The reproductive characteristics of remote mating, an absence of precopulatory mate screening, internal fertilization and embryonic brooding are shared between passively pollinated plants and a phylogenetically diverse group of sessile aquatic invertebrates. Here, we further characterize the sexual compatibility system of one such invertebrate, the colonial ascidian Diplosoma listerianum. All 66 reciprocal pairings of 12 genetic individuals were carried out. Fecundities of crosses varied widely and suggested a continuous scale of sexual compatibility. Of the 11 animals from the same population c. 40% of crosses were completely incompatible with a further c. 20% having obvious partial compatibility (reduced fecundity). We are unaware of other studies documenting such high levels of sexual incompatibility in unrelated individuals. RAPD fingerprinting was used to estimate relatedness among the 12 individuals after a known pedigree was successfully reconstructed to validate the technique. In contrast to previous results, no correlation between genetic similarity and sexual compatibility was detected. The blocking of many genotypes of sperm is expected to severely modify realized paternity away from 'fair raffle' expectations and probably reduce levels of intra-brood genetic diversity in this obligatorily promiscuous mating system. One adaptive benefit may be to reduce the bombardment of the female reproductive system by outcrossed sperm with conflicting evolutionary interests, so as to maintain female control of somatic : gametic investment.

Animals↗