Nongonococcal urethritis and other selected sexually transmitted diseases of public health importance. Report of a WHO Scientific Group.
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Chancroid↗
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Results for “Sexual selection”
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[Properties of the receptive structure controlling sex hormone activity and sexual selectivity of biologically active substances].
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4-Aminobenzoic Acid↗
Treatment guidelines for selected sexually transmitted diseases.
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Anti-Bacterial Agents↗
Gonorrhea among men who have sex with men--selected sexually transmitted diseases clinics, 1993-1996.
Among men who have sex with men (MSM), gonorrhea trends may reflect changes in sexual behaviors that also influence risk for human immunodeficiency virus (HIV) infection. Data from the Gonococcal Isolate Surveillance Project (GISP) were used to assess trends in gonococcal infection (GC) among MSM. For the subset of GISP sites where a substantial proportion of GC cases were in MSM, a special survey of the local areas was conducted to describe factors associated with GC in MSM. This report summarizes the results of that survey, which indicate that the number and proportion of MSM diagnosed with GC has increased in the sexually transmitted diseases (STD) clinics of several large cities in the United States.
Gonorrhea↗
From the Centers for Disease Control and Prevention. Gonorrhea among men who have sex with men--selected sexually transmitted diseases clinics, 1993-1996.
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Gonorrhea↗
Evolutionary innovation in behavior and speciation: opportunities for behavioral neuroethology.
Populations of animals differentiate by speciation. How speciation takes place, for long a puzzle for evolutionary biologists, should be regarded as a research opportunity for neuroethologists and comparative behaviorists. It is now clear that behavior may play an important part in the process of speciation. The existence of sexually dimorphic anatomy and behavior in many animals has provided a rich subject for investigation by comparative neurobiologists and behaviorists, who emphasize analysis of proximate mechanisms that generate dimorphism in phenotype. However, sexual dimorphisms also figure prominently in the theory of sexual selection. Sexual selection is viewed as a primary behavioral mechanism in the process of speciation. Some examples of 'explosive' speciation are presented, and the putative role that sexual selection plays in these cases is reviewed. A consideration of any evolutionary selective process must include genetics, and I will briefly summarize studies that indicate that even complex behavioral systems such as sexual selection, which sociobiologists refer to as a 'strategy', can have a relatively simple genetic basis.
Animals↗
Symmetry breaking and coarsening in spatially distributed evolutionary processes including sexual reproduction and disruptive selection.
Sexual reproduction presents significant challenges to formal treatment of evolutionary processes. A starting point for systematic treatments of ecological and evolutionary phenomena has been provided by the gene-centered view of evolution which assigns effective fitness to each allele instead of each organism. The gene-centered view can be formalized as a dynamic mean-field approximation applied to genes in reproduction and selection dynamics. We show that the gene-centered view breaks down for symmetry breaking and pattern formation within a population and show that spatial distributions of organisms with local mating neighborhoods in the presence of disruptive selection give rise to such symmetry breaking and pattern formation in the genetic composition of local populations. Global dynamics follows conventional coarsening of systems with nonconserved order parameters. The results have significant implications for the ecology of genetic diversity and species formation.
Alleles↗
Center of body mass and the evolution of female body shape.
Among primates, the genus Homo has a unique sexual dimorphism in general body shape. The stenotypic female "hourglass figure" has often been attributed to sexual selection. Sexual dimorphism both in shape and in position of the center of body mass (CoM) emerges during puberty and is related to hormonal influences. These are only the proximal and not the ultimate causes of this feature. This article explores the hypothesis that the evolutionary (i.e., ultimate) reason for female body shape and male preference for a lower waist-to-hip ratio (WHR) is due to the acquisition of bipedal locomotion and different biomechanical constraints on each sex. The demands of pregnancy and subsequently carrying infants may have more tightly constrained CoM in females than in males. A lower-position of CoM relative to height (RCoM=(CoM/height)*100%) would contribute to better stability during pregnancy and infant carrying. Using body measurements from 119 female students, we show that RCoM correlates negatively with only maximal thigh circumference and positively with only WHR and shoulder width. The relationship between RCoM and traits that best characterize female body shape seems to confirm a hypothesis of biomechanical selection pressure that may have acted on Homo female morphology, thus contributing to sexual dimorphism.
Adult↗
Parallel evolution of sexual isolation in sticklebacks.
Mechanisms of speciation are not well understood, despite decades of study. Recent work has focused on how natural and sexual selection cause sexual isolation. Here, we investigate the roles of divergent natural and sexual selection in the evolution of sexual isolation between sympatric species of threespine sticklebacks. We test the importance of morphological and behavioral traits in conferring sexual isolation and examine to what extent these traits have diverged in parallel between multiple, independently evolved species pairs. We use the patterns of evolution in ecological and mating traits to infer the likely nature of selection on sexual isolation. Strong parallel evolution implicates ecologically based divergent natural and/or sexual selection, whereas arbitrary directionality implicates nonecological sexual selection or drift. In multiple pairs we find that sexual isolation arises in the same way: assortative mating on body size and asymmetric isolation due to male nuptial color. Body size and color have diverged in a strongly parallel manner, similar to ecological traits. The data implicate ecologically based divergent natural and sexual selection as engines of speciation in this group.
Analysis of Variance↗
Social organization and mating success in local song populations of village indigobirds, Vidua chalybeata.
Behavioral interactions among color-marked individual Vidua chalybeata that shared common song dialects were observed for 5 years in two populations at Lochinvar National Park, Zambia. Social interactions involved males visiting and competing for mating sites and female visiting male in an apparent sampling of potential copulating partners. Differences in mating success among the polygynous males were compared with male behavior and territory resources, and criteria were developed to test the importance of intrasexual male competition and female mate choice in explaining the mating system of the populations. Song behavior best explained differences in mating success of males, with lesser effects of neighboring males and the defensible resources around the call-sites. The social organization of song populations resembles that of a dispersed lek with females visiting many males but mating with few males. We discuss the observations on indigobirds in relation to behavioral selection, sexual selection, and mating systems. Mating systems of certain populations and species are compared using statistics of individual mating success.
Aggression↗
Spatial memory and adaptive specialization of the hippocampus.
The hippocampus plays an important role in spatial memory and spatial cognition in birds and mammals. Natural selection, sexual selection and artificial selection have resulted in an increase in the size of the hippocampus in a remarkably diverse group of animals that rely on spatial abilities to solve ecologically important problems. Food-storing birds remember the locations of large numbers of scattered caches. Polygynous male voles traverse large home ranges in search of mates. Kangaroo rats both cache food and exhibit a sex difference in home range size. In all of these species, an increase in the size of the hippocampus is associated with superior spatial ability. Artificial selection for homing ability has produced a comparable increase in the size of the hippocampus in homing pigeons, compared with other strains of domestic pigeon. Despite differences among these animals in their histories of selection and the genetic backgrounds on which selection has acted, there is a common relationship between relative hippocampal size and spatial ability.
Adaptation, Physiological↗
Genetic differentiation and reproductive isolation in a Cyprinodon fish species flock from Laguna Chichancanab, Mexico.
The Cyprinodon species flock from Laguna Chichancanab, aged 8000 years, provides another potential case of sympatric speciation. The flock consists of seven morphologically distinct species, each within partially different trophic niches, and a group of specimens which cannot unequivocally be assigned to one of these species. Genetic analyses, based on mtDNA and five microsatellite loci, revealed significant genetic differentiation of one species, C. maya, from other members of the species flock, providing strong evidence for reproductive isolation. For the remaining members of the flock significant genetic structuring was detected, with some evidence of gene flow with the most abundant species C. beltrani. These analyses suggest that speciation proceeds with ongoing hybridisation, and further suggest that the morphologically unidentifiable specimens found in the lake are probably hybrids. I propose that in the Cyprinodon species flock besides disruptive selection sexual selection plays an important part in achieving and maintaining reproductive isolation.
Animals↗
General models of multilocus evolution.
In 1991, Barton and Turelli developed recursions to describe the evolution of multilocus systems under arbitrary forms of selection. This article generalizes their approach to allow for arbitrary modes of inheritance, including diploidy, polyploidy, sex linkage, cytoplasmic inheritance, and genomic imprinting. The framework is also extended to allow for other deterministic evolutionary forces, including migration and mutation. Exact recursions that fully describe the state of the population are presented; these are implemented in a computer algebra package (available on the Web at http://helios.bto.ed.ac.uk/evolgen). Despite the generality of our framework, it can describe evolutionary dynamics exactly by just two equations. These recursions can be further simplified using a "quasi-linkage equilibrium" (QLE) approximation. We illustrate the methods by finding the effect of natural selection, sexual selection, mutation, and migration on the genetic composition of a population.
Emigration and Immigration↗
(Evolutionary) Theories of warfare in preindustrial (foraging) societies.
I present an inventory of theories of war causation (and on the origin of war) in preindustrial (traditional, foraging, 'primitive', hunter-gatherer, band- and tribe-level) societies, with emphasis on the roles of natural selection, sexual selection and kin selection. Also the school of sociocultural evolution is briefly discussed.
Biological Evolution↗
Genetic constraints on floral evolution in a sexually dimorphic plant revealed by artificial selection.
Sexual dimorphism is one of the most widespread and recognizable patterns of phenotypic variation in the biotic world. Sexual dimorphism in floral display is striking in the dioecious plant Silene latifolia, with males making many, small flowers compared to females. We investigated this dimorphism via artificial selection on two populations to determine whether genetic variation exists within populations for flower size and the extent of the between-sex correlation, whether a flower size and number trade-off exists within each sex, and whether pollen and ovule production vary with flower size. We selected for decreased flower size (calyx width) in females and increased flower size in males and measured the response to selection in size and correlated responses in flower dry mass, flower number, and pollen or ovule number per flower. Four bouts of selection in each of two selection programs were performed, for a total of three selection lines to decrease size, three to increase it, and two control lines. Flower size always significantly responded to selection and we always found a significant correlated response in the sex not under selection. Selection decreased but did not eliminate the sexual dimorphism in flower dry mass and number. A negative relationship between flower size and number within each sex was revealed. Whereas ovule number showed a significant correlated response to selection on flower size, pollen number did not. Our results indicate that although substantial additive genetic variation for flower size exists, the high between-sex genetic correlation would likely constrain flower size from becoming more sexually dimorphic. Furthermore, floral display within each sex is constrained by a flower size and number trade-off. Given this trade-off and lack of variation in pollen production with flower size, we suggest that sexual dimorphism evolved via sexual selection to increase flower number in males but not females.
Biological Evolution↗
Long-term paternity skew and the opportunity for selection in a mammal with reversed sexual size dimorphism.
Most mammalian groups are characterized by male-biased sexual size dimorphism, in which size-dependent male-male competition and reproductive skew are tightly linked. By comparison, little is known about the opportunity for sexual selection in mammalian systems without male-biased dimorphism, where the traits under sexual selection might be less obvious. We examined 10 years of parentage data in a colony of greater horseshoe bats (Rhinolophus ferrumequinum) to determine the magnitude of male reproductive skew and the opportunity for sexual selection in a mammal in which females are the larger sex. Annual paternity success was weakly skewed but consistent patterns led to strong longitudinal paternity skew among breeders. Just three males accounted for a third of all paternity assignments, representing at least a fifth of all colony offspring born in a decade. Paternity success was in part determined by age but was not influenced by dispersal status. Our results show that paternity skew and the opportunity for sexual selection in a species with reversed sexual size dimorphism can approach levels reported for classical examples of species with polygyny and male-biased dimorphism, even where the traits under sexual selection are not known.
Animals↗
Sexual conflict and indirect benefits.
Recent work on sexual selection and sexual conflict has explored the influence of indirect effects on the evolution of female mating behaviour. It has been suggested that the importance of these effects has been underestimated and that the influence of indirect effects may actually be of relatively greater significance than direct effects. Additionally, it has also been suggested that all indirect effects, both good genes and sexy son, are qualitatively equivalent. Here a counterpoint to these suggestions is offered. We argue two main points: (1) it is unlikely that indirect effects will commonly outweigh direct effects, and (2) that there are important differences between good genes and sexy son indirect effects that must be recognized. We suggest that acknowledgement of these distinctions will lead to increased understanding of processes operating in both sexual conflict and sexual selection.
Adaptation, Physiological↗
The influence of sexual dimorphism in body size and mouth morphology on diet selection and sexual segregation in cervids.
In mammals patterns of food resource distribution influence female distribution, leading to aggregation and favouring the evolution of a polygynous mating system. Under polygyny, sexual selection favours an increase of the male body size, since larger bodied males have competitive advantage in fights for mates. As a result, sexual body size dimorphism is a general rule in polygynous artiodactyls and is correlated with the degree of polygyny. Sex differences in body size lead to differences in energy requirements and food selection between the sexes. This has led to the sexual size dimorphism hypothesis being used to explain sexual segregation in ungulates, although from the available studies, it is not possible to deduce a consistent pattern between sexes in the use of forage of different abundance or quality. Two other groups of hypotheses have been put forward to explain sexual segregation in ungulates. These are based on reproductive strategy and social factors, both of which are independent of body size. The mechanistic explanation for differences in food selection ability and intake rate between animals of different body size and how this can lead to an understanding of the sex differences in diet and sexual segregation, both of which are intimately linked, is discussed.
Animal Nutritional Physiological Phenomena↗