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PubMed1976

Estimation of assortative mating preferences in the Arctic skua.

Methods are described for the maximum likelihood estimation of mating preferences in models of assortative mating for monogamous and polygamous organisms. These methods are applied to data of matings of the three phenotypes, pale, intermediated and dark of the Arctic Skua. The data were obtained by exhaustive surveys of the Arctic Skua populations on the islands of Fair Isle and Foula. The data give evidence of significant assortative mating of pale birds on Foula and intermediate birds on Fair Isle. The combined data show that there is very highly significant assortative mating, but only of intermediates. In previous surveys, data, in which intermediates and darks were not distinguished, were obtained from a number of islands in the Shetlands. These data, combined with the present data, show that the overall assortative mating of pale is very highly significant with no evidience of heterogeneity. The assortative mating of intermediate birds on Fair Isle agrees with other evidence showing that inermediate males have an advantage as a result of sexual selection.

Animals↗
PubMed2005

Contrasting patterns of polymorphism and divergence on the Z chromosome and autosomes in two Ficedula flycatcher species.

In geographic areas where pied and collared flycatchers (Ficedula hypoleuca and F. albicollis) breed in sympatry, hybridization occurs, leading to gene flow (introgression) between the two recently diverged species. Notably, while such introgression is observable at autosomal loci it is apparently absent at the Z chromosome, suggesting an important role for genes on the Z chromosome in creating reproductive isolation during speciation. To further understand the role of Z-linked loci in the formation of new species, we studied genetic variation of the two species from regions where they live in allopatry. We analyzed patterns of polymorphism and divergence in introns from 9 Z-linked and 23 autosomal genes in pied and collared flycatcher males. Average variation on the Z chromosome is greatly reduced compared to neutral expectations based on autosomal diversity in both species. We also observe significant heterogeneity between patterns of polymorphism and divergence at Z-linked loci and a relative absence of polymorphisms that are shared by the two species on the Z chromosome compared to the autosomes. We suggest that these observations may indicate the action of recurrent selective sweeps on the Z chromosome during the evolution of the two species, which may be caused by sexual selection acting on Z-linked genes. Alternatively, reduced variation on the Z chromosome could result from substantially higher levels of introgression at autosomal than at Z-linked loci or from a complex demographic history, such as a population bottleneck.

Animals↗
PubMed2003

Group sex, sex change, and parasitic males: sexual strategies among the fishes and their neurobiological correlates.

Sexual selection, in the form of intrasexual competition and mate choice, has driven the evolution of a variety of sexual phenotypes amongst the vertebrates (Andersson, 1994). As a result, vertebrate species utilize many different approaches to acquire fertilizations. Humans and other primates show a wide range of sexual behaviors, but this range is dwarfed by the remarkable variation seen in advanced fishes. The goals of this review are (a) to acquaint the reader with the tremendous sexual diversity exhibited by fishes, (b) to demonstrate how this diversity provides unique opportunities to examine the neurobiological correlates of vertebrate sexual strategies, and (c) to highlight the parallels between the neuroendocrine correlates of the sexual strategies of fish with the mechanisms underlying sexual phenotypes in other vertebrates, showing the utility of fish studies for understanding sexual variation in general.

Animal Communication↗
PubMed2005

Relative abundance and the species-specific reinforcement of male mating preference in the Chrysochus (Coleoptera: Chrysomelidae) hybrid zone.

Most studies of reinforcement have focused on the evolution of either female choice or male mating cues, following the long-held view in sexual selection theory that mating mistakes are typically more costly for females than for males. However, factors such as conspecific sperm precedence can buffer females against the cost of mating mistakes, suggesting that in some hybrid zones mating mistakes may be more costly for males than for females. Thus, the historical bias in reinforcement research may underestimate its frequency. In this study, we present evidence that reinforcement has driven the evolution of male choice in a hybrid zone between the highly promiscuous leaf beetles Chrysochus cobaltinus and C. auratus, the hybrids of which have extremely low fitness. In addition, there is evidence for male choice in these beetles and that male mating mistakes may be costly, due to reduced opportunities to mate with conspecific females. The present study combines laboratory and field methods to quantify the strength of sexual isolation, test the hypothesis of reproductive character displacement, and assess the link between relative abundance and the strength of selection against hybridization. We document that, while sexual isolation is weak, it is sufficient to produce positive assortative mating. In addition, reproductive character displacement was only detected in the relatively rare species. The strong postzygotic barriers in this system are sufficient to generate the bimodality that characterizes this hybrid zone, but the weak sexual isolation is not, calling into question whether strong prezygotic isolation is necessary for the maintenance of bimodality. Growing evidence that the cost of mating mistakes is sufficient to shape the evolution of male mate choice suggests that the reinforcement of male mate choice may prove to be a widespread occurrence.

Animals↗
PubMed2005

Phenotypic plasticity in the developmental integration of morphological trade-offs and secondary sexual trait compensation.

Trait exaggeration through sexual selection will tale place alongside other changes in phenotype. Exaggerated morphology might be compensated by parallel changes in traits that support, enhance or facilitate exaggeration: 'secondary sexual trait compensation' (SSTC). Alternatively, exaggeration might be realized at the expense of other traits through morphological trade-offs. For the most part, SSTC has only been examined interspecifically. For these phenomena to be important intraspecifically, the sexual trait must be developmentally integrated with the compensatory or competing trait. We studied developmental integration in two species with different development: the holometabolous beetle Onthophagus taurus and the hemimetabolous earwig Forficula auricularia. Male-dimorphic variation in trait exaggeration was exploited to expose both trade-offs and SSTC. We found evidence for morphological trade-offs in O. taurus, but no F. auricularia, supporting the notion that trade-offs are more likely in closed developmetal systems. However, we found these trade-offs were not limited solely to traits growing close together. Developmental integration of structures involved in SSTC were detected in both species. The developmental integration of SSTC was phenotypically plastic, such that the compensation for relatively larger sexual traits was greater in the exasperated male morphs. Evidence of intraspecific SSTC demands studies of the selective, genetic and developmental architecture of phenotypic integration.

Animals↗
PubMed2003

Prevalence of sexually transmitted infections and performance of STI syndromes against aetiological diagnosis, in female sex workers of red light area in Surat, India.

OBJECTIVES: To measure prevalence of selected sexually transmitted infections (STI) and HIV among female sex workers (SWs) in the red light area of Surat, India, and to evaluate the performance of STI syndrome guidelines (for general population women in India) in this group against the standard aetiological diagnosis of STIs by laboratory methods. METHODS: In a cross sectional study, 124 out of an estimated total of 500 SWs were mobilised to a health camp near the red light area during 2000. After obtaining consent, a behavioural questionnaire was administered, followed by clinical examination and specimen collection for different STIs. 118 SWs completed all aspects of the survey. HIV testing was unlinked and anonymous. RESULTS: The mean number of different sexual partners of SWs per day was five. 94.9% reported consistent condom use with the clients. 58.5% of SWs had no symptoms related to STDs at the time of examination. Reported symptoms included lower abdominal pain (19.5%), abnormal vaginal discharge (12.7%), painful sexual intercourse (12.7%), painful micturition (11.0%), itching around the genital area (10.2%), and genital ulcer (5.9%). The prevalence of STI "syndromes" were vaginal discharge syndrome 51.7%, pain in lower abdomen 19.5%, enlarged inguinal lymph nodes 11.9%, and genital ulcer 5.9%. Based on the laboratory reports (excluding HIV tests), 62 (52.5%) SWs did not have any of the four tested STIs. Prevalence of laboratory confirmed STIs were syphilis 22.7% (based on reactive syphilis serology tests), gonorrhoea 16.9%, genital chlamydial infection 8.5%, and trichomoniasis 14.4%. HIV prevalence was 43.2%. The performance of Indian recommended treatment guidelines for vaginal discharge syndrome (VDS) and genital ulcer syndrome (GUS) against aetiological diagnosis was poor. CONCLUSION: Prevalence of different STIs and HIV among the FSWs in the Surat red light area is high despite high reported condom use with clients. Syndromic case management is missing a large number of asymptomatic cases and providing treatment in the absence of disease. Therefore, it is necessary to explore alternative strategies for control of STIs in female sex workers. STI services need to be improved.

Adolescent↗
PubMed1991

Sexual showiness and parasite load: correlations without parasite coevolutionary cycles.

Hamilton & Zuk (1982, Science 218, 384-387.) produced a model of sexual selection in which coevolutionary cycles of host and parasites generate consistently positive correlations between parent and offspring viability, and that animals choose mates for genetic disease resistance by scrutinizing characters whose full expression is dependent on health and vigour. They predicted a positive correlation between sexual showiness and parasite burden across species, and a negative correlation within a species. First, recent suggestions that interspecific correlations in the opposite direction to that indicated above are consistent with the mechanisms of Hamilton & Zuk's model are discussed. Second, it is shown that the model's predictions can be produced by heritable variation maintained by non-parasite fluctuating selection. In this case, the parasites associated with degree of sexual showiness are those able to amplify any initial heritable differences in vigour. Alternative sources of positive correlation between parent and offspring viability, which include the indirect effects of climatic change and exclude the need for host-parasite coevolutionary cycles, are also proposed.

Animals↗
PubMed1985

[Natural selection].

Much of the resistance against Darwin's theory of natural selection has been due to misunderstandings. It is shown that natural selection is not a tautology and that it is a two-step process. The first step, the production of variation, is under the control of chance; the second step, selection proper, is an anti-chance process, but subject to many constraints. The target of selection is the individual as a whole, and many neutral mutations can be retained as hitchhikers of successful genotypes. Sexual selection results from selection for pure reproductive success.

Animals↗
PubMed1976

Ethological isolation and mating experience in Drosophila paulistorum.

With few exceptions, previously published experiments documenting ethological isolation between Drosophila populations have used young virgin females. We have observed directly females of Drosophila paulistorum semispecies in choice experiments with both homogamic and heterogamic males. Aged females' sexual selection did not differ from that of young females. Previous heterogamic copulatory experience did not change the degree of sexual isolation; however, females with homogamic copulatory experience showed a significantly higher preference for homogamic males.

Aging↗
PubMed2002

Genetic and demographic responses of mercury-exposed mosquitofish (Gambusia holbrooki) populations: temporal stability and reproductive components of fitness.

Two previous mesocosm studies showed changes in glucosephosphate isomerase-2 (Gpi-2) allele frequencies in mosquitofish populations exposed to mercury for 111 d or two years. A previous selection component analysis of single-generation populations exposed for 111 d to 18 microg/L Hg suggested that female sexual selection and fecundity selection could contribute to changes in Gpi-2 allele frequencies. The present multigeneration study was conducted to determine the stability of Gpi-2 allele frequencies over four years of mercury exposure, measure the reproductive fitness of Gpi-2 genotypes inhabiting control and mercury-contaminated mesocosms to determine a mechanism explaining changes in Gpi-2 allele frequencies, investigate differences in the demographic characteristics of mercury-exposed and control populations, and investigate the water quality of the mesocosms to determine if variables other than mercury show concordant patterns among mesocosms. Differences in Gpi-2 allele frequencies between control and mercury-exposed populations were stable over four years (approximately eight generations) of mercury exposure. Mercury-exposed female mosquitofish had a lower probability of being gravid than control females (p = 0.001). Mercury-exposed females also had lower fecundity (total number of eggs and embryos) than control females (p = 0.036). Unlike the results of the more intense mercury exposures in the single generation study, no strong evidence was found that Gpi-2 genotype influenced fecundity or the probability of being gravid in both control and mercury-exposed females. The quantification of fitness components is difficult but has the potential to enhance our understanding of how toxicants alter allele frequencies in exposed populations.

Animals↗
PubMed2006

Heritability and heterochrony of polychromatism in a Lake Victoria Cichlid fish: Stepping stones for speciation?

In many haplochromine cichlid fish, male nuptial coloration is subject to female mate choice and plays a central role in the evolution of reproductive isolation between incipient species. Intraspecific variation in male coloration may serve as a target for diversifying sexual selection and provide a starting point for species divergence. Here, we investigated a polychromatism in Neochromis omnicaeruleus, a haplochromine from Lake Victoria, East-Africa. In this species, male coloration ranges from skyblue to yellow-red and females are grey-blue to yellow. We found that both genetic and environmental factors influence the expression of these colours during individual development. In a natural population, we found that male colour was associated with size and sexual maturity: yellow males were smaller than blue males and tended to be sexually immature. In females, size and maturity did not differ between colour types. Laboratory crosses revealed that there is a heritable component to the observed colour variation: yellow parents produced more yellow offspring than blue parents. Together with repeated aquarium observations of yellow individuals that gradually become blue, these data suggest that yellow males change to blue as they approach sexual maturity, and that the occurrence and timing of this transition is influenced by both environmental and genetic effects. The significance of this mechanism of colour expression as a possible target for divergent selection remains to be evaluated.

Africa, Eastern↗
PubMed1990

Biological signals as handicaps.

An ESS model of Zahavi's handicap principle is constructed. This allows a formal exposition of how the handicap principle works, and shows that its essential elements are strategic. The handicap model is about signalling, and it is proved under fairly general conditions that if the handicap principle's conditions are met, then an evolutionarily stable signalling equilibrium exists in a biological signalling system, and that any signalling equilibrium satisfies the conditions of the handicap principle. Zahavi's major claims for the handicap principle are thus vindicated. The place of cheating is discussed in view of the honesty that follows from the handicap principle. Parallel signalling models in economics are discussed. Interpretations of the handicap principle are compared. The models are not fully explicit about how females use information about male quality, and, less seriously, have no genetics. A companion paper remedies both defects in a model of the handicap principle at work in sexual selection.

Animal Communication↗
PubMed2001

The effect of transient food stress on female mate preference in the stalk-eyed fly Cyrtodiopsis dalmanni.

The effect of transient nutritional stress (sucrose culture medium) on female mate preference was investigated in the stalk-eyed fly Cyrtodiopsis dalmanni. Two experimental treatments were run in parallel. In the first, female preference was initially tested on corn (standard medium) and subsequently on sucrose (novel medium). In the second, female preference was tested in the reverse order: sucrose then corn. Females fed on corn had stronger preferences for large-eyespan males than females fed on sucrose. Female age, experience or the order of exposure to culture media had no effects on the strength of preference. An additional experiment demonstrated that the sucrose diet reduced the number of developing and mature eggs. We discuss the adaptive significance of changes in female preference due to transient nutritional stress, and the effect of changes in female preference on the strength of sexual selection.

Animals↗
PubMed2000

Rapid evolution of male reproductive genes in the descent of man.

A diverse body of morphological and genetic evidence has suggested that traits pertaining to male reproduction may have evolved much more rapidly than other types of character. Recently, DNA sequence comparisons have also shown a very high level of divergence in male reproductive proteins between closely related Drosophila species, among marine invertebrates and between mouse and rat. Here we show that rapid evolution of male reproductive genes is observable in primates and is quite notable in the lineages to human and chimpanzee. Nevertheless, rapid evolution by itself is not necessarily an indication of positive darwinian selection; relaxation of negative selection is often equally compatible with the DNA sequence data. By taking three statistical approaches, we show that positive darwinian selection is often the driving force behind this rapid evolution. These results open up opportunities to test the hypothesis that sexual selection plays some role in the molecular evolution of higher primates.

Amino Acid Substitution↗
PubMedDate not supplied

A Japanese view on speciation: "Sumiwake" explosive speciation of the cichlids in Lake Victoria.

Imanishi's "mental" (cerebral) view of speciation is presented, in Mizuhata's revision. The key concept here is the "ethological partition" of the species. Members of each species=society (etho-species) share the same mental (brain) software, irrespective of their genetic structure. Cerebral animals perform active programmed selection, not to be confused with passive, non-programmed "natural selection" as in Neo-Darwinism. The program includes mating-choice of peculiar characters, distinct from the Neo-Darwinian sexual selection supposed due to the specific choosy genes. Speciation can occur, as a "partition of species=society", with bifurcation of mate-choosing program in the parent species. A main promoter for this bifurcation is species-specific "passion" for especially significant characters: long necks, ornamental antlers, ocelli feathers, bright nuptial colors etc. The cichlids in Lake Victoria achieved explosive speciation, while retaining their genetic homogeneity completely. Therefore it is illogical to attribute this divergence to extraordinary mutations in "action controlling genes". The origin of species=society (etho-species) can trace along to the Cambrian Period.

Animals↗
PubMed2006

Comparative phylogenetic analysis of male alternative reproductive tactics in ray-finned fishes.

Using comparative phylogenetic analysis, we analyzed the evolution of male alternative reproductive tactics (MARTs) in ray-finned fishes (Actinopterygii). Numerous independent origins for each type of MART (involving sneaker males, female mimics, pirates, and satellite males) indicate that these behaviors have been highly labile across actinopterygiian evolution, consistent with a previous notion that convergent selection in fishes can readily mold the underlying suites of reproductive hormones into similar behaviors. The evolutionary appearance of MARTs was significantly correlated with the presence of sexually selected traits in bourgeois males (P = 0.001) but not with the presence of male parental care. This suggests that MARTs often arise from selection on some males to circumvent bourgeois male investment in mate monopolization, rather than to avoid male brood care per se. We found parsimony evidence for an evolutionary progression of MARTs wherein sneaking is usually the evolutionary precursor to the presumably more complex MARTs of female mimicry and cooperative satellite behavior. Nest piracy appears not to be part of this evolutionary progression, possibly because its late onset in the life cycle of most ray-finned fishes reduces the effects of selection on this reproductive tactic.

Animals↗
PubMed2004

Can too strong female choice deteriorate male ornamentation?

Competition for limited resources can have fundamental implications for population dynamics. However, the effects of resource depletion have rarely been discussed in the context of sexual selection, even though mate choice typically favours males who outperform others in securing access to some limited resource. Here, we develop a model to investigate the question of resource competition as a form of male-male competition in the context of male sexual displays. We phrase our model in terms of male bowerbirds either searching for or stealing resources (ornamental objects) valued by females, and compare the model findings with published studies of time allocation to various activities in different species of bowerbirds. The basic idea of the model, however, extends to cases where the resource is used less directly for the development of sexual ornamentation, such as males excluding others' access to food. We show that if males compete for resources used in sexual displays, intense female preference for high-quality displays can lead to poorer prospects for efficient choice by females. This is because males benefit from excluding others' access to resources used in displays, damaging the overall efficiency of resource use in the population, and the accuracy with which females can judge male ability to gain such resources. The evolution of female choice may therefore have a self-limiting nature when it poses a selection pressure on male resource acquisition.

Animals↗