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PubMed2003

The effect of past condition on a multicomponent sexual signal.

Sexual-selection theory predicts that multiple signals may reveal male condition at different stages of life, thus allowing females to make a more reliable assessment of male quality. While the effect of current condition on signal design is well established, few studies have experimentally investigated the effects of past condition. We therefore manipulated the nutritional condition of male nymph field crickets Gryllus campestris and assessed the enduring effects on multiple components of the adult calling song. Food-restricted males had longer nymphal development times and smaller adult body sizes than nymphs with ad libitum food access. Nymphal feeding conditions specifically affected the allometric relationship between body size and harp size, as food-restricted males developed comparatively small harps, leading to a calling song of higher carrier frequency than that produced by similar-sized control males. Other calling-song components, notably chirp rate and chirp intensity, were not affected by the nymphal food treatment, exposing carrier frequency as the key component indicating past condition. In a previous study we established chirp rate as the sole indicator of current condition. The combined results represent experimental evidence of a multicomponent sexual signal that provides distinct information on male condition during different stages of life.

Animals↗

PubMed2005

Character displacement as the "best of a bad situation": fitness trade-offs resulting from selection to minimize resource and mate competition.

Character displacement has long been considered a major cause of adaptive diversification. When species compete for resources or mates, character displacement minimizes competition by promoting divergence in phenotypes associated with resource use (ecological character displacement) or mate attraction (reproductive character displacement). In this study, we investigated whether character displacement can also have pleiotropic effects that lead to fitness trade-offs between the benefits of avoiding competition and costs accrued in other fitness components. We show that both reproductive and ecological character displacement have caused spadefoot toads to evolve smaller body size in the presence of a heterospecific competitor. Although this shift in size likely arose as a by-product of character displacement acting to promote divergence between species in mating behavior and larval development, it concomitantly reduces offspring survival, female fecundity, and sexual selection on males. Thus, character displacement may represent the "best of a bad situation" in that it lessens competition, but at a cost. Individuals in sympatry with the displaced phenotype will have higher fitness than those without the displaced trait because they experience reduced competition, but they may have reduced fitness relative to individuals in allopatry. Such a fitness trade-off can limit the conditions under which character displacement evolves and may even increase the risk of "Darwinian extinction" in sympatric populations. Consequently, character displacement may not always promote diversification in the manner that is often expected.

Animals↗

PubMed2002

Are all grandmothers equal? A review and a preliminary test of the "grandmother hypothesis" in Tokugawa Japan.

An unresolved question arising from human evolutionary research relates to the function of the postreproductive period in human females. If menopause is not merely an artifact resulting from the benefits of civilization, there must be an adaptive mechanism favoring the offspring of women who continue to thrive well past the time of their last ovulation. The "grandmother hypothesis" was developed on the basis of the original suggestion by Williams (1957 Evolution 11:32-39) that "stopping early" would benefit already-born children. This idea, combined with the concepts of kin selection (Hamilton 1964 J Theor Biol 7:1-52) and parental investment (Trivers 1972 Sexual Selection and the Descent of Man, Chicago: Aldine, p. 136-179), was expanded to suggest that postreproductive women (in contrast to males) contribute to their inclusive fitness by extending support to their grandchildren. We used discrete time event history analysis (Allison [1984] Event History Analysis, Newbury Park: Sage; Allison [1995] Survival Analysis, Cary, NC: SAS Institute) and logistic regression on data provided in population registers (Shūmon Aratame Chō, or SAC) from a village in central Japan, covering the period from 1671-1871, in a preliminary investigation of the effects of household grandparental presence on the probability of a child's death. We found that after accounting for the presence of other household members, the only grandparent whose presence exerted a consistent negative effect on the likelihood of a child's death was the mother's mother. Due to the small sample size of households that contained maternal grandmothers, these results failed to achieve statistical significance. Their importance, however, is in what they suggest about future research, i.e., census data from preindustrial societies can provide a basis for testing evolutionary proposals, including the "grandmother hypothesis."

Adaptation, Physiological↗

PubMed2006

The evolution of condition-dependent sexual dimorphism.

Theory suggests that the net benefit of allocating resources to a sexual trait depends both on the strength of sexual selection on that trait and on individual condition. This predicts a tight coevolution between sexual dimorphism and condition dependence and suggests that these patterns of within-sex and between-sex variation may share a common genetic and developmental basis. Although condition-dependent expression of sexual traits is widely documented, the extent of covariation between condition dependence and sexual dimorphism remains poorly known. I investigated the effects of condition (larval diet quality) on multivariate sexual dimorphism in the fly Telostylinus angusticollis (Neriidae). Condition determined the direction of sexual size dimorphism and modulated sexual shape dimorphism by affecting allometric slopes and/or intercepts of sexually homologous traits in both sexes. Although the greatest responses to condition manipulation were observed in male sexual traits, both sexual and nonsexual traits exhibited substantial variation in the nature and magnitude of condition effects. Nonetheless, condition dependence and sexual dimorphism were remarkably congruent: variation in the strength of condition effects on male traits explained more than 90% of the variation in the magnitude of sexual dimorphism, whether quantified in terms of trait size or allometric slope. The genetic mechanisms that give rise to multivariate sexual dimorphism in body shape thus function in a strongly condition-dependent manner in this species, suggesting a common genetic basis for body shape variation within and between sexes.

Animals↗

PubMed2003

Sexually transmitted infections prevalence rates in slum communities of Dhaka, Bangladesh.

The study objective was to estimate the prevalence of selected sexually transmitted infections (STIs) and associated factors among Dhaka slum dwellers. Blood and urine specimens were collected from 1534 men and women. Participants in this cross-sectional study responded to a questionnaire, providing socioeconomic data, symptomatology and treatment-seeking behaviour. Specimens were tested for syphilis, hepatitis B (HBsAg), Neisseria gonorrhoeae, Chlamydia trachomatis, and HIV. Serologic evidence of syphilis infection was found in 6.0% of respondents, HBsAg in 3.8%. Prevalence rates of gonorrhoea and chlamydia were 1.7% and <1%, respectively. No HIV infections were found. Men were more than twice as likely as women to be infected with syphilis or HBsAg carriers. Behaviours facilitating STI transmission were common among men. Syphilis infection is prevalent enough to warrant the initiation of screening programmes in this population. The prevalence rate of hepatitis B carriage suggests that this population would benefit from universal vaccination against hepatitis B.

Adolescent↗

PubMed2000

Sex gene pool evolution and speciation: a new paradigm.

In this paper, we review the literature on the growing body of data demonstrating the rapid evolution of sex and reproduction related (SRR) genes and show how a paradigm shift to the study of SRR genes can provide new approaches to solving some of the old problems in evolutionary biology. The argument is based on (1) the growing scope and importance of sexual selection in evolution, (2) the growing number of case studies showing rapid evolution of sexual traits in a wide variety of taxa, (3) the faster rate of DNA sequence divergence in genes affecting sexual function and fertility, (4) the evidence for the involvement of novel traits/genes in sexual functions, and (5) a proposed sex/non-sex dichotomy of the gene pool affecting viability versus fertility. It is argued that the adoption of the sex/non-sex dichotomy of genes/traits can provide new perspectives on such problems as species concepts, modes (allopatric/sympatric) of speciation, Haldane's rule, reinforcement, and the founder effect. It is proposed that the evolutionary study of genes affecting viability versus fertility is the key to understanding the genetic basis of speciation.

Animals↗

PubMed2005

Measurement of concurrent selection episodes.

Current methods for measuring selection with longitudinal data have been developed with the assumption that episodes of selection are sequential. However, a number of empirical examinations have demonstrated that natural and sexual selection may act concurrently and in opposing directions. Other recent work has highlighted the difficulty of assigning fitness values for survival when reproduction and mortality within a population temporally overlap. I treat these as facets of a single problem; how to analyze selection where mortality and reproduction are concurrent. To address this problem, I formalize a method to estimate total fitness of individuals over a period of time utilizing longitudinal data. I then show how the fitness may be partitioned to provide two separate estimates of fitness for reproductive opportunity and reproductive success. In addition, another total fitness estimate for the period can be obtained from the two partitioned estimates. This procedure will allow calculation of total fitness where there are some missing datapoints for reproductive success of an individual. A simulation indicates that bias is generally low for the various fitness estimates. These methods should expand our ability to understand the interaction of different selection episodes.

Bias↗

PubMed2004

Chromosomal polymorphism, morphometric traits and mating success in Leptysma argentina Bruner (Orthoptera).

The South-American species Leptysma argentina Bruner is polymorphic for a centric fusion between chromosomal pairs 3 and 6 (fusion 3/6). Cytogenetic and morphological studies revealed that fusion 3/6 significantly increases some morphometric variables in males. A selection components study showed that the fusion is positively selected for longevity, the direct effect being exerted on thorax height. Moreover, a unisexual approach revealed that sexual male selection acts by increasing third femur length. In the present study the effect of fusion 3/6 on morphometric variables and the effect of body size and karyotype on mating success in both males and females were analysed through a bisexual approach. Total body length (TL) and third femur length (FL) were significantly larger amongst the fusion carrier females. Besides, the largest females and the carriers of the fusion have increased mating success. The selection differential suggests that directional sexual selection favours the females with increased TL and fusion dosage; however, the selection gradient revealed that none of the variables here analysed is a direct target of sexual selection. The male sexual selection study agrees with previous results, showing the importance of the third pair of legs in male mating success among grasshoppers.

Animals↗

PubMed1997

Sex chromosome meiotic drive in stalk-eyed flies.

Meiotically driven sex chromosomes can quickly spread to fixation and cause population extinction unless balanced by selection or suppressed by genetic modifiers. We report results of genetic analyses that demonstrate that extreme female-biased sex ratios in two sister species of stalk-eyed flies, Cyrtodiopsis dalmanni and C. whitei, are due to a meiotic drive element on the X chromosome (Xd). Relatively high frequencies of Xd in C. dalmanni and C. whitei (13-17% and 29%, respectively) cause female-biased sex ratios in natural populations of both species. Sex ratio distortion is associated with spermatid degeneration in male carriers of Xd. Variation in sex ratios is caused by Y-linked and autosomal factors that decrease the intensity of meiotic drive. Y-linked polymorphism for resistance to drive exists in C. dalmanni in which a resistant Y chromosome reduces the intensity and reverses the direction of meiotic drive. When paired with Xd, modifying Y chromosomes (Ym) cause the transmission of predominantly Y-bearing sperm, and on average, production of 63% male progeny. The absence of sex ratio distortion in closely related monomorphic outgroup species suggests that this meiotic drive system may predate the origin of C. whitei and C. dalmanni. We discuss factors likely to be involved in the persistence of these sex-linked polymorphisms and consider the impact of Xd on the operational sex ratio and the intensity of sexual selection in these extremely sexually dimorphic flies.

Animals↗

PubMed2004

Evolution of color variation in dragon lizards: quantitative tests of the role of crypsis and local adaptation.

Many animal species display striking color differences with respect to geographic location, sex, and body region. Traditional adaptive explanations for such complex patterns invoke an interaction between selection for conspicuous signals and natural selection for crypsis. Although there is now a substantial body of evidence supporting the role of sexual selection for signaling functions, quantitative studies of crypsis remain comparatively rare. Here, we combine objective measures of coloration with information on predator visual sensitivities to study the role of crypsis in the evolution of color variation in an Australian lizard species complex (Ctenophorus decresii). We apply a model that allows us to quantify crypsis in terms of the visual contrast of the lizards against their natural backgrounds, as perceived by potential avian predators. We then use these quantitative estimates of crypsis to answer the following questions. Are there significant differences in crypsis/conspicuousness among populations? Are there significant differences in crypsis conspicuousness between the sexes? Are body regions "exposed" to visual predators more cryptic than "hidden" body regions? Is there evidence for local adaptation with respect to crypsis against different substrates? In general, our results confirmed that there are real differences in crypsis/conspicuousness both between populations and between sexes; that exposed body regions were significantly more cryptic than hidden ones, particularly in females; and that females, but not males, are more cryptic against their own local background than against the background of other populations [corrected]. Body regions that varied most in contrast between the sexes and between populations were also most conspicuous and are emphasized by males during social and sexual signaling. However, results varied with respect to the aspect of coloration studied. Results based on chromatic contrast ("hue" of color) provided better support for the crypsis hypothesis than did results based on achromatic contrast ("brightness" of color). Taken together, these results support the view that crypsis plays a substantial role in the evolution of color variation and that color patterns represent a balance between the need for conspicuousness for signaling and the need for crypsis to avoid predation.

Adaptation, Physiological↗

PubMed2006

March 27, 1827 and what happened later--the impact of psychiatry on evolutionary theory.

In the interaction between Psychiatry and evolutionary theory the force of the impact has not always been in one direction. The Brownes, father and son, had an influence on the development of Darwin's theory at different points in the nineteenth century. The crystallization by Miskolczy in 1933 of the concept that schizophrenia is a disorder that is specific to Homo sapiens is another example. In 1964 the formulation of the central paradox of psychosis by Huxley, Mayr and co-authors and the subsequent critique by Kuttner et al. of the solution Huxley et al. had offered opened up evolutionary approaches to aetiology. Here it is argued that a resolution of this paradox requires identification of the speciation event for modern H. sapiens and elucidation of its neuroanatomical and physiological consequences. It necessitates a saltational account of species transitions and the recognition of species-specific genetic variation. Pursuit of these objectives leads to the hypothesis that speciation events occur selectively on the heterogametic chromosome (the Y in mammals) and are followed by a phase of sexual selection to establish a new specific mate recognition system. In H. sapiens the core component of this system is the capacity for language; the nuclear symptoms of schizophrenia are necessary clues to its neural structure.

Animals↗

PubMed2001

Costs of sexual traits: a mismatch between theoretical considerations and empirical evidence.

Costs of sexual traits are of central importance to the theory of sexual selection. To qualify as a cost in line with theoretical models, empirical studies must demonstrate that sexual traits cause negative effects on one component of fitness of the trait bearer. Moreover, it must be demonstrated that the costs are differential such that negative effects on fitness are more severe for individuals in poor condition than for individuals in good condition. However, in the current literature, there is confusion over what qualifies as a cost, and costs are often anticipated based on findings of increased expenditure. Consequently, it seems that the generally accepted notion that sexual traits are costly is in fact based almost exclusively on indirect evidence and that direct empirical evidence is very scarce.

Amphibians↗

PubMed2004

Female mating bias results in conflicting sex-specific offspring fitness.

Indirect-benefit models of sexual selection assert that females gain heritable offspring advantages through a mating bias for males of superior genetic quality. This has generally been tested by associating a simple morphological quality indicator (for example, bird tail length) with offspring viability. However, selection acts simultaneously on many characters, limiting the ability to detect significant associations, especially if the simple indicator is weakly correlated to male fitness. Furthermore, recent conceptual developments suggest that the benefits gained from such mating biases may be sex-specific because of sexually antagonistic genes that differentially influence male and female reproductive ability. A more suitable test of the indirect-benefit model would examine associations between an aggregate quality indicator (such as male mating success) and gender-specific adult fitness components, under the expectation that these components may trade off. Here, we show that a father's mating success in the cricket, Allonemobius socius, is positively genetically correlated with his son's mating success but negatively with his daughter's reproductive success. This provides empirical evidence that a female mating bias can result in sexually antagonistic offspring fitness.

Animals↗

PubMed2007

Sexually transmitted infections and risk factors among truck stand workers in Dhaka, Bangladesh.

OBJECTIVE: This study was conducted to determine the prevalence of selected sexually transmitted infections (STIs) and their risk factors among workers in and near a truck stand in Dhaka, Bangladesh. STUDY DESIGN: A random sample of 696 men and 206 women were recruited into a cross-sectional study using a census that enumerated transport agents, motor mechanics, laborers, and vendors in Tejgaon truck stand. RESULTS: The prevalence rates of syphilis (rapid plasma reagin and Treponema pallidum hemagglutination), gonorrhea (polymerase chain reaction [PCR]), and chlamydial infections (PCR) among men were 4.1%, 7.7%, and 2.3%, respectively, and among women were 2.9%, 8.3%, and 5.2%. Multivariable analysis revealed that having >or=2 sex partners in the last month, never using a condom with sex workers, and ever injecting narcotics were significant predictors of STI among men. Being never married, working as a laborer, older age, and living within the truck stand were significant predictors of practicing high-risk behaviors among men, but none predicted infection with STIs. CONCLUSIONS: Both behavioral and STI data suggest that truck stand workers should be included in the STI/HIV intervention programs.

Adolescent↗

PubMed2003

The role of mother-daughter sexual risk communication in reducing sexual risk behaviors among urban adolescent females: a prospective study.

PURPOSE: To prospectively examine the relationship between mother-daughter communication about sex and selected sexual risk behaviors among inner-city adolescent females. METHODS: Participants were 219 sexually experienced females, 12 to 19 years of age, recruited from an inner-city adolescent medicine clinic in Philadelphia, PA, and randomly assigned to the control group of an HIV-risk reduction intervention study. Analyses were limited to data from control group participants to avoid confounding intervention effects. Poisson regression was employed to model three self-reported sexual risk behaviors: number of male sexual partners, number of episodes of sexual intercourse, and number of episodes of unprotected intercourse. Mediation effects were evaluated using variables from the Theory of Planned Behavior. Data were analyzed using Poisson regression. RESULTS: Higher levels of mother-daughter sexual risk communication were associated with fewer episodes of sexual intercourse and unprotected intercourse at 3-month follow-up. There was evidence that the relationship of communication to unprotected intercourse was mediated by condom use self-efficacy. Mother-daughter sexual risk communication was not significantly associated with adolescents' reports of numbers of male sexual partner. CONCLUSIONS: This prospective study supports the notion that mothers who communicate with their daughters about sex can affect their daughters' sexual behaviors in positive ways. These findings lend support for the design and implementation of family-based approaches to improve parent-adolescent sexual risk communication as one means of reducing HIV-related sexual risk behaviors among inner-city adolescent females.

Adolescent↗

PubMed2002

Understanding parasite strategies: a state-dependent approach?

Understanding and predicting parasite strategies is of interest not only for parasitologists, but also for anyone interested in epidemiology, control strategies and evolutionary medicine. From an ecological and evolutionary perspective, parasites are an important feature of their hosts' selective environment, and may have diverse roles, ranging from the evolution of host sex to host-sexual selection behavior. Generally, it is the hosts and their biology that have been the focus of these evolutionary investigations, but we approach the subject from the parasites' perspective, illustrating the sophistication of parasite strategies in dealing with contrasting and unpredictable environments.

Animals↗

PubMed2006

Evolutionary conflicts of interest between males and females.

Sexual conflict arises from differences in the evolutionary interests of males and females and can occur over traits related to courtship, mating and fertilisation through to parental investment. Theory shows that sexual conflict can lead to sexually antagonistic coevolution (SAC), where adaptation in one sex can lead to counter-adaptation in the other. Thus, sexual conflict can lead to evolutionary change within species. In addition, SAC can--through its effects on traits related to the probability of mating and of zygote formation--potentially lead to reproductive isolation. In this review, I discuss that, although sexual conflict is ubiquitous, the actual expression of sexual conflict leading to SAC is less frequent. The balance between the benefits and costs of the manipulation of one sex by the other, and the availability of mechanisms by which conflict is expressed, determine whether actual sexual conflict is likely to occur. New insights address the relationship between sexual conflict and conflict resolution, adaptation, sexual selection and fitness. I suggest that it will be useful to examine systematically the parallels and contrasts between sexual and other evolutionary conflicts. Understanding why some traits, but not others, are subject to evolutionary change by SAC will require data on the mechanisms of the traits involved and on the relative benefits and costs of manipulation and resistance to manipulation.

Animals↗

PubMed2004

Chemo-orientation using conspecific chemical cues in the stripe-necked terrapin (Mauremys leprosa).

Although chemical communication has been studied intensively in may reptilian species, little attention has been paid to the role that chemical signals play in aquatic reptiles, such as freshwater turtles. Here, I tested the hypothesis that the stripe-necked terrapin (Mauremys leprosa), an abundant freshwater turtle that inhabits the Iberian peninsula, is able to recognize chemical cues from conspecifics in the water and to modify its behavior in response to such cues. I compared the time spent by adult males and adult females in clean water to the time spent in water that presumably contained their own odor, odor from other males, and odor from other females, both during and outside the mating season. Results show that outside the mating season, both males and females avoid water that contains chemical cues from conspecifics of the opposite sex. During the mating season, male turtles clearly select water with chemical cues from females. Moreover, males prefer to occupy water from their home containers over clean water, and avoid water with chemical cues from other conspecific males. Conversely, during the mating season, females prefer to occupy water with chemical cues from other females, but do not select water from their home containers or water from males. The evolution of chemical communication in turtles, its relation to sexual selection processes, and the implications for turtle behavior are discussed.

Animal Communication↗