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Results for “Sexual selection”

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At least 703 records · Page 39Linked to original sources
PubMed2006

Genetic mating patterns studied in pools with manipulated nest site availability in two populations of Pomatoschistus minutus.

Pomatoschistus minutus show paternal care in a resource defence mating system. We investigated the effect of nest-site availability on parasitic spawning. Each experimental pool contained four potentially nest-building males, four females and nests-sites in shortage (2) or excess (6). Both treatments were conducted in two populations; one with natural nest-sites in excess, one with a nest-site shortage. Microsatellite-DNA revealed that all nest-holders had fertilized most of the eggs they tended. Yet, 35% of the nests contained eggs fertilized by another male and 14.4% of the males had performed parasitic spawning. There was no site or treatment effect. Several females spawned in two nests, which coincided with parasitic spawnings, suggesting a cost to the nest-holder in terms of lost mating success. Nest-holders with and without eggs and non-nesting males all spawned parasitically, generating a significantly lower opportunity for sexual selection compared to if there had been no parasitic spawning.

Animals↗
PubMed2002

Sperm-female coevolution in Drosophila.

Rapid evolution of reproductive traits has been attributed to sexual selection arising from interaction between the sexes. However, little is known about the nature of selection driving the evolution of interacting sex-specific phenotypes. Using populations of Drosophila melanogaster selected for divergent sperm length or female sperm-storage organ length, we experimentally show that male fertilization success is determined by an interaction between sperm and female morphology. In addition, sperm length evolution occurred as a correlated response to selection on the female reproductive tract. Giant sperm tails are the cellular equivalent of the peacock's tail, having evolved because females evolved reproductive tracts that selectively bias paternity in favor of males with longer sperm.

Animals↗
PubMed1995

Brain changes and negative symptoms in schizophrenia.

Negative symptoms (and cognitive impairments) in schizophrenia are a correlate of early onset and poor outcome. It is plausible that they are related to an arrest of brain development, for which there is now considerable evidence, but the precise relationship is elusive. In one post-mortem study negative symptoms were related to a reduction in brain length and in an MRI study to an asymmetry of sulcal CSF. It is proposed that the phenomena of psychosis (including negative symptoms) can be understood as part of the diversity of human personality structure generated by a process of sexual selection acting on a sexual dimorphism for cerebral asymmetry.

Age of Onset↗
PubMed2003

Reproductive behavior in the squid Sepioteuthis australis from South Australia: interactions on the spawning grounds.

Squid behavior is synonymous with distinctive body patterns, postures, and movements that constitute a complex visual communication system. These communications are particularly obvious during reproduction. They are important for sexual selection and have been identified as a potential means of species differentiation. Here we present a detailed account of copulation, mating, and egg deposition behaviors from in situ observations of the squid Sepioteuthis australis from South Australia. We identified four mating types from 85 separate mating attempts: "Male-upturned mating" (64% of mating attempts); "Sneaker mating" (33%); "Male-parallel" (2%); and "Head-to-head" (1%). Intervals between successive egg deposition behaviors were clearly bimodal, with modes at 2.5 s and 70.0 s. Ninety-three percent of egg capsules contained 3 or 4 eggs (mean = 3.54), and each egg cluster contained between 218 and 1922 egg capsules (mean = 893.9). The reproductive behavior of S. australis from South Australia was different from that described for other cephalopod species. More importantly, comparison between these results and those for other populations of S. australis suggests that behavior may differ from one population to another.

Agonistic Behavior↗
PubMed1990

[The selection of sexual partners of different species by mammals].

It appears biologically sensible that every animal seeks its mating partner within its own species. Sexual contact with alien species may occur when animals are isolated from members of their own species, particularly, however, after they have been raised in the environment of alien species. Copulations of this nature do not, as a rule, result in offspring, although an entire series of bastards among closely related species is known. Among domestic animals bastardization is partly planned systematically as this has advantages in comparison to original forms. Sodomy, i.e. interspecific sexual contact between a human being and an animal, was already described in ancient times.

Animals↗
PubMed2006

Long tails affect swimming performance and habitat choice in the male guppy.

Sexual selection often favors male secondary sexual traits, although in some cases the elaborate traits incur costs to the males with respect to natural selection. Males of the guppy Poecilia reticulata have longer tails (caudal fins) than females, and the long tails contribute to the mating success of the males through female mate choice. We examined the effect of tail length on the swimming performance of male and female guppies. In a laboratory experiment, males with longer tails exhibited poorer swimming performance than those with shorter tails. However, this effect was not apparent in females. In addition, in a feral population, tail length of males was negatively correlated with water flow velocity in their microhabitats. Although body size of females was negatively correlated with water flow velocity in their microhabitats, tail length of females showed no significant correlation with degree of water flow. These results suggest that the long tail of male guppies incurs costs, such as a decrease in swimming performance, to the males with respect to natural selection and consequently limits their choice of habitats to those with slow water flow.

Animals↗
PubMed2005

Testosterone, testes size, and mating success in birds: a comparative study.

Reproductive behaviors of vertebrates are often underpinned by temporal patterns of hormone secretion. We investigated interspecific patterns of circulating testosterone in male birds to test the hypothesis that testosterone plays a crucial role in sexual selection as determined by degree of polygyny and extra-pair paternity. We predicted that the evolution of increased levels of polygyny and extra-pair paternity would have resulted in the evolution of increased levels of testosterone to allow males more efficiently to compete for mates. This hypothesis was tested in comparative analyses of 116 species of birds using Generalized Least Squares Models. We assessed the importance of latitudinal distribution, because this can confound the relationship between testosterone and mating success. There were weak positive phylogenetic correlations between measures of testosterone and estimates of mating success at the social level, but this association appeared to be confounded by latitudinal distribution, a significant correlate of testosterone titers. However, we found a significantly positive relationship between peak and residual peak testosterone (which is the peak testosterone level that is controlled for the baseline level) and extra-pair paternity independent of latitude. These results suggest that selection pressures arising from social and sexual mating differently affected testosterone levels with the former being mediated by factors associated with latitudinal distribution. An analysis of residual testes size revealed a positive association between peak and residual testosterone and testes size relative to body size. In a path analysis, we show that relative testis size primarily evolved in association with intense sperm competition and thus high sperm production, and these mechanisms had a secondary impact on blood testosterone levels at a phylogenetic scale. Our results suggest that sperm competition has played an important role in the evolution of reproductive mechanisms in birds.

Analysis of Variance↗
PubMed2003

Paternity analysis reveals opposing selection pressures on crown coloration in the blue tit (Parus caeruleus).

In socially monogamous species, extra-pair paternity can increase the variance in reproductive success and thereby the potential for sexual selection on male ornaments. We studied whether male secondary sexual ornaments are selected through within- and/or extra-pair reproductive success in the blue tit (Parus caeruleus). Male blue tits display a bright blue crown plumage, which reflects substantially in the ultraviolet (UV) and previously has been indicated to be an important sexual signal. We show that males with a more UV-shifted crown hue were less cuckolded, which probably resulted from female preference for more ornamented mates. By contrast, however, older males and males with a less UV-shifted hue sired more extra-pair young. This probably did not reflect direct female preference, since cuckolders were not less UV-ornamented than the males they cuckolded. Alternatively, a trade-off between UV ornamentation and other traits that enhance extra-pair success could explain this pattern. Our results might reflect two alternative male mating tactics, where more UV-ornamented males maximize within-pair success and less UV-ornamented males maximize extra-pair success. Since crown colour was selected in opposite directions by within-pair and extra-pair paternity, directional selection through extra-pair matings seemed weak, at least in this population and breeding season. Reduced intensity of sexual selection due to alternative mating tactics constitutes a potential mechanism maintaining additive genetic variance of male ornaments.

Animals↗
PubMed2005

Assessing the potential for an ongoing arms race within and between the sexes: selection and heritable variation.

In promiscuous species, sexual selection generates two opposing male traits: offense (acquiring new mates and supplanting stored sperm) and defense (enforcing fidelity on one's mates and preventing sperm displacement when this fails). Coevolution between these traits requires both additive genetic variation and associated natural selection. Previous work with Drosophila melanogaster found autosomal genetic variation for these traits among inbred lines from a mixture of populations, but only nonheritable genetic variation was found within a single outbred population. These results do not support ongoing antagonistic coevolution between offense and defense, nor between either of these male traits and female reproductive characters. Here we use a new method (hemiclonal analysis) to study genomewide genetic variation in a large outbred laboratory population of D. melanogaster. Hemiclonal analysis estimates the additive genetic variation among random, genomewide haplotypes taken from a large, outbred, locally adapted laboratory population and determines the direction of the selection gradient on this variation. In contrast to earlier studies, we found low but biologically significant heritable variation for defensive and offensive offspring production as well as all their components (P1, fidelity, P2, and remating). Genetic correlations between these traits were substantially different from those reported for inbred lines. A positive genetic correlation was found between defense and offense, demonstrating that some shared genes influence both traits. In addition to this common variation, evidence for unique genetic variation for each trait was also found, supporting an ongoing coevolutionary arms race between defense and offense. Reproductive conflict between males can strongly influence female fitness. Correspondingly, we found genetic variation in both defense and offense that affected female fitness. No evidence was found for intersexual conflict in the context of male defense, but we found substantial intersexual conflict in the context of male offensive sperm competitive ability. These results indicate that conflict between competing males also promotes an associated arms race between the sexes.

Analysis of Variance↗
PubMed1998

Sex and conflict.

Evolutionary conflict occurs when the deterministic spread of an allele lowers the fitness either of its bearer or of other individuals in the population, leading to selection for suppressors. Sex promotes conflict because associations between alleles are temporary. Differing selection on males and females, sexual selection, and differences in transmission patterns between classes of nuclear and cytoplasmic genes can all give rise to conflict. Inert Y chromosomes, uniparental inheritance of cytoplasmic genes, mating strains and sexes, and many features of sexual behavior may have evolved in part as a result of evolutionary conflict. Estimates of its quantitative importance, however, are still needed.

Alleles↗
PubMed2003

Genetic variance and phenotypic plasticity in a component of female mate choice in an ultrasonic moth.

Female response to male advertisement signals in lesser waxmoths showed substantial genetic variation, phenotypic plasticity across rearing environments, and genotype-by-environment interactions resulting in crossing reaction norms. These results represent two previously underemphasized means by which genetic variation may be maintained in sexually selected traits: genetic variation in female response to male traits, and variation in the selection acting on both males and females. Genotype-by-environment interactions and reaction norms that cross indicate that divergent selection may act on male and female sexual traits if the level of environmental change is high. The processes that contribute to the maintenance of genetic variation may thus also contribute to population differentiation.

Analysis of Variance↗
PubMed2004

Direct selection on male attractiveness and female preference fails to produce a response.

BACKGROUND: Theoretical studies suggest that direct and indirect selection have the potential to cause substantial evolutionary change in female mate choice. Similarly, sexual selection is considered a strong force in the evolution of male attractiveness and the exaggeration of secondary sexual traits. Few studies have, however, directly tested how female mate choice and male attractiveness respond to selection. Here we report the results of a selection experiment in which we selected directly on female mating preference for attractive males and, independently, on male attractiveness in the guppy, Poecilia reticulata. We measured the direct and correlated responses of female mate choice and male attractiveness to selection and the correlated responses of male ornamental traits, female fecundity and adult male and female survival. RESULTS: Surprisingly, neither female mate choice nor male attractiveness responded significantly to direct or to indirect selection. Fecundity did differ significantly among lines in a way that suggests a possible sexually-antagonistic cost to male attractiveness. CONCLUSIONS: The opportunity for evolutionary change in female mate choice and male attractiveness may be much smaller than predicted by current theory, and may thus have important consequences for how we understand the evolution of female mate choice and male attractiveness. We discuss a number of factors that may have constrained the response of female choice and male attractiveness to selection, including low heritabilities, low levels of genetic (co)variation in the multivariate direction of selection, sexually-antagonistic constraint on sexual selection and the "environmental covariance hypothesis".

Animals↗
PubMed2002

The evolution of alternative cryptic female choice strategies in age-structured populations.

Cryptic female choice is a potentially important aspect of the sexual selection process. According to the theory of sexual dialectics, postcopulation manipulation of relative male fertilization success can provide an avenue by which females can circumvent attempts by males to control female reproduction. Here I use stochastic models to investigate the evolution of cryptic female choice in populations with and without age structure. In populations without age structure, cryptic female choice will evolve only when (1) precopulatory mate choice by females is inefficient, (2) variation in male fitness is correlated with a trait upon which a female can base her choice of mates, and (3) the cost of multiple mating is not too high. In populations with age structure, similar conditions apply. However, selection sometimes favors females that employ alternative strategies of female choice at different ages. These results help to define the types of biological systems in which we should expect to see the evolution of cryptic female choice. They also illustrate that the evolution of choice strategies in females may be complex and may mirror in some important respects the evolution of alternative mating tactics in males.

Age Factors↗
PubMed2000

Sexually transmitted diseases in polygynous mating systems: prevalence and impact on reproductive success.

Studies of disease in relation to animal mating systems have focused on sexual selection and the evolution of sexual reproduction. Relatively little work has examined other aspects of ecological and evolutionary relationships between host social and sexual behaviour, and dynamics and prevalence of infectious diseases; this is particularly evident with respect to sexually transmitted diseases (STDs). Here, we use a simulation approach to investigate rates of STD spread in host mating systems ranging from permanent monogamy to serial polygyny or polyandry and complete promiscuity. The model assumes that one sex (female) is differentially attracted to the other, such that groups of varying size are formed within which mating and disease transmission occur. The results show that equilibrium disease levels are generally higher in females than males and are a function of variance in male mating success and the likelihood of a female switching groups between mating seasons. Moreover, initial rates of disease spread (determining whether an STD establishes in a population) depend on patterns of host movement between groups, variance in male mating success and host life history (e.g. mortality rates). Male reproductive success can be reduced substantially by a sterilizing STD and this reduction is greater in males that are more 'attractive' to females. In contrast, females that associate with more attractive males have lower absolute fitness than females associating with less attractive males. Thus, the potential for STDs to act as a constraint on directional selection processes leading to polygyny (or polyandry) is likely to depend on the details of mate choice and group dynamics.

Animals↗
PubMed1986

The relationship between the sexual attitudes of parents and their college daughters' or sons' sexual attitudes and sexual behavior.

This study determined if three selected sexual attitudes of parents were related to similar sexual attitudes of their college daughters or sons and to five sexual behaviors. Only never married, college freshmen (N = 83) with both parents participating were utilized. A self-report questionnaire was administered to students at a large midwestern university and distributed to and returned from parents by mail. The Pearson product-moment correlation and the stepwise and multiple regressions were used to test four hypotheses. Mothers' sexual attitudes had a stronger relationship than fathers' attitudes with offspring sexual attitudes and behaviors, particularly for daughters. Generally, mothers with the most positive attitudes toward sexual-self had daughters who were more responsive relative to personal sexual expression (masturbation frequency and orgasmic experience), but who were not any more involved heterosexually (frequency of coitus and number of coital partners). Fathers' sexual attitudes had little relationship to offspring sexual attitudes and behavior. None of the male students' sexual behaviors were related strongly to parent sexual attitudes. Implications for school and parent sexuality education programs are briefly discussed.

Adolescent↗
PubMed2005

Sex differences in the neural correlates of child facial resemblance: an event-related fMRI study.

Detection of genetic relatedness (i.e. kinship) impacts the social, parental, and sexual behavior of many species. In humans, self-referent phenotype matching based on facial resemblance may indicate kinship. For example, faces that resemble ours are perceived as more trustworthy and attractive. Sex differences in behavioral reactions to facial resemblance among children have also been demonstrated and are consistent with evolutionary theory suggesting that resemblance might serve as a paternity cue. Using event-related fMRI, we show that specific regions of the brain are implicated in processing facial resemblance and a sex difference in cortical response to facial resemblance expressed in children. We found a consistent activation in the fusiform gyrus across all face conditions, which is consistent with previous research on face processing. There were no sex differences in overall response to faces in the fusiform gyrus, and also to faces that did not resemble subjects. When resemblance was not modeled, females showed greater activation to child faces than males. Consistent with parental investment theory and theories of sexual selection, males showed greater cortical activity than females in response to children's faces that resembled them. These data suggest natural selection may have crafted a sexually differentiated neuro-sensory module implicated in detection of facial resemblance that may serve as a kin detection and paternity cue. This process may capitalize on neural substrates involved in self-referent processing and familiarity detection.

Adult↗
PubMed2005

Fitness correlates of song repertoire size in free-living song sparrows (Melospiza melodia).

Models of sexual selection propose that exaggerated secondary sexual ornaments indicate a male's own fitness and the fitness of his offspring. These hypotheses have rarely been thoroughly tested in free-living individuals because overall fitness, as opposed to fitness components, is difficult to measure. We used 20 years of data from song sparrows (Melospiza melodia) inhabiting Mandarte Island, British Columbia, Canada, to test whether a male's song repertoire size, a secondary sexual trait, predicted overall measures of male or offspring fitness. Males with larger song repertoires contributed more independent and recruited offspring, and independent and recruited grandoffspring, to Mandarte's population. This was because these males lived longer and reared a greater proportion of hatched chicks to independence from parental care, not because females mated to males with larger repertoires laid or hatched more eggs. Furthermore, independent offspring of males with larger repertoires were more likely to recruit and then to leave more grandoffspring than were offspring of males with small repertoires. Although we cannot distinguish whether observed fitness variation reflected genetic or environmental effects on males or their offspring, these data suggest that female song sparrows would gain immediate and intergenerational fitness benefits by pairing with males with large song repertoires.

Animals↗