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Results for “Sexual selection”

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PubMed2002

Frequency-dependent selection in sexual family-structured populations.

In this paper, a two-phenotype, single-locus, n -allele matrix game diploid model incorporating interactions between full sibs influencing personal fitness is investigated. Necessary and sufficient conditions for an ESS are given. We show that if a strategy is an ESS for this model with the payoff matrix A, then it must be an ESS for the standard game formulation with payoff matrix A+(r/2) A(T) where r is the probability to interact with a sib, but it is also possible that no ESS exists. Moreover, under the assumption of weak selection, the partial change in phenotype frequencies brings the population closer to an ESS when it exists.

Altruism↗

PubMed2005

Psychology: red enhances human performance in contests.

Red coloration is a sexually selected, testosterone-dependent signal of male quality in a variety of animals, and in some non-human species a male's dominance can be experimentally increased by attaching artificial red stimuli. Here we show that a similar effect can influence the outcome of physical contests in humans--across a range of sports, we find that wearing red is consistently associated with a higher probability of winning. These results indicate not only that sexual selection may have influenced the evolution of human response to colours, but also that the colour of sportswear needs to be taken into account to ensure a level playing field in sport.

Aggression↗

PubMed2004

The modern theory of biological evolution: an expanded synthesis.

In 1858, two naturalists, Charles Darwin and Alfred Russel Wallace, independently proposed natural selection as the basic mechanism responsible for the origin of new phenotypic variants and, ultimately, new species. A large body of evidence for this hypothesis was published in Darwin's Origin of Species one year later, the appearance of which provoked other leading scientists like August Weismann to adopt and amplify Darwin's perspective. Weismann's neo-Darwinian theory of evolution was further elaborated, most notably in a series of books by Theodosius Dobzhansky, Ernst Mayr, Julian Huxley and others. In this article we first summarize the history of life on Earth and provide recent evidence demonstrating that Darwin's dilemma (the apparent missing Precambrian record of life) has been resolved. Next, the historical development and structure of the "modern synthesis" is described within the context of the following topics: paleobiology and rates of evolution, mass extinctions and species selection, macroevolution and punctuated equilibrium, sexual reproduction and recombination, sexual selection and altruism, endosymbiosis and eukaryotic cell evolution, evolutionary developmental biology, phenotypic plasticity, epigenetic inheritance and molecular evolution, experimental bacterial evolution, and computer simulations (in silico evolution of digital organisms). In addition, we discuss the expansion of the modern synthesis, embracing all branches of scientific disciplines. It is concluded that the basic tenets of the synthetic theory have survived, but in modified form. These sub-theories require continued elaboration, particularly in light of molecular biology, to answer open-ended questions concerning the mechanisms of evolution in all five kingdoms of life.

Animals↗

PubMed2002

How well do mating frequency and duration predict paternity success in the polygynandrous water strider Aquarius remigis?

The relationship between mating success and paternity success is a key component of sexual selection but has seldom been estimated for species in which both sexes mate with many partners (polygynandry). We used a modification of Parker's sterile male technique to measure this relationship for the water strider Aquarius remigis in 47 laboratory populations simulating natural conditions of polygynandry. We also tested the hypothesis that prolonged copulation, a characteristic of this species, enhances paternity success. Mating behavior and paternity success were assayed for four days while males and females freely interacted. Paternity success was also assayed for an additional 7 days when females were isolated from males. Mating success significantly predicted paternity success and accounted for < or = 36% of the variance. Copulation duration was negatively related to both mating success and paternity success and did not explain any of the residual variance in paternity success. Thus, we found no evidence that prolonged copulation functions as a paternity assurance strategy in this species. Comparisons of sterile and fertile males suggested that paternity success is directly influenced by the quantity of sperm transferred. Our results support previous studies that have used mating success to estimate sexual selection, but also highlight the potential importance of sperm competition and other postinsemination processes.

Animals↗

PubMed1999

Population density influences male-male competition in guppies.

This study tested the general prediction that population density affects male-male competition, female mate choice and the opportunity for sexual selection. By manipulating the density of guppies, Poecilia reticulata, while keeping the sex ratio constant, I found that male mating tactics were phenotypically plastic with respect to density. As density increased, males decreased their courtship displays. Male-male competition and mate searching were highest at intermediate densities. Population density had no significant effect on the total number of copulations, copulatory tactics or the percentage of postcopulatory guarding. Female preference for males with a higher percentage of orange coloration was similar at all density levels. The 'opportunity for sexual selection', which estimates the upper limit to which a selected trait can shift if directional selection is operating and was calculated as the variance in number of copulations per male divided by the square of the mean number of copulations, was negatively associated with population density. This may be due to the decrease in male-male competition at high density rather than female preference which was similar across density treatments. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed2004

The species flocks of East African cichlid fishes: recent advances in molecular phylogenetics and population genetics.

With more than 3,000 species, the fish family Cichlidae is one of the most species-rich families of vertebrates. Cichlids occur in southern and central America, Africa, Madagascar, and India. The hotspot of their biodiversity is East Africa, where they form adaptive radiations composed of hundreds of endemic species in several lakes of various sizes and ages. The unparalleled species richness of East African cichlids has been something of a conundrum for evolutionary biologists and ecologists, since it has been in doubt whether these hundreds of species arose by allopatric speciation or whether it is necessary to invoke somewhat less traditional models of speciation, such as micro-allopatric, peripatric, or even sympatric speciation or evolution through sexual selection mediated by female choice. Ernst Mayr's analyses of these evolutionary uniquely diverse species assemblages have contributed to a more direct approach to this problem and have led to a deeper understanding of the patterns and processes that caused the formation of these huge groups of species. We review here recent molecular data on population differentiation and phylogenetics, which have helped to unravel, to some extent, the patterns and processes that led to the formation and ecological maintenance of cichlid species flocks. It is becoming apparent that sexually selected traits do play an important role in speciation in micro-allopatric or even sympatric settings. Species richness seems to be roughly correlated with the surface area, but not the age, of the lakes. We observe that the oldest lineages of a species flock of cichlids are often less species-rich and live in the open water or deepwater habitats. While the species flocks of the Lake Malawai and the Lake Victoria areas were shown to be monophyletic, the cichlid assemblage of Lake Tanganyika seems to consist of several independent species flocks. Cichlids emerge as an evolutionary model system in which many fundamental questions in evolution and ecology can be tested successfully, yet for other fish species flocks the relative importance of alternative mechanisms of speciation is likely to differ from that in cichlid fish.

Africa, Eastern↗

PubMed2005

Gene conversion drives the evolution of HINTW, an ampliconic gene on the female-specific avian W chromosome.

The HINTW gene on the female-specific W chromosome of chicken and other birds is amplified and present in numerous copies. Moreover, as HINTW is distinctly different from its homolog on the Z chromosome (HINTZ), is a candidate gene in avian sex determination, and evolves rapidly under positive selection, it shows several common features to ampliconic and testis-specific genes on the mammalian Y chromosome. A phylogenetic analysis within galliform birds (chicken, turkey, quail, and pheasant) shows that individual HINTW copies within each species are more similar to each other than to gene copies of related species. Such convergent evolution is most easily explained by recurrent events of gene conversion, the rate of which we estimated at 10(-6)-10(-5) per site and generation. A significantly higher GC content of HINTW than of other W-linked genes is consistent with biased gene conversion increasing the fixation probability of mutations involving G and C nucleotides. Furthermore, and as a likely consequence, the neutral substitution rate is almost twice as high in HINTW as in other W-linked genes. The region on W encompassing the HINTW gene cluster is not covered in the initial assembly of the chicken genome, but analysis of raw sequence reads indicates that gene copy number is significantly higher than a previous estimate of 40. While sexual selection is one of several factors that potentially affect the evolution of ampliconic, male-specific genes on the mammalian Y chromosome, data from HINTW provide evidence that gene amplification followed by gene conversion can evolve in female-specific chromosomes in the absence of sexual selection. The presence of multiple and highly similar copies of HINTW may be related to protein function, but, more generally, amplification and conversion offers a means to the avoidance of accumulation of deleterious mutations in nonrecombining chromosomes.

Animals↗

PubMed2001

Testosterone influences basal metabolic rate in male house sparrows: a new cost of dominance signalling?

Sexually selected signals of individual dominance have profound effects on access to resources, mate choice and gene flow. However, why such signals should honestly reflect individual quality is poorly understood. Many such signals are known to develop under the influence of testosterone. We conducted an experiment in male house sparrows in which testosterone was manipulated independently during two periods: before the onset of the breeding season and prior to the autumn moult. We then measured the effects of these manipulations on basal metabolic rate and on the size of the chest bib, a sexually selected signal. The results demonstrate that testosterone simultaneously affects both signal development and basal metabolic rate in the house sparrow (Passer domesticus). This evidence, therefore, supports a novel conclusion: that testosterone-dependent signals act as honest indicators of male quality possibly because only high-quality individuals can sustain the energetic costs associated with signal development.

Animals↗

PubMed1999

DNA analyses support the hypothesis that infanticide is adaptive in langur monkeys.

Although the killing of dependent infants by adult males is a widespread phenomenon among primates, its causes and consequences still remain hotly debated. According to the sexual selection hypothesis, infanticidal males will gain a reproductive advantage provided that only unrelated infants are killed and that the males increase their chances of siring the next infants. Alternatively, the social pathology hypothesis interprets infanticide as a result of crowded living conditions and, thus, as not providing any advantage. Based on DNA analyses of wild Hanuman langurs (Presbytis entellus) we present the first evidence that male attackers were not related to their infant victims. Furthermore, in all cases the presumed killers were the likely fathers of the subsequent infants. Our data, therefore, strongly support the sexual selection hypothesis interpreting infanticide as an evolved, adaptive male reproductive tactic.

Adaptation, Biological↗

PubMed2005

Rapid evolution of postzygotic reproductive isolation in stalk-eyed flies.

We test the relative rates of evolution of pre- and postzygotic reproductive isolation using eight populations of the sexually dimorphic stalk-eyed flies Cyrtodiopsis dalmanni and C. whitei. Flies from these populations exhibit few morphological differences yet experience strong sexual selection on male eyestalks. To measure reproductive isolation we housed one male and three female flies from within and between these populations in replicate cages and then recorded mating behavior, sperm transfer, progeny production, and hybrid fertility. Using a phylogeny based on partial sequences of two mitochondrial genes, we found that premating isolation, postmating isolation prior to hybrid eclosion, and female hybrid sterility evolve gradually with respect to mitochondrial DNA sequence divergence. In contrast, male hybrid sterility evolves much more rapidly-at least twice as fast as any other form of reproductive isolation. Hybrid sterility, therefore, obeys Haldane's rule. Although some brood sex ratios were female biased, average brood sex ratio did not covary with genetic distance, as would be expected if hybrid inviability obeyed Haldane's rule. The likelihood that forces including sexual selection and intra- and intergenomic conflict may have contributed to these patterns is discussed.

Animals↗

PubMed1997

Facial asymmetry as an indicator of psychological, emotional, and physiological distress.

Fluctuating asymmetry (FA) is deviation from bilateral symmetry in morphological traits with asymmetry values that are normally distributed with a mean of 0. FA is produced by genetic or environmental perturbations of developmental design and may play a role in human sexual selection. K. Grammer and R. Thornhill (1994) found that facial FA negatively covaries with observer ratings of attractiveness, dominance, sexiness, and health. Using self-reports, observer ratings, daily diary reports, and psychophysiological measures, the authors assessed the relationship between facial FA and health in 2 samples of undergraduates (N = 101). Results partially replicate and extend those of K. Grammer and R. Thornhill (1994) and suggest that facial FA may signal psychological, emotional, and physiological distress. Discussion integrates the authors' findings with previous research on FA and suggests future research needed to clarify the role of FA in human sexual selection.

Adolescent↗

PubMed2004

Effects of developmental environment on signal-preference coupling in a Hawaiian cricket.

Previous work has suggested that developmental temperature influences expression of the adult male calling song of the cricket, a sexually selected mate recognition signal. The role of developmental temperature in shaping female preference functions, and thus its influence on signal-preference coupling has not been investigated. In this study, the effects of developmental temperature are examined in both males and females of the Hawaiian cricket, Laupala cerasina, to determine the degree of signal-preference matching between male song and female preference due to developmental environment. We found that rearing females in different temperature environments affected adult female acoustic preference functions in the same direction as male calling song, thereby influencing variation in adult reproductive behavior in such a way that male and female components remain coordinated. However, we further demonstrate that for male song, the effect of the rearing environment is not permanent but appears only to exert influence for a period of days. This mid-term temperature effect is distinct from the effect of short-term ambient temperature, which influences song in a matter of minutes and has been well documented. Signal-preference coordination, and sexual selection pressures due to mismatching within natural populations, likely will be influenced by nymphal developmental environments of males and females, as well as by adult singing and preference environments.

Animal Communication↗

PubMed2006

Adaptive genetic complementarity in mate choice coexists with selection for elaborate sexual traits.

Choice of genetically unrelated mates is widely documented, yet it is not known how self-referential mate choice can co-occur with commonly observed directional selection on sexual displays. Across 10 breeding seasons in a wild bird population, we found strong fitness benefits of matings between genetically unrelated partners and show that self-referential choice of genetically unrelated mates alternates with sexual selection on elaborate plumage. Seasonal cycles of diminishing variation in ornamentation, caused by early pairing of the most elaborated males, and influx of increasingly genetically unrelated available mates caused by female-biased dispersal, lead to temporal fluctuations in the target of mate choice and enabled coexistence of directional selection for ornament elaboration with adaptive pairing of genetically unrelated partners.

Adaptation, Physiological↗

PubMed2002

Quality of song learning affects female response to male bird song.

Bird song is unusual as a sexually selected trait because its expression depends on learning as well as genetic and other environmental factors. Prior work has demonstrated that males who are deprived of the opportunity to learn produce songs that function little if at all in male-female interactions. We asked whether more subtle variation in male song-learning abilities influences female response to song. Using a copulation solicitation assay, we measured the response of female song sparrows (Melospiza melodia) to songs of laboratory-reared males that differed in the amount of learned versus invented material that they included and in the degree to which learned material accurately matched the model from which it was copied. Females responded significantly more to songs that had been learned better, by either measure. Females did not discriminate between the best-learned songs of laboratory-reared males and songs of wild males used as models during learning. These results provide, to our knowledge, a first experimental demonstration that variation in learning abilities among males plays a functionally important part in the expression of a sexually selected trait, and further provide support for the hypothesis that song functions as an indicator of male quality because it reflects variation in response to early developmental stress.

Animals↗

PubMed2005

The evolution of male genitalia: patterns of genetic variation and covariation in the genital sclerites of the dung beetle Onthophagus taurus.

Three main hypotheses, have been invoked to explain divergent genital evolution, the lock and key, pleiotropy, and sexual selection hypotheses, each of which make different predictions about how genital traits are inherited. Here we used a half-sib breeding design to examine the patterns of genetic variation and covariation between male genital sclerites, and their covariance with general body morphology in the dung beetle Onthophagus taurus. We found CV(A)'s and CV(P)'s were similar for both genital and general morphological traits and that CV(R)'s were large for both trait types. We found that male genital sclerites were negatively genetically correlated with general morphological traits. Variation in male genital morphology has direct implications for a male's fertilization success and the resulting sexual selection acting on male genitalia is predicted to maintain high levels of additive genetic variance. Contrary to this prediction, we found that individual genital sclerites all had low levels of additive genetic variance and large maternal and environmental sources of variation. Our data suggest that the genital sclerites in O. taurus are not inherited independently but as a genetically integrated unit. More importantly, the way the different sclerites function to influence male fertilization success reflects this genetic integration. Even though levels of V(A) in individual genital sclerites may be low, there may still be sufficient V(A) in multivariate trait space for selection to generate evolutionary change in the overall morphology of male genitalia.

Animals↗

PubMed2004

Male heterozygosity predicts territory size, song structure and reproductive success in a cooperatively breeding bird.

Recent studies of non-social animals have shown that sexually selected traits signal at least one measure of genetic quality: heterozygosity. To determine whether similar cues reveal group quality in more complex social systems, we examined the relationship between territory size, song structure and heterozygosity in the subdesert mesite (Monias benschi), a group-living bird endemic to Madagascar. Using nine polymorphic microsatellite loci, we found that heterozygosity predicted both the size of territories and the structure of songs used to defend them: more heterozygous groups had larger territories, and more heterozygous males used longer, lower-pitched trills in their songs. Heterozygosity was linked to territory size and song structure in males, but not in females, implying that these traits are sexually selected by female choice and/or male-male competition. To our knowledge, this study provides the first direct evidence in any animal that territory size is related to genetic diversity. We also found a positive association between seasonal reproductive success and heterozygosity, suggesting that this heritable characteristic is a reliable indicator of group quality and fitness. Given that heterozygosity predicts song structure in males, and can therefore be determined by listening to acoustic cues, we identify a mechanism by which social animals may assess rival groups, prospective partners and group mates, information of potential importance in guiding decisions related to conflict, breeding and dispersal.

Animals↗

PubMed2002

New cases of inter-community infanticide by male chimpanzees at Ngogo, Kibale National Park, Uganda.

Infanticide by males has been recorded in four chimpanzee populations, including that in Kibale National Park, Uganda. Some infanticidal attacks occur during inter-community aggression. The sexual selection hypothesis does not easily explain these attacks because they may not directly increase male mating opportunities. However, females in the attackers' community may benefit by expanding their foraging ranges and thereby improving their reproductive success; thus infanticide may increase male reproductive success indirectly. We report two new cases of infanticide by male chimpanzees at Ngogo, Kibale National Park. Like two previous cases, these occurred during a boundary patrol and were almost certainly between-community infanticides. The patrolling males attacked despite the proximity of males from the victims' presumed community. This probably explains why, unlike the earlier cases, they did not completely cannibalize their victims. Such attacks seem to be relatively common at Ngogo and infanticide may be an important source of infant mortality in neighboring communities. Our observations cannot resolve questions about the sexual selection hypothesis. However, they are consistent with the range expansion hypothesis: the infanticides occurred during a period of frequent encounters between communities associated with a mast fruiting event, and Ngogo community members greatly increased their use of areas near the attack site during another mast fruiting event one year later. Our observations contribute to growing evidence that lethal intergroup aggression is a common characteristic of wild chimpanzee populations.

Aggression↗

PubMed1994

Natural space-use patterns and hippocampal size in kangaroo rats.

The size of the hippocampus, a forebrain structure that processes spatial information, correlates with the need to relocate food caches by passerine birds and with sex-specific patterns of space use in microtine rodents. The influences on hippocampal anatomy of sexual selection within species, and natural selection between species, have not yet been studied in concert, however. Here we report that natural space-use patterns predict hippocampal size within and between two species of kangaroo rats (Dipodomys). Differences in foraging behavior suggest that Merriam's kangaroo rats (D. merriami) require better spatial abilities than bannertail kangaroo rats (D. spectabilis). Sex-specific differences in mating strategy suggest that males of both species require more spatial ability than females. As predicted, hippocampal size (relative to brain size) is larger in Merriam's than in bannertail kangaroo rats, and males have larger hippocampi than females in both species. Males of a third species (D. ordii) also have smaller hippocampi than Merriam's kangaroo rat males, despite being similar to Merriam's in brain and body size. These results suggest that both natural and sexual selection affect the relative size and perhaps function of mammalian hippocampi. They also reassert that measures of functional subunits of the brain reveal more about brain evolution than measures of total brain size.

Animals↗