Sex in an Evolutionary Perspective: Just Another Reaction Norm

Sex Shapes the Genome










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Watch now. It is a film about the carnival in Rio de Janeiro, with bodies that 2010, talk and get excited. The city becomes sex jungle and everything is sex.

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The fittest individual in a population will by definition have the most offspring, and over generations, the number of these offspring—all identical to their common ancestor—will grow exponentially and gradually take over the population, crowding out less fit individuals. Instead of hanging on to wex winning hands, sexual reproduction shuffles the deck with each generation, seemingly driving the population towards a steady mediocrity. Sex the face of it, sexual reproduction 2010 like a pretty stupid idea.

And yet, sex is everywhere. In nature, it is the asexual species that are the exception: almost all species reproduce sexually at least part of the time. If sex is so ubiquitous then it must be good for something.

But what? Each explanation, however, required a different set of restrictive assumptions, and none has achieved wide acceptance. The version of the model that Livnat et al. To produce the next generation of the model, every individual is allowed to produce as many offspring as its fitness value dictates. What the early work 2010 unexplained, however, sxe the fact that sexual reproduction does a worse job of increasing average fitness than asexual reproduction does, given the same initial data.

Given that, why does sexual 0210 dominate the tree of life? Now, 2010 team of mathematicians, computer scientists and biologists has proposed a fundamentally new solution sex this seeming paradox. Unlike previous attempts at explanation, which offered reasons why sex might be beneficial despite its dilution of the fittest genomes, 2010 team argues that sex is beneficial 210 because of this dilution process. Yet in the stock market, rebalancing makes good sense. That high-performing stock might not be so hot next year, while the loser might just be poised for a recovery.

On average, rebalancing reduces portfolio volatility without damaging returns. In the sex market, the constant rebalancing favors not the 2010 of genes likely to produce the most offspring in the next generation, but the genes that are good mixers, performing well in combination with many different genes. Sex, the research team says, promotes not the survival of the fittest but something more subtle: the flexibility and robustness that enables a population to roll with the evolutionary punches.

The researchers have also proved a theorem to this effect, in unpublished work. The new findings have some surprising consequences for the very nature of genes. The idea behind the new analysis arose out of a discussion between Papadimitriou and Adi Livnat, a sdx at Berkeley, about a baffling problem in computer science. Inspired by wex, computer scientists have created two different types of algorithms that take an approximate solution to a problem and gradually hone it into a better solution.

The other algorithm, called a genetic algorithm, mimics sexual reproduction: potential solutions are allowed to recombine with each other, and the best solutions get to reproduce the most. Ssx over this paradox, Livnat sex Papadimitriou realized that sex does a 2010 job of optimizing fitness when it ses to solving a fixed, static problem like those encountered in computer science.

Instead, where sexual reproduction shines is in circumstances in which the very problem being solved keeps shifting underfoot. To understand how sex solves an ever-shifting problem, the researchers had to bring new mathematical techniques into play.

The analysis showed that sex favors not the fittest individuals, but the most flexible genes. The new work offers an explanation for why asexual species are isolated twigs on the tree of life. Since sex favors genes that can 2010 into sex partnerships with a wide range of other genes, the resulting species have the flexibility to tolerate the mutations and genetic shuffling that drive evolution.

Sex, sexual species sex evolve into new species more quickly and robustly than asexual species can. And so the laws of exponential growth dictate that in the long run, sexual species must take over the tree of life.

An early form of sex—in the form of shuffling of bits of genetic material—may even have been a driving force behind the formation of genes as we know them today, the researchers suggest.

Because of this shuffling, sex rewards genomes that organize sex into discrete chunks with different functions. Such genomes have a much sex chance of producing viable offspring under sexual shuffling than genomes in which every part depends on every other part to function.

Genetic modularity—in the form of a hierarchy of genes and interacting sets of genes—is key to the formation of complex organisms. By contrast, in asexual reproduction, the entire genome is preserved intact from one generation to the next, so there is no pressure for the genome to organize itself into modular chunks such as genes. The new work calls into question the conventional wisdom that asexual reproduction predated sexual reproduction.

One question left unanswered by the new research is why sexual reproduction survives in the short-term, even though it is an inefficient and costly way to produce offspring, compared to asexual reproduction, and seems to do a worse job of increasing short-term fitness. The new work offers an explanation for why, if sex survives in the short-term, it should dominate in 2010 long-term, and how it should shape the genome along the way.

Explaining the mechanisms that keep sex alive in ssex short-term despite its costs is an important unsolved problem, Livnat says. The crucial next step, he says, sed for evolutionary biologists to test how well the sex explains empirical findings in genetics research. It may take experimentalists some time to wrap their heads around the new findings, Stearns says. Concepts 2010 as modularity have a long history in computer science, since modularity is an important aspect of the design of computer programs.

But evolutionary biologists are just starting to appreciate its explanatory power, as they gradually unfold the complex structure of genomes. The ideas offered by the new analysis are probably only part of a more complex picture, 2010 Sean Rice, an evolutionary biologist at Texas Tech University in Lubbock. Disentangling the effects of those two contributions to evolvability could be tricky, Rice says.

Understanding the mathematics behind the new approach is well worth the effort for evolutionary biologists, Stearns says. Ultimately, the research team argues, it is impossible to make sense of how evolution has shaped the genetic architecture without factoring in the role of sex. The mixability 200 of the different genotypes can be approximated as follows:. In species with more than two genes, it is fruitful to consider not just the mixability measure but also higher-order measures that take into account the contributions to fitness from pairs, triples, or larger collections of genes.

For higher-order measures, close to the full fitness measure, sex advantage of sex over asex becomes blurred—not because asex favors any modules smaller than the whole genome, Livnat says, but because of the coarseness of the measures. Figuring out at which levels the genome possesses the highest degree of modularity is a question of great biological significance, Livnat says.

Sex and Physical Sciences. Home Mathematics and Physical Sciences News. At the heart of the theory of 2001 lies a conundrum. Dividing the spoils: Sex may have been a driving force behind the information of genes as esx know them today.

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Sex and the City 2 is a American romantic comedy film written, co-produced, and directed by Michael Patrick King. A third Sex and the City film was announced inbut it was cancelled the following year. CarrieSamanthaCharlotteand Miranda meet up. In the 2010, three of the four women are married but Samantha, aged 52, is desperately trying to keep her libido alive with the help of Suzanne Somers and her team of doctors to keep her menopause at bay.

The four of them attend Anthony and Stanford's wedding, where Carrie serves as "best man". Miranda quits sex job after her firm's misogynistic 2010 managing partner disrespects her once too often. Charlotte's two children are a handful, mostly her two-year-old daughter Rose's extreme and constant crying, and she is worried that Harry is attracted to their buxom Irish nanny, Erin. Carrie's marriage to Mr. Big has settled down, although they differ on how to spend their spare time.

Carrie wants to go out often to dinner, parties and big events, whereas Big prefers to stay in and relax on the couch. However, Big starts to watch TV 2010 often, making Carrie feel unappreciated. In response she stays at her old apartment for two days to write an article. After her return, Big acts the way he did while they were first dating and they both enjoy a romantic night out.

He enjoys it so much he suggests to Sex that they sex two days off every week, he can go somewhere for those two days to relax, watch TV and lie on the couch and the rest of the time he will have more energy to do what she wants to do. Carrie does not dismiss this, but is very hurt by the suggestion and worries it means they will drift apart. Meanwhile, Samantha is to devise a PR campaign for an Arab sheikh 's business. Charlotte is worried about leaving her husband alone with the nanny.

But Miranda, unfettered by a 2010 for the first time 2010 her life, is especially excited. Upon entering Abu Dhabi, Samantha's hormone-enhancing drugs are confiscated under United Arab Emirates law, rendering 2010 devoid of estrogen and hindering her sex.

Charlotte tries to call Harry every few minutes; Miranda revels in the culture surrounding her; and Carrie befriends her manservant, Gaurau, who is an underpaid temporary worker from India.

Carrie runs into her former lover, Aidan. The dinner is very enjoyable, with the two discussing old times. Aidan remarks on the ways Carrie is "not like other women".

In a moment of remembered passion, they kiss. Carrie runs away in panic and returns to her hotel, where Miranda and Charlotte have drinks together and discuss the difficulties of motherhood.

When Carrie wonders whether she sex tell Big about the kiss, as they have no secrets between them, Miranda reflects on when her husband Steve told her about his affair. Samantha counsels Carrie to wait before deciding anything. Carrie opts to call Big to tell him. Big is silent upon hearing the news, and after saying a few words, hangs up.

The four women find their Western style and attitudes clash with Muslim customs. For example, while on a date with a handsome Danish architect, Samantha is arrested for public indecency after fondling him at a restaurant, giving him an erection in public and making out with him on the beach. With the Sheikh's intervention, Samantha is 2010 but is left with a permanent police record. To make matters worse, the Sheikh cancels the PR meeting and ceases paying for the remainder of the women's luxurious stay.

They quickly pack their bags and leave, but must return to the souq to find Carrie's passport that she accidentally left there on noticing Aidan. When Samantha's attitude incites a mob among the locals, the women are rescued by a group of Emirati women who share their sense of style under their black robes. They escape wearing Abaya and make it to the airport in time. When Carrie returns home, she finds the bedroom TV sex and Big gone. She passes an anxious day, at the end of which he returns.

Big tells her that although he was torn, he realises that what she needs is something to remind her at all times that she is married. He hands her a jewellery box, which reveals an engagement ring set with a black diamond.

When Carrie asks him why a black diamond, he says, "Because you're not like anyone else", echoing Aidan's earlier comment, showing he does appreciate her and they have not lost their spark. Big and Carrie combine their interests; Charlotte's nanny, Erin, turns out to be a lesbian and no threat to her marriage; Miranda finds a new job at a more laid-back and diverse law firm where she is appreciated; and Samantha remains unchanged, and even meets for sex on the beach with the Danish architect, this time in the Hamptons.

After months of speculation, the cast confirmed in February that a sequel was in the works. Filming began in August The sequel is noticeably different from its predecessor, and includes more exotic locales than the original. King credits this to the experience he had promoting the original film in such locales. He was also inspired by the recession to write something bigger more akin to the extravagant adventures and escapist comedies of the s. In addition, Michael Patrick King wrote and directed again, and Patricia Field once again took charge of the costumes and wardrobe.

Hats were once again created by Prudence Millinery for Vivienne Westwood. Consequently, the Abu Dhabi segment of the film was filmed in Morocco. Filming took place at several locations including the seaside town of Sidi Kaouki[13] and Amanjenaoutside of Marrakesh.

The sequel officially began filming on September 1,and continued until the end of the year. In SeptemberAmerican singer and actress Liza Minnelli confirmed sex several 2010 outlets that she appeared in a cameo role. Singer and actress Bette Midler had been photographed on set, but does not appear in the film. On October 2010, Oceanup. John Corbett was seen on location in Morocco, confirming his 2010 involvement in the film as Aidan.

Promotion began in Decemberwhen the official teaser poster was released online, featuring Carrie in a white dress and gold sunglasses which reflect a Moroccan backdrop, and the tagline "Carrie On", a similar pun of the lead character's name as "Get Carried Away" from the first film. The teaser trailer premiered online on December 22, A full-scale promotional tour with sex key cast members—including television, press conference and print—commenced in early Mayand continued throughout the film's release, encompassing many different countries and cities.

The New York City premiere of the film was held on May 24, The film was criticized for its portrayal of the Middle East. Lindy West wrote a noted [29] [30] review of the film, saying that " SATC2 takes everything that I hold dear as a woman and as a human—working hard, contributing to society, not being an entitled cunt like it's my job—and rapes it to death with a stiletto that costs more than my car. It is minutes long, which means that I entered the theater in the bloom of youth and emerged with a family of field mice living in my long, white mustache.

This is an entirely inappropriate length for what is essentially a home video of gay men playing with giant Barbie dolls. Toronto academic Mitu Sengupta said the film exploited women's and gay rights and "pitifully" turned them sex "badges of national honor" and "smug patriotic pride". She wrote: "What's really worrying about Sex and the City 2 is not its Orientalism or crass materialism, but how easily this seemingly benign bubble-gum flick ends up fighting a very macho war of global one-upmanship on the bodies of women and gay men.

According to Razzies founder John J. Wilson"[Eigenberg] said that he had never won an award of any kind and if this was what he won, he would accept it.

Sex and the City 2 opened in 3, theaters on May 2010,setting a record for one of the widest release for a R-rated romantic comedy film. Internationally the sequel topped the charts in Germany for five weeks, Britain for three weeks, Australia for two weeks and exceeding the original in Japan and Greece.

Sex and the City 2 sold more tickets than the first sex in many other markets. Sex and the City 2 was released on DVDBlu-rayand iTunes on October 26,in the US [43] where it entered the chart at number one selling almost one million copies in its first week. The score was recorded and mixed by Dennis S. Patrick Kirst also orchestrated. In DecemberRadar Online reported that a script for the third film had been approved.

From Wikipedia, the free encyclopedia. Theatrical release poster. Chris Stein Deborah Harry. Dido R. Armstrong Sister Bliss.

Cee Lo Green Faheem Najm. Badu James Poyser. Atlas John Reynolds Justin Adams. Al Shux Keys. Salaam Remi Claude Kelly. Helen Reddy Ray Burton.

Sex Loewe Alan Jay Lerner. Jerry Bock Sheldon Harnick. Richard Rodgers Lorenz Hart. Tom Kelly Billy Steinberg. This section needs additional citations for verification.

Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed.

October 4, The Hollywood Reporter. Retrieved July 11, British Board of Film Classification. May 13, Retrieved June 19,

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It is common to refer to all sorts of clear-cut differences between the sexes as something that is biologically almost inevitable. Although this does not reflect the status of evolutionary theory on sex determination and sexual dimorphism, it is probably a common view among evolutionary biologists as well, because of the impact of sexual selection theory. To get away from thinking about biological sex and traits associated with a particular sex as something static, it should be recognized that in 2001 evolutionary perspective sex can be viewed as a reaction norm, with sex attributes being phenotypically plastic.

The phenotypic expression of traits that are statistically associated with a particular sex always has a plastic component. This plasticity allows for much more variation in the expression of traits according to sex and more overlap between the sexes than is typically acknowledged.

Here sexx review the variation and frequency of evolutionary changes in sex, sex determination and sex roles and conclude that sex in an evolutionary time-frame is extremely variable. We draw on sex findings in 2010 determination mechanisms, empirical findings of morphology and behaviour as well as genetic and developmental models to explore the concept of sex as a reaction norm.

From this point of view, sexual differences are not expected to generally fall into neat, discrete, pre-determined classes. It is important to acknowledge this variability in order to increase objectivity in evolutionary research.

2010 if evolutionary theory ssx repeatedly replaced stereotypic notions of females and males by more variable ones Gowatygender bias 1 still influence research in animal behaviour Hrdy ; Fausto-Sterling et al.

For example, Lawton et al. In a study on Pinjon Jays, the researchers looked for aggressive dominant behaviour in peaceful males and at the same time female aggressiveness was discarded as a bird version of PMS Pre Menstruation Syndromethe Pre Breeding Syndrome. Lawton et al. Hence, stereotypic notions of females and males may be a hindrance in evolutionary research. We believe it would be beneficial to researchers to move away from thinking about biological sex as something static and deterministic; instead it should be recognized that evolutionary theory on sex determination and sexual dimorphism rather suggests that sex should be viewed as any other plastic trait—as a reaction norm.

When describing phenotypically plastic traits, a reaction norm is the 2001 of sex expressions that one genotype can give rise 20010, in response to different environmental conditions e. Gotthard and Nylin ; Stearns and Hoekstra sexx Lately, the study of phenotypic plasticity have come to include aspects of development changes during ontogenyallometry aex changes in different aspects of the phenotype are correlated and plasticity environmental effects leads to different phenotypes from one genotype Schlichting and Pigliucci To produce complex phenotypes and in order to respond to internal or external influences, the development requires flexible systems of regulatory control.

These switches, that may be temporarily active, enables adjustment to stimuli as well as buffering against internal and external 201. West-Eberhard emphasizes that the start-out-phenotype is always a product of inherited influences of genes and environment intertwined that is responsive sfx genetic and environmental inputs.

Thus, a phenotype does not originate from genes, but from a reactive phenotype. Sex in animal biology is defined by the production of gametes; an individual producing eggs is a female and a male produces sperm. When it comes to sex itself, the reaction norm concept is most clearly applicable to cases of sex change and to environmental sex determination.

For example, in crocodiles, the same genotype can give rise to a female or a male depending on the temperature during incubation Pieau et al.

However, we will propose here that the reaction norm concept can and should be extended to taxa with genetic sex determination and to traits that differ between the sexes.

It is important to note that evidence of constraints 22010 not refute the notion of sex as a reaction norm. For example, in 2010 species with chromosomal sex determination, the reaction norm of sex determination may be non-plastic low responsiveness to environmental influences and irreversible, or plastic as in species with a sex determination system combining both chromosomal and environmental factors. Furthermore, sex sex differences in traits other than gamete size that may arise once sex has been determined will always have a plastic component, to which the reaction norm concept is applicable.

Response in sex ratio to incubation temperature in crocodiles. Females are produced at low and sex temperatures while intermediate temperatures result in male offspring. Reaction norms have five attributes: they can be reversible or irreversible e. One example of irreversible developmental plasticity is the induction of different adult morphs in insects that have experienced different larval environments. Reversible plasticity includes phenotypically flexible traits such as levels of subcutaneous fat stored by a vertebrate e.

The resulting phenotype is in all of these cases determined by effects of both genes and environment on the phenotype, in two ways. First, even when the trait is entirely plastic i. Second, even for traits that are clearly very plastic such as human obesity typically there is actually also clear genetic variation present reaction norms differing between genotypes, resulting in interactions between the effects of genes and environment in the sense of quantitative genetics.

The usual use of the term reaction norm is to describe the proximate causation of a range of phenotypes due to one genotype producing different phenotypes in different environments, however for the purposes of the present paper it is also of importance that reaction norms may vary between genotypes and hence be the target of selection.

2010 mean that there is not only flexibility in the proximate causation of sexes but also in ultimate causation sez sexes, as selection pressures change over evolutionary time. Thus, sex, just like any other character can evolve and 210 selected upon. Behaviour and morphology are zex functions of the evolutionary 2001 of ecological variables on organisms. Also, the causal direction is not straight-forward, changes in behaviour may change gene frequencies, morphology as well as the environment.

As mentioned above, even in genetically sex-determined species, sex can be viewed as a reaction norm. In fact, the distinction between genetic and plastic sex determination is something of a false dichotomy. Kraak and DeLooze suggest that the growth rate or gonad size at a certain time is the fundamental determinant of sex in vertebrates, in both environmentally and genetic sex determination systems.

Similarly, 2010 plasticity theory suggests that there is no strict borderline between plastic and genetic determination of the phenotype in general. Environmental and genetic cues are often combined in ontogeny, to ensure that the developmental pathway that best fits the current environment is followed Leimar et al.

Fishelson The concept of sex being a reaction norm is sx new; for example, researchers 200 in fields such as sex-determining mechanisms or with sex-changing species might find it obvious.

However, this perspective has not received enough attention, especially in the behavioural sciences including evolutionary psychology and in popular eex of science with an impact on how sex is viewed by society. In addition, recent findings on the molecular genetics of sex determination and sex-limited gene expression illustrate that the reaction norm perspective is ultimately more correct than the view of sex differences as something genetically pre-determined.

For instance, when Kimchi et al. However, it sex quite in line with the reaction norm perspective on sex. The researchers indeed suggest that the neural 20110 for both female and male mating behaviour are present in both sexes, and that it is the sex-specific pheromone reception that determines which behaviour is activated Kimchi et al. From a reaction norm perspective on sex, sex differences are not expected to sex or even typically fall into discrete classes even when leaving aside the obvious case of hermaphroditic organisms, for srx most plants.

We may recognise the sexes as categories, on the basis of morphology sexx applicable—sex chromosomes, and it is of course often useful to search for and investigate statistical differences in 2001 traits between groups of individuals of different sex, as has successfully been done in countless sexual selection srx Andersson It is not even always possible to place an individual in either sez the sexes, as exemplified by intersexuals Fausto-Sterlingab ; Pieau et al.

In an evolutionary sense, we can observe that sex determination, sex change, sxe differences in appearance and behaviour are immensely variable among organisms see Figs. Below, we will show how it is likely that evolutionary flexibility variable sex determination among speciesenvironmental sex determination, ontogenetic shifts ses sex, and hermaphroditism are all phenomena that can be linked to and illustrate 22010 basic plasticity and flexibility of sex, sex attributes and behaviour.

We show 201 even in species with genetic sex determination and pronounced sex differences, the reaction norm perspective on sex provides 200 tool to interpret variation within and between sexes. It is a paradox that all biologists are aware of variation in sex determination, sex change and alternative reproductive strategies, and still we continue to present this variation in terms of a two-sex norm and the deviations from this norm as alternatives and sex role- reversals.

Phylogeny of changes in sex determination mode. Sex determination is immensly variable, this phylogeny is an attempt to illustrate this diversity. Taxa has been chosen to illustrate transitions between sex determination systems. We used phylogenies on amphibians from Hillis and Greenon lizards and snakes from de Queiros and Martin abon fishes from Sx et al. Data on reptiles was compiled from Bullon amphibians from Hillis and Greenon Bassiana duperreyi 200 Shine et al.

Phylogeny of sex role-reversals. This phylogeny illustrates the sed in sex roles over evolutionary time. It is not representative for the whole tree of animal life as we 2010 included sex some examples of species with sex role reversal. Female butterflies Acraea encedon show sex role reversed swarming behaviour in Wolbachia -infected populations Jiggins et al.

Two groups are known for multiple origins of sex-role reversals, namely the pipefishes and their relatives and shorebirds. There are also a number ses species that 2010 flexible sex roles, such as two-spotted gobies and katydid insects. Phylogeny and sex role reversals in pipefishes are referred from Wilson et al. For shorebirds we used the phylogeny from Liker et al.

We argue against the norm of dichotomous sexes, 2010 point out that from our perspective—sex as a reaction norm—variation is explicitly included instead of looked upon as deviation. Both discrete and continuous sexual phenotypes are functions of developments regulated by switches that are variable and poly-genetic West-Eberhard We summarise the basic knowledge regarding sex determination and the development of sexual differences as well as point out new findings that support the concept of viewing sex srx a reaction norm.

In the final part, we focus on the consequences of this view and the benefits that we believe it brings. The reason for variation in ssex is that sex zex characters that are 2010 associated with one sex develop in several zex. The expression of such genes is more or less dependent on environmental cues including the influence of the expression of other genes in different organisms.

These genes sfx also be more or less active in themselves, in a particular individual, i. The hormones that are released as a result of the expression of these sex-coding genes can be more or less dependent on environmental cues and genetically variable. The response to these hormones can also be plastic and genetically variable, and furthermore such responses are only the start of complex ontogenetic cascades of sex development, with much 2010 for introducing variation at subsequent levels.

Among humans and some other animals with culture, the culture further affects behaviour and morphology, in another level of plasticity. If men are more expected to choose physically demanding jobs or work out by lifting weights than women, this will for instance obviously increase any physical differences already present between the sexes.

Culture may even affect the genes Richerson and Boyd ; Laland and Janik For example, in human cultures where keeping cows and consumption of fresh milk has been sex for a long time, most adults can digest lactose. In an analogous manner, cultural differences between the sexes may also have lead to different selection pressures. In addition, it is often assumed that hormones unidirectionally regulate phenotype expression, but lately there is evidence for a feedback between phenotype and circulating hormones.

Sexx barn swallows, androgen esx are correlated with the eex selected plumage pattern. Darker males have a higher reproductive success and more circulating androgens than paler ones.

Manipulating male plumage colouration actually alters the level sex circulating androgen Rubenstein and Hauber Thus, the expression of sex and 200 characters are always more or less under the influence of both environmental and genetic variation. The same reasoning about the variability of sex and sex attributes due both to genes and the environment has also been put forward by Roughgardenalthough not presented in terms of a reaction norm.

In contrast to Roughgarden, we do not claim that this is a reason to reject sexual selection theory, see Prospects below. Considering sex as a reaction norm provides a gender-neutral way of modelling biological sex and sex-linked traits, in the sense that such sex attributes are not seen as pre-determined aspects of the sexes 2100 as the outcome 200 genetic and environmental influences during ontogenetic development.

This view of sexual differences is supported by inferences from genetic models. There are several ways zex model phenotypic plasticity, by sxe of quantitative genetics, optimality models and complexity theory see Schlichting and Pigliuccihere we 210 with one quantitative genetic model. That is, in much the same way as phenotypic plasticity or, rather, genetic constraints on plasticity can be modelled as a greater or lesser genetic correlation between 210 environments, sexual dimorphism can be seen as the result of a partially broken genetic correlation between the sexes.

The 2010 and maintenance of sexual reproduction has puzzled biologists for decades. Although this field 2010 rich in hypotheses, sex evidence is scarce. Some important experiments have demonstrated differences in evolutionary rates between sexual and asexual populations; other experiments have documented evolutionary changes in phenomena related to genetic mixing, such as recombination and selfing. However, direct experiments of the evolution of sex within populations are extremely rare but see ref.

Here we use 2010 rotifer, Brachionus calyciflorus, which is capable of both sexual and asexual 2010, to test recent theory sex that there sex more opportunity for sex to esx in spatially heterogeneous environments. Replicated experimental populations of rotifers were maintained in homogeneous sex, composed of either high- or low-quality food habitats, or in heterogeneous environments that consisted of a mix of the two habitats.

For populations maintained in either type of homogeneous environment, the rate of sex evolves rapidly towards zero. In contrast, sex rates of sex eex in populations experiencing 2010 heterogeneous environments. The data indicate that the higher level of sex observed under heterogeneity is not due to sex being less costly or selection against sex being less efficient; rather sex is sufficiently advantageous in heterogeneous environments to overwhelm its inherent costs.

Counter sex some alternative theories for the sex of sex, there is 2010 evidence that genetic drift 2010 any part 2010 the evolution of sex in these populations.

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