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Sex: Origin and Evolutionary Relevance RONALDO FERNANDES Universidade Federal do Rio de Janeiro Museu Nacional [email protected] Biologist take on Astrobiology Life shapes planets Life shapes planets Human impact is extensive Life shapes planets Human impact is extensive Shaped the terrain Human influence Life shapes planets Human impact is extensive Shaped the terrain Changed the composition of the atmosphere Human influence Life shapes planets Human impact is extensive Shaped the terrain Changed the composition of the atmosphere Increased the acidification of the oceans Human influence Life shapes planets Human impact is extensive Shaped the terrain Changed the composition of the atmosphere Increased Added the acidification of the oceans new materials to the surface Human influence Life shapes planets Human though interference is not necessary, Life shapes planets Human interference is not necessary, though Vegetation shaped the land Biotic influence Life shapes planets Human interference is not necessary, though Vegetation shaped the land Photosynthesis changed the atmosphere fixing CO2 and freeing O2 Biotic influence Life shapes planets Human interference is not necessary, though Vegetation shaped the land Photosynthesis changed the atmosphere fixing CO2 and freeing O2 Oxigen changed the minerals Biotic influence Life shapes planets Holmes (2003) explored a scenario where life come to be extinct on Earth Life shapes planets Without photosynthesis, CO2 will quickly accumulate in the atmosphere, depleting the oxygen Life shapes planets Without photosynthesis, CO2 will quickly accumulate in the atmosphere, depleting the oxygen The greenhouse effect will rise temperatures and sea level Life shapes planets Without photosynthesis, CO2 will quickly accumulate in the atmosphere, depleting the oxygen The greenhouse effect will rise temperatures and sea level Without vegetation soil will wash off into the seas leaving a bare rock and sand surface Life shapes planets Life shapes planets In the long run, the greenhouse effect, through positive feedback, can increase to levels similar to Venus, leaving Earth uninhabitable Life shapes planets Evolution: Basic concepts Evolution Evolution is the change in the heritable characteristics of biological populations over successive generations Evolution Evolution is the change in the heritable characteristics of biological populations over successive generations As such, there are evolutionary mechanisms that increase or decrease variation in populations over successive generations Mechanisms Natural Selection Mutation Genetic Drift Genetic Hitchhiking Genetic Flow Mechanisms Natural Selection Natural Selection Originally introduced in 1859 by a joint presentation of Alfred Wallace and Charles Darwin Natural Selection Originally introduced in 1858 by a joint presentation of Alfred Wallace and Charles Darwin Further elaborated in 1859 by Darwin’s book, On the Origin of the Species On the origin of species (1859) Natural Selection 1. Phenotypic Variation 2. Differential Fitness 3. Heritability of Fitness The descent of man (1871) Sexual Selection Sex Why Sex? Ameivul a nativa Ameivula nativa Parthenogenic species Ameivula nativa Parthenogenic • species All individuals are female Ameivula nativa Parthenogenic Compared species to other similar species, a female of Ameivula nativa produces about twice the number of females of a sexual species Ameivula nativa Parthenogenic species Compared to other similar species, a female of Ameivula nativa produces about twice the number of females of a sexual species If sex is so costly, why even bother? Cost of sex Near all Eukaryotes are sexual species Cost of sex Near • all Eukaryotes are sexual species Sort of. Fungi and protozoans don’t have males and females but, still, produce a number of mating types Cost of sex Near Also, all Eukaryotes are sexual species it is possible that most if not all asexual Eukaryotes are descendants of sexual species Cost of sex Near all Eukaryotes are sexual species Also, it is possible that most if not all asexual Eukaryotes are descendants of sexual species • Considering that sex needs a lot of energy, it is likely to be related to the origin of the Eukaryotes, about the time O2 would become easily available Trichoma s giemsa Cost of sex Near all Eukaryotes are sexual species Also, it is possible that most if not all asexual Eukaryotes are descendants of sexual species Being such a widespread feature suggest it might be an adaptive advantage Sex amplifies variation August Weismann (1889) Sexual reproduction can also increases the differences between individuals… Such differences afford the material by means which natural selection is able to increase or weaken each character according to the needs of the species. Sex amplifies variation It is possible that sex evolve to generate variation. Sex amplifies variation It is possible that sex evolve to generate variation. However… Sex amplifies variation It is possible that sex evolve to generate variation. However… 1. Sex not necessarily increase variation Variability decrease caused by sex Sex amplifies variation It is possible that sex evolve to generate variation. However… 1. Sex not necessarily increase variation 2. Variation through sex often reduces fitness Fitness reduction caused by sex Modern models of sex evolution Selection varies with time Modern models of sex evolution Selection • varies with time Sex can break genetic associations created by past selection that are not favorable anymore Modern models of sex evolution Selection varies with time • Sex can break genetic associations created by past selection that are not favorable anymore • The Red Queen hypothesis for evolution of sex Red Queen Modern models of sex evolution Selection varies with time • Sex can break genetic associations created by past selection that are not favorable anymore • The Red Queen hypothesis for evolution of sex • Sex can be an effective defense against parasites as it allows hosts to shuffle their genes in combinations harder to parasites to adapt to Modern models of sex evolution Selection varies with time • Sex can break genetic associations created by past selection that are not favorable anymore • The Red Queen hypothesis for evolution of sex • Sex can be an effective defense against parasites as it allows hosts to shuffle their genes in combinations harder to parasites to adapt to • Studies with sexual and asexual snails seems to conform to the Red Queen hypothesis Modern models of sex evolution Selection varies with time Selection varies over space • If selection varies with space, migration can cause some genetic associations to be locally detrimental • In such case, sexual species can quickly break deleterious associations by crossing locals with migrants Modern models of sex evolution Selection varies with time Selection varies over space Rates of sex vary among individuals • In many organisms, sex become more common if they are in poor conditions • Under stress circumstances, an organism’ genotype may not match the environment requirements • Sex would allow those organisms to quickly change their genotype Modern models of sex evolution Selection varies with time Selection varies over space Rates of sex vary among individuals Populations are finite Modern models of sex evolution Selection varies with time Selection varies over space Rates of sex vary among individuals Populations are finite • In a finite population, it is conceivable that the best genotypes could be lost in stochastic processes • Sexual organisms has a better chance to regain those genotypes through recombination than asexual ones through mutation Sexual Selection Sexual Selection Sexual selection is a special case of natural selection where mating success is favored instead of fitness Sexual Selection Sexual selection is a special case of natural selection where mating success is favored instead of fitness There are two kinds of sexual selection: Sexual Selection Sexual selection is a special case of natural selection where mating success is favored instead of fitness There 1. are two kinds of sexual selection: Members of one sex create a reproductive differential by competing among themselves for opportunities to mate Ritual Male Combat Ritual Male Combat Sperm Competitio n Sexual Selection Sexual selection is a special case of natural selection where mating success is favored instead of fitness There are two kinds of sexual selection: 1. Members of one sex create a reproductive differential by competing among themselves for opportunities to mate 2. Members of one sex create a reproductive differential in the other sex by selecting mates Sexual dimorphism in Xiphophorus Sexual Selection The concept of sexual selection was poorly received by the Victorian society Sexual Selection The concept of sexual selection was poorly received by the Victorian society Wallace was one of the main critics. He accepted the competition among males but reject the concept of female choice Sexual Selection The concept of sexual selection was poorly received by the Victorian society Wallace was one of the main critics. He accepted the competition among males but reject the concept of female choice Although much of the reaction was misogynist bias, Darwin also argued that “man has ultimately become superior to woman” Sexual Selection Acceptance started in 1930, when Fisher further developed the theory and introduced the Fisherian runaway, which describes how sexual selection accelerates the preference for a specific ornament, causing both the trait and the female preference for it to increase in a positive feedback runaway cycle Male long-tailed windowbird Sexual Selection Recently, there is a renewed interest in sexual selection, with the proposal of new theories: Sexual Selection Recently, there is a renewed interest in sexual selection, with the proposal of new theories: • The Handicap Principle suggests males with a serious handicap that survive until the age of reproduction may be regarded as extremely fit by females, as they were able to overcome their limitations Sexual Selection Recently, there is a renewed interest in sexual selection, with the proposal of new theories: • The Chase Away theory proposes the evolution of exaggerated male display characters is based on antagonistic coevolution between sexes Sexual Selection Recently, there is a renewed interest in sexual selection, with the proposal of new theories: • The idea of sexual selection as protection against extinction as it is efficient in removing undesired traits from the population Sexual Selection Recently, there is a renewed interest in sexual selection, with the proposal of new theories: • The Sensorial Exploitation, in which exaggerated male traits may provide sensory stimulation females find hard to resist Tungara Frog Tungara Frog Case study Frog Physalaemus signifer, a common species from Rio de Janeiro Physalaemu s signifer Case study Frog Physalaemus signifer, a common species from Rio de Janeiro Ph.D. thesis of Marcos Bilates Field work was done mainly at Magé between 2009 and 2011 Experiments Nacional were done at the Museu Case study Field work revealed females did not have a bias for heavier males Also, coupling was independent from overall size Finally, no significant difference in size or mass among singer and satellite males Experiments Case study Females did not showed preference for: • Calls with an added chuck • Difference in the tone • Duration of the calls Case study Females did showed preference for: • Calls with more repetitions • Louder calls Physalaemu s signifer Acknowledgments Marcos Bilates Renato Feio