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Edits to the page on sexual dimorphism section- Birds: This difference produces a stronger female choice since they have more risk in producing offspring. This balance keeps the dimorphism alive in these species and ensures that the next generation of successful males will also display these traits that are attractive to the females. This occurs because the species is more focused on survival than reproduction, causing a shift into a less ornate state. Migratory patterns and behaviors also influence sexual dimorphisms. This aspect also stems back to the size dimorphism in species. It has been shown that the larger males are better at coping with the difficulties of migration and thusly are more successful in reproducing when reaching the breeding destination (Rubolini, 2004). When viewing this in an evolutionary standpoint many theories and explanations come to consideration. If these are the result for every migration and breeding season the expected results should be a shift towards a larger male population through sexual selection. Sexual selection is strong when the factor of environmental selection is also introduced. The environmental selection may support a smaller chick size if those chicks were born in an area that allowed them to grow to a larger size, even though under normal conditions they would not be able to reach this optimal size for migration. When the environment gives advantages and disadvantages of this sort. The strength of selection is weakened and the environmental forces are given greater morphological weight. The sexual dimorphism could also produce a change in timing of migration leading to differences in mating success within the bird population (Kissner, 2003). When the dimorphism produces that large of a variation between the sexes and between the members of the sexes multiple evolutionary effects can take place. This timing could eve lead to a speciation phenomenon if the variation becomes strongly drastic and favorable towards two different outcomes.

Final Draft Starts here Birds are the basis for a many evolutionary questions throughout time. Time, money and effort have been exerted to study and understand the world of birds. Sexual dimorphism in many of bird species offers a complex social and genetic outlook. The development of phenotypic dimorphism can be explained by the presence of sexual selection and subsets of this concept. Selection is one of the strongest in influencing the habits and looks of a species. In birds sexual dimorphism plays a vital role for sexual selection through differences in plumage, size, hormones, migratory patterns, and even on a genetic level of selection. Throughout evolution different organisms have developed their own mating rituals and practices. A sexual dimorphism takes place when between the two sexes of a species their phenotypes differ dramatically. This difference could be in size, color and even sounds they produce. Sexual dimorphism in birds has been linked to various evolutionary concepts including female selection, sexual selection and intersexual competition. The size of birds is one of the most common aspects of the phenotype to express a dimorphism. In many species that exhibit any kind of sexual dimorphism there is a difference in the sizes between the sexes. For instance a sexual dimorphism in the bird species called the great bustard arose which made the males almost double the size of the females (Alonso, 2009). This means that over time larger males have been successful at mating. When these larger males in this species mate, their genes that have lead them to become larger are passed on to the next generation, which produces larger male offspring. Also when the females decide to mate with the males due to their size they are showing preference for the larger males. This makes it so the smaller males are unable to mate and essentially there will be a time when the weight will shift to only producing heavy males and smaller females. This is a prime example of sexual selection in a species, which has influenced the phenotype of the species over time and produced an evolution towards a larger male being more reproductively successful than its smaller competition. There is a genetic basis for a sexual dimorphism in bird species. Studies have shown that the genetics can either be from an allele that is only present in one sex or a same allele just represented differently in the sexes (Coyne, 2008). If the allele is only contained in the male this proves that the sexual dimorphism is more genetic based. Again the genes are passed on because the more fit males who contain these genes are producing more viable offspring. The genes that are in both of the sexes are more complicated to follow. This shows that those genes are expressed differently in each of the sexes if there is a sexual dimorphism present. The genes in the males may be turned on or off to affect the phenotypes (Coyne, 2008). Selection and male competition for mates are the primary sources of evolution when the allele’s function differentiates between the sexes. Evolution for sexual dimorphism also includes social mating systems and its contributions. Social mating systems have been found to have a strong influence towards the development of sexual dimorphisms in birds, it was found that these systems strongly influenced the differences in plumage across a variety of species (Dunn, 2001). Social mating systems can be viewed as another aspect of sexual selection in species and evolution. The females develop a choice and preference in their mate. This choice then leads to a variation in approaches toward mating by the male counterparts of the species. Also the females can pass this preference onto their daughters and further propagate the evolution of dimorphism and males displaying these ornate mating. The variation in many bird species leads to extravagant plumage. The cost and benefit of the plumage is often considered in these species. Although the male is now extra attractive towards potential mates he is now more easily spotted by predators due to this extravagance. There must be a balance between the benefit of mating and the potential for predation associated with a more lavished plumage. The development of flashy plumage is supported by the evolutionary concept of sexual selection; the males develop this trait further because of the strong selection for it. Considerations must be made as to whether the dimorphism involves a hormonal basis or not. As with many other organisms the hormone testosterone causes developmental changes in the male sex of a species. These sex characteristics are often dependent upon this hormone but not exclusively. In birds however some secondary sex characteristics are not hormone dependent, for example flashy plumage (Owens, 1995). When this is true, this means that although the flashiest peacock is beautiful and eye-catching it does not necessarily reflect on his ability to produce offspring. The females may then be tricked and over-look a fit male when focusing on this one sexual dimorphic trait alone. The peacock however would not develop the same behaviors due to the lack of testosterone. So when studying sexual dimorphisms through and evolutionary lens precaution must be taken. Is the dimorphism the only indicator of sexual selection and fitness for this species, or do other behavioral factors influence the mate choice? Also you must consider that many females may not even choose a mate due to their potential for producing successful offspring and furthering their genes. The females may be exhibiting a runaway selection where their choice is at random and not controlled by fitness at all. This really changes the perspective of sexual dimorphism being a result evolution. Studies have shown that different traits showing sexual dimorphism are not all due to the same types of evolutionary forces. For instance, plumage being dependent on female choice, but a difference arises when discussing size dimorphism. It has been shown that the size dimorphism can be attributed to a intrasexual competition (Owens, 1998). Intrasexual competition stems from a male-male competition for mates. Thusly, when discussing size males are trying to overcome each other for the right to reproduce. This competition can become costly because many males fight for the ability to mate or retain their mate after they have already successful mated with their female of choice. They need to be of a healthy size and demonstrate an efficient use of energy towards retaining their dominance over an area or a female. Also their size should be present in the next generation that they have produced and the offspring size must be beneficial towards chick development. Migratory patterns and behaviors also influence sexual dimorphisms. This aspect also stems back to the size dimorphism in species. It has been shown that the larger males are better at coping with the difficulties of migration and thusly are more successful in reproducing when reaching the breeding destination (Rubolini, 2004). When viewing this in an evolutionary standpoint many theories and explanations come to consideration. If these are the result for every migration and breeding season the expected results should be a shift towards a larger male population through sexual selection. Sexual selection is strong when the factor of environmental selection is also introduced. The environmental selection may support a smaller chick size if those chicks were born in an area that allowed them to grow to a larger size, even though under normal conditions they would not be able to reach this optimal size for migration. When the environment gives advantages and disadvantages of this sort. The strength of selection is weakened and the environmental forces are given greater morphological weight. The sexual dimorphism could also produce a change in timing of migration leading to differences in mating success within the bird population (Kissner, 2003). When the dimorphism produces that large of a variation between the sexes and between the members of the sexes multiple evolutionary effects can take place. This timing could eve lead to a speciation phenomenon if the variation becomes strongly drastic and favorable towards two different outcomes. Sexual dimorphism also produces an imbalance in investment for the sexes. Females tend to invest greater resources due to the fact that the egg is larger than the sperm and requires more energy to produce. Often in sexually dimorphic species of birds, the males do not contribute much effort in raising the offspring as the females. This difference produces a stronger female choice since they have more risk in producing offspring. The females need to know that their Offspring will survive and be fit enough to pass on their genes and contribute to the population. The males then develop these defining characteristics in order to obtain a mate and show that the male offspring of their reproduction will also be successful at finding a mate. Males that are successful can mate with a multitude of females and spread their genes in every direction. This aspect ensures that the risks they are taking in becoming sexually dimorphic are less than the reward of producing large amounts of offspring. This balance keeps the dimorphism alive in these species and ensures that the next generation of successful males will also display these traits that are attractive to the females. Finally, through this paper many ways of interaction between evolution and sexual dimorphism in birds have been discussed. The main point being that evolution has had a major effect in developing these differing traits between the sexes. Through factors such as sexual selection and intrasexual competition there has been change in the way these species develop into viable adults. Birds may differ between the sexes in size, plumage and behavior and all these traits have an evolutionary basis as to why they formed and became necessary for the survival of these species.

References Alonso, Juan C., Magaña, Marina, Alonso, Javier A., Palacín, Carlos, Martín, Carlos A.,Martín, Beatriz,. (2009). The most extreme sexual size dimorphism among birds: Allometry, selection, and early juvenile development in the great bustard ( otis tarda ). Tauk the Auk, 126(3), 657-665. Benito, M. M., & González-Solís, J. (2007). Sex ratio, sex-specific chick mortality and sexual size dimorphism in birds. Journal of Evolutionary Biology, 20(4), 1522-1530. Coyne, Jerry A., Kay, Emily H.,Pruett-Jones, Stephen,. (2008). The genetic basis of sexual dimorphism in birds. EVO Evolution, 62(1), 214-219. Diego Rubolini, Fernando Spina, & Nicola Saino. (2004). Protandry and sexual dimorphism in trans-saharan migratory birds. Behavioral Ecology, 15(4), 592-601. Dunn, Peter O., Whittingham, Linda A., Pitcher,Trevor E.,. (2001). Mating systems, sperm competition, and the evolution of sexual dimorphism in birds. EVO Evolution, 55(1), 161-175. Kissner, K. J., Weatherhead, P. J., & Francis, C. M. (2003). Sexual size dimorphism and timing of spring migration in birds. Journal of Evolutionary Biology, 16(1), 154-162. Owens, I. P. F., Hartley,I.R.,. (1998). Sexual dimorphism in birds: Why are there so many different forms of dimorphism? Proceedings: Biological Sciences, 265(1394), 397. Owens, I. P. F., Short,R.V.,. (1995). Hormonal basis of sexual dimorphism in birds: Implications for new theories of sexual selection. Trends in Ecology & Evolution., 10(REF), 44.

Where are your 3 suggestions and 1 citation/sentence? Larson.309 (talk) 18:16, 12 October 2014 (UTC) I'm sorry for my confusion and lack of thoroughness with the directions, here is my work. https://en.wikipedia.org/wiki/Sexual_dimorphism I had some concerns with this section and the facts presented and some that were not mentioned at all. 1.) There still can be a dimorphism and equal parental contributions from both sexes. Although males do not produce eggs many stay and provide food while the females protect the offspring. The statement made only provided the extremes of sexually dimorphic males either providing no contribution or all contributions after reproduction. 2.) The topic of monogamous relationships between the birds was not mentioned. 3.) Also not all phenotypes correlate to fitness and there is a type of female selection called runaway sexual selection that is solely due to the female preference of the males and produces a positive feedback for this preferred trait. Also not all male dimorphic traits are due to hormones like testosterone, instead they are a naturally occurring part of development, for example plumage.

Sexual dimorphism in birds due to evolution through natural selection

Annotated bibliography: Alonso, Juan C., Magaña, Marina, Alonso, Javier A., Palacín, Carlos, Martín, Carlos A.,Martín, Beatriz,. (2009). The most extreme sexual size dimorphism among birds: Allometry, selection, and early juvenile development in the great bustard ( otis tarda ). Tauk the Auk, 126(3), 657-665. -Discussion of the sexual selection of the bird, great bustard, which has selected for large males that are double the size of the females. This study involves the evolution of size and toe length for the male population of one species.

Coyne, Jerry A., Kay, Emily H.,Pruett-Jones, Stephen,. (2008). The genetic basis of sexual dimorphism in birds. EVO Evolution, 62(1), 214-219. -Discussion of the process of evolutionary genetics where the study examines whether the basis is from either a limited sex allele or an allele that is present in both sexes but is shown only in one. This study finds the genetic reasons for why males show different phenotypes than their female counterparts.

Dunn, Peter O., Whittingham, Linda A., Pitcher,Trevor E.,. (2001). Mating systems, sperm competition, and the evolution of sexual dimorphism in birds. EVO Evolution, 55(1), 161-175. -This study offers a wide examination of over 1000 species of birds and questions the effect of sperm competition by a correlation with testis size. Also examined was the social mating system and its contributions to sexual dimorphism. These factors were then tested to find whether they had an evolutionary basis in birds.

Owens, I. P. F., Hartley,I.R.,. (1998). Sexual dimorphism in birds: Why are there so many different forms of dimorphism? Proceedings: Biological Sciences, 265(1394), 397. -This study breaks up the many ways that sexual dimorphism enacts in bird species and correlates them to a pattern of evolution. Also examined were the different style of bird matings including monogamous relationships. The study refers not only to genetic factors but strongly relies on the environmental aspect of the bird life.

Owens, I. P. F., Short,R.V.,. (1995). Hormonal basis of sexual dimorphism in birds: Implications for new theories of sexual selection. Trends in Ecology & Evolution., 10(REF), 44. -This study focuses on the gonadal influence on sexual dimorphisms in birds. This raises questions over hormonal influences on evolution and the genetic make-up of all things and their effects. Also the study discusses hormones as being a control for the dimorphism.