Tawny Owl Research Paper
The tawny owl, otherwise known by its scientific name, Strix Aluco, or simply the brown owl, is a bird native to much of Eurasia. The tawny owl is known for it’s small, compact body, as well as its brown colorations as it is named for. This specific breed of owl is known in folklore to have an uncanny sense of sight during the night time, however this has been disproven through the work of Selig Hecht and Maurice Pirenne (Hecht and Pirenne, 1940). It was actually proven through their work that the tawny owl, however able to see a more broad range, has a similar to our own vision at low light visibilities. Much of this was thought to be true, along with the myth that this specific species of owl brings bad luck and death because of the fact that the tawny owl is a nocturnal bird of prey, and it possesses a very well known and sinister call.
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The tawny owl is a member of the family of owls Strigidae, and the genus, Strix, which is comprised of wood owls.
The tawny owl is also very territorial, when some fledglings age they starve if they do not find their own space to nest when the care of their parents ends. Possibly the most intriguing topic when the tawny owl is brought up would be the recent learning that with the warming of the climate where the tawny owl resides, this species has actually been evolving before our very eyes (Karell et al, 2011). The tawny owl has gradually become more tawny essentially, over the period of time during this study. The owl has been “micro evolving” as the climate has been warming. From the presence of more white, which would camouflage the bird during long winter months against the snow, to more brown which will be better suited with less snow. In this paper, discussion of just how these changes occur, with respect to relevant chemistry, biology, genetics, and evolution will be
discussed.
The findings of Karell, Ahola, Karstinen, Valkama, and Brommer spark the question of just how do these changes occur. How does the climate change specifically impact the microevolution of the tawny owl? Does the climate actually do this? There has been other speculation that due to pleiotropic effects, the offspring that show the brown phenotype would also have thinner feathers. This would be due to the fact that the offspring are micro evolving thinner feathers because they wouldn’t need the insulation that the more grey/white feathers provide. In fact, this was found to be true. The tawny owls that received the gene coding for brown feathers also have thinner feathers (Koskenpato et al, 2016). This pleiotropic effect is very interesting, and also related to phenotypic plasticity. Phenotypic plasticity is described as the way a single genotype can contain the ability to code for multiple phenotypes, such as how the tawny owl contains a gene that codes for both the relative thickness or thinness of its feathers as well as the color of its feathers (Grenier et al, 2016). Along with the phenotypic plasticity of the color and thickness, a study was completed on the tawny owl in regards to the melanocortin system of the tawny owl, and how that plays into the pigmentation of the owl pleiotropically. Specifically, the levels of melanocortin system genes which are known to have many pleiotropic effects were examined to see if they had effects on melanogenesis, or coloration caused by melanin (Emaresi et al, 2013). It was in fact determined that the pleiotropy caused from the melanocortin system very well could be applied to many phenotypes ranging from the morphology, to the physiology of the tawny owl.
Tawny owls exhibit viability selection, which is a form of natural selection that measures the probability of one surviving to the age of reproduction. This form of selection was affected by the selection on colors throughout tawny owls and portrayed strong selection on the genetically inherited phenotypic trait in tawny owls, which is color. Tawny owls with darker pigments tend to have shorter breeding lifespans, although their pigments have no effect on the number of offspring they are able to produce. Tawny owls who are characterized with grey pigments tend to produce about 33% more offspring throughout their lifetimes as compared to brown pigmented tawny owls (Brommer, Ahola, Karstinen 2005).
There has been no documented correlation of pairing based on color between female and male tawny owls. Therefore, we can conclude that mating is generally randomized throughout tawny owl plumage colors. The plumage coloration of these owls is determined through simple mendelian inheritance, with brown being dominant allele and grey being recessive allele (Karell et al. 2011). In these birds, plumage color is a type of phenotypic polymorphism that is dictated based upon genetic factors. The pheomelanin based plumage coloration, although equally distributed between males and females, is a highly heritable trait in tawny owls. Color polymorphism is evolutionarily very recurrent in many owls, as compared to other bird species. Tawny owl plumage coloration varies from pale grey to reddish brown in color, but the colors are mainly classified into the two groups of grey and brown coloration (Brommer, Ahola, Karstinen 2005).
The climate changes resulting from global warming have transformed natural selection. As a result of milder winters, there has been a significant increase in brown tawny owls over the last fifty years. The increase in brown tawny owls indicates that climate change may be a factor in the evolution in these birds in order to achieve increased survival needs. The increase in brown tawny owls also indicates a micro evolutionary change in the tawny owl species (Karell et al. 2011). To confirm that climate change is part of the reason why these owls are changing color so rapidly a study was done by a group testing the genetic codings of the owl. Though the owls only have two different possible phenotypes there have been many changes in the population of the Strix aluco. We can look at the changes and conclude that they are a result of phenotypic plasticity within the owl population. The Strix Aluco has been moving from a more predominantly white population to about a 50% split, if the change continues at this rate we could even see the population swing to favor the darker feathered owls. The places that most of the diversity within the population has come from is in Northern Africa. “The two copies of the control region both appear to have functional components; however, they average 17% divergent within individuals, whereas copies of the same control region average only 1.55% divergence across all Europe.”(Brito, 2005)
As stated before, grey tawny owls tend to have a longer breeding life spans, as compared to brown tawny owls. In addition, grey tawny owls are genetically inclined to having higher amounts of white blood cells in their bodies, as well as having lower amounts of parasites in their blood. Another beneficial inheritance of the grey tawny owls is that their light feathers may provide a more superior insulation role, which benefits survival in frigid conditions. (Brommer, Ahola, Karstinen 2005). The lack of insulation in brown tawny owls benefits them in warmer climates, which is related to their evolution within warmer climates. If tawny owls had assortative mating, these factors may clearly be beneficial to certain aspects of the species overall. Through extensive research done by many groups across the world during the last 50 or so years, we can conclude that the changes in the Strix Aluco’s color is in direct relation to phenotypic plasticity. As the owls continue to breed and spread throughout Eurasia and Northern Africa the color is slowly changing from predominantly white to brown. This shows that as temperatures have risen it has caused a direct effect on a species dominant genotype. As the cold seasons grow shorter and the warm seasons get longer it has become more beneficial for the Strix Aluco to be brown instead of white.
The tawny owl is a member of the family of owls Strigidae, and the genus, Strix, which is comprised of wood owls.
The tawny owl is also very territorial, when some fledglings age they starve if they do not find their own space to nest when the care of their parents ends. Possibly the most intriguing topic when the tawny owl is brought up would be the recent learning that with the warming of the climate where the tawny owl resides, this species has actually been evolving before our very eyes (Karell et al, 2011). The tawny owl has gradually become more tawny essentially, over the period of time during this study. The owl has been “micro evolving” as the climate has been warming. From the presence of more white, which would camouflage the bird during long winter months against the snow, to more brown which will be better suited with less snow. In this paper, discussion of just how these changes occur, with respect to relevant chemistry, biology, genetics, and evolution will be
discussed.
The findings of Karell, Ahola, Karstinen, Valkama, and Brommer spark the question of just how do these changes occur. How does the climate change specifically impact the microevolution of the tawny owl? Does the climate actually do this? There has been other speculation that due to pleiotropic effects, the offspring that show the brown phenotype would also have thinner feathers. This would be due to the fact that the offspring are micro evolving thinner feathers because they wouldn’t need the insulation that the more grey/white feathers provide. In fact, this was found to be true. The tawny owls that received the gene coding for brown feathers also have thinner feathers (Koskenpato et al, 2016). This pleiotropic effect is very interesting, and also related to phenotypic plasticity. Phenotypic plasticity is described as the way a single genotype can contain the ability to code for multiple phenotypes, such as how the tawny owl contains a gene that codes for both the relative thickness or thinness of its feathers as well as the color of its feathers (Grenier et al, 2016). Along with the phenotypic plasticity of the color and thickness, a study was completed on the tawny owl in regards to the melanocortin system of the tawny owl, and how that plays into the pigmentation of the owl pleiotropically. Specifically, the levels of melanocortin system genes which are known to have many pleiotropic effects were examined to see if they had effects on melanogenesis, or coloration caused by melanin (Emaresi et al, 2013). It was in fact determined that the pleiotropy caused from the melanocortin system very well could be applied to many phenotypes ranging from the morphology, to the physiology of the tawny owl.
Tawny owls exhibit viability selection, which is a form of natural selection that measures the probability of one surviving to the age of reproduction. This form of selection was affected by the selection on colors throughout tawny owls and portrayed strong selection on the genetically inherited phenotypic trait in tawny owls, which is color. Tawny owls with darker pigments tend to have shorter breeding lifespans, although their pigments have no effect on the number of offspring they are able to produce. Tawny owls who are characterized with grey pigments tend to produce about 33% more offspring throughout their lifetimes as compared to brown pigmented tawny owls (Brommer, Ahola, Karstinen 2005).
There has been no documented correlation of pairing based on color between female and male tawny owls. Therefore, we can conclude that mating is generally randomized throughout tawny owl plumage colors. The plumage coloration of these owls is determined through simple mendelian inheritance, with brown being dominant allele and grey being recessive allele (Karell et al. 2011). In these birds, plumage color is a type of phenotypic polymorphism that is dictated based upon genetic factors. The pheomelanin based plumage coloration, although equally distributed between males and females, is a highly heritable trait in tawny owls. Color polymorphism is evolutionarily very recurrent in many owls, as compared to other bird species. Tawny owl plumage coloration varies from pale grey to reddish brown in color, but the colors are mainly classified into the two groups of grey and brown coloration (Brommer, Ahola, Karstinen 2005).
The climate changes resulting from global warming have transformed natural selection. As a result of milder winters, there has been a significant increase in brown tawny owls over the last fifty years. The increase in brown tawny owls indicates that climate change may be a factor in the evolution in these birds in order to achieve increased survival needs. The increase in brown tawny owls also indicates a micro evolutionary change in the tawny owl species (Karell et al. 2011). To confirm that climate change is part of the reason why these owls are changing color so rapidly a study was done by a group testing the genetic codings of the owl. Though the owls only have two different possible phenotypes there have been many changes in the population of the Strix aluco. We can look at the changes and conclude that they are a result of phenotypic plasticity within the owl population. The Strix Aluco has been moving from a more predominantly white population to about a 50% split, if the change continues at this rate we could even see the population swing to favor the darker feathered owls. The places that most of the diversity within the population has come from is in Northern Africa. “The two copies of the control region both appear to have functional components; however, they average 17% divergent within individuals, whereas copies of the same control region average only 1.55% divergence across all Europe.”(Brito, 2005)
As stated before, grey tawny owls tend to have a longer breeding life spans, as compared to brown tawny owls. In addition, grey tawny owls are genetically inclined to having higher amounts of white blood cells in their bodies, as well as having lower amounts of parasites in their blood. Another beneficial inheritance of the grey tawny owls is that their light feathers may provide a more superior insulation role, which benefits survival in frigid conditions. (Brommer, Ahola, Karstinen 2005). The lack of insulation in brown tawny owls benefits them in warmer climates, which is related to their evolution within warmer climates. If tawny owls had assortative mating, these factors may clearly be beneficial to certain aspects of the species overall. Through extensive research done by many groups across the world during the last 50 or so years, we can conclude that the changes in the Strix Aluco’s color is in direct relation to phenotypic plasticity. As the owls continue to breed and spread throughout Eurasia and Northern Africa the color is slowly changing from predominantly white to brown. This shows that as temperatures have risen it has caused a direct effect on a species dominant genotype. As the cold seasons grow shorter and the warm seasons get longer it has become more beneficial for the Strix Aluco to be brown instead of white.