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Hunter Abraham EEOB 3310 Annotated Bibliography 9/15/14

How does inbreeding contribute to evolution?

Charlesworth, B. & Charlesworth, D. (1987). Inbreeding Depression and its Evolutionary Consequences. Illinois: Annual Reviews Inc. In this article, the authors discuss that the evidence that the evolution of breeding systems of animals and plants has been influenced by inbreeding depression. They discuss the genetic theory of inbreeding depression and heterosis and observe experimental data that has to do with the strength of inbreeding depression. Pusey, Anne & Wolf, Marisa. (1996). Inbreeding avoidance in animals. Minnesota: Elsevier Science Ltd. This article discusses inbreeding depression and different ways to avoid inbreeding depression. The authors also discuss outbreeding depression and the idea that animals have evolved mechanisms to avoid outbreeding. Jain, S. K. (1976). The Evolution of Inbreeding in Plants. California: Annual Reviews Inc. This article discusses the evolution of inbreeding specifically in plants. It discusses the breeding systems and the genetic variation that controls these breeding systems. It also talks about the issues there are with inbreeding in plants. Shields, William M. (1982). Philopatry, Inbreeding, and the Evolution of Sex. New York: State University of New York Press. This article discusses the concept of dispersal and philopatry and why it is a common practice in organisms. It also talks about inbreeding: if it is adaptive and why it occurs. Sex is another topic discussed in this article as well and why organisms mate with other organisms that are so similar and why they mate at all. Keller, Lukas F. & Waller, Donald M. (2002). Inbreeding Effects in Wild Populations. Wisconsin: Elsevier Science Ltd. This article discusses if inbreeding affects the demography and persistence of natural populations. The authors discuss the fact that they now have an increased ability to detect inbreeding depression in wild populations. They also talk about the effects of the inbreeding depression in the wild.

https://en.wikipedia.org/wiki/Inbreeding

Ways to improve: 1.	More examples 2.	Elaborate more on how to measure inbreeding 3.	Mentions effects of outbreeding after inbreeding, but not anything about crossbreeding

Added sentence: Crossbreeding between populations also often has positive effects on fitness-related traits. Lynch, Michael. (1991). The Genetic Interpretation of Inbreeding Depression and Outbreeding Depression. Oregon: Society for the Study of Evolution.

EDITS https://en.wikipedia.org/wiki/Inbreeding -In a study on an island population of song sparrows, individuals who were inbred showed significantly lower survival rates than outbred individuals during a severe winter weather related population crash. These studies show that inbreeding depression and ecological factors have an influence on survival. -The mice that are inbred typically show considerably lower survival rates. -Inbreeding history of the population should also be considered when discussing the variation in the severity of inbreeding depression between and within species. With persistent inbreeding, there is evidence that shows inbreeding depression becoming less severe. This is associated with the unmasking and eliminating of severely deleterious recessive alleles. It is not likely, though, that eliminating can be so complete that inbreeding depression is only a temporary phenomenon. Eliminating slightly deleterious mutations through inbreeding under moderate selection is not as effective. Fixation of alleles most likely occurs through Muller’s Ratchet, when an asexual population’s genomes accumulate deleterious mutations that are irreversible. -The advantages of inbreeding may be the result of a tendency to preserve the structures of alleles interacting at different loci that have been adapted together by a common selective history.

https://en.wikipedia.org/wiki/Population_fragmentation -When a population is small, the influence of genetic drift increases, which leads to less and/or random fixation of alleles. In turn, this leads to increased homozygosity, negatively affecting individual fitness. The performance of plants may be compromised by less effective selection which causes an accumulation of deleterious mutations in small populations. Since individuals in small populations are more likely to be related, they are more likely to inbreed. A reduction in fitness may occur in small plant populations because of mutation accumulation, reduced genetic diversity, and increased inbreeding. Over time, the evolutionary potential and a species’ ability to adapt to a changing environment, such as climate change, is decreased.

https://en.wikipedia.org/wiki/Partial_dominance_hypothesis_theory -The partial dominance hypothesis theory states that inbreeding depression is the result of the frequency increase of homozygous deleterious recessive or partially recessive alleles. The partial dominance hypothesis can be explained by looking at a population that is divided into a large number of separately inbred lines. Deleterious alleles will eventually be eliminated from some lines and become fixed in other lines, while some lines disappear because of fixation of deleterious alleles. This will cause an overall decline in population and trait value, but then increase to a trait value that is equal to or greater than the trait value in the original population. Crossing inbred lines restores fitness in the overdominance hypothesis and a fitness increase in the partial dominance hypothesis.

FINAL DRAFT STARTS HERE How is Evolution Influenced by Inbreeding?

Inbreeding produces offspring by breeding individuals or organisms that are closely genetically related. Inbreeding can lead to inbreeding depression, which is the reduction of biological fitness in a population. The deleterious effects of inbreeding on a population’s fitness can be seen and are well documented in natural populations. However, since most studies of inbreeding in humans have been focused on pre-reproductive stages in the life cycle, not much is known about inbreeding effects in humans (Ober et al., 1999). Inbreeding affects animals, plants, and humans all in different ways. This paper will discuss these effects of inbreeding in general, and in various populations and environments. Inbreeding depression, mentioned above, and its harmful effects have been being studied for many centuries. It has been found that the main consequence of inbreeding is homozygosis, which is when the union of gametes with one or more identical alleles forms a zygote (Charlesworth, 1987). The disadvantages of inbreeding are a result of its tendency to decrease heterozygosity, speed up the fixation of alleles, and decrease genetic variance of individuals and populations. The advantages of inbreeding may be the result of a tendency to preserve the structures of alleles interacting at different loci that have been adapted together by a common selective history (Sheilds, 1982). Inbreeding in species that are normally outbred almost always reduces the fitness (Drayton et al., 2010). However, it has been suggested that offspring that have been inbred and survive increased adolescent mortality might be more fit than offspring that has been outbred (Pusey & Wolf). Even though inbreeding depression may be most strongly conveyed in early life stages, inbreeding can also produce deleterious consequences in adults. These consequences include sperm deformities and sterility. Drayton et al. predict that inbreeding will cause reduction of some components of male fitness such as performance capacity, immune function, and overall fitness (2010). Inbreeding depression most likely increases as later life stages are reached (Pusey & Wolf, 1996). Inbreeding also may affect sexual traits because heterozygosity is lower at loci that directly code for them. But, if sexual traits are condition dependent, and an individual’s ability to obtain energetic and nutrient resources needed for sexual signaling is reduced by inbreeding, then reduction in sexual traits is expected. In sexually selected traits, inbreeding depression could also indicate that these traits may expose a male’s genome-wide heterozygosity to females. Studies on the evolution of female mate choice show that females may benefit if they mate with males that have above average heterozygosity because under certain conditions (mostly based on immigration rates between populations), males that have greater heterozygosity more often carry locally rare alleles that are not similar to those in females. When females mate with these males, the offspring also have an above average heterozygosity, therefore leading to an increased fitness in the offspring. A declination of sexual trait expression because of inbreeding shows direct evidence that these traits may signal genome-wide heterozygosity (Drayton et al., 2010). Inbreeding history of the population should also be considered when discussing the variation in the severity of inbreeding depression between and within species. With persistent inbreeding, there is evidence that shows inbreeding depression becoming less severe. This is associated with the unmasking and eliminating of severely deleterious recessive alleles. It is not likely, though, that eliminating can be so complete that inbreeding depression is only a temporary phenomenon. Eliminating slightly deleterious mutations through inbreeding under moderate selection is not as effective. Fixation of alleles most likely occurs through Muller’s Ratchet, when an asexual population’s genomes accumulate deleterious mutations that are irreversible (Pusey & Wolf, 1996). However, one study suggests that long term inbreeding does not lead to noticeable effects on fetal growth and development (Rao & Inbaraj, 1980). Inbred and outbred land snails and white-footed mice were released from captivity and their survival was compared. The individuals that were inbred showed considerably lower survival rates. In another study on an island population of song sparrows, individuals who were inbred showed significantly lower survival rates than outbred individuals during a severe winter weather related population crash. These studies show that inbreeding depression and ecological factors have an influence on survival (Pusey & Wolf, 1996). Habitat fragmentation, the loss of a species’ suitable habitat and the separation of individuals into a number of different habitats, has caused many populations of plant species to decrease in size and become more isolated. The main genetic consequences of habitat fragmentation are loss of genetic variance and increased inbreeding in populations and an increase in genetic differentiation among populations. Lower population sizes result in the reduction of genetic variation and an increase of inbreeding, which lead to reduced population performance. When a population is small, the influence of genetic drift increases, which leads to less and/or random fixation of alleles. In turn, this leads to increased homozygosity, negatively affecting individual fitness. The performance of plants may be compromised by less effective selection which causes an accumulation of deleterious mutations in small populations. Since individuals in small populations are more likely to be related, they are more likely to inbreed. A reduction in fitness may occur in small plant populations because of mutation accumulation, reduced genetic diversity, and increased inbreeding. Over time, the evolutionary potential and a species’ ability to adapt to a changing environment, such as climate change, is decreased (Leimu et al., 2010). There are two main theories that were proposed to explain inbreeding depression and heterosis, the improved function of a biological trait in a hybrid offspring. The first theory is the overdominance hypothesis (Charlesworth, 1987). This hypothesis states that heterozygotes have the superior fitness and they inbreed; this leads to homozygosity and causes a decrease in fitness. The second theory is the partial dominance hypothesis theory, which states that inbreeding depression is the result of the frequency increase of homozygous deleterious recessive or partially recessive alleles. These two hypotheses have different predictions concerning the mean trait value of a population going through continued inbreeding. Overdominance inbreeding causes a continued decline in the trait value by increasing the frequency of homozygotes. The partial dominance hypothesis can be explained by looking at a population that is divided into a large number of separately inbred lines. Deleterious alleles will eventually be eliminated from some lines and become fixed in other lines, while some lines disappear because of fixation of deleterious alleles. This will cause an overall decline in population and trait value, but then increase to a trait value that is equal to or greater than the trait value in the original population. Crossing inbred lines restores fitness in the overdominance hypothesis and a fitness increase in the partial dominance hypothesis (Roff, 2002). The deleterious consequences of inbreeding offer the possibility that species have evolved behaviors that lower the frequency of inbreeding (Blouin, 1988). There are several ways inbreeding is avoided. One way is by dispersal of individuals from their natural group or site. Dispersal is widespread in mammals and birds, and it has also been observed in amphibians, reptiles, insects, and fish. The dispersal patterns cause close relatives to be separated, preventing close inbreeding. However, this question is still quarrelsome: have these dispersal patterns evolved as inbreeding avoidance mechanisms or from intrasexual or resource competition? The importance of these factors, of course, varies among species, but it can be difficult to measure their contribution to patterns of dispersal. The importance of inbreeding avoidance in dispersal has been shown in studies of mammals. Male white-footed mice dispersed further from home than predicted based solely on male competition. In social mammals, females are more likely to disperse in species where male domination in groups exceeds the time it takes until daughters reach sexual maturity. However, other studies show that dispersal is contingent on the presence of an individual’s relatives. Research done on Townsend voles shows that males dispersed further if their close female relatives remained in their natural home range. Young male and female meadow voles are more likely to disperse when with siblings versus when they are with non-siblings (Pusey & Wolf, 1996). In contrast, philopatry, the tendency of an organism to stay or return to its home area, is the most common pattern of dispersal that is observed in nature; philopatry promotes inbreeding (Shields, 1982). Another way to avoid inbreeding is through recognition and avoidance of kin as mates. Cases of dispersal where it is contingent on relatives, as discussed previously, proves that kin recognition and avoidance is occurring. In natural populations, many primates show frequencies that are lower than were expected of mating between relatives in the same group, even if they are more distantly related. Prairie dogs are one example of an animal that avoids mating with close living and closely related kin. There is also some evidence that show that close relatives are unattractive as mates (Pusey & Wolf, 1996). In conclusion, inbreeding can, but not always, have many negative effects on a population, causing a reduction in fitness. Many individuals have evolved mechanisms to avoid inbreeding, but sometimes it just cannot be avoided. Inbreeding is not only the result of genetics or an individual’s actions, but ecological factors can also play a role. Although inbreeding depression is shown most in the early stages of life, it also has deleterious effects in adults and increases as later stages of life are reached. Although studies are still being done, researchers have grasped a great deal of concepts to explain inbreeding and its consequences.

References

Blouin, S.F. & Blouin, M. 1988. Inbreeding Avoidance Behaviors. Trends in Ecology And Evolution 3:230-233.

Charlesworth, B. & Charlesworth, D. 1987. Inbreeding Depression and its Evolutionary Consequences. Annual Review of Ecology and Systematics 18:237-268.

Drayton, J. M., Milner, R. N. C., Hall, M. D., & Jennions, M. D. 2010. Inbreeding and courtship calling in the cricket Teleogryllus commodus. Journal of Evolutionary Biology. 24:47-58.

Keller, Lukas F. & Waller, Donald M. 2002. Inbreeding Effects in Wild Populations. Trends in Ecology and Evolution 17:230-241.

Leimu, R., Vergeer, P., Angeloni, F., & Ouborg, N. J. 2010. Habitat fragmentation, climate change, and inbreeding in plants. The Year in Ecology and Conservation Biology 1195:84-98.

Ober, C., Hyslop, T., & Hauck, W. W. 1999. Inbreeding Effects on Fertility in Humans: Evidence for Reproductive Compensation. American Journal of Human Genetics 64:225-231.

Pusey, A. & Wolf, M. 1996. Inbreeding avoidance in animals. Trends in Ecology and Evolution 11:201-206.

Rao, P.S.S. & Inbaraj, S.D. 1980. Inbreeding effects on fetal growth and development. Journal of Medical Genetics 17:27-33.

Roff, D.A. 2002. Inbreeding Depression: Tests of the Overdominance and Partial Dominance Hypotheses. Evolution 56:768-775.

Shields, W. M. 1982. Philopatry, Inbreeding, and the Evolution of Sex. Print. 50-69.