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Annotated Bibliography Daniel Koman Topic: How does genetic diversity impact evolutionary potential? BioMed Central Limited. (2012, October 23). Hanging in there: Koalas have low genetic diversity. ScienceDaily. Retrieved September 14, 2014 from www.sciencedaily.com/releases/2012/10/121023204636.htm Summary: Species rely on genetic diversity to survive. Recently it has been discovered through historic mitochondrial DNA that Koalas have very low genetic diversity. This has been going on for the past 120 years and is due in the fact that koalas have been interbreeding because of a lack of population size.

William Amos and John Harwood. Philosophical Transactions: Biological Sciences, Vol. 353, No. 1366, Evolution of Biological Diversity: From Population Differentiation to Speculation (Feb. 28, 1998), pp. 177-186 Summary: This article talks about different factors and mechanism that lead to lowering genetic diversity. These mechanisms discussed include population size and variability, heterozygote instability, and interbreeding depression. Understanding the mechanisms that put organisms in low biological diversity will be key in understand its evolutionary implications. Fowler, E., Houlden, B., Hoeben. P., & Timms, P. (2000). Genetic diversity and gene flow among southeastern Queensland koalas (Phascolarctos cinereus). Molecular Ecology, 9(2), 155-164. Summary: Habitual fragmentation and destruction associated with rapid urbanization is threatening the survival of koalas. This article talks about measuring the koala’s genetic variation in mitochondria DNA. The article discusses the low genetic diversity in the mammals and the implications on this bottle neck.

Paetkau, D., Waits, L. P., Clarkson, P. L., Craighead, L., Vyse, E., Ward, R., & Strobeck, C. (April 01, 1998). Variation in Genetic Diversity across the Range of North American Brown Bears. Conservation Biology, 12, 2, 418-429. Summary: Article discussed the importance of genetic diversity and its impact on evolutionary potential. A prime example is large carnivores like bears. Because of the fact bears have a low distribution density and highly influenced with human caused losses in genetic variation. Bradshaw, C., Isagi, Y., Kaneko, S., Brook, B., Bowman, D., & Frankham, R. (2007). Low genetic diversity in the bottlenecked population of endangered non-native banteng in northern Australia. Molecular Ecology, 16(14), 2998-3008. Summary: Endangered species wild banteg like in south East Asia. Researchers in Garig Gunak Barlu National Park study the wild population there which was started in 1849 with only 20 individuals. Researchers student the microsatellites and expressed concern for low genetic variability among the populations

Assignment October 15th: Nobody commented on my change.

Paper:
Factors Leading to Low Genetic Diversity and its Evolutionary Limitations and Consequences Daniel Koman Thursday 3:00

Genetic variability is the foundation for all speciation and adaptation processes (Amos 2014). Genetic diversity is an essential population trait connected to a species survivability and evolutionary potential (Caplins 2014). One consequence of low genetic diversity is inbreeding depression. This phenomenon can have severely destructive effects in a population. Inbreeding depression occurs when similar deleterious alleles in populations appear in homozygous condition. This occurs more often in small populations and populations with lower genetic variation. In these populations, there are increased odds that an offspring acquires a set of deleterious alleles because relatives that share a high proportion of their genome in common are forced to mate. Along with inbreeding depression, low genetic diversity limits a species evolutionary potential. A greater variation of alleles present increases the ability of a population to survive in a changing environment through adaptation (Amos 2014). Adaptation is a key mechanism essential for a species to persist through disease and other random events that change selective pressures.

There are a few main factors that can cause a species to lose biodiversity including habitat fragmentation and climate change. Habitat fragmentation occurs when a species preferred environment changes drastically. It is often caused by humans and leads to a sharp decrease in population size and diversity (Paetkau 1998). Along with habitat fragmentation, climate change can also decrease genetic diversity. Through a similar mechanism, drastic climate change can force many individuals in a population out of its survivable range. This shift can cause a high proportion of a population to die, resulting in a decreased population size and biodiversity (Caplins 2014). Migration is one mechanism for species to combat these unavoidable events that decreases biodiversity (Caplins 2014). Through taking alleles from different, neighboring populations, migration introduce these alleles into the gene pool. Genetic diversity stands as a complicated and essential trait for every species. This paper will review many examples of different factors that lead to low genetic diversity along with way species combat low genetic diversity.

There are many factors that lead to populations of species losing their genetic variability. Some of these factors include habitat fragmentation, the founder effect, natural disaster (including extreme climate change), and genetic drift. Habitat fragmentation is a common, essential factor for humans to keep in mind during urban development that involves habitat disruption. An clear example of how habitat fragmentations effects cause a decrease in genetic diversity is displayed in Queensland koalas over the past century. In 1998, it was estimated that the koala populations had reduced to about 50% of their size in 1927 (Fowler 1998). This reduction is believed to be primarily due to the disappearance of suitable habitat in the area for the koalas. These habitats being destroyed due to rapidly growing human settlement in Queensland Australia posed a realistic threat to the koala populations (Fowler 1998). The urbanization has caused a massive decrease in population size along with a decrease in the migration ability for small populations. Researchers biodiversity though the koala’s genetic variation at various locations on chromosomes. Using a combined heteroduplex analysis and a gel electrophoresis technique, mitochondrial DNA variation was examined for variability (Fowler 1998). Results showed significant levels of heterogeneity in populations that were not spatiality limited and high levels of homogeneity in isolated populations. These results display the detrimental effects that habitat fragmentation has on species biodiversity. When a smaller population becomes isolated from other sub-populations, migration cannot occur and genes, through genetic drift, move toward fixation.

Another main factor that leads to low genetic diversity is the founder effect. When a population is founded by a small number of individuals, genetic drift causes decreased genetic diversity. An example of the founder effect is displayed in a non-native banteng population in northern Australia. These populations, in Barlu National Park, were founded by twenty individuals in 1849, after being introduced through a failed British outpost (Bradshaw 2007). Researchers used twelve microsatellite loci to compare the relative biodiversity of the wild banteng of northern Australia to other native Asian wild banteng populations. The average heterozygosity of the founding Australian banteng population was 28% as compared to that of 67% in the native Asian wild populations (Bradshaw 2007). The Australian benteng was also seen with an inbreeding coefficient of 0.58, which is high compared to similar mammal species to the benteng (Bradshaw 2007). These numbers display the lower levels of genetic diversity compared to other native populations. The benteng population in northern Australia is currently at risk for endangerment due to these low biodiversity levels. The founder effect is also displayed in the Afongnak Island elk population. These Alaskan elk populations were founded in 1929 from eight individuals and rapidly grew to a size of 1,400 (Hundertmark 2009). As expected, the founding populations in the Alaskan elk populations lacked the number of alleles found in the parent population. However, when examining fifteen microsatellites, the results yielded insignificant findings, which bring into question the ability from microsatellite variability to determine genetic diversity (Hundertmark 2009). Factors that cause genetic variation to decrease in native and non-native species population are often caused by humans, reinforcing the necessity of careful animal human interactions. These mechanisms that lower biodiversity and population size need to be avoided if possible in order to maintain healthy populations of animals. One way a species can combat low genetic diversity is through effective migration. Migration introduces new alleles into populations, adding diversity to the individuals its composed of. One example of migration being a successful mechanism for combating low genetic diversity can be observed in North American brown bears (Paetkau 1998). These bears historically have been exposed to high levels of human-caused population fragmentation, which has caused their habitats to shift primarily to isolated northern mountainous regions. This habitat shift, along with high levels of hunting, has resulted in a substantial decrease in their population size. Examining eight variable microsatellite makers, researchers tracked the genetic diversity of many North American brown bear populations (Paetkau 1998). Although the results among the populations varied, a consistent trend relating to gene flow took precedence. Researchers discovered the main factor affecting the small population’s genetic diversity is its connectedness to the larger, more diverse populations (Paetkau 1998). The migratory effects of neighboring populations allowed for small populations to maintain genetic diversity. One specific population, the Kodiak Archipelago Island, had bears introduced when there was a glacier connecting the Alaskan island to the mainland. Currently, this island is completely isolated from other bears populations on the mainland. Due to this isolation, no migration occurred with the mainland, which has resulted in the Kodiak Archipelago Island population to remain at the lowest level of genetic diversity (Paetkau 1998). Another example of migration’s effects on genetic diversity is displayed in research ob populations of Alpine butterflies. Theses butterflies endured a harsh winter in 2003 during which between 60 and 100 percent of the population declined (Caplins 2014). However, over the next two years the allelic diversity at many microsatellites did not change. The originally unexpected result showed no evidence for a genetic bottleneck; however, it did show an interaction between metapopulation connectivity and biodiversity recovery rate (Caplins 2014). The result displayed an increase in genetic collapse in populations that had lower connectivity. A network of populations that exchange genes can also reduce the effects of other gene elimination mechanisms, such as genetic drift. Future research involving genetic bottlenecks must include landscape structure along with the genetic collapse event in order to gain a full understand of habitat fragmentation and severe climate change events (Caplins 2014). Factors that lead to decreased genetic diversity and the ways species combat low levels of genetic diversity are cornerstone biological mechanisms that researchers and engineers must attempt to understand. When a population decreases in size, genetic factors such as inbreeding depression and genetic drift can push the population to the point of extinction (Boff 2014). Due to the high deleterious effects of inbreeding depression, maintaining effective levels of biodiversity is an essential aspect in a species ability to adapt and speciate. Although inbreeding depression is a difficult mechanism to measure, future research should focus on side effects of the depression. Researcher Tim Janicke and his team are exploring the effects of inbreeding on male and female behavior, particularity sexual selection (2014). Further understanding of these mechanisms will better allow for a greater understanding of the importance of biodiversity and will equip ecologists with the ability to maintain health species diversities. Engineers must also keep these biodiversity collapsing mechanisms in mind during habitat fragmentation. Engineers are the catalyst behind the urbanization of humans and the destruction of many species habits. Understanding the importance of maintaining sufficient gene connectivity should be a key factor in all urban planning. Human involvement and awareness needs to increase for the ecosystem and its species to avoid extinction, and maintaining high levels of genetic variability is a primary factor.

Sources

Amos, W., Harwood, J. 1998. Evolution of Biological Diversity: From Population

Differentiation to Speculation. Philosophical Transactions: Biological Sciences, 353:

177-186.

Boff, S., Soro, A., Paxton, R., Alves-dos-Santos, I. 2014. Island isolation reduces genetic

diversity and connectivity but does not significantly elevate diploid male production in a

neotropical orchid bee. Conservative Gentics. 151: 1123-1135.

Bradshaw, C., Isagi, Y., Kaneko, S., Brook, B., Bowman, D., & Frankham, R. 2007. Low genetic diversity in the bottlenecked population of endangered non-native banteng in northern Australia. Molecular Ecology. 16: 2998-3008

Caplins, S., Gilbert. K., Ciotir, C., Roland, J., Matter, S., Keyghobadi, N. Landscape structure and the genetic effects of a population collapse. The Royal Society Publishing, 2014, 1-9.

Fowler, E., Houlden, B., Hoeben. P., & Timms, P. 2000. Genetic diversity and gene flow

among southeastern Queensland koalas (Phascolarctos cinereus). Molecular Ecology.

9: 155-164.

Hundertmark, K., Van Daele, L. 2009. Founder effect and bottleneck signatures in an introduced,

insular population of elk. Conservative Gentics. 11:139-148.

Janicke, T., Vellnow, N., Lamy, T., Chapuis, E., David, P. 2014 Inbreeding depression of mating

behavior and its reproductive consequences in a freshwater snail. Behavioral Ecology.

25: 288-299 Paetkau, D., Waits, L. P., Clarkson, P. L., Craighead, L., Vyse, E., Ward, R., & Strobeck, C. 1998. Variation in Genetic Diversity across the Range of North American Brown Bears. Conservation Biology. 12: 418-429.

11/17/2014 wiki edit
I wrote the following on the Genetic variability page.

Factors that Decrease Genetic Variability
There are many sources that decrease genetic variability in a population:

An example of a species disrupted by habitat fragmentation is displayed in Queensland koalas over the past century. After seeing their populations size almost divide in half due to human caused habitat destruction, the koalas lost their ability to migrate between sub-populations. This event resulted in populations with low genetic diversity, especially those more isolated than others.
 * Habitat fragmentation describes a discontinuity in an organisms habitat resulting from a geological process or a human caused event. This action causes a decreased size of the populations habitat and an increased difficulty for emigration and immigration events. These events result in a greater change for factors such as genetic drift to lower genetic diversity.


 * The founder effect is an event that results in populations with low genetic diversity. The founder effect occurs when a population is founded by few individuals, resulting in poor sampling of alleles in a population.

An example of a popultaion that experienced the founder effects is dispalyed with Afognak Island elk population. The population was founded by eight individuates in the early 1900's and quickly grew to a size 1,400. However, even when the population size increased, the genetic variation remained low.


 * Climate Change is the drastic change in annual weather patterns. These changes in weather patterns can yield negative consequences for genetic diversity.  Driving species out of their fundamental niche, climate changes can lower population size and genetic variation drastically.