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October 1 update https://en.wikipedia.org/wiki/Sympatric_speciation

Amy Gravelle EEOB 3310; Recitation: Tues 10:20am

Topic: Several ecotypes of Killer Whales (Orcinus Orca) exist throughout different geographic regions in the world. Sympatric speciation has occurred within the species, but the speciation events were caused by a variety of different traits changing depending on where that species is from/lives. What is the driving evolutionary force/trait behind each speciation event and will it continue to happen to killer whales in regions where speciation has not yet been completed?

Sources: 1)	Foote, A. D., J. Newton, M. C. Avila-Arcos, M.-L. Kampmann, J. A. Samaniego, K. Post, A. Rosing-Asvid, M.-H. S. Sinding, and M. T. P. Gilbert. "Tracking Niche Variation over Millennial Timescales in Sympatric Killer Whale Lineages." Proceedings of the Royal Society B: Biological Sciences 280.1768 (2013): 20131481. Web. 14 Sept. 2014.

This article discusses the speciation between two sympatric types of orcas in the northern Atlantic that have vastly different diets: one type feeds on small mammals and the other type feeds on fish. Different feeding habits will affect mating habits. This difference indicates the two types of orcas are in different trophic levels in their given ecosystem—despite being of the same species and having the same mDNA. The results concluded that there is some speciation beginning to happen between some types of orcas, but it is still very early compared to those in the Pacific Ocean.

2)	Foote, Andrew D., Julia T. Vilstrup, Renaud De Stephanis, Philippe Verborgh, Sandra C. Abel Nielsen, Robert Deaville, Lars Kleivane, Vidal Martín, Patrick J. O. Miller, Nils Øien, Monica Pérez-Gil, Morten Rasmussen, Robert J. Reid, Kelly M. Robertson, Emer Rogan, Tiu Similä, Maria L. Tejedor, Heike Vester, Gísli A. Víkingsson, Eske Willerslev, M. Thomas P. Gilbert, and Stuart B. Piertney. "Genetic Differentiation among North Atlantic Killer Whale Populations." Molecular Ecology 20.3 (2011): 629-41. Wiley Online Library. Web. 14 Sept. 2014.

This article discusses the sequencing methods of finding 3 different sequences for the same species of killer whales within the Northern Atlantic Ocean. It gave significant evidence that there is speciation occurring within the orca population based on latitude and dietary habits. These results were put against the speciation that has occurred in the Pacific Ocean which strongly suggests that another speciation event is in the beginning stages.

3)	Morin, P. A., F. I. Archer, A. D. Foote, J. Vilstrup, E. E. Allen, P. Wade, J. Durban, K. Parsons, R. Pitman, L. Li, P. Bouffard, S. C. Abel Nielsen, M. Rasmussen, E. Willerslev, M. T. P. Gilbert, and T. Harkins. "Complete Mitochondrial Genome Phylogeographic Analysis of Killer Whales (Orcinus Orca) Indicates Multiple Species." Genome Research 20.7 (2010): 908-16. Pub Med Central. Web. 14 Sept. 2014.

This article discusses the research and findings of a study that analyzed mitochondrial DNA of several different killer whale ecotypes from all around the world. The results indicated that there are 2 distinct speciation events that have already occurred and one that is in the process of slowly occurring now due to some subspecies sequence being observed. This ties in with the other research being done to prove that some sympatric speciation has in fact occurred within killer whales and some is currently occurring based on location and diet which then in turn alters mating behaviors.

4)	Baird, R. W., Abrams, P. A., & Dill, L. M. (1992). Possible indirect interactions between transient and resident killer whales: Implications for the evolution of foraging specializations in the genus orcinus. Oecologia, 89(1), 125-132. JSTOR. Web. 14 Sept 2014.

This article is from 1991 and it discusses the sympatric speciation that was discovered in killer whales in the Pacific Ocean around Washington state and British Columbia, Canada. The methods were mostly based on using models and observations of frequencies within populations instead of more modern practices of sequencing DNA.

5)	Matkin, C. O., Durban, J. W., Saulitis, E. L., Andrews, R. D., Straley, J. M., Matkin, D. R., & Ellis, G. M. (2012). Contrasting abundance and residency patterns of two sympatric populations of transient killer whales (Orcinus orca) in the northern Gulf of Alaska. Fishery Bulletin, 110(2). 143-155. Web. 14 Sept 2014.

This article discusses research done on two distinct sympatric types of killer whales in the Gulf of Alaska that both exclusively eat mammals as their diet. However, they live in slightly different locations within the Gulf area. The methods included taking pictures of individuals in each population comparing their dorsal fins on the left side to identify them over the course of 27 years. The results showed us that even though they are at a similar status on the food chain, the two populations had enough differences to separate geographically and reproductively.

Nov 17 Insert on page: https://en.wikipedia.org/wiki/Killer_whale in the talk section

The evolution of the sympatric speciation events is an important part of the killer whale's history. There is strong evidence that historically the Earth’s killer whale population went through a severe genetic bottleneck around 145,000 to 200,000 years ago.[2] It is predicted that this bottleneck event occurred as a result of some sort of drastic weather and/or climate change. However the speciation of the killer whales has proved to have preserved a large amount of the variability in the mitochondrial DNA within populations globally—which is unusual following a bottleneck event. The speciation is also supported by the geographical findings in the last few decades in which both the transient and residential ecotypes have been spotted in the same regions of the world in which most of these populations are found in residence near the Pacific waters and off the coast of Alaska. Despite their being within close proximity of one another, the varying diets between the transient and residential killer whale populations has since decreased the need to compete for resources and therefore almost eliminates the need to interact with the other population. This also enhances the speciation even more so because of limited interaction. In the social context of killer whales, continuing the use of vocal sounds between pods has helped maintain the concept of staying within one’s own pod. This proves the successful avoidance of excessive inbreeding in the natal pods. The separation of natal pods in general also strengthens the speciation event. Individuals more like one another, but not genetically identical, are kept closer together and are more likely to remain there thus creating a social separation between subspecies.

It is also evident that these separate subspecies have begun to diverge into even smaller subgroups based on genetic differences as well. [3]This indicates that there is enough genetic similarities between subspecies to allow for further unique patterns to emerge in these smaller subgroups.

FINAL DRAFT SUBMISSION

Evolutionary Forces of the Speciation of Killer Whales (Orcinus Orca)

There have been countless examples of distinctive evolutionary events to explain how living species on Earth today have become the way they are. Scientists have studied phylogenies, genetics, behaviors, and ecologies of numerous species on the planet in order to gain a better understanding of the organisms that surround us to provide insight on our own evolution as homo sapiens. One of the most unique scenarios has been the species Orinus orca, commonly known as killer whales, undergoing a sympatric speciation pattern. Sympatric speciation is an evolutionary phenomena that results from the absence of reproduction between two or more populations that live in the same area. This eventually will lead to the delineation of two separate species within an already existing species if sustained for a long period of time. Speciation and the likelihood of speciation occurring does not happen overnight and for no reason. With the case of the whales, there is strong evidence that the Earth’s killer whale population went through a severe genetic bottleneck around 145,000 to 200,000 years ago (Morin, et al, 2010). It is predicted that this event occurred as a result of drastic weather and climate changes, such as an ice age period. Bottleneck events are notorious for decreasing the variation of genes among any population or species. It is impossible to verify this event occurring, however current genetic investigations have proven high variability in a conserved domain of a control region of mitochondrial DNA within populations around the world. High genetic variability is correlated with a smaller population size, which is a key characteristic after a bottleneck event has occurred. This also means that any natural selection occurring shortly afterwards on the killer whales had very little effect because the distribution of genes was skewed due to the bottleneck event itself. Only the individuals that remained in the population could pass on their genes, so the accurate allele frequencies in the initial population are not well represented. Today, there is a distinct separation of three main types of killer whale populations: resident populations, offshore populations, and transient populations. Transient populations are the less related to the offshore and resident populations (Matkin 2012).They typically live in very small groups, travel often, and their diet is mostly comprised of marine mammals. Due to their small groupings, or pods, there is proof of a very low coefficient of relatedness between them and the residents and offshores. The resident populations live in pods of 10-20 whales and mostly consume fish, while the offshore populations live in the largest pods around 75-100 whales. The offshores are aptly named in that they frequently travel far from the shoreline to feed on larger schools of fish. It is likely that the offshore subspecies separated through allopatric speciation instead of sympatric due to their widely varying geographical location. However, a common theme of relatedness among all three types is present: as the hierarchical groupings increase, the coefficients of relatedness greatly decrease (Pilot, et al 2009). For example, coefficient of relatedness between pods of whales was significantly higher than the relatedness between populations, and individual populations were more related than each of the ecotypes as a whole. The coefficients of relatedness are important to understanding the mating patterns of these organisms. Living in pods at the size of 100 individuals is a prime set up for inbreeding to occur. For a while, before more genetic testing was readily available to prove otherwise, scientists were on the track of thinking that killer whales were in fact inbreeding in some areas. Their prime evidence was that there was only small amounts of dispersal between separate pods within a single population (Hoelzel, Dover 1990). More recent studies have proven that inbreeding within these populations is simply avoided due to the fact that whales, usually males, mate with individuals in other pods or families temporarily. This temporary mating method is actually how most mating events occur for these animals and it can also explain the low coefficients of relatedness. A slight increase in genetic variance within a given group of organisms can provide a variety of advantages such as removal of a deleterious gene that might otherwise be amplified in a small population. Relatedness can also be evaluated between females and males. In both the transient and resident ecotypes the males had a higher coefficient of relatedness between each other than the females did (Pilot, et al 2009). Females and males in these populations tend to utilize different breeding methods. Males tend to mate outside of their natal pod—the one in which they were born—like in the instance of the temporary mating in other pods. Conversely, females tend to maintain maternal kinship within their natal population. The result of these behaviors explains the varying coefficients of relatedness. Females within a pod or population will be more related to their offspring than males will (Foote 2011). Once again we have evidence of temporary reproduction in surrounding pods occurring as mentioned earlier. There is almost no female mediated gene flow within the killer whale species. These facts allow us to prove that all lineages are controlled maternally which gives helpful insight when genetic information is compared between individuals. Scientists can better distinguish and keep track of different pods and families. Supporting a speciation event, especially a sympatric one, can be complicated at times. Often times an allopatric speciation event is caused by a physical barrier that prevents two populations from sharing alleles. To test for speciation, scientists allow individuals from both populations to mate and then their compatibility is determined (Foote 2013). However, this is not the case with the killer whales. Any type of trait can be used to differentiate populations that have speciated from one another. One crucial trait to support the speciation of the killer whale species is the location in which they reside. There are some hypotheses that have predicted a separation of alleles caused by a drastic climate change thousands of years ago—potentially relating to the bottleneck event (Hoelzel 2002). However both the transient and residential ecotypes have been spotted in the same geographic regions of the world (Morin et al 2010). Therefore, a sympatric speciation has been hypothesized and proven by numerous researchers over the last twenty years or so. Most of these populations are residing near the Pacific waters off the coast of Alaska (Morin et al 2010). Since location only explains what type of speciation has occurred, the distinction between the three ecotypes of killer whales is what allows scientists to verify that there are distinct subspecies that have emerged. As mentioned earlier, diet is a key differentiating trait that perhaps sparked an initial separation of populations. The food consumed by a group of organisms may seem like a simple trait that should not be significant. However it is comparable to how humans are divided into cultures that share unique diets and food customs. Although these are often based on location and what is typically available geographically, the same principle of how the majority of families pass on their eating traditions can be applied here. Since whales provide parental care as a pod it is not surprising that they would continue to pass down the ‘tradition’ of hunting and eating the same types of organisms. The transient killer whale populations eat mostly marine mammals and the resident killer whale populations eat mostly fish (Baird 1992). Because of this, fhoel Behavior is another important trait to analyze when distinguishing lineages of a species. Killer whales are interesting in that they are extremely social. Not only do they travel in their pods—which is the equivalent to several families combined—but their mannerisms come into play as well. Vocalizing sounds is one particular behavior that can easily be studied and analyzed. Each pod has a unique set of vocals that each individual produces to signal to each other. Numerous species of animals in the world today have a similar strategy to this too, but for killer whales this becomes more evolutionarily significant. The vocal sounds are often used for keeping track of males that have left their natal pod to mate (Lennard 2010). After mating, the males typically return to their original pod. This is an important aspect of the socialness and again disproves the possibility of excessive inbreeding within the populations. Sufficient gene flow is permitted without losing the natal pod’s sense of socialness or ‘family’. Maintaining natal pods is significant for the topic of speciation. Individuals more like one another are kept closer together in their pods and are more likely to remain within their pods thus creating more social separation between the two subspecies. Using modern technology, genetic testing and coding provides the most factual information possible for determining a speciation event. Environmental observations can be useful, but again sympatric speciation is more difficult to notice and diagnose. There is evidence that the transient and residential subspecies have entirely different haplotypes indicating a separation of alleles. It is also evident that these separate subspecies have begun to diverge into even smaller subgroups based on genetic differences as well (Lennard 2000). This indicates that there is enough genetic similarities between subspecies to allow for further unique patterns to emerge in these smaller subgroups. Speciation as a whole is a scientific phenomenon in the grand scheme of evolutionary history. Sympatric speciation in particular is sometimes hard to believe that a collection of traits made a big enough impact to prevent two groups from reproducing and passing alleles back and forth to maintain the original species. Killer whales have proven to have undergone sympatric speciation into two specific subspecies, resident and transient. Varying behavioral, genetic, and geographic traits that likely originated from a rare dispersal of alleles after a historic bottleneck event backing up the division within the species. Further investigation comparing relatedness and mating patterns continues to support this hypothesis as well. It is impossible to tell what is in store for this amazing species next, but if it is anything like similar events in the past, it will provide an increased diversity in the aquatic biome and allow for further evolutionary investigation to better learn about the past, present, and future of life on Earth. References Baird, R. W., Abrams, P. A., & Dill, L. M. 1992. Possible indirect interactions between transient and resident killer whales: Implications for the evolution of foraging specializations in the genus orcinus. Oecologia, 89(1), 125-132. JSTOR. Foote, Andrew D., Julia T. Vilstrup, Renaud De Stephanis, Philippe Verborgh, Sandra C. Abel Nielsen, Robert Deaville, Lars Kleivane, Vidal Martín, Patrick J. O. Miller, Nils Øien, Monica Pérez-Gil, Morten Rasmussen, Robert J. Reid, Kelly M. Robertson, Emer Rogan, Tiu Similä, Maria L. Tejedor, Heike Vester, Gísli A. Víkingsson, Eske Willerslev, M. Thomas P. Gilbert, and Stuart B. Piertney. Genetic Differentiation among North Atlantic Killer Whale Populations. Molecular Ecology 20.3 (2011): 629-41. Wiley Online Library. Foote, A. D., J. Newton, M. C. Avila-Arcos, M.-L. Kampmann, J. A. Samaniego, K. Post, A. Rosing-Asvid, M.-H. S. Sinding, and M. T. P. Gilbert. Tracking Niche Variation over Millennial Timescales in Sympatric Killer Whale Lineages. Proceedings of the Royal Society B: Biological Sciences 280.1768 (2013): 20131481. Hoelzel, A. R., and Gabriel A. Dover. Genetic Differentiation Between Sympatric Killer Whale Populations. Heredity 66 (1990): 191-95. Genetical Society of Great Britain. Hoelzel, A. R., Ada Natoli, Marilyn E. Dahlheim, Carlos Olavarria, Robin W. Baird, and Nancy A. Black. Low Worldwide Genetic Diversity In The Killer Whale ( Orcinus Orca ): Implications For Demographic History. Proceedings of the Royal Society B: Biological Sciences 269.1499 (2002): 1467-473. National Center for Biotechnology Information. Proceedings of The Royal Society. Matkin, C. O., Durban, J. W., Saulitis, E. L., Andrews, R. D., Straley, J. M., Matkin, D. R., & Ellis, G. M. (2012). Contrasting abundance and residency patterns of two sympatric populations of transient killer whales (Orcinus orca) in the northern Gulf of Alaska. Fishery Bulletin, 110(2). 143-155. Pilot, M., M. E. Dahlheim, and A. R. Hoelzel. Social Cohesion among Kin, Gene Flow without Dispersal and the Evolution of Population Genetic Structure in the Killer Whale. Journal of Evolutionary Biology 23.1 (2009): 20-31. Wiley Online Library.