User:Robbins.260/sandbox

Are bull sharks and their osmoregulatory capabilities a process for evolutionary and reproductive success? I am a fisheries and aquatic sciences major that is interested in fish ecology and biodiversity within freshwater ecosystems. The study of bull sharks in freshwater systems adds a different element to my interests. Not all fish have the capabilities to survive in both freshwater and saltwater, so the fact that bull sharks can allows for some evolutionary discussion on osmoregulation. This discussion of bull sharks will help me be able to contribute to such pages as “Predation” and “Reproductive Success”.

Annotated Bibliography

Manzon, L. A. (2002). The Role of Prolactin in Fish Osmoregulation: A Review. General and Comparative Endocrinology, 125(2), 291-310.

The protein hormone prolactin was discovered to have many more uses than originally thought, one of those uses being a catalyst in osmoregulation amongst fish. Protein hormone prolactin (PRL) is discussed thoroughly within this review and describes how the protein may have had an evolutionary effect on growth in fish. Manzon covers all dimensions of the effects of PRL and focuses on the effect of osmoregulatory behavior. The PRL is an important aspect because of its scarcity in fish species, helping to separate its evolutionary differences.

Hammerschlag, N. (2006). Osmoregulation in elasmobranchs: a review for fish biologists, behaviourists and ecologists. Marine and Freshwater Behaviour and Physiology, 39(3), 209-228.

Types of elasombranch fish have the capability to osmoregulate. Hammerschlag covers recent research and historical findings to help demonstrate the reasoning and functionality of osmoregulation in fish. Osmoregulation deals with salt content stabilization within fish that travel between saltwater and freshwater. This adaptation may be used for bull sharks in certain ways. Those ways being: high juvenile survival rate, versatile predation strategies, and habitat determination due to human impacts. Future research may be done, via telemetry, to help track where these sharks go at different ages. Osmoregulation is an evolutionary advantage for the small fish amount of species it incorporates.

Heupel, M., & Simpfendorfer, C. (2008). Movement and distribution of young bull sharks Carcharhinus leucas in a variable estuarine environment. AQUATIC BIOLOGY, 1, 277-289.

The testing done within this article is describing the movement of juvenile bull sharks through their development. Heupel and Simpfendorfer discuss how osmoregulation may be critical to bull shark well—being. This conclusion is derived from the tracking of bull sharks from birth to juvenile state while tracking their geographic location during that time frame. Bull sharks may use osmoregulation to help maintain peak energetic states. Even though the bull sharks have the capability to live in all salinity levels, staying in certain areas helps keep energy levels at optimum rates. This shows an evolutionary benefit of osmoregulation to allow bull sharks to have high survival rates because of their young being able to adapt to different environments.

Heupel, M., & Simpfendorfer, C. (2011). Estuarine nursery areas provide a low-mortality environment for young bull sharks Carcharhinus leucas. Marine Ecology Progress Series, 433, 237-244.

Bull sharks have become dominant predators in the marine world and a lot of that is due to their complex reproductive process. Bull sharks are diadromous, meaning they can swim between freshwater and saltwater very efficiently. Heupel and Simpfendorfer describe the reproductive process of bull sharks and how their interactive use of estuaries increases survival rate. The young sharks do not encounter the same predation in the freshwater systems as they would in saltwater oceans. The adaptation of osmoregulation allows for the bull shark to reproduce in freshwater systems to give their offspring a higher chance of survival.

Stinchcombe, J. R., & Kirkpatrick, M. (2012). Genetics and evolution of function-valued traits: understanding environmentally responsive phenotypes. Trends in Ecology & Evolution, 27(11), 637-647.

Natural selection deals with the phenotypes that prove best for survival rate. This article discusses traits in detail and deals with function-valued traits in specific. A function-valued trait is any trait that changes due to another variable. If you apply this concept towards bull sharks there are conclusions that can be made to make osmoregulation an adaptive phenotype that became dominant over time. Variation amongst a population allows for phenotypes that are more suitable to survive. Within bull sharks, osmoregulation may have only been found in a certain number of them thousands of years ago. As time has gone on, those that expressed the phenotype for osmoregulation have had a better survival rate due to reproduction in freshwater systems. The gene is now at a peak prominence in all individuals and helps explains the genetics of evolution of function-valued traits.

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

Revisions and Additions
I added a sentence to the freshwater tolerance section. That sentence being, this is thought to be a physiological strategy to help with juvenile survival rates and a way to increase overall fitness of bull sharks. I did this to help further explain the advantage that bull sharks have by reproducing in freshwater systems. Nowhere in the article were the terms "juvenile survival rate" and "fitness" used. I thought adding these two key terms to the section would help identify the evolutionary benefits from this adaptation. Also, the article never discusses the topic of euryhaline organisms. This encompasses all organisms that can live in high and low salinity levels and should not be confused with elasmobranch species that just incorporates cartilaginous fish. One other contribution that should be made is the discussion of the protein hormone prolactin. Prolactin is a catalyst in osmoregulation and therefore helps the bull shark adjust more efficiently. The section of freshwater tolerance discusses a lot of the physiological adjustments made for osmoregulation and the protein hormone prolactin should be included to add detail and clarification to the section. Robbins.260 (talk) 09:02, 1 October 2014 (UTC)

FINAL DRAFT STARTS HERE
Osmoregulation Within Bull Sharks in Relation to Evolutionary Biology

Bull sharks, or Carcharhinus leucas, are a species of fish that have been the subject of many research projects due to their ability to osmoregulate. This term, osmoregulate, refers to the shark’s ability to actively hold or lose salts within their body, which allows them to swim in both saltwater and freshwater. Not all fish species have the capacity to perform this adaptive task. Even one of the bull sharks closest relatives, the sandbar shark, has yet to evolve and take on the same capabilities (McAuley et al. 2007). There are multiple factors that may have lead to the evolutionary skill of osmoregulation. Migration and Dispersal, the movement of populations, to find resources such as food, may have driven the bull shark to adapt to estuarine systems. The brackish systems near river mouths may have helped with reproductive success, therefore; natural selection may have pushed for osmoregulating bull sharks because of their greater relative fitness in coastal waters. Identifying the speciation of the bull shark also helps draw conclusions that the population may have suffered a population bottleneck. These distinct evolutionary references may help find an answer to the bull sharks unique capability. Migration is defined as movement among populations. Bull sharks are a widely spread species that cover oceans across the globe. These populations are dense in shallow coastal waters that are relatively warmer than most areas. Estuarine settings, where freshwater and saltwater meet, are highly productive ecosystems that hold many trophic levels and provide large amounts of resources, such as food, for bull sharks. The density of these populations may have lead to the forming of metapopulations, spatially separated populations of the same species, within freshwater due to lack of food sources in oceanic settings. Another angle of evolutionary biology is that populations contain variance amongst individuals. There must have been variance of alleles in historic populations of bull sharks. A certain allele coded for the ability to osmoregulate. Not all the bull sharks alive had this gene, but the advantage of housing this gene lead to the success of bull sharks that could travel to freshwater systems and forage without limitation. Dispersal is another mechanism of evolution and is the movement away from a population’s original location. Dispersal is a fundamental adaptation for species. This process helps stimulate gene flow and the movement of alleles. These dispersal characteristics would help explain the adaptation of osmoregulation within bull sharks. The variance in alleles would allow certain bull sharks, which have the osmoregulating gene, to adapt to freshwater systems along the coasts and thrive over multiple generations. Another theory to account for the development of osmoregulation within bull sharks would be natural selection and the increase of reproductive success within estuarine settings. Bull sharks have a tendency to reproduce within estuarine systems that contain a lower salt content than oceanic systems (Heupel; Simpfendorfer 2008). These brackish systems allow for a reproductive setting that is not inhabited by apex predators that will prey on young bull sharks. The bull sharks that reproduced in more predated areas would suffer in their reproductive rates. From an evolutionary biology standpoint the bull sharks that initially reproduced in these brackish systems would have a higher relative fitness than those that reproduced in deeper oceanic settings (Heupel; Simpfendorfer 2011). The shallow waters of the coastal systems are a natural protector against predators. Larger predators rarely swim in shallow waters and the terrestrial settings adjacent to the shallows also allow for protection. Natural selection occurs when genotypes have differential reproductive success. Therefore, this relative fitness comparison clearly represents natural selection. There is also evidence that bull shark populations may have encountered a population bottleneck during the last ice age (Tillett et al. 2012). A population bottleneck is a rapid decease in population size. Sampling juveniles in multiple nurseries and comparing their structure in microsatellites had demonstrated this because of the similarity in quantitative trait loci (Tillet et al. 2012). This bottleneck favored bull sharks that were capable of osmoregulation because modern day bull sharks are capable of osmoregulation and there has not been a clearly defined bottleneck since the Pleistocene epoch (Tillet et al. 2012). It is clear that expansion occurred after the population bottleneck because bull sharks are a very stable population throughout the world. When analyzing the phylogeny of the bull shark it is noticeable that even its closest relatives are incapable of osmoregulation. One of the closest relatives to the bull shark is the sandbar shark. The sandbar shark has a very similar size, color, and habitat, but it does not have ability for osmoregulation. The genus of both species is Carcharhinus while the bull shark is Carcharhinus leucas and the sandbar shark Carcharhinus plumbeus (McAuley et al. 2007). The bull shark and sandbar shark are also part of the subclass called elasmobranchii. This subclass encompasses some sharks, rays, and skates. Their jaws, lack of swim bladders, and scale patterns differentiate Elasmobranchii from other cartilaginous fishes (Pratt et al. 1990). The bull shark is a fish that is diadromous, meaning they can swim between saltwater and freshwater with ease (Heupel; Simpfendorfer 2011). These fish also fall under the category of euryhaline. Euryhaline refers to an organism that is able to adapt to a wide range of salinities. The bull shark is one of the only cartilaginous fishes that have been reported in freshwater systems. Many of the euryhaline species are bony fish such as salmon and tilapia that are not closely related to the bull shark. These bony fish actively lose salt through their gills while bull sharks use a different system that incorporates the retention of urea within their blood (Pillans; Franklin 2004). These descriptive differences can be explained through evolutionary concepts that were previously discussed. The most convincing argument stands to be a population bottleneck that happened during the last ice age (Tillett et al. 2012). This bottleneck may have separated the bull shark from the rest of the elasmobranchii subclass and favored the genes for an osmoregulatory system. The divergence of the bull shark may also be explained through sympatric speciation and niche partitioning. Sympatric speciation refers to the speciation of organisms in the absence of physical or spatial barriers. Looking back at the comparisons made between sandbar sharks and bull sharks we can conclude that since their habitat, size, coloration, and geographical distribution are the same there must not have been any physical barriers separating them. This would rule out the idea of allopatric speciation, which is the speciation following subdivision of a population due to physical barriers. Although, There is a lack of research done comparing these two shark species under the concept of sympatric speciation but assumptions can be made to justify sympatry. One obvious difference between sandbar sharks and bull sharks that may explain their sympatric speciation is their reproductive habits. The sandbar shark deposits its pups within estuarine settings, but is never found in actual freshwater. Those pups stay within those estuarine setting for about a year and then make their way offshore (Knickle). The bull shark pups are also hatched in these estuarine nurseries, but instead of making their way offshore, the pups actually swim farther upstream in their first year of life (Heupel; Simpendorfer. 2008). This difference also emphasizes the fact that the bull sharks can osmoregulate, even as a pup, unlike its counterpart the sandbar shark. These differences in behavior and resource use may have lead to niche partitioning. Niche partitioning is selection driven speciation that facilitates different patterns of resource usage. This term can be applied towards the bull sharks use of freshwater ecosystems. The bull shark uses the freshwater ecosystem not only for reproductive advantages, but for individual energy advantages as well. Younger bull sharks are not able to osmoregulate as well as mature bull sharks (Heupel; Simpendorfer 2008). The younger bull sharks are better suited for lower salinity environments by allocating less energy for osmoregulation and more energy for predation and survival. The pups are born into low salinity levels and therefore are well suited for those areas and not marine areas with high salt concentrations. This is an example of niche partitioning because the bull shark is using freshwater resources differently than other organisms within its genus, especially the sandbar shark. The bull shark has become a very interesting specimen to researchers and scientists alike because of its unique capability of osmoregulation. There are still disconnects and a lack of evidence on how exactly the bull shark has developed this skill to survive in both saltwater and freshwater. The theories described are just a brief list of the plausible possibilities of how the bull shark developed into a master of osmoregulation. Evolutionary biology helps explains the bull sharks adaptive techniques by using terms like migration, natural selection, population bottlenecks, sympatric speciation, and niche partitioning. These concepts highlight clear pathways of possibilities for the evolution of the osmoregulatory system of the bull shark. We cannot be sure if these evolutionary theories are true without further study and comparisons, but they are grounds for more research of Carcharhinus leucas.

References Daly, R., Smale, M. J., Cowley, P. D., & Froneman, P. W. 2014. Residency Patterns and Migration Dynamics of Adult Bull Sharks (Carcharhinus leucas) on the East Coast of Southern Africa. PLoS ONE, 9, e109357.

Hammerschlag, N. 2006. Osmoregulation in elasmobranchs: a review for fish biologists, behaviourists and ecologists. Marine and Freshwater Behaviour and Physiology, 39, 209-228.

Hammerschlag, N., Graham, F., Nelson, E., Hartog, K., & Hammerschlag-Peyer, C. 2014. Habitat Partitioning and Intrapopulation Variation in Migration Patterns of Sympatric Apex-Predatory Sharks Across a Dynamic Marine Landscape. Integrative and Comparative Biology, 54, E84.

Heupel, M., & Simpfendorfer, C. 2011. Estuarine nursery areas provide a low-mortality environment for young bull sharks Carcharhinus leucas. Marine Ecology Progress Series, 433, 237-244.

Heupel, M., & Simpfendorfer, C. 2008. Movement and distribution of young bull sharks Carcharhinus leucas in a variable estuarine environment. AQUATIC BIOLOGY, 1, 277-289.

Knickle, C. (n.d.). Sandbar Shark. Florida Museum of Natural History. Retrieved October 28, 2014, from http://web.archive.org/web/2008053115061

McAuley, R., Simpfendorfer, C., Hyndes, G., & Lenanton, R. 2007. Distribution and reproductive biology of the sandbar shark, Carcharhinus plumbeus (Nardo), in Western Australian waters. Marine and Freshwater Research, 58, 116-126.

Pillans, R. D., & Franklin, C. E. 2004. Plasma osmolyte concentrations and rectal gland mass of bull sharks Carcharhinus leucas, captured along a salinity gradient. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 138, 363-371.

Pratt, H., Gruber, S., & Taniuchi, T. 1990. Elasmobranchs as Living Resources: Advances in the Biology, Ecology, Systematics, and the Status of the Fisheries. NOAA Technical Report NMFS, 90, 9-14.

Tillett, B. J., Meekan, M. G., Field, I. C., Thorburn, D. C., & Ovenden, J. R. 2012. Evidence for reproductive philopatry in the bull shark Carcharhinus leucas. Journal of Fish Biology, 80, 2140-2158.

Evolutionary Disconnect
The bull shark is a special case in evolutionary history. Some of its closest living relatives do not have the capabilities to osmoregulation. The bull shark’s genus, Carcharhinus, is shared by the sand bar shark that is not capable of osmoregulation. Although, bull sharks share the same family, Carcharhinidae, with the little known river sharks as well as the same subclass, Elasmobranchii. This allows for some evolutionary predictions of where the bull shark first originated. Is it a river shark turned to the sea? Or a sea shark turned towards the river? The bull shark just has very much in common with river sharks, glyphis, and its own genus of Carcharhinus, but the evolutionary question still stands, where exactly did this shark come from and when ? Much more evolutionary evidence is needed to draw a sound conclusion of the bull sharks phylogeny.

These fish also fall under the category of euryhaline fish. Euryhaline refers to an organism that is able to adapt to a wide range of salinities. The bull shark is one of the only cartilaginous fishes that have been reported in freshwater systems. Many of the euryhaline species are bony fish such as salmon and tilapia and do not qualify as fish that are closely related to bull sharks due to their physiological makeup. Evolutionary assumptions can be made to help explain this sort of evolutionary disconnect; one being that the bull shark encountered a population bottleneck that occurred during the last ice age. This bottleneck may have separated the bull shark from the rest of the elasmobranchii subclass and favored the genes for an osmoregulatory system.

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