User:Hagerty.49/sandbox

Topic: Evolutionary development of turtle morphology

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

Suggestions to the Talk page: I have some more suggestions for the ‘Anatomy and morphology’ section. It could be improved by providing some explanation as to why freshwater turtles are generally smaller than sea turtles. It would be helpful to add something about why some turtles contract their necks under their spine while others contract their necks to the side, and what the costs and benefits to each behavior are. I also think that the small section on intelligence should either be updated or removed; more information is needed to make it relevant.
 * When I tried to add a sentence to this article after putting these suggestions in the Talk page, I realized that it is a semi-protected article so I wasn't able to edit it. This was the sentence I was going to add in the 'Anatomy and morphology' section: "Giant body size among turtles and tortoises is advantageous because it enables them to survive longer when resources are scarce, allowing them to travel longer distances between feeding sites, and also reduces predation risk." The citation would be from this source: http://rsbl.royalsocietypublishing.org/content/7/4/558.full

Because I wasn't able to add this sentence, I added one to a similar article: https://en.wikipedia.org/wiki/Sea_turtle

Sentence: "Larger hatchlings have a higher probability of survival than smaller individuals, which can be explained by the fact that larger offspring are faster and thus less exposed to predation."

Citation: Janzen, F. J., G. L. Paukstis, and J. K. Tucker. 2000. Experimental analysis of an early life-history stage: selection on size of hatchling turtles. Ecology 81.8: 2290. [1] http://rsbl.royalsocietypublishing.org/content/7/4/558.full

Annotated Bibliography

Eguchi, T., J. A. Seminoff, R. A. LeRoux, D. Prosperi, D. L. Dutton, and P. H. Dutton. 2012. Morpholoy and growth rates of the green sea turtle (Chelonia mydas) in a northern-most temperate foraging ground. Herpetologica 68(1): 76-87.

This article focuses on body size and growth rates of green sea turtles in San Diego Bay, California. The study was carried out over a range of 21 years, and investigates anthropogenic effects on somatic growth rates of the turtles. Specifically, a power plant had been discharging effluent into the bay during a large portion of the study, and the researchers found that this had a direct effect on turtle body length. The findings of this study will help me expand on my topic by providing outlook on how humans have shaped the evolution of turtle morphology, and the effects that a changing environment can have on the species.

Jaffe, A. L., G. J. Slater, and M. E. Alfaro. 2011. The evolution of island gigantism and body size variation in tortoises and turtles. Biology Letters 7(4): 558-561.

This article addresses the fact that the specific causes of such extreme size diversity among turtles and tortoises are not well known or understood. The researchers carried out an experimental comparative analysis of body size evolution in turtles and tortoises, and found that habitats largely influence morphology. A phylogenetic approach was used to help analyze body size variations, which is an important evolutionary technique. This paper will be beneficial by helping me better understand how habitat size and location have contributed to the development of certain body sizes among different species of turtles over time, while also helping me consider turtle phylogeny.

Janzen, F. J., G. L. Paukstis, and J. K. Tucker. 2000. Experimental analysis of an early life-history stage: selection on size of hatchling turtles. Ecology 81.8: 2290.

This article presents a study on how natural selection acts on key traits during the early life of the red-eared slider turtle. The researchers set up a mark-recapture experiment on turtle hatchlings, and included meteorological and predator observations in their data. They found that the effect of size-dependent predation on survivorship influenced selection for larger individuals. This will advance my topic by providing information on how interactions with other species have affected, and continue to affect, turtle morphology.

Maffuci, F. et al. 2013. Bone density in the loggerhead turtle: functional implications for stage specific aquatic habits. Journal of Zoology 291(4): 243-248.

This articles focuses on the relationship between bone density and body size in loggerhead sea turtles. The researchers aimed to find functional explanations for the animal’s aquatic behaviors and habits. They found that overall size and bone density in the humerus were correlated, and uncovered information on how turtles developed their underwater locomotive techniques. This study will enhance the development of my topic by helping me consider how the need for stability and agility in water has shaped the evolution of turtle morphology.

Wang, Z. et al. 2013. The draft genomes of soft-shell turtle and green sea turtle yield insights into the development and evolution of the turtle-specific body plan. Nature Genetics 45: 701-706.

The study presented in this article aims to answer questions about the origin of the body plan of turtles. The genomes of a soft-shell turtle and a green sea turtle were analyzed, and the locations of certain genes helped the researchers explain how the unique morphology of turtles came about. They found that much could be understood by considering the hourglass model of embryonic development, a format that will help me better grasp the time in a turtle’s life history when most morphological developments take place.

'''FINAL DRAFT STARTS HERE '''

Evolutionary Development of Chelonian Morphology

How did chelonians, or turtles and tortoises, develop into the shelled reptiles that everyone is familiar with today? Why do they possess circular-shaped shells, four short limbs, a long neck that can retract into the shell, or a tail? The evolution of turtle morphology is a complex topic, involving many different explanations. In fact, the events leading to and shaping the chelonian body plan are not well understood (Jaffe et al. 2011). However, experiments conducted in recent years have shed some light on the subject. After examining the results of such research, it appears that the morphology of extant turtles and tortoises is due largely in part to habitat influence, size dependent predation, body functionality, important occurrences in various developmental stages, and even anthropogenic impacts. Understanding how each of these events influences body development will provide further insight into the evolutionary basis of chelonian morphology. Kuratani et al. discuss how the appearance of a shell requires “unusual musculoskeletal elements” which makes the turtle a perfect candidate to help gain knowledge on the emergence of new structures in developmental biology, along with a better grasp on the increasing complexity arising from evolution. As with any species, the habitat quality will have an effect on the size and shape of turtles and tortoises. The variety of habitats that chelonians occupy is a leading explanation for body size variation. Oceanic island tortoises and sea turtles have larger optimal body sizes than freshwater turtles and mainland tortoises, with the largest of all being sea turtles (Jaffe et al. 2011). The reason for this is correlated with the vastness of the ocean, and the fact that sea turtles travel such far distances (Jaffe et al. 2011). Having more room to live enables more room for growth. Another way habitat influences morphology has to do with the presence of nearby species. If one species of turtle is sharing its habitat with another, there is a chance that sympatric hybridization could occur (Lutterschmidt et al. 2007). Sympatric species are those that live in the same geographic area and have encounters with one another on a regular basis. Hybridization refers to the offspring produced by the mating of one species with another. Sympatric hybridization events can lead to variations in chelonian shell morphology (Lutterschmidt et al. 2007). A recent study found evidence of such an event involving the Three-toed box turtle (Terrapene carolina triunguis) and the Ornate box turtle (Terrapene ornata ornata). The shells of the hybrid offspring more closely resemble that of the Three-toed box turtle as opposed to the Ornate box turtle (Lutterschmidt et al. 2007). These hybrids provide novel individuals for natural selection to act on, and populations evolve if there is a response to selection. The study also represents that when two species hybridize, certain morphological aspects of one species can override those of the other, which can lead to genetic change over time. Overall, it is clear that habitat influence is an important factor impacting chelonian body size evolution. Another determinant of turtle morphology is size dependent predation. Many evolutionary biologists have focused on how an individual’s phenotype affects performance, which in turn affects reproductive success, or fitness (Janzen et al. 2007). One study that focused on this cycle revealed that predation has the most obvious effect on the evolution of turtle hatchling size (Janzen et. al 2007). The researchers compared the mortality rates of turtles with different phenotypes as they journey from their nest to the sea. There were a few different hypotheses for why larger hatchlings survive better than smaller hatchlings, and the prevailing one stated that larger turtles would be preyed upon at a lower rate. Predators can only functionally intake so much; larger individuals are not targeted as often. The study also shows that body size is positively correlated with speed, so larger turtles are exposed to predators for a shorter amount of time. This has an obvious impact on morphological evolution. The turtles that survive and make it to the sea to eventually reproduce and pass on their genes are the ones that will shape the genetics of the population as a whole. The fact that there is size dependent predation on chelonians has led to the evolutionary development of large body sizes. A simple observation of a sea turtle next to a land tortoise would demonstrate that the body of the sea turtle is more streamlined—longer, thinner, and less resistant to the current of water—than that of the chelonian that spends its time on land. Most people could quite easily come to the conclusion that this can be explained by the fact that the more streamlined morphology is more functional for swimming underwater. A study was conducted in 2013 that examined a slightly less obvious aspect of the functionality of turtle morphology: bone density. Aquatic chelonians have evolved buoyancy control mechanisms that involve changes in skeletal density associated with foraging strategies; lower bone density enables deep diving and quicker movements (Maffuci et al. 2013). After measuring the density of the humerus in loggerhead turtles (Caretta caretta), the researchers found that bone density was positively correlated with body size. Smaller, younger turtles have lower bone densities. Adult loggerheads forage on the floor of shallow benthic zones, so they do not require low bone density needed to dive deep and chase prey (Maffuci et al. 2013). This study provides insight to how functionality can drive evolution. The characteristic that proves most functional for a particular habit is the one that is selected for and leads to population evolution. As stated earlier, the origin of the unique body plan of turtles and tortoises is not clearly defined. However, it is assumed that turtles are a sister group of crocodilians and birds (Wang et al. 2013). A group of researchers studied the phylogeny and genomes of two turtle species: the soft-shell turtle (Pelodiscus sinensis) and the green sea turtle (Chelonia mydas) to find answers to the evolutionary question of chelonian body plan origin. They discovered that much of the morphology is determined after vertebrate development. The turtles first establish a vertebrate body plan similar to chickens, and then diverge from the plan to develop turtle-specific characteristics such as the carapacial ridge, which leads to shell development (Wang et al. 2013). This shift in the early developmental stage plays a crucial role in the evolution of turtle-specific morphology. Another shift that affects chelonian morphology involves a change in diet across life stages. Green turtles shift from an omnivorous diet of planktonic material as juveniles to an herbivorous diet of algae and seagrass material as adults, and there is a concurrent transformation of skull morphology (Nishizawa et al. 2010). This presents further evidence of how pivotal transitions in developmental stages have influenced body size among chelonian species. One more factor that has modified turtle morphology is one that has become increasingly more prominent in recent years: anthropogenic impacts. Human activities have direct effects on the environment, and a changing environment can shape the evolution of a species. A study conducted from 1990 to 2011 that examined somatic growth rates of green sea turtles revealed how humans have impacted chelonian morphology. A power plant in San Diego Bay, California was discharging heated effluent into the bay from 1960 until 2010, and the environment alteration led to increased growth rates in turtles (Eguchi et al. 2012). Not only did the effluent warm the water, which heightened growth rates during times when the water is usually too cold for turtles to be active, but it also increased productivity of more protein-rich food sources for the turtles (Eguchi et al. 2012). Because of the higher growth rates, the turtles in California grew larger and reproductive output increased. The findings provide another example of the impact a diet can have on a turtle’s morphology, as discussed previously. The termination of the power plant operation is leading the bay ecosystem back to its natural state, and decreased somatic growth rates are expected (Eguchi et al. 2012). The results of the study clearly show the impact of anthropogenic effects on turtle morphology. Another study on nest relocation provides further evidence of how humans can shape chelonian morphological evolution. Researchers examined the effects of nest relocation on the endangered giant South American turtle, Podocnemis expansa. They discovered that turtle clutches that were transplanted to a new location had higher mortality rates and more morphological abnormalities compared to nontransplanted clutches (Jaffé et al. 2008). The study was carried out to increase understanding of turtle conservation. It was originally believed that nest relocation could be a useful conservation technique. The results clearly demonstrate that humans should not manipulate or relocate turtle clutches, and impart strong evidence of the detrimental effects that anthropogenic activity can cause. Even though it was realized that the nest relocation tactic should no longer be carried out, the events occurring because of it will always have a mark in the evolution of the species involved. Whether it is deliberate or not, humans alter the environment in ways that can also alter the morphology of chelonian species. In conclusion, the evolutionary development of chelonian morphology is a multi-faceted topic. A morphological characteristic is ideal if it is functionally beneficial for an individual. The structure of an organism must match its function. This idea can be seen as a driving force of body development in turtles and tortoises. Somatic characteristics of these species have arisen due to various events in their evolutionary histories and the origin of their body plan cannot be fully explained at present. However, some answers lie in the influence and magnitude of their habitats, the prevalence of size dependent predation on hatchlings, the functionality of their morphology with regards to foraging, different developmental events, and the actions of humans. Further study is required to enhance and refine these explanations, and to uncover novel clarifications for the evolution of body size and shape among turtles and tortoises.

References

Eguchi, T., J. A. Seminoff, R. A. LeRoux, D. Prosperi, D. L. Dutton, and P. H. Dutton. 2012. Morpholoy and growth rates of the green sea turtle (Chelonia mydas) in a northern-most temperate foraging ground. Herpetologica 68(1): 76-87.

Jaffe, A. L., G. J. Slater, and M. E. Alfaro. 2011. The evolution of island gigantism and body size variation in tortoises and turtles. Biology Letters 7(4): 558-561.

Jaffé, R., C. Peñaloza, and G. R. Barreto. 2008. Monitoring an endangered freshwater turtle management program: effects of nest relocation on growth and locomotive performance of the giant South American turtle (Podocnemis expansa, Podocnemididae). Chelonian Conservation and Biology 7(2): 213-222.

Janzen, F. J., G. L. Paukstis, and J. K. Tucker. 2000. Experimental analysis of an early life-history stage: selection on size of hatchling turtles. Functional Ecology 21: 162-170.

Kuratani, S., S. Kuraku, and H. Nagashima. 2011. Evolutionary developmental perspective for 	the origin of turtles: the folding theory for the shell based on the developmental nature of the carapacial ridge. Evolution & Development 13: 1-14.

Lutterschmidt, W.I., S. A. Escobar, and E. D. Wilson. 2007. Multivariate analyses of shell morphology of putative hybrid box turtles. Southeastern Naturalist 6(4): 571-576.

Maffuci, F. et al. 2013. Bone density in the loggerhead turtle: functional implications for stage specific aquatic habits. Journal of Zoology 291(4): 243-248.

Nishizawa, H., M. Asahara, N. Kamezaki, and N. Arai. 2010. Differences in the skull morphology between juvenile and adult green turtles: implications for the ontogenetic diet shift. Current Herpetology 29(2): 97-101.

Wang, Z. et al. 2013. The draft genomes of soft-shell turtle and green sea turtle yield insights into the development and evolution of the turtle-specific body plan. Nature Genetics 45: 701-706.