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| Of Manatee Bones, Germs In A Jar, And The Evolution Of Us |
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| SciMed - Biology | |||
| TS-Si News Service | |||
| Friday, 09 May 2008 17:00 | |||
 The Manatee (family Trichechidae, genus Trichechus) are large, gentle, and fully aquatic mammals. The name manatà meant "breast" to the original Taino peoples of the Caribbean (commonly known today as a sea cow).
Manatees comprise three of the four living species in the order Sirenia (the two others are the Eastern Hemisphere dugong and the Sirenia. The closest living relatives are the Proboscidea (elephants) and Hyracoidea (hyraxes).
They are herbivores and customarily eat over 60 different plant species such as algae, mangrove leaves, and turtle grass, but sometimes eat small amounts of fish from nets. An adult manatee can weigh up to 909.1 kg (2000 lbs.) and eat up to 9% of its body weight (approx. 82 kg or 81.8 lbs.) per day.
Manatees typically inhabit warm, shallow, coastal estuarine waters and cannot survive below 15°C (288 K; 60°F). Their natural source for warm waters during the winter is warm spring-fed rivers. The West Indian Manatee migrates into Florida rivers such as the Crystal, Homosassa, and the Chassawohitzka, where the head springs maintain a year round temperature of 22°C (299 K; 72°F).
The Endangered Manatee. The manatee population of Florida (T. manatus) is difficult to determine, but estimates range between 1-3,000. Although manatees have few natural predators (alligators, crocodiles, orcas and sharks), all three species are listed by the International Union for Conservation of Nature (IUCN) as vulnerable to extinction.
The main threat to USA manatees is being struck by boats or slashed with propellers. Recorded Manatee deaths in Florida caused by humans have reached 20%-40% of their population. In the video, a manatee injured by a boat is rescued at Crystal River in Citrus County, Florida, near Three Sisters Springs. The manatee subsequently died of her injuries.
Note. The manatee has been linked to folklore on mermaids. Native Americans ground their bones for asthma and earache remedies.
In West African folklore, the manatee was sacred and thought to have been once human. Killing one was taboo and required penance.
Video courtesy of Save The Manatee (2-17-07). Time 02:18 Broadly stated, developmental biologists study how a single fertilized ovum can yield all the complexity of life, whether it be human or other animals, insects, or flowers. A fundamental question is how an initially symmetric or unformed structure can give rise to highly complex three-dimensional functional organs and tissues.
Parallel genetic origins of pelvic reduction in vertebrates. Michael D. Shapiro, Michael A. Bell, and David M. Kingsley. PNAS 103(37) 13753-13758 doi: 10.1073 / pnas.0604706103 [ Download PDF ]
Kingsley's 2006 study appeared in the Proceedings of the National Academy of Sciences (PNAS). The research was important for a number of reasons. It was part of a larger inquiry into the extent of chance and order in
 evolution. The possible repeatibility of evolution is a major question: if we had to start all over again, would evolutionary history repeat itself? Are there fundamental processes that combine and recombine to yield the seeming complexity of the living world? And how do we account for variations and mutability from a more standard pattern?  Part of the answer lies in distinguishing between fundamental processes and superficial appearance (what something is vs. what it looks like). Kingsley, professor of developmental biology at the Stanford University School of Medicine and an investigator at the Howard Hughes Medical Institute (HHMI), said at the time of his research that "It's striking that evolution might use the same mechanism over and over". In biology, there is an important diference between
physiology, which deals primarily with function, and morphology, which refers to the outward appearance (color, pattern, shape, structure) of an organism and its component parts. This means that even if two very different animals share common genomic/genetic mechanisms of evolution, the underlying mechanisms may be robustly general, quite apart from their outward appearance. There are clear implications for organ development, the preservation of sexual dimorphism, and a variety of physical structures. For quite some time, scientists had been accumulating evidence that evolution isn't so random after all. In 1988, Dr. Richard E. Lenski, an evolutionary biologist at Michigan State University (MSU), loaded 12 genetically identical populations of E. coli bacteria into bottles of broth. Lenski and his colleagues followed the evolutionary fates of their bacteria for more than 30,000 bacterial generations.
Lenski's beautiful experiment became one of the strongest examples of repeatability: all 12 populations show the same patterns of competitive improvement and increased cell size. Moreover, all 12 populations lost their ability to break down and use ribose (a sugar). Even more, the genetic changes underlying these adaptations were generally similar. For example, every population lost its ability to break down ribose by losing a long stretch of
DNA from the same gene. Comparable findings have emerged from studies of diverse life forms, such as cichlids (fish) and sunflowers. Scientists have found species that evolve independently in separate occasions. Each time one of the species newly evolves, its genetic makeup is much the same. Some features are inevitably adaptive, like vision, and the essence of humanity — intelligence and self-awareness.
David Kingsley's findings suggested that mutations in the same gene may be responsible for the evolution of leglessness in animals as distantly related as 1,000-pound manatees in Florida and fish no larger than a human index finger that live in lakes and streams around the world.
The reason the asymmetric pelvic bones are important goes back to work Kingsley published in 2004. In that paper, Kingsley's lab showed that mutations in a gene called PitX1 were responsible for the loss of pelvic fins in three different species of a fish called the threespine stickleback. In each of the species, the
mutation arose independently as the fish evolved in lakes or streams where a more streamlined shape held some evolutionary advantage. Molecular biologists approach biology at the molecular level, with studies that overlap areas of biology and chemistry, particularly those of
genetics and biochemistry. The biologists work on improving their understanding of the interactions between the various systems of a cell, including those between DNA, RNA and protein biosynthesis. Learning how these interactions are regulated can reveal a good deal about the processes presered and shared between species. An active molecule can be cis-acting (from the Latin word cis — "on the same side as") or the opposite, trans-acting ("acting from a different molecule"). How a cis-acting molecule can act upon a trans-acting molecule depends on a region of DNA or RNA that regulates the expression of genes located on that same
chromosome strand. This is the cis-element (or cis-regulatory element) that often bind sites of one or more trans-acting factors. A good example of this process involves the PITX1 gene.  In technical terms, the human gene, Paired-like homeodomain
transcription factor 1 (PITX1), encodes a member of the RIEG/PITX homeobox family, which is in the bicoid class of homeodomain proteins. Members of the homeobox family are involved in organ development and left-right asymmetry. This protein acts as a transcriptional regulator involved in basal and hormone-regulated activity of prolactin and has been associated with autism by some authorities. At the time, Kingsley's work was the first to show that a single gene could be responsible for a large evolutionary change, such as the loss of an entire set of fins, in natural populations. It was particularly interesting that the mutation arose independently in populations separated by thousands of miles. Mouse researchers had also known that a PitX1 mutation eliminated hind limbs in mice, albeit under artificial conditions. What's more, in both mice and sticklebacks with a PitX1 mutation, the residual pelvis tended to be larger on the left than the right.
That finding is what started Kingsley thinking about manatees — large, ocean-going mammals — as well as whales, snakes and skinks, all of which evolved from four-legged ancestors. He theorized that if a PitX1 mutation was responsible for pelvic reductions in several species of sticklebacks and had a similar role in laboratory mice, it might be a mutation used widely by evolution.
As luck would have it, Kingsley made contact with Sentiel Rommel, PhD, a manatee researcher from the Florida Fish and Wildlife Research Institute, who had collected pelvic bones from manatees during autopsies. Kingsley convinced Rommel to send the collection of bones, each about the size of a child's fist. When Kingsley weighed the rudimentary bones, he found that manatees showed the same characteristic asymmetry found in mice and sticklebacks.
The asymmetry observed in manatee pelvic bones suggests that PitX1 may have been used repeatedly as animals evolved from their four-legged ancestors. However, as Kingsley noted, further studies would be required to pinpoint the DNA changes in Pitx1 or other genes that are associated with pelvic reduction in manatees and other organisms. That work continues today wit consistent results. Although Kingsley had no genetic evidence of a PitX1 mutation in manatees at the time, he has extended his asymmetry observations to other animals. To date, he has not yet found a cache of snake or whale pelvises.
Still, Kingsley is heartened by the morphological similarities his team has observed between pelvic reduction in very different animals. "It's encouraging because it means that if you are looking at the genetic mechanisms of evolution in one animal, your results may turn out to be surprisingly general," he said.
In the same 2006 paper, Kingsley and postdoctoral scholar Michael Shapiro, PhD, showed evidence that distantly related species of ninespine sticklebacks, in addition to their threespine cousins, evolved their sleeker shape with help from a PitX1 mutation.
This work was funded by the Helen Hay Whitney Foundation, the Burroughs Wellcome Fund and the National Institutes of Health (NIH).
 The TS-Si News Service is a collaborative effort by TS-Si.org editors, contributors, and corresponding institutions. The sources can include the cited individuals and organizations, as well as TS-Si.org staff contributions. Articles and news reports do not necessarily convey official positions of TS-Si, its partners, or affiliates.We welcome your comments. Use the form below to leave a public comment or send private correspondence via the TS-Si Contact Page. We will not divulge any personal details or place you on a mailing list without your permission. TS-Si is dedicated to the acceptance, medical treatment, and legal protection of individuals correcting the misalignment of their brains and their anatomical sex, while supporting their transition into society as hormonally reconstituted and surgically corrected citizens. 
 
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