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With growing evidence for the presence of feathers in theropod dinosaurs, scientists have become increasingly interested in what adaptive function the earliest feathers served. The three predominant hypotheses are 1) flight, 2) thermoregulation, and 3) visual display. While the first two hypotheses have each received considerable attention and analysis, the third has often been mentioned yet has been inadequately described and analyzed. We define the visual display hypothesis as predicting that theropod feathers served primarily in the creation of a visual cue capable of triggering a behavioral response in an individual perceiving this cue. We analyze fossil evidence regarding whether such a cue could have been generated and perceived, discuss plausible scenarios in which this type of visual cue could have developed, and highlight areas where more data are needed to further support or falsify this hypothesis. We hope that by developing and articulating hypotheses such as this, it will provide other researchers a framework in which to place future discoveries in order to better understand the presence of early feathers on theropod dinosaurs.
Ubiquitin is a conserved eukaryotic protein essential to cellular survival. Although it contributes to various cellular processes including vesicular trafficking and signal transduction, it is primarily known for its role in protein homeostasis. Specifically, ubiquitin serves as a tag placed on unneeded cellular proteins that targets them for proteasomal degradation. After transcription and post-translational modification, ubiquitin monomers may become activated and conjugated to target proteins through the E1/E2/E3 enzymatic pathway. Multiple additional conjugations of ubiquitin monomers results in the creation of polyubiquitin chains, which signals the protein for degradation in the 26S proteasome. Here a review of this process, along with a number of ubiquitin's other roles, is presented.
Siren intermedia and Amphiuma tridactylum are aquatic salamanders that live in temporal ponds, swamps, sloughs, ditches, and sluggish streams. The salamanders' population dynamics, especially survivorship, and migration patterns are generally unknown in the Mississippi Delta. At Delta State University's Center for Science and Environment Education, five small ponds were used to develop a model to determine selected population parameters of S. intermedia and A. tridactylum. Modified minnow traps baited with bacon were used to capture the salamanders safely without disturbing the habitat. Upon capture, length (cm) and weight (g) were determined. Each individual was tagged by inserting a Passive Integrated Transponder (PIT tag) into the muscular portion of the tail. They were then returned to the original pond of capture. The goal of this project was to determine the population size, survivorship, and migration patterns of S. intermedia and A. tridactylum. Fifty two S. intermedia and 29 A. tridactylum were captured from February 2008 through April 2010. Both species had small population sizes with large 95% confidence intervals. This model may be useful for wetland restoration and wildlife management in the Mississippi Delta.
Restriction fragment length polymorphisms (RFLPs) are variations in DNA sequences that can be detected by digestion with restriction enzymes. RFLPs are used to study variation and evolution within populations. This study focused on a specific PvFLP occurring within the human ACTG2 (formerly ACTA3) gene. ACTG2 encodes a γ-actin specifically expressed in mammalian enteric muscle. The RFLP occurs within the first intron and, while not a linkage marker for any genetic condition, has implications as a marker in human evolution. Humans normally have two copies of each chromosome. Each chromosome contributes one allele towards the pair examined using Mendelian genetics. An earlier study of the RFLP, conducted among Japanese and Caucasian populations, published the finding that the RFLP allele occurred twenty-one times more frequently in Caucasian populations. This study expanded analysis on this RFLP by surveying allelic frequencies in African Americans. Two hypotheses to explain earlier allelic results were tested: (1) the RFLP occurred after human migration from Africa, and some unknown selection pressure existed that maintained the RFLP among Caucasians, or (2) the original, small Caucasian sample size accounted for the observed result. In the African Americans sample, as well as an expanded Caucasian sample, both forms of the RFLP were distributed evenly after random sampling analysis. The results suggest a sampling error as the most likely explanation for earlier studies conducted on Caucasians.