Browsing by Author "Davis, Scott K."
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Item Dental variation and biological affinity among middle Holocene human populations in North America(1995-08) Powell, Joseph Frederick; Steele, D. Gentry; Waters, Michael R.; Carlson, David Lee; Davis, Scott K.; Dettwyler, Katherine A.The "Tripartite" model of the peopling of the New World presents the hypothesis that all Native American linguistic, dental, and genetic variation was the result of three migratory "waves" from northeast Asia, whose descendants are modern Amerindian, Na-Dene, and Aleut-Eskimo populations. Several hypotheses were derived from this model, and tested using dental morphological and metric traits from middle Holocene (5,000 - 8,000 yr B.P.) Amerindians: (1) all middle Holocene groups share dental traits with northern Asian "Sinodont" populations, reflecting their origin from a northern Asian founding population; (2) middle Holocene Amerindians exhibit close biological affinity with later Holocene Amerindians, followed by other New World populations and northern Asians, reflecting the historical sequence of divergence among these groups; (3) early Amerindian dental variation is limited due to late Pleistocene founding events. Dental metric and nonrnetric traits, known to be under strong genetic control, were recorded for 573 middle Holocene individuals from nine sites in eastern North America. All data were corrected for age and sex variation and observer error, and were tested using a wide range of statistical methods. Results were compared to expected patterns of variation from simulations of various evolutionary forces such as genetic drift and gene flow. The dental phenotypic homogeneity of Amerindians is not clearly not supported by analyses of middle Holocene metric and nonimetric dental traits. Nonmetric traits exhibit significant among-group variation, as do metric trait means. Discriminant function results and plots of biological distances reveal that middle Holocene skeletal samples do not have strong affinities with other North American or Asian populations. When middle Holocene samples were forced into one of the three New World subgroups (Aleut-Eskimo, Na-Dene, and Amerindian), they were classified as Amerindians. However, plots of biological distances revealed no clear three-way division of populations in the New World. The middle Holocene data exhibit significant spatial structure for dental metric and The "Tripartite" model of the peopling of the New World presents the hypothesis that all Native American linguistic, dental, and genetic variation was the result of three migratory "waves" from northeast Asia, whose descendants are modern Amerindian, Na-Dene, and Aleut-Eskimo populations. Several hypotheses were derived from this model, and tested using dental morphological and metric traits from middle Holocene (5,000 - 8,000 yr B.P.) Amerindians: (1) all middle Holocene groups share dental traits with northern Asian "Sinodont" populations, reflecting their origin from a northern Asian founding population; (2) middle Holocene Amerindians exhibit close biological affinity with later Holocene Amerindians, followed by other New World populations and northern Asians, reflecting the historical sequence of divergence among these groups; (3) early Amerindian dental variation is limited due to late Pleistocene founding events. Dental metric and nomnetric traits, known to be under strong genetic control, were recorded for 573 middle Holocene individuals from nine sites in eastern North America. All data were corrected for age and sex variation and observer error, and were tested using a wide range of statistical methods. Results were compared to expected patterns of variation from simulations of various evolutionary forces such as genetic drift and gene flow. The dental phenotypic homogeneity of Amerindians is not clearly not supported by analyses of middle Holocene metric and nomnetric dental traits. Nonmetric traits exhibit significant among-group variation, as do metric trait means. Discriminant function results and plots of biological distances reveal that middle Holocene skeletal samples do not have strong affinities with other North American or Asian populations. When middle Holocene samples were forced into one of the three New World subgroups (Aleut-Eskimo, Na-Dene, and Amerindian), they were classified as Amerindians. However, plots of biological distances revealed no clear three-way division of populations in the New World. The middle Holocene data exhibit significant spatial structure for dental metric and noinnetric traits, and fits the expectations of a model of isolation by spatial and temporal distance. In situ evolutionary processes, rather than late Pleistocene founding events, appear to be important in structuring the biological variation of Amerindians.Item Evolution of the cytochrome c oxidase subunit II gene in primates and rodents(1993) Adkins, Ronald Mark; Honeycutt, Rodney L.; Bickham, John W.; Davis, Scott K.; Jacobs, Louis L.; Woolley, James B.The genetics of the mitochondrial cytochrome c oxidase subunit II (COII) gene was examined in an array of primates, rodents and representatives of other orders of placental mammals. Among primates these phylogenetic conclusions were supported: (1) tarsiers are sister to monkeys and apes, (2) the aye-aye is sister to a group containing all lemurs and lorises, (3) dwarf lemurs are more closely related to other lemurs than to lorises, and (4) the ring-tail lemur is sister to gentle lemurs (Hapalemur) rather than to other members of the genus Lemur. COII was inappropriate for addressing most systematic questions among rodents. In comparisons among orders of mammals, COII supported the monophyly of Chiroptera, in contrast to restricted claims that one suborder of bats is more closely related to primates. Relationships among orders could not be determined with a reasonable degree of confidence. In agreement with previous genetic studies of nuclear gene sequences, COII appeared to be evolving more rapidly in rodents than in artiodactyls. However, this difference was not statistically significant. COII and cytochrome c interact during respiration and both have been found to be evolving very rapidly in higher primates, where the COII gene has presumably undergone a change in conformation. The period of accelerated evolution was found to coincide with the origin of higher primates (monkeys and apes). The cytochrome c gene also underwent a period of rapid evolution during this period. These results suggest coevolution between a mitochondrial (COII) and nuclear (cytochrome c) genetic system.Item Fatty acid elongation and desaturation in bovine tissues(1988) St. John, Lori Ceanne; Smith, Stephen B.; Cross, H. Russell; Davis, Scott K.; Ringer, Larry J.Initially, assay conditions were established for the fatty acid elongation and desaturation pathways of bovine liver and adipose tissue microsomes; rat liver microsomes were used as a reference. Rat liver elongation activity was .503 [plus or minus] .020 nmol*min^-1*mg protein^-1; bovine liver microsomal elongation activity was substantially lower, with a mean value of .148 [plus or minus] .020 nmol*min^-1*mg protein^-1. The elongation activity associated with bovine adipose tissue microsomes (.419 [plus or minus] .102 nmol*min^-1*mg protein^-1, respectively no desaturase activity was observed in bovine liver microsomes. Eight Angus and seven Braford heifers were slaughtered at approximately 12 months of age. Actual and adjusted fat thickness were higher in the Angus cattle as compared to the Braford heifers. There were no differences (P >.05) observed in adipose cell size or cells per gram tissue among the Angus and Braford breeds. Therefore, the increase in subcutaneous adipose tissue was not due to hypertrophy of the adipose cells, but was the result of a greater number of subcutaneous adipocytes in the Angus heifers. Subcutaneous adipose tissue and liver samples were taken from the cattle immediately after slaughter for the elongation and desaturation assays. The elongation rate was approximately five times greater in the adipose tissue in comparison to the liver, whereas all the desaturase activity was observed in the adipose tissue and none was observed in the liver. The inability of liver to desaturate stearate was in agreement with the fatty acid profile data which indicated less oleate and more stearate in liver than in adipose tissue. In comparing the elongation rate to the desaturation rates, it was observed that the desaturation activity was one-third the elongation activity. There were no significant differences found between the Angus and Braford heifers for the elongation or desaturation activities. To conclude, the data suggest that the conversion of palmitate to oleate occurs predominantly in the adipose tissue of cattle and the rate-limiting process may be the addition of the double bond (desaturation) and not the addition of 2 carbons to the fatty acid (elongation).Item Involvement of the endogenous opioid peptides in suckling-induced inhibition of LH release(1991) Wu, Tao-Yiao Johnny; Harms, Paul G.; McArthur, Newell H.; Davis, Scott K.; Welsh, Thomas H.Two studies were conducted to further understand the involvement of the endogenous opioid peptides (EOPs) in suckling-induced inhibition of LH release. Experiment A in the first study was designed to evaluate the effect of naloxone (NAL) infusion (1.0 mg/kg bw/h) on serum LH and hypothalamic LHRH content in 1 week ovariectomized suckled (8 pups/animal) rats after 18 h pup removal, and after 18 h resuckling. Pup removal resulted in an increase (p<0.05) in serum LH and a decrease (p<0.10) in hypothalamic LHRH content. On the other hand, subsequent resuckling decreased (p<0.05) serum LH and increased (p<0.10) hypothalamic LRH content. NAL did not influence (p>0.10) serum LH in suckled or nonsuckled rats. Hypothalamic LHRH content in NAL-treated rats was not changed upon pup removal or subsequent resuckling. Experiment B was designed to evaluate the effect of NAL on serum LH and hypothalamic HRH content in suckled rats. Serum LH increased (p<0.10 and p<0.005, respectively) in response to 18- and 36-h NAL infusion. Hypothalamic LHRH content decreased (p<0.025) after 18 h of NAL infusion, but increased to control concentrations after 36 h of NAL infusion Experiment C was designed to evaluate the effect of pup removal during NAL infusion on serum LH and hypothalamic LHRH content. Pup removal during the latter 18 h of a 36 h NAL infusion did not further influence (p>0.10) LH release nor did it influence (p>0.10) hypothalamic LHRH content. The second study was designed to evaluate the effect of NAL infusion (1.0 mg/kg bw/h for 7 days) in ovariectomized suckled rats, and ovariectomy on LHRH neuron morphology using immunocytochemistry. NAL did not influence LHRH immunoreactivity in the infundibulum (INF) nor was it able to influence neuronal morphology. In contrast, rats ovariectomized for 3 weeks had a greater proportion (48% vs 25%, respectively) of smooth LHRH neurons compared to diestrous rats...Item Population structures, evolutionary relationships and genetic effects of domestication in American Penaeid shrimp(1991) Sunden, Sara Louise Faivre; Davis, Scott K.; Johnston, J. Spencer; Taylor, Jeremy F.; Walter, John P.; Womack, James E.Starch-gel electrophoresis of enzymatic proteins, restriction fragment length polymorphisms and random amplified polymorphic DNA w ere used to evaluate population structures of three species of Penaeid shrimp: Penaeus vannamei, P. stylirostris, and P. duorarum. The effects of domestication on two aquaculture populations of P. vannamei were also examined with these markers. Allozymes and the mitochondrial Cytochrome Oxidase I gene were used to establish the evolutionary relationships between species in the genus. A species-specific identification system using allozyme allele profiles was also developed. P. vannamei was polymorphic at three of 14 allozyme loci, while P. stylirostris and P. duorarum were polymorphic at five of 10 loci and four of eight loci, respectively. The frequency of the most common mitochondrial haplotype was <95% in all natural populations. Restriction site variation in the nuclear 28s ribosomal genes was not detected in any species, but the frequency of ribosomal DNA length variants in P. stylirostris was different (p<0.005) between Mexico and Ecuador. Eight of ten random amplified polymorphic DNA markers were variable in P. stylirostris, the only species tested. Allele and haplotype F[ST] values of 0.163 to 0.892 for P. stylirostris indicate more population subdivision than in P. duorarum and P. vannamei with F[ST] values of 0.004 to 0.017 and 0.007 to 0.049, respectively. The effective size of a closed aquaculture population managed to avoid inbreeding was estimated to be 8.3 to 12 individuals using mitochondrial markers and 203 to 282 individuals using allozymes. In a second aquaculture population founded by 20 shrimp, the estimates of effective size were 5.8 to 12 (mitochondrial) and 31 to 41 (allozymes.) Phylogenetic groupings based on allozymes and DNA sequences were consistent with current taxonomic classification into subgenera, but disputed the traditional designation of the subgenus Litopeneaus as primitive. A species identification system was developed using allozyme allele profiles. As few as three loci were sufficient to differentiate shrimp of American origin from indigenous Australian and Asian species. Every American species had a unique allele profile across the thirteen loci used.Item Pyramiding the Delta-endotoxin from Bacillus thuringiensis with plant resistance traits in cotton(1993) Sachs, Eric Scott; Benedict, John; Stelly, David; Davis, Scott K.; Taylor, Jeremy F.Insects are likely to develop resistance to Bacillus thuringiensis spp. kurstaki CrylA insecticidal proteins expressed in cotton (Gossypium hirsutum L.) unless strategies are implemented to counter pest adaptation. Three studies were undertaken to evaluate the potential for pyramiding the CrylA protein with other plant insect-resistance traits to increase insect resistance and improve the durability of cotton expressing a crylA gene. First, the expression of two foreign crylA genes was characterized in insect-resistant cotton lines derived in three backgrounds. Next, the effects of pyramiding the CrylA(b) protein with the high-terpenoid plant insect-resistance trait on tobacco budworm [Heliothis virescens (F.)] growth, survival, and feeding behavior were examined in field and laboratory no-choice and free-choice experiments. Finally, the effects of pyramiding the CrylA(b) protein with other antibiotic or antixenotic plant insect-resistance traits on cotton injury and yield were examined in free-choice field experiments in two environments. CrylA gene expression was variable and influenced by genetic and environmental factors. Variation from site of insertion and cotton background effects may provide significant opportunity for increasing crylA gene expression using traditional breeding techniques. Plant-to-plant variation from epistatic and/or somaclonal effects caused CrylA protein concentration to behave as a quantitative trait. The strong influence of environmental factors on crylA gene expression shows the importance of controlling environmental variation in experiments designed to evaluate crylA expression or plant insect-resistance. Pyramiding the CrylA(b) protein with the high-terpenoid plant insect-resistance trait injury compared to using the CrylA(b) protein alone. Pyramiding the CrylA(b) protein with other antibiotic or antixenotic plant insect-resistance traits effectively reduced budworm-bollworm injury to flower buds and bolls compared to using the CrylA(b) protein alone. The glabrous, nectariless, and high-terpenoid traits were useful pyramiding characters. These results demonstrate that gene pyramiding can be an effective strategy for improving the insect resistance and durability of cotton producing the CrylA(b) protein.Item Regulation and evolution of the patatin multigene family : suggestions of combinatorial interactions directing tissue-specific gene expression(1992) May, Gregory DeWitt; Park, William D.; Cobb, D. Gregory; Davis, Scott K.; Funkhouser, Edward A.While much has been written about the evolution of new tissues or organs, little is known about the origin of the regulatory elements that direct gene expression in new structures. Questions also arise about how new regulatory elements are integrated into the complex physiology of new tissues. To examine these questions, the patatin multigene family was used as a model system. Patatin is a family of lipid acyl hydrolases that accounts for 30-40% of the total protein in potato tubers. The Class-I genes, which produce the majority of the patatin protein in tubers, can also be induced to express at high levels in stems and leaves by 0.2 -0.3 M sucrose. However, under normal conditions, they are almost totally tuber-specific. To examine how "tuber-specific" genes could have evolved from regulatory elements in non-tuberizing species, the expression of the endogenous patatin genes in tomato and tobacco were compared to that of potato Class-I patatin promoters using transgenic plants. Patatin promoters were also isolated and characterized from tobacco and evolutionarily divergent species of wild potato. These promoters contain sequences characteristic of both the Class-I and Class-II patatin genes. However, their patterns of expression are unlike those of any previously reported patatin genes. They were neither sucrose inducible nor tuber-specific and were wound-inducible, unlike potato Class-I patatin genes which are turned off by wounding. Because the major soybean vegetative storage protein (VSP) serves similar roles in soybeans to that served by patatin in potatoes, vsp promoter expression in transgenic potato plants was also examined. Although vsp is normally expressed in soybean leaves, it was tuber-specific when introduced into potato plants. Like Class-I patatin, vsp could be induced to express in leaves by sucrose, but unlike patatin, vsp could also be induced by methyl jasmonate, systemin and oligourinides...Item Restriction fragment length polymorphism analysis of bovine DNA for the fatty acid-binding protein and stearoyl-CoA desaturase 1 genes(1993) Wilson, John Joseph; Smith, Stephen B.; Davis, Scott K.; Savell, Jeffrey W.; Sams, Alan R.Two bovine populations were studied to identify restriction fragment length polymorphisms (RFLPs) for stearoyl-CoA desaturase (SCD1). The cattle represented purebred Angus (n = 32), and American Wagyu (n = 10). Detection of the bovine SCD1 gene was accomplished by hybridization of a $sp{32}$P-labeled rat SCD1 cDNA to the bovine samples. Hybridization and washing conditions indicated that the rat cDNA probe was not very homologous to the bovine DNA. Digestion of the animals DNA with Taq 1 yielded bands of 19.7 kb, 7.4 kb and 6.6 kb. Separate digestions of the DNA with Pvu II yielded bands of 20 kb and 1.8 kb. A single digest with Eco R1 resulted in a single banding pattern of 8 kb. The results indicate that the Angus cattle tested had greater hot carcass weight and lower intramuscular adipose tissue scored than the American Wagyu when the 7.4 kb allele was present. Presence of the heterozygous allelic form (19.7 kb and 7.4 kb) produced greater saturated fatty acid development in the Angus and unsaturated fatty acid synthesis in the American Wagyu cattle. Heifers had a greater amount of intramuscular adipose tissue and less hot carcass weight than steers in the study with Angus cattle of different phenotypes. The SCD1 gene probe produces results that are positive for many traits at this time and further research needs to be completed before final determination is made as to its use in a selection program.