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At least 631 records · Page 35Linked to original sources
PubMed1984

Epidemiology of tick-borne diseases of cattle in Zimbabwe. II. Anaplasmosis.

A survey on the incidence of antibodies to Anaplasma marginale in one- to three-year-old cattle was carried out in Zimbabwe using the capillary tube agglutination test. Antibodies were detected in all but one of 118 batches of sera collected from different localities throughout the country. There was no clear relationship between the frequency of occurrence of positive serological reactors, which was similar in both commercial and communal farming areas, and the incidence of clinical anaplasmosis. However, the highest numbers of cattle exhibiting positive reactions were generally recorded from the areas that were most heavily tick infested. There was evidence that wild ungulates may serve as reservoirs of infection as antibodies to A. marginale were detected in sera from buffalo (Syncerus caffer) and impala (Aepyceros melampus).

Anaplasma↗
PubMed1996

The molecular evolution of vertebrate growth hormones: a pattern of near-stasis interrupted by sustained bursts of rapid change.

It has been demonstrated previously that in mammals the evolution of pituitary growth hormone shows an unusual pattern, with an underlying slow rate and at least two sustained bursts of rapid evolution (in the artiodactyls and primates), during which the rate increased at least 25-fold. It is demonstrated here that a similar pattern applies for growth hormone evolution throughout the vertebrates, with a basal rate similar to that seen in mammals, but bursts of rapid evolution in the amphibia and the elasmobranchs, and several bursts in the teleosts. The placental growth-hormone-like proteins of primates show a similar pattern. It is argued that the bursts of evolution seen for growth hormone are a consequence of selection and that this may reflect changes in the functions of the hormone additional to its basic growth-promoting actions.

Animals↗
PubMed1987

An evaluation of the molecular clock hypothesis using mammalian DNA sequences.

A statistical analysis of extensive DNA sequence data from primates, rodents, and artiodactyls clearly indicates that no global molecular clock exists in mammals. Rates of nucleotide substitution in rodents are estimated to be four to eight times higher than those in higher primates and two to four times higher than those in artiodactyls. There is strong evidence for lower substitution rates in apes and humans than in monkeys, supporting the hominoid slowdown hypothesis. There is also evidence for lower rates in humans than in apes, suggesting a further rate slowdown in the human lineage after the separation of humans from apes. By contrast, substitution rates are nearly equal in mouse and rat. These results suggest that differences in generation time or, more precisely, in the number of germline DNA replications per year are the primary cause of rate differences in mammals. Further, these differences are more in line with the neutral mutation hypothesis than if the rates are the same for short- and long-living mammals.

Animals↗
PubMed1997

Artiodactyl interspersed DNA repeats in cetacean genomes.

Interspersed repeats that emerged at different evolutionary times are informative in mammalian phylogeny. Here we show that the ancient short interspersed elements (SINEs) ARE1 and ARE2 are abundantly present in the genomes of artiodactyls and cetaceans but not in other mammalian genomes. This supports the classification of the cetaceans with the artiodactyls by a shared character that is unlikely to be the result of convergence.

Animals↗
PubMed1998

Synonymous and nonsynonymous rate variation in nuclear genes of mammals.

A maximum likelihood approach was used to estimate the synonymous and nonsynonymous substitution rates in 48 nuclear genes from primates, artiodactyls, and rodents. A codon-substitution model was assumed, which accounts for the genetic code structure, transition/transversion bias, and base frequency biases at codon positions. Likelihood ratio tests were applied to test the constancy of nonsynonymous to synonymous rate ratios among branches (evolutionary lineages). It is found that at 22 of the 48 nuclear loci examined, the nonsynonymous/synonymous rate ratio varies significantly across branches of the tree. The result provides strong evidence against a strictly neutral model of molecular evolution. Our likelihood estimates of synonymous and nonsynonymous rates differ considerably from previous results obtained from approximate pairwise sequence comparisons. The differences between the methods are explored by detailed analyses of data from several genes. Transition/transversion rate bias and codon frequency biases are found to have significant effects on the estimation of synonymous and nonsynonymous rates, and approximate methods do not adequately account for those factors. The likelihood approach is preferable, even for pairwise sequence comparison, because more realistic models about the mutation and substitution processes can be incorporated in the analysis.

Animals↗