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Biomedical subjects

A C Wilson

Publications and source records attributed to A C Wilson.

At least 235 records · Page 13Linked to original sources
PubMed1976

Penguin evolution: protein comparisons demonstrate phylogenetic relationship to flying aquatic birds.

Quantitative immunological comparisons of three avian proteins, transferrin, ovalbumin, and penalbumin, indicate that penguins are phylogenetically most closely related to loons, albatrosses, herons, and grebes. These data support the theory that the ancestors of penguins were flying oceanic birds and that flightlessness in penguins has evolved independently from flightlessness in ratites.

Amino Acid Sequence↗
PubMed1976

Evolution of flightless land birds on southern continents: transferrin comparison shows monophyletic origin of ratites.

A biochemical approach was used to study the evolution of ratite birds, i.e., the ostriches, rheas, cassowaries, emus, and kiwis. Quantitative immunological comparison of transferrin from ratites, tinamous, and other flying birds indicates that all the ratites and tinamous are allied phylogenetically and that they are of monophyletic origin relative to other birds. To explain the current geographic distribution of ratites and the magnitude of the transferrin distances, it is supposed that the ancestors of these flightless birds walked across land bridges between the southern continents during Cretaceous times.

Amino Acid Sequence↗
PubMed1976

Amino acid sequence and immunological properties of chalchalaca egg white lysozyme.

The amino acid sequence of lysozyme c from chachalaca egg white was determined. Like other bird lysozymes c, that of the chachalaca has 129 amino acid residues. It differs from other avian lysozymes c by 2 to 31 amino acid substitutions as well as by being devoid of phenylalanine. It contains substitutions at 9 positions which are invariant in the other 7 bird lysozymes of known sequence. Although the chachalaca is classified zoologically in the order Galliformes, which includes chickens and other pheasant-like birds, its lysozyme differs more from those of pheasant-like birds than do the lysozymes c of ducks. Phylogenetic analysis of the sequence comparisons confirms that the lineage leading to chachalaca lysozyme c separated from that leading to other galliform lysozymes c before the duck lysozyme c lineage did. This indicates a contrast between protein evolution and evolution at the organismal level. Immunological comparison of chachalaca lysozyme c with other lysozymes of known sequence provides further support for the proposal that immunological cross-reactivity is strongly dependent on degree of sequence resemblance among bird lysozymes.

Amino Acid Sequence↗
PubMed1976

Rates of evolution in seed plants: Net increase in diversity of chromosome numbers and species numbers through time.

An approach was made to the problem of estimating rates of chromosomal evolution in plants. This was done by considering variability in chromosome number within genera whose ages are known approximately from fossil and biogeographic evidence. The relative increases in chromosome number diversity per lineage per unit time were as follows: herbaceous angiosperms, 100; woody angiosperms, 14; conifers, 2; and cycads, 0. Rates of increase in species diversity were estimated in an analogous way. These rates were strongly correlated with the karyotypic rates.These evolutionary rate differences between major groups of seed plants are largely explicable in terms of the breeding structures of populations. Herbs usually have small to moderate effective population sizes, and relatively high dispersability. By contrast, woody angiosperms and gymnosperms are usually obligate outbreeders with large effective population sizes and low dispersability. Thus the probability of fixing and dispersing new karyotypes or novel character ensembles is higher in herbs than in other seed plants.

Journal Article↗
PubMed1975

Immunological comparison of azurins of known amino acid sequence. Dependence of cross-reactivity upon sequence resemblance.

To examine further the dependence of immunological cross-reactivity on sequence resemblance among proteins, we carried out micro-complement fixation studies with rabbit antisera to bacterial azurins of known amino acid sequence. There is a strong correlation (r = 0.9) between number of amino acid substitutions and degree of antigenic difference (immunological distance) among these azurins. The antigenic effects of amino acid substitutions are thus approximately equal and approximately additive. Similar observations and inferences were made before with a series of bird lysozymes. Indeed, the same approximate relationship between immunological distance (y) and percent difference in amino acid sequence (x) holds for both azurins and lysozymes, namely y congruent to 5x. An explanation is given for the dependence of immunological cross-reactivity on sequence resemblance among proteins. This entails reviewing evidence regarding the nature and number of antigenic sites on globular protein antigens as well as evidence for the existence of evolutionary biases against substitutions that are internal or cause large conformational changes. The explanation we give may apply only to those naturally occurring, globular, monomeric, isofunctional proteins whose sequences differ substantially from that of any rabbit protein.

Amino Acid Sequence↗
PubMed1975

Slow evolutionary loss of the potential for interspecific hybridization in birds: a manifestation of slow regulatory evolution.

Birds have lost the potential for interspecific hybridization slowly. This inference emerges from protein comparisons made on 36 pairs of bird species capable of hybridization. Micro-complement fixation tests show that hybridizable pairs of bird species differ by an average of 12 units of albumin immunological distance and 25 units of transferrin immunological distance. As these proteins evolve at a known and rather steady rate, it is inferred that the average hybridization species pair diverged from a common ancestor about 22 million years ago. The corresponding period for frog species pairs capable of hybridization is about 21 million years, while for hybridizable placental mammals it is only 2 to 3 million years. Thus birds resemble frogs in having lost the potential for interspecific hybridization about 10 times as slowly as have mammals. Birds have also been evolving very slowly at the anatomical level, particularly within the last 25 million years, according to Simpson, Romer, and many other vertebrate zoologists. In this respect they resemble frogs and differ from placental mammals, which have been undergoing unusually rapid anatomical evolution. Chromosomal evolution is also thought to have proceeded very slowly in both birds and frogs, relative to mammals. The above observations are consistent with the hypothesis that evolutionary changes in regulatory systems, that is, changes in the patterns of gene expression, provide the basis for both anatomical evolution and the evolutionary loss of hybridization potential.

Animals↗
PubMed1975

Social structuring of mammalian populations and rate of chromosomal evolution.

To test the hypothesis that the evolution of organisms is dependent to a large degree on gene rearrangement, we devised a way of estimating rates of evolutionary change in karyotype. This non-biochemical method is based on consideration of chromosomal variability within taxonomic groups having a fossil record. The results show that chromosomal evolution has been faster in placental mammals than in other vertebrates or molluscs. This finding is consistent with published evidence that placentals have also been evolving unusually fast in anatomy and way of life. However, the structural genes of placentals seem not to have experienced accelerated evolution. Possibly, therefore, anatomical evolution may be facilitated by gene rearrangement. To explain how placentals achieved this rate of chromosomal evolution, we consider the process by which a new gene arrangement becomes fixed and spreads. The structure and dynamics of placental populations may be especially favorable for this process. The key factor involved seems to be the type of social behavior which produces small effective population sizes and inbreeding. As Bush points out elsewhere, such social structuring of populations may promote rapid fixation of gene rearrangements and rapid speciation.

Animals↗
PubMed1974

Convergent morphological evolution detected by studying proteins of tree frogs in the Hyla eximia species group.

Protein studies have uncovered an apparent case of convergent evolution among North American tree frogs. The species Hyla eximia and Hyla regilla are so similar in external morphology that the "wrightorum" subspecies is assigned by some authorities to H. eximia and by others to H. regilla. Yet microcomplement fixation experiments show that "wrightorum" albumin, though virtually indistinguishable from authentic H. eximia albumin, differs as much from H. regilla albumin as from albumins of species outside the genus Hyla, such as Acris crepitans. The morphological resemblance of "wrightorum" to H. regilla is thus probably due to convergence.

Amino Acid Sequence↗
PubMed1974

Two types of molecular evolution. Evidence from studies of interspecific hybridization.

To assess the significance of macromolecular sequence differences among species, we compared the serum albumins of 81 pairs of vertebrate species capable of producing viable hybrids. Micro-complement fixation experiments showed that the average difference between the albumins within such pairs was only 3 immunological distance units for placental mammals (31 pairs), but 36 units for frogs (50 pairs). Albumin immunological distance is strongly correlated with other measures of genetic distance, including those made with DNA annealing techniques. It therefore seems likely that mammalian species pairs capable of hybridization are far more similar at the macromolecular sequence level than is the case for most hybridizable frogs. We think the most likely explanation for the marked molecular restriction on hybridization among mammals is that the ratio of regulatory evolution to protein evolution is higher for mammals than for frogs. Mammals may have experienced unusually rapid regulatory evolution; indeed, this could be the factor responsible for their unusually rapid anatomical evolution.

Amino Acid Sequence↗
PubMed1974

The importance of gene rearrangement in evolution: evidence from studies on rates of chromosomal, protein, and anatomical evolution.

We have compared the relative rates of protein evolution and chromosomal evolution in frogs and mammals. The average rate of change in chromosome number has been about 20 times faster in mammals than in frogs. Whereas it takes only 3.5 million years, on the average, for a pair of mammal species to develop a difference in chromosome number, the corresponding period for frogs is 70 million years. In contrast, the rate of protein evolution in mammals has been roughly equal to that in frogs. The rapid rate of gene rearrangement in mammals parallels both their rapid anatomical evolution and their rapid evolutionary loss of the potential for interspecific hybridization. Thus, gene rearrangements may be more important than point mutations as sources for evolutionary changes in anatomy and way of life.

Adaptation, Biological↗