Primate evolutionary genetics.
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Biomedical subjects
O A Ryder
Publications and source records attributed to O A Ryder.
Human and ape molecular clocks and constraints on paleontological hypotheses.
Although the relationships of the living hominoid primates (humans and apes) are well known, the relationships of the fossil species, times of divergence of both living and fossil species, and the biogeographic history of hominoids are not well established. Divergence times of living species, estimated from molecular clocks, have the potential to constrain hypotheses of the relationships of fossil species. In this study, new DNA sequences from nine protein-coding nuclear genes in great apes are added to existing datasets to increase the precision of molecular time estimates bearing on the evolutionary history of apes and humans. The divergence of Old World monkeys and hominoids at the Oligocene-Miocene boundary (approximately 23 million years ago) provides the best primate calibration point and yields a time and 95% confidence interval of 5.4 +/- 1.1 million years ago (36 nuclear genes) for the human-chimpanzee divergence. Older splitting events are estimated as 6.4 +/- 1.5 million years ago (gorilla, 31 genes), 11.3 +/- 1.3 million years ago (orangutan, 33 genes), and 14.9 +/- 2.0 million years ago (gibbon, 27 genes). Based on these molecular constraints, we find that several proposed phylogenies of fossil hominoid taxa are unlikely to be correct.
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Genetic studies of blood markers in Przewalski's horses.
Ninety-six Przewalski's horses (Equus przewalskii) were blood typed using systems of inherited blood variants known to be highly effective for parentage testing of domestic horses (E. caballus). Sixteen red cell antigenic factors detected using sera prepared by alloimmunization of domestic horses were shown to be inherited in six systems (A, C, D, P, Q, and U) and in the same patterns as domestic horses. Family data confirmed autosomal, codominant inheritance at five loci of serum protein variants (Al, Tf, Xk, Pi, and Es) and three loci of red cell proteins (PGM, PHI, and Hb). One serum protein locus (Gc) and two red cell protein loci (PGD and CA) appeared to be monomorphic. Despite the narrow genetic base and high inbreeding coefficients of captive Przewalski's horses, average heterozygosity calculated over 18 loci was estimated to be 0.320 +/- 0.05, which was similar to that found in five breeds of domestic horses.
Alleles↗
Allozyme variation and differentiation in African and Indian rhinoceroses.
We studied variation at 25 to 31 allozymic loci in African and Asian rhinoceroses. Four taxa in three genera were examined: African Ceratotherium simum simum (northern white rhinoceros), C. s. cottoni (southern white rhinoceros), Diceros bicornis (black rhinoceros), and Rhinoceros unicornis (Indian rhinoceros). Extremely small amounts of intraspecific variation were observed in sample sizes of 2 to 10 presumably unrelated individuals per taxon: P = .00-.10, H = 0.00-0.02. We examined demographic bottlenecks and sampling errors as possible reasons for the low levels of detectable variation. The very small intraspecific genetic distance (D = 0.005) between the two living white rhinoceros subspecies is far less than the distance that has been reported for other mammal subspecies. The mean D value of 0.32 +/- 0.11 between the two African genera was also less than expected given the divergence time of greater than 7 million years suggested by the fossil record. Rhinoceroses may be evolving more slowly at the structural gene loci than are some other mammal groups. The estimate of D = 1.05 +/- 0.24 for the African-Indian split supports this idea, as the lineage diverged at least 26 million years ago. Our results contribute to the currently available scientific information on which management decisions aimed toward saving endangered rhinoceroses should be based.
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Genomic distribution of heterochromatic sequences in equids: implications to rapid chromosomal evolution.
We describe a molecular model for rapid chromosomal evolution that proposes tandemly repeated DNA sequences as a driving force. A prediction of this model is that when extensive rearrangements of euchromatin have been facilitated by heterochromatin, genomes will be characterized by tandemly repeated sequences that have actively changed chromosomal fields by intragenomic movement. Alternatively, it is proposed that in conservative chromosomal lineage each class of tandemly repeated sequences will be restricted to a specific chromosomal field. To provide baseline data to test this model we examined four classes of tandemly repeated elements in six species of equids (Equus). Distribution of these sequences among species, as determined from slot blot analysis, and restriction site variation, shown by Southern blot hybridization, document that these sequences are in an evolutionarily dynamic state, and in situ hybridization documents extensive intragenomic movement among nonhomologous chromosomes and chromosomal fields. These data are interpreted as being compatible with the predictions of this model. Although this is clearly not the sole molecular factor driving chromosomal evolution, the model appears to be viable as an explanation of certain patterns of chromosomal evolution such as karyotypic megaevolution and some types of karyotypic orthoselection.
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Chromosomal and mitochondrial DNA variation in orang utans.
Wild-born orang utans held in zoos do not have their geographic origins defined, which has complicated comparisons of the two subspecies of orang utans (Bornean orang utans, Pongo pygmaeus pygmaeus, and Sumatran orang utans, P. pygmaeus abelii). The resulting confusion concerning the subspecies identity of individual orang utans and a larger controversy over the desirability of utilizing subspecies designations in orang utan breeding programs has focused attention on the need for a phylogenetic analysis of the species and an examination of the appropriateness of the subspecific designations. Previous studies have suggested that an inversion in the second chromosome pair (PPY2) is a diagnostic subspecies marker and that mitochondrial DNA (mtDNA) and nuclear genetic markers may also be used to identify the subspecies origin of individual orang utans. In an effort to assist zoological parks in examining the question of genetic divergence of orang utan subspecies, we have studied the chromosomes of 144 orang utans, including 58 wild-born individuals. To gain insight into phylogenetic divisions of these apes, mtDNA restriction cleavage site variation has been investigated in 14 individuals whose karyotypic status was known. These investigations have confirmed the existence of two phylogenetic lineages of orang utans based on mtDNA cleavage patterns and demonstrated that these lineages correspond with the two populations characterized by the G-banded morphology of the second pair of chromosomes. The two orang utan phylogenetic units comprise individuals that generally conform to the recognized allopatric, morphological subspecies. Based on current knowledge, the view that the named orangutan subspecies each constitute a distinct phylogenetic lineage more consistent with species-level divergence is supported.
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Male mule foal qualifies as the offspring of a female mule and jack donkey.
Whereas mules are normally considered sterile, reports of fertile female mules persist. However, none subjected to cytogenetical and blood typing analyses could be confirmed as having indeed been mules that transmitted maternal markers to their alleged offspring. Reported here is the case of a cytogenetically verified female mule whose alleged male foal qualifies as offspring by a male donkey. The male foal is karyotypically a mule.
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Diploid chromosome number and chromosomal variation in the white rhinoceros (Ceratotherium simum).
Chromosomal studies were conducted on 38 white rhinoceroses representing both the northern and southern subspecies and one subspecies hybrid. Improvements in tissue culture methods and harvesting techniques have made it possible to obtain a highly repeatable diploid number of 82 chromosomes for both subspecies. Comparison of G-banded karyotypes from the two subspecies failed to indicate a difference in banding pattern, but did reveal size polymorphisms involving short arm additions in five individuals. Chromosomal polymorphism, resulting in three individuals with a diploid number of 2n = 81, was noted in northern white rhinoceroses.
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