Articles - Plant and Animal Sciences | The Scientist Magazine®

Francisco J. Ayala Department of Ecology and Evolutionary Biology University of California Irvine, Calif. Latimeria chalumnae was discovered 50 years ago, one of a group of fishes (coelacanths) thought to have died out 80 million years ago. Latimeria raised hopes of gathering direct information on the transition from fish to amphibians, because coelacanths were thought to be ancestral to the tetrapods. Studies of Latimeria anatomy and physiology have shown that it is not the missing link between fish and land vertebrates. There are also fears that it will become extinct in the near future. P.L. Forey, "Golden jubilee for the coelacanth Latimeria chalumnae," Nature, 336 (6201), 727-32, 22/29 December 1988. Proconsul is a prehistoric ape discovered in 1927, when a left upper jawbone was found in a limestone quarry in western Kenya. A skull was discovered in 1948, other remains in 1951, and many more since 1984. Proconsul lived 18 million years ago during the Lower Miocene. It shares some features with modern gorillas and chimpanzees, but most of these features are relatively unspecialized, which suggests that Proconsul repesents the last common ancestor of all great apes and humans. A. Walker, M. Teaford, "The hunt for Proconsul," Scientific American, 260 (1), 76-82, January 1989. Interspecific hybridization between the viviparous fishes Poeciliopsis monacha and P. lucida produces in nature two all-female forms, one a diploid, the other a triploid. These females must be inseminated by males of P. lucida in order to reproduce. According to a recent paper, unisexual clones differ in their ability to attract P. lucida males. These prefer conspecific females to unisexuals and learn to discriminate against the latter, but this learning does not generalize to new clones. Thus, unfamiliar clones are more likely to be courted than familiar ones, and individuals of a clone that is rare in a population are more likely to be impregnated than those of a common one. V. Keegan-Rogers, R.J. Schultz, "Sexual selection among clones of unisexual fish (Poeciliopsis: Poeciliidae): Genetic factors and rare-female advantage," American Naturalist, 132 (6), 846-68, December 1988. The left brain hemisphere of the macaque monkey is better than the right hemisphere at distinguishing between tilted lines, whereas the right hemisphere is better at discriminating faces. Thus, lateralization of cognitive processing has evolved in primates independently of language or handedness. Cerebral lateralization in monkeys provides a model for investigating the biological basis of hemispheric specialization in humans. C.R. Hamilton, B.A. Vermeire, "Complementary hemispheric specialization in monkeys," Science, 242 (4885), 1691-4, 23 December 1988. Genetic diversity is very high among natural clones of the soil bacterium Pseudomonas cepacia, higher than reported for any other bacterial species. Amount and pattern of genetic diversity are correlated with variability of the habitat from which the bacterial clones are isolated. This suggests that the source of bacterial strains used in genetic engineering will affect the success of planned releases into the environment. J.V. McArthur, D.A. Kovacia, M.H. Smith, "Genetic diversity in natural populations of a soil bacterium across a landscape gradient," Proceedings of the National Academy of Sciences of the United States of America, 85 (24), 9621-4, December 1988. Codon usage varies strikingly among 91 Drosophila melanogaster genes. Genes with a high G + C content at silent sites are more highly expressed, whereas G + C content is reduced in sequences subject to weaker selective constraints. The variation of selective constraints on silent substitutions handicaps the use of rates of silent substitution as molecular clocks. D.C. Shields, P.M. Sharp, D.G. Higgins, F. Wright, "`Silent' sites in Drosophila genes are not neutral: evidence of selection among synonymous codons," Molecular Biology and Evolution, 5 (6), 704-16, November 1988.

Articles - Plant and Animal Sciences

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