chemical and physical properties to ordinary crude oil.
SPECIATION AND MUTATIONS
Paigen K. 1989. Experimental approaches to the study of regulatory evolution. American Naturalist 134:440-458.
Summary. Regulatory polymorphisms have been described for the genes for production of beta-globin in man and beta-glucuronidase in mice. Several steps in the regulatory process could potentially be modified by mutation, but only a limited number of such mutations is actually found. The types of mutations differ in different systems, and the regulatory differences between closely related species can be different from the polymorphisms found within a species. The types of mutations actually known in the condition called thalassemia are listed. Single substitutions accounted for 28 out of the 37 mutants known. Addition or deletion of one or a few bases were found in nine cases, the longest being a 25-base genetic deletion. The results suggest that speciation events may involve genetic mechanisms beyond those normally observed within populations.
SPECIATION, BOTTLENECKS AND ENVIRONMENTAL STRESS
Carson HL, Wisotzkey RG. 1989. Increase in genetic variance following a population bottleneck. American Naturalist 134:668-673.
Summary. A laboratory population of an endemic Hawaiian species of Drosophila was accidentally subjected to sustained high temperatures which killed most of the flies. The population was reconstituted from about a half dozen larvae which survived. After this population bottleneck, new combinations of chromosome 4 inversions were noted. This increase in genetic variance is the opposite of the decrease generally expected after a population bottleneck. The author does not discuss the possible effect of the high temperature, which has been reported to increase the rates of recombination in Drosophila (see Parsons 1988, Biological Journal of the Linnaean Society 35:49-68).
TAPHONOMY, FOSSILS AND CATASTROPHES
Greenstein BJ. 1989. Mass mortality of the West-Indian echinoid Diadema antillarum (Echinodermata: Echinoidea): a natural experiment in taphonomy. Palaios 4:487-492.
Summary. During 1983 a mass die-off of sea urchins occurred throughout the Caribbean, due to disease. Mortality rates exceeded 98% in Jamaica and Curacao, and probably elsewhere. Samples taken around the island of Bonaire showed no increase in echinoderm material associated with this mass mortality event, indicating that the reef environment was not favorable to the preservation of evidence for echinoid mass mortality. Mass preservation of echinoderms in the fossil record should be interpreted as the result of unusual taphonomic processes such as rapid burial by catastrophes.