Jody Hey                  Evolutionary Genetics

  Professor    -     Department of Genetics     -   Rutgers University

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Abstracts of Some Papers not available at PubMed

Hey, J., R. S. Waples, M. L. Arnold, R. K. Butlin, and R. G. Harrison. 2003. Understanding and confronting species uncertainty in biology and conservation. Trends in Ecology and Evolution 18:597-603.

 Abstract: Recent essays on the species problem have emphasized the commonality that many species concepts have with basic evolutionary theory. Although true, such consensus fails to address the nature of the ambiguity that is associated with species-related research. We argue that biologists who endure the species problem can benefit from a synthesis in which individual taxonomic species are used as hypotheses of evolutionary entities. We discuss two sources of species uncertainty: one that is a semantic confusion, and a second that is caused by the inherent uncertainty of evolutionary entities. The former can be dispelled with careful communication, whereas the latter is a conventional scientific uncertainty that can only be mitigated by research. This scientific uncertainty cannot be `solved' or stamped out, but neither need it be ignored or feared.

Eanes, W. F., D. Wesley, J. Hey, D. Houle and J. W. Ajioka, 1987 The fitness consequences of P-element insertion in Drosophila melanogaster. Genetical Research 52: 17-26.

abstract - In this study we estimate the frequency at which P-element insertion events, as identified by in situ hybridization, generate lethal and mild viability mutation. The frequency of lethal mutations generated per insertion event was 0.004. Viability dropped on average 1% per insertion event. Our results indicate that is deletions and rearrangements resulting from the mobilization of P elements already in place and not the insertions per se that cause the drastic effects on viability and fitness observed in most studies of P-M dysgenesis-derived mutations. Elements of five other families (I, copia, 412, B104, and gypsy) were not mobilized in these crosses. Finally, we contrast the density of P elements on the X chromosome with the density on the four autosomal arms in a collection of thirty genomes from an African population. The relative number of P elements on the X chromosomes is too high to be explained by either a hemizygous selection or a neutrality model. The possible reasons for the failure to detect selection are discussed.

abstract - From 1981 to 1983, 15,0997 X chromosomes were genetically extracted from a number of North American populations of D. melanogaster and were electrophoretically screened for rare mobility variants of glucose-6-phosphate dehydrogenase (G6PD). Overall, 13 rare variants were recovered for a frequency of about 10^-3. Eleven variants affect electrophoretic mobility and are apparently structural, and two variants exhibit low G6PD activity. One low activity variant is closely associated with a P-element insertion at 18D12-31. All of the variants were subjected to the previously described genetic scheme used to identify relative in vivo activity differences between the two common electrophoretic variants associated with the global polymorphism. Most of the rare variants exhibit apparent in vivo activities that are similar to one of the other of the common variants, and these specific rare variants appear to be geographically widespread. Several variants have significantly reduced function. All of the variants were measure for larval specific activity for G6PD as a first measure of in vitro activity. It appears that specific activity alone is not a sufficient predictor for G6PD in vivo function.

abstract - We report here a study of viability inbreeding depression associated with the X chromosome of Drosophila melanogaster. Fifty wild chromosomes from Mt. Sinai, New York, and 90 wild chromosomes from Death Valley, California, were extracted using the marked FM6 balancer chromosome and viabilities measure for homozygous and heterozygous females, and for hemizygous males, relative to FM6 males as a standard genotype. No statistically significant female genetic load was observed for either chromosome set, although a 95% confidence limit estimated the total load <0.046 for the samples pooled. About 10% of the Death Valley chromosomes appear to be "supervital" as homozygotes. There is little evidence for a pervasive sex-limited detrimental load on the X chromosomes: the evidence indicates nearly identical viability effects on males and homozygous females excluding the supervital chromosomes. The average degree of dominance for viability polygenes is estimated between 0.23 to 0.36, which is consistent with autosomal variation and implies near additivity. We conclude that there is little genetic load associated with viability variation on the X chromosome and that the substantial reduction in total fitness observed for chromosomes homozygosity in an earlier study may be due largely to sex-limited fertility in females.

abstract - An experiment was conducted to test whether or not inbreeding affects the sex ratio of Leptopilina heterotoma, a hymenopteran parasitoid of Drosophila melanogaster. To determine whether a female's own degree of inbreeding and the degree of relatedness between her and her mate has an affect on the sex ratio of her progeny, a two-way ANOVA design was used. The first level of treatment compared inbred and outbred laying females while the second level compared matings with brothers and with unrelated males. The principle conclusion is that inbreeding at either level has no effect on the total sex ratio; however, because data on the laying schedule were also collected, a curious secondary result emerged. All of the females, regardless of treatment, tended to lay male eggs over the same time period; but for the laying schedule of females eggs, there was a significant interaction between the two treatments; and beyond that, a strongly significant difference was determined by the laying female's degree of inbreeding. In general, outbred females tended to lay females eggs later than inbred females. This difference caused inbred females to produce a relatively lower female-biased sex ratio early in the laying period, but to produce a relatively higher female-biased sex ratio later in the laying period. The implications of this curious result are discussed, although no simple interpretation seems possible.

Hey, J., 1992 Using phylogenetic trees to study speciation and extinction. Evolution 46: 627-640.

abstract - One tool in the study of the forces that determine species diversity is the null, or simple, model. The fit of predictions to observations, good or bad, leads to a useful paradigm or to knowledge of forces not accounted for, respectively. It is shown how simple models of speciation and extinction lead directly to predictions of the structure of phylogenetic trees. These predictions include both essential attributes of phylogenetic trees: lengths, in the form of internode distances; and topology, in the form of internode links. These models also lead directly to statistical tests which can be used to compare predictions with phylogenetic trees that are estimated from data. Two different models and eight data sets are considered. A model without species extinction consistently yielded predictions closer to observations than did a model that included extinction. It is proposed that it may be useful to think of the diversification of recently formed monophyletic groups as a random speciation process without extinction.

Hey, J. 1989 Speciation via hybrid dysgenesis: negative evidence from the Drosophila affinis subgroup. Genetica 78 97-104.

abstract - With the realization that some transposable elements cause hybrid dysgenesis in Drosophila melanogaster, have come proposals that speciation may be one result of their action. One characteristic of hybrid dysgenesis is that the progeny of dysgenic individuals exhibit an elevated mutation rate. Dysgenic speciation models were tested by studying hybrids of four interfertile species and semispecies of the Drosophila affinis subgroup. A study of the progeny of all possible mating pairs found no evidence for an increased visible mutation rate.

abstract The historical population genetic processes associated with the divergence of members of the Drosophila virilis species group were examined using DNA sequence variation from two loci. New data on DNA sequence variation from the oskar locus, taken from within and among all five closely related taxa in the virilis phylad of the D. virilis species group, were examined and compared to similar data previously collected from the period locus. Overall, the oskar and period data sets reveal similar patterns of variation. Both loci support the conclusion that the two subspecies of D. americana have had a large historical population size and are exchanging genes in nature. From these data there is little reason to consider them as distinct taxa. In the case of Drosophila novamexicana, from which six lines were sequenced at each locus, there is an intriguing difference in the pattern seen at the two loci. Both loci reveal two distinct groups that are considerably divergent from each other, with very little evidence of gene flow between them. However, the grouping of lines into distinct sub-groups based on oskar is different from the grouping based on period. The simplest explanation seems to be that D. novamexicana includes two distinct species, and that the sample of six lines happens to include cases of recent gene exchange. Alternatively, both oskar and period could be linked to sites of strong balancing selection and limited recombination.

abstract - Several studies of intraspecific and interspecific DNA sequence variation from Drosophila loci have revealed a pattern of low intraspecific variation from genomic regions of low recombination. The mechanisms consistently invoked to explain these patterns are the selective sweep of advantageous mutations together with genetic hitchhiking of linked loci. To examine the effect of selective sweeps on genetic divergence during speciation, we studied two loci in different genomic regions thought to be subject to selective sweeps. We obtained DNA sequences from 1.1 kilobase pair portions of the fourth chromosome locus cubitus interruptusDominant (ci^D) and from the asense locus near the telomere of the X chromosome. At ci^D, we found very low variation among multiple lines of Drosophila mauritiana and D. sechellia. This finding is consistent with an earlier report of very low variation in D. melanogaster and D. simulans at ci^D, and supports the conclusion of selective sweeps and genetic hitchhiking on the non-recombining fourth chromosome. The pattern of variation found at asense suggests that a selective sweep has occurred recently at the tip of the X chromosome in D. simulans, but not in D. melanogaster or D. mauritiana. The data from ci^D and asense are compared with data from three X chromosome loci (period, zeste, and yolk protein 2) that experience normal levels of recombination. By examining estimated genealogies and the rates at which different classes of mutations have accumulated, we conclude that selective sweeps are common occurrences on the fourth chromosome while less common near the tip of the X chromosome. An interesting pattern of low variation at ci^D among D. simulans, D. mauritiana, and D. sechellia suggests that a selective sweep may have occurred among these forms even after divergence into separate species had begun.

Hey, J.H. and D. Houle. 1987 Habitat choice in the Drosophila affinis subgroup. Heredity 58: 463-471. 

abstract - We investigated habitat choice in there species of Drosophila in seven mark-release-recapture experiments. We captured and recaptured flies in two floristically distinct habitats, and released them on the ecotone between the two.  We recovered a total of 3800 marked flies. D. affinis males consistently showed a slight, significant tendency to return to the habitat of capture.  D. athabasca, algonquin and D. affinis  females showed no significant habitat fidelity., but did not choose differently from affinis males.  Our data suggests that the choice observed is not due to differences in they physiological condition of the flies.  The level of choice is probably too small to have an appreciable impact on gene frequencies.

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