Bruce Wallace

Merging and transformation of raster images for cartoon animation

The task of assembling drawings and backgrounds together for each frame of an animated sequence has always been a tedious undertaking using conventional animation camera stands and has contributed to the high cost of animation production. In addition, the physical limitations that these camera stands place on the manipulation of the individual artwork levels restricts the total image-making possibilities afforded by traditional cartoon animation. Documents containing all frame assembly information must also be maintained.n This paper presents several computer methods for assisting in the production of cartoon animation, both to reduce expense and to improve the overall quality.n Merging is the process of combining levels of artwork into a final composite frame using digital computer graphics. The term “level” refers to a single painted drawing (cel) or background. A method for the simulation of any hypothetical animation camera set-up is introduced. A technique is presented for reducing the total number of merges by retaining merged groups consisting of individual levels which do not change over successive frames. Lastly, a sequence-editing system which controls precise definition of an animated sequence, is described. Also discussed is the actual method for merging any two adjacent levels and several computational and storage optimizations to speed the process.

Observations on the Microdispersion of Drosophila melanogaster

Natural populations live for the most part in unbounded areas. The effective population size of a local population of any species, then, is related to the movement of individuals and to their mating habits. Either limited dispersal or predispersal mating would tend to reduce the effective size of the population and to promote inbreeding. Dispersal over extended distances, the systematic dispersion of large segments of the population, and the postponement of mating until dispersion has occurred would tend to diminish inbreeding and to increase the effective size of the local population.

The migration of a mutant gene into isolated populations of Drosophila Melanogaster

Sepia (eyed) D. melanogaster females were allowed to enter ‘bottle’ populations of wildtype D. melanogaster flies at rare, sporadic intervals. The frequency of sepia-eyed individuals in these populations was determined much more by selective forces than by numbers of immigrant individuals. Populations with no sepia individuals averaged nearly 3 immigrant individuals; those with more than 25% (homozygous) sepia flies averaged about 6 immigrants. After 34 generations, the average frequency of the sepia gene is about 0.28; this may represent the average frequency of any allele introduced into the wildtype populations by these migrant flies.

The Establishment of Novel Mate-Recognition Systems in Introgressive Hybrid Drosophila Populations

Closely related species—for example, members of the same genus often coexist within small geographic areas. Drosophila pseudoobscura and D. persimilis can serve as a familiar example. Although their geographic distributions differ (Dobzhansky and Epling, 1944), as do their local spatial, feeding, and temporal preferences (Dobzhansky, 1951; Dobzhansky et al., 1956), members of these two species do nevertheless encounter one another where they occur sympatrically. They can, for example, be taken in the same trap. There, mating flies can be frequently observed, but when females are distributed individually among culture bottles, hybrid progeny are rarely encountered. Dobzhansky et al. (1968) report that among several thousand progenies examined over several decades, only two were of hybrid origin. [Reasons for believing that gene exchange between these species may be even rarer than these two cases would suggest are given by Dobzhansky (1951, 1973).] A preference for mating with a member of one’s own species (ethological isolation) is a necessary feature common to all congeneric species pairs living in sympatry.

The fate of several migrant genes in isolated populations of Drosophila melanogaster

Sepia-eyed flies carrying the slow electrophoretic variant of either Est-6 or Adh were introduced in low numbers and at infrequent intervals into populations of wildtype flies (+se/+se) that were also homozygous for the fast moving variant of either Est-6 (50 populations) or Adh (50 populations). After 24 generations, the frequency of the sepia alleles was approximately 25%, although there was considerable variation from population to population. The fate of the Est-6 slow allele corresponded closely to that of sepia (which is located ten map units distant), although one population retained the slow allozyme variant but rejected sepia. The Adh slow allele was also retained by many populations. A number of them retained Adh-S but not sepia, and vice versa; these loci are on different chromosomes. The advantage of sepia heterozygotes was estimated to be about twice that of wildtype homozygotes. The data suggest that the selective advantage resides not with the sepia locus itself, but with a nearby chromosomal region.

The fate ofSepia in small populations ofDrosophila melanogaster

Asepia gene found inD. melanogaster collected in North Carolina, and wildtype flies from North Carolina, Bogotá, Barcelona, and California were used to strt 120 cultures that were maintained by mass transfers of adults every third week for more than a year. The frequency ofsepia was determined in these cultures at the termination of the experiment. Thesepia gene was present in considerable frequency (16%–65%) in all backgrounds except one; in cultures involving wildtype chromosomes from North Carolina, it was virtually eliminated. Each of the wildtype backgrounds exhibited a characteristic final frequency ofsepia, suggesting that they had reached at least quasi-stable equilibria. Although it is likely that the retention ofsepia depended upon the superiority of flies heterozygous for this mutant, the technique does not reveal whethersepia itself was involved in the apparent heterosis.

Variation in the abillties of different strains of Drosophila melanogaster to utilize diverse carbon sources

In several experiments, flies of different geographic origins have been tested for their abilities to produce adult progeny on culture media containing primarily one or the other of several sugars. Flies of different origins differ in their abilities to produce progeny on a given sugar; flies of a single origin differ on different sugars. The data reveal a strong strain-sugar interaction as well. Strains of flies maintained for two or more years by mass transfer on culture media containing one or the other of several sugars, including xylose and lactose, adapt to that culture medium. Hybrid flies-either between lines within localities or between localities-are best able to produce offspring on xylose-containing medium.

Natural and radiation-induced chromosomal polymorphism in Drosophila.

Abstract This report deals with the retention of radiation-induced inversions in small populations of Drosophila pseudoobscura whose parental flies were from different geographic origins. 50 populations were studied; 5 were found to be polymorphic for newly-induced autosomal inversions 6 months to one year later. 3 of these polymorphisms persisted for another 2 years when the experiment was terminated. 3 of the 5 original polymorphisms involved chromosome-two, a chromosome that is generally monomorphic in natural populations. The restriction of naturally-occurring polymorphisms in this species to chromosome-three cannot be explained, then, by the absence of fitness heterosis in individuals heterozygous for genes on other chromosomes. Nor can such a lack of fitness heterosis explain the tendency for closely related species (such as D. pseudoobscura and D. persimilis) to utilize homologous chromosomes for adaptive polymorphisms. Alternative possibilities are discussed.

Commentary: Radioactive Wastes and Damage to Marine Communities

The long-term effects of the marine disposal of radioactive wastes and thermal effluents from nuclear power plants on the ecological communities of estuaries and coastal waters are postulated. Methods for measuring population fitness in relation to dynamic cycling and the relationship of radioinduced mutations to population dynamics are reviewed. The need for laboratory and field studies to evaluate the effects of radiation on marine communities is emphasized. (CH)