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H L Carson

Publications and source records attributed to H L Carson.

At least 37 records · Page 2Linked to original sources
PubMed1979

Change in a secondary sexual character as evidence of incipient speciation in Drosophila silvestris.

Search for genetic changes that are pivotal in species formation has led to intraspecific studies of Drosophila silvestris, a giant species found only on the geologically new island of Hawaii. Males bear large, curved, modified bristles or cilia on the dorsal surface of the foreleg tibia and tarsus. In males from the south and west parts of the island there are two rows of cilia separated by a naked area, but in males from the north and east there is a mean of between 20 and 30 additional cilia between the two major rows on the tibia. These extra cilia are absent in closely related species of this subgroup, including the sympatric species D. heteroneura and three species from adjacent islands. Males use the foreleg tibiae in vibratory movements against the female's abdomen during courtship, so this character difference is likely to be important in the reproductive biology of the species. Inversion polymorphisms are similar in both northeast and southwest populations; they show large and strikingly parallel altitudinal shifts in frequency distributions involving the same inversions. Populations from various parts of the island cannot be distinguished by routine electrophoresis of soluble proteins encoded by 25 loci. Thus the "extra cilia" character is superimposed on a more ancient genetic background of similarity involving both chromosomal and electrophoretic polymorphisms. We interpret the extra cilia as a specific new embellishment of a secondary sexual character brought about by altered sexual selection occurring very recently in one part of the species range. This suggests incipient speciation.

Journal Article↗
PubMed1979

Regulation of the tissue specificity of an enzyme by a cis-acting genetic element: evidence from interspecific Drosophila hybrids.

Homologous genes for alcohol dehydrogenase (alcohol:NAD+ oxidoreductase, EC 1.1.1.1) are expressed in qualitatively different patterns during the development of two closely related species of Hawaiian Drosophila. In interspecific hybrids, each parental structural allele is expressed according to the developmental program characteristic of the species from which it is derived. This provides strong evidence for a cis acting control element.

Alcohol Oxidoreductases↗
PubMed1977

Behavioral differences among isogenic strains of Drosophila mercatorum.

Mating propensity in eight all-female laboratory lines was measured. The lines are completely isogenic, but each has a different past history. In all cases, mating propensity was significantly lower than in the bisexual controls; in some cases, mating speed was less by a factor of 10. Three of the four lines deriving from the same wild strain are not only different from the parent strain but also different from each other. A highly significant difference exists between two strains recently obtained by selection for parthenogenesis from the same natural population. One strain appears to produce a substance which reduces mating propensity of control females if females from the two strains are reared together in the same vial. As none of the strains was behaviorally selected prior to testing, these behaviors appear to be incidental accompaniments of the very powerful isogenizing effect of the genetic system in these parthenogenetic strains. Indeed, the data show that partial isolation from sexual reproduction can arise wholly by chance. This may have some relevance to theories of species origin which are accompanied by a strong initial founder effect.

Animals↗
PubMed1977

Genetic variation in Hawaiian Drosophila. IV. Allozymic similarity between D. silvestris and D. heteroneura from the island of Hawaii.

The species are endemic to the newest island in the archipelago and are broadly sympatric. They are easily distinguished morphologically in both sexes. Using standard electrophoretic procedures, we have examined 25 loci encoding for structural proteins from 539 silvestris and 325 heteroneura collected at three widely-separated localities where the two species are sympatric. Pairwise comparisons within and between the species show the following coefficients of genetic identity (NEI'S I): within silvestris, 0.961 +/- 0.01; within heteroneura, 0.949 +/- 0.02; between silvestris and heteroneura, 0.939 +/- 0.01. Neither the differences within nor between the species are significant. There are no fixed allelic diffrences either within or between the species. At the three areas of sympatry, the species show gene frequency differences (P less than 0.05) at 9,11 and 13 loci respectively. This is not much different from the variation within either one of the species across the three localities. The two species have similar heterozygosity (H) levels (silvestris, 0.083; heteroneura, 0.089) and percent of polymorphic loci (both 0.37). It is suggested that despite their morphological divergence, these species are much more newly formed than classical sibling species. Significant allozymic differences may not have had time to accumulate.

Alleles↗
PubMed1976

The population genetics of parthenogenetic strains of Drosophila mercatorium. II The capacity for parthenogenesis in a natural, bisexual population.

Drosophila mercatorum is a bisexual species, but certain strains are capable of parthenogenetic reproduction in the laboratory. We investigated the parthenogenetic capacity of the virgin daughters of females captured from a natural, bisexual population in Hawaii. An isozyme survey indicated the natural population is polymorphic at about 50% of its loci, and its individuals heterozygous at 18% of their loci. The predominant mode of parthogenesis in D. mercatorum causes homozygosity for all loci in a single generation. Despite this radical change in genetic state, 23% of the virgin female lines produced adult parthenogenetic progeny, and 16% produced parthenogenetic progeny themselves capable of parthenogenetic reproduction. The parthenogenetic rats as measured by the number of parthenogenetic progeny themselves capable of parthenogenesis divided by the number of eggs laid is arougn 10(-5) for the virgin female lines. We argue that one of the major reasons for this low rate is that very few of the impaternate zygotes have a genotype that can survive and reproduce under the genetic conditions imposed by parthenogenetic reproduction. This intense selective bottleneck can be passed in a single generation if enough unfertilized eggs are laid, and once passed is accompanied by a large (perhaps a thousandfold) increase in the rate of parthenogenesis and by modifications in many phenotypic traits such as morphology and behavior.

Animals↗
PubMed1975

Drosophila hybrids in nature: proof of gene exchange between sympatric species.

Genetic studies of two closely related endemic Hawaiian species show that in one area of sympatry about 2 percent of the naturally occurring individuals are hybrids. More than 20 times this many would be expected if the population consisted of a single panmictic unit. Despite hybridization, natural selection appears to maintain the essential integrity of each separate gene pool.

Animals↗
PubMed1975

Allozymic and chromosomal similarity in two Drosophila species.

D. setosimentum and ochrobasis are a pair of very close, partly sympatric species endemic to Hawaii island. Males of the two species differ strikingly in wing-pattern and there are altitudinal and breeding-site differences. Similarity indices have been calculated for both chromosomal (C) ald allozymic (A) variants. Within the main populations of each species both kinds of data give coefficients above 0.98. Interspecific comparison of the main populations shows 0.66 (C) and 0.79 (A). An isolated population of ochrobasis from Kohala Volcano (Ohu), when compared with setosimentum, shows 0.68 (C) and 0.98 (A). Chromosomes are thus much more sensitive than allozymes in distinguishing these species; the same is true in the case of D. silvestris and heteroneura from the same forests. These morphologically distinct species, when compared, show 0.96 (A). All four species appear to be very new in the historical sense. In one area, about 2% of wild-caught D. setosimentum/ochrobasis are interspecific hybrids although adequate samples indicate that the separate gene pools have not broken down. The specific names should be retained but the two entities are perhaps best described as quite advanced semispecies in which reproductive isolation in nature is now nearly complete.

Animals↗
PubMed1974

Ethological isolation among three species of the planitibia subgroup of Hawaiian Drosophila.

Drosophila heteroneura and D. silvestris are sympatric species living on the island of Hawaii, while D. planitibia is allopatric on the nearby island of Maui. A pronounced ethological isolation is found between the sympatric species, and none between allopatric ones, except that D. planitibia females discriminate against D. heteroneura males. Male hybrids are sterile in allopatric crosses but fertile in sympatric ones. The ethological isolation and the hybrid sterility are uncorrelated. This is expected if premating isolation between closely related species is an ad hoc product of natural selection, while postmating isolation is an incidental result of genetic divergence. Some exceptions to the rule are discussed.

Animals↗
PubMed1974

Three flies and three islands: parallel evolution in Drosophila.

Most organisms are evolutionary conservatives; they may subdivide their niches but tend to remain within them. Yet the fossil record shows many cases of breakthrough to a new mode of life. How may such evolutionary innovation be recognized at this time level? Three species of Drosophila have accomplished an innovation in that they breed as obligate commensals on tropical land crabs. This could be dismissed as a curious aberration were it not for the fact that the three flies concerned represent three different phyletic lines of the family. Although Drosophila is abundant on the continents, these three parallel innovative evolutions have occurred on islands. The proposal is made that the genetic systems of many conservative groups of organisms carry variability that would permit them to evolve in a novel direction. The realization of this capacity, however, is possible only under special environmental conditions.

Adaptation, Biological↗
PubMed1973

The genetic system in parthenogenetic strains of Drosophila mercatorum.

Five parthenogenetic laboratory strains of Drosophila mercatorum have been examined for their mode of diploidization in the eggs of females. Diploidization occurs either by pronuclear duplication leading to complete homozygosity or by nuclear fusion. If the latter occurs between pronuclei from different secondary oocytes, heterozygosity can be maintained. Each of the five strains shows some nuclear fusion and three show significantly different amounts, ranging from about 21% to less than 1%. Even in strains with a strong tendency towards homozygosity, it is argued that this dual system of nuclear reconstitution provides for genetic recombination; thus, the strains retain considerable evolutionary potential.

Animals↗
PubMed1973

Selection for mating reluctance in females of a diploid parthenogenetic strain of Drosophila mercatorum.

A diploid parthenogenetic strain of Drosophila mercatorum was outcrossed to produce genetic variance among the impaternate female offspring. Selection experiments were carried out for reluctance of the parthenogenetic females to mate. After only two cycles of selection, a parthenogenetic strain which is significantly less receptive to males from three different bisexual strains was obtained. It was also found that there is some degree of sexual isolation among the three bisexual strains used. The results support the idea that selection can render a newly produced diploid parthenogenetic strain behaviorally different from its bisexual ancestor. This appears to provide a framework which can explain the natural coexistence of diploid bisexual and diploid parthenogenetic biotypes in some species of insects.

Animals↗