PubMed Health⌕ Search

Biomedical subjects

H L Carson

Publications and source records attributed to H L Carson.

At least 19 recordsLinked to original sources
PubMed2001

A new era in science at Washington University, St. Louis: Viktor Hamburger's zoology department in the 1940's.

In the early 1940s, the administration of the College of Arts and Sciences at Washington University, St. Louis was firmly in the hands of classical scholars who were not inclined to promote the development of modern research on scientific subjects. Funds supporting research in biology favored the School of Medicine and the Missouri Botanical Garden. Viktor Hamburger arrived at Washington University in 1935. At about the time he became the Acting Chairman of Zoology in 1942, research work in the biological departments began a dramatic surge that has continued to this day. For 65 years under his counsel and leadership, basic biology has thrived at this fine institution. As an early faculty recruit, I recount here a few personal recollections from those formative years.

Embryology↗
PubMed1994

Change in male secondary sexual characters in artificial interspecific hybrid populations.

The interfertile Hawaiian species Drosophila silvestris and Drosophila heteroneura were hybridized, forming reciprocal populations; the SH hybrid line was begun with D. silvestris female parents, and the HS hybrid line was begun with D. heteroneura female parents. Mass laboratory cultures were maintained for 14 generations without artificial selection. The species differ strikingly in two male secondary sexual characters, head shape and foreleg tibial cilia number. These characters are known to be quantitative characters that are influenced by both sex-linked and autosomal factors and appear to be involved in sexual selection. In the later generations (4-14), head shape in SH flies changes significantly; cilia number changes in both SH and HS populations. In terms of the parental phenotypes, the SH population evolved toward a heteroneura-like head while simultaneously evolving toward a silvestris-like tibia. In the HS population, there was no significant change in head shape, but cilia number decreased, making it more like the parental heteroneura. Accordingly, these two secondary sexual characters pursue separate evolutionary pathways. We suggest that these changes are brought about by selection occurring naturally during the later generations.

Animals↗
PubMed1991

Sexual behavior in laboratory strains of Drosophila mercatorum that have spontaneously adopted parthenogenesis.

Three instances are described in which bisexual laboratory strains spontaneously adopted an exclusively parthenogenetic mode of reproduction, even in the presence of fertile, bisexual males. The few males produced by the parthenogenetic strains lack a Y chromosome and are sterile but, nevertheless, showed no correlated impairment of normal mating behavior. In contrast, females show a strong reluctance to accept copulation. This behavioral correlate of parthenogenesis also has been observed previously in experimentally produced parthenogenetic lines. We suggest that genetic breakdown in female mating behavior may contribute to an evolutionary stimulus that results in a selective increase in the frequency of diploidizing events in unfertilized eggs. This ultimately might lead to the origin of an exclusively parthenogenetic reproductive mode.

Animals↗
PubMed1990

Extinction and recolonization of local populations on a growing shield volcano.

Volcanic action has resulted in the burial of the surfaces of Mauna Loa and Kilauea, Hawaii, by new lava flows at rates as high as 90% per 1000 years. Local populations of organisms on such volcanoes are continually being exterminated; survival of the species requires colonization of younger flows. Certain populations of the endemic Hawaiian species Drosophila silvestris exemplify such events in microcosm. Local populations at the base of an altitudinal cline were destroyed by two explosive eruptions within the last 2100 years. Natural recolonization restored the cline except for one young population that is genetically discordant with altitude.

Journal Article↗
PubMed1989

Chromosomal inversion patterning and population differentiation in a young insular species, Drosophila silvestris.

The recently evolved Hawaiian species Drosophila silvestris has a subdivided population structure and shows great spatial heterogeneity in chromosome inversion distributions and frequencies within its extremely limited geographic range. Pattern analysis of the 11 chromosomal polymorphisms in the context of the recently discovered morphological and behavioral divergence within the species has elucidated the history of the chromosomal differentiation. We identify four chronological groups of inversions and their probable sites of origin. Spread of the derived "3-row" bristle morphotype on the Hilo side of the Island of Hawaii has been accompanied by the acquisition of six new inversion polymorphisms. Three phylogenetically old inversions show correlations with altitude, and there are multiple cross-correlations between inversions on the same and different chromosomes, reflecting complex interaction systems. Quantification of the genetic population structure of D. silvestris by hierarchical F statistics reveals a dramatic level of genetic differentiation for an evolutionarily new species of such restricted range. This level exceeds that of older, continental Drosophila species. There is, however, minimal concordance between the chromosomal variation and the morphological-behavioral discontinuity, a consequence of the extensive cytological variation within each morphotype. Such a fragmented gene pool favors the rapid evolution and continued divergence of this insular species.

Animals↗
PubMed1988

Induced and natural break sites in the chromosomes of Hawaiian Drosophila.

gamma-Irradiation of a laboratory strain of the Hawaiian species Drosophila heteroneura yielded 310 breaks in the five major acrocentric polytene chromosomes. Their map positions conform to the Poisson distribution, unlike most of the 436 natural breaks mapped in 105 closely related species endemic to Hawaii. Genome element E is longer and has more induced breaks than the others. Both in Hawaiian and related species groups, this element shows increased polymorphism and fixation of naturally occurring inversions. The X chromosome (element A) also accumulates many natural breaks; the majority of the resulting aberrations become fixed rather than remain as polymorphisms. Although size may play a small role in initial break distribution, the major effects relative to the establishment of a rearrangement in natural populations are ascribed to the interaction of selection and drift. Nonconformance of the natural breaks to the Poisson distribution appears to be due to the tendency for breaks to accumulate both in the proximal euchromatic portion of each arm and in heterochromatic regions that are not replicated in the polytene chromosomes.

Animals↗
PubMed1985

Behavioral facilitation of reproduction in sexual and parthenogenetic Drosophila.

In a normal bisexual laboratory strain of Drosophila mercatorum, females housed with either fertile or sterile males lay more eggs than do females housed in pairs or as isolates. Females of a derived parthenogenetic strain have suffered genetic loss of this behavioral facilitation of egg production, a loss comparable to the loss of sexual receptivity. Despite these losses there has been a large increase in fecundity in the parthenogenetic strain. These findings are compared with those in a parthenogenetic lizard.

Animals↗
PubMed1984

Artificial selection for a secondary sexual character in males of Drosophila silvestris from Hawaii.

Drosophila silvestris is endemic to the rain forests of Hawaii Island. In populations from the northeast side, the male foreleg tibia bears about 100 long cilia; these are used as a brush to stimulate the female during courtship. Cyclical family selection for high and low cilia number was carried out on progeny of lines started from single wild isofemales collected at a single site. Significant response in both directions was obtained; in the third generation the lines differed by a mean of 25 cilia. Despite much effort to save them, both lines died out without further advance; the low cilia number line died after five and the high cilia number line died after nine generations. The data are compatible with the view that the cilia character is polygenic and is maintained in nature by a stabilizing sexual selection that also favors a polygenic heterozygous state. Although selection in these experiments resulted in dysgenesis, such a result is not inevitable. Disorganization and reorganization of such a genetic system following a population bottleneck might be important as a predisposing condition for the emergence of a specifically novel and possibly isolating mode of courtship.

Journal Article↗
PubMed1984

Inheritance of a secondary sexual character in Drosophila silvestris.

Reciprocal crosses were carried out between laboratory stock specimens obtained from two races of Drosophila silvestris from the island of Hawaii that differ in a quantitative secondary sexual character. The race from the Hilo side of the island has a novel attribute, consisting of an extra row of cilia on the tibia of males, which is used during courtship. With regard to this character, sex-linked genes contribute about 30% of the difference, and the remaining 70% of the difference between the races is produced by genes on at least two autosomes. The novel character appears to have been the outcome of altered sexual selection in the Hilo-side race. In an altered genetic environment, resulting from a founder event or random genetic drift, sexual selection may take a new direction. Such a shift may serve as a model for incipient speciation.

Animals↗
PubMed1984

Chromosomal mapping of a middle-repetitive DNA sequence in a cluster of five species of Hawaiian Drosophila.

We describe the properties of a repetitive transposable element isolated from a chromosomal site close to the Adh (alcohol dehydrogenase gene) region of the Hawaiian Drosophila species, D. heteroneura. The cloned element is less than 2 kilobases in length. Although its polytene chromosome sites are constant in an individual, it shows a pattern of in situ hybridization that varies both within and between five species of the D. planitibia subgroup. These species are closely related, having diverged at various times from 0.5 to 5 million years ago. The distribution of the element appears to reflect the evolutionary relationships of the species except that the differences between D. planitibia and D. differens are ambiguous. Evidence of ragged excision of the element is found in one species.

Alcohol Dehydrogenase↗
PubMed1982

Evolution of Drosophila on the newer Hawaiian volcanoes.

The 20-year odyssey taken by the Hawaiian Drosophila project has recently become focussed on a selected microcosm: this consists of the Island of Hawaii ("the Big Island") and one of its endemic species. Drosophila silvestris. Both the island and the species are considerably less than one million years old. Along with a morphologically distinct, but partially sympatric, close relative, D. heteroneura, silvestris inhabits moderate-altitude rainforests. They are the only members of the planitibia subgroup that occur on this island. The distribution of these species discontinuous due to the dissection of the forests by recent lava flows and to the irregular distribution of their main host plants. Although allozyme heterozygosity within both species is considerable, local populations of both species show high similarity coefficients. The two species are, furthermore, virtually indistinguishable electrophoretically; nevertheless, significant differences in single-copy DNA have been demonstrated. Within silvestris, five inversion polymorphisms are widespread; six others have more restricted distributions. Populations in some of the geologically newer areas are the most polymorphic, both chromosomally and morphologically. Altitudinal clines of gene arrangement frequency are clear in areas on both sides of the island. The same inversions are involved in these clines on the two sides of the island. Males of silvestris from populations from the north and east side of the island ("Hilo-side") display a novel morphological secondary sexual character. This is absent not only from south and west ("Kona-side") silvestris but also from heteroneura and from the three closely related species endemic to older adjacent islands. In view of the phylogenetic novelty of this evolutionary development, Hilo-side silvestris is judged to be derived from Kona-side rather than vice versa. The character in question involves the addition of about 25 large cilia to the dorsal surface of the tibia of the male. This portio of the leg is used in a very specific fashion to stimulate the female's abdomen during the courtship ritual. Studies of sexual behaviour of individuals drawn from various natural and laboratory populations of silvestris and its relatives have been carried out. Hybrid sterility and/or inviability is lacking in crosses both within and between populations of heterneura and silvestra. An interesting regularity has been widely observed; there is a positive correlation between the phylogenetic age of the population and the degree of discrimination by the female sex in mating. When this principle is applied to silvestris populations, the Kona-side populations of Hualalai volcano are judged to be the oldest in the species. As expected, Hilo-side populations with the novel bristle character appear to be newly-derived...

Animals↗
PubMed1981

Sexual selection in Drosophila silvestris of Hawaii.

Previous discovery that Drosophila melanogaster females tend to discriminate in mating against phenotypes of earliest courting males prompted a study of the Hawaiian species D. silvestris. Tibial bristle variation in males from opposite coasts of the island of Hawaii functions in courtship, and the possibility that females can distinguish males differing in the tibial trait is explored. Mating tests, designed to give each female and male an alternative choice between two individuals of opposite sex every 30 min, consisted of intrapopulation tests with a strain derived from an eastern (Kilauea) population and interpopulation tests between that strain and one derived from a western (Kahuku) population. Males were given initial combat tests, with "winners" then used in mating (except one test with "loser" males). Matings (52-55%) were classified into categories according to the readiness of the female to mate and sequence of courtship. Low-threshold females (accepting the first male after less than four courtship bouts) occurred at 30-35%. Among intrapopulational tests, females (with higher threshold) accepted first- and second-courting males about equally (25:36, respectively), but for male success in mating, the winning of initial intermale combats and the uniformity of courtship effort tended to be important criteria. Among interpopulation tests, homogamic matings were nearly equal (25% each), but heterogamic matings contrasted in that Kilauea females were reluctant to mate with Kahuku males (14%), while reciprocal matings occurred most frequently (34%). Females favored males second to court, particularly when a Kilauea male (with extra tibial bristles) was the second male. Thus a morphological feature likely to be influential in mating is demonstrated to be so; and sexual selection is operating via male-male combat plus discrimination in favor of particular opposite-sex individuals in this species.

Journal Article↗
PubMed1981

Location of the 18/28S ribosomal RNA genes in two Hawaiian Drosophila species by monoclonal immunological identification of RNA.DNA hybrids in situ.

Using both heterologous rabbit antisera and mouse monoclonal antibody to RNA.DNA hybrids, we have mapped the in situ hybridization locus of the 18/28S ribosomal RNA fraction to a single large band on polytene autosome 3 in Drosophila heteroneura and Drosophila silvestris. This portion of the chromosome is not physically connected with the nucleolus at the end of larval salivary gland development. In mature larvae, little or no hybridization with the material in the nucleolus can be detected. In younger larvae, hybridization of the ribosomal RNA probe to the nucleolus itself can be observed. The chromosome 3 locus is the only band in the polytene genome that shows variation in size and intensity of staining between populations and species. The interband chromosome regions that are immediately distal or proximal to the 18/28S rRNA locus have been involved in a disproportionately large number of natural inversion breaks observed in the euchromatic portion of the polytene chromosome. In 104 species of Hawaiian Drosophila in which chromosome 3 polytene sequences have been determined, 15 breaks occur in these two regions. On a random basis, only one such break is expected. We propose that this locus may be flanked by substantial heterochromatic blocks which are not represented in the salivary gland chromosome.

Animals↗