ON THE HISTORY AND CHARACTERISTICS OF SOME MULTIPLE DISCOVERIES IN BOTANY, 1648–1965

Historians and others have given attention to multiple independent discoveries because of their implications for the nature of scientific discovery in general. However, previously published lists of such discoveries include almost no examples from botany. That this has been a matter of oversight is shown by the presentation of 22 cases of multiple botanical discoveries, the circumstances of which are briefly described. These examples show a number of the same general characteristics as those in other fields of science. They range in importance from the broadly sweeping to the narrowly specific, and show various degrees of simultaneity. They illustrate the problems of interpretation involved in judging functional equivalence, identity of central message, and priority. The bearing of some of the examples on various theories of the cause of multiple discoveries is also discussed. It is concluded that multiple discoveries have probably occurred as frequently in botany as in other sciences, and they display the same characteristics and generate the same problems of interpretation.     

The Last Passage: Recovering a Death of Our Own

The Last Passage: Recovering. Death of Our Own. Donald Heinz. New York: Oxford University Press. 1999. 296 pp.     

EMBRYONIC GENETIC LOAD IN THE HIGHBUSH BLUEBERRY,VACCINIUM CORYMBOSUM (ERICACEAE)

Hand-pollinations of 28 autotetraploid V. corymbosum accessions from a single population resulted in lower self- than outcross seed set. Fertility varied widely, ranging from clones that were effectively female sterile to individuals with high seed yields in both matings. Self- and outcross fertility were highly correlated. A genetic load model was invoked to explain these phenomena. Reduced self-fertility was attributed to homozygosity for sublethal mutations at loci controlling embryo development, or to loss of heterotic interactions at these loci. Near zero cross-fertility in some clones may be evidence of partially dominant mutational load. Estimates of the number of lethal equivalents per zygote carried by individuals in this population ranged from 2.2 to 20.4, with a mean of 9.6. Embryonic genetic load at the individual level was significantly correlated with heterozygosity at nine enzyme loci. Low pollen viability and reduced receptivity to pollen from any source were also noted in the low fertility genotypes. It is suggested that gametic, gametophytic, and embryonic development are symptomatic of the amount of genetic load carried by individuals.     

FOSSIL FUNGI (ENDOGONACEAE) FROM THE TRIASSIC OF ANTARCTICA

Fungal sporocarps are described from Triassic silicified peat deposits from Antarctica. Sporocarps possess a two-layered wall and contain a single spore. The outer layer is mycelial; the inner layer, noncellular. The combination of primitive and advanced features suggests that this fungus is intermediate in complexity between the lower and evolutionarily more advanced fungi. The Antarctic fungus and morphologically similar fossils resemble extant members of the Endogonaceae, but appear to have been saprophytes rather than mycorrhizal symbionts.     

Serologic evidence of a Rickettsia akari-like infection among wild-caught rodents in Orange County and humans in Los Angeles County, California.

We detected antibodies reactive with Rickettsia akari, the etiologic agent of rickettsialpox in humans and in 83 of 359 (23%) rodents belonging to several species, collected in Orange County, CA. Reciprocal antibody titers >1:16 to R. akari were detected in native mice and rats (Peromyscus maniculatus, P. eremicus, and Neotoma fuscipes) and in Old World mice and rats (Mus musculus, Rattus rattus, and R. norvegicus), representing the first time that antibodies reactive with this agent have been detected in four of these species and the first report of these antibodies in rodents and humans west of the Mississippi River. We then tested serum samples from individuals who used a free clinic in downtown Los Angeles and found that 25 of 299 (8%) of these individuals had antibody titers >1:64 to R. akari. Serologic evidence suggested that R. akari or a closely related rickettsia is prevalent among several rodent species at these localities and that infection spills over into certain segments of the human population. Isolation or molecular confirmation of the agent is needed to conclusively state that R. akari is the etiologic agent infecting these rodents.     

Latitudinal variation in population structure of wintering Pacific Black Brant

ABSTRACT.   Latitudinal variation in population structure during the winter has been reported in many migratory birds, but has been documented in few species of waterfowl. Variation in environmental and social conditions at wintering sites can potentially influence the population dynamics of differential migrants. We examined latitudinal variation in sex and age classes of wintering Pacific Black Brant ( Branta bernicla nigricans ). Brant are distributed along a wide latitudinal gradient from Alaska to Mexico during the winter. Accordingly, migration distances for brant using different wintering locations are highly variable and winter settlement patterns are likely associated with a spatially variable food resource. We used resightings of brant banded in southwestern Alaska to examine sex and age ratios of birds wintering at Boundary Bay in British Columbia, and at San Quintin Bay, Ojo de Liebre Lagoon, and San Ignacio Lagoon in Baja California from 1998 to 2000. Sex ratios were similar among wintering locations for adults and were consistent with the mating strategy of geese. The distribution of juveniles varied among wintering areas, with greater proportions of juveniles observed at northern (San Quintin Bay and Ojo de Liebre Lagoon) than at southern (San Ignacio Lagoon) locations in Baja California. We suggest that age-related variation in the winter distribution of Pacific Black Brant is mediated by variation in productivity among individuals at different wintering locations and by social interactions among wintering family groups.     

Historical shrub–grass transitions in the northern Chihuahuan Desert: modeling the effects of shifting rainfall seasonality and event size over a landscape gradient

We use a spatially explicit landscape model to investigate the potential role of rainfall on shrub–grass transitions in the Jornada Basin of southern New Mexico during the past century. In long‐term simulations (1915–1998) along a 2700 m transect running from a dry lake bed to the foothills of a small mountain, we test two hypotheses: (i) that wetter winters and drier summers may have facilitated shrub encroachment in grasslands, and (ii) that increases in large precipitation events may have increased soil water recharge at deeper layers, thus favoring shrub establishment and growth. Our model simulations generally support the hypothesis that wetter winters and drier summers may have played a key role, but we are unable to reproduce the major shifts from grass‐ to shrub‐domination that occurred in this landscape during the early part of the 1900s; furthermore, the positive shrub response to wetter winters and drier summers was only realized subsequent to the drought of 1951–1956, which was a relatively short ‘window of opportunity’ for increased shrub establishment and growth. Our simulations also generally support the hypothesis that an increase in the number of large precipitation events may also have favored shrub establishment and growth, although these results are equivocal, depending upon what constitutes a ‘large’ event and the timing of such events. We found complex interactions among (i) the amount/seasonality of rainfall, (ii) its redistribution in the landscape via run‐on and runoff, (iii) the depth of the soil water recharge, and (iv) subsequent water availability for the growth and reproduction of shrubs vs. herbaceous plants at various landscape positions. Our results suggest that only a mechanistic understanding of these interactions, plus the role of domestic cattle grazing, will enable us to elucidate fully the relative importance of biotic vs. abiotic factors in vegetation dynamics in this semiarid landscape.