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A large number of random primers are available to generate random amplified polymorphic DNA (RAPD) markers; however, not all primers are equally informative. The focus of this research was to identify a small set of RAPD primers that can adequately describe the relationships among major North American soybean [Glycine max (L.) Merr.] ancestors and selected plant introductions (PIs). Two hundred eighty-one polymorphic RAPD fragments evaluated on 35 ancestors and PIs were screened for reproducibility and levels of diversity. Principal-components analysis (PCA) was employed to identify RAPD fragments associated with the largest sources of variation. Hierarchical and nonhierarchical cluster analyses were used to depict the relationships among the 35 genotypes. One hundred twenty RAPD fragments from 64 random primers were highly reproducible and had polymorphism information content (PIC) scores [is greater than or equal to] 0.30. Principal-components analysis revealed that eight components explained 60% of the total variation. Stepwise removal of fragments from individual primers revealed that fragments from only 35 primers were critical to the analysis. The product-moment correlation of pairwise distances estimated from the complete RAPD fragment data set and this core data set was 0.86 (P [is less than] 0.0001). Results from cluster analysis confirmed that this set of 35 primers provides an accurate measurement of the relationships among the 35 genotypes. These primers will be useful for estimating relationships between exotic accessions and the current North American genetic base., Molecular markers have provided a powerful new tool for breeders to search for new sources of variation and to investigate genetic factors controlling quantitatively inherited traits. Many types of molecular [...]

Glacial landforms of the North American prairie can be divided into two suites that result from different styles of ice flow: (1) a lowland suite of level-to-streamlined till consistent with formation beneath ice streams, and (2) an upland and lobe-margin suite of thick, hummocky till and glacial thrust blocks consistent with formation at ice-stream and ice-lobe margins. Southern Laurentide ice lobes hypothetically functioned as outlets of ice streams. Broad branching low-lands bounded by escarpments mark the stable positions of the ice streams that fed the lobes. If the lobes and ice streams were similar to modern ice streams, their fast flow was facilitated by high subglacial water pressure. Favorable geology and topography in the midcontinent encouraged nonuniform ice flow and controlled the location of ice streams and outlet lobes.

Submicrometer variations in the median diameter of siliciclastic mud in Orca Basin, northern Gulf of Mexico, sensitively monitor Laurentide ice sheet runoff to the gulf during early stages of the last deglaciation. Grain-size data document a prominent pulse of very fine-grained sediment to the northern Gulf from 12.6 to 12.0 ka, corresponding with the well-known sea-surface meltwater spike in [Delta]18O records. Meltwater megafloods at this time eroded and transported large volumes of clay to the Gulf via the Mississippi River system. The nonquartzose megaflood sediments appear to have been derived from clay-rich midcontinental terrace deposits rather than from glacial outwash supplied by the Laurentide ice margin. Sediment grain-size data, in combination with other terrigenous proxies (clay minerals and reworked calcareous nannofossils), indicate substantial variability in deglacial meltwater discharge and associated sediment load of meltwater runoff. This variability reflects changes in continental plumbing consistent with terrestrial records of North American deglaciation.

Stratal patterns of the Middle Ordovician Hagan K-bentonite complex and associated rocks show that the Black River-Trenton unconformity in the North American midcontinent formed through the complex interplay of eustasy, sediment accumulation rates, siliciclastic influx, bathymetry, seawater chemistry, and perhaps local tectonic uplift. The unconformity is diachronous and is an amalgamated surface that resulted from local late Turinian lowstand exposure followed by regional early Chatfieidian transgressive drowning and sediment starvation. The duration of the unconformity is greatest in southern Wisconsin, northern Illinois, and northern Indiana, where the Deicke and Millbrig K-bentonite Beds converge at the unconformity. On the basis of published isotopic ages for the Deicke and Millbrig beds, it is possible that in these regions erosion and nondeposition spanned a period of as much as 3.2 m.y. Two broad coeval depositional settings are recognized within the North American midcontinent during early Chatfieldian time. (1) An inner shelf, subtidal facies of fossiliferous shale (Spechts Ferry Shale Member and Ion Shale Member of the Decorah Formation) and argiliaceous lime mudstone and skeletal wackestone (Guttenberg and Kings Lake Limestone Members) extended from the Canadian shield and Transcontinental arch southeastward through Minnesota, Wisconsin, Iowa, and Missouri. (2) A seaward, relatively deep subtidal, sediment-starved, middle sheff extended eastward from the Mississippi Valley region to the Taconian foreland basins in the central and southern Appalachians and southward through the pericratonic Arkoma and Black Warrior basins. In the inner shelf region, the Black River-Trenton unconformity is a composite of at least two prominent hardground omission surfaces, one at the top of the Castlewood and Carimona Limestone Members and the other at the top of the Guttenberg and Kings Lake Limestone Members, both merging to a single surface in the middle shelf region. The inner and middle shelves redeveloped later in approximately the same regions during Devonian and Mississippian tine.

Several strategies can be used to restore Atlantic sturgeon stocks in the North American coastal regions. These include harvest stoppages to permit natural recolonization and reintroduction or supplementation processes such as hatchery-based stocking. Harvest stoppages avoid the genetic risks of hatchery-based stocking, but natural recovery may take long periods of time before appropriate population levels are reached.

Harlequin Ducks (Histrionicus histrionicus) were observed breeding on a tributary of the northwestern arm of Hebron Fiord, Labrador. Peak population numbers were 11 males and 13 females on 17 June; females consistently outnumbered males. Breeding was confirmed by the presence of a nest with eggs and the presence of downy chicks., Harlequin Ducks (Histrionicus histrionicus) have a disjunct, Holarctic distribution with distinct populations in northwestern North America and Asia, Iceland, Greenland, and eastern North America (Palmer 1976, Montevecchi et al. 1995). [...]

Comparisons of the physiognomy of leaves from modern vegetation of known climates with that of Eocene and Oligocene fossil leaf assemblages from middle latitudes of western North America indicate paleoaltitudes comparable or higher than those at present. Using canonical correspondence analysis, a multivariate statistical approach that includes nonlinear relationships between characters and environmental parameters, we relate leaf physiognomy of fossil samples to modern vegetation of known environmental parameters, including moist enthalpy of the atmosphere, a thermodynamically conserved quantity of the atmosphere that varies with altitude. By estimating enthalpy values for both lowland leaf assemblages and coeval interior leaf assemblages, altitudes for the interior assemblages can be estimated to [+ or -]890 m. In northeastern Washington and southern British Columbia, the high Eocene altitudes indicate subsidence, or collapse, of an area undergoing crustal extension and may reflect an immediately preceding period of uplift that triggered the extension. Similarly, other areas that have undergone Cenozoic crustal extension appear to have been at least as high as they are at present. Three sites from the Rocky Mountains also indicate elevations at least as high as at present, and therefore suggest subsidence, either resulting from cooling of a hot upper mantle or erosion and isostatic compensation of surrounding terrain. High altitudes during Eocene and Oligocene time in western North America appear to have been normal, even in areas such as the Green River basin, and therefore cast doubt on the commonly inferred late Cenozoic uplift of that region.

The influence of founding bottlenecks on genetic variation in the European starling (Sturnus vulgaris) in North America is discussed, and the genetic variation is compared to the variation in the home range. Enzyme electrophoresis was used for the study. The effect of the founding bottleneck was in agreement with theoretical predictions and it appears that theoretical predictions of bottlenecks are valuable for allozyme data and apply under a variety of conditions. .

As rifts propagate through oceanic plates, they must occasionally intersect subduction zones, unless subduction-related stresses are sufficient to terminate propagation. If propagators do reach subduction zones, there are possible consequences for continental margin evolution, depending on the geometry of propagation. For example, if the left-offset propagators that approached the western North American continental margin reached the Farallon-North America subduction zone and continued to propagate down the subducting Farallon plate, they would have transferred already-subducted Farallon lithosphere to the Pacific plate. Basal shear stresses between the resulting northwest-moving parts of the subducted slab and the overriding continent could have led to rifting of the continental margin. The intersections of the only two left-offset propagators that appear to have reached this margin correlate spatially and possibly temporally with the initiation of the two most unique Neogene geologic structures of the western North American continental margin, the Gulf of California and the Transverse Ranges, suggesting a possible causal relationship.

A billion years ago, a huge rift nearly cleaved North America down the middle. And then it failed. Researchers may be getting close to finding out why. On a bright [...]

The western margin of the North American continent, comprising the Cordilleran mountain chain that runs from Alaska to Mexico, consists of scores of continental jigsaw pieces of different origins, sizes [...]

One of the most significant impediments to progress in forecasting weather over North America is the relative paucity of routine observations over data-sparse regions adjacent to the United States. Prospectus Development Team Seven was convened to consider ways to promote research that seeks to determine implementations of observing systems that are optimal for weather prediction in the United States. An 'optimal' measurement system is considered to be one that maximizes the ratio of societal benefit to overall cost. The thrust of the conclusions is that existing means of estimating the value of current observing systems and the potential benefits of new or proposed observing systems are underutilized. At the same time, no rational way exists for comparing the cost of observations across the spectrum of federal agencies responsible for measuring the atmosphere and ocean. The authors suggest that a rational procedure for configuring an observation system that is optimal for weather prediction would consist of the following steps. 1) Identify specific forecast problems arising from insufficient data. Examples might include hurricane landfall and intensity forecasts, 24-h forecasts of intense extratropical cyclones affecting the West Coast and Alaska, and medium-range forecasts of severe weather for all of North America. 2) Use contemporary modeling techniques, such as observing system simulation experiments, ensemble forecasting, and model adjoint-derived sensitivities, to delineate measurement requirements for each specific forecasting problem and identify candidate observing systems and data assimilation techniques that could be brought to bear on each problem. 3) Estimate the incremental forecast improvements that could plausibly result from the added or reconfigured data and the societal benefits that would accrue from such improvements. 4) Estimate the overall cost (to the nation, not to specific federal agencies) of obtaining the data by the various candidate techniques and the benefits that are projected to result. 5) Use standard cost-benefit analysis as a basis for deciding the optimal deployment of measuring systems. The authors believe that a rational approach to atmospheric measurement is critical to further improvements in weather prediction and that such improvements might very well be made within the current budget of routine observations, integrated across all of the responsible federal agencies. This document outlines a proposed strategy for rationalizing atmosphere observations in aid of weather prediction in the United States. The paper begins with a summary of recommendations.

The nature of the Great Valley basement, whether oceanic or continental, has long been a source of controversy. A velocity model (derived from a 200-km-long east-west reflection-refraction profile collected south of the Mendocino triple junction, northern California, in 1993), further constrained by density and magnetic models, reveals an ophiolite underlying the Great Valley (Great Valley ophiolite), which in turn is underlain by a westward extension of lower-density continental crust (Sierran affinity material). We used an integrated modeling philosophy, first modeling the seismic-refraction data to obtain a final velocity model, and then modeling the long-wavelength features of the gravity data to obtain a final density model that is constrained in the upper crust by our velocity model. The crustal section of Great Valley ophiolite is 7-8 km thick, and the Great Valley ophiolite relict oceanic Moho is at 11-16 km depth. The Great Valley ophiolite does not extend west beneath the Coast Ranges, but only as far as the western margin of the Great Valley, where the 5-7-km-thick Great Valley ophiolite mantle section dips west into the present-day mantle. There are 16-18 km of lower-density Sierran affinity material beneath the Great Valley ophiolite mantle section, such that a second, deeper, 'present-day' continental Moho is at about 34 km depth. At mid-crustal depths, the boundary between the eastern extent of the Great Valley ophiolite and the western extent of Sierran affinity material is a near-vertical velocity and density discontinuity about 80 km east of the western margin of the Great Valley. Our model has important implications for crustal growth at the North American continental margin. We suggest that a thick ophiolite sequence was obducted onto continental material, probably during the Jurassic Nevadan orogeny, so that the Great Valley basement is oceanic crust above oceanic mantle vertically stacked above continental crust and continental mantle.

Models integrating geodynamic and stratigraphic processes show that some gross features of Phanerozoic North American cratonic strata can be explained with dynamic topographies generated by subduction and cycles of supercontinent aggregation and dispersal. A three-dimensional finite-element model is used to calculate mantle flow beneath North America during Phanerozoic time in response to episodes of subduction at cratonic margins and two cycles of supercontinent formation and breakup. Dynamic topographies calculated by the flow models are used as input to a stratigraphic model that also includes background subsidence, eustasy, denudation, clastic and carbonate deposition, compaction, and isostasy. These models successfully reproduce aspects of the Sloss sequences; the best matches were obtained by combining two wavelengths of dynamic topography with second-order eustasy. Long-wavelength dynamic topography generates first-order stratal cyclicity. Periods of erosion were shorter when North America was over a dynamic topography low than when it was over a high. Long-wavelength dynamic topography also explains the absence of Mesozoic strata on the eastern portion of the craton. Characteristic stratal patterns are shown to result from subduction-related dynamic topography, although sensitive to sediment supply and other subsidence mechanisms. Aspects of Upper Cretaceous stratal patterns may be explained by the effects of Farallon plate subduction. Generally, strata deposited in a dynamic topography depression have low preservation potential because the topography is reversible. Thus, ancient subduction-related dynamic topography is most likely to be represented by unconformities.

Simple and multivariate linear models were used to demonstrate the influence of mechanical design and climate on stem morphology and branching architecture in 25 species of North American columnar cacti. The effect of phyletic inertia was tested by the method of independent contrasts. Stem girth was found to increase significantly slower with increased height within taxa (cross-sectional stem area [varies] [[plant height].sup.0.603]), than across taxon (cross-sectional stem area [varies] [[plant height].sup.1.451]). Juveniles are shown to be mechanically overbuilt and subsequently grow into more slender adult forms determined in part by structural limitations and the optimization of other stem functions. We make a structural analogy of relatively rigid columnar cacti to concrete columns and compare plants and models with similar growth forms lacking woody skeletons (barrel cacti). Taxa with woody support achieved a surface-to-volume ratio six times greater than taxa without woody support. Across taxon, cooler winter temperatures were associated with larger stem girths, and greater annual precipitation was associated with less frequent branching. The relationship between total plant surface and volume approaches isometry within taxa, but across taxon average individuals are scaled replicates. We hypothesize that architecture and average plant height are adjusted, in an evolutionary sense, to maintain geometric similitude between surface and volume along a climatic gradient. Key words: branching architecture; Cactaceae; climate; columnar cacti; mechanical design; Pachycereeae; phyletic inertia; stem morphology.

The North American monsoon is an important feature of the atmospheric circulation over the continent, with a research literature that dates back almost 100 years. The authors review the wide range of past and current research dealing with the meteorological and climatological aspects of the North American monsoon, highlighting historical development and major research themes. The domain of the North American monsoon is large, extending over much of the western United States from its region of greatest influence in northwestern Mexico. Regarding the debate over moisture source regions and water vapor advection into southwestern North America, there is general agreement that the bulk of monsoon moisture is advected at low levels from the eastern tropical Pacific Ocean and the Gulf of California, while the Gulf of Mexico may contribute some upper-level moisture (although mixing occurs over the Sierra Madre Occidental). Surges of low-level moisture from the Gulf of California are a significant part of intraseasonal monsoon variability, and they are associated with the configuration of upper-level mid-latitude troughs and tropical easterly waves at the synoptic scale, as well as the presence of low-level jets, a thermal low, and associated dynamics (including the important effects of local topography) at the mesoscale. Seasonally, the gulf surges and the latitudinal position of the midtropospheric subtropical ridge over southwestern North America appear to be responsible for much spatial and temporal variability in precipitation. Interannual variability of the North American monsoon system is high, but it is not strongly linked to El Nino or other common sources of interannual circulation variability. Recent mesoscale field measurements gathered during the South-West Area Monsoon Project have highlighted the complex nature of the monsoon-related severe storm environment and associated difficulties in modeling and forecasting.

The validity of Rapoport's rule, which states the existence of a positive correlation between the latitudinal extent of the geographical range of organisms and the latitude wherein said organisms are found, is examined using a species of columnar cacti growing in North and South America. This is achieved using two databases containing a total of 3,250 records. Results show that Rapaport's rule is applicable in Mexico but not in Argentina. Moreover, cacti in the North and South American regions exhibit contrasting behavior.

We investigated the importance of wind-assisted flight for northward (spring) migration by Western Sandpipers (Calidris mauri) along the Pacific Coast of North America. Using current models of energy costs of flight and recent data on the phenology of migration, we estimated the energy (fat) requirements for migration in calm winds and with wind-assisted flight for different rates of fat deposition: (1) a variable rate, assuming that birds deposit the minimum amount of fat required to reach the next stopover site; (2) a constant maximum rate of 1.0 g/day; and (3) a lower constant rate of 0.4 g/day. We tested these models by comparing conservative estimates of predicted body mass along the migration route with empirical data on body mass of Western Sandpipers at different stopover sites and upon arrival at the breeding grounds. In calm conditions, birds would have to deposit unrealistically high amounts of fat (up to 330% of observed values) to maintain body mass above absolute lean mass values. Fat-deposition rates of 1.0 g/day and 0.4 g/day, in calm conditions, resulted in a steady decline in body mass along the migration route, with predicted body masses on arrival in Alaska of only 60% (13.6 g) and 26% (5.9 g) of average lean mass (22.7 g). Conversely, birds migrating with wind assistance would be able to complete migration with fat-deposition rates as low as 0.4 g/day, similar to values reported for this size bird from field studies. Our results extend the conclusion of the importance of winds for large, long-distance migrants to a small, short-distance migrant. We suggest that the migratory decisions of birds are more strongly influenced by the frequency and duration of winds aloft, i.e. by events during the flight phase, than by events during the stopover phase of migration, such as fat-deposition rate, that have been the focus of much recent migration theory.

The presence of conflicts in the allocation of resources among the different functions of an organism is a fundamental postulate of modern ecology. It is assumed that reproduction occurs at a cost because it monopolizes resources that could be used for other functions (e.g., growth). These conflicts may be particularly evident under stressful conditions, such as under low water or nutrient availability, or under severe climatic conditions. There we may expect to find strong negative relationships between an organism's growth and reproduction. We studied a population of Pinus banksiana (Pinaceae) at the northern limit of the species distribution, in subarctic Quebec (Canada) where Pinus banksiana occupies nutrient-poor, sandy terraces along the Great Whale river. Serotinous cones of Pinus banksiana produced between 1969 and 1992 were sampled to estimate interannual variations in several variables representing reproduction, and to relate these to climate and tree growth. Climate appears to influence each developmental stage involved in the production of viable seeds, from the time of cone initiation to that of seed maturation. In general, reproductive variables are positively related to high temperatures during the three growing seasons required for seed production; growth is also positively correlated to summer temperatures. Consequently, investment in maturing seeds is positively associated with growth. Thus, both reproduction and growth covary with climate: during relatively warm and long growing seasons, resource allocation to both functions increases. Under these conditions, no trade-off is apparent. Key words: climate; cost of reproduction; dendrochronology; partial Mantel test; Pinaceae; Pinus banksiana; seed production; subarctic Quebec; trade-off.

Reproductive and vegetative remains of Eucommia from 25 localities in the United States, Canada, and Mexico document the wide distribution of this genus in North America during the Cenozoic. Autofluorescent elastic latex filaments bearing capitate termini are preserved in nearly all of the remains and provide conclusive evidence of their affinity to Eucommia. Four species of Eucommia are recognized on the basis of the characteristic samaras: E. eocenica from middle Eocene strata of the Mississippi Embayment in Missouri, Tennessee and Mississippi; E. montana from early Eocene to early Oligocene localities in British Columbia, Washington, Oregon, Utah, Colorado, and Montana; E. constans from Neogene rocks in central Mexico; and E. jeffersonensis n. sp. from the latest Eocene or earliest Oligocene John Day Formation of Oregon. Atypical specimens of E. montana and E. eocenica are the first records of two-seeded fruits for the genus. Eucommia leaves from Eocene localities in British Columbia and Mississippi are the first records of Eucommia foliage in North America whose identifications are confirmed by the presence of capitate latex strands. These leaves and a specimen from Oregon are referred to E. rolandii n. sp. Fruit evolution in Eucommia may have involved increases in samara size and symmetry, and reduction in seed number from two to one, perhaps as adaptations for wind dispersal. All fossil Eucommia samaras from North America are smaller and less symmetrical than those of the living species, E. ulmoides. Preliminary flight tests of E. ulmoides samaras and of models of the fossils suggest that E. ulmoides fruits are aerodynamically better suited for wind dispersal than the fossils. Key words: angiosperms; anemochory; Cenozoic; Eucommia; Eucommiaceae; latex; North America; paleobotany; phytogeography.

Pleistocene glaciations had a profound effect upon the biota of North America. Prior to the Pleistocene (> 2.5 MYBP), a continuous highland region with a very different drainage pattern existed [...]

Chrysothamnus nauseosus (Asteraceae) is a complex polymorphic shrub species widely distributed in western North America. In a study of 86 populations belonging to 15 subspecies, achene mass varied among populations over a sevenfold range. Achene mass was closely correlated with capitulum size at the subspecies level, varied little between wild-growing and common-garden-grown members of a population, and was under strong genetic control. Subspecies with the heaviest achenes are restricted to specialized edaphic environments (dunes and badlands) or late seral montane riparian communities, while subspecies that are widely distributed and that occur in early seral habitats have less heavy achenes. Selection on achene mass has apparently been a notable feature of the adaptive radiation of Chrysothamnus nauseosus into the wide array of habitats it currently occupies. Within a wild population, achene mass was greater for plants fruiting in midautumn than for plants fruiting early or late in the autumn, and this same trend was observed within individual plants in garden populations, indicating environmental control, perhaps through resource limitation. Highly significant between-plant differences in achene mass were found in both wild and garden populations, suggesting that within-population genetic variation is sufficient to permit continuing selection. Key words: adaptive radiation, Asteraceae; Chrysothamnus nauseosus; composite shrub; edaphic endemism; rubber rabbitbrush; seed dispersal; seed size.

A magnetic polarity stratigraphy and a corresponding paleomagnetic pole position are reported from 113 sampling sites representing 3000 m of Upper Triassic continental sedimentary rocks that crop out in the Dan River-Danville basin of North Carolina and Virginia. Characteristic magnetizations isolated by thermal demagnetization for either the hematite-bearing red siltstones or the interbedded magnetite-bearing gray to black mudstones of the Leakesville Formation are indistinguishable in mean direction and pass reversal tests. The magnetic polarity sequence consists of 11 magnetozones that vary from [approximately equal to]100 m to 800 m in thickness and can be uniquely correlated within biostratigraphic constraints to magnetochrons E9n to E14n of the Newark geomagnetic polarity time scale. According to this correlation, the sampled section is the age equivalent of the uppermost Stockton, the entire Lockatong, and the low-ermost Passaic formations of the Newark basin, and represents [approximately equal to]7.5 m.y. of deposition. The late Carnian Dan River-Danville paleopole is located at 55.4 [degrees] N 100.1 [degrees] E ([A.sub.95] = 1.9 [degrees]), which is not significantly different from paleopoles reported from essentially coeval rocks in the Newark basin. Considering that the Dan River-Danville and Newark basins are [approximately equal to]600 km apart, the close agreement of the coeval paleopoles argues strongly for the overall tectonic coherence of these rift basins with respect to each other and, most probably, with respect to cratonic North America. Discordant latest Triassic paleopoles from the southwestern United States, which have tended to be attributed to fast apparent polar wander for North America in the Late Triassic and predict anomalously high paleolatitudes for eastern North America, are best accounted for by a large net clockwise rotation of the Colorado Plateau.

A broad genetic base for a crop species such as wheat (Triticum spp.) may be important to reduce genetic vulnerability and assure long-term potential for genetic gun. The number and diversity of original ancestors can provide insight into relative genetic diversity within and among gene pools. Based on the coefficient of parentage values between cultivars and ancestral Kan, the relative genetic contributions of ancestral lines to spring wheat (Triticum aestivum L.) cultivars were computed for successive 25-yr time periods. The cultivars were from Canada (47), the USA (133), and Mexico (90). Genetic backgrounds were studied for important changes in the ancestral base over time and to determine trends that continue today. About 124 ancestors, tracing to 32 countries on five continents, were found to have contributed to the North American spring wheat gene PoolCanadian western red spring cultivars released before 19M had an intermediate level of ancestral diversity. Their post-1975 cultivars have narrow ancestral diversities probably due to strict quality regulations. They consist primarily of `Thatcher' germplasm modified by a set of pest resistance genes carefully managed in backcross schemes. Before 1950, the U.S. hard red spring wheat cultivars traced to the same Matcher ancestors but also to `Kota' and `Yaroslav'. Many more ancestors were added to this base after 1950 and especially after 1975. This was a side effect of the incorporation of pest resistance, most notably from sources `Gabo-Timstein', `Frontana', and `Kenya Sr, and reduced height sources, most notably CIMMYT cultivars with new ancestry from `Kenya 324' and Turkey. CIMMYT cultivars have also expanded their genetic base over time, with the systematic incorporation of new ancestry from various sources including winter wheats. Introduction of novel alleles from wild ancestors or other sources should contribute to future broadening of the genetic base, maximizing genetic gains, and reducing genetic vulnerability of the gene pools., Concern about a perceived lack of genetic diversity and the resulting genetic vulnerability of our food plants has lead researchers to assess the situation in different crops. In wheat, the [...]

Genetic diversity constitutes the raw material for plant improvement, and it can provide protection aping genetic vulnerability to biotic and abiotic stream. Our objectives were to determine patterns of relatedness using the coefficient of parentage (COP) matrix among 270 spring wheat (Triticum aestivum L.) cultivars and to compote mean COP values for major regional breeding programs. The collection included most important cultivars released during this century from Canada (47), the USA (133), and Mexico (90). Cluster analysis, based on the COP matrix, resulted in 20 major clusters of few or more entries and six small dusters of two cultivars each. The first three axes from a principle coordinate analysis of the intercluster COP matrix showed (i) a group of seven clusters including most hard red spring cultivars (HRS) from the USA, and Canada (CWRS), based mainly on a `Marquis' background, (ii) a group of nine interrelated clusters including most cultivars from CIMMYT (Mexico), (iii) two interrelated dusters including mostly white wheats, and (iv) two small clusters including mostly old Canadian cultivars. Mean COP values were computed among cultivars released during three successive tune periods for major regional breeding programs. The CWRS cultivars have become progressively more interrelated based on a Thatcher background. Average COP values (0.58 among modern cultivars) for this class were higher than values reported for winter wheat, barley (Hordeum vulgare L.), and oat (Avena sativa L.) gene pools. The HRS wheats showed a fairly high but slowly decreasing interrelatedness (COP = 0.22) among modem cultivars, with some regional differences. CIMMYT cultivars were less interrelated (COP = 0.15-0.20) and comparable to levels reported for soft red winter wheat and barley. Quality requirements and kernel type have probably been major factors in maintaining relatively high COP in the CWRS bud somewhat less in the HRS in the USA. CIMMYT cultivars, in general, do not have quality restrictions, allowing the introduction of more diversity., Bread wheat (Triticum aestivum L.), as a crop, has a history of several thousand years with many parts of the world having developed locally adapted landraces. In the Western hemisphere, [...]

The Newark Supergroup currently includes nine stratigraphic groups, each of which applies to part or all of the rock column of only one or a few basins. Because the group nomenclature within the Newark Supergroup is neither inclusive nor parallel in its concepts, nearly half of the strata within the Newark Supergroup lacks any group placement. A new system is proposed herein that (1) establishes unambiguous group boundaries, (2) places all Newark Supergroup strata into groups, (3) reduces the number of group names from nine to three, (4) creates parallelism between groups and three major successive tectonic events that created the rift basins containing the Newark Supergroup, and (5) coincidentally provides isochronous or nearly isochronous group boundaries. These proposed groups are (1) the Chatham Group (Middle Triassic to basal Lower Jurassic sedimentary rocks), (2) the Meriden Group (Lower Jurassic extrusive volcanic and sedimentary rocks), and (3) the Agawam Group (new name) (Lower Jurassic sedimentary rocks above all early Mesozoic igneous intrusive and extrusive rocks). This new rock classification system makes use of the fact that a discrete interval of synchronous or nearly synchronous volcanism and plutonism occurred throughout the early Mesozoic rift system of eastern North America. The presence or absence of volcanic rocks provides a powerful stratigraphic tool for establishing regional groups and group boundaries. The presence of sedimentary rocks injected by diabase dikes and sills, in the absence of extrusive volcanic rocks, places Newark Supergroup rocks in the Chatham Group. The presence of extrusive volcanic rocks, interbedded with sedimentary rocks injected by dia-base dikes and sills, places Newark Super-group rocks in the Meriden Group. The presence of sedimentary rocks lacking both extrusive volcanic rocks and diabase dikes and sills, places Newark Supergroup rocks in the Agawam Group. Application of this new regional group stratigraphy to the early Mesozoic rift basins requires revision of the stratigraphy of several basins to make formation boundaries match group boundaries.

The existence of strong summer thermal gradients in North America is investigated using palaeoecological methods. These gradients are believed to have been formed by the combination of high summer insolation and the presence of the Laurentide ice sheet during the period when the last glacial climate was shifting to the present interglacial climate. Reconstructions of temperature gradients for the late-glacial period in the study region are found to be much stronger than those of the modern period.

The cap of the anterior loop of the uncut m1 in Microtus richardsoni is simple, as it is in other Microtus spp., not highly complex like the respective cap in Arvicola terrestris. This supports the placement of M. richardsoni in the genus Microtus., INTRODUCTION Systematists have long disputed the generic position of the North American water vole, a relatively large and semiaquatic arvicoline rodent with a limited geographic range in the western United [...]

An ocean circulation model is used to study the surface water circulation, salinity and dissolved oxygen of the transgressive phase of the Cretaceous North American seaway. The amount of solar insolation affects the zonal wind stress curl and wind magnitude which affect the strength of the western and eastern boundary currents. The freshening of surface water is prevented by short surface water residence times. High deep water exchange rates and low deep water residence times lead to low apparent oxygen utilization.

We investigated avian grit use by examining the gizzard contents of 1440 birds collected from 12 states. Grit was present in gizzards of 62 of 90 species and varied greatly in number and mean particle size. Gizzards of granivorous birds contained more grit particles than those of insectivores, omnivotes, and frugivores. Grit particle characteristics (mean size, shape, and surface texture) did not differ among birds consuming different diets. Mean grit size increased linearly with the common logarithm of the bird body mass. Within avian species, grit-use patterns did not differ by gender. Grit use is widespread among birds, and diet strongly influences the amount of grit used by birds., Best and Gionfriddo (1991) characterized grit use by 22 species of North American birds. The impetus for that work was the relevance of grit use to avian mortality caused by [...]

Patterns of staining intensity and heterodimer positions observed in gel electrophoresis indicate that the dioecius tree Maclura pomifera is an autopolyploid with tetrasomic inheritance. M. pomifera is endemic to North America, and the female plant produces large and many-seeded multiple fruits. The deviations from tetrasomic ratios observed in the segregation arrays are attributed to the double-reduction genotypes. Autopolyploidy, through production of unbalanced sex chromosome ratios, may be the reason for the peculiarity of sexual expression seen in these plants.

External features of the tail and pelage, and quantitative cranial characteristics were used to discriminate Peromyscus leucopus from P. maniculatus (n = 204) from northeastern North America. Species assignments were based on the phenotype of salivary amylase. Characteristics of the pelage and tail yielded correct identification of 55% of adult specimens. A previously published discriminant-function equation based on 11 cranial measurements correctly classified 66% of adults and 56% of specimens of all age classes. Two new discriminant equations were generated based on 12 and 11 skull measurements, respectively. The first equation correctly classified 100% of skulls in two separate datasets (n = 164; n = 50), and the second correctly classified 94% in a single dataset (n = 195). Key words: Peromyscus maniculatus, Peromyscus leucopus, identification, cranial morphology, discriminant function

Legacy of the European crucible? European biota may be much better competitors, especially under disturbance and fragmented conditions, than their North American counterparts Over the last 500 years, nearly 2000 [...]

Eastern Asian-eastern North American disjuncts in four genera were examined for allozyme divergence and sequence divergence of the internal transcribed spacers (ITS) of nuclear ribosomal DNA. The disjunct pairs of taxa include Caulophyllum robustum-C. thalictroides, Menispermum dauricum-M. canadense, Penthorum chinense-P. sedoides, and Phryma leptostachya var. asiatica-P. leptostachya var. leptostachya. Allozyme divergence was comparable in Caulophyllum and Penthorum (genetic identities of 0.534 and 0.546) and was considerably higher than between pairs of taxa in Menispermum (0.273) and Phryma (0.291). Caulophyllum and Penthorum, which have the highest genetic identities at allozyme loci, also have low ITS sequence divergences (1.30 and 1.65%, respectively). Phryma, which has low isozyme identity, also has the highest ITS sequence divergence (4.46%). The two taxa of Menispermum have low ITS sequence divergence (0.93%) despite having a low identity (0.273) at allozyme loci. The results suggest that divergence between the taxa in the four genera are not the result of a single historical event. Estimated divergence times are reasonably consistent with a late Miocene disjunction for Caulophyllum and Penthorum, whereas the age of the Phryma disjunction is calculated at over 20 million years. The nonconcordant divergences between allozymes and ITS sequences in Menispermum may be caused by concerted evolution in the latter or possibly longer generation time in the woody plants. Additional molecular data are needed to clarify the situation. Key words: allozymes; disjunct species; ITS sequences; molecular divergence.

The differential thermal sensitivity of the mussels Mytilus trossulus and M. galloprovincialis is responsible for the distribution of the former in the northern colder region and the latter in the southern region of the Pacific coast of the USA. An eight week exposure to 13 degree centrigrade or heat shock at higher temperature results in higher levels of hsp70 in M. trossulus as compared to M. galloprovincialis. The level of ubiquitin conjugates is also higher in M.trossulus. These difference may be responsible for geographical segregation of the mussels.

The rifted continental margin of Laurentia (now North America) records continental breakup and the opening of the lapetus Ocean in latest Precambrian to earliest Paleozoic time (1). Collisions during later [...], The Argentine Precordillera is a continental fragment rifted from the Ouachita embayment of the southern margin of Laurentia (North America) during Cambrian time [about 515 million years ago (Ma)] and accreted to the western margin of Gondwana (South America) during Ordovician time (about 455 Ma). Similarities of Cambrian stratigraphic successions and faunas, Grenville basement rocks, and dimensions link the Argentine Precordillera to the Ouachita embayment. Evidence of rifting during Cambrian time and of a wide ocean basin during Ordovician time indicates that the Precordillera traveled as an independent microcontinent to collide with Gondwana.

To understand the patterns of lithofacies, marine faunas, organic-carbon enrichment, isotopes, and trace elements deposited in the early Turonian Western Interior seaway, we conducted circulation experiments using a three-dimensional, turbulent flow, coastal ocean model driven by GENESIS, a climate model developed at the National Center for Atmospheric Research (NCAR). Circulation and chemical evolution of the seaway waters are computed under the following initial and boundary conditions: (1) paleobathymetry according to a new interpretation of the lithostratigraphy and biostratigraphy; (2) temperatures and salinities of the Boreal and Tethys oceans and adjacent drainage basins based on isotopic data, atmospheric temperatures, and precipitation-evaporation magnitudes computed by GENESIS; and (3) mean annual wind stresses over the seaway computed by GENESIS. Results show that the seaway exported freshened water much like Hudson Bay today. Runoff from eastern drainages exited the seaway as a northern coastal jet; runoff from western drainages exited as a southern coastal jet. Both jets simultaneously drew in surface Tethyan and Boreal waters, creating a strong counterclockwise gyre occupying the entire north-south extent of the seaway. The curious stratal and faunal variations of the early Turonian deposits arise from this gyre and its associated water masses.

We used a numerical ice-sheet model to reconstruct the North American Laurentide Ice Sheet during the last glacial maximum. Our model simulates ice-sheet conditions that can be specified experimentally as either a rigid substrate (hard bed) or a wet, deformable till (soft bed); basal sliding is excluded. We use geologic records of former basal ice-sheet processes to prescribe the distribution of hard and soft beds. Our reconstruction of the Laurentide Ice Sheet is significantly lower in ice-surface height and contains less ice volume than the CLIMAP (maximum) reconstruction. In contrast, our reconstruction agrees well with the ICE-4G reconstruction, both in height and volume. Because the ICE-4G reconstruction is based on the inversion of relative sea-level data, whereas our reconstruction is based on glacial geology and ice mechanics, this agreement suggests that soft beds provide a glaciological mechanism to explain the shape and volume of the Laurentide Ice Sheet that is most consistent with observations of relative sea-level change and other geodynamic considerations.

Unlike other freshwater bivalves that survive for months in deionized water, Dreissena polymorpha requires minimal concentrations of Na, K, Mg, and Cl in the bathing medium for long-term survival. Although ion transport rates are higher in D. polymorpha compared to other freshwater bivalves, they tend to have lower blood solute concentrations. D. polymorpha has an unusually "leaky" epithelium with a high paracellular permeability to solutes. Thus, even with high transport rates, it may not be possible for zebra mussels to retain higher blood solutes because of the extensive passive loss of ions. Under a hyperosmotic stress, D. polymorpha will rapidly osmoconform (about 12 hr) due primarily to the diffusion of solutes and partially to the osmotic loss of water. D. polymorpha is not capable of surviving an imbalance of Na/K in the external medium. In the absence of K the cells will tend to lose volume to achieve isosmotic balance with the blood, but the animals usually die within a few days. If D. polymorpha is exposed to excess K in the environment (1 mM), they will accumulate K in the blood. If the K enters the cells, cellular volume would expand due to increase in osmolyte concentration, yet, if K remains in the blood, there will be an electrochemical imbalance. In either case, the animal cannot survive much longer than a day. When Na and K are present in the medium in a balanced combination approximated by artificial seawater (ASW), D. polymorpha will survive an acute transfer to 100 mosm ASW indefinitely (months). Our preliminary studies have shown that D. polymorpha will tolerate step-wise acclimation to solutions [greater than]250 mosm provided the changes in salinity do not exceed 50-100 mosm. Freshwater bivalves, unlike the marine bivalves, have limited free amino acids in their body fluids and must rely on inorganic ions for osmotic regulation. The free amino acids serve as an important osmolyte buffer for volume regulation when an animal experiences an environment of changing salinity. The inability of Dreissena, and perhaps other freshwater bivalves, to tolerate hyperosmotically induced dehydration may be due, in part, to the inability to accumulate or retain sufficient intracellular K to facilitate regulatory volume adjustments.

The zebra mussel, Dreissena polymorpha (Pallas), was introduced into North America in 1986. Initial North American (N.A.) studies suggested that physiological responses varied between N.A. and European populations. However, literature review indicates agreement on most aspects of physiological adaptation including: respiratory responses; hypoxia/anoxia tolerance; salinity limits; emersion tolerance; freezing resistance; environmental pH limits; calcium limits; starvation responses; and bioenergetic partitioning. The main differences among N.A. and European mussels appear to be elevated upper thermal limits and temperatures for optimum growth among N.A. populations. N.A. zebra mussels probably originated from the northern shore of the Black Sea in the warmest portion of the mussel's European range. However, most European physiological data come from northern Europe where populations may be adapted to colder temperatures. Alternatively, N.A. research suggests that mussels may have a capacity for seasonal temperature acclimatization such that responses recorded in warmer N.A. waters may be different from those recorded in northern Europe even after short-term laboratory acclimation. Studies of genetic variation and physiological response among European and N.A. D. polymorpha populations are required to elucidate the basis for physiological differentiation. Recently evolved D. polymorpha has poor resistance adaptations compared to unionacean and sphaeriid bivalves with longer freshwater fossil histories. Poor resistance adaptations make it less suited for stable habitats, instead, its high fecundities, early maturity, and rapid growth are adaptations to unstable habitats where extensive resistance adaptations are of little value.

The reproductive cycle of the zebra mussel (Dreissena polymorpha) is highly variable throughout its range in Europe, Russia, and North America. The environmental factors influencing this variation are poorly understood, but successful reproduction is occurring in areas where it was initially believed that adult zebra mussels could not survive (i.e., southern United States). The differences in mussel reproduction occurring from site-to-site make it difficult to predict timing of specific events, such as the start of larval production, that are important in initiating containment or control procedures. For example, the amount of time required for a fertilized egg to develop into a juvenile mussel can be as short as 8 days, or as long as 240 days. Release of gametes by adults can be a highly synchronized event, focused over a 1-2 week period, or it can be completely non-synchronized, occurring throughout the year. Zebra mussels in some localities start spawning at water temperatures of 12-13 [degrees] C, but do not start until water temperatures reaches 22 [degrees] C at other sites. While some of this variability in reproductive behavior stems from mussel adaptation to local conditions, part is due to difficulties in sampling these events. It is difficult to determine reproductive success of a specific population because of the problems in separating locally produced larvae from larvae drifting in from other areas. Further research is needed not only on the relationship between reproduction and environment at the community level, but also on the variability in response of individual mussels.

North America's Great Lakes have recently been invaded by two genetically and morphologically distinct species of Dreissena. The zebra mussel (Dreissena polymorpha) became established in Lake St. Clair of the Laurentian Great Lakes in 1986 and spread throughout eastern North America. The second dreissenid, termed the quagga mussel, has been identified as Dreissena bugensis Andrusov, 1897. The quagga occurs in the Dnieper River drainage of Ukraine and now in the lower Great Lakes of North America. In the Dnieper River, populations of D. polymorpha have been largely replaced by D. bugensis; anecdotal evidence indicates that similar trends may be occurring in the lower Laurentian Great Lakes. Dreissena bugensis occurs as deep as 130 m in the Great Lakes, but in Ukraine is known from only 0-28 m. Dreissena bugensis is more abundant than D. polymorpha in deeper waters in Dneiper River reservoirs. The conclusion that North American quagga mussels have a lower thermal maximum than zebra mussels is not supported by observations made of populations in Ukraine. In the Dnieper River drainage, quagga mussels are less tolerant of salinity than zebra mussels, yet both dreissenids have acclimated to salinities higher than North American populations; eventual colonization into estuarine and coastal areas of North America cannot be ignored.

The expansion of zebra mussel distribution into inland waterways of North America portends significant abiotic and biotic changes mediated either directly or indirectly by Dreissena. Dreissena fouls a wide array of submerged substrates including rock surfaces, macrophytes, native molluscs, canal and dock walls, and watercraft and motor out-drives. Fouling of water intake pipes and associated installations can severely impair water delivery to hydroelectric, municipal and industrial users, necessitating proactive or reactive control measures. Mussels increase water clarity by removing suspended clay, silt, bacteria, phytoplankton, and small zooplankton. Clear water phases associated with Dreissena grazing may exceed in magnitude and duration those generated by zooplankton grazing. Enhanced water clarity increases light transmittance and growth of benthic plants. Some benthic invertebrates (e.g., unionid molluscs) are adversely affected by Dreissena, whereas others, including amphipod crustaceans, exploit structure associated with or wastes generated by zebra mussels. Dreissena is exploited by a host of predators, most notably waterfowl, fish and crayfish. Waterfowl predators that consume contaminated Dreissena have elevated concentrations of organic pesticides and polychlorinated biphenyl compounds. Invasion of shallow lakes and ponds by Dreissena may divert production and biomass from pelagic to benthic foodwebs, shifting ecosystems to an alternative state.

In 1989, zebra mussels received national attention in North America when they reached densities exceeding 750,000/[m.sup.2] in a water withdrawal facility along the shore of western Lake Erie of the Laurentian Great Lakes. Although water withdrawal problems caused by zebra mussels have been of immediate concern, ecological impacts attributed to mussels are likely to be the more important long-term issue for surface waters in North America. To date, the epizoic colonization (i.e., infestation) of unionid bivalve mollusks by zebra mussels has caused the most direct and severe ecological impact. Infestation of and resulting impacts caused by zebra mussels on unionids in the Great Lakes began in 1988. By 1990, mortality of unionids was occurring at some locations; by 1991, extant populations of unionids in western Lake Erie were nearly extirpated; by 1992, unionid populations in the southern half of Lake St. Clair were extirpated; by 1993, unionids in widely separated geographic areas of the Great Lakes and the Mississippi River showed high mortality due to mussel infestation. All infested unionid species in the Great Lakes (23) have become infested and exhibited mortality within two to four years after heavy infestation began. Data indicate that mean zebra mussel densities >5,000-6,000/[m.sup.2] and infestation intensities >100-200/unionid in the presence of heavy zebra mussel recruitment results in near total mortality of unionids. At present, all unionid species in rivers, streams, and lakes that sympatrically occur with zebra mussels have been infested and, in many locations, negatively impacted by zebra mussels. We do not know the potential consequences of infestation on the 297 unionid species found in North America, but believe zebra mussels pose an immediate threat to the abundance and diversity of unionids.

Since the discovery of the zebra mussel, Dreissena polymorpha, in the Great Lakes in 1988 comparisons have been made with mussel populations in Europe and the former Soviet Union. These comparisons include: Population dynamics, growth and mortality rates, ecological tolerances and requirements, dispersal rates and patterns, and ecological impacts. North American studies, mostly on the zebra mussel and a few on a second introduced species, the quagga mussel, Dreissena bugensis, have revealed some similarities and some differences. To date it appears that North American populations of zebra mussels are similar to European populations in their basic biological characteristics, population growth and mortality rates, and dispersal mechanisms and rates. Relative to European populations differences have been demonstrated for: (1) individual growth rates; (2) life spans; (3) calcium and pH tolerances and requirements; (4) potential distribution limits; and (5) population densities of veligers and adults. In addition, studies on the occurrence of the two dreissenid species in the Great Lakes are showing differences in their modes of life, depth distributions, and growth rates. As both species spread throughout North America, comparisons between species and waterbodies will enhance our ability to more effectively control these troublesome species.