Randomly amplified polymorphic DNA analysis (RAPD) of Artemisia subgenus Tridentatae species and hybrids

Species of Artemisia (subgenus Tridentatae ) dominate much of western North America. The genetic variation that allows this broad ecological adaptation is facilitated by hybridization and polyploidization. Three separate studies were performed in this group using randomly amplified polymorphic DNA (RAPD). Fifty-seven 10-mer primers generated nearly 400 markers from genomic DNA obtained from leaf tissue. These studies were (1) a measure of the variability of plants within and between populations and between subspecies using 5 A. tridentata ssp. wyomingensis populations, 2 A. cana ssp. cana populations, and 1 A. cana ssp. viscidula population; (2) an examination of the hypothesis that tetraploid (4 x ) Artemisia tridentata spp. vaseyana derives de novo from diploid (2 x ) populations via antopolyploidy; and (3) an examination of the validity of the status of putative hybrids that have been produced by controlled pollination. These later hybrid combinations- A. tridentata ssp. tridentata × A. t. ssp. vaseyana , A. t. ssp. wyomingensis × A. tripartita , and A. cana ssp. cana A. tridentata ssp. wyomingensis - were made to combine traits of parental taxa in unique combinations with possible management application. RAPD marker data were subjected to similarity and UPGMA clustering analyses. RAPD markers were effective in measuring genetic diversity at different systematic levels. Individual plants within a population were approximately 55% to > 80% similar to one another; populations within subspecies gave corresponding values of similarity, probably a result of the combined effects of large population sizes and wind pollination. The 2 subspecies of A. cana were approximately 45% similar. At least some 4 x populations of A. tridentata ssp. vaseyana apparently derive de novo from 2 x plants based on their being embedded in 2 x phenogram groups, thus reinforcing evidence that autopolyploidy plays an important role in Tridentatae population biology. Two ( A. tridentata ssp. tridentata × A. t. ssp. vaseyana and A. cana ssp. cana × A. tridentata ssp. wyomingensis ) of the 3 putative hybrid combinations were confirmed to include hybrids. These hybrids may have potential in management applications. Additional use of RAPD technology combined with other techniques may be useful in delimiting genetic characteristics and in guiding artificial selection in Tridentatae .     

Taxonomy of Sphaeromeria, Artemisia , and Tanacetum (Compositae, Anthemideae) based on randomly amplified polymorphic DNA (RAPD)

Relationships within, between, and among the Anthemideae genera Sphaeromeria, Artemisia , and Tanacetum were investigated using 238 randomly amplified polymorphic DNA (RAPD) markers obtained from twenty 10-mer primers amplified on genomic DNA. Forty-one populations from 16 taxa (15 species) were studied. Jaccard's coefficient of similarity and UPGMA clustering analysis were used to construct phenograms. T tests were used to make comparisons between samples at various systematic levels. DNA markers were 75% similar for conspecific populations. Sixteen Sphaeromeria populations (5 species) showed an average interspecific similarity of 21%. Interspecific similarity among 23 Artemisia populations (8 species with 2 subspecies of A. tridentata included) averaged 27%. Two Tanacetum species (1 population each) were 89% similar. The high similarity of Tanacetum species was in the range of observed values for conspecific populations; indeed those 2 species ( T. vulgare and T. boreale ) have been considered conspecific by some authors. The 3 subgenera of Artemisia studied ( Artemisia, Dracunculus , and Tridentatae ) formed separate groups. In comparison among the genera, Sphaeromeria was 18% similar to Artemisia (more similar to subgenus Tridentatae than the other Artemisia subgenera); intergeneric comparisons of Sphaeromeria and Artemisia and Tanacetum , which supports previously established morphological distinctions. Sphaeromeria potentilloides may be misplaced in the genus Sphaeromeria based on DNA marker results. It is likely that North American Anthemideae are circumboreal derivatives of ancestral Eurasian stock and that Sphaeromeria is derived from an Artemisia -like ancestor.     

Genetic analysis of the rare species Salix arizonica (Salicacea) and associated willows in Arizona and Utah

Management decisions affecting the rare plant Arizona willow ( Salix arizonica ) will be aided by understanding genetic similarities among populations of this species. Random Amplified Polymorphic DNA (RAPD) analysis was conducted on 20 populations of S. arizonica , 12 populations of 5 congeners, and 2 samples of outgroup, Populus tremuloides . A phenogram based on DNA markers shows clear separation of populations of S. arizonica from those of co-occurring willow species, but similarity is low (～ 37%) between Utah and Arizona populations of S. arizonica . Evaluation of the relationship of habitat characteristics and geographic distance to genetic similarity reveals that environment and genetic similarity are poorly correlated. Considering Arizona versus Utah populations, we found a significant negative relationship between geographic distance and genetic similarity ( r = 0.936), but no significant relationship between interpopulation distance and genetic similarity within Arizona or Utah. The wide geographic disjunction of S. arizonica populations in Utah and Arizona appears to have existed for a long period during which genetic drift, random mutations, and selection for somewhat different habitats have pushed the 2 regional complexes along separate evolutionary trajectories. Preservation of genetic variation within S. arizonica will require protection of multiple populations in Arizona and Utah.     

Isozymes of an autopolyploid shrub, Atriplex canescens (Chenopodiaceae)

Diploid, tetraploid, and hexaploid populations of Atriplex canescens ( x =9) were examined for 18 isozyme systems. Of 24 interpretable loci, only one locus (Per 1 ) was polymorphic. Another locus (Per 2 ) showed a dosage effect. Genetic distance values, D, ranged from near 0 to 0.05, which are in the normal range for local species races. Results from clonal ramets gave identical results. The data and analyses support an essentially autopolyploid origin for the polyploid populations examined.     

Long-term effects of tebuthiuron on Bromus tectorum

Use of herbicides to thin dense stands of Artemisia spp. (sagebrush) can free up resources for herbaceous plants and increase forage production, but may also facilitate weed invasion. We revisited a sagebrush thinning experiment in a north central Wyoming big sagebrush–grassland 11 years after application of tebuthiuron (N-[5-(1,1- dimethylethyl)-1,3,4-thiadiazol-2-yl]-N-N′-dimethylurea) to determine the long-term responses of shrubs, available soil resources, perennial grasses, and Bromus tectorum L. (downy brome). Tebuthiuron reduced shrub cover by more than half, from 31% in untreated plots to 15% in treated plots ( P = 0.002), and increased downy brome cover approximately 4-fold, from 0.9% in untreated plots to 3.5% in treated plots ( P = 0.02). Treatment with tebuthiuron also resulted in marginally significant increases in cover of perennial grasses (from 9% to 12.3%; P = 0.07) and bare ground (from 39.1% to 43.9%; P = 0.08). In comparisons of resource availability among microsites, available NO 3 was higher under dead sagebrush than under live sagebrush ( P = 0.03). No significant differences in soil water content were detected. The relatively recent expansion of downy brome populations at this site and the high NO 3 –N levels observed under dead sagebrush suggest that conditions facilitating downy brome invasion may persist for many years following sagebrush thinning. We demonstrate that sagebrush thinning can cause increases in downy brome populations years after initial treatment and suggest that managers should use caution when considering thinning sagebrush if downy brome is present, even if initial populations are small.     

Polymorphic Indian ricegrass populations result from overlapping waves of migration

Indian ricegrass ( Achnatherum hymenoides [Roem. & Schult.] Barkworth) is a rangeland species native to western North America with populations that may exhibit distinct seed-size morphs borne on separate plants. These morphs are often associated with very different levels of seed dormancy. We compared RAPD profiles of the relatively infrequent and highly dormant jumbo seed morph to its more germinable small or large (non-jumbo) companion seed morphs collected from 9 sites where they were sympatric. Jumbo seed accessions from 9 additional sites that did not exhibit seed polymorphism were included to better sample this seed morph across the species' range. Sympatric seed morphs were consistently distinguishable by their RAPD profiles, and sympatric seed morphs were no more likely to cluster together than nonsympatric seed morphs. The ability of sympatric seed morphs to maintain their genetic identity is compatible with the hypothesis of a predominately autogamous breeding system. Furthermore, these data support the hypothesis that local polymorphic populations result from overlapping waves of migration with distinct geographical origins. The jumbo seed morphs exhibited moderate correlation between genetic distance and geographic distance, but the non-jumbo seed morphs exhibited no such correlation. Jumbo seed morphs that were collected at or east of the Continental Divide in New Mexico and Colorado are more genetically homogeneous than those west of the Continental Divide, and non-jumbo seed morphs from the east are more genetically variable than jumbo seed morphs from the same locations. This suggests that gene flow eastward across the Rocky Mountains has been more frequent for the non-jumbo seed morphs than for the jumbo seed morphs.     

Relationship between cheatgrass coverage and the relative abundance of snakes on Antelope Island, Utah

Cheatgrass ( Bromus tectorum ) is an invasive annual known to negatively impact many shrub-dependent organisms; however, relatively little research has examined how it affects snake communities. Bromus tectorum is abundant at Antelope Island State Park, Davis County, Utah, and could be a possible threat to snake populations. Study sites representing different B. tectorum coverage percentages were established to measure relative abundance of snakes. Snakes were captured from June to September 2005 primarily by using funnel traps attached to drift-fence arrays. Linear regression revealed a negative relationship between B. tectorum coverage (%) and the relative abundance of the Great Basin gopher snake ( Pituophis catenifer deserticola ) and the western racer ( Coluber mormon ). These results (1) suggest that B. tectorum invasions result in reduced snake abundance in shrubsteppe habitat on Antelope Island and (2) add to our understanding of the relationships between B. tectorum and native fauna.     

Biochemical differentiation in the Idaho ground squirrel, Spermophilus brunneus (Rodenta: Scuridae)

Spermophilus brunneus is restricted to a 90 × 125-km area of west central Idaho, with two distinct (northern and southern) groups of populations within this limited range. Morphological differences in pelage length and coloration, external and cranial measurements, and bacula suggest that these groups are either very distinct subspecies or species. We used starch-gel electrophoresis to estimate the amount of genetic differentiation accompanying these morphological differences by assaying genetic variation at 31 loci in the two geographic groups. Fifteen loci were polymorphic (13 in the northern group, 12 in the southern), and mean heterozygosity (H) was high (12.3% northern and 10.8% southern). Nei's genetic distance (0.057) is in the range usually associated with subspecific differences. However, Jaccard's association coefficient (0.893) is about the same as that found between several ground squirrel taxa currently recognized as species. The high levels of heterozygosity suggest that S. brunneus is a neoendemic rather than a paleoendemic species.     

Leafhopper assemblages on native and reseeded grasslands in southwestern Montana

Using sweep samples, we surveyed leafhoppers (Homoptera: Cicadellidae) on grassland sites in the Gallatin Valley of Montana during 1988 and 1991. We sampled 12 sites representing 2 habitat types defined by their dominant plant species in an undisturbed state ( Stipa comata / Bouteloua gracilis and Festuca idahoensis / Agropyron spicatum ). At half of the sites the native plant communities were present, whereas the remainder had been reseeded with either Agropyron spicatum (to replace the S. comata / B. gracilis assemblage ) or Bromus inermis (to replace the F. idahoensis / A. spicatum assemblage). We found at least 66 species of leafhoppers among 44,428 adults collected. Seven taxa comprised 83% of all individuals collected: Doratura stylata (26%), Ceratagallia spp. (18%), Endria inimica (17%), Orocastus perpusillus (7%), Sorhoanus spp. (6%), Athysanella spp. (5%), and Psammotettix lividellus (4%). Sites with similar vegetation had broadly similar leafhopper assemblages, and assemblages differed most between the relatively xeric Stipa comata / Bouteloua gracilis sites and the more mesic sites dominated by Bromus inermis . The composition of a leafhopper assemblage at a site tended to be more similar to those on noncontiguous sites with the same overall vegetation than to those on contiguous sites with different vegetation. These patterns are likely related to the fact that many Cicadellidae are host specialists. In fact, variation in abundance of some of the most common leafhopper taxa on our sites was correlated with the percent cover of their known host plants. Our analyses of the leafhopper assemblages generally support the contention that terrestrial plant associations are among the more useful indicators of insect community composition.     

Evolutionary differentiation within the northern Great Basin pocket gopher, Thomomys townsendii II. Genetic variation and biogeographic considerations

Geographic and nongeographic variation in morphology was examined in Thomomys townsendii . A univariate analysis of external and cranial characters from a large population sample (66 adults; fusion of cranial sutures used as aging criteria) was used to assess variation among three adult age classes and between sexes. Only minor variation is apparent among age classes; however, sexual dimorphism is pronounced. Univariate and multivariate techniques were used to analyze external and cranial measurements and pelage characters for adults throughout the species range. These analyses show little to support the seven subspecific designations recognized by Davis (1937). The general pattern is one of homogeneity throughout the range of Thomomys townsendii . With the possible exception of T. t. nevadensis samples, current subspecies are not defined as morphological units. In fact, differentiation is found among populations within some subspecies. The most apparent pattern seen in these analyses is the divergence between the Humboldt River (including Honey Lake Valley samples) and Snake River systems. These results will be considered with those of a companion paper on the genetic variation in this species to more adequately assess the patterns of differentiation in Thomomys townsendii .     

Allozyme electrophoresis demonstrates the presence of a species boundary in freshwater crabs (Decapoda: Potamonautidae)

Potamonautes granularis, P. perlatus and P. sidneyi are morphologically similar species of freshwater crab occurring in the middle to lower reaches of rivers. Potamonautes perlatus and P. sidneyi are known to exhibit clinal morphological differentiation between two distinct morphotypes and their specific status has remained obscured. This study investigates the species boundaries between these three species, as well as genetic differentiation and gene flow between populations within each species, using allozyme electrophoresis. Twenty-five populations (including two P. granularis, 10 P. perlatus and 13 P. sidneyi populations) were utilized, collected along a transect of 2300 km. Individuals were screened for 11 presumptive loci, using a horizontal starch-gel electrophoresis protocol. Mean genetic identities obtained in pair-wise comparisons of populations of different species (I =0.748-0.846) were typical of interspecific comparisons. Diffuse species boundaries (over which gene flow and hybridization may be possible) were observed between P. granularis and P. perlatus, and between P. perlatus and P. sidneyi. A fixed allele difference at the ME locus distinguished P. granularis and P. sidneyi. Hierarchical F -statistics revealed significant genetic sub-structuring between populations within each species and within the entire sample, illustrating low-levels of gene flow. Although some regional groupings were evident from the genetic data, no distinct distance-related patterns, or patterns of clinal variation could be observed. Patterns of genetic differentiation resemble a patchwork that is probably the product of mutations, genetic drift, balanced by low levels of gene flow, and natural selection. The extensive morphological variation must now be seen against the backdrop of three genetically defined species.     

Deer mouse ( Peromyscus maniculatus ) home-range size and fidelity in sage-steppe habitat

Within a species, home-range size can vary due to factors such as sex, mass, age, and breeding condition of individuals as well as habitat type, food availability, population density, and season. The objectives of this study were to estimate home ranges of deer mice ( Peromyscus maniculatus ) in sage-steppe habitat and to test the hypothesis that several factors (sex, mass, reproductive status, and seasonality) affect home-range size. We also tested the hypothesis that deer mice exhibit home-range fidelity over time. Passive integrated transponder (PIT) technology was used to estimate home ranges in June and September 2006. Home-range estimates varied from 360 m 2 to 5868 m 2 (65 individuals, 753 observations). Home-range size increased by approximately 60% from June to September. Besides seasonality, none of the other predictors of home range were informative in explaining the variation in home range. Deer mice recaptured in September (3 months after initial capture) had high fidelity in home-range use (42.1% [SE = 8.4%] overlap with 74.1% [SE = 8.7%] area conserved; n = 9). All animals for which home range was estimated in both seasons retained some fraction of their June home range in September. Results support the use of combined location data collected over long periods, such as weeks or months, to estimate home range for deer mice. The results have implications for deer mouse–pathogen ecology, particularly with respect to modeling transmission of Sin Nombre virus—a pathogen that is directly transmitted by deer mice.     

Evolutionary differentiation within the northern Great Basin pocket gopher, Thomomys townsendii I. Morphological variation

Geographic and nongeographic variation in morphology was examined in Thomomys townsendii . A univariate analysis of external and cranial characters from a large population sample (66 adults; fusion of cranial sutures used as aging criteria) was used to assess variation among three adult age classes and between sexes. Only minor variation is apparent among age classes; however, sexual dimorphism is pronounced. Univariate and multivariate techniques were used to analyze external and cranial measurements and pelage characters for adults throughout the species range. These analyses show little to support the seven subspecific designations recognized by Davis (1937). The general pattern is one of homogeneity throughout the range of Thomomys townsendii . With the possible exception of T. t. nevadensis samples, current subspecies are not defined as morphological units. In fact, differentiation is found among populations within some subspecies. The most apparent pattern seen in these analyses is the divergence between the Humboldt River (including Honey Lake Valley samples) and Snake River systems. These results will be considered with those of a companion paper on the genetic variation in this species to more adequately assess the patterns of differentiation in Thomomys townsendii .     

Genetic differentiation and gene flow of Porcellionides pruinosus (Crustacea: Isopoda: Oniscidea) in Tunisia

Iso-enzymatic polymorphism analysis was carried out on Tunisian populations of Porcellionides pruinosus to clarify their confused taxonomic status, previously revealed by reproductive and morphological approaches. Seventeen allozyme loci were studied, using horizontal starch gel electrophoresis, in 230 adult specimens belonging to nine populations of P. pruinosus located in north, central and south Tunisia, to assess the levels of their intra-genetic and inter-genetic diversity, and to analyse their genetic structure. Our results indicate a low genetic variability with a polymorphism ratio ranging from 29.4% in Tabarka to 47.1% in the Garat Nâam and Raccada populations, and the mean number of alleles per locus was estimated at 1.51 ± 0.15. The direct-count of heterozygosity ranged between 8.1% and 15%. Substantial estimates of demic structuring were found at the total population (F_ST = 0.198), with a generalized and significant heterozygote deficiency detected in every population (with a mean value for all populations of F_IS = 0.372). Genetic distances between the studied populations were low, indicating that they belong to the same species. Nevertheless, the genetic analyses showed the divergence of the population of Tabarka from all the other studied populations, with the lowest mean gene flow, 0.58, and the highest mean genetic distance, (0.182) obtained also by the morphological and reproductive approaches.     

Natural enemy assemblages on native and reseeded grasslands in southwestern Montana: a family-level analysis

We conducted a 2-year survey, using sweep sampling and family-level taxon identification, of the predatory and parasitoid insects on grassland sites in the Gallatin Valley of southwestern Montana. The 25 sites were divided into 4 habitat classes: 2 native habitat types ( Stipa comata/Bouteloua gracilis and Festuca idahoensis/Agropyron spicatum ) and 2 that had been reseeded with either crested wheatgrass ( Agropyron cristatum ) or smooth brome ( Bromus inermis ). Our major goal was to make quantitative comparisons of the abundance of insects among native and reseeded habitats. Of 51 families in 5 insect orders identified, 7 Hymenoptera (Encyrtidae, Braconidae, Ichneumonidae, Pteromalidae, Eulophidae, Scelionidae, and Torymidae), 3 Hemiptera (Lygaeidae, Nabidae, and Reduviidae), 1 Coleoptera (Coccinellidae), and 1 Diptera (Asilidae) comprised 90% of the natural enemies sampled. Ordination analyses provided no strong evidence that the 4 habitat classes contained distinct overall natural enemy communities. However, contiguous native and reseeded sites usually had relatively different overall natural enemy assemblages, suggesting that vegetation was often a more important correlate of community composition than was close spatial proximity of sites. Furthermore, several common families exhibited differential abundances across habitat classes in one or both years. For example, in 1989, Eulophidae, Pteromalidae, and Torymidae were more abundant on native Festuca/Agropyron sites, whereas Encyrtidae and Nabidae were more abundant on Festuca/Agropyron sites reseeded with Bromus inermis . Although analyses of insect assemblages classified to the family level provide somewhat limited information on functional ecological differences among habitats, they allow one to survey a broad array of taxa to identify focal groups for future conservation and land management studies.     

Evaluating plant invasions from both habitat and species perspectives

We present an approach to quantitatively assess nonnative plant invasions at landscape scales from both habitat and species perspectives. Our case study included 34 nonnative species found in 142 plots (0.1 ha) in 14 vegetation types within the Grand Staircase-Escalante National Monument, Utah. A plot invasion index, based on nonnative species richness and cover, showed that only 16 of 142 plots were heavily invaded. A species invasive index, based on frequency, cover, and number of vegetation types invaded, showed that only 7 of 34 plant species were highly invasive. Multiple regressions using habitat characteristics (moisture index, elevation, soil P, native species richness, maximum crust development class, bare ground, and rock) explained 60% of variation in nonnative species richness and 46% of variation in nonnative species cover. Three mesic habitats (aspen, wet meadow, and perennial riparian types) were particularly invaded (31 of 34 nonnative species studied were found in these types). Species-specific logistic regression models for the 7 most invasive species correctly predicted occurrence 89% of the time on average (from 80% for Bromus tectorum , a habitat generalist, to 93% for Tamarix spp., a habitat specialist). Even with such a modest sampling intensity (<0.1% of the landscape), this multiscale sampling scheme was effective at evaluating habitat vulnerability to invasion and the occurrence of the 7 most invasive nonnative species. This approach could be applied in other natural areas to develop strategies to document invasive species and invaded habitats.     

Stem growth and longevity dynamics for Salix arizonica dorn

Diameter-age relationships of Salix arizonica (Arizona willow) stems were investigated for 5 populations on the Markagunt, Paunsaugunt, and Sevier plateaus in southern and central Utah. Of the 430 stems studied, none exceeded 26 mm in diameter at ground level (estimated age of 19 yr). Equations developed for predicting age from stem diameters consistently accounted for over 90% of the observed variation. Slopes of predictive equations were homogenous across the 3 sites considered in detail. At 2 sties 46% and 38% of the stems exceed 10 mm (～ 7 yr old) diameter at ground level. At a 3rd site, no stems survived to exceed that size. Stem-age profiles at specific sites may thus be useful for assessing the relative favorability of local environments for the species.     

Respiration characteristics differ among cheatgrass ( Bromus tectorum L.) populations

Cheatgrass ( Bromus tectorum L.) is a dominant weed that has increased the frequency of wildfire in the Great Basin since its introduction about 100 yr ago. This study examines characteristics of respiratory metabolism in several different populations. Seeds from 6 populations were germinated and metabolic heat rates (q) and dark respiration rates (R co2 ) of all seedlings were measured calorimetrically at 15° and 25° C or (for 3 populations) at 5° intervals from 5° to 35° C. Growth rates, substrate carbon conversion efficiencies, and Arrhenius temperature coefficients were calculated from the data. Results show that cheatgrass metabolism is most efficient at temperatures near 0° C; at temperatures above 20-25° C, efficiency goes to zero. Cheatgrass populations differ in their temperature dependencies of substrate carbon conversion efficiency and predicted growth rate. Measurements of respiratory heat and CO 2 rates as functions of temperature can be made relatively quickly and used to aid understanding of metabolic adaptation by invasive and native species to the environment.     

Genetic and morphometric variation in the potamonautid river crab Potamonautes parvispina (Decapoda: Potamonautidae) from two Western Cape rivers,South Africa

Patterns of genetic and morphometric variation amongst five populations of Potamonautes parvispina from two rivers in the Western Cape, were examined. Genetic variation at 14 loci was investigated using protein gel electrophoresis. The results showed that the populations were genetically invariant within and between the two drainage systems. Discriminant functions analyses of seven carapace variables demonstrated regional differentiation between the population groups in the two drainage systems. Other morphometric characters exhibited a significant degree of variation within drainage systems. Morphometric data were highly variable and were discordant with the genetic data, which suggests that environmental factors may be responsible for the large degree of phenotypic plasticity. Results from the present study are discussed in terms of widespread gene flow and recent population divergence.     

Effects of islanding on the genetics of Niviventer confucianus (Mamalia: Rodentia: Muridae) populations in the Thousand Island Lake region

The impact of islanding on the genetics of the dominant species, Niviventer confucianus, was analysed using 13 microsatellite markers. All 16 populations are of high genetic diversity with a total of 134 alleles. The average number of effective alleles (Ne) is 6; the average expected heterozygosity (H_E) and polymorphic information content (PIC) are 0.823 and 0.763, respectively. Landscape fragmentation might contribute to weak genetic differentiation among 13 island populations. Values of F_ST simulated by Structure 2.3.4 implied that the 16 populations could be assigned into three clusters, from which we postulated the possible dispersion history. Pairwise F_ST tests showed that genetic differences mainly occurred between small island populations and others. Currently, habitat area appears to be the main factor affecting the genetics of Niviventer confucianus, and not the distances between islands. Hence we suggest that more attention should be paid to habitat area in the future.