Substantial Intraspecific Variation Research Articles

Salinity Tolerance in Phaseolus Species during Early Vegetative Growth

ABSTRACTThe genus Phaseolus includes important cultivated species as well as wild species with diverse ecological adaptations. Characterization of the ecological adaptations of the wild species would be useful for improved understanding, conservation, and utilization of these genetic resources. Salinity tolerance during vegetative growth was evaluated for 132 accessions for 14 wild Phaseolus species (P. acutifolius A. Gray, P. angustissimus A. Gray, P. carteri Freytag & Debouck, P. filiformis Bentham, P. glabellus Piper, P. leptostachyus Bentham, P. lunatus L., P. micranthus Hook & Arnold, P. microcarpus Mart, P. mcvaughii A. Delgado, P. oligospermus Piper, and P. vulgaris L.) and 11 accessions representing five cultivated species (P. acutifolius, P. coccineus L., P. lunatus L., P. polyanthus Greenman, and P. vulgaris) in nutrient solution containing 0 and 180 m M sodium chloride for 21 d. When plants were salinized after the emergence of the first trifoliate leaf, wild accessions of P. acutifolius, P. filiformis, P. lunatus, and P. vulgaris showed a wide range of variation in their salinity tolerance as defined by total dry weight reduction (PR) as a percentage of the unsalinized controls, salt susceptibility index (SSI), and root: shoot ratio (RSR). SSI and PR were correlated positively, indicating either trait could be used to select salt‐tolerant accessions. Cluster analysis revealed substantial intraspecific and interspecific variation in salinity tolerance. Salinity tolerance was observed in wild P. micranthus, P. mcvaughii, P. lunatus, cultivated P. coccineus, and several accessions of wild P. filiformis, and P. vulgaris Of these, P. filiformis was noteworthy in having 9 of 11 accessions rated as highly tolerant. Wild P. vulgaris was more salinity tolerant than the three cultivated P. vulgaris accessions included in the study. Many tolerant accessions originated in arid, coastal, or saline areas. We conclude that the genus Phaseolus has substantial diversity in salinity tolerance.

Freezing Tolerance of Six Cultivars of Buffalograss

Freezing tolerance is an important trait that determines geographical adaptation of a turfgrass. This study was conducted to assess the relative freezing tolerance, seasonal changes in freezing tolerance (LT50), and winter survival of six cultivars of buffalograss [Buchloë dactyloides (Nutt.) Engelm.]. The cultivars 91‐118, Tatanka, Texoka, Stampede, UCR‐95, and 609 were grown in the field at Fort Collins, CO. From September 1998 to April 1999 and from October 1999 to May 2000, stolons were sampled monthly from each plot and subjected to laboratory freezing tests. Survival and recovery following the freezing test indicated that all cultivars had similar LT50 in September and gradually increased in winter hardiness during fall. However, the capacity to acclimate and the maximum freezing tolerance were significantly different among the cultivars. Ranking of grasses for mean LT50 (°C) was Tatanka (−18.1) = 91‐118 (−18.0) ≤ Texoka (−17.1) < 609 (−14.4) < Stampede (−12.4) < UCR‐95 (−9.2) during midwinter in 1998‐1999 and Texoka (−21.7) = 91‐118 (−21.6) = Tatanka (−21.0) < 609 (−15.8) = Stampede (−15.1) < UCR‐95 (−14.0) during midwinter in 1999‐2000. Following freezing treatments, Tatanka and 91‐118 maintained a higher relative shoot and root regrowth than other cultivars. Root regrowth was reduced by freezing to a greater extent than shoot regrowth for all cultivars. Field winter survival, a measure of winter hardiness, in 1998, 1999, and 2000 was generally in agreement with laboratory test results, showing that Stampede, 609, and UCR‐95 were more susceptible to winterkill than 91‐118 and Tatanka. The differences in freezing tolerance among the cultivars tested indicates substantial intraspecific variation that may be used for breeding improvement.

Monomer composition of polysaccharides of seed cell walls and the taxonomy of the Vochysiaceae

The distribution of polysaccharides from the seed cell walls of 57 samples of Vochysiaceae native to Brazil were studied, comprising 16 species distributed among the genera Callisthene, Qualea, Salvertia and Vochysia. The polysaccharides were extracted with hot water, then hydrolyzed with the resulting monomers analyzed by HPLC. All samples yielded arabinose, galactose, glucose, mannose and rhamnose, the relative amounts of each monomer, however, varying from one sample to another. Arabinose was always the predominant component, which implies that it might possibly be used as a marker of the Vochysiaceae. The quantitative distribution of monosaccharides was similar between the species of Qualea and Callisthene, characterized by the predominance of arabinose and mannose, and between the species of Salvertia and Vochysia, which contained higher amounts of arabinose and galactose. Such results are consistent with affinities inferred from floral morphology, wood anatomy and molecular data. Substantial intraspecific variation was observed for some species. UPGMA analysis based on the distribution of the monosaccharides reveals two main clusters, according to the links commented above. The resultant phenogram is not coherent with the current sectional classification of the Vochysiaceae, but the differences in the monosaccharides distribution between the two clusters are strongly supported by ANOVA.

A FUNDAMENTAL TRADE-OFF IN RESOURCE EXPLOITATION BYDAPHNIAAND CONSEQUENCES TO PLANKTON COMMUNITIES

The genus Daphnia (Crustacea: Branchipoda) includes a diversity of species that are generalist grazers on plankton in freshwater lakes. Despite substantial intraspecific variation in body size, explanations of functional differences among Daphnia species continue to emphasize body size. In this study, we ask whether Daphnia in a relatively narrow range of body sizes differ in ability to exploit the array of resources commonly encountered in lakes. We compared juvenile growth rates of several clones and species of Daphnia fed natural planktonic resources that differed in overall dietary richness. We observed, both among and within species, a trade-off between growth rates in rich and poor resource conditions. We compared the ability of different species and clones to exploit natural resources in a lake mesocosm experiment, testing the prediction that clones displaying the greatest growth rates in rich resource conditions would have the highest minimum resource requirements. Using 8000-L whole water column enclosures, replicate populations of D. rosea and two different morphs of D. pulicaria were established separately in monoculture in a thermally stratified lake. An additional treatment without crustacean zooplankton was also established. We quantified resources in the enclosures using multiple indirect measures (e.g., chlorophyll a) and a growth bioassay. Results supported predictions; rankings of resource levels achieved in the different treatments suggest that Daphnia trade off high maximum growth rates for low minimum resource requirements. This field experiment also documented large differences among the species and clones of Daphnia in their impact on phytoplankton resources, water clarity, and formation of calcite particles (whiting). We suggest that these large ecological effects stem from the trade-off in abilities to use rich vs. poor resources and constitute an important aspect of grazer–resource interactions. We review the literature on growth and reproductive responses of zooplankton species to resource level and find general agreement with the concept of a trade-off between abilities to exploit rich and poor resource conditions. A reanalysis of data from a comprehensive study on Daphniidae growth confirms our results and suggests that the breadth of species in this family conforms to the trade-off. Furthermore, the trade-off is only weakly, and not significantly, associated with body size. Our study presents a new framework for understanding the functional significance of daphniid diversity to plankton food webs and illustrates how an ecological trade-off provides a means of linking species diversity to ecosystem function.

Seed mass and early survivorship of tree species in upland clearings and shelterwoods

We examined recommended sowing densities of 25 North American tree species (26 observations) to measure the relationship between juvenile survivorship and seed mass in large clearings and shelterwoods. Two models for expressing the relationship (simple power law or a cumulative negative exponential adjusted to account for rodent-repellent application and seedbed type) all showed that survivorship is highly dependent on seed mass. For a small seed, mineral soil and thin humus confer roughly equally high survivorship. Leaf litter is very poor, and undisturbed thick moss appears to be the worst possible organic seedbed on upland sites. An examination of 30 records of Picea glauca (Moench) Voss survivorship (3- to 6-year-old cohorts) on mineral soil revealed substantial intraspecific variation with only 50% of the values within twofold of the predicted value.

Prospects for increasing the salt tolerance of forest trees: a review.

Three major themes related to the improvement of salt tolerance in forest tree species are examined. First, evidence demonstrating that substantial intraspecific variation in salt tolerance exists in many species is presented. This evidence is important because it suggests that efforts to improve salt tolerance through conventional plant breeding techniques are justified. Second, the physiological and genetic mechanisms controlling salt tolerance are discussed briefly. Although salt tolerance involves the integration of numerous physiological processes, there is considerable evidence that differences in the ability to exclude Na(+) and Cl(-) from leaves are the most important factors underlying intraspecific differences in tolerance. It is also becoming apparent that, although salt tolerance is a multigenic trait, major genes play an important role. Third, progress to date in improving salt tolerance of forest tree species is assessed. Compared with agricultural crops, relatively little progress has been made with either conventional or biotechnological methods, but field trials designed to test clones identified as salt tolerant in screening trials are underway now in several countries. We conclude that there is justification for cautious optimism about the prospects for improving salt tolerance in forest tree species.

Genome size and base composition in Medicago sativa and M. truncatula species

The genome size (1C value) and base composition of 14 ecotypes of two species of tetraploid and diploid Medicago have been assessed by flow cytometry. These parameters vary both between and within species. The diploid annual Medicago truncatula Gaertn. had the smallest genome of the group studied (which also covered M. sativa L. subsp. sativa, M. sativa L. subsp. caerulea (Less. ex Ledeb.) Schmalh., M. sativa L. subsp. quasifalcata Sinsk., M. sativa L. subsp. x varia (Martyn) Arcangeli; however, its ecotypes revealed substantial intraspecific variation. The smallest M. truncatula genome observed was ecotype 108-1 with 1C = 0.49 pg and 38.1% GC and the largest was Jemalong with 1C = 0.57 pg and 38.6% GC. The degree of polysomaty in these Medicago was low, although in some tissues the frequency of cells with 4C nuclei reached 50%.

Oviposition choice and larval survival of Dasineura marginemtorquens (Diptera: Cecidomyiidae) on resistant and susceptible Salix viminalis

Abstract. Substantial intraspecific variation exists in Salix viminalis resistance to the gall midge Dasineura marginemtorquens. Earlier work has found this variation to have a large genetic component. Willow clones are stable in their resistances between midge generations and different nutrient levels in both field and laboratory culture. This study reports the results of laboratory experiments on female oviposition choice and larval survival on potted plants from clones that are very different in resistance as determined in field studies. In choice experiments using pairs of plants, the average female midge did not prefer susceptible willow clones over resistant ones for oviposition. In about one third of the replicates, midges actually laid more eggs on the resistant clone. Further work is necessary to examine the nature of variation among midges in discrimination of these plant types. Resistance is manifested as great differences in larval survival. Six days after oviposition survival was 92% on susceptible plants but only 6% on resistant ones. Galls developed on all of the susceptible plants, while in 73% of the resistant plants galls were not even initiated. The plant traits causing resistance are enigmatic. Larval behaviour suggests that resistant plants interfere with feeding behaviour. On resistant plants, most larvae wander for more than 24 h without initiating any galls before dying. On susceptible plants many first instar larvae begin feeding and initiate galls within this period.

Geographic and Seasonal Variation in Fragrance Choices and Preferences of Male Euglossine Bees

Variation in choices and preferences for fragrances are examined for a large portion of the euglossine bee assemblages of Barro Colorado Island (BCI) and Cerro Campana, Panama. Census data were obtained from a year-long baiting program utilizing 16 chemical attractants. Interand intraspecific variation in fragrance choices occurred. Within sites, fragrance choices of species overlapped considerably, but each species was attracted to a unique set of baits. For some species, choices of infrequently visited chemicals differed among sites. The five baits preferred by most species were the same for both sites. Geographic variation in intraspecific fragrance preferences occurred for seven of eleven species that were abundant at both BCI and Cerro Campana. Seasonal variation in fragrance preferences occurred for 16 of 21 species on BCI. The lack of seasonal shifts was not related to the number of fragrances to which a species was attracted. Indirect evidence exists for age-dependent shifts in chemical preferences by bees. Substantial intraspecific variation in fragrance preferences occurs and is related to some combination of season, age, and geography. The degree to which natural fragrances are available and genetic differences among individuals affect variation in choices and preferences for fragrances remains unknown. THE NATURAL HISTORY OF THE NEOTROPICAL Euglossini (Apidae), commonly known as orchid bees, is unusual and male behavior is both perplexing and intriguing. Male bees utilize the same nectar sources as females (Ackerman 1985), and their foraging behavior at these flowers is similar (Ackerman et al. 1982). Males differ from females in that they have no role in nest construction or in cell provisioning. Furthermore, male bees collect fragrances from a variety of sources, including rotting fruits and wood, tree bark, exposed roots, and flowers (Ackerman

Morphological and DNA sequence variation in the kelp Costaria costata (Phaeophyta)

Kelp species show substantial intraspecific morphological variation. The annual kelp, Costaria costata (C. Agardh) Saunders, is found in the lower intertidal and subtidal regions of shores which vary in exposure from strongly wave-exposed to sheltered. Phenotypic variation was studied in this monotypic genus. Individuals of C. costata were collected from two morphologically-distinct populations (one wave-exposed and the other wave-sheltered) at Cape Beale and Stanley Park, Vancouver, Canada, in May 1985. Analysis of morphological variation, using multivariate statistical techniques, indicated significant differentiation between plants from the two sites. Blade widths and thicknesses were the major discriminating variables. Restriction fragment length polymorphism (RFLP) analysis of nuclear DNA with 42 anonymous probes demonstrated one polymorphism. Most of the probes are hypothesized to encode highly repeated, dispersed sequences. These repeat sequence probes comprised 80.9% of all cloned fragments. Primary sequence analysis of 1595 base pairs of small-subunit ribosomal DNA and 204 base pairs of upstream sequence (probe pCc 18) failed to show any divergence between plants from the two sites.