CONFLICTING SELECTION FROM AN ANTAGONIST AND A MUTUALIST ENHANCES PHENOTYPIC VARIATION IN A PLANT

The raw material for evolution is variation. Consequently, identifying the factors that generate, maintain, and erode phenotypic and genetic variation in ecologically important traits within and among populations is important. Although persistent directional or stabilizing selection can deplete variation, spatial variation in conflicting directional selection can enhance variation. Here, we present evidence that phenotypic variation in limber pine (Pinus flexilis) cone structure is enhanced by conflicting selection pressures exerted by its mutualistic seed disperser (Clark's nutcracker Nucifraga columbiana) and an antagonistic seed predator (pine squirrel Tamiasciurus spp.). Phenotypic variation in cone structure was bimodal and about two times greater where both agents of selection co‐occurred than where one (the seed predator) was absent. Within the region where both agents of selection co‐occurred, bimodality in cone structure was pronounced where there appears to be a mosaic of habitats with some persistent habitats supporting only the seed disperser. These results indicate that conflicting selection stemming from spatial variation in community diversity can enhance phenotypic variation in ecologically important traits.     

Spatial Variation in δ15N and δ13C Isotopes in the San Juan River, New Mexico and Utah: Implications for the Conservation of Native Fishes

Synopsis Spatial patterns of resource use by small-bodied fishes in the San Juan River were examined using stable isotopes. Using δ¹⁵N of fishes as an index of trophic position, our data suggest both native and non-native fishes primarily consumed macro-invertebrates. The δ¹³C of these fishes further suggested a detritus-based food web, from which most species fed on chironomids in low-velocity habitats. A two-way ANOVA revealed a significant interaction between trophic level of fish species and longitudinal position in the river. This interaction was primarily attributed to a decline in trophic level of non-native red shiner Cyprinella lutrensis, relative to other species, in upstream reaches of the river. In addition, ANCOVA results suggest trophic position of fishes was dependent on channel type (primary vs. secondary), as there was less variability in resource use in secondary channels. These data provided a spatial framework of trophic interactions that can be used to predict the outcome of management actions. Overall, we confirmed high overlap in resource used between native and non-native fishes. However, spatial variation in trophic interactions both longitudinally and laterally in the river present a challenge to resource managers attempting to managing entire river systems.     

Structural organization of the nuclear ribosomal RNA genes in Cannabis and Humulus (Cannabaceae)

The structural organization of the nuclear ribosomal DNA (rDNA) of Humulus lupulus, H. japonicus and Cannabis sativa was determined by restriction site mapping. A high degree of DNA sequence similarity was evident in the coding regions of the rDNA repeats of the taxa and supports the placement of Cannabis and Humulus in one family, Cannabaceae. However, the presence of a BstEII site, an additional SacI site, absence of the SpeI site and positional differences of the SspI sites in the 25 S gene distinguished H. japonicus from H. lupulus. Humulus lupulus has an additional EcoRV site in the IGS region. A XhoI site in the 18S region of C. sativa distinguishes it from the two hop species. The diagnostic differences in the IGS of C. sativa include the EcoRI, HindIII and XhoI sites. These sites were not detected in the IGS of the two hop species.     

Phenotypic gender variation within inflorescences of the protogynous species Helleborus foetidus L. (Ranunculaceae)

In the protogynous species H. foetidus, I investigated if investment in sexual structures and seed set shows any trend with position in the flower-opening sequence. In four-flower inflorescences, stamen number decreased with flower position i.e. was highest for the earliest flower and lowest for the latest flower. Ovule number was significantly higher in the latest flower. Stamen and ovule number did not covary, indicating that there is no structural gender trade-off in this species. Seed set (i.e. percentage of ovules producing seed) did not differ between control plants and pollen-supplemented plants and the effect of pollen supplementation did not vary among positions. Seed set showed marginally significant differences between control plants and simulated-herbivory plants, but the effects of this treatment varied significantly among positions. Significant among-position variation in seed set was observed in the control plants but not the simulated-herbivory plants. Seed set of latest-opening flowers of simulated-herbivory plants was significantly higher than that of latest-opening flowers of control plants. H. foetidus support Brunet and Charlesworth's (1995) prediction that in plants with protogynous flowers, later-opening flowers should specialize as female flowers, at least under conditions of high resource availability.     

Study on Tandem Repeat Sequence Variation in Sheep mtDNA D-loop Region

The 75-nt-long tandem repeat sequence in the control region of mtDNA of 77 individuals, of which 69 were from different indigenous sheep breeds in China and 8 were from imported breeds, was sequenced and analyzed to investigate the origin and differentiation of Chinese indigenous sheep breeds and also the genetic diversities and relationships among them. A total of 28 variable sites were detected within 309 repeated sequences, among which 7 sites were singleton variable sites with two variants, 1 site was a singleton variable site with three variants, and 20 sites were parsimony informative sites with two variants. A total of 63 haplotypes were sorted from 28 polymorphic sites, among which two main and basic haplotypes, namely, Hap 1 and Hap 3 were present at a much higher proportion, at 12.94% and 30.42%, respectively. It could be inferred that Chinese indigenous sheep breeds originated from two maternal ancestors because of the maternal inheritance characteristics of the mtDNA. Altay sheep and Kazakstan sheep are closely related and do not differentiate significantly. Mongolian sheep and Ujumuqin sheep also share a close relationship. Tibetan sheep, Mongolian sheep, and Ujumuqin sheep have lower genetic diversity than Altay sheep and Kazakstan sheep.     

Relationship Between Ploidy Variation of Citrus Calli and Competence for Somatic Embryogenesis

This study focuses on the relationship between the genetic variation of calli and the competence for somatic embryogenesis in citrus. The DNA content of 35 citrus calli of different genotypes was measured three times by flow cytometry during a period of four years. The results showed that 71.4% of the genotypes had a progressive increase of varied cells, while those of Page tangelo, Shamouti sweet orange, Russ navel orange and Cleopatra decreased; significant difference in the variation degree (percentages) existed among genotypes. Studies carried out on the induction of somatic embryogenesis revealed that 9 out of the 35 genotypes had still kept the competence of somatic embryogenesis, and the rest 26 had lost the competence. Correlation analysis indicated that there was no significant relationship between the variation degree and the embryogenesis competence r=−0.10 (P<0.01), neither for the relationship between the subculture duration and the regeneration capacity.     

Reproductive modes of three Ligularia weeds (Asteraceae) in grasslands in Qinghai-Tibet Plateau and their implications for grassland management

Ligularia virgaurea, L. sagitta and L. przewalskii are noxious weeds that are widely distributed in psychro-grasslands in the east of Qinghai-Tibet Plateau of China. However, little is known about reproductive modes and genetic diversity in the populations of L. virgaurea and L. sagitta under different environmental conditions, although such information is available for L. przewalskii. In this study, two experiments were conducted to examine the ex situ clonal growth of these weeds, and to determine the effects of reproductive modes on the diversity of their populations, using random amplified polymorphic DNA (RAPD) analysis. Transplanted seedlings of L. sagitta and L. virgaurea showed considerable clonal growth by forming rhizomes and ramets. The RAPD analysis showed that all individuals collected from natural populations were genetically different, indicating that no individuals originated from clonal growth. It is concluded that L. virgaurea and L. sagitta have the capacity for clonal growth, but the expression of their clonality is constrained by their growing conditions in natural grasslands. Sexual reproduction plays the major role in their population diversity in natural habitats, which requires that the control measures for these weeds should be targeted at the sexually reproducing populations.     

Intraspecific sequence variation of chloroplast DNA among the component species of deciduous broad-leaved forests in Japan

To select appropriate plant materials for a phylogeography of deciduous broad-leaved forests in Japan, we surveyed intraspecific chloroplast DNA variation in 34 species found in these forests. A relatively large number of intraspecific cpDNA variations were detected in ten species: Carpinus japonica (nucleotide diversity π=0.00083), C. laxiflora (π=0.00221), Magnolia obovata (π=0.00134), Lindera triloba (π=0.00255), L. obtusiloba (π=0.00289), Pourthiaea villosa var. leavis (π=0.00263), Acer japonicum (π=0.00170), A. micranthum (π=0.00237), Euonymus oxyphyllus (π=0.00322) and Styrax obassia (π=0.00100).     

Barley anther culture: effects of annual cycle and spike position on microspore embryogenesis and albinism

The effect of donor plants annual cycle and anther/spike position on the production of microspore-derived plants and albinism were studied. We used the winter cv. Igri and the spring cv. Cork, known to respond similarly in anther culture but to produce 78% and 2% of green plants, respectively. In both cvs. the number of microspore-derived plants was significantly higher when the anthers were collected from January to July than from August to December. However, during this period the proportion of albino plants was not altered. Conversely, the anther response decreased from 76.6 to 31.5% in Igri and from 58.8 to 32.0% in Cork when the donor spike originates from the main shoot or the fourth tiller. Significantly, anthers collected from spike of the second tiller enabled us to drastically increase the proportion of regenerated green plantlets, by 16% in Igri and 1800% in Cork.     

Nuclear DNA content of Vitis vinifera cultivars and ploidy level analyses of somatic embryo-derived plants obtained from anther culture

Flow cytometry was employed to determine the ploidy level of Vitis vinifera L. somatic embryo-derived plants obtained from anther culture. Only one among the 41 analysed plants (2.4%) presented somaclonal variation (tetraploidy); the other plants were diploid. No significant differences (P≤0.05) were detected between diploid and parental field plants. No haploid or aneuploid plants were observed. The nuclear DNA content of nine V. vinifera cultivars was also estimated using flow cytometry. A non-significant variation was found among the cultivars, with DNA content ranging from 1.17 pg/2C (cv. ‘Tinta Barroca’ and ‘Viosinho’) to 1.26 pg/2C (cv. ‘Cabernet Sauvignon’). These results and previous studies on other Vitis species suggest that Vitis genome is stable with regard to nuclear DNA content.