Pollen competition as a unilateral reproductive barrier between sympatric diploid and tetraploid Chamerion angustifolium

Speciation requires the evolution of barriers to gene exchange between descendant and progenitor populations. Cryptic reproductive barriers in plants arise after pollination but before fertilization as a result of pollen competition and interactions between male gametophytes and female reproductive tissues. We tested for such gametic isolation between the polyploid Chamerion angustifolium and its diploid progenitor by conducting single (diploid or tetraploid) and mixed ploidy (1 : 1 diploid and tetraploid) pollinations on both cytotypes and inferring siring success from paternity analysis and pollen-tube counts. In mixed pollinations, polyploids sired most (79%) of their own seeds as well as those of diploids (61%) (correcting for triploid block, siring success was 70% and 83%, respectively). In single donor pollinations, pollen tubes from tetraploids were more numerous than those from diploids at four different positions in each style and for both diploid and tetraploid pollen recipients. The lack of a pollen donor x recipient interaction indicates that the tetraploid siring advantage is a result of pollen competition rather than pollen-pistil interactions. Such unilateral pollen precedence results in an asymmetrical pattern of isolation, with tetraploids experiencing less gene flow than diploids. It also enhances tetraploid establishment in sympatric populations, by maximizing tetraploid success and simultaneously diminishing that of diploids through the production of inviable triploid offspring.     

Morphology of the prairie dog gallbladder: normal characteristics and changes during early lithogenesis

Studies were undertaken to describe the normal structure of the prairie dog gallbladder and adjacent cystic duct, and then to determine sequential changes that occurred as abnormalities in bile composition developed during high cholesterol feeding. Control animals were fed a diet with trace cholesterol, while experimental animals were fed a diet enriched with 1.2% cholesterol for 1, 2, 3, or 4 weeks. Light microscopy and scanning and transmission electron microscopy were used to characterize morphologic changes at each time interval. Biliary lipid composition was altered in all experimental groups, evidenced by significant decreases in bile-acid-to-cholesterol ratios. Cholesterol crystals appeared in experimental bile at 1 and 2 weeks, while stones formed at 3 and 4 weeks. The cystic duct and neck of the gallbladder occasionally displayed goblet cells. Little mucus was demonstrable in principal cells of the gallbladder, but much more in those lining the cystic duct. After 2 weeks of lithogenic diet, there was an increase in mucus content and secretion from all areas, as well as an influx of polymorphonuclear and mononuclear leukocytes. Accumulation of plasma cells in the lamina propria was an especially prominent feature of experimental tissues. These results suggest that 1) there is regional heterogeneity in the mucus content of the gallbladder and cystic duct of the prairie dog, and 2) both regions respond to lithogenesis with mucus hypersecretion and acute and chronic inflammatory changes prior to the appearance of cholesterol gallstones.     

Phenotypic selection in a natural population of Impatiens pallida Nutt. (Balsaminaceae)

In the annual plant Impatiens pallida, individuals exhibit a floral heteromorphism consisting of autogamously selfing, cleistogamous (CL) flowers and partially outcrossing, chasmogamous (CH) flowers. As part of an investigation into natural selection and mating system evolution in I. pallida, we measured the magnitude and direction of phenotypic selection on nine life history characters (two traits measured on three dates, one measured on two dates and one measured once). Three of these characters were positively correlated with the ratio of CH/CL flowers produced per plant, which is an important determinant of the mating system. Values for the nine characters and three different measures of fitness (viability, fecundity, lifetime) were estimated for 500 plants in five locations over a single growing season. Based on lifetime fitness, linear selection differentials were significant for all nine characters, indicating a selective advantage to tall, leafy, highly branched plants that flowered early. However, only two of these characters had a direct effect on fitness. Selection was significant on all nine characters when based on fecundity as well as lifetime fitness; however, only three of five characters examined had significant selection based on viability fitness. For all fitness components, the frequency of significant linear and nonlinear selection coefficients was comparable (23% vs 17% of all cases, respectively), but nonlinear coefficients were generally larger. Finally, the magnitude and direction of direct linear selection was heterogeneous among locations, for all characters and all fitness components. Collectively these results suggest that selection is strong, favouring large size, high allocation to reproduction and high CH/CL flower ratios. However, any directional evolutionary changes in vegetative or reproductive characters may be constrained by strong non-linear and correlational selection.     

Cytotype distribution at a diploid-tetraploid contact zone in Chamerion (Epilobium) angustifolium (Onagraceae)

In North America, the geographic distributions of diploid and tetraploid Chamerion (formerly Epilobium) angustifolium overlap in a narrow zone along the southern border of the boreal forest and along the Rocky Mountains. We examined the frequency and distribution of diploid and tetraploid cytotypes in a narrow (5 km) zone of sympatry across an elevational gradient and in putatively uniform diploid and tetraploid reference populations on the Beartooth Pass, in the Rocky Mountains of southern Montana-northern Wyoming. All five reference populations sampled were dominated by a single cytotype, but only one was completely uniform. In the zone of sympatry, 27 transects were sampled every 2 m for a total of 238 plants. Reproductive status (vegetative, flower buds, open flowers) was recorded, and the ploidy of each plant was determined by flow cytometry. Diploid and tetraploid plants predominated (36 and 55%, respectively) but were heterogeneously distributed among the transects. Six of the 27 transects were fixed for a single cytotype (four transects, diploid; two transects, tetraploid), and in seven others either diploids or tetraploids predominated (frequency >75%). Triploids represented 9% of the total sample and occurred most frequently in transects containing both diploids and tetraploids (G = 3.4, df = 2, P = 0.07). Diploids were more often reproductive (in bud, flower, or fruit) than either triploids or tetraploids (G = 12.0, df = 2, P < 0.001) and were the only cytotype to have produced open flowers. These results suggest that the zone of sympatry is best characterized as a mosaic rather than a cline, with diploid and tetraploids in close proximity and that the distribution of polyploidy is regulated by ecological sorting in a heterogeneous physical environment.     

Acute lymphoblastic leukaemia: cyclical chemotherapy with three combinations of four drugs (COAP-POMP-CART regimen).

Forty-two adults and children with previously untreated acute lymphoblastic leukaemia (ALL) were entered into a programme of chemotherapy in which three combinations, each of four drugs were administered in a predetermined cyclical rotation together with cranial irradiation and intrathecal injections of methotrexate. Forty-one patients (98%) entered remission and no patient developed neuroleukaemia. Relapse of ALL occurred in 10 patients, and three patients died during remission, while eight patients stopped treatment after two and a half years and have remained in remission for two to 26 months. Comparison of remission and survival experience in this mixed group of children and adults with the experience of children treated at Memphis and in the Medical Research Council''s UKALL-I trial showed no significant differences. On the other hand, analysis by prognostic factors showed that neither age nor blast cell count at presentation had any adverse effect in patients treated in this study. No relapses occurred in nine patients with blast cell counts greater than 20 x 109/1 at presentation. This regimen is effective treatment for ALL and may be of special value in patients with poor prognoses. The regiment has not as yet proved superior for the treatment of children with ALL who do not have adverse prognostic features.     

Assessing the maternal origin in the polyploid complex of <Emphasis Type="Italic">Camellia reticulata</Emphasis> based on the chloroplast <Emphasis Type="Italic">rpl</Emphasis>16 intron sequences: implications for camellia cross breeding

Camellia reticulata is a well-known woody ornamental species endemic to Southwest China. It represents a polyploid complex with diploids, allotetraploids, and allohexaploids. The parentage of the allotetraploids and allohexaploids has been reported by genomic in situ hybridization, but the maternal parents still remain unknown. In this study, sequences of the chloroplast rpl16 intron of 105 cultivars of C. reticulata and 7 congeneric species were used to infer the maternal origin of the allopolyploids. The results showed that (1) the allotetraploids were derived from C. pitardii as the maternal parental species and the diploid C. reticulata as the paternal parental species; (2) the allohexaploid C. reticulata was derived from the allotetraploid C. reticulata as the maternal parent and C. saluenensis as the paternal parent; and (3) the C. reticulata cultivars were derived from hexaploid C. reticulata as the maternal parents. These results indicated that C. pitardii, the allotetraploid and allohexaploid C. reticulata may serve as good potential maternal parents for the cross breeding of Camellia.