Karyotypic studies in Turnera sidoides complex (Turneraceae, Leiocarpae)

Turnera sidoides, with the most southerly distribution of all Turnera species in America, is a complex of obligately outcrossing perennial herbs. Karyotypes of the five subspecies of T. sidoides (x = 7) are described for the first time utilizing root-tip mitotic metaphases. Different ploidy levels were found for all of the subspecies, ranging from diploid to octoploid. The results obtained, coupled with available meiotic and preliminary biosystematic data, support the hypothesis of autopolyploidy within this species complex. Although detailed karyotype analysis shows a high degree of intraspecific uniformity, subspecies may be differentiated by the number, type, and position of satellites, suggesting that chromosome rearrangements may also be involved in the karyotypic evolution of T. sidoides. Karyotype data, coupled with morphological and anatomical features, suggest the removal of T. sidoides from series Leiocarpae.     

Cytogeography of the South American Turnera sidoides L. complex (Turneraceae, Leiocarpae)

New chromosome number determinations are presented for 48 populations of five subspecies of Turnera sidoides. Chromosome counts in sspp. carnea, holosericea, integrifolia and sidoides confirm previous data while, in ssp. pinnatifida , the numbers 2n=2x = 14 and 2n = 6x = 42 are reported for the first time. The results show that polyploidy is a very frequent phenomenon. Populations are primarily tetraploids (2n = 4x = 28), while diploids (2n = 2x = 14), hexaploids (2n = 6x =42) and octoploids (2rc = 8x = 56) are less frequent. Diploid, tetraploid and hexaploid cytotypes occur in sspp. carnea and pinnatifida , whereas tetraploids and hexaploids are known in ssp. holosericea. Turnera sidoides ssp. integrifolia shows a polyploid series with ploidy levels from 2x to 8x. The ssp. sidoides appears to be uniformly tetraploid, with the exception of an isolated pentaploid (2rc = 5x = 35). On the basis of these counts and previous reports the geographical distribution of the cytotypes has been determined and related to climatic and ecological factors.     

Evidence of 2n microspore production in a natural diploid population of Turnera sidoides subsp. carnea and its relevance in the evolution of the T. sidoides (Turneraceae) autopolyploid complex

Turnera sidoides is a complex of distylous perennial rhizomatous herbs that includes five subspecies. Since polyploidy has played a prominent role within this species (x?=?7), ongoing studies in T. sidoides are focused on the understanding of the mechanisms involved in the origin and the establishment of polyploids. Therefore, aiming to contribute to the understanding of the mode of polyploid formation, in this study we investigated the frequency of unreduced microspores in a natural diploid population of T. sidoides subsp. carnea by analyzing the size range of pollen and the constitution of the sporads. The results showed that some of the individuals studied produced 2n and 4n microspores, both in short- and long-styled floral morphs. The analysis performed documents the production of unreduced microspores in T. sidoides subsp. carnea and provides evidence that support the hypothesis of sexual polyploidization as one of the most probable mechanisms involved in the origin of polyploids within this species complex. The role of unreduced pollen in the establishment and persistence of newly formed polyploids in diploid populations of T. sidoides is also discussed.     

Colleters in Turnera and Piriqueta (Turneraceae)

The anatomy of colleters was examined by light and scanning electron microscopy in 25 species of Turnera and nine species of Piriqueta. Based on morphology, four categories of colleters were recognized: standard, sessile, lachrymiform and trochleariform, all of which differ in shape and length/width ratio. They all have a similar anatomy: they consist of an axis of parenchymatous cells, sheathed by a palisade epidermis. The standard type is the most widespread in the studied taxa; the lachrymiform example was found in those species of Piriqueta with setiform glandular hairs; only one trochleariform example appeared in T: diffusa. The sessile type is considered to be a morphological transitional form between extrafloral nectaries and colleters. This is the first record of sessile, lachrymiform and trochleariform colleters. The anatomy of colleters is compared with other secretory structures such as glandular trichomes and extrafloral nectaries.     

Pollen competition in Turnera ulmifolia (Turneraceae)

We performed mixed pollinations, involving self vs. within- or between-population pollen, and used starch gel electrophoresis to assay 2,210 progeny to detect pollen competition in Turnera ulmifolia. Within populations there was no evidence for a competitive advantage to outcross pollen. Between populations a marked advantage to self pollen occurred for most populations, and the extent of this competitive advantage was correlated with increasing morphological divergence of the outcross pollen donor population. A comparison of rates of ovule abortion revealed that the biased paternity ratios cannot be the result of ovule abortion alone, and that pollen competition must be the major contributing factor. We suggest that reproductive divergence among the populations, perhaps through adaptation to different pollinators or through the evolution of increased selling, has resulted in the evolution of reproductive isolation through pollen competition.     

Morph-Specific Proteins in Pollen and Styles of Distylous Turnera (Turneraceae)

We used nondenaturing isoelectric focusing (IEF) in a survey of plants from 11 populations to identify style and pollen proteins unique to the short-styled morph of Turnera scabra, T. subulata and T. krapovickasii. Three protein bands [approximately isoelectric points (pIs) 6.1, 6.3 and 6.5] were found only in styles and stigmas of short-styled plants while two bands (approximately pIs 6.7 and 6.8, M(r) 56 and 59 kD) occur only in pollen of short-styled plants. Some of these bands appear very late in development, within 24 hr before flowering. Two isozyme loci were mapped to an 8.7 cM region spanning the distyly locus. Using these isozyme markers we identified progeny exhibiting recombination adjacent to the distyly locus. No recombinants between the distyly locus and the locus or loci controlling the presence of the short-styled morph-specific proteins were obtained. This suggests that the loci encoding these proteins are either extremely tightly linked to the distyly locus and in complete disequilibrium with the S allele or exhibit morph-limited expression. Crosses to a plant showing an unusual style protein phenotype demonstrated that an additional unlinked locus is required for full expression of the style proteins. The function of the morph-specific proteins is unknown.     

Inheritance of plastid DNA in the Turnera ulmifolia complex (Turneraceae)

We used PCR to amplify most of the rbcL gene and identified restriction fragment length polymorphisms to study the inheritance of chloroplast DNA (cpDNA) in the cross between two taxonomic varieties of the Turnera ulmifolia L. complex, vars. angustifolia and velutina. We identified an Alu I restriction site polymorphism that distinguished the parental plants. All 23 progeny from the cross var. angustifolia × var. velutina, where var. angustifolia was the maternal parent, possessed the paternal cpDNA. Results for the reciprocal cross were more varied, and the 16 progeny showed maternal, paternal, or biparental inheritance. We believe this represents the first study of plastid inheritance for any species in the Tumeraceae. The results are unusual and warrant further investigation using other species in this family.     

Characterization and localization of short-specific polygalacturonase in distylous Turnera subulata (Turneraceae)

We describe for distylous Turnera subulata a polygalacturonase specific to short-styled plants that is localized to the style transmitting tissue (the tissue through which pollen tubes grow). The polygalacturonase gene is linked to and may be upregulated by the S allele of the distyly locus. Because of its tissue-specific location, the polygalacturonase may be involved in the self-incompatibility response, acting in a complementary or antagonistic manner, or possibly in signalling downstream events. A pollen-specific polygalacturonase was also identified and may be a member of a small multigene family of pollen polygalacturonases. The role, if any, played by the pollen polygalacturonase in distyly, is presently unknown.     

Inheritance of spontaneous mutant homostyles in Turnera subulata x krapovickasii and in autotetraploid T. scabra (Turneraceae)

To explore the genetic architecture of distyly in Turnera spp., we determined the inheritance and compatibility behaviour of two spontaneous homostyled mutants. A long-homostyled mutant shoot arose on an otherwise short-styled plant that was an artificial hybrid (Turnera subulata x T. krapovickasii) between two diploid distylous species. The mutation appears to be an allele, SH, of the distyly locus with the dominance relationships, S>SH>s, where S confers the short-styled phenotype, SH confers homostyly in SHSH and SHs genotypes, and ss genotypes are long-styled. Aberrant segregation ratios were observed among some crosses and might be the result of pollen competition. Compatibility relationships are consistent with the hypothesis that a gene complex determines distyly. Infrequently, revertant short-styled flowers have appeared on cuttings of the T. subulata x T. krapovickasii mutant and on occasion, short-styled progeny have appeared in crosses where none were expected. A second mutant homostyle was discovered in autotetraploid T. scabra. The mutation is inherited as above, however, tetrasomic inheritance occurs at the locus. This homostyled mutant carries two copies of the SH allele and has the duplex genotype SHSHss. Compatibility relationships were as observed above. The occurrence of homostyled mutants is consistent with the hypothesis that a linked gene complex underlies the inheritance of distyly in Turnera but we cannot discount the hypothesis that an allelic series is responsible.     

Distribution of style and pollen polygalacturonases among distylous and homostylous Turnera and Piriqueta spp. (Turneraceae)

We explore the distribution of a style and pollen polygalacturonase in a number of distylous and homostylous species of Turnera, and two species of Piriqueta (Turneraceae). We show, using immunoblotting with antibodies made against these proteins, that the style polygalacturonase is specific to styles of short-styled plants of all the six distylous species of Turnera we have investigated. Styles of a somatic homostylous mutant derived from a short-styled plant do not possess the style polygalacturonase. Distylous P. caroliniana did not appear to possess this protein. We show that the pollen polygalacturonase, while associated with the short-styled morph in three species, is polymorphic among short-styled plants of T. krapovickasii, and absent from T. joelii, T. grandiflora and P. caroliniana. These data support a role for the style polygalacturonase in distyly, possibly in the incompatibility system, but cast doubt on any role for the pollen polygalacturonase. In concert with the predictions for the mode of origin, and the response of styles of homostylous species to pollen from long- and short-styled plants, we find that none of the homostylous species possess the style polygalacturonase. The pollen polygalacturonase does occur in some homostylous species, but not in others. It is not clear that the pollen polygalacturonase, however, provides a marker for the mode of origin of homostyly.     

Patterns of cytotype variation of <Emphasis Type="Italic">Turnera sidoides</Emphasis> subsp. <Emphasis Type="Italic">pinnatifida</Emphasis> (Turneraceae) in mountain ranges of central Argentina

Cytogeographical variability among 564 plants from 26 populations of Turnera sidoides subsp. pinnatifida in mountain ranges of central Argentina was analysed with meiotic chromosome counts and flow cytometry and is described at regional and local scales. Populations were primarily tetraploids (2n = 4x = 28), although diploid (2n = 2x = 14), hexaploid (2n = 2x = 42), and mixed populations of diploids and triploids (2n = 3x = 21) were also found. Diploids, triploids, and hexaploids were fewer in number and restricted to narrow areas, while tetraploids were the most common and geographically widespread cytotype. Diploids grew at higher altitudes and in colder and wet locations; tetraploids had the broadest ecological spectrum, while hexaploids occurred at the lowest altitudes and in drier conditions. The cytotypes were also spatially segregated at a microgeographical scale. Diploids grew in the piedmont, tetraploids were in the adjacent valley, and in the contact zone of both cytotypes, patches of diploids and triploids were found. At a regional scale, the distribution of the cytotypes may be governed by a combination of ecological and historical variables, while segregation in the contact zone may be independent of the selective environment because the cytotypes are unable to coexist as a result of reproductive exclusion. The role of triploids is also discussed.     

Geographic patterns of genetic variation in native pecans

A structured collection of 80 seedling pecan trees [Carya illinoinensis (Wangenh.) K. Koch], representing 19 putatively native pecan populations across the species range, was evaluated at three plastid and 14 nuclear microsatellite (simple sequence repeat, SSR) loci. Data were analyzed using a priori population designations and also within a Bayesian framework, in which individuals were assigned to clusters regardless of population of origin. Population genetic analyses using a priori populations, clusters based on chloroplast microsatellite data (cpSSR), and clusters based on nuclear microsatellite data (nSSR) yielded consistent results. For all groupings, cpSSR variation exhibited more geographic structure than the nSSR data. Furthermore, cpSSR microsatellite diversity decreased with increasing latitude, but this pattern was not observed with the nuclear data. Contrasting patterns in plastid and nuclear genetic diversity demonstrate unique aspects of postglacial recolonization reflected in the movement of seeds versus pollen. These data suggest that plastid SSRs are useful tools for identifying population structure in pecan and hold promise for ongoing efforts to identify and conserve representative germplasm in ex situ collections.     

Geographic variation in the greater Japanese shrew-mole,Urotrichus talpoides: Combining morphological and chromosomal patterns

Although much information on the species dynamics of small mammals may be gleaned from the integration of morphological and molecular data sets, the two are not routinely combined when species boundaries and definitions are investigated. The greater Japanese shrew-mole (Urotrichus talpoides) presents a rare example of intraspecific and geographical euchromatic chromosomal variation. In this study a combination of 2D landmark-based and outline-based geometric morphometric methods were used to provide the first quantitative examination of variation in skull morphology occurring between populations of U. talpoides. Geographic variation was found to be most conspicuous in ventral and dorsal cranial morphology, and less evident for outline-based analyses of the dentary, thereby indicating differing magnitudes of skeletal plasticity associated with geographic variation in each system. Both ventral and dorsal cranial morphology differed significantly between shrew-moles from western and eastern Honshu, in agreement with previously identified chromosomal variation boundaries. Inclusion of other island populations revealed shape differences between shrew-moles in Kyushu, Tsushima and North Honshu. These results lend general support for the unification of morphological and chromosomal data when assessing species boundaries.     

Geographic variation in morphological and reproductive characters of coastal and tableland populations ofBlandfordia grandiflora (Liliaceae)

For tenBlandfordia grandiflora populations spanning about 90% of the species' range, univariate and multivariate analyses on 14 vegetative and reproductive characters separated plants into distinct coastal and tableland groups. Distinguishing characters were number of flowers and leaves, leaf length and width, and inflorescence stalk height and diameter; coastal plants were larger than tableland plants. In a transplant experiment, coastal and tableland plants retained their phenotypic distinctness, indicating that vegetative morphology was genetically determined. Coastal plants exhibited clinal variation with latitude. Compared to tableland plants, coastal plants had higher pollen: ovule ratios, and produced fewer but heavier seeds per flower. Tableland and coastal plants are phenotypically distinct, indicating that separate subspecific status is warranted.     

Meiotic recombination in Turnera (Turneraceae): extreme sexual difference in rates, but no evidence for recombination suppression associated with the distyly (S) locus

To explore the rate of recombination resulting from male vs female meiosis, crosses were performed using distylous Turnera subulata as well as a cross involving the introgression of genes from T. krapovickasii into T. subulata. We assayed four loci on the chromosome bearing the S-locus as well as two loci on each of two other linkage groups. Substantial and consistent dimorphism in recombination rates was found with female meiosis resulting in as much as a approximately 6-fold increase relative to male. Aberrant single locus segregation ratios occurred for some loci, particularly when the male (pollen) parent was heterozygous and the cross involved introgressed genes. The extreme trend of greater recombination resulting from female meiosis was, however, maintained in crosses where no aberrant ratios occurred, indicating that the sex dimorphism in recombination is not the result of aberrant segregation. We also exploited this distylous species and tested whether there is recombination suppression around the S-locus because of an inversion or other chromosome rearrangement(s). We found no significant evidence for recombination suppression.     

Evolutionary genetics of Metridium senile. II. Geographic patterns of allozyme variation

Electrophoretic surveys have demonstrated that populations of the sea anemone Metridium senile along the northeast coast of the United States are polymorphic at four enzyme loci. Phosphoglucose isomerase (PGI) has two alleles in most populations, phosphoglucomutase (PGM) has three alleles, and two leucine aminopeptidase loci have two common alleles each. Phosphoglucose isomerase displays clinal variation and an apparent association with environmental temperature. Phosphoglucomutase shows clinal variation north of Cape Cod for two of the three alleles, while the two leucine aminopeptidase loci are not clinal. All loci show a great deal of variation in populations on Cape Cod, but there is no apparent systematic pattern to this variation. Temperature may be a selective agent in the maintenance of the PGI and PGM clines, although other possibilities cannot presently be completely excluded.Supported by Grant T-4 from the Health Research and Services Foundation, NSF DEB77-14442, NIH GM25809, and NIH GM28024.