Artificial Crosses Research Articles

Gene Flow in Lichens

Experimental studies of the evolutionary biology of lichen fungi have been hampered by massive difficulties of in vitro culture and artificial crosses are still not possible. Gene flow in these organisms is demonstrated here for the first time by the analysis of secondary products in the progeny of individuals from natural populations of mixed chemotypes of the Cladonia chlorophaea complex. All of the chemotypes in this study have been interpreted as distinct sibling species. In the Appalachian Mountains of North Carolina, however, the grayi and merochlorophaea chemotypes are found to belong to a single interbreeding populations that is reproductively isolated from the cryptochlorophaea chemotype. In the Coastal Plain, the cryptochlorophaea chemotype hybridizes with the local endemic perlomera chemotype. This study has major impact for species concept in lichens because consideration of neither morphologial tendencies nor biogenetic relationships of the secondary products could have predicted its result.

GENE FLOW IN LICHENS

Experimental studies of the evolutionary biology of lichen fungi have been hampered by massive difficulties of in vitro culture and artificial crosses are still not possible. Gene flow in these organisms is demonstrated here for the first time by the analysis of secondary products in the progeny of individuals from natural populations of mixed chemotypes of the Cladonia chlorophaea complex. All of the chemotypes in this study have been interpreted as distinct sibling species. In the Appalachian Mountains of North Carolina, however, the grayi and merochlorophaea chemotypes are found to belong to a single interbreeding populations that is reproductively isolated from the cryptochlorophaea chemotype. In the Coastal Plain, the cryptochlorophaea chemotype hybridizes with the local endemic perlomera chemotype. This study has major impact for species concept in lichens because consideration of neither morphologial tendencies nor biogenetic relationships of the secondary products could have predicted its result.

REPRODUCTIVE BIOLOGY OF ERYTHRONIUM GRANDIFLORUM VARIETIES GRANDIFLORUM AND CANDIDUM (LILIACEAE)

This four‐year (1982–1986) study compared the pollination biology and cytology of a relatively rare taxon, Erythronium grandiflorum Pursh var. candidum (Piper) Abrams, with that of a geographically widespread sister taxon, E. grandiflorum var. grandiflorum, in the Pacific Northwest. Breeding studies were used to study the reproductive systems of the taxa, to test for interfertility between them, and to seek abnormalities in the breeding system of the rare taxon that might account for its relative rarity. Chromosomes were counted in both taxa and in hybrids from artificial crosses. Ranges of the two taxa were determined from field studies and herbarium specimens. Although the ranges of the taxa overlap in part, populations are usually allopatric. Phenological factors are probably minor in preventing cross‐pollination between the taxa. Both taxa are protogynous obligate outcrossers pollinated by bees. Seed production apparently is not pollinator‐limited. The two taxa are interfertile only when individuals from allopatric populations are artificially crossed, and thus should be considered two biological species. When the taxa overlap in floral phenology in sympatric populations, they exhibit reciprocal incompatibility. Such incompatibility between closely related perennial species is unusual. It may have arisen via natural selection in mixed populations. Alternatively, if populations of each taxon vary with regard to their incompatibility alleles, they may have acquired their fertility barriers by chance before populations of the two taxa came into contact with each other.

A Study on Tansy Chemotypes

According to Scheu (5), a "pure chemical race" is defined using one oil component, which can be unequivocally considered as the main component. However, another way of defining a chemotype is to observe the whole peak distribution of the chromatogram (6). For example, following crossings between camphor and thujone chemotypes, the thujone types are divided into two different thujone types, thujone A and B (3,4). In this study, 80 per cent of the progeny of the artificial crosses of tansy ( TANACETUM VULGARE L.) appeared to belong to so-called "well-defined chemotypes", in which the concentration of the main component varied between 41-99 per cent. The "well-defined chemotypes" were distributed among eight main groups: sabinene, thujone, umbellulone, camphor, bornyl acetate, alpha-pinene, 1,8-cineole, and germacrene-D. The sesquiterpene germacrene-D was identified for the first time in the present study in the essential oil of tansy. Most of these "well-defined chemotypes" were again divided into subgroups A and B. In addition to the "well-defined chemotypes", a number of "mixed chemotypes" were also detected in the crossings. Those chemotypes accounted for 20 per cent of the whole crossing material.

Cytotaxonomic Studies in the Genus Urginea Stein in West Africa. III. The Case of Urginea Indica (Roxb.) Kunth in Nigeria

Urginea indica (Roxb.) Kunth is a morphologically variable species of wide distribution in the Old World. In West Tropical Africa, it has been considered to consist of a large form and a dwarf form. The large form was investigated morphologically in the field and in the laboratory, as well as karyotypically. Four morphological variants were encountered in the field. They differ in both vegetative and floral morphology, were found in different populations, and showed differences in ecological preferences. Biometrical analysis of vegetative and floral morphology showed that the four variants are distinct and separate but not immediately recognizable taxa. Preliminary karyotype analysis showed that they are similar but not identical in karyomorphology. Artificial crosses between them failed to produce viable seeds. It is concluded that U. indica is an incipient polyspecies or species complex. Urginea indica (Roxb.) Kunth is one of the four species of Urginea recognized in the latest revision of Liliaceae in Flora of West Tropical Africa (Hepper, 1968). It is distinguished from the other species by its globose capsule. It is widespread in the Old World tropics, inhabiting savanna vegetation of tropical and subtropical areas of Africa, southern India and further east (Thiselton-Dyer, 1898). In Nigeria, it is widespread in the central segment of the country, occurring between latitudes 70N and 1 00N. It occurs in open, heavy soil with a top layer of humus or in clay soil of seasonally flooded plains. It occurs in different ecological niches in various soil types within the savanna region and shows a variety of morphological forms. Hepper (1968) observed this morphological variation and contended that there are at least two different forms of this variable species: a large form and a dwarf form. These two are easily distinguishable in the field. The large form has light green leaves whose undersurface, immediately out of the bulb, is pinkish; the reproductive shoot is also pinkish, 45-150 cm tall, with not less than 15 flowers in the lax, racemose inflorescence. The tepal is also pinkish with a greenish keel. Leaves and flowers are never borne together. The dwarf form, on the other hand, has dark green leaves; the reproductive shoot is green, generally less than 40 cm tall, with flowers usually ranging between one and 12; the tepals are yellowish green with a green keel. Leaves and flowers are never borne together. Field studies of this taxon during vegetative growth and flowering revealed that Hepper's contention was a rather conservative estimate. The present paper therefore aims at establishing the taxonomic status of U. indica through morphological studies, starting with the

Procedure for artificial cross pollination in clove (Syzygium aromaticum)

A technique for artificial cross pollination in clove is described. This involves emasculating flowers two days before anthesis, and pollinating four days later. Following this procedure a seed set of approximately 25% can be expected.

Variation and taxonomy of Biscutella valentina in Spain

Morphological studies have been made on herbarium specimens and 25 population samples of Biscutella valentina (Cruciferae) in Spain. The discontinuities in morphological characters warrant the recognition of three varieties, var. leptophylla, var. pinnata, and var. valentina, from the mass collections, and a fourth taxon, var. tenuicaulis, based on herbarium material. Experimental cultivation revealed that the combination of distinguishing characters for each taxon is genetically fixed while the observed phenotypic plastic range of the vegetative features is not wide enough to affect their taxonomic importance. Artificial crosses performed reciprocally in various combinations on seven of the populations representing three of the varieties resulted in the production of fertile hybrids. A key for identifying the varieties is presented.

ESTIMATION OF SELFING RATE IN A NATURAL POPULATION OF SCROPHULARIA NODOSA L. USING ALLOZYMES

The genetics of 4 polymorphic enzyme systems PO, 6PGDH, PGM1 and PGM2, is investigated in a seed population derived from a natural population of Scrophularia nodosa. No linkage was detected between any of the four loci. Two of the loci are used to estimate outcrossing rates in a natural population by single-locus as well as multilocus methods. The absence of selfing is in contradiction with the expectations. Testing the fitness of alien pollen against self pollen by performing artificial crosses with different pollen mixtures with PO as a genetic marker revealed no differences between alien and own pollen. Therefore the mechanism preventing self-pollination in this natural population of S. nodosa remains unresolved. The ecological significance of the observed mating system is discussed.

ARTIFICIAL EARTH SATELLITES CROSSING THE FIELDS OF VIEW OF, AND COLLIDING WITH, ORBITING SPACE TELESCOPES

ABSTRACT Predictions of possible interference and damage caused to future space telescopes by Artificial Earth Satellites (AES), including Monte Carlo simulations of AES angular velocities and separations, and the impact of these phenomena on the design of both the instruments and their guidance systems, are considered. Calculations suggest that AES will cross the field of view of the Hubble Space Telescope (HST) with significant frequencies and brightnesses, and firmware changes in the Fine Guidance Sensors have been implemented. The brightest, slowest-moving AES is likely to degrade or damage Faint Object Spectrograph red-sensitive image-tube photocathodes once in a five-year mission. AES will degrade a few percent of Faint Object Camera frames and streak many Wide-Field and Planetary Camera frames. HST will likely be hit by a 5-mm AES fragment, and has a 1 percent chance of being destroyed by a 110-cm fragment, during a 17-year mission. Placing space telescopes in geosynchronous orbit is suggested.

Breeding behaviour of Solanum khasianum Clarke

In nature, Solanum khasianumClarke (syn. S. variumDunal) is a self pollinated plant. However, artificial cross pollination is feasible when pollination is done around the time of anthesis, which is between 09.30 and 10.00. Due to prevalence of heterostyly bud selection has to be highly specific.

Effects of High Tissue Concentrations of Selenium on Reproduction by Bluegills

Abstract Recent studies have associated high body concentrations of selenium with declines in fish populations inhabiting cooling reservoirs of coal-fired electric power plants. Because some evidence indicated that these declines resulted from reduced reproduction, we made a series of 18 artificial crosses of bluegills Lepomis macrochirus possessing high and low body concentrations of Se to determine whether elevated Se in parents reduced viability of gametes or increased mortality of embryos and larvae. Bluegills with high body concentrations of Se were obtained from Hyco Reservoir (cooling water source of a coal-fired power plant) and those with low body concentrations were obtained from nearby Roxboro City Lake, North Carolina. Neither percent fertilization nor percent hatch of eggs differed significantly among the parent combinations. However, all crosses (8) that included females with high Se body concentrations resulted in larvae with edema; such larvae did not survive to the swim-up stage. Only one...

HYBRIDS BETWEEN DUTCH TORMENTILLAE (POTENTILLA, ROSACEAE)

SUMMARY Hybridization in Dutch populations of Potentilla anglica, P. erecta and P. reptans was investigated. Chromosome counts were carried out for 342 plants collected from 40 populations. The chromosome number 2n = 56 was established for 52 plants all belonging to P. anglica, while 225 plants were found to possess 2n = 28. Of these 117 were identified as P. erecta and 108 as P. reptans. The number of 2n = 42 was counted for 50 specimens which belonged all, except 6 P. × mixta plants, to P. × suberecta. In 15 counts intermediate chromosome numbers were ascertained between 2n = 28 and 2n = 42, and between 2n = 42 and 2n = 56, which most probably were due to back crossing of P. × suberecta with one of the parental species. P. × suberecta was found in 13 populations and P. × mixta in only two. The hybrid P. erecta × reptans was not met with. Detailed study of some P. × suberecta populations revealed that this hybrid always grew mixed up with P. erecta, often in large quantities. In morphological characters and ecological amplitude it ranged from P. erecta to P. anglica. Its pollen and fruit fertility was c. 1/3 respectively c. 2/3 of that of the parental species. The functioning of the pollen was investigated in five P. erecta populations. Transport of pollen was found to occur by wind, but chiefly by insects from the families: Syrphidae, Muscidae, Tachninidae, Chloropidae and Thripidae. Artificial cross fertilisation yielded more mature seeds than id. self fertilisation, while apogamy was not demonstrated. Finally, literature data and own observations were combined in a hybridization scheme.

Aspects of Reproductive Isolation between Campostoma oligolepis and Campostoma anomalum pullum (Cypriniformes: Cyprinidae) in Northern Illinois

Reproductive isolation was examined between northern sympatric populations of Campostoma oligolepis and C. anomalum pullum. Some C. a. pullum populations are essentially isolated in upstream areas, but C. oligolepis are never found breeding in the absence of C. a. pullum and occasional interbreeding occurs. Ecological differences probably do not contribute much to reproductive isolation in areas where C. oligolepis occurs. The breeding period of C. oligolepis is shorter and ends more abruptly, although there is considerable temporal overlap between the two species. Postmating isolation through asymmetric hybrid inviability is important. Artificial crosses involving 0Y Campostoma anomalum pullum x 9 C. oligolepis showed increased embryo mortality during the tailbud stage of development. Morphological intermediates may have a higher mortality rate. INTRODUCTION The North American cyprinid genus Campostoma consists of four species and has been the subject of numerous systematic studies (Ross, 1958; Burr, 1976a, b; Burr and Smith, 1976; Buth and Burr, 1978; Rakocinski, 1980; Sewell et al., 1980; Zimmerman et al., 1980; Burr and Cashner, 1983). Buth and Burr (1978) showed C. anomalum and C. oligolepis to be closely related, and equidistant from the more primitive C. ornatum. However, their study also raised some questions concerning relationships between two subspecies of C. anomalum, C. a. anomalum and C. a. pullum, with C. oligolepis. Campostoma a. anomalum populations were genetically more similar to C. oligolepis populations than were northern C. a. pullum populations. However, geographical and morphological data do not unequivocally support this interpretation (Burr, 1976a, b; Burr and Smith, 1976; Burr and Cashner, 1983). Campostoma oligolepis is sympatric with C. a. pullum throughout much of its range (Burr and Smith, 1976), and it is also occasionally syntopic with C. pauciradii (Burr and Cashner, 1983), although it does not come into contact with C. a. anomalum. Some populations of C. a. anomalum and C. a. pullum intergrade geographically (Burr, 1976b; Trautman, 1981). Burr and Smith (1976) proposed that C. oligolepis diverged in the Ozark uplands, sometime during the Pleistocene; however, new findings of an extended range for C. oligolepis and of the previously unknown C. pauciradii may make a reconsideration of this hypothesis necessary (Burr and Cashner, 1983). Reproductive isolation between sympatric populations of Campostoma oligolepis and C. anomalum pullum is incomplete as these fishes hybridize in northern Illinois (Rakocinski, 1980). Buth and Burr (1978) also suggested the occurrence of introgression in Illinois populations. The presumption of complete reproductive isolation has also been challenged for C. oligolepis and C. a. pullum in the Ozark uplands (Sewell et al., 1980). Burr and Cashner (1983) found limited hybridization between C. oligolepis and C. pauciradii, mainly due to habitat disturbance. In spite of such interbreeding, gene pools of these species have apparently remained distinct throughout their respective ranges (Buth and Burr, 1978; Zimmerman et al., 1980). Since C. oligolepis is in secondary contact with C. a. pullum, and since interbreeding may occur, isolating mechanisms may be especially important. The purpose of this study is to examine some factors affecting genetic integrity of northern sympatric populations of these two species.

Meiotic behavior of a Male‐Fertile Triploid Arachis L. Hybrid1

A triploid hybrid (2n = 30) from a cross between Arachis hypogaea L. (2n = 40) and F1 hybrid (2n = 20) from A. cardenasii Krap. et Greg. nom. nud. and A. chacoensis Krap. et Greg. nom. nud. was male fertile, and produced up to 92% stained, uniform pollen grains. Meiotic analyses of the fertile triploid revealed that meiosis I was irregular, with the univalents lagging at anaphase and all 30 chromosomes were incorporated into one cell after anaphase I. Telophase I was not observed in these cells. Meiosis II resulted in dyad formation instead of tetrads. Normal appearing pollen grains were formed which transmitted 30 chromosomes to progeny produced from artificial cross pollinations with A. hypogaea

Reproductive Biology of the Granite Outcrop Endemic Sedum pusillum (Crassulaceae)

Sedum pusillum, a succulent winter annual endemic to granitic outcrops in the south- eastern United States, is self-compatible. Comparisons of F1 progeny from artificial crosses in a population from South Carolina demonstrated either no difference in success for outcrossed versus selfed plants (percentage germination, pollen stainability) or slightly greater success for selfed progeny (survival to adult size, survival to flowering). Outcrossing may be promoted in the field by protandry, extrorse dehiscence of the anthers, and spatial separation of the stamens and pistils. Although S. pusillum has some pollinators in common with Diamorpha smallii, another outcrop endemic and supposed close relative, hybrids between the two taxa could not be produced in artificial crosses. In addition to these primary cytological and genetic barriers to crossing are a number of ecological and phenological differences that should result in complete reproductive isolation in natural populations.

Cruzamentos entre Arachis hypogaea e as espécies A. diogoi e A. spp (30006, 30035)

Artificial crosses were made between A. hypogaea, using lines of 'Tatu', 'Roxo', Tatui x Roxo 80-1 and the cultivar Tatui as female parents and introduced plants of items 30001 and 30005 reported as belonging to A. diogoi and of 30006 and 30035 of A. spp, under greenhouse conditions. From the pollinated flowers of A. hypogaea x A. diogoi, 53.4 and 45.2% gave rise to pegs and fruits with normal seeds, respectively. The amount of viable pollen grains ranged from 4.8 to 13.4 with an average of 8.3% in this cross compared to 97.2 and 95.7% observed for A. hypogaea and A. diogoi. In the crosses A. hypogaea x A. sp. 30006 and A. hypogaea x A. sp. 30035, 13 and 9 normal fruits with 22 and 15 viable seeds were obtained, respectively. The pollen viability varied from 3.5 to 15 with mean of 10% in the former cross and was around 9.9% in the latter, compared with 97.8 and 98.2% noted for A. sp. 30006 and for A. sp. 30035. These results showed that plants previously classified as A. diogoi belong to another species. They also demonstrated the possibilities of using A. diogoi, A. sp. 30006 and A. sp. 30035 in the peanut genetic improvement.

A COMPARISON OF MULTIVARIATE METHODS FOR THE DETECTION OF HYBRIDIZATION

SummaryPrincipal component analysis (PCA), Wells' hybrid distance diagram, principal coordinate analysis (PCO) using weighted Gower metrics, and canonical variate analysis (CVA) were compared using data from artificial crosses of sunfish (Lepomis) and putative hybridization in Juniperus. The results were similar between the two data sets in that using the weighted characters (F ratios from ANOVA of the parents) produced well resolved parental groups and generally ordinated the hybrids between the parents. The F weighted PCO and Wells' distance diagrams were found to be better suited for the analysis of hybridization than PCA or CVA. Several limitations of PCA and CVA are discussed.

Evidence for a polymorphism in gametic segregation using a malate dehydrogenase locus in the tetraploid treefrog Hyla versicolor.

Artificial cross combinations of tetraploid Hyla versicolor were analyzed electrophoretically using a polymorphic malate dehydrogenase locus (MDH-1) to determine the mechanism of chromosome segregation. Models for differentiating between disomic and tetrasomic inheritance are presented and tested. In some crosses progeny genotypes fit a disomic mode of segregation. In other crosses there is only evidence for a tetrasomic mode of segregation. Additional crosses produced genotypic ratios which conformed to either a disomic or tetrasomic mode of segregation. The same type of inheritance was demonstrated for any individual when used in multiple cross combinations. These results suggest that there exists in H. versicolor a polymorphism with respect to segregation of gametes, resulting from differences in chromosome pairings during meiosis I.

Estimates of Hybridization between Two Species of Catostomids in the Columbia River

Extent of hybridization is described between two sympatric catostomids, Catostomus macrocheilus and C. columbianus, from the Hanford Reach of the Columbia River, southeastern Washington state. Estimated percentage of hybrids based on presence of intermediate meristic characters ranged from 12.4 to 14.6% of the total sucker population. Discriminant function analysis reduced subjective variability and lowered estimates of hybridization to 3.0 to 7.1%. Principal component analysis also provided evidence that the suspected hybrids were intermediate between populations of C. macrocheilus and C. columbianus. Meristic characters contributed most to all methods of treatment, with number of lateral line scales the best single criterion for species separation. Any analysis of closely related species would benefit from examination of offspring from artificial crosses and from knowledge of allopatric population characteristics. Breakdown of isolating mechanisms leading to C. macrocheilus X C. columbianus crosses may result from overlap in spawning time and incomplete habitat segregation. Morphological and coloration differences at spawning may provide a basis for species recognition, thus providing some degree of ethological isolation.

Allozyme Divergence in Coreopsis cyclocarpa (Compositae)

Coreopsis cyclocarpa is a diploid, suffrutescent perennial occurring in the grasslands of high plateau regions of Mexico. The species consists of two allo- patric varieties, var. pinnatisecta and the typical one. They are very similar morpho- logically and appear to differ only by a feature of the leaves. The two infraspecific taxa are highly interfertile. Electrophoresis was utilized to ascertain the amount of divergence between the varieties at 20 genetic loci coding for soluble enzymes. There is high genetic identity among populations of the same variety, with mean values of 0.98 for populations of var. cyclocarpa and 0.95 for var. pinnatisecta. When comparing mean identities for populations of the two varieties, the value is 0.75, indicating genetic divergence between the taxa. It is suggested that genetic differentiation between the two varieties is a reflection of the time they have been isolated. In an earlier study one of us (Crawford 1970) reported on the mor- phology, flavonoid chemistry, chromosome number, and artificial hy- bridizations involving Coreopsis cyclocarpa Blake and C. pinnatisecta Blake. The two taxa are perennial suffructescent plants growing in the moun- tains of Mexico with the latter found primarily in the states of Oaxaca and Guerrero and the former in Jalisco. Both taxa flower at the same time of year and occur in similar open grassy areas of high plateau regions (Crawford 1970). The present known geographic ranges of the two taxa indicate a disjunction of about 700 km, although additional collecting in Guerrero and Michoacan might narrow this hiatus. The only reliable morphological character for distinguishing them is leaf mor- phology, with C. cyclocarpa having simple linear leaves whereas those of C. pinnatisecta are pinnatisect with linear segments (Crawford 1970). Both taxa are diploid with a chromosome number of 2n = 24, and artificial crosses in the greenhouse produced fully fertile F1, F2, and backcross hybrids. Meiosis was regular and seed set was not reduced (Crawford 1970). In addition, the leaf characters used to separate the two taxa segregate in the F2 generation. On the basis of these data, the two taxa were reduced to varietal status. The purpose of the present study was to measure genetic divergence between the two varieties of Coreopsis cyclo- carpa utilizing data from the electrophoretic separation of allozymes. The advantages of enzyme electrophoresis for addressing systematic ques- tions in plants were discussed by Gottlieb (1977a, 1981 a), who also point- ed out that most electrophoretic studies comparing different taxa have been done with annuals, there being a paucity of data for perennial angiosperms. The present study of allozymes in woody, perennial, in- terfertile, morphologically similar plants will provide data for the com-