Viable F1 Research Articles

INTROGRESSION BETWEEN THE CULTIVATED HEXAPLOID OAT A. SATIVA AND THE TETRAPLOID WILD A. MAGNA AND A. MURPHYI

Introgression between the hexaploid (2n = 42) oat A. sativa and the newly discovered tetraploid (2n = 28) species A. magna and A. murphyi was studied by the rate of stabilization of chromosome number, restoration of fertility of pentaploid hybrid derivatives and the ultimate gene transfer between the tetraploid and the hexaploid levels. The complete self-sterility of the pentaploid F1 hybrids was overcome by massive back-pollination to the parental species. Great variation in chromosome number (12-48) was found among the viable F1 female gametes. Meiotically stable and reasonably fertile derivatives were selected only at the F2 of the BC and in a relatively small proportion. Gene transfer between the tetraploid and the hexaploid species was demonstrated by introducing the allele for nonshattering seed from the cultivated oat A. sativa to both A. magna and A. murphyi, and lemma hairiness from the tetraploids to the hexaploid level. The possible exploitation of introgression between the polyploid oats for breeding purposes has been pointed out and the potential of A. magna and A. murphyi as cultivated oats has been briefly discussed.

The genetics of Artemia salina. VII. Reproductive isolation.

Fifteen of 20 gonochoristic Artemia populations are crossfertile with diploid San Francisco shrimps, producing fertile F1 and viable F2 progeny. Partial sex linkage of white eye was observed and frequency of crossing over between the white and sex loci did not exceed the range of values observed in San Francisco shrimps. Possible mechanisms for wide dispersal of this diploid genotype are discussed. Five populations are reproductively isolated from San Francisco shrimps: Mono Lake, Hidalgo, Lake Urmia, San Bartolomeo, and Tunisia. The last two are inter-fertile.

A Quantitative Study of Long-Term Courtship: I. Ethological Isolation Between Sympatric Populations of the Midas Cichlid, Cichlasoma Citrinellum, and the Arrow Cichlid, C. Zaliosum

AbstractI. Cichlasoma citrinellum is a cichlid fish found in the Great Lakes and crater lakes of Nicaragua. It is sympatric with C. zaliosum in Lake Apoyo, a Nicaraguan crater lake. C. zaliosum is confined to that lake and is closely related to C. citrinellum; it probably arose from C. citrinellum in Lake Apoyo. C. labiatum is endemic to the Great Lakes and is also closely related to C. citrinellum. All three species have complex reproductive behavior involving a prolonged courtship with pair bondings, followed by a period of joint parental defense and care of the offspring. 2. Fish from sympatric populations of C. citrinellum and C. zaliosum interbred and produced viable F1 offspring in the laboratory, when given no choice except a mate of the opposite species. 3. Given a choice, C. citrinellum and C. zaliosum from both allopatric and sympatric populations formed only homospecific pairs, but the allopatric test was not conclusive. 4. C. labiatum was tested in a mate choice situation with an allopatric population of C. citrinellum and showed incomplete behavioral isolation. 5. Ethological isolating mechanisms are sufficient to explain the maintenance of species isolation between C. citrinellurn and C. zaliosum in a sympatric situation in Lake Apoyo.

<i>Hisbiscus</i> 属植物に関する研究(第8報)

1. F1 seeds and plants were obtained by interspecific crosses between three East-Asian species of Hibiscus, paramutabilis×syriacus, syriacus×paramutabilis and syriacus×sinosyriacus.2. Different strains of syriacus resulted in different vigor of the F1 plants in all of the three crosses. Only one out of the six strains used for cross pollination produced healthy hybrid plants which successfully reached maturity (Table 1).3. The color, form, size and number of flowers varied considerably even among the hybrid plants originating from the same combination of parents. Some of the hybrids seemed promising for ornamental purpose in that they had larger size and number of flowers than their parents (Table 2, Fig. I).4. The seasonal trends of flowering in F1 plants, of which mother plants were syriacus, showed a pattern more or less similar to that of syriacus or intermediate between those of the parents, while the hybrids originating from paramutabilis mothers produced the largest number of flower in August, when the parent species produced the least number (Fig. 2).5. The hybrid trees were largely similar to syriacus in their habit. The total number of flowers produced in a season tended to be greater in trees with bigger crown, but was little influenced by the number of current-year branches (Fig. 3).6. Hybrid plants were generally intermediate between the parents with respect to such morphological characters as the shape and size of leaf, flower stalk, peduncle and bractlet, the density of hairs on hairs on leaf surface, etc., though there were some exceptions (Table 3 and 5, Fig. 4 and 5).7. As compared with that of parents, the pollen of the hybrids was somewhat smaller in mean grain size, greater in size variation and lower in fertility (Table 6, Fig. 6).8. The meiosis was fairly normal in pollen mother cells of the three parent species, each having 40 bivalent chromosomes. In F1 cells, the sinapsis and tetrad-formation were also normal without any multipolarity and other serious abnormalities, though a few delayed univalents appeared in some cells (Fig. 7).9. Back-crosses with the parents were proved to be fertile. Viable F2 seeds were also obtained by reciprocal crosses between the F1 hybrids (Table 7, 8).

Isolation of viable F1 seeds of some interspecific crosses by X-ray photography

Some of the hybrid seeds obtained by interspecific crosses show lack of proper development of seed parts like embryo or endosperm. If such seeds are sown, no plant is usually obtained. However, if the internal details of the seeds are known prior to sowing, embryo culture method may be resorted to for the under-developed seeds and the unfortunate loss of hybrid plants may probably be avoided. The use of X-ray photography was found to be very promising and was employed to assess the internal condition of the hybrid seeds obtained from the interspecific crossing programme, viz, 1. Oryza sativa × O. officinalis, 2. Abelmoschus esculentus × A. moschatus, 3. Lycopersicum esculentum × L. pimpinellifolium and 4. Solanum melongena × S. testiculatum. The special advantages of this technique are, that a. it is possible to know the internal development of F1 seeds without causing any damage to them; b. knowing the condition of the seed, adequate care could be provided to individual seeds as judged by the radiographs; c. it is a very quick and sure method which could be used by the geneticists and breeders in their distant crossing programmes.

Studies on two populations of Ixodes kingi Bishopp (Ixodidae).

Studies on tick size, distribution, and hosts are made of two populations of Ixodes kingi Bishopp, the individuals of which appear to differ only in size. In Canada large specimens were collected only in Alberta and mainly from carnivores and ground squirrels, while small specimens were found only in British Columbia and mostly on pocket gophers and mice but occasionally on weasels. A study of available United States material revealed a similar pattern, the two populations being separated by the Rocky Mountains and the Wasatch Range, but each containing a scattered few specimens of intermediate size. It was shown that individuals of the two populations will interbreed and yield viable F2 larvae. It is suggested that the species is in a state of evolutionary divergence northwards.

THE GONADS AND REPRODUCTION OF THREE INTERGENERIC SUNFISH (FAMILY CENTRARCHIDAE) HYBRIDS.

The sterility of species hybrids has been known since the time of the ancient Greeks. Aristotle discussed at length the sterility of the mule (Dobzhansky, 1951). Hybrid sterility due to abnormal gonad development, especially in the male, is very common in viable F1 species hybrids in animals (Stebbins, 1966). The literature on hybrid sterility is extensive, and comprehensive reviews by Dobzhansky (1951), White (1954), and Stebbins (1958) are available. In the class Osteichthyes, the study of hybrid sterility is difficult because the chromosomes are, in general, too small and too numerous to permit detailed study (White, 1954). Therefore most of the studies have been concerned with gross and histological examination of the gonads and attempts at obtaining F2 and backcross offspring. In the Centrarchidae (sunfish family) there have been conflicting reports concerning the sterility of species hybrids. Earlier workers (Hubbs and Hubbs, 1932; 1933) concluded that with rare exceptions all species hybrids within the genus Lepomis were sterile. Ricker (1948) was apparently the first author to find that all centrarchid hybrids were not sterile. Since that time an increasing number of authors have found fertile centrarchid hybrids (Lagler and Steinmetz, 1957; Childers and Bennett, 1961; Smitherman and Hester, 1962; Childers, 1967). Roberts (1964) found karyotypic polymorphism in Lepomis cyanellus. He suggested that the conflicting reports might be attributed to the use of fish of the same species but with different karyotypes. Becak et al. (1966) have demonstrated intraindividual chromosomal polymorphism in Lepomis cyanellus. Childers (1967) found the following intergeneric centrarchid hybrids to be fertile: Chaenobryttus gulosus X Lepomis cyanellus, L. cyanellus X C. gulosus, L. microlophus X C. gulosus and C. gulosus X L. macrochirus. Birdsong and Yerger (1967) found that in the latter hybrid some of the testes were represented by mere strands of tissue, but three of 24 male hybrids produced normal spermatozoa. One hybrid female had well developed ovaries with a large number of apparently normal eggs. White (1954) suggested that experimental hybridization may reveal the extent and nature of the isolating mechanisms separating two species. It was the purpose of the present investigations to study the reproduction of the following intergeneric hybrids: Micropterus salmoides (the largemouth bass) X Chaenobryttus gulosus (the warmouth), C. gulosus X M. salmoides, and C. gulosus X Lepomis macrochirus (the bluegill), with special reference to hybrid sterility and the interpretation of this information with respect to the isolating mechanisms separating these species. In the above hybrid designations and throughout this paper the female is listed first. According to present centrarchid taxonomy the first two hybrids are intertribal crosses, and the last hybrid is an intratribal cross. 1 Based on a portion of a thesis submitted to the Department of Zoology, North Carolina State University at Raleigh, in partial fulfillment of the requirements for the degree of Doctor of Philosophy. 2 Present address: Department of Biology, Western Carolina University, Cullowhee, N. C. 28723.

Genetically fixed characters and evolutionary divergence.

Data from hybridization permit assessment of relationships of the toads (genus Bufo ) which occur on all continents except Australia and permit a crude estimate of the degree of genetic change with time. The evidence indicates that toads have been very conservative with respect to change. A major dichotomy into broad-skulled, warmth-adapted and narrow-skulled, cold-adapted types occurred in the New World 15 million or more years ago. The narrow-skulled toads have reached Africa at least twice. Hybridization between Eurasian and New World species shows that after separation for an estimated 10 million years some species remain genetically similar enough to produce viable F1 hybrids in both reciprocals of the cross. Broad-skulled toads appear to have been in Africa for at least 15 million years, as indicated by the fossil record, and in their main radiation they have changed their chromosomal number from 2n=22 to 2n=20. Nevertheless, their females form viable F1 hybrids with New World broad-skulled males after presumed isolation for more than 15 million years. Intermediate types live today in the New World connecting both skull types, and some cross easily with both. Evolutionary conservatism of Bufo with respect to genetic compatibility contrasts with the rapid change in Rana .

The sensitivity of various germ-cell stages of the male mouse to radiation induced translocations.

Adult male BALB/c mice were given whole body X-irradiation with 300 R. Directly after X-irradiation each male was mated to one virgin female of the same strain and received one fresh female per week during 9 weeks. The male F1 offspring was killed when mature and the testes removed and analysed for the presence of chromosome rearrangements at diakinesis — first metaphase stage of meiosis. Whereas no aberration was recorded among the 171 F1 ♀♀ from the control series, chromosomal abnormalities were observed in 41 F1 ♀♀ from the irradiated series. The incidence of males with aberrations was respectively 5.1% the first week, 10.4% the second week, 21.7% the third week, 2.2% the fourth week and 6.3% the fifth. No aberration was observed in the 129 F1 males sired between the sixth and ninth weeks. It may be concluded that irradiated spermatids yield approximately four times as many cases of aberration in viable F1 ♀♀ as do irradiated mature spermatozoa and about ten times as many as the most mature spermatocytes whereas no aberrations were recovered from irradiation of the spermatogonia. The most common aberrations found in the F1 males of the irradiated series were the reciprocal translocations.

RELATIONSHIP OF TAXA IN GENUS MEDICAGO AS REVEALED BY HYBRIDIZATION.: II. M. PIRONAE × M. DAGHESTANICA WITH REFERENCE TO M. SATIVA

Medicago pironae Vis. and M. daghestanica Rupr. are related to the extent that viable F1 hybrids can be easily obtained. These species should, therefore, be grouped taxonomically closer than has been done in the past. Their relationship to M. sativa L. is more remote, as judged by failure in hybridization. The M. pironae × M. daghestanica F1 hybrids were completely self-sterile and sterile on backcrossing to both parents. Pollen of the hybrids was close to 100% protoplasm-empty. Meiosis proceeded irregularly in 55% of metaphase I and diakinesis cells. At AI and All chromatin bridges were observed in 65% and 90% of cells, respectively. At pachytene, strands of unequal lengths and different chromomere patterns indicated cryptic chromosomal or genie dissimilarities.

Studies on the physiology and genetics of the rotifer, Asplanchna. 3. Results of outcrossing, selfing, and selection.

AbstractSympatric populations of Asplanchna brightwelli and A. girodi do not hybridize, so that these two morphological species represent distinct biological species or syngens. Populations of A. brightwelli from Tennessee and Indiana may be crossed to give viable F1, F2, and backcross generations. These two widely separated populations may thus be assigned to a single biological species. A program of repeated selfing with selection for high clonal viability has been carried out with A. brightwelli. Clonal viability declined with the first selfing, then rose with succeeding generations of selfing and selection, to or above the viability of clones obtained by inbreeding within the parental mixed stock. Selfing also led to an increase in the homogeneity of the growth rates of groups of sibling clones obtained by selfing, suggesting increased homozygosity in the selfed, selected lines. The results of the selfing and selection experiments suggest that wild stocks of Asplanchna are heterozygous for a number of recessive detrimental and lethal genes affecting the growth rate and viability of clones. The heterozygosity of the natural populations, together with the failure of geographically isolated populations of a morphological species to become reproductively isolated, suggests that these rotifers are not extreme inbreeders. It is suggested that the maintenance of recessive detrimentals in these rotifers, in which the males are haploid, may indicate that the phenotype of a male is determined to a large extent by the genotype of its mother. Such maternal effects would protect detrimentals from selection in the male offspring of heterozygous females.

A Behavioral Study of Two Races of the Fall Webworm, Hyphantria cunea, (Lepidoptera: Arctiidae) in Louisiana

Fall webworms, Hyphantria cunea (Drury), found in Louisiana differ in appearance and morphology. Those designated as an “orange race” construct compact nests. Nests of the black race are diffuse and generally subdivided into several small nests. The “black race” infests 34 hosts, of which sweetgum, persimmon, and willow seem to be preferred, and the “orange race” infests 7 hosts, of which pecan and persimmon are preferred. Adults of the two forms will cross in the laboratory and produce viable Fi and F2 progeny. There are considerable clifferences in manner of egg deposition and larval behavior.

Investigations on F1 and F2 hybrids between Brassica oleraceae Var. Acephala and Raphanus sativus

A cross was made between B. oleraceae var. acephala and R. sativus. The use of a piece of cotton soaked with the growth regulator, N-m-tolyphthalamic acid at 100 ppm and attached to the pedicel at the time of pollination resulted in set of several pods with one viable seed. The hybrid kale x radish appeared vegetatively intermediate between the parents except for the flower color which resembled the radish. The F1 plant propagated asexually and maintained under screen isolation cages with pollinating insects for a period of four years yielded only one viable F2 seed. The single F2 plant obtained, an allotetraploid, failed to yield any fertile seeds through selfing. Backcrossing of this F2 plant to the radish has yielded two seeds.

Cytotaxonomy of Australian Danthonia

Cytological and cytogenetic studies of 29 Australian species of Danthonia revealed an extensive polyploid series ranging from 2n = 24 to 2n = 120. Meiosis was regular and fertility high in the species. Field hybrids were detected by aberrant chromosome number, meiotic behaviour, and reduced fertility. An extensive series of interspecific crosses resulted in some viable hybrids but many combinations failed or gave F1 plants which failed to flower. Most viable F1 plants were highly sterile. Diploid hybrids were completely sterile, but in higher polyploids crossing was more often successful and hybrids had increased fertility. Meiotic pairing and chiasma frequency were drastically reduced in all F1s. Multivalent associations indicated gross structural rearrangements. The restoration of fertility by chromosome doubling indicated cryptic structural changes. Neither cross compatibility nor meiotic behaviour showed any strong relationship with taxonomic grouping. These results together with the intermediate morphology of F1s and the increased morphological variation in polyploid forms of D. caespitosa and D. linkii strongly suggest alloploidy as the main mechanism of evolution of the polyploid species. Twenty-three of the species had Panicoid type of epidermis and Festucoid chloroplast arrangement. The exceptions were D. pallida, D. procera, D. frigicla, D. nivicola, D. nudiflora, and D. sp. indescr. These studies throw light on the relationship of the arid form, D. bipartita, the alpine forms D. frigida, D. nivicola, and D. nuclifiora, and the highly variable forms such as D. caespitosa and D. linkii with the rest of the genus. Plant improvement by conventional methods would be virtually impossible unless restricted to high polyploids and intraspecific crossing, but true-breeding, highly fertile amphidiploids could be produced.