EVOLUTIONARY STUDIES OF ATRIPLEX: PHYLOGENETIC RELATIONSHIPS OF ATRIPLEX PLEIANTHA

Atriplex pleiantha Weber differs from all other species of Atriplex in having 1) multiple female flowers subtended by two bracts, 2) female flowers with a perianth, and 3) embryos with radicles pointing downwards. Because of these significant differences it is proposed that Atriplex pleiantha be elevated to the level of a separate genus and be designated Proatriplex pleiantha (Weber) Stutz & Chu. The closest relatives of Proatriplex appear to be Archiatriplex, Endolepis, Exomis, and Microgynoecium. These are all diploid, monoecious annuals, have non-Kranz type leaf anatomy, and female flowers with a perianth.     

EVOLUTIONARY STUDIES OF ATRIPLEX: A RELIC GIGAS DIPLOID POPULATION OF ATRIPLEX CANESCENS

Growing on shifting sand dunes in central Utah is a small endemic population of a gigas form of A triplex canescens. Whereas normal A. canescens usually grows to a height of three to four feet and occasionally to five or six feet, the gigas form often reaches ten and sometimes twelve feet. All normal A. canescens so far examined (67 populations) have 2n = 36 chromosomes; the gigas form has 2n = 18 chromosomes. Several lines of evidence suggest that the gigas form is a relic diploid and the normal form is an autotetraploid derived from it. The growth rate of seedlings and new twigs is nearly twice as great in the diploid as in the tetraploid. Seed germination is faster and much better in the diploid. The tetraploid is reproductively isolated from the diploid because of a much earlier flowering period. The diploid plants possess many attributes which make them uniquely adapted to the drifting sand dune habitat.     

PHOTOSYNTHESIS IN THE ANOMALOUS SECONDARY WOOD OF ATRIPLEX CONFERTIFOLIA STEMS

The anomalous secondary wood of A triplex confertifolia stems consists of vascular strands of xylem, phloem, and parenchyma embedded in fiberous conjunctive tissue. The included parenchyma contains chloroplasts and is capable of photosynthesis, as measured by¹⁴CO₂ uptake by wood in the light.     

EVOLUTIONARY STUDIES OF ATRIPLEX: ADAPTIVE PRODUCTS FROM THE NATURAL HYBRID, 6N A. TRIDENTATA x 4N A. CANESCENS

Much of the variation in hexaploid Atriplex tridentata appears to have come from tetraploid A. canescens by introgression. Among the recombinations, three types appear to have become established as new, adaptive, hexaploid derivatives. One of these is a robust, woody form near Knolls, Utah, another is a widespread, low-growing, shrubby form in Lander County, Nevada, the other is an upright bushy, canescens-like form near Grantsville, Utah.     

CHROMOSOME RACES IN CLAYTONIA LANCEOLATA (PORTULACACEAE)

Chromosome numbers of n = 8, 12, and 16 were determined for 11 populations of Claytonia lanceolata occurring in the southwestern Rocky Mountains of Utah. No evidence of the wide infra-populational variation of chromosome numbers known in the related eastern species, C. virginica, was observed. The chromosome numbers in C. lanceolata probably evolved from a base number of x = 8. Diploids(n = 8) apparently produced tetraploids (n = 16) of putative autoploid origin. Pairing relationships, including the presence of univalents, bivalents, and trivalents, suggest the chromosome numbers of n = 12 are triploids derived from natural hybridization between diploids and tetraploids. Higher chromosome numbers previously reported in C. lanceolata from Colorado, and presumably based on x = 12, can be explained by subsequent polyploid increases in the triploids. The diploid and tetraploid populations analyzed in this study occupy different ecological habitats. The diploids occur at lower elevations along the foothills, whereas the tetraploids are restricted to higher montane and sub-alpine elevations. The triploids were discovered at intermediate elevations.     

THE CHROMOSOME RACES OF ZINNIA JUNIPERIFOLIA

A comparative study of the distribution, habitat, morphology and cytology of diploid (n = 10) and tetraploid races of Z. juniperifolia of the subgenus Diplothrix (COMPOSITAE-Heliantheae) was carried out to elucidate their relationships. There is a positive correlation between chromosome number and many floral and vegetative characters, including pollen size. Chiasmata frequency is about 0.63 and 0.62 per chromosome in the diploid and in the tetraploid respectively. Multivalents are common in the latter. Although attempts to obtain colchicine-induced tetraploids have failed, available morphological, cytological and chromatographic evidence indicate the tetraploid may be of autoploid origin. Alternative ancestries involving other species of the subgenus are discussed. Taxonomically the tetraploid is considered a race of Z. juniperifolia.     

水貂的染色体研究

采用复制带、C带和硝酸银染色等分带技术研究了水貂的核型和带型。结果表明,2n=30,枝型为10（M）＋16（SM）＋2（A）,XX（M）。C-带显示该水貂的一些染色体的结构异染色质比较丰富,从着丝粒区域延伸到两臂上,No.5染色体着丝粒结构异染色质有些弱化;X染色体的结构异染色质较常染色体的丰富。Ag-NORs有3个,分布在No.8染色体的次缢痕区域和一条No.2染色体长臂接近着丝粒的区域。     

CHROMOSOME RACES AND STRUCTURAL HETEROZYGOSITY IN CALYCADENIA CILIOSA GREENE (ASTERACEAE)

A biosystematic study of Calycadenia ciliosa resulted in the recognition of five homoploid (n = 6) chromosome races. The cytogenetic evidence indicates that each of these races is differentiated from its nearest relative by a single reciprocal chromosome translocation, although at one point in the evolutionary history a pericentric inversion may have been a concurrent cytological event. The data also show that the chromosome phylogeny includes two instances of redundant translocation. Mean pollen stainabilities of interracial hybrids range from 16–80%. In a survey of four natural populations 30–60% of the individuals sampled were found to be structurally heterozygous for reciprocal chromosome translocations. Pericentric inversion heterozygosity was also detected in one population. Another population contained morphologically indistinguishable individuals separated by as little as 120 m that were differentiated by a minimum of four chromosome translocations. These observations were compared with similar instances in other species in an effort to determine their significance in the process of plant evolution.     

中国刺猬的染色体研究

本文采用全血培养和骨髓染色体制片法,对分布于我国南京市郊和济南市郊的刺猬染色体进行了组型、C-带、G-带和银染色的观察分析,并与东欧、西欧两种刺猬比较,它们之间的核型及带型差异显著;又将南京、济南及金清波(1985)报道的河南新乡三地分布的刺猬进行比较,它们的核型及带型也显示出一定差异,这种多态性在分类和进化上有一定的意义。     

FEMALE FECUNDITY IN A HYBRID ZONE BETWEEN TWO CHROMOSOME RACES OF THE SCELOPORUS GRAMMICUS COMPLEX (SAURIA,PHRYNOSOMATIDAE)

Individuals of the F5 and FM2 cytotypes of the Sceloporus grammicus complex form a narrow zone of parapatric hybridization near Tulancingo, Hidalgo, Mexico. Reproductive parameters were examined among chromosomally parental and hybrid females to assess the degree to which reduced clutch size is correlated with the level of chromosomal heterozygosity. Although clutch size in the two parental groups was highly correlated with female body size, this was not the case for females with intermediate karyotypes. These females displayed increased levels of infertility manifested as smaller clutches and as inviable embryos. F₁ females produced the smallest average clutches and suffered the most precipitous fecundity loss (up to 75%). The number of heterozygous marker chromosomes and heterozygosity at chromosome 2 had significant effects on the number of viable embryos. Analysis of embryo karyotypes revealed the production of triploid offspring and an excess number of embryos heterozygous at chromosome 1. Differences in viability, among females heterozygous for the same number of chromosomes, suggest that genetic background of the female and/or sire may be an important factor in determining reproductive success.     

黑线姬鼠华北亚种染色体研究

本文采用骨髓染色体制片法,对分布于山东的黑线姬鼠华北亚种的染色体组型,C-带、G-带和银染核型进行了分析研究。其核型为2n=48=38 T+8 M+XY。X为较小的端着丝粒染色体,Y为组型中最大的染色体。几乎每个常染色体的着丝粒区都具异染色质。性染色体的异染色质丰富。No.10和No.18染色体具NOR(?)。每条染色体都显示出较清晰的G-带。同时对黑线姬鼠精母细胞的减数分裂进行了观察,并将山东标本与欧洲标本的核型进行了比较,其性染色体有显著差异。     

臭鼩染色体的研究

本文采用骨髓染色体制片法,对捕自我国浙江萧山市的臭鼩进行了组型、G-带、C-带和核仁组织区银染的观察分析。结果表明,我国臭鼩染色体数目为2n=40,组型为8(m)+2(sm)+10(st)+18(t),性染色体为,(?):X(m或sm),Y(m或sm);♀:XX(m或sm)。G-带较为丰富,每一对染色体都有其特定的带型,较易于辨别与配对。在C-带方前,4对中间着丝粒染色体与5对亚端着丝粒染色体均具有不同程度的着丝粒带,1对亚中着丝粒染色体与9对端着丝粒染色体缺乏C-带物质,性染色体具丰富的远端带及中间带.银染的结果显示,第5、12和13对染色体具银染物质。     

DYNAMICS OF A NOVEL CHROMOSOMAL POLYMORPHISM WITHIN A HYBRID ZONE BETWEEN TWO CHROMOSOME RACES OF THE SCELOPORUS GRAMMICUS COMPLEX (SAURIA,PHRYNOSOMATIDAE)

Several chromosome races of the mesquite lizard, Sceloporus grammicus complex, hybridize at localities in central Mexico. In most cases, the hybridizing populations are delineated by centric fissions at one or more of the macrochromosomes. One notable exception is the Tulancingo hybrid zone between the F5 and FM2 cytotypes. In addition to fission and/or inversion differences at chromosomes 1, 3, 4, and 6, these races differ by a complex rearrangement of chromosome 2, which carries the nucleolus-organizer region in this species. The meiotic consequences of heterozygosity at this chromosome were examined in males to assess the potential for this chromosome to contribute to the dynamics of the hybrid zone. Chromosomal analysis revealed several putative F₁ hybrids and confirmed the production of nonparental chromosomal morphologies through recombination. Pachytene analysis revealed meiotic pairing difficulties associated with chromosome 2 in males heterozygous for the parental chromosomal morphologies. Significant aneuploidy is expected because of random disjunction of the chromosome-2 elements. As a result, these males likely suffer reduced fertiliity and fitness. In contrast, males heterozygous for recombinant chromosomal morphologies displayed low levels of meiotic irregularities and presumably exhibit higher fertility than individuals heterozygous for parental morphologies. It is hypothesized that the recombinant phenotypes facilitate gene flow between the F5 and FM2 cytotypes.     

CYTOGENETIC ANALYSIS OF CHROMOSOMAL INTERMEDIATES FROM A HYBRID ZONE BETWEEN TWO CHROMOSOME RACES OF THE SCELOPORUS GRAMMICUS COMPLEX (SAURIA,PHRYNOSOMATIDAE)

Underdominance for chromosomal rearrangements is the central assumption of several models of chromosomally based speciation including the cascade model, proposed for the Sceloporus grammicus complex. Several cytotypes of the S. grammicus complex hybridize at localities in central México. A hybrid zone between two of the most chromosomally divergent races (= cytotypes) of S. grammicus (F5, 2n = 34 and FM2, 2n = 44–46) was examined to assess the meiotic effects of heterozygosity at multiple chromosomes. Meiosis was examined in males heterozygous for “simple” Robertsonian fissions at chromosomes 1, 3, 4, and 6 and/or a pericentric inversion at chromosome 4. Analysis of synaptonemal complexes and chromosomal configurations at diakinesis showed trivalent formation in fission heterozygotes and heterosynapsis (lack of reverse-loop formation) in an inversion heterozygote. Analysis of metaphase II configurations revealed primarily balanced segregation and low levels of nondisjunction regardless of chromosomal background. The lack of underdominance associated with “simple” fission heterozygosity in this narrow hybrid zone contradicts the key premise of most chromosomally based models of speciation.     

蓟属两种植物的染色体研究

本文对蓟属（Ｃｉｒｓｉｕｍ）的两个形态相似的近缘种大刺儿菜和小刺儿菜进行了染色体研究,其中后者为首次报道。观察结果表明：两个种的染色体数目均为２ｎ＝２ｘ＝３４：它们的核型是：大刺儿菜．２ｎ＝２ｘ＝３４＝２０ｍ＋１２ｓｍ＋２ｓｔ：小刺儿菜．２ｎ＝２ｘ＝３４＝２２ｍ＋１０ｋｍ（２ＳＡＴ）＋２ｓｔ。通过核型比较,认为它们是两个独立的种．而且后者比前者进化。     

ULTRASTRUCTURAL STUDIES OF RADIATION-INDUCED CHROMOSOME DAMAGE

The fine structure of radiation-induced chromosomal aberrations in Potorous tridactylis (rat kangaroo) cells was examined in situ by electron microscopy. The observations on the structure of terminal deletions (acentric fragments), anaphase bridges and "gaps," sidearm bridges, and specialized regions, such as the nucleolus organizer, are discussed in detail. Conclusions based on these observations are the following: (a) damage is physically expressed only at anaphase; (b) a gap region is composed of two subunits, each of which is about 800–1000 A in diameter and may correspond to a half-chromatid structure; (c) the ends of acentric fragments are structurally similar to normal chromosome ends, except where the break occurs in a specific region such as the secondary constriction; (d) at metaphase the fragment and the main portion of the chromosome move as a single unit to the equator, and the two units are disconnected only at the onset of anaphase; (e) sidearm bridges appear to be exchanges, involving a subchromatid unit. The interpretation of this evidence is consistent with the hypothesis that the chromosome is a multistranded structure.     

蒿属植物的染色体数目和核型研究（一）

本文报道了我国蒿属６种的染色体核型,它们的核型公式分别为：牡蒿（ＡｒｔｅｍｉｓｉａｊａｐｏｎｉｃａＴｈｕｎｂ．）２ｎ＝１８＝１２ｍ＋６ｓｍ（２ＳＡＴ）;西南牡蒿（Ａ．ｐａｒｖｉｆｌｏｒａＢｕｃｂ．－Ｈａｍ．ｅｘＲｏｘｂ．）２ｎ＝３６＝３０ｍ＋４ｓｍ＋２ｓｔ（６ＳＡＴ）;多花蒿（Ａ．ｍｙｒｉａｎｔｈａＷａｌｌ．ｅｘＢｅｓｓ．）２ｎ＝３６＝３０ｍ＋６ｓｍ：牛尾蒿（Ａ．ｄｕｂｉａＷａｌｌ．ｅｘＢｅｓｓ．）２ｎ＝３６＝２８ｍ＋８ｓｍ（２ＳＡＴ）;野艾蒿（Ａ．ｌａｖａｎｄｕｌａｅｆｏｌｉａＤＣ．）２ｎ＝５４＝４２ｍ＋１２ｓｍ;荚毛蒿（Ａ．ｖｅｌｕｔｉｎａＰａｍｐ．）２ｎ＝５４＝３６ｍ＋１８ｓｍ．