滇蜀豹子花核型及其变异研究

本文详细报道了滇蜀豹子花的核型,发现居群中存在两种细胞型,即A型和B型。A型参考核型为2n = 24＝2m(2SAT)+2sm+8st(4SAT)+12t(2SAT),其第3号两条同源染色体长臂均无居间随体：B型参考核型为2n=24＝2m(2SAT)+2sm+8st(2SAT)+12t(3SAT)+0—1b,其第3号一条同源染色体长臂紧靠着丝点处有一大而明显的居间随体,而另一条同源染色体则无,构成明显的3号染色体的结构杂合性。统计表明,居群中二者的比例近似为1A;2B。研究还发现了大量的体细胞染色体结构变异核型,表明滇蜀豹子花核型尚未趋于稳定,还处于强烈分化之中,高频率的体细胞染色体结构变异是其种内分化不可忽视的一种进化要素。     

The evolution of pathways for aromatic hydrocarbon oxidation inPseudomonas

The organisation and nucleotide sequences coding for the catabolism of benzene, toluene (and xylenes), naphthalene and biphenylvia catechol and the extradiol (meta) cleavage pathway inPseudomonas are reviewed and the various factors which may have played a part in their evolution are considered. The data suggests that the complete pathways have evolved in a modular way probably from at least three elements. The commonmeta pathway operons, downstream from the ferredoxin-like protein adjacent to the gene for catechol 2,3-dioxygenase, are highly homologous and clearly share a common ancestry. This common module may have become fused to a gene or genes the product(s) of which could convert a stable chemical (benzoate, salicylate, toluene, benzene, phenol) to catechol, thus forming the lower pathway operons found in modern strains. The upper pathway operons might then have been acquired as a third module at a later stage thus increasing the catabolic versatility of the host strains.     

Heterogeneity in the concerted evolution process of a tandem satellite array in meadow mice (Microtus)

The evolutionary history of a 160-bp tandem satellite array, originally described from Microtus chrotorrhinus and called MSAT-160, was examined in related species of arvicolid rodents by sequence analyses, quantitative dot blotting, and Southern blotting. Results indicate that MSAT-160 is present in 12 of the 20 species and subspecies of Microtus assayed, but not in species belonging to any of the eight other genera examined. DNA from each species containing MSAT-160 was digested with 12 restriction endonucleases and restriction patterns were obtained reflecting the variable extent of homogenization of any given variant in different species. For example, with MboI digestion, M. chrotorrhinus produced a type A ladder pattern where most monomers contain the restriction site, M. ochrogaster generated a type B pattern where most monomers lack the site, and M. agrestis yielded a pattern intermediate between the A and B types. Further, dot blotting revealed copy-number differences between species. These findings indicate that changes in the periodic structure and amount of satellite DNA have occured since these species last shared a common ancestor. In addition, various species-pacific patterns were documented, illustrating that mechanism other than genomewide homogenization, such as stochastic mutation, out-of-register crossing over, deletion, and random amplification also play a role in structuring tandem arrays. Stochastic mutation and homogenization rates in satellite DNA, levels of species diversity, and magnitudes of chromosomal divergence differ significantly in Microtus, Mus, and Ctenomys, the three rodent lineages examined.     

Evolutionary study of multigenic families mapping close to the human MHC class I region

Summary During a search for novel coding sequences within the human MHC class I region (chromosome 6p21.3), we found an exon (named B30-2) coding for a 166-amino-acid peptide which is very similar to the C-terminal domain of several coding sequences: human 52-kD Sjögren's syndrome nuclear antigen A/Ro (SS-A/Ro) and ret finger protein (RFP), Xenopus nuclear factor 7 (XNF7), and bovine butyrophilin. The first three of these proteins share similarities over the whole length of the molecule whereas butyrophilin is similar in the C-terminal domain. The N-terminal domain of butyrophilin is similar to rat myelin/oligodendrocyte glycoprotein (MOG) and chicken B blood group system (B-G) protein. These domains are components of a new subfamily of the immunoglobulin superfamily (IgSF). Butyrophilin is thus a mosaic protein composed of the MOG/B-G Ig-like domain and the C-terminal domain of 52-kD SS-A/Ro, RFP, and XNF7 (1330-2-like domain). Moreover, in situ hybridization shows that RFP, butyrophilin, and MOG map to the human chromosome 6p2l.3-6p22 region and are thus close to the MHC class I genes. It is therefore possible that the butyrophilin gene is the product of an exon shuffling event which occurred between ancestors of the RFP and MOG genes. To our knowledge, this is the first example of the colocalization of a chimeric gene and its putative progenitors. Finally, regulatory protein T-lymphocyte 1 (Rpt-1) shares similarities with the N-terminal halves of RFP, 52-kD SS-A/Ro, and XNF7, but not with the B30-2-like domain. We show that the ancestral Rpt-l gene evolved by overprinting. Correspondence to: P. Pontarotti     

Time and biosequences

In this paper we discuss and demonstrate the importance of several factors relative to the relationship between time and evolution of biosequences. In both quantitative and qualitative measurements of the genetic distances, the compositional constraints of the nucleotide sequences play a very important role. We demonstrate that when homologous sequences significantly differ in base composition we get erratic branching order and/or wrong evaluation of the evolutionary rates. We must consider that every gene may have a different evolutionary dynamic along its sequence, generally linked to its functional constraints; this too can seriously affect its clocklike behavior. We report some cases showing how these factors can affect the quantitative measurements of the genetic distances of biosequences. Presented at the NATO Advanced Research Workshop onGenome Organization and Evolution, Spetsai, Greece, 16–22 September 1992     

Prey processing in Leurognathus marmoratus and the evolution of form, and function in desmognathine salamanders (Plethodontidae)

Function and biological role of morphological specialization in desmognathine salamanders are analysed in the light of studies of feeding in Leurognatthus marmoratus. Nine morphological features uniquely characterize the Desmognathinae as compared to its sister group, the Plethodontinae, and other salamanders: (1) heavily ossified and strongly articulated skull and mandible; (2) flat, wedgelike head profile; (3) stalked occipital condyles; (4) modified atlas; (5) modified anterior trunk vertebrae; (6) atlanto-mandibular ligaments; (7) enlarged dorsal spinal muscles; (8) enlarged quadrato-pectoralis muscles; and (9) hind limbs relatively larger than forelimbs. Dorsoventral head mobility is increased at the atlanto-occipital joint by the stalked occipital condyles which simultaneously increase the mechanical advantage of the hypertrophied axial muscles that cross the joint. During head depression the atlanto-mandibular ligaments are placed in tension. Force generated by the quadrato-pectoralis muscles is transmitted directly to the mandible, creating a powerful bite with the jaws in full occlusion. Desmognathines use an efficient static pressure system for subduing and/or killing prey items held in the jaws, not a kinetic-inertial mechanism, as previously suggested. Leurognathus exhibits a behaviour ('head-tucking') unique to desmognathines that is consistent with the static-pressure hypothesis. Several desmognathine features (1, 2, 5, 7, 9) are not explicable as adaptations for feeding; these function as locomotory specializations for burrowing, especially for wedging under rocks within and alongside streams. Desmognathines use head-tucking during such wedging and burrowing movements, thus locomotory specializations act in concert with the feeding specializations. We suggest that origin of the atlanto-mandibular ligaments can be considered a 'key innovation' in that it allowed the secondary invasion of stream habitats by adults of ancestral desmognathines.     

A cladistic analysis of Nassauvia Comm. ex Juss. (Asteraceae, Mutisieae) and related genera

FREIRE, S. E., CRISCI, J. V. & KATINAS, L., 1993. A cladistic analysis of Nassauvia Comm. ex Juss. (Asteraceae, Mutisieae) and related genera. Nassauvia and the most closely related genera Calopappus and Triptilion from the southern Andes and Patagonia of South America, form a monophyletic group diagnosed by the following synapomorphies: cypsela trichomes single two-celled, cypsela testa with strengthened cells, pollen grains spheroidal to spheroidal-oblate, colpi membrane with sexine processes, pappus bristles two to six, and pappus deciduous. Furthermore, Nassauvia, Triptilion, and Calopappus form a group with two other Andean genera, Moscharia and Polyachyrus, diagnosed by occurrence of pseudocephalia and a reduction in the number of flowers to five, three or one. A cladistic analysis of the group was undertaken using 35 characters from morphology, anatomy, and palynology. The monophyletic terminal taxa were the 38 species of Nassauvia, the genus Triptilion, the monotypic genus Calopappus, the genus Polyachyrus, and the genus Moscharia. Character polarity was based on outgroup comparison using Cephalopappus. The analysis resulted in 223 equally parsimonious cladograms, each with 70 steps and a consistency index of 0.57. A successive weighting procedure was applied, resulting in 15 cladograms with a consistency index of 0.82. Results of the cladistic analysis support most of the current systematic classification of Nassauvia, with three exceptions: (1) Nassauvia (excluding Calopappus) is paraphyletic; (2) section Masligophorus appears to be a polyphyletic group (N. pygmaea does not cluster with the remaining species of the section); (3) section Panargyrum (without N. lagascae= section Caloptilium) appears to be a paraphyletic group. The capitula arranged in cymose conflorescences in Triptilion are regarded as a primitive condition which gave rise to all stages present in Nassauvia (conflorescence spicate, pseudocephalium, capitula solitary). The capitula arranged in pseudocephalia in Moscharia and Polyachyrus are regarded as a parallel development to the pseudocephalium found in Nassauvia. Nassauvia, subgenus Strongyloma appears as the most primitive taxon, with its spicate conflorescence, whereas section Masligophorus with its solitary capitulum is thought-derived. These results correspond well with cytological data where species of the subgenus Strongyloma have n= 11 and the species of section Masligophorus are tetraploids (n = 22).     

Variation among early Homo crania from Olduvai Gorge and the Koobi Fora region

Fossils recognized as early Homo were discovered first at Olduvai Gorge in 1959 and 1960. Teeth, skull parts and hand bones representing three individuals were found in Bed I, and more material followed from Bed I and lower Bed II. By 1964, L.S.B. Leakey, P.V. Tobias, and J.R. Napier were ready to name Homo habilis. But almost as soon as they had, there was confusion over the hypodigm of the new species. Tobias himself suggested that OH 13 resembles Homo erectus from Java, and he noted that OH 16 has teeth as large as those of Australopithecus. By the early 1970s, however, Tobias had put these thoughts behind him and returned to the opinion that all of the Olduvai remains are Homo habilis. At about this time, important discoveries began to flow from the Koobi Fora region in Kenya. To most observers, crania such as KNM-ER 1470 confirmed the presence of Homo in East Africa at an early date. Some of the other specimens were problematical. A.C. Walker and R.E. Leakey raised the possibility that larger skulls including KNM-ER 1470 differ significantly from smaller-brained, small-toothed individuals such as KNM-ER 1813. Other workers emphasized that there are differences of shape as well as size among the hominids from Koobi Fora. There is now substantial support for the view that in the Turkana and perhaps also in the Olduvai assemblages, there is more variation than would be expected among male and female conspecifics. One way to approach this question of sorting would be to compare all of the new fossils against the original material from Olduvai which was used to characterize Homo habilis in 1964. A problem is that the Olduvai remains are fragmentary, and none of them provides much information about vault form or facial structure. An alternative is to work first with the better crania, even if these are from other sites. I have elected to treat KNM-ER 1470 and KNM-ER 1813 as key individuals. Comparisons are based on discrete anatomy and measurements. Metric results are displayed with ratio diagrams, by which similarity in proportions for several skulls can be assessed in respect to a single specimen selected as a standard. Crania from Olduvai examined in this way are generally smaller than KNM-ER 1470, although OH 7 has a relatively long parietal. In the Koobi Fora assemblage, there is variation in brow thickness, frontal flattening and parietal shape relative to KNM-ER 1470. These comparisons are instructive, but vault proportions do not help much with the sorting process. Contrasts in the face are much more striking. Measurements treated in ratio diagrams show that both KNM-ER 1813 and OH 24 have relatively short faces with low cheek bones, small orbits and low nasal openings. Also, they display more projection of the midfacial region, just below the nose. This is not readily interpreted to be a female characteristic, since in most hominoid primates the females tend to have flatter lower faces than the males. The obvious size differences among these individuals have usually been interpreted as sex dimorphism, but, in fact, two taxa may be sampled at Olduvai and in the Turkana basin at the beginning of the Pleistocene. One large-brained group made up of KNM-ER 1470, several other Koobi Fora specimens, and probably OH 7, can be called Homo habilis. If these skulls go with femora such as KNM-ER 1481 and the KNM-ER3228 hip, then this species is close in postcranial anatomy to Homo erectus. The other taxon, including small-brained individuals such as KNM-ER 1813 and probably OH 13, seems also to be Homo rather than Australopithecus. If the OH 62 skeleton is part of this assemblage, then the small hominids have postcranial proportions unlike those of Homo erectus. However, it is too early to point unequivocally to one or the other of these groups as the ancestors of later humans. Both differ from Homo erectus in important ways, and both need to be better understood before we can map the earliest history of the Homo clade. © 1993 Wiley-Liss, Inc.     

Evolutionary genetics of the Drosophila alcohol dehydrogenase gene-enzyme system

Evolutionary genetics embodies a broad research area that ranges from the DNA level to studies of genetic aspects in populations. In all cases the purpose is to determine the impact of genetic variation on evolutionary change. The broad range of evolutionary genetics requires the involvement of a diverse group of researchers: molecular biologists, (population) geneticists, biochemists, physiologists, ecologists, ethologists and theorists, each of which has its own insights and interests. For example, biochemists are often not concerned with the physiological function of a protein (with respect to pH, substrates, temperature, etc.), while ecologists, in turn, are often not interested in the biochemical-physiological aspects underlying the traits they study. This review deals with several evolutionary aspects of the Drosophila alcohol dehydrogenase gene-enzyme system, and includes my own personal viewpoints. I have tried to condense and integrate the current knowledge in this field as it has developed since the comprehensive review by van Delden (1982). Details on specific issues may be gained from Sofer and Martin (1987), Sullivan, Atkinson and Starmer (1990); Chambers (1988, 1991); Geer, Miller and Heinstra (1991); and Winberg and McKinley-McKee (1992).Dedicated to Professor Billy W. Geer, because of his contributions to knowledge of the biochemical genetics of Drosophila.