苔草属植物的返祖两性小穗

本文报告了大别苔(Carex dabiecnsis)和白鳞苔草(C.polyschoena)的返祖小穗。这些返祖小穗中的类型之一具有与篙草属(Kobresia)以及Schoenoxiphium属完全相似的两性结构小穗,在这一类型的小穗中,它们生有一雌花及其在上的雄花。如图所示,大别苔和白鳞苔草中第(3)类型的返祖小穗和Schoenoxiphium属以及嵩草属的第1、2类型的小穗基本上没有区别,这些返祖小穗的发现证明果胞是苔草属的真正小穗,而且可以证明现存苔草的单性小穗是起源于具两性小穗的祖先。因此,可以相信具有两性结构的返祖小穗的发现进一步揭示了苔草亚科中Schoenoxiphium属,蒿草属,钩轴莎属和苔草属之间的系统发育的亲缘关系。     

Dinner at Baby's: Werewolves,dinosaur jaws,hen's teeth,and horse toes

Occasionally traits arise that appear to be atavistic throwbacks to the remote past. How can this make evolutionary sense?     

Atavisms and the homology of hyobranchial elements in lower vertebrates

The homology of branchial arch segments in salamanders has been a matter of controversy since the last century. Many investigators term the most medial paired elements of salamander branchial arches “ceratobranchials” and the next distal paired elements “epibranchials.” This suggests that the first two segmental elements of the salamander branchial arch are not homologous with elements occupying the same position in ray-finned fishes, Latimeria, “rhipidistians,” and lungfishes, in which these bones are called hypobranchials and ceratobranchials, respectively. Three lines of evidence suggest that it is more parsimonious to interpret urodele branchial arch segments as being homologous with those of other vertebrate clades?(1) comparative osteology, (2) comparative myology, and (3) the discovery of cartilaginous structures forming a third segmental unit that we interpret as atavistic epibranchials of the branchial arch in one population of the salamander Notophthalmus viridescens. These structures possess all the defining attributes of atavisms, and illustrate the special role that atavistic features play in resolving questions of homology recognition.     

Proteromorphosis of Neospathodus (Conodonta) during the Permian–Triassic crisis and recovery

The Permian–Triassic evolution of platform conodonts (Gondolellidae) consists mainly of the development of the carina and the platform. During the sublethal environmental stress conditions subsequent to the Permian–Triassic extinction, the Wuchiapingian–Griesbachian Clarkina lineage is replaced by the primitive looking platform-lacking Dienerian–Aegean Neospathodus kummeli–Kashmirella timorensis lineage. It is assumed that, above Jinogondolella denticulata, end of the Capitanian Jinogondolella lineage, “Neospathodus” arcucristatus, an atavistic blade-like homeomorph that lacks a platform, underlies Protoclarkina crofti, of the base of the anagenetic Clarkina lineage. These primitive-looking forms are derived from their immediate ancestors by retrograde evolution, a phenomenon that has been described as proteromorphosis. Such events suggest that proteromorphosis occurs during periods of crisis, with the sudden reappearance of homeomorphic forms that are atavistic representatives of the clade. The phenomenon is further substantiated by several additional retrogradations that pace the Triassic, a period prone to such events.     

Random Amplified Polymorphic DNA Variation among and within Selected Ixora (Rubiaceae) Populations and Mutants

Random amplified polymorphic DNA (RAPD) analysis was used tostudy variation among and within selectedIxora (Rubiaceae) populationsand mutants. Six populations of I. congesta yielded identicalbanding patterns suggesting genetic uniformity of this species.However, six populations of I. coccinea varieties (three red-flowered,two yellow-flowered and one red-flowered wild-type) exhibitedinfraspecific differences in RAPD profiles. Small and largeleaves of an atavistic mutant cultivar of I. coccinea were alsosubjected to RAPD analysis. An extra band was amplified in thelarge leaves that was absent in small leaves, suggesting thatthe phenotypic alteration in this taxon is due to genetic mutationrather than epigenetic changes. Similarly, an extra band wasdetected in the white sectors of I. Variegated compared to thegreen sectors, suggesting that the shoot apical meristems ofthis cultivar exist as a genetic chimera. DNA gel blot hybridizationwas performed to confirm the specificities of selected bands.Our study indicates that differences among individuals of variouspopulations and mutants may be detected using RAPD markers.Copyright 1999 Annals of Botany Company Ixora L., variegated variety, RAPD fingerprinting, DNA gel blot, intraspecific genetic similarity, atavistic mutant.     

Regulation of destructive processes occurring in the body during senescence and in oncogenesis: A hypothesis

A hypothesis has been put forward according to which destructive processes occurring in the body during senescence and in oncogenesis are regulated by an atavistic mechanism of apical dominance described by plant physiologists. This mechanism is inherited from the first on Earth metazoans that behaved the mode of life attached to benthos and to underwater objects and were modular.     

Separase anxiety: dissolving the sister bond and more

Separase is a protease that cleaves the bonds between sister chromatids during cell division. Until now, separase was thought to be a somewhat repressed protease, cleaving only a few substrates in a very controlled fashion. New findings in this issue raise the possibility that separase has some of the atavistic impulses that characterize caspases, its more destructive relatives.     

Comparative anatomical analysis of human trisomies 13, 18, and 21: I. The forelimb

Human trisomies 13, 18, and 21 exhibit specific neuromuscular phenotypes (Pettersen and Bersu, '82) which include a high proportion of neuromuscular forelimb variations, many of which are atavistic in nature (de Beer, '58; Barash et al., '79; Aziz, '81a). In order to test the neuromuscular phenotype, examine the atavistic nature, and analyze the developmental delay of the trisomy forearm musculature, we dissected the forelimbs of five trisomy 13, ten trisomy 18, and two trisomy 21 cases. Our dissections compare favorably with the existing published trisomy cases (Opitz et al., '79; Pettersen and Bersu, '82). Additionally, we found significant differences in the stage at which developmental arrest occurred in trisomies 13 and 18 for the pectoral complex, extensor digitorum profundus, and intrinsic hand musculature. Some of these muscles, which occur normally in nonhuman primates (Cihak, '67, '69; Dunlap et al., '85), also appear briefly in normal human ontogeny (Cihak, '72), constituting further evidence for developmental delay in aneuploids. The disproportionately effected limb tissues also lend support to the evidence for some degree of autonomy in their development in normal individuals. Our observations are consistent with Shapiro's amplified developmental instability model ('83). Aneuploids may be viewed as genetic variants from which much may be learned about normal limb development, how aneuploidy affects dysmorphogenesis, and the kind of information which exists on the duplicated (or monosomic) chromosome.     

The tumor as an atavistic adaptive reaction in environmental conditions]

In sponges, coelenterates, bryozoans, and ascidians, blastogenesis associated with the formation of resting buds and resting blastogenetic structures is similar to the oncogenesis. Just as the tumours, such buds and structures: 1) when released from control of the parent organism, developed independently of the latter and cause its destruction; 2) originate due to the action of various external and internal causes; 3) are hardy to anoxia, dehydration, overcooling; 4) consist of little differentiated and de-differentiated cells. These similarities can be explained in the frame of hypothesis which considers tumours an atavistic resting structure.     

DEVELOPMENTAL MECHANISMS UNDERLYING THE FORMATION OF ATAVISMS

1. Atavisms emerge as evidence of localized modifications in development of an organ or of one of its parts. Different developmental processes can be triggered within the same organ rudiment, presumably in response to the same stimulus. We saw that that stimulus can have a genetic basis in a mutational event, which can be selected for. We also saw that atavism can be produced by experimental manipulation within developing systems -increased growth of the chick fibula, enamel production from avian ectoderm, and balancer formation in amphibians. Such atavisms are not based on heritable genetic changes. They indicate the developmental plasticity that exists within embryos and the relative ease with which development can be switched from one programme to another. 2. Examination of mutants (wingless chicks), limbless vertebrates and experimental manipulation of embryos, shows that cell death, inductive tissue interactions and altered patterns of growth are developmental mechanisms used in the formation of atavisms. 3. Differential development mechanisms can be triggered within the same organ at the same time to produce atavisms. In the guinea pig, formation of atavistic digit V involves prolongation of growth of metatarsal V whereas formation of atavistic digit I involves development of a new metatarsal I. 4. Secondary functional modifications ensure that the atavism is integrated with the other components of the functional unit, as illustrated by extra digits in horses or guinea pigs and fibulae in birds. Atavistic 2nd and 4th digits in horses arise by continued growth of their primordia. A consequent reduction in the growth rate of digit 3, the normal single functional digit, enables all three digits to attain approximately equal lengths and so potentially to function. The altered functional load transmitted to the limbs results in secondary but correlated alterations in muscles and skeletal elements in other portions of the limbs. The fact that embryonic digit 2 normally develops to a more advanced state than digit 4 explains why digit 2 more often develops atavistically, for if variation in growth rate is the basis for the atavistic digit, digit 2 has an advantage over digit 4. 5. Atavisms should not be an embarrassment to the evolutionary biologist. They are the outward and visible sign of a hidden potential for morphology change possessed by all organisms. Neither basic capacity to form the organ nor patterning information is lost. Modification of components of inductive tissue interactions helps to explain how organs are lost during evolution (also see Regal, 1977); retention of the basic mechanism explains how structures can be revived as atavisms (also see Rachootin & Thomson, 1981). Frequency of atavisms thus provides an indication of the degree of modification or loss of the underlying developmental programme.     

Phylogenetic memory of developing mammalian dentition

Structures suppressed during evolution can be retraced due to atavisms and vestiges. Atavism is an exceptional emergence of an ancestral form in a living individual. In contrast, ancestral vestige regularly occurs in all members of an actual species. We surveyed data about the vestigial and atavistic teeth in mammals, updated them by recent findings in mouse and human embryos, and discussed their ontogenetic and evolutionary implications. In the mouse incisor and diastema regions, dental placodes are transiently distinct being morphologically similar to the early tooth primordia in reptiles. Two large vestigial buds emerge in front of the prospective first molar and presumably correspond to the premolars eliminated during mouse evolution. The incorporation of the posterior premolar vestige into the lower first molar illustrates the putative mechanism of evolutionary disappearance of the last premolar in the mice. In mutant mice, devious development of the ancestral tooth primordia might lead to their revivification and origin of atavistic supernumerary teeth. Similarity in the developmental schedule between three molars in mice and the respective third and fourth deciduous premolar and the first molar in humans raises a question about putative homology of these teeth. The complex patterning of the vestibular and dental epithelium in human embryos is reminiscent of the pattern of "Zahnreihen" in lower vertebrates. A hypothesis was presented about the developmental relationship between the structures at the external aspect of the dentition in mammals (oral vestibule, pre-lacteal teeth, paramolar cusps/teeth), the tooth glands in reptiles, and the earliest teeth in lower vertebrates.     

Regeneration of Haller's sensory organ in two species of hard ticks of the genus Haemaphysalis (Acari: Ixodidae)

A study of Haller's organ regeneration in nymphs and adults of Haemaphysalis turturis and parthenogenetic females of H. longicornis, from which the forelegs had been amputated during the previous instar, revealed structural changes in regenerated organs. The adult regenerates reestablished atavistic structural features, while the nymphal regenerates retained larval features, which is typical of regenerates of two other genera examined previously (Ixodes and Hyalomma). Data on regeneration of Haller's sensory organ testify to an ancient character of the genus, standing closely to the base of the phylogenetic tree of hard ticks.     

Supernumerary molars in anthropoidea,adapidae, and Archaeolemur: Implications for primate dental homologies

The model of primate dental homologies and development recently proposed by Schwartz ('75, '78) is re-evaluated in view of documented exceptions to his account of postcanine supernumerary teeth in both anthropoids and prosimians. Schwartz concluded that catarrhines and living indriids retain only two true molars in each dental quadrant. As many as six molars on one side of the jaw can develop in rare instances in catarrhines, and supernumerary molars are also known for a wide range of other primates, including Cebidae, Adapidae, and subfossil Indriidae. Polydontia cannot be explained exclusively by atavistic development. More convincing explanations regard supernumerary teeth as the result of excessive growth of the dental lamina or localized twinning of tooth buds during early development. Conventional dental formulae of catarrhines and indriids including three permanent molars remain the most plausible.     

Specific features of the external morphology of starry flounder Platichthys stellatus at atavism in the body color

An analysis of the morphology of starry flounder Platichthys stellatus, completely pigmented from both sides, was performed. It considerably differs from common individuals (pigmented from only one side) by several characters. The right eye in the atavistic specimen was located on the upper part of the head, and there was a deep notch between the eye and the dorsal fin. The differences between body proportions and sizes of fins in bilaterally pigmented and common flounder specimens were also detected. Based on an analysis of the data obtained, opinions concerning the causes of these morphological deviations in bilaterally pigmented flounder individuals are provided.     

Monocotylar seedlings: a review of evidence supporting an origin by fusion

The structure and growth of the seedling, as described in the literature, is discussed for both monocotylar Dicotyledones and for Monocotyledones (several Apiaceae, Ranunculaceae and Gesneriaceae; species of Combretum, Peperomia, Cyclamen, Corydalis and Pinguicula , and also anomalous syncotylar examples of Impatiens, Butomus, Agave, Cordyline, Dioscorea, Pitcairnia and Costus ). In all examples the single cotyledon appears to be derived, phylogenetically, from an ancestral pair which has fused, often with no remaining trace of their double origin, to give an apparatus which buries the unexpanded plumule and radicle deeply in the ground early in germination. No evidence for suppression of one of the ancestral pair of cotyledons was found in any species.
The syncotylar theory of the origin of monocotyledons of Sargant (1903) is supported and extended to apply to all known monocotylar species. The anomalous appearance of paired cotyledons in Agapanthus and Cyrtanthus apparently results from twinning, as known in Sinapis and Centranthus , not to atavistic reformation.     

Atavisms: medical, genetic, and evolutionary implications

Traits expected to be lost in the evolutionary history of a species occasionally reappear apparently out of the blue. Such traits as extra nipples or tails in humans, hind limbs in whales, teeth in birds, or wings in wingless stick insects remind us that certain genetic information is not completely lost, but can be reactivated. Atavisms seem to violate one of the central evolutionary principles, known as Dollo's law, that "an organism is unable to return, even partially, to a previous stage already realized in the ranks of its ancestors." Although it is still not clear what triggers and controls the reactivation of dormant traits, atavisms are a challenge to evolutionary biologists and geneticists. This article presents some of the more striking examples of atavisms, discusses some of the currently controversial issues like human quadrupedalism, and reviews the progress made in explaining some of the mechanisms that can lead to atavistic features.     

Darwinian criminality theory: a tragic chapter in history.

Darwinists once believed that individual human beings occasionally reverted, both physically and mentally, to a prehuman stage of evolutionary development. This person was called an atavistic criminal type. As a result of this belief, the focus in Darwinian criminology was on identifying the criminal type who should be imprisoned permanently to protect society, even if the particular offense committed was minor. Conversely, if a "non-criminal type" committed even a serious offense, it was an aberration, and therefore, they concluded, imprisonment would serve no purpose. Darwinian criminologists believed punishment must fit the criminal and not the crime. Criminologists widely adopted this theory to explain crime and, as a result, it influenced both public opinion and official policy. The "criminal physical type" stereotype is still very much with us, even though the theory of evolutionary throwbacks (atavisms) as a causative factor in criminality was empirically disproved decades ago.     

DNA synthesis,reduction, and elimination during life cycles of the eimeriine coccidian, Eimeria tenella and the haemogregarine, Hepatozoon domerguei

The occurrence of zygotic nuclear reduction and the haploid state of postzygotic stages were demonstrated in Eimeria tenella (Coccidia, Eimeriina) and Hepatozoon domerguei (Coccidia, Adeleina) by direct measurement of DNA by microdensitometry. Nuclear divisions, which were probably mitotic, were demonstrated in the macrogametocytes of a species of Hepatocystis (Coccidia, Haemosporina). The macrogametocytes of E. tenella were Feulgen negative but gametocytes of both sexes of H. domerguei were Feulgen positive and had DNA values estimated at about twice the haploid amount. This latter finding was interpreted as DNA synthesis preceding a maturation process which involved mitotic divisions and led to micro- and macrogamete formation. In macrogametogenesis this may be an atavistic trait, recapitulating the evolution of sexuality or a method for increased RNA synthesis.     

Regeneration of Haller's sensory organ in the tickIxodes ricinus L.

Amputation of legs in nymphs of ticks, obtained from the first laboratory generation, resulted in regeneration of the legs after moulting to adults. Haller's sensory organ on the upper surface of each foreleg tarsus was significantly modified following regeneration. Haller's organ in non-amputated legs of the experimental ticks remained unchanged, being comparable to controls.Pored olfactory sensilla in the anterior pit, in a capsule and on a distal knoll usually increased in number, as well as grooved, thin and conical sensilla. Bordering gustatory and double-walled postcapsular sensilla either decreased or increased in number. All additional sensilla were consistent in their location. Form of the anterior pit and capsule's aperture also deeply changed after the regeneration. The authors distinguish this changes as atavistic.No correlation between changes in different parts of the organ were found.A phenomenon of induction was discovered in our study: if a distal part of tick's gnathosoma was amputated together with the left foreleg, Haller's organ in the right, untreated leg possessed the same changes after moulting as the regenerated organ in the previously amputated left foreleg.     

Taxon mapping exemplifies punctuated equilibrium and atavistic saltation

Two or more exemplars of the same taxon forming a nonmonophyletic group on a molecular tree may be viewed as representing surviving populations of a deep shared ancestral taxon, and if different species of the same genus, then theoretically phenotypically static remnants of punctuated equilibrium. That taxon may be mapped on a molecular cladogram and evolutionarily resolved at the taxon level inclusive of all exemplars. The technique for mapping taxa on a molecular tree, termed here caulistics, is much like mapping traits but recovers macroevolutionary information at the taxon level. All lineages arising from the mapped taxon are its direct descendants. Mapped taxa superimposed or overlapping may reveal packaged adaptive traits. When a mapped taxon is well split by another mapped taxon on a molecular tree, atavistic saltation based on triggering an epigenetically retained trait complex is a theoretical explanation. Caulistics combines traditional taxonomy and molecular phylogenetics to reveal previously unknown aspects of the macroevolutionary past.