共查询到20条相似文献,搜索用时 15 毫秒
1.
A. V. Martynov 《Biology Bulletin》2012,39(5):393-401
Ontogeny is considered as a process that allows linking two key components of biological systematics in an objective way: historically independent character attribution and phylogeny. It is proposed to designate the general theory that unifies the ??static?? traditional taxonomy and the dynamic evolutionary process on the basis of ontogenetic transformation of shapes of organisms as the ontogenetic systematics. One of the important practical applications is a new model of the evolution of bilaterian animals, which supposes an ancestral status of clonal asexual reproduction and its multiple reduction in different lines of Bilatera. 相似文献
2.
A. V. Martynov 《Moscow University Biological Sciences Bulletin》2010,65(4):145-147
Over the past decade, the morphological paradigm in the traditional field of systematics and evolutionary biology has been
challenged and has actually been replaced by the molecular paradigm. In this study, an attempt is made to evaluate the current
state of the problem concerning the relationship between the fundamentals of systematics and evolution. It is shown that the
interrelatedness of evolution, ontogeny, systematics, and phylogenetics is deeply underestimated in the approaches used in
recent research. Instead of considering the above fields of biology as separate categories, as is common in recent studies,
the synthetic concept of ontogenetic systematics is proposed, which unifies them into an integrated process. 相似文献
3.
DAVID M. WILLIAMS ROBERT W. SCOTLAND STEPHEN BLACKMORE 《Biological journal of the Linnean Society. Linnean Society of London》1990,39(2):99-108
Much recent literature focuses on whether ontogenetic information can be used as a direct criterion for determining the polarity of character trasformations in systematic analysis. This paper reviews the relevant literature and concludes that the ontogenetic criterion is dependent on parsimony rather than the sequence observed during ontogeny. It is not, therefore, based on the discredited arguments of recapitulation. From the perspective of phyologenetic systematics the ontogenetic criterion is a valid means of polarizing character transformations that represents a special case of a broader methodology involving parsimony. The alternative perspective perspective of patttern cladistics holds that polarity should be contained within the data and not imposed upon it. Thus, ontogeny is not required to polarize characters, but ontogenetic information can generate unequivocal character interpretations in terms of the relative generality of related attributes, and in the sense that absence precedes presence. Furthermore, ontogeny is central to systematics, providing empirical evidence of character transformation, information on the whole life cycle and an escape from systematics being teleologically related to phylogenetic inference and the theory of evolution. 相似文献
4.
Phylogenetic interpretation of ontogenetic change: sorting out the actual and artefactual in an empirical case study of centrarchid fishes 总被引:1,自引:0,他引:1
PAULA M. MABEE 《Zoological Journal of the Linnean Society》1993,107(3):175-291
Hypothesized relationships between ontogenetic and phylogenetic change in morphological characters were empirically tested in centrarchid fishes by comparing observed patterns of character development with patterns of character evolution as inferred from a representative phylogenetic hypothesis. This phylogeny was based on 56–61 morphological characters that were polarized by outgroup comparison. Through these comparisons, evolutionary changes in character ontogeny were categorized in one of eight classes (terminal addition, terminal deletion, terminal substitution, non-terminal addition, non-terminal deletion, non-terminal substitution, ontogenetic reversal and substitution). The relative frequencies of each of these classes provided an empirical basis from which assumptions underlying hypothesized relationships between ontogeny and phylogeny were tested. In order to test hypothesized relationships between ontogeny and phylogeny that involve assumptions about the relative frequencies of terminal change (e.g. the use of ontogeny as a homology criterion), two additional phylogenies were generated in which terminal addition and terminal deletion were maximized and minimized for all characters. Character state change interpreted from these phylogenies thus represents the maxima and minima of the frequency range of terminal addition and terminal deletion for the 8.7 × 1036 trees possible for centrarchids. It was found for these data that terminal change accounts for c. 75% of the character state change. This suggests either that early ontogeny is conserved in evolution or that interpretation and classification of evolutionary changes in ontogeny is biased in part by the way that characters are recognized, delimited and coded. It was found that ontogenetic interpretation is influenced by two levels of homology decision: an initial decision involving delimitation of the character (the ontogenetic sequence), and the subsequent recognition of homologous components of developmental sequences. Recognition of phylogenetic homology among individual components of developmental sequences is necessary for interpretation of evolutionary changes in ontogeny as either terminal or non-terminal. If development is the primary criterion applied in recognizing individual homologies among parts of ontogenetic sequences, the only possible interpretation of phylogenetic differences is that of terminal change. If homologies of the components cannot be ascertained, recognition of the homology of the developmental sequence as a whole will result in the interpretation of evolutionary differences as substitutions. Particularly when the objective of a study is to discover how ontogeny has evolved, criteria in addition to ontogeny must be used to recognize homology. Interpretation is also dependent upon delimitation within an ontogenetic sequence. This is in part a function of the way that an investigator ‘sees’ and codes characters. Binary and multistate characters influence interpretation differently and predictably. The use of ontogeny for determining phylogenetic polarity as previously proposed rests on the assumptions that ancestral ontogenies are conserved and that character evolution occurs predominantly through terminal addition. It was found for these data that terminal addition may comprise a maximum of 51.9% of the total character state change. It is concluded that the ontogenetic criterion is not a reliable indicator of phylogenetic polarity. Process and pattern data are collected simultaneously by those engaged in comparative morphological studies of development. The set of alternative explanatory processes is limited in the process of observing development. These form necessary starting points for the research of developmental biologists. Separating ‘empirical’ results from interpretational influences requires awareness of potential biases in the course of character selection, coding and interpretation. Consideration of the interpretational problems involved in identifying and classifying phylogenetic changes in ontogeny leads to a re-evaluation of the purpose, usefulness and information conveyed by the current classification system. It is recommended that alternative classification schemes be pursued. 相似文献
5.
Pavlinov IIa 《Zhurnal obshche? biologii》2004,65(4):334-366
Evolutionary idea is the core of the modern biology. Due to this, phylogenetics dealing with historical reconstructions in biology takes a priority position among biological disciplines. The second half of the 20th century witnessed growth of a great interest to phylogenetic reconstructions at macrotaxonomic level which replaced microevolutionary studies dominating during the 30s-60s. This meant shift from population thinking to phylogenetic one but it was not revival of the classical phylogenetics; rather, a new approach emerged that was baptized The New Phylogenetics. It arose as a result of merging of three disciplines which were developing independently during 60s-70s, namely cladistics, numerical phyletics, and molecular phylogenetics (now basically genophyletics). Thus, the new phylogenetics could be defined as a branch of evolutionary biology aimed at elaboration of "parsimonious" cladistic hypotheses by means of numerical methods on the basis of mostly molecular data. Classical phylogenetics, as a historical predecessor of the new one, emerged on the basis of the naturphilosophical worldview which included a superorganismal idea of biota. Accordingly to that view, historical development (the phylogeny) was thought an analogy of individual one (the ontogeny) so its most basical features were progressive parallel developments of "parts" (taxa), supplemented with Darwinian concept of monophyly. Two predominating traditions were diverged within classical phylogenetics according to a particular interpretation of relation between these concepts. One of them (Cope, Severtzow) belittled monophyly and paid most attention to progressive parallel developments of morphological traits. Such an attitude turned this kind of phylogenetics to be rather the semogenetics dealing primarily with evolution of structures and not of taxa. Another tradition (Haeckel) considered both monophyletic and parallel origins of taxa jointly: in the middle of 20th century it was split into phylistics (Rasnitsyn's term; close to Simpsonian evolutionary taxonomy) belonging rather to the classical realm, and Hennigian cladistics that pays attention to origin of monophyletic taxa exclusively. In early of the 20th century, microevolutionary doctrine became predominating in evolutionary studies. Its core is the population thinking accompanied by the phenetic one based on equation of kinship to overall similarity. They were connected to positivist philosophy and hence were characterized by reductionism at both ontological and epistemological levels. It led to fall of classical phylogenetics but created the prerequisites for the new phylogenetics which also appeared to be full of reductionism. The new rise of phylogenetic (rather than tree) thinking during the last third of the 20th century was caused by lost of explanatory power of population one and by development of the new worldview and new epistemological premises. That new worldview is based on the synergetic (Prigoginian) model of development of non-equilibrium systems: evolution of the biota, a part of which is phylogeny, is considered as such a development. At epistemological level, the principal premise appeared to be fall of positivism which was replaced by post-positivism argumentation schemes. Input of cladistics into new phylogenetics is twofold. On the one hand, it reduced phylogeny to cladistic history lacking any adaptivist interpretation and presuming minimal evolution model. From this it followed reduction of kinship relation to sister-group relation lacking any reference to real time scale and to ancestor-descendant relation. On the other hand, cladistics elaborated methodology of phylogenetic reconstructions based on the synapomorphy principle, the outgroup concept became its part. The both inputs served as premises of incorporation of both numerical techniques and molecular data into phylogenetic reconstruction. Numerical phyletics provided the new phylogenetics with easily manipulated algorithms of cladogram construing and thus made phylogenetic reconstructions operational and repetitive. The above phenetic formula "kinship = similarity" appeared to be a keystone for development of the genophyletics. Within numerical phyletics, a lot of computer programs were elaborated which allow to manipulate with evolutionary scenario during phylogenetic reconstructions. They make it possible to reconstruct both clado- and semogeneses based on the same formalized methods. Multiplicity of numerical approaches indicates that, just as in the case of numerical phenetics, choice of adequate method(s) should be based on biologically sound theory. The main input of genophyletics (= molecular phylogenetics) into the new phylogenetics was due to completely new factology which makes it possible to compare directly such far distant taxa as prokaryotes and higher eukaryotes. Genophyletics is based on the theory of neutral evolution borrowed from microevolutionary theory and on the molecular clock hypothesis which is now considered largely inadequate. The future developments of genophyletics will be aimed at clarification of such fundamental (and "classical" by origin) problems as application of character and homology concepts to molecular structures. The new phylogenetics itself is differentiated into several schools caused basically by diversity of various approaches existing within each of its "roots". Cladistics makes new phylogenetics splitted into evolutionary and parsimonious ontological viewpoints. Numerical phyletics divides it into statistical and (again) parsimonious methodologies. Molecular phylogenetics is opposite by its factological basis to morphological one. The new phylogenetics has significance impact onto the "newest" systematics. From one side, it gives ontological status back to macrotaxa they have lost due to "new" systematics based on population thinking. From another side, it rejects some basical principles of classical phylogenetic (originally Linnean) taxonomy such as recognitions of fixed taxonomic ranks designated by respective terms and definition of taxic names not by the diagnostic characters but by reference to the ancestor. The latter makes the PhyloCode overburdened ideologically and the "newest" systematics self-controversial, as concept of ancestor has been acknowledged non-operational from the very beginning of cladistics. Relation between classical and new phylogenetics is twofold. At the one hand, general phylogenetic hypothesis (in its classical sense) can be treated as a combination of cladogenetic and semogenetic reconstructions. Such a consideration is bound to pay close attention to the uncertainty relation principle which, in case of the phylogenetics, means that the general phylogenetic hypothesis cannot be more certain than any of initial cladogenetic or semogenetic hypotheses. From this standpoint, the new phylogenetics makes it possible to reconstruct phylogeny following epistemological principle "from simple to complex". It elaborates a kind of null hypotheses about evolutionary history which are more easy to test as compared to classical hypotheses. Afterward, such hypotheses are possible to be completed toward the classical, more content-wise ones by adding anagenetic information to the cladogenetic one. At another hand, reconstructions elaborated within the new phylogenetics could be considered as specific null hypotheses about both clado- and semogeneses. They are to be tested subsequently by mean of various models, including those borrowed from "classical" morphology. The future development of the new phylogenetics is supposed to be connected with getting out of plethora of reductionism inherited by it from population thinking and specification of object domain of the phylogenetics. As the latter is a part of an evolutionary theory, its future developments will be adjusted with the latter. Lately predominating neodarwinism is now being replaced by the epigenetic evolutionary theory to which phylistics (one of the modern versions of classical phylogenetics) seems to be more correspondent. 相似文献
6.
The magnitude and ontogenetic patterns of intraspecific variation can provide important insights into the evolution and development of organisms. Understanding the intraspecific variation of organisms is also a key to correctly pursuing studies in major fields of palaeontology. However, intraspecific variation has been largely overlooked in ectocochleate cephalopods, particularly nautilids. Furthermore, little is known regarding the evolutionary pattern. Here, we present morphological data for the Cretaceous nautilid Eutrephoceras dekayi (Morton) and the modern nautilid Nautilus pompilius Linnaeus through ontogeny. The data are used to describe conch morphology and to elucidate the evolutionary patterns of intraspecific variation. We discovered a similar overall pattern of growth trajectories and the presence of morphological changes at hatching and maturity in both taxa. We also found that intraspecific variation is higher in earlier ontogeny than in later ontogeny in both taxa. The high variation in earlier ontogeny may imply increased flexibility in changing the timing of developmental events, which probably played an important role in nautilid evolution. We assume that the decrease in variation in later ontogeny reflects developmental constraints. Lastly, we compared the similarity/dissimilarity of ontogenetic patterns of variation between taxa. Results reveal that the similarity/dissimilarity of the ontogenetic pattern differs between E. dekayi and N. pompilius. We conclude that this shift in the ontogenetic pattern of variation may be rooted in changes in the developmental programme of nautilids through time. We propose that studying ontogenetic patterns of intraspecific variation can provide new insights into the evolution and development of organisms. 相似文献
7.
M. A. Shishkin 《Paleontological Journal》2012,46(4):331-342
Morphogenetic mechanisms form an integrity purposed to secure the due course of ontogeny towards the adult norm. This purposefulness is a principal feature of living organization that requires an explanation. Each step in evolution is a compelled reorganization of the ontogenetic system towards a new ultimate goal (system??s equilibrium state), i.e., a new norm. An increase in stability of realization of the latter, caused by natural selection, results in progressive remodeling of ontogeny of the evolutionary novelty which spreads in succeeding life cycles towards the earlier stages. As a result, the difference between current ontogenetic record of the novelty and the ancestral developmental pattern tends to change more and more from the prolonging (recapitulative) to divergent one, corresponding to Baer??s law. In the fossil record, the changes caused by these stabilizing processes result in a number of manifestations, such as initially labile expression of new acquisitions, the remodeling of their morphogenesis with time and the predominant maintenance of ancestral traits in late ontogeny of the closest descendants. 相似文献
8.
Maglia Anne M.; Pugener L. AnalIa; Trueb Linda 《Integrative and comparative biology》2001,41(3):538-551
Hypotheses of relationships are critical to describing and understandingpatterns of evolution within groups of organisms. But rarelyhas a comparative, historical approach been employed to studydevelopmental change, particularly among anurans. A recent resurgenceof interest in collecting basic ontogenetic information providesus with the opportunity to compare ontogenetic trajectoriesin a phylogenetic framework. Larval skeletons and osteologicaldevelopment were examined for 22 taxa and compared to two hypothesesof relationshipsthat of Cannatella, and one proposedherein based on 41 morphological characters from larvae and62 from adults. Larval characters were mapped on the alternatecladograms using the ACCTRAN optimization criterion. Severallarval features are highly conserved among some anurans, suggestingthat there is some level of canalization of morphology earlyin ontogeny. In contrast, a number of morphologies vary amonggroups, supporting the fact that there have been major evolutionarymodifications to anuran larval morphologies early in ontogenyand in the early evolutionary history of anurans. 相似文献
9.
Agnese Lanzetti Roberto Portela-Miguez Vincent Fernandez Anjali Goswami 《Evolution & development》2023,25(4-5):257-273
Ontogeny plays a key role in the evolution of organisms, as changes during the complex processes of development can allow for new traits to arise. Identifying changes in ontogenetic allometry—the relationship between skull shape and size during growth—can reveal the processes underlying major evolutionary transformations. Baleen whales (Mysticeti, Cetacea) underwent major morphological changes in transitioning from their ancestral raptorial feeding mode to the three specialized filter-feeding modes observed in extant taxa. Heterochronic processes have been implicated in the evolution of these feeding modes, and their associated specialized cranial morphologies, but their role has never been tested with quantitative data. Here, we quantified skull shapes ontogeny and reconstructed ancestral allometric trajectories using 3D geometric morphometrics and phylogenetic comparative methods on sample representing modern mysticetes diversity. Our results demonstrate that Mysticeti, while having a common developmental trajectory, present distinct cranial shapes from early in their ontogeny corresponding to their different feeding ecologies. Size is the main driver of shape disparity across mysticetes. Disparate heterochronic processes are evident in the evolution of the group: skim feeders present accelerated growth relative to the ancestral nodes, while Balaenopteridae have overall slower growth, or pedomorphosis. Gray whales are the only taxon with a relatively faster rate of growth in this group, which might be connected to its unique benthic feeding strategy. Reconstructed ancestral allometries and related skull shapes indicate that extinct taxa used less specialized filter-feeding modes, a finding broadly in line with the available fossil evidence. 相似文献
10.
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12.
Flexicalymene retrorsa minuens from the uppermost 3 m of the Waynesville Formation of the Cincinnatian Series (Upper Ordovician) of North America lived approximately 445 Ma and exhibited marked reduction in maximum size relative to its stratigraphically subjacent sister subspecies, Flexicalymene retrorsa retrorsa. Phylogenetic analysis is consistent with the notion that F. retrorsa retrorsa was the ancestor of F. retrorsa minuens. F. retrorsa minuens has been claimed to differ from F. retrorsa retrorsa"in size alone," and thus presents a plausible example of global paedomorphic evolution in trilobites. Despite strong similarity in the overall form of the two subspecies, F. retrorsa minuens is neither a dwarf nor a simple progenetic descendant of F. retrorsa retrorsa. More complex patterns of global heterochronic paedomorphosis, such as a neotonic decrease in the rate of progress along a common ontogenetic trajectory with respect to size, coupled with growth cessation at a small size, "sequential" progenesis, or non-uniform changes in the rate of progress along a shared ontogenetic trajectory with respect to size, can also be rejected. Rather, differences between these subspecies are more consistent with localized changes in rates of character development than with a global heterochronic modification of the ancestral ontogeny. The evolution of F. retrorsa minuens from F. retrorsa retrorsa was largely dominated by modifications of the development of characters already evident in the ancestral ontogeny, not by the origin of novel structures. Factors promoting size reduction in F. retrorsa minuens appear to have been specific to this subspecies, because other co-occurring taxa, including other trilobite species, do not show marked differences in mean size. 相似文献
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14.
Kieran P. McNulty 《Evolutionary biology》2012,39(4):488-498
Evolutionary developmental biology is quickly transforming our understanding of how lineages evolve through the modification of ontogenetic processes. Yet, while great strides have been made in the study of neontological forms, it is much more difficult to apply the principles of evo-devo to the miserly fossil record. Because fossils are static entities, we as researchers can only infer evolution and development by drawing connections between them. The choices of how we join specimens together??juveniles to adults to study ontogeny, taxon to taxon to study evolution??can dramatically affect our results. Here, I examine paedomorphism in the fossil hominin species Australopithecus africanus. Using extant African apes as proxies for ancestral hominin morphology, I demonstrate that Sts 71 is most similar to a sub-adult African ape, suggesting that A. africanus is paedomorphic relative to the presumed ancestral form. I then plot ontogenetic size and shape in extant great apes, humans, and A. africanus in order to assess patterns of ontogenetic allometry. Results indicate that ontogenetic allometry in A. africanus, subsequent to M1 occlusion is similar to that in modern humans and bonobos; gorillas, chimpanzees, and orangutans share a different pattern of size-shape relationship. Combined with results from the analysis of paedomorphism plus knowledge about the developmental chronologies of this group, these findings suggest that paedomorphism in A. africanus arises relatively early in ontogeny. 相似文献
15.
Identification of the ontogenetic status of an extinct organism is complex, and yet this underpins major areas of research, from taxonomy and systematics to ecology and evolution. In the case of the non-avialan dinosaurs, at least some were reproductively mature before they were skeletally mature, and a lack of consensus on how to define an ‘adult’ animal causes problems for even basic scientific investigations. Here we review the current methods available to determine the age of non-avialan dinosaurs, discuss the definitions of different ontogenetic stages, and summarize the implications of these disparate definitions for dinosaur palaeontology. Most critically, a growing body of evidence suggests that many dinosaurs that would be considered ‘adults’ in a modern-day field study are considered ‘juveniles’ or ‘subadults’ in palaeontological contexts. 相似文献
16.
《Lichenologist (London, England)》1998,30(4-5):489-500
The use of ascoma ontogeny in the systematics of lichenized asco-mycetes is reviewed briefly. Two recently studied examples are discussed to illustrate the use of ontogenetic studies to discover phylogenetic relationships. As one example, theAgyriaceaewas mainly circumscribed by the ascus type and included diverse genera.Xylographais characterized by lirelliform apothecia. However, the ascoma development shares the ontogenetic pattern observed inTrapeliaand its placement in the family was confirmed. In contrast,Anamylopsoraexhibited a substantially different apothecial development and was separated as a family of its own. As a second example, theCandelariaceaeis based on chemical characters. With the detection of pulvinic acid derivatives also in the genusLecanora, the distinction of theCandelariaceaeandLecanoraceaebecame doubtful. Therefore, the ascoma ontogeny was employed to evaluate this classification and is illustrated here in detail forCandelaria fibrosa. The substantial similarity of the ascoma development found in both families suggests that both might be better united. Finally, a general discussion of the significance of ontogenetic characters in lichen taxonomy is included. 相似文献
17.
Pigliucci M 《American journal of botany》1997,84(7):887-895
While phenotypic plasticity has been the focus of much research and debate in the recent ecological and evolutionary literature, the developmental nature of the phenomenon has been mostly overlooked. A developmental perspective must ultimately be an integral part of our understanding of how organisms cope with heterogeneous environments. In this paper I use the rapid cycling Arabidopsis thaliana to address the following questions concerning developmental plasticity. (1) Are there genetic and/or environmental differences in parameters describing ontogenetic trajectories? (2) Is ontogenetic variation produced by differences in genotypes and/or environments for two crucial traits of the reproductive phase of the life cycle, stem elongation and flower production? (3) Is there ontogenetic variability for the correlation between the two characters? I found genetic variation, plasticity, and variation for plasticity affecting at least some of the growth parameters, indicating potential for evolution via heterochronic shifts in ontogenetic trajectories. Within-population differences among families are determined before the onset of the reproductive phase, while among-population variation is the result of divergence during the reproductive phase of the ontogeny. Finally, the ontogenetic profiles of character correlations are very distinct between the ecologically meaningful categories of early- and late-flowering “ecotypes” in this species, and show susceptibility to environmental change. 相似文献
18.
Richmond JQ 《Evolution & development》2006,8(6):477-490
This study uses a phylogenetic framework to explore the causes of parallelism in two North American scincid lizard assemblages: the skiltonianus and fasciatus species groups of the genus Plestiodon. Each group consists of several closely related species with conserved neonate morphology; features that distinguish species become accentuated during ontogeny, and these differences often resemble different endpoints along a developmental continuum. This continuum is believed to be an expression of the ancestral ontogeny, and has led to the hypothesis that evolutionary change in development has generated much of the observed morphological diversity. However, progress on understanding these mechanisms is limited by a lack of well-supported phylogenetic data for the fasciatus group, and for Plestiodon in general. Recent phylogenetic studies on the skiltonianus group have revealed previously undetected cases of parallelism, and raise the possibility that similar cases have yet to be discovered in the fasciatus group. Here, I estimate a phylogeny to test the monophyly of the fasciatus group and infer its relationship with other North American Plestiodon using 2537 bp from six mtDNA genes. I use the phylogeny to reconstruct the mode (graduated vs. punctuated) and direction of body size evolution, to map the evolution of two predominant color morphs, and to test whether size and color pattern evolve concertedly. The results show that the morphotypes of the traditional fasciatus group constitute good species, but that the species group is rendered paraphyletic by several geographically overlapping species that deviate from the fasciatus-like ontogeny. Body size evolution has occurred gradually and bi-directionally, and shifts to large body size have been consistently associated with the loss of the striped color pattern during ontogeny. I show that parallelism, a lack of rigorous phylogenetic analysis, and a reliance on shared ontogenetic features for predicting phylogenetic relatedness, has misled the traditional systematics of these lizards, but that general ideas concerning the role of development in their morphological evolution remain supported. I close by proposing that the processes influencing repeated phyletic patterns in the skiltonianus and fasciatus groups represent adherence to an ancestral ground state, and discuss the importance of using phylogenies for the initial characterization of evolutionary changes in development. 相似文献
19.
Systematics involves resolving both the taxonomy and phylogenetic placement of organisms. We review the advantages and disadvantages of the two kinds of information commonly used for such inferences--morphological and molecular data--as applied to the systematics of metazoan parasites generally, with special attention to the malaria parasites. The problems that potentially confound the use of morphology in parasites include challenges to consistent specimen preservation, plasticity of features depending on hosts or other environmental factors, and morphological convergence. Molecular characters such as DNA sequences present an alternative data source and are particularly useful when not all the parasite's life stages are present or when parasitaemia is low. Nonetheless, molecular data can bring challenges that include troublesome DNA isolation, paralogous gene copies, difficulty in developing molecular markers, and preferential amplification in mixed species infections. Given the differential benefits and shortcomings of both molecular and morphological characters, both should be implemented in parasite taxonomy and phylogenetics. 相似文献
20.
G. Malmberg 《Hydrobiologia》1986,132(1):23-29
The evolution of certain ontogenetic processes appears to be of special importance to subsequent evolution of a phyletic line, and their occurrence suggests there are various evolutionary capacity levels occupied by major taxa. Two groups that are at the same evolutionary capacity level probably originated in common within that level, which in turn is often shared with several other groups. Morphogenesis by invagination is characteristic of an early evolutionary capacity level common to poriferans, cnidarians, deuterostomes, and platyhelminths, inter alia. In the early ontogeny of the former three groups, this process produces the blastopore and archenteron, but in platyhelminths, e.g. rhabdocoels, two different processes form the digestive system: the mouth forms by invagination and the intestine by a split in the mesenchyme/parenchyma. I have selected some characters and processes to illustrate evolutionary capacity levels and to describe the possible origin of a number of invertebrate groups from various levels and their inter-relationships. My analysis on the basis of evolutionary capacity levels suggests that the deuterostomes originated early (very likely before mollusks and annelids), that tegumental absorption of nutriments is the original mode of nutriment uptake and so predates intestinal ingestion in Platyhelminthes, that ontogenetic characters show that the presumed origin of cercomeromorphaeans from rhabdocoels is improbable, and that features of ontogeny and life cycles indicate that the major parasitic platyhelminth classes arose through progressive rather than regressive evolution. Thus the non-parasitic and the parasitic platyhelminth classes very likely belong to separate evolutionary lines, all originating from the same evolutionary capacity level. 相似文献