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Cladocera are the ecologically most important group within the Branchiopoda. They are unquestionably branchiopods but their evolutionary origin remains unclear. One favored explanation of their origin is that they evolved from a reproductive larva of a clam shrimp‐like ancestor. To reveal a transformation and identify (potential) changes in chronology (heterochrony), we investigated and compared the development of representatives of two clam shrimp taxa, one of the Spinicaudata (Leptestheria dahalacensis) and one of the Cyclestherida (Cyclestheria hislopi), the sister group of Cladocera. Both taxa develop indirectly although the exact modes are quite different. The development of the nervous system, labeled and analyzed using immunohistochemical techniques and confocal microscopy, and that of the external morphology, scanned with an electron microscope, was investigated. L. dahalacensis hatch as a free‐swimming nauplius and the nervous system and external morphology develop gradually. In C. hislopi, on the other hand, several internal and external structures develop before the hatching of a nonswimming embryo‐like larva which is still carried in a dorsal brood pouch. The development in L. dahalacensis is directed from anterior to posterior, whereas in C. hislopi a more synchronous anterior and posterior differentiation is present. A comparison of both developmental sequences gives us the first indications of the evolutionary transformation which the Cladocera may have undergone from a clam shrimp‐like ancestor. J. Morphol., 2012. © 2012 Wiley Periodicals, Inc. 相似文献
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Neil John McMillan 《Ichnos》2013,20(3):203-212
A new genus and species of alga called Sinoglypha nassichuki is identified and described from Guadalupian rocks of the Delaware Basin, New Mexico. It occurs in tilted to almost upright position in laminites generally accepted as being deposited in deep, anoxic water. The fossils are noncalcareous, having a wavy nature. They are not classed as trace fossils of animals. They are leafy, 2–5 cm long and may be preserved in original position. If Sinoglypha is an alga it leads to the tentative, but not new, conclusion that perhaps the water was not deep but shallow enough for light penetration—30 meters for the upper part of the Bell Canyon Formation. 相似文献
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Morphological transformations can be generated by evolutionary changes in the sequence of developmental events. In this study, we examined the evolutionary dynamics of the developmental sequence on a macroevolutionary scale in teleosts. Using the information from previous reports describing the development of 31 species, we extracted the developmental sequences of 19 landmark events involving the formation of phylogenetically conserved body parts; we then inferred ancestral developmental sequences by two different parsimony‐based methods—event‐pairing and continuous analysis. The phylogenetic comparisons of these sequences revealed event‐dependent heterogeneity in the frequency of sequence changes. Most of the sequence changes occurred as exchanges of temporally neighboring events. These heterochronic changes in developmental sequences accumulated along evolutionary time, but the precise distribution of the changes over the teleostean phylogeny remains unclear due to technical limitations. 相似文献
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We suggest a new procedure to search for the genes with horizontal transfer events in their evolutionary history. The search is based on analysis of topology difference between the phylogenetic trees of gene (protein) groups and the corresponding phylogenetic species trees. Numeric values are introduced to measure the discrepancy between the trees. This approach was applied to analyze 40 prokaryotic genomes classified into 132 classes of orthologs. This resulted in a list of the candidate genes for which the hypothesis of horizontal transfer in evolution looks true. 相似文献
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Frédéric Legendre Cyrille A. D'Haese Pierre Deleporte Roseli Pellens Michael F. Whiting Klaus Schliep Philippe Grandcolas 《Biological journal of the Linnean Society. Linnean Society of London》2014,111(1):58-77
The adequacy and utility of behavioural characters in phylogenetics is widely acknowledged, especially for stereotyped behaviours. However, the most common behaviours are not stereotyped, and these are usually seen as inappropriate or more difficult to analyze in a phylogenetic context. A few methods have been proposed to deal with such data, although they have never been tested on samples larger than six species, which limits their evolutionary interest. In the present study, we perform behavioural observations on 13 cockroach species and derive behavioural phylogenetic characters with the successive event‐pairing method. We combine these characters with morphological and molecular data (approximately 6800 bp) in a phylogenetic study of 41 species. We then reconstruct ancestral states of the behavioural data to study evolution of social behaviour in these insects with regard to their social systems (i.e. solitary, gregarious, and subsocial) and diversity of habitat choice. We report for the first time that nonstereotyped behavioural data are adequate for phylogenetic analyses: they are no more homoplastic than traditional data, and support several phylogenetic relationships that we discuss. From an evolutionary perspective, we show that the solitary species Thanatophyllum akinetum does not display original behavioural interactions, suggesting phylogenetic inertia of interactive behaviours despite a radical change in social structure. Conversely, the subsocial species Parasphaeria boleiriana shows original behavioural interactions, which could result from its peculiar social system or habitat. We conclude that phylogenetic approaches in studies of behaviour are useful for deciphering evolution of behaviour and discriminating between its different modalities, even for nonstereotyped characters. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 58–77. 相似文献
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Many species exhibit polyploidy. The presence of more than one diploid set of similar chromosomes in polyploids can affect the assortment of homologous chromosomes, resulting in unbalanced gametes. Therefore, a mechanism is required to ensure the correct assortment and segregation of chromosomes for gamete formation. Ploidy has been shown to affect gene expression. We present in this study an example of a major effect on a phenotype induced by ploidy within the Triticeae. We demonstrate that centromeres associate early during anther development in polyploid species. In contrast, centromeres in diploid species only associate at the onset of meiotic prophase. We propose that this mechanism provides a potential route by which chromosomes can start to be sorted before meiosis in polyploids. This explains previous reports indicating that meiotic prophase is shorter in polyploids than in their diploid progenitors. Even artificial polyploids exhibit this phenotype, suggesting that the mechanism must be present in diploids, but only expressed in the presence of more than one diploid set of chromosomes. 相似文献
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卵巢发育阻滞的人工三倍体鱼减数分裂染色体配对的光镜观察 总被引：4，自引：0，他引：4
采用界面铺张制片和硝酸银一步染色的方法,对人工三倍体水晶彩鲫卵巢发育阻滞型个体的减数分裂染色体配对进行了光镜观察。在分化有初级卵母细胞的卵巢发育阻滞型的三倍体鱼中,减数分裂粗线期细胞主要的由二价体和单价体组成,也见有少量三价体和其它多价体,其染色体成员数大多在９０左右;在不同细胞间,染色体的大小变化较大;配对联会过程中形成的配对叉和产生的特异蛋白在一些细胞中明显可见。文中讨论了三倍体染色体配对紊乱 相似文献
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Wenya Yuan Xingwang Li Yuxiao Chang Ruoyu Wen Guoxing Chen Qifa Zhang Changyin Wu 《The Plant journal : for cell and molecular biology》2009,59(2):303-315
Meiosis is essential for eukaryotic sexual reproduction and important for genetic diversity among individuals. Although a number of genes regulating homologous chromosome pairing and synapsis have been identified in the plant kingdom, their molecular basis remains poorly understood. In this study, we identified a novel gene, PAIR3 ( HOMOLOGOUS PAIRING ABERRATION IN RICE MEIOSIS 3 ), required for homologous chromosome pairing and synapsis in rice. Two independent alleles, designated pair3-1 and pair3-2 , were identified in our T-DNA insertional mutant library which could not form bivalents due to failure of homologous chromosome pairing and synapsis at diakinesis, resulting in sterility in both male and female gametes. Suppression of PAIR3 by RNAi produced similar results to the T-DNA insertion lines. PAIR3 encodes a protein that contains putative coiled-coil motifs, but does not have any close homologs in other organisms. PAIR3 is preferentially expressed in reproductive organs, especially in pollen mother cells and the ovule tissues during meiosis. Our results suggest that PAIR3 plays a crucial role in homologous chromosome pairing and synapsis in meiosis. 相似文献