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1.
Evolutionary and ecological consequences of interspecific hybridization in cladocerans 总被引:6,自引:0,他引:6
The evolutionary process of interspecific hybridization in cladocerans is reviewed based on ecological and population genetic data. The evolutionary consequences of hybridization, biogeographic patterns and fitness comparisons are analyzed within the conceptual framework of theories on hybridization. Among species of theD. longispina complex no interpopulational transition zones (hybrid zones) have been detected, but rather patchy distributions of hybrids and parentals have been found. Hybrids occur across broad geographic ranges and can be more abundant than parental species. Due to asexual reproduction (ameiotic parthenogenesis), hybrid breakdown can be avoided, and hybrids can even (temporarily) combine advantageous traits of both parental species. Evolutionary consequences may arise from repeated backcrossing, which in some cases results in introgression and patterns of reticulate evolution.Those forms which possess in some considerable degree the character of species, but which are so closely similar to some other forms, or are so closely linked to them by intermediate gradations, that naturalists do not like to rank them as distinct species, are in several respects the most important to us (Charles Robert Darwin 1859) 相似文献
2.
M Poras 《Comptes rendus des séances de l'Académie des sciences. Série D, Sciences naturelles》1977,284(6):457-460
The percentage of laying females and laying time, are compared between mature females (diapause break by chilling) and diapause strain females (diapause not broken by chilling) reared with mature male or diapause male or without male. For the same physiological state of the females (mature or diapause) there is no difference in the percentage of females laying, when they are reared with mature male or with diapause one or none; but the laying time is shortest with mature male, longer with male in diapause, even longer without male. Parthenogenetic egg-pods can be obtain. Rearing with mature males does not break the reproductive diapause of females. In parthenogenetic egg-pods the number of eggs is short for low diapause females; greater for mature ones and greatest for females with strong diapause broken by a corpus allatum implant of mature female of Locusta migratoria. Corpus allatum of the low diapause strain of females of Tetrix undulata have less activity than that of mature females. Few parthenogenetic eggs develop, even less hatch. In Tetrix undulata parthenogenesis is accidental. 相似文献
3.
K. Rohde 《Cellular and molecular life sciences : CMLS》1981,37(4):359-361
Summary Niche width of ectoparasites of marine fishes, as measured by host range and microhabitat width, is not affected by the number of species in a community. There is no reduction in species numbers of Monogenea due to greater numbers of other parasite species, and frequencies of infection with Monogenea are greater in tropical, species-rich communities.Supported by grants from the Australian Research Grants Committee and the University of New England. M. Heap provided valuable technical assistance, and F. Roubal made his data onAcanthopagrus australis available to me. 相似文献
4.
Malaria results in up to 2.5 million deaths annually, with young children and pregnant women at greatest risk. The great
majority of severe disease is caused by Plasmodium falciparum. A characteristic feature of infection with P. falciparum is the accumulation or sequestration of parasite-infected red blood cells (RBCs) in various organs, such as the brain, lung
and placenta, and together with other factors is important in the pathogenesis of severe forms of malaria. Sequestration results
from adhesive interactions between parasite-derived proteins expressed on the surface of infected RBCs and a number of host
molecules on the surface of endothelial cells, placental cells and uninfected RBCs. Some receptors for parasite adhesion have
been implicated in particular malaria syndromes, such as intercellular adhesion molecule 1 in cerebral malaria and chondroitin
sulfate A and hyaluronic acid in placental infection. The principal parasite ligand and antigen on the RBC surface, P. falciparum erythrocyte membrane protein 1 encoded by a multigene family termed var, is clonally variant, enabling evasion of specific immune responses. An understanding of these host-parasite interactions
in the context of clinical disease and immunity may reveal potential targets to prevent or treat severe forms of malaria.
Received 25 June 2001; received after revision 22 August 2001; accepted 24 August 2001 相似文献
5.
R. Matthey 《Cellular and molecular life sciences : CMLS》1946,2(7):260-261
Summary The males of two species of Palestine,Saga ephippigera
Fisch. andS. gracilipes
Uvar have respectively 33 and 31 chromosomes in the diploid state.S. pedo
Pallas, a parthenogenetic thelytoc species largely distributed in Europe, has 68 chromosomes and probably represents a tetraploid. The cells of the three species have identical dimensions and the polyploidS. pedo is even the smallest in size. 相似文献
6.
Saeki K 《Cellular and molecular life sciences : CMLS》2011,68(8):1327-1339
The establishment and maintenance of rhizobium–legume symbioses require a sequence of highly regulated and coordinated events
between the organisms. Although the interaction is mutually beneficial under nitrogen-limited conditions, it can resemble
a pathogenic infection at some stages. Some host legumes mount defense reactions, including the production of reactive oxygen
species (ROS) and defensin-like antimicrobial compounds. To subvert these host defenses, the infecting rhizobial cells can
use measures to passively protect themselves and actively modulate host functions. This review first describes the establishment
and maintenance of active nodules, as well as the external and endogenous attack and threat stages. Next, recent studies of
ROS scavenging enzymes, the BacA protein originally found in Sinorhizobium meliloti, and the type III/IV secretion systems are discussed, with a focus on two legume–rhizobium model systems. 相似文献
7.
8.
N. M. Ali 《Cellular and molecular life sciences : CMLS》1984,40(2):197-198
Summary Experimental infection byDiplostomum phoxini of the brain of laboratory hatched and rearedPhoxinus phoxinus induces the migration along the Xth cranial nerve of periodic acid Schiff positive granular leucocytes (PAS-GLs). These differentiate and grow into cells that lie between the parasite and the neurones of the host. The transformed cells are associated with elevated levels of heparin and serotonin in the brain; little histamine was detected. The reactive cell is identified as a mast cell.This work was carried out with M.R.L. Johnston's guidance. Teresa Townshend is thanked for assistance with techniques to hatch and raiseP. phoxinus. 相似文献
9.
D. G. Müller M. N. Clayton G. Gassmann W. Boland F. -J. Marner L. Jaenicke 《Cellular and molecular life sciences : CMLS》1984,40(2):211-212
Summary
Hormosira banksii is a taxonomically isolated brown seaweed endemic to Australia and New Zealand. The sperm attractant of this species has been isolated and identified as trans-1-vinyl-2-(1E, 3Z-hexadienyl)-cyclopropane (I) (hormosirene).Hormosira is the first organism in which a cyclopropane derivative has been found to act as a hormone in sexual reproduction. The implication of this finding in relation to phylogeny and phytogeography is discussed.Acknowledgment. A substantial part of this work was supported by Deutsche Forschungsgemeinschaft (DFG). 相似文献
10.
W. Medway 《Cellular and molecular life sciences : CMLS》1979,35(9):1158-1159
Summary Bisaluminemia was found in a female bottlenosed dolphin (Turiops truncatus) on routine examination. There is no association with disease.Acknowledgment. I. wish to thank Dr G. W. Jones, Lincolnton, NC for providing me with the dolphin sera and Mr R. Quinlan of Quinlan Enterprises, Lincolnton, NC for providing the animals. 相似文献
11.
S. B. J. Menken 《Cellular and molecular life sciences : CMLS》1982,38(12):1461-1462
Summary Eight hymenopterous and 1 dipterous species, all endoparasitic in eggs, larvae, or pupae of small ermine moths (Yponomeuta) were investigated for their allozyme variation at 3–29 loci. The mean heterozygosity level of the hymenopterous species is one-third of that of the dipterous species. Zymogram patterns of the parasite larvae do not interfere with those of the host. 相似文献
12.
Freshwater gastropods (Basommatophora and Prosobranchia) harbor a variety of mating systems. In particular, apomictic parthenogenesis in prosobranchs and self-fertilization in the hermaphrodite pulmonates may be viable alternatives to outcrossing sexuality in a number of species. The coexistence of different mating systems in extant populations provides opportunities to examine the forces directing their evolution. We review the models analyzing and predicting genetic variability in subdivided populations, with an emphasis on the effects of inbreeding. Population genetic data on freshwater pulmonates are examined in the context of selfing rates and the loss of variability under selfing. Furthermore, the genetic and demographic factors thought to influence mating system evolution are considered, and we highlight the different approaches available to estimate mating system parameters, in particular the selfing rate. Recent population biological studies on polyploid species (Bulinus truncatus, Ancylus fluviatilis) indicate that selfing is the predominant mating system. These studies have contributed to a deeper understanding of conceptual issues in the evolution of selfing rates. Throughout, we emphasize the need for further carefully designed studies. 相似文献
13.
Sarti P Fiori PL Forte E Rappelli P Teixeira M Mastronicola D Sanciu G Giuffré A Brunori M 《Cellular and molecular life sciences : CMLS》2004,61(5):618-623
Besides possessing many physiological roles, nitric oxide (NO) produced by the immune system in infectious diseases has antimicrobial effects. Trichomoniasis, the most widespread non-viral sexually transmitted disease caused by the microaerophilic protist Trichomonas vaginalis, often evolves into a chronic infection, with the parasite able to survive in the microaerobic, NO-enriched vaginal environment. We relate this property to the finding that T. vaginalis degrades NO under anaerobic conditions, as assessed amperometrically. This activity, which is maximal (133 ± 41 nmol NO/108 cells per minute at 20°C) at low NO concentrations ( 1.2 M), was found to be: (i) NADH dependent, (ii) cyanide insensitive and (iii) inhibited by O2. These features are consistent with those of the Escherichia coli A-type flavoprotein (ATF), recently discovered to be endowed with NO reductase activity. Using antibodies against the ATF from E. coli, a protein band was immunodetected in the parasite grown in a standard medium. If confirmed, the expression of an ATF in eukaryotes suggests that the genes coding for ATFs were transferred during evolution from anaerobic Prokarya to pathogenic protists, to increase their fitness for the microaerobic, parasitic life style. Thus the demonstration of an ATF in T. vaginalis would appear relevant to both pathology and evolutionary biology. Interestingly, genomic analysis has recently demonstrated that Giardia intestinalis and other pathogenic protists have genes coding for ATFs.Received 1 November 2003; received after revision 5 January 2004; accepted 13 January 2004 相似文献
14.
H. Müller-Schärer C. Lehr M. Klein K. Marquardt 《Cellular and molecular life sciences : CMLS》1991,47(8):859-864
Allozyme frequencies of 15 enzyme loci, 14 of which were polymorphic, were used to characterize sevenTerellia virens populations originating from three allopatrically distributedCentaurea species. The two populations whose origins were geographically furthest apart, from Israel (onC. iberica) and from Switzerland (onC. vallesiaca), showed relatively high values of genetic distance from the 5 populations sampled in Austria and Hungary (onC. maculosa) (Nei's D>0.07). The latter five displayed a high degree of genetic similarity. No diagnostic (fixed) allelic differences were observed between these three groups ofT. virens populations, but they could be well characterized by significant differences in allelic frequencies at 9 enzyme loci. Independently of this study, the populations from Switzerland (C. vallesiaca) and eastern Austria (C. maculosa) were selected as potential source populations for future introductions into North America for the biological control of introducedC. maculosa andC. diffusa. Based on the observed genetic differences and results from field experiments on the host specificity of these two potential source populations, it is argued that host specificity screening tests should be conducted separately for local (host plant) populations, as such populations might accept a different set of hosts. Biotype mismatch and the risk of spill-overs to native species could thus possibly be reduced. 相似文献
15.
Recently discovered representatives of the Class Bdelloidea from Tertiary amber from the Dominican Republic represent the oldest known fossils of the Phylum Rotifera. Assuming that the fossil bdelloids had a similar mode of reproduction as present day members of the Class (apomictic thelytoky), then contrary to current thought, some lines of parthenogenetic organisms are not doomed to an early extinction and have evolved built-in mechanisms for genetic diversity. 相似文献
16.
Y. Takenouchi 《Cellular and molecular life sciences : CMLS》1978,34(4):444-445
Summary The chromosomes of the so-called rice water weevil,Lissorhoptrus oryzophilus, Kuschel obtained from Tokoname City, Aichi Prefecture, were studied in both oogonial and oocyte-maturation divisions in squash and sectioned slides, respectively. The chromosome number was confirmed as exactly 33 in both divisions. No reduction division takes place. It is therefore concluded thatLissorhoptrus oryzophilus is a parthenogenetic triploid in Tokoname City. 相似文献
17.
To have sex, or not to have sex, is a question posed by many microorganisms. In favor of a sexual lifestyle is the associated
rearrangement of genetic material that confers potential fitness advantages, including resistance to antimicrobial agents.
The asexual lifestyle also has benefits, as it preserves complex combinations of genes that may be optimal for pathogenesis.
For this reason, it was thought that several pathogenic fungi favored strictly asexual modes of reproduction. Recent approaches
using genome sequencing, population analysis, and experimental techniques have now revised this simplistic picture. It is
now apparent that many pathogenic fungi have retained the ability to undergo sexual reproduction, although reproduction is
primarily clonal in origin. In this review, we highlight the current understanding of sexual programs in the Candida clade of species. We also examine evidence that sexual-related processes can be used for functions in addition to mating
and recombination in these organisms. 相似文献
18.
Arginase expression in peritoneal macrophages and increase in circulating polyamine levels in mice infected with Schistosoma mansoni 总被引:5,自引:0,他引:5
Abdallahi OM Bensalem H Augier R Diagana M De Reggi M Gharib B 《Cellular and molecular life sciences : CMLS》2001,58(9):1350-1357
We investigated the nitric oxide (NO) synthase and arginase pathways in resident peritoneal macrophages of mice infected
with the tropical parasite Schistosoma mansoni. The two enzymes may have opposite effects, insofar as NO may be involved in the killing of the parasite whereas arginase
may stimulate parasite growth via polyamine synthesis. We determined the effects of the infection on the expression and activity
of the two enzymes in macrophages, before and after cytokine activation. Cells from infected mice expressed the hepatic type
I arginase, whereas in control cells, the enzyme was expressed only after cytokine activation, as were NO synthase II and
type II arginase in both groups of cells. Moreover, we found that in infected mice, arginase expression in macrophages was
associated with a ten fold increase in the concentration of circulating ornithine-derived polyamines. This may be of pathological
importance, since parasitic helminths are though to be dependent on their hosts for the uptake and interconversion of polyamines.
Received 13 March 2001; received after revision 4 May 2001; accepted 7 June 2001 相似文献
19.
Alain Debec William Sullivan Monica Bettencourt-Dias 《Cellular and molecular life sciences : CMLS》2010,67(13):2173-2194
Centrioles are cylinders made of nine microtubule (MT) triplets present in many eukaryotes. Early studies, where centrosomes
were seen at the poles of the mitotic spindle led to their coining as “the organ for cell division”. However, a variety of subsequent observational and functional studies showed that centrosomes might not always be essential
for mitosis. Here we review the arguments in this debate. We describe the centriole structure and its distribution in the
eukaryotic tree of life and clarify its role in the organization of the centrosome and cilia, with an historical perspective.
An important aspect of the debate addressed in this review is how centrioles are inherited and the role of the spindle in
this process. In particular, germline inheritance of centrosomes, such as their de novo formation in parthenogenetic species,
poses many interesting questions. We finish by discussing the most likely functions of centrioles and laying out new research
avenues. 相似文献
20.
R. Bertolani S. Garagna G. C. Manicardi C. A. Redi 《Cellular and molecular life sciences : CMLS》1987,43(2):210-213
Summary The morphotype, chromosome number and Feulgen-DNA content of bisexual and unisexual populations ofMacrobiotus pseudohufelandi were examined. Individuals of unisexual populations were triploid with ameiotic parthenogenesis. Their lowest Feulgen-DNA content is about three-fold that of sperm from a bisexual population. Egg shell shape also differs in the two types of population. However, the highest Feulgen-DNA content was the same (24 A.U.) in both diploid and triploid animals.Study funded by MPI grant. 相似文献