Parthenogenesis in Reptiles

SYNOPSIS. The discovery of parthenogenesis in reptiles cameabout through the casual observation ol the lack of males inseveral species of lizards. Nineteen all female species andsubspecies from five genera and three families of lizards havebeen named or recognized. Actual proof of parthenogenesis, however,has been demonstrated foi only seven ol these. Studies in variationof parthcnogens versus the variation ot sympatric bisexual specieshave been made on six species. Tn general the paithenogens arcmuch less variable than bisexual species. Males have been found in most ot the paithenogens studied. Atleast some of these seem lo result from crosses between paithenogensand males of sympatric bisexual species. In a few instances,however, this seems unlikely. The evidence supporting the Inbrid origin of these males rests on a few studies which showthat these males have one more genome than the female paitheuogensthey resemble. The evolution and origin of paithenogens probably is throughhybridization followed by fuither hvbridization in some generaleading to triploidy. Evidence for these Inpotheses is piovidedby a number of karyotypc studies, skin transplants, and studiesof various proteins. One study indicates that the somatic chromosomenumber is icstored during oogenesis by an endoduplication immediatelypreceeding meiosis. Cuemuluphonis uniparens, the species inwhich this phenomenon was demonstrated, is a triploid Evolutionary aspects ol parthenogenesis are discussed.     

Parthenogenesis in Tubificidae

The ability of tubificids to reproduce parthenogenetically following or in place of bisexual reproduction has been proved. During parthenogenesis the spermatogenesis ceases at an early stage of sexual cell development, which, together with some peculiarities of the structure of the sexual system, rules out the possibility of self-fertilization in the worms. For two years of cultivation the life cycles of 3 parthenogenetic generations in Tubifex tubifex and 2 in Limnodrilus hoffmeisteri were traced.     

Parthenogenesis in Parasitic Helminths

SYNOPSIS. In neinatodes, parthenogenesis, meiotic or more oftenmitotic with polyploidy, occurs in the orders Tylenchida andRhabditida. It has evolved independently within the variousfamilies and even certain genera, replacing the usual amphimixisin some species and supplementing it in others with one or moreparthenogenetic generations. Polyploidy, haploidy, abnormalspennatogenesis and absence of sperms have been cited as evidenceof parthenogenesis in some adult cestodes and digenetic trematodes,especially dioecious species in those predominantly hermaphroditicgroups. Evidence now favors interpretation of reproduction bygerminal sacs in trematodes as diploid parthenogenesis whichcan be continued through an indefinite number of generationsin some species by transplanting germinal sacs from infectedto uninfected snails.     

Parthenogenesis in cucurbita

Ohne Zusammenfassung     

Parthenogenesis in mammals

A review of studies dealing with spontaneous and induced parthenogenesis in mammals. The main methods of artificial egg activation, ways of their development and causes of mortality of the parthenogenetic mouse embryos are considered. The possibilities of using parthenogenesis for solving urgent problems of mammalian developmental biology are estimated and prospects of further studies in this field are outlined.     

动物的孤雌生殖

孤雌生殖（parthenogenesis）也叫做“单性生殖或处女生殖”。孤雌生殖的定义是：“雌性个体产生的卵,无需受精．可发育成新雌性个体。”植物也可能有类似的情形,但植物受精作用的细节多少有些不同,所以这个定义只适用于动物。     

Parthenogenesis and Polyploidy in Beetles

SYNOPSIS. Most contemporary authorities on the taxonomy of Coleopteraagree that its three-quarter million described species and subspeciesshould be placed in three suborders: Archostemata, Adephaga,and Polyphaga. Judged by the absence of males or the occurrenceof variant sex ratios, parthenogenesis occurs in all three.Those that have been studied cytologically and a tew that cansafely be surmised are discussed with reference to their probableorigin and evolutionary significance.     

Experimentelle Erzeugung erblicher Parthenogenesis

Ohne Zusammenfassung     

Inheritance during Parthenogenesis in DAPHNIA MAGNA

Natural populations of Daphnia magna have been found which are polymorphic for electrophoretic variants of supernatant malic dehydrogenase, esterase, and alkaline phosphatase. Using these enzyme variants as genetic markers it has been possible to demonstrate the absence of recombination during parthenogenetic reproduction. Genetic uniformity is expected within parthenogenetic clones derived from a single female.     

哺乳动物孤雌干细胞与孤雌生殖

未受精的孤雌胚胎衍生的孤雌胚胎干细胞(parthenogenetic embryonic stem cells,pESCs),具有与胚胎干细胞(embryonic stem cells,ESCs)相似的多向分化和自我更新能力,且具备来.源广泛、获取高效及低致瘤性等优势,因此成为近年来的研究热点.该文概述了pESCs特殊...     

Parthenogenesis in Xenopus eggs requires centrosomal integrity

Xenopus eggs are laid arrested at second metaphase of meiosis lacking a functional centrosome. Upon fertilization, the sperm provides the active centrosome that is required for cleavage to occur. The injection of purified centrosomes mimics fertilization and leads to tadpole formation (parthenogenesis). In this work we show that the parthenogenetic activity of centrosomes is inactivated by urea concentrations higher than 2 M. The loss of activity is correlated with a progressive destruction of the centriolar cylinder and extraction of proteins. This shows that centrosomes are relatively sensitive to urea since complete protein unfolding and solubilization of proteins normally occurs at urea concentrations as high as 8-10 M. When present, the parthenogenetic activity is always associated with a pelletable fraction showing that it cannot be solubilized by urea. The parthenogenetic activity is progressively inactivated by salt concentrations higher than 2 M (NaCl or KCl). However, only a few proteins are extracted by these treatments and the centrosome ultrastructure is not affected. This shows that both parthenogenetic activity and centrosomal structure are resistant to relatively high ionic strength. Indeed, most protein structures held by electrostatic forces are dissociated by 2 M salt. The loss of parthenogenetic activity produced at higher salt concentrations, while the structure of the centrosome is unaffected, is an apparent paradox. We interpret this result as meaning that the native state of centrosomes is held together by forces that favor functional denaturation by high ionic strength. The respective effects of urea and salts on centrosomal structure and activity suggest that the centrosome is mainly held together by hydrogen and hydrophobic bonds. The in vitro microtubule nucleating activity of centrosomes can be inactivated at salt or urea concentrations that do not affect the parthenogenetic activity. Since egg cleavage requires the formation of microtubule asters, we conclude that the extracted or denatured microtubule nucleating activity of centrosomes can be complemented by components present in the egg cytoplasm. Both parthenogenetic and microtubule nucleating activities are abolished by protease treatments but resist nuclease action. Since we find no RNA in centrosomes treated by RNase, they probably do not contain a protected RNA. Taken together, these results are consistent with the idea that the whole or part of the centrosome structure acts as a seed to start the centrosome duplication cycle in Xenopus eggs.     

Evolution and Ecology of Parthenogenesis in Earthworms

A model for the origin of parthenogenesis in hermaphroditesis developed. If a dominant mutation causing parthenogeneticdevelopment of eggs without affecting meiotic production ofsperm arises, the parthenogens will increase in frequency tofixation. Concomitantly, there is selection for reallocationof resources from male to female-related functions in both parthenogeneticand sexual individuals. Occasional fertilization of unreducedeggs may produce polyploid clones. Both the loss of male-relatedstructures and polyploidy are common in parthenogenetic earthworms.Parthenogenesis should be favored in patchy and temporally unstablehabitats, in which -selection may be expected, because it facilitatescolonization and rapid population growth, and because selectionby the biotic component of the environment presumably is reduced.Parthenogenetic earthworms commonly occur in decaying logs,leaf litter, and the upper, organic layers of the soil, whereassexual species more often inhabit the deeper, more stable soilhorizons. Long-term persistence of clones depends on their abilityto survive and reproduce under a variety of environmental conditions.It is proposed that successful clones possess "general purpose"genotypes that allow persistence in spite of temporal changesand facilitate active dispersal through heterogeneous environmentsbetween patches of prime habitat. Two common clones of the parthenogeneticearthworm Octolasion tyrtaeum seem to possess general purposegenotypes, as they occur in a wide variety of soil and habitattypes and are geographically widespread.     

Genomic Imprinting and Problem of Parthenogenesis in Mammals

Genomic imprinting belongs by its nature to problems of epigenetics, which studies hereditary changes in gene expression not related to defective sequences of DNA nucleotides. Epigenetic mechanisms of control, including genomic imprinting, are involved in many processes of normal and pathological development of humans and animals. Disturbances of genomic imprinting may lead to various consequences, such as formation of developmental anomalies and syndromes in humans, appearance of the large offspring syndrome and increased mortality upon cloning of mammals, and death of parthenogenetic embryos soon after implantation and beginning of organogenesis. The death of diploid parthenogenetic or androgenetic mammalian embryos is determined by the absence of expression of the genes of imprinted loci of the maternal or paternal genome, which leads to significant defects in development of tissues and organs. A review is provided of the studies aimed at search of possible normalization of misbalanced gene activity and modulation of genomic imprinting effects during parthenogenetic development in mammals.__________Translated from Ontogenez, Vol. 36, No. 4, 2005, pp. 300–309.Original Russian Text Copyright © 2005 by Platonov.     

Parthenogenesis in Psocids (Insecta: Psocoptera)

SYNOPSIS. Obligate thelytokous parthenogenesis and, more rarely,facultative thelytoky are known to occur in psocids. The formerphenomenon is known in 28 species. The latter is known onlyin two species, both of which have obligatorily thelytokousforms as well as bisexual ones. Attempts to force thelytokousfemales to mate have been carried out for four nominal species.All have failed. Differences in color or color pattern betweenthe bisexual and thelytokous forms of a nominal species havebeen observed in two instances. In Echmepteryx hageni this seemsto involve divergence where the two forms occur sympatricallybut on different habitats. Investigations of geographic distributionof bisexual and thelytokous forms of a nominal species showin several cases that the thelytokous forms are much more widespreadthan the bisexual ones. In eastern United States, bisexual formstend to occur peripherally and in ecologically unusual areas.The areas of occurrence of bisexual populations may be relictual,and some of them may have been Pleistocene refugia. Most ofthese areas correspond to areas where coniferous trees now forman important part of the forest.     

Parthenogenesis of rabbit oocytes activated by different stimuli

Oocyte activation is one of the essential elements determining the success of nuclear transfer and the subsequent development of cloned embryos both in vitro and in vivo. Experiments were conducted to optimize the protocol for oocyte activation in a regular nuclear transfer study. In vivo derived oocytes were collected at 14–15 h from New Zealand white rabbits after ovulation treatment and were activated +18 h post-ovulation treatment. Single activation agents including calcium ionophore (A23187, 5 μM, 5 min), ethanol (Eth, 7%, 7 min), and thimerosal (200 μM, 10 min) were tested. Cleavage rates were highest in the ethanol-treated group (37%) compared to other treatments (19–25%). Very low blastocyst rates (2–3%) resulted which were not significantly different among treatments (P>0.05). Combined single agent treatment (calcium stimulators) with protein kinase inhibitor, 6-DMAP were used to achieve a full oocyte activation. Both pronuclear and blastocyst formation rates were significantly higher (P<0.05) in the Eth+6-DMAP treatment group (38 and 27%) than in the other groups (16–21 and 7–9%, respectively, P<0.05). Low (0.2 mM) and high (2.5 mM) concentrations of 6-DMAP treatments with different treatment lengths (1.5 and 3.5 h) in the combined groups were also compared. Blastocyst formation and cleavage rates were greater in the high concentration with less treatment time groups (36% versus 4–20%, P<0.05). In conclusion, single activation agents, either Ca²⁺ stimulators or protein kinase inhibitors, could not fully activate mature rabbit oocytes. The best activation procedure obtained in this study was the Eth+6-DMAP combined treatment, which may be incorporated into regular nuclear transfer or cloning protocols.     

Systematic and Evolutionary Implications of Parthenogenesis in the Hymenoptera

SYNOPSIS. Two types of parthenogenesis, arrhenotoky and thelytoky,exist in the Hymenoptera. Arrhenotoky, the development of malesfrom unfertilized eggs, is present in all wasps and bees. Thelytoky,the development of diploid females from unfertilized eggs, ispresent in a few species. Two types of thelytoky, apomixis andautomixis, are known. Most thelytokous Hymenoptera are automictic.No meiosis, only mitosis, occurs in apomixis. Meiosis does occurin automixis, allowing crossing-over and segregation of genes.Advantages of thelytoky are that heterotic combinations becomefixed, gene loss is reduced, and reproduction requires onlya single individual. One advantage of arrhenotoky is that geneticload in males is eliminated. Both environmental and geneticfactors contribute to sex-determination in the haplodiploidsystem of Hymenoptera. Haplodiploidy can facilitate the evolutionof social behavior. Parthenogenesis creates some taxonomic problemssince thelytokous clones do not fit the generally accepted biologicalspecies concept. Some members of bisexual populations probablyacquirethelytoky, forming their own clones, races, or species.