Search results for "Parthenogenesis"
showing 10 items of 60 documents
Large Hardy-Weinberg equilibrium deviations in the Daphnia longispina of Lake El Tobar
1995
The population structure of Daphnia longispina in Lake El Tobar, Spain was studied by measuring variation at the aldehyde oxidase (AO), phosphoglucose isomerase (PGI) and phosphoglucose mutase (PGM) loci in each of 1337 individuals from four collections. In 9 of the 12 comparisons between observed allele frequencies and those expected by Hardy-Weinberg equilibrium there was an excess of heterozygotes. We found 27 of the potential number of 54 composite electromorphs (‘clones’) based on the three allozymes. Clone diversities were rather high in all collections. Three clones reached frequencies of over 25% and different clones were dominant in each of the four collections. Strong temporal var…
Variability for mixis initiation in Brachionus plicatilis
2001
Deductions from both evolutionary models and inductive argumentation from empirical data support the notion of intraspecific variability for the initiation of sexual reproduction (mixis) within rotifer populations. In this study, we focus on the time and density at which mixis is initiated in a growing population. Cyclical parthenogenetic clones of Brachionus plicatilis established by hatching of resting eggs, isolated from a natural habitat, have been tested at the start of their sexual phase. Clones exhibited great variation for this trait, their time of switching to sexual reproduction being correlated with population density. Most of the variation for mixis initiation has either low or …
Optimal rates of bisexual reproduction in cyclical parthenogens with density‐dependent growth
1999
This work explores theoretical patterns of reproduction that maximize the production of resting eggs and the long-term fitness of genotypes in cyclical parthenogens. Our focus is on density-dependent reproduction as it influences the consequences of a trade-off between producing amictic daughters – which reproduce parthenogenetically and subitaneously – and producing mictic daughters – which undergo meiosis and bisexual reproduction. Amictic females increase competitive ability and allow the population to achieve a larger size; mictic females directly contribute to population survival through harsh periods by producing resting eggs. Although morphologically indistinguishable, the two types …
Mixis strategies and resting eeg production of rotifers living in temporally-varying habitats
1993
A dynamic model based on six differential equations has been developed to explore the control of mixis of rotifers living in temporally-varying habitats. The equations give variation rates of amictic females, three stages of mictic females, males and resting eggs. The model takes into account some constraints on mixis (e.g., male-female encounter probability and effort involved in resting egg production) and its predictions have been generated by computer simulation using parameter values from the literature. For simulation, a time-dependent birth rate function was assumed to account for changes in the environment, and several mixis patterns (i.e., moment of mixis induction and mictic rate …
Mate recognition as a reproductive barrier in sexual and parthenogenetic Eucypris virens (Crustacea, Ostracoda)
2013
Mate selection is one of the motors of evolution and of particular importance in the case of organisms in which sexual and parthenogenetic populations coexist. Sexual populations of the ostracod species complex Eucypris virens are often mixed with parthenogenetic ones. A powerful mate selection mechanism must exist to avoid time, energy and sperm loss, for the maintenance and success of sexual reproduction in these mixed populations. There are four types of E. virens individuals: males (diploid), sexual females (diploid) and asexual females (parthenogenetic and either di- or triploid). From one parthenogenetic population and two populations with males of E. virens, we sampled early stage ju…
Selection of low investment in sex in a cyclically parthenogenetic rotifer
2009
Cyclical parthenogens, which combine asexual and sexual reproduction, are good models for research into the ecological and population processes affecting the evolutionary maintenance of sex. Sex in cyclically parthenogenetic rotifers is necessary for diapausing egg production, which is essential to survive adverse conditions between planktonic growing seasons. However, within a planktonic season sexual reproduction prevents clonal proliferation. Hence, clones with a low propensity for sex should be selected, becoming dominant in the population as the growing season progresses. In this context, we studied the dynamics of the heritable variation in propensity for sexual reproduction among clo…
Mictic patterns of the rotifer Brachionus plicatilis Müller in small ponds
1995
Populations of the rotifer Brachionus plicatilis were monitored in three small ponds in a marsh on the Mediterranean coast. Samples were taken approximately every three weeks from July 1992 to November 1993. Salinity, temperature, conductivity, pH and oxygen concentration were measured in the field. Population density was determined from preserved quantitative samples. Individuals were classified as mictic females, amictic females, non-ovigerous females, and males, differentiating between two morphotypes (‘S’ and ‘L’). From these counts, a level of mixis was calculated. We also determined the proportion of mictic females in natural populations by culturing females isolated from fresh sample…
The parasitoid species complex associated with sexual and parthenogenetic Naryciinae (Lepidoptera: Psychidae): Integrating ecological and molecular a…
2011
This study describes the parasitoid species complex associated with seven closely related species of sexual (Siederia rupicollella, S. listerella, Dahlica lazuri, D. charlottae and D. lichenella) and parthenogenetic (Dahlica fennicella and D. triquetrella) Naryciinae (Lepidoptera: Psychidae) in Central Finland. A thorough ecological analysis of all the species of parasitoids recorded was combined with analyses of molecular data. Mitochondrial and nuclear DNA data were obtained from all the species in order to (1) detect cryptic species associated with host specialization, (2) assign undescribed males to females, and (3) verify the morphological identification of closely related species. A D…
Pyriproxyfen, a juvenoid hormone analog, does not induce male production in parthenogenetic lineages of Eucypris virens (Crustacea: Ostracoda)
2007
Analogs of juvenoid hormones are increasingly recommended for controlling insect pests in agriculture. One of these analogs, pyriproxyfen, was found to be very potent in inducing male production in Daphnia under laboratory conditions, even after acute exposure. Other studies also demonstrated a major role of juvenoid hormones for the sex determination in arthropods that have sex chromosomes. We exposed parthenogenetic lineages of the freshwater ostracod Eucypris virens to a wide range of pyriproxyfen concentrations, and compared mortality and fecundity between treated and control animals. Animals exposed to the highest concentrations of pyriproxyfen (3-30 nM) experienced a higher mortality …
Association of female aging with decreased parthenogenetic activation, raised MPF, and MAPKs activities and reduced levels of glutathione S-transfera…
2004
This study aims to determine in the mouse whether oocytes from reproductively old females exhibit a different susceptibility to be parthenogenetically activated when compared to oocytes from young females. At the age of 10–12 (young-female group) or 60–62 (old-female group) weeks, hybrid female mice were superovulated using pregnant mare's serum gonadotropin (PMSG) followed by human chorionic gonadotropin (hCG) 48 hr later. After removing the cumulus cells, oocytes were exposed to any of two different activating protocols: (a) 6-min exposure to 8% ethanol; and (b) treatment with 200 μM thimerosal for 15 min followed by 8 mM dithiothreitol (DTT) for 30 min. Oocytes from old female mice displ…