Search results for "parthenogenesis"
showing 10 items of 60 documents
Insulin-like peptides involved in photoperiodism in the aphid Acyrthosiphon pisum
2019
Aphids were the first animals reported as photoperiodic as their life cycles are strongly determined by the photoperiod. During the favourable seasons (characterised by long days) aphid populations consist exclusively of viviparous parthenogenetic females (known as virginoparae). Shortening of the photoperiod in autumn is perceived by aphids as the signal that anticipates the harsh season, leading to a switch in the reproductive mode giving place to the sexual morphs (oviparae females and males) that mate and lay winter-resistant (diapause-like) eggs. The molecular and cellular basis governing the switch between the two reproductive modes are far from being understood. Classical experiments…
Exceptional cryptic diversity and multiple origins of parthenogenesis in a freshwater ostracod.
2009
The persistence of asexual reproduction in many taxa depends on a balance between the origin of new asexual lineages and the extinction of old ones. This turnover determines the diversity of extant asexual populations and so influences the interaction between sexual and asexual modes of reproduction. Species with mixed reproduction, like the freshwater ostracod (Crustacea) morphospecies Eucypris virens, are a good model to examine these dynamics. This species is also a geographic parthenogen, in which sexual females and males co-exist with asexual females in the circum-Mediterranean area only, whereas asexual females occur all over Europe. A molecular phylogeny of E. virens based on the mit…
A mathematical model for the phase of sexual reproduction in monogonont rotifers
2000
Recently, the optimal sex allocation in monogonont rotifers is studied in [1], and, as a closely related question, the relative frequencies of the relevant types of mictic females. The authors focus on the evolution of the age at which young mictic females lose their fertilization susceptibility and they address the threshold age of fertilization that maximizes resting egg production. Assuming that a stationary population is achieved, with stable age distribution, they obtain their results, without knowing the stationary population. Our aim is to study this problem in the framework of the theory of nonlinear age-dependent population dynamics developed by G. F. Webb in [13], which is more ap…
Effect of dietary supplementation with a mixture of Vitamins C and E on fertilization of tertiary butyl hydroperoxide-treated oocytes and parthenogen…
2002
The present study aims to analyze the effect of dietary supplementation with a mixture of Vitamins C and E on fertilization and later development of tertiary butyl hydroperoxide (tBH)-treated mouse oocytes and on parthenogenetic activation of freshly ovulated mouse oocytes. We fed hybrid mice a standard diet supplemented or not supplemented with Vitamins C and E from the first day of weaning until the age of 12 weeks. We noted no significant effect of diet on fertilization rate, percentage of total and hatching blastocysts, total number of cells, mitotic index and percentage of apoptotic nuclei at 120 h post-insemination of oocytes incubated for 15 min in the presence of 0, 1, 5 and 10 micr…
High mitochondrial DNA sequence diversity in the parthenogenetic earthworm Dendrobaena octaedra
2010
Apomictic parthenogens are clonal organisms with limited genetic opportunity for increasing diversity beyond mutation. However, such species can be successful and have been shown to harbor more genetic diversity than might be expected. Here we surveyed diversity of the cytochrome oxidase subunit I gene from the mitochondrial genome of the earthworm Dendrobaena octaedra, an apomictic parthenogen. Diversity estimates made previously from allozyme markers for this species were high, but could have been affected by a detection bias, namely variable expression of alleles in the polyploid genome. We found similarly high mtDNA diversity over three localities in Finland, each represented by two sit…
When to be sexual: sex allocation theory and population density-dependent induction of sex in cyclical parthenogens
2008
The timing of sex is a critical fitness component in the cyclically parthenogenetic life-cycle of rotifers. It has been hypothesized that sex in rotifers is optimally timed to high population density because male‐female encounters are more probable. Because sexual females produce either males or, if inseminated, diapausing eggs, the advantage of a higher male‐female encounter rate is that allocation to male production can be lower. This is paradoxical in the context of the sex allocation theory developed for rotifers, as the theory predicts equal numbers of male-producing and diapausing-egg producing females. We investigated this paradox using both empirical data and theoretical analysis. L…
Sex Loss in Monogonont Rotifers
2009
Monogonont rotifers are small, aquatic invertebrates capable of asexual and sexual reproduction. Sexual reproduction is required to produce diapausing eggs, which are able to survive adverse periods that typically occur every year. Their cyclically parthenogenetic life-cycle is believed to retain the advantages of recombination while minimizing the cost of sex. However, this life cycle is also thought to be unstable due to periodic loss of sexual reproduction by directional selection. Explaining the evolutionary dynamics of the monogonont rotifer life cycle is important for understanding how cyclical parthenogenesis is maintained, and for comparing monogononts with their close relatives, th…
Evolutionary dynamics of ‘the’ bdelloid and monogonont rotifer life-history patterns
2006
Substantial differences in both life-table characteristics and reproductive patterns distinguish bdelloid from monogonont rotifers. Bdelloids reproduce only asexually, whereas most monogononts are cyclical parthenogens. We explore some of the adaptive consequences of these life-history differences using a computer model to simulate the evolutionary acquisition of new beneficial mutations. A one-locus mutation-selection regime based on the life-history characteristics of bdelloids indicates that asexuals can maintain higher levels of both allelic and genotypic diversity over a longer time period than obligate sexuals. These results are produced by differences in the magnitude of random genet…
PARASITES AND SEXUAL REPRODUCTION IN PSYCHID MOTHS
2004
Persistence of sexual reproduction among coexisting asexual competitors has been a major paradox in evolutionary biology. The number of empirical studies is still very limited, as few systems with coexisting sexual and strictly asexual lineages have been found. We studied the ecological mechanisms behind the simultaneous coexistence of a sexually and an asexually reproducing closely related species of psychid moth in Central Finland between 1999 and 2001. The two species compete for the same resources and are often infected by the same hymenopteran parasitoids. They are extremely morphologically and behaviorally similar and can be separated only by their reproductive strategy (sexual vs. as…
The nucleus negatively controls the synthesis of mitochondrial proteins in the sea urchin egg.
1983
Enucleation of Paracentrotus lividus eggs, followed by parthenogenetic activation induces a sharp increase in the synthesis of mitochondrial proteins as shown by electrofluorography after in vivo labeling with radioactive amino acids. These results further substantiate the hypothesis that the cell nucleus negatively controls mitochondrial replication in the sea urchin egg.