Search results for "Sexual Reproduction"
showing 5 items of 95 documents
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…
Ecological genetics of a cyclical parthenogen in temporary habitats
1995
Populations of the rotifer Brachionus plicatilis inhabiting three temporary ponds in Torreblanca Marsh (Castellon, Spain) were regularly screened for allozyme variation, sexual reproduction levels and population densities during an annual cycle. Relevant ecological parameters in the ponds were also recorded. The electrophoretic survey of the three ponds (Poza Sur, Poza Norte and Canal Central) revealed a high level of overall genetic polymorphism in four marker loci, but only 13 multilocus genotypes were found. We classified clones into three clonal groups (SS, SM, L) characterized by unique arrays of alleles in the four marker loci, and significant differences in body shape and size. Clona…
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…
Modelling the relationship between sexual reproduction and rhizome growth in Posidonia oceanica (L.) Delile
2006
The relationship between flowering and growth performance of Posidonia oceanica (L.) Delile in meadows distributed along the south-eastern coast of Sicily (Italy) was investigated by means of a statistical model (generalized linear mixed model) combined with the lepidochronological analysis. Over a 28-year period, 67 floral stalk remains were observed. The highest flowering index was recorded in lepidochronological year 1998 (10.1%) and the Inflorescence Frequency per age showed a clear decrease corresponding to 15-year-old shoots. The sexual reproductive event had positive effects on rhizome elongation (cm year−1) and leaf production (no. leaves year−1) in the same flowering year, whilst n…