Effects Of Sexual Reproduction Research Articles

Effects of sexual reproduction of the inferior competitor Brachionus calyciflorus on its fitness against Brachionus angularis

Sexual reproduction adversely affects the population growth of cyclic parthenogenetic animals. The density-dependent sexual reproduction of a superior competitor could mediate the coexistence. However, the cost of sex may make the inferior competitor more vulnerable. To investigate the effect of sexual reproduction on the inferior competitor, we experimentally paired the competition of one Brachionus angularis clone against three Brachionus calyciflorus clones. One of the B. calyciflorus clones showed a low propensity for sexual reproduction, while the other two showed high propensities. The results show that all B. calyciflorus clones were excluded in the competition for resources at low food level. The increased food level promoted the competition persistence, but the clones did not show a clear pattern. Both the cumulative population density and resting egg production increased with the food level. The cumulative population density decreased with the mixis investment, while the resting egg production increased with the mixis investment. A trade-off between the population growth and sexual reproduction was observed in this research. The results indicate that although higher mixis investment resulted in a lower population density, it would not determinately accelerate the exclusion process of the inferior competitor. On the contrary, higher mixis investment promoted resting egg production before being excluded and thus promised a long-term benefit. In conclusion, our results suggest that mixis investment, to some extent, favored the excluded inferior competitor under fierce competition or some other adverse conditions.

Farmers’ unconscious incorporation of sexually-produced genotypes into the germplasm of a vegetatively-propagated crop (Oxalis tuberosa Mol.)

Clonal propagation and sexual reproduction have diametrically opposite effects on the genetic diversity of crops, permitting, respectively, the conservation of existing genotypes or the creation of new diversity. Oxalis tuberosa Mol. (‘‘oca’’) exhibits a heteromorphic selfincompatibility system and is traditionally propagated clonally but is capable of sexual reproduction. In this study we investigated the influence of sexual reproduction on the in situ genetic diversity of a vegetatively propagated crop, taking oca as a model plant. The occurrence of sexual reproduction in natural conditions and its use by farmers were studied through surveys and interviews, while the effect of sexual reproduction on the in situ genetic diversity was evaluated using microsatellite analysis. Plantlets issuing from sexual reproduction were encountered in five of the nine visited communities. The interviews indicated that six out of the nine interviewed farmers were likely, albeit unconsciously, incorporating clonal lineages issuing from sexual reproduction into their varieties. The microsatellite analysis indicated a strong effect of such incorporations on the genetic diversity of the plant varieties. Assignment tests confirmed the allogamy of oca. ‘‘Complex varieties’’, made up of individuals exhibiting genetically differentiated genotypes,weremost likely the result of recent crossing. Unconscious incorporation of newgenotypes into the cultivated oca germplasm is therefore highly likely, raising the question of its potential occurrence in other vegetatively propagated crops. These findings could have an important effect on the adaptive potential of oca, especially in light of the genetic erosion that threatens the crop

The cost of reproduction to the clonal herb Asarum canadense (wild ginger)

The cost of reproduction to the clonal understorey herb Asarum canadense (wild ginger) was examined by measuring subsequent growth and storage. All connected vegetative rhizome was controlled and fully measured. Three important aspects of reproductive effort were addressed: (i) the effect of sexual reproduction on subsequent storage and growth of fragments, (ii) the effect of asexual reproduction on subsequent storage and growth of fragments, and (iii) a comparison to determine the least costly method of reproduction. It was found that sexual reproduction in wild ginger has an energy cost that diverts energy from storage and growth. Asexual reproduction represents neither a net energy cost nor gain to the fragment and is the least costly mode of reproduction to wild ginger. Key words: Asarum canadense, reproduction, rhizome, clonal.

Phenotypic variation, sexual reproduction and evolutionary population dynamics

AbstractI studied the effects of introducing phenotypic variation into a well‐known single species model for a population with discrete, non‐overlapping generations. The phenotypes differed in their dynamic behaviour. The analysis was made under the assumption that the population was in an evolutionary stable state. Differences in the timing of the competitive impacts of the phenotypes on each other had a strong simplifying effect on the dynamics. This result could also be applied to competition between species. The effect of sexual reproduction on the dynamics of the population was analysed by assuming the simplest genetic model of one locus with two alleles. Sexual reproduction made the system much more stable in the (mathematical) sense that the number of attractors was reduced and their basins of attraction enlarged. In a dominant system sex tended to increase the frequency of the recessive allele, and in an overdominant system it induced gene frequencies of 1/2. Whether the attractors in the dominant system tended to be simpler or more complex than the attractors in the asexual system depended on the phenotype of the recessive homozygote. The overdominant sexual system tended to have simpler dynamics than the corresponding asexual population. A 2‐locus model was used to study whether sexuals can invade an asexual population and vice versa. One locus coded for sexual and asexual reproduction, while the other coded for the dynamics. Enhanced stability through sexual reproduction seemed to be the reason why there was a clear asymmetry favouring sex in this evolutionary context.

Population subdivision in Australian temperate marine invertebrates: Larval connections versus historical factors*

AbstractThis paper reviews the use of genetic data, in combination with manipulative experimentation, to infer the mode of reproduction and the extent and directionality of dispersal for a range of Australian temperate marine invertebrates. Local populations of obligately sexually reproducing species have been inferred to be strongly interconnected by larval dispersal, over distances of thousands of kilometres. Their larvae may be subject to strong post‐settlement selection, but this selection is independent of obvious geographic or intertidal gradients. Within local populations selection may therefore result in apparently chaotic genetic patchiness which is eliminated by the effects of sexual reproduction and the widespread dispersal and mixing of the colonizing larvae of each generation. In partial contrast, local populations of species which rely on asexual reproduction for the maintenance of populations show evidence of similar larval connections, but no recent settlement of their sexually generated larvae has been demonstrated. The apparent connectedness of these populations may reflect either historical events or a more episodic pattern of settlement by sexually generated larvae. Local populations of these species are more highly differentiated as a result of the continued asexual replication of a limited number of genotypes. In one of these species, reciprocal transplantation of the clones within and among populations has revealed that resident clones can be highly locally adapted (as reflected by much higher asexual fecundity), which implies that selection is an important determinant of the composition of local populations. Nevertheless, the failure to detect continuing sexual recruitment into these populations obscures the evolutionary significance of this finding.

The Cost of Sexual Reproduction in Ragwort (Senecio jacobaea L.)

Probability of overwinter survival is inversely related to the allocation of resources to sexual reproduction in thepreceding summer. There is a marked similarity between the 2 study sites in the relationship between numbers of flowerheads and rootstock volume. The effect of herbivory on overwinter survival of plants varies with site and timing of feeding. Different herbivores may either exacerbate the effect of sexual reproduction on survival (eg through root feeding), reduce the effect (eg through early consumption of flowers) or have no influence on the effect of sexual reproduction on survival (eg by consumption of flowers later in the season). -from Authors

Evolutionarily stable dispersal strategies

Using the idea that life-history parameters are subject to natural selection and should approach values that are stable optima, with the population immune to invasion by mutant individuals, we derive an analytic expression for the evolutionarily stable dispersal rate in a stochastic island model with random site extinction. The results provide interesting contrasts between three different optimization criteria: species survival, individual fitness and gene fitness. We also consider the effects of sexual reproduction, and of localized migration (stepping-stone structure).

A Comparison of Virulence Phenotypes in Wheat Stem Rust Populations Reproducing Sexually and Asexually

ROELFS, A. P., and J. V. GROTH. 1980. A comparison of virulence phenotypes in wheat stem rust populations reproducing sexually and asexually. Phytopathology 70:855-862. The number and distribution of 16 loci expressing virulence were loci expressing virulence per isolate was about 6 and 10 for the sexual and compared in two populations of wheat stem rust in the USA. In 1975, asexual populations, respectively. The distribution of numbers of loci samples were collected from a population on barley and wheat in Idaho and expressing virulence differences between pairs of isolates was nearly Washington that undergoes sexual reproduction annually and from a random in the sexual population, while it was characterized by clusters of population east of the Rocky Mountains that reproduces asexually. phenotypes in the asexual population. These clusters differed from one Virulence was determined by inoculating 16 wheat lines, each differing by a another by 4 to 10 genes expressing virulence; genotypes within clusters single gene for stem rust resistance. The sexual population had a larger differed by 1 to 2 loci. None of the loci, examined in all of their paired frequency of distinct phenotypes expressed as a percentage. In the sexual combinations, deviated strongly from expected mean frequencies based on population, the frequency was 23.5% with 426 isolates and in the asexual products of individual locus frequencies, providing no evidence for strong population it was 0.07% with 2,377 isolates. Simpson's measure of diversity positive or negative fitness effects associated with individual genes. was 0.974 and 0.501 for the two populations, respectively. Mean number of Eradication of common barberry (Berberis vulgaris L.) from the model in 1971 (6). If certain conditions were met, the latter model wheat fields of the central Great Plains of North America was predicted two effects of sexual reproduction: first accelerated completed, for all practical purposes, by 1928. The effects of this evolutionary adaptation; and second more variable progeny, eradication on populations of stem rust of wheat (Puccinia resulting in production of some offspring of high fitness. The first graminis Pers. f. sp. tritici) have been the subject of much debate effect will occur if the population size, N, is about equal to or larger and speculation. One obvious effect noted was that the source of than 10 M-', where p is the mutation rate. The second effect required local, often early, epidemics of stem rust was eliminated (13). The frequent, large environmental fluctuations. Both of these claim (11) has been made that barberry eradication increased the conditions are met in stem rust. Populations are generally very average useful life of resistance genes in wheat (Triticum aestivum large, and the major component of the environment of the rust L.). Comparisons of this sort are confounded, however, by fungus-the host-changes frequently and dramatically, as differences in agronomic practices, the extent of monoculture, and compared with that of parasites in natural biota or with that of the wheat cultivars used before and after eradication. Thus, all nonparasites. Additionally, the physical environment changes as perceived differences in useful life of resistant cultivars cannot the season progresses and the pathogen spreads to new areas. necessarily be attributed to eradication of barberry and its Accelerated evolutionary adaptation is difficult or impossible to