two iranian strains of brachionus rotifers were cultured under different food and salinity regimes. the rotiferswere fed with five algal types (freshwater and marine chlorella vulgaris, nannochloropsis occulata, isochrysisgalbana and scenedesmus obliquus) at three different salinities (5, 15 and 25 g/l) and their reproductive and growth parameters were assessed. the maximum number of ovigerous ...

the aim of this investigation was to study macroscopic and microscopic structures of ovaries in barbus grypus of karoon river and their changes during annual maturation cycle. for this purpose, 120 adult  b.grypus with a mean weight of 835.0 to 1012.0 g, were caught from karoon river and transferred alive to the laboratory. after biometrical studies, the weights and morphological appearances of...

growth and reproductive attributes were determined for capoeta damascina, an endemic fish species from west of iran. a total of 147 specimens of both sexes were sampled monthly from november 2008 to october 2009. the overall sex ratio was female biased. males were aged 0-4 years and females 0-5 years. the von bertalanffy growth parameters were estimated as; linf=34.81 cm, k=0.27 year-1, t0=-0.6...

background: diminished libido and sexual dysfunction are unusually common among male epileptic patients. the most important etiologic factor may be antiepileptic drugs (aeds)-induced androgen deficiency. we compared reproductive hormone levels among men with epilepsy taking various aeds and normal controls. methods: subjects were 59 male epileptic patients who aged 24 ± 5 years. they had been r...

The maintenance of sex is an unresolved paradox in evolutionary biology, given the inherent twofold fitness advantage for asexuals. Parasitic helminths offer a unique opportunity to address this enigma. Parasites that can create novel antigenic strains are able to escape pre-existing host immunity. Viruses produce diversity through mutation with rapid clonal proliferation. The long generation t...

Population density can profoundly influence fitness-related traits and population dynamics, and density dependence plays a key role in many prominent ecological and evolutionary hypotheses. Here, we evaluated how individual-level changes in population density affect growth rate and embryo production early in reproductive maturity in two different asexual lineages of Potamopyrgus antipodarum, a ...

Sexual reproduction is both extremely costly and widespread relative to asexual reproduction, meaning that it must also confer profound advantages in order to persist. One theorized benefit of sex is that it facilitates the clearance of harmful mutations, which would accumulate more rapidly in the absence of recombination. The extent to which ineffective purifying selection and mutation accumul...

We consider the evolutionary basis of intertemporal choice and time discounting, in particular, when there are intergenerational transfers. We show that the notion of “reproductive value” from biology provides the utility criterion for a parent to optimize the allocation of resources between transfers to offspring and for promoting her own survival to the next period. This optimization has a na...

The aims of this study were to determine (i) whether adaptation under strong selection occurred through mutations in a narrow target of one or a few nucleotide sites or a broad target of numerous sites and (ii) whether the programs of adaptation previously observed from three experimental populations were unique or shared among populations that underwent parallel evolution. We used archived pop...

Asexuality is rare in animals in spite of its apparent advantage relative to sexual reproduction, indicating that it must be associated with profound costs [1-9]. One expectation is that reproductive advantages gained by new asexual lineages will be quickly eroded over time [3, 5-7]. Ancient asexual taxa that have evolved and adapted without sex would be "scandalous" exceptions to this rule, bu...