Search results for "reproduction"
showing 10 items of 752 documents
Not all sex ratios are equal : the Fisher condition, parental care and sexual selection
2017
The term ‘sex roles’ encapsulates male–female differences in mate searching, competitive traits that increase mating/fertilization opportunities, choosiness about mates and parental care. Theoretical models suggest that biased sex ratios drive the evolution of sex roles. To model sex role evolution, it is essential to note that in most sexually reproducing species (haplodiploid insects are an exception), each offspring has one father and one mother. Consequently, the total number of offspring produced by each sex is identical, so the mean number of offspring produced by individuals of each sex depends on the sex ratio (Fisher condition). Similarly, the total number of heterosexual matings …
Acute, chronic and sublethal effects of the herbicide propanil on Daphnia magna.
2003
Acute and chronic toxicity tests with propanil were conducted on Daphnia magna. The 24 and 48 h LC50 were 43.74 and 5.01 mg/l respectively. Chronic toxicity tests were carried out using sublethal propanil concentrations (0.07, 0.10, 0.21 and 0.55 mg/l) during 21 days. The effect of propanil on survival, reproduction and growth of D. magna organisms was monitored. The parameters used to evaluate herbicide effect on reproduction were: mean total young ones per female, mean brood size, time to first reproduction, mean number broods per female and intrinsic rate of natural increase (r). Survival and growth (body length) were also determined after 21 days of exposure to the herbicide. Reproducti…
Genetic correlation between resistance to oxidative stress and reproductive life span in a bird species.
2010
Evolutionary theories propose that aging is the result of a trade-off between self-maintenance and reproduction, and oxidative stress may play a crucial role in such a trade-off. Phenotypic manipulations have revealed that a high investment in reproduction leads to a decline in the organism's resistance to oxidative stress, which could in turn accelerate aging. Here, by using quantitative genetic analyses as a tool to disentangle genetic effects from phenotypic variances, the relationship between resistance to oxidative stress at sexual maturity and two key reproductive life-history traits (i.e., number of breeding events during life and age at last reproduction) was analyzed in cross-foste…
Despidos laborales. Fracturas sociales e identitarias
2008
The thousands of collective dismissals which have opened the beginning of the century in Spain do not just mean nearly two hundred thousand jobs (lots of them with a very long validity) and the same amount of broken life projects, but also ways of social reproduction, broken identities, institutions and social guarantees that crumble. Amazingly, these social upheavals often become eclipsed by discourses that appeal to economic considerations, the requirements of modernization or the requests of the logic of globalization. At this article, the consequences of the break of the social link intertwined along the second half of the twentieth century are investigated. For that, we have been rebui…
Salinity effects on asexual reproduction of Carybdea sp. (Cnidaria: Cubozoa)
2014
6 pages, 2 figures, 1 table, supplementary data http://plankt.oxfordjournals.org/content/36/2/585/suppl/DC1
Oral administration of pharmacological doses of Vitamins C and E reduces reproductive fitness and impairs the ovarian and uterine functions of female…
2002
This study aims to ascertain whether oral administration of pharmacological doses of Vitamins C and E has any detrimental effect on reproductive fitness of female mice. We fed hybrid female mice from the first day of weaning a standard diet supplemented or not supplemented with pharmacological doses of Vitamins C and E. At the age of 28 weeks, we individually caged females with a male for the rest of their reproductive life. We performed a series of mating experiments to ascertain the number of oocytes ovulated and the potential for embryo development in vitro to the blastocyst stage and in vivo to Day 12 of gestation. The antioxidant diet decreased the frequency of litters, litter size, to…
Sister-chromatid exchange in cultured lymphocytes of ewes and their newborn lambs
1984
The incidence of sister-chromatid exchange (SCE) in cultured lymphocytes of ewes and their newborn lambs was determined using the BrdU-Giemsa technique. In all ewe-lamb pairs, the SCE rate in the lambs was less than that of the ewes. The mean SCE frequencies per chromosome of the ewes after lambing and of the newborn lambs were 0.1909 and 0.1581, respectively. The statistical analysis shows that a significant difference exists between SCE in the adult female sheep and their lambs. At the same time, a negative correlation was observed between SCE rate and cell proliferation. The results of this study are compared with those of previous reports on age-dependency of SCE.
Hydrodynamism and its influence on the reproductive condition of the edible sea urchin Paracentrotus lividus
2013
Despite the large body of work published in the last two decades on the reproduction of the sea urchin Paracentrotus lividus, the reproductive aspects linked to hydrodynamic conditions and their influence on gonad production remain poorly understood. The present paper aims to evaluate the effect of hydrodynamism on the reproductive cycle of P. lividus. Variability in the gonadosomatic index (GSI) of P. lividus was estimated seasonally from 2007 to 2008 at two shallow sub-littoral flat basaltic areas at Ustica Island (Western Mediterranean). GSI was higher in the sites characterized by low hydrodynamism than in those with high hydrodynamism. Results also suggest a possible role for hydrodyna…
Parent–offspring conflict and the genetic trade-offs shaping parental investment
2015
The genetic conflict between parents and their offspring is a cornerstone of kin selection theory and the gene-centred view of evolution, but whether it actually occurs in natural systems remains an open question. Conflict operates only if parenting is driven by genetic trade-offs between offspring performance and the parent's ability to raise additional offspring, and its expression critically depends on the shape of these trade-offs. Here we investigate the occurrence and nature of genetic conflict in an insect with maternal care, the earwig Forficula auricularia. Specifically, we test for a direct response to experimental selection on female future reproduction and correlated responses i…
Virgins in the wild: mating status affects the behavior of a parasitoid foraging in the field
2008
In haplodiploid organisms, virgin females can produce offspring, albeit only sons. They may therefore face a trade-off between either: (1) searching for hosts and producing sons immediately; or (2) searching for mates and perhaps producing both sons and daughters later in life. Although this trade-off raises a theoretical interest, it has not been approached experimentally. The objective of this article is thus to document the effect of mating status on the foraging behavior of a haplodiploid parasitoid. For this, we recorded the behavior of virgin and mated female Lysiphlebus testaceipes (Hymenoptera: Braconidae) after being released, in the field, on a colony of their aphid hosts. Half of…