Search results for "SEX RATIO"
showing 10 items of 121 documents
Variable male potential rate of reproduction: high male mating capacity as an adaptation to parasite–induced excess of females?
2003
Numerous animals are known to harbour intracytoplasmic symbionts that gain transmission to a new host generation via female eggs and not male sperm. Bacteria of the genus Wolbachia are a typical example. They infect a large range of arthropod species and manipulate host reproduction in several ways. In terrestrial isopods (woodlice), Wolbachia are responsible for converting males into females (feminization (F)) in some species, or for infertility in certain host crosses in other species (cytoplasmic incompatibility (CI)). Wolbachia with the F phenotype impose a strong excess of females on their host populations, while Wolbachia expressing CI do not. Here, we test the possibility that male m…
Population structure and recruitment of the ectoparasite Argulus coregoni Thorell (Crustacea: Branchiura) on a fish farm
2003
The population structure and recruitment of Argulus coregoni was monitored at a Finnish fish farm during the open water periods of 1999 and 2001 by weekly sampling of attached argulids. In 2001 the numbers of rainbow trout examined increased in the autumn when the A. coregoni population was declining. When the water temperature exceeded 10 degrees C, at the end of May, A. coregoni egg hatching commenced. A mean number of 98 (S.D. +/- 5.4) juvenile A. coregoni was recorded on each fish, before the start of female egg laying in July 1999. The abundance of lice was lower in 2001. The main recruitment of A. coregoni juveniles occurred in early summer, but the hatching of eggs continued until Se…
Quantitative measure of sexual selection with respect to the operational sex ratio: a comparison of selection indices
2006
Despite numerous indices proposed to predict the evolution of mating systems, a unified measure of sexual selection has remained elusive. Three previous studies have compared indices of sexual selection under laboratory conditions. Here, we use a genetic study to compare the most widely used measures of sexual selection in natural populations. We explored the mating and reproductive successes of male and female bank voles,Clethrionomys glareolus, across manipulated operational sex ratios (OSRs) by genotyping all adult and pup bank voles on 13 islands using six microsatellite loci. We used Bateman's principles (IsandIand Bateman gradients) and selection coefficients (s′ andβ′) to evaluate, f…
Immunogenetics, Gender, and Longevity
2007
In this article we discuss relevant data on aging, longevity, and gender with particular focus on inflammation gene polymorphisms which could affect an individual's chance to reach the extreme limit of human life. The present review is not an extensive revision of the literature, but rather an expert opinion based on selected data from the authors' laboratories. In 2000-2005 in the more developed regions, the life expectancy at birth is 71.9 years for men (78.3 in Japan) and 79.3 years for women (86.3 in Japan). Indeed, gender accounts for important differences in the prevalence of a variety of age-related diseases. Considering people of far-advanced age, demographic data document a clear-c…
Quantitative parameters and ecological implications of a specialized tritrophic interaction involving a seed-feeding tortricid, Pseudargyrotoza conwa…
2014
Producción Científica
Maternal investment in relation to sex ratio and offspring number in a small mammal – a case for Trivers and Willard theory?
2009
1. Optimal parental sex allocation depends on the balance between the costs of investing into sons vs. daughters and the benefits calculated as fitness returns. The outcome of this equation varies with the life history of the species, as well as the state of the individual and the quality of the environment. 2. We studied maternal allocation and subsequent fecundity costs of bank voles, Myodes glareolus, by manipulating both the postnatal sex ratio (all-male/all-female litters) and the quality of rearing environment (through manipulation of litter size by -2/+2 pups) of their offspring in a laboratory setting. 3. We found that mothers clearly biased their allocation to female rather than ma…
Coexistence of three microsporidia parasites in populations of the freshwater amphipod Gammarus roeseli: evidence for vertical transmission and posit…
2004
We investigated the prevalence, transmission mode and fitness effects of infections by obligatory intracellular, microsporidian parasites in the freshwater amphipod Gammarus roeseli. We found three different microsporidia species in this host, all using transovarial (vertical) transmission. All three coexist at different prevalences in two host populations, but bi-infected individuals were rarely found, suggesting no (or very little) horizontal transmission. It is predicted that vertically-transmitted parasites may exhibit sex-specific virulence in their hosts, or they may have either positive or neutral effects on host fitness. All three species differed in their transmission efficiency an…
Proximate factors affecting the larval life history of Acanthocephalus lucii (Acanthocephala).
2007
The growth and eventual size of larval helminths in their intermediate hosts presumably has a variety of fitness consequences. Therefore, elucidating the proximate factors affecting parasite development within intermediate hosts should provide insight into the evolution of parasite life histories. An experimental infection that resulted in heavy intensities of an acanthocephalan (Acanthocephalus lucii) in its isopod intermediate host (Asellus aquaticus) permitted the examination of parasite developmental responses to variable levels of resource availability and intraspecific competition. Isopods were infected by exposure to egg-containing fish feces, and larval infrapopulations were monitor…
Stigma and functioning in patients with bipolar disorder
2011
Abstract Objective The aim of this study was to investigate the impact of self-rated stigma and functioning in patients with bipolar disorder in Latin-America. Methods Two-hundred and forty-one participants with bipolar disorder were recruited from three Latin American countries (Argentina, Brazil, and Colombia). Functional impairment was assessed with the Functioning Assessment Short Test (FAST) and experiences with and impact of perceived stigma was evaluated using the Inventory of Stigmatizing Experiences (ISE). Results Higher scores of self-perceived stigma were correlated with lower scores of functioning. After multiple regression analysis, being on disability benefit, current mood sym…
Unmatedness promotes the evolution of helping more in diplodiploids than in haplodiploids
2014
The predominance of haplodiploidy (where males develop from unfertilized haploid eggs and females from fertilized diploid eggs) among eusocial species has inspired a body of research that focuses on the possible role of relatedness asymmetries in the evolution of helping and eusociality. Previous theory has shown that in order for relatedness asymmetries to favor the evolution of helping, there needs to be variation in sex ratios among nests in the population (i.e., split sex ratios). In haplodiploid species, unmated females can produce a brood of all males, and this is considered the most likely mechanism for split sex ratios at the origin of helping. In contrast, in diploidiploids unmated…