Search results for "SEX RATIO"
showing 10 items of 121 documents
Social structure in termite societies
1989
The societies of Isoptera and Hymenoptera differ in two general features. 1. The termite societies are bisexual. From a primitive symmetry between both sexes, many asymmetries appeared during the course of their evolution. These asymmetries are related either to a sexual dimorphism, or a biased sex ratio, or both, and are differently expressed in the separate castes of a given species. 2. The hemimetabolous development allows a termite to take part in the social tasks before the end of its postembryonic development, and even to reproduce at a larval stage (neoteny). Thus Isoptera exhibit a polymorphism of larvae, unlike Hymenoptera where a polymorphism of imagoes is observed. Moreover, an i…
A trade-off between current and future sex allocation revealed by maternal energy budget in a small mammal.
2011
Sex-allocation theories generally assume differential fitness costs of raising sons and daughters. Yet, experimental confirmation of such costs is scarce and potential mechanisms are rarely addressed. While the most universal measure of physiological costs is energy expenditure, only one study has related the maternal energy budget to experimentally controlled offspring sex. Here, we experimentally test this in the bank vole (Myodes glareolus) by simultaneously manipulating the litter's size and sex ratio immediately after birth. Two weeks after manipulation, when mothers were at the peak of lactation and were pregnant with concurrent litters, we assessed their energy budget. We found that …
Sex–biased maternal investment in voles: importance of environmental conditions
2004
Adaptive bias in sex allocation is traditionally proposed to be related to the condition of mothers as well as to the unequal fitness values of produced sexes. A positive relationship between mother condition and investment into male offspring is often predicted. This relationship was also recently found to depend on environmental conditions. We studied these causalities experimentally using a design where winter food supply was manipulated in eight outdoor-enclosed populations of field voles Microtus agrestis. At the beginning of the breeding season in spring, food-supplemented mothers seemed to be in a similar condition, measured as body mass, head width, body condition index and parasite…
Characteristics and Changes over Time of Alcohol-Related Chronic Liver Diseases in Italy
2018
Introduction. To evaluate the characteristics of alcohol-related chronic liver disease (CLD) in Italy and their potential changes over time. Patients and Methods. Subjects with CLD were enrolled in two national surveys performed in 2001 and in 2014 in Italy. The two surveys prospectively recruited patients aged ≥ 18 years referring to more than 80 Italian liver units scattered all over the country using similar clinical approach, analytical methods, and threshold of risky alcohol intake definition (≥ 3 units/day in men and ≥ 2 units/day in women). Results. Out of 12,256 enrolled subjects, 2,717 (22.2%) reported a risky alcohol intake. Of them, anti-HCV positive was observed in 48.3% of subj…
Biological Aspects of Squids (loligo sp.) Caught by Fishermen in Manokwari Waters
2019
Squid (Loligo sp.) is one of the fisheries commodities caught in Manokwari waters. The aim of this study was to determine the biological aspects of Loligo sp. including the sex ratio, size distribution, growth pattern, and the lengthy relationship of Loligo sp. from Manokwari waters. This research was conducted in January until March 2017, in three landing sites of squid (Loligo sp) namely Fanindi Pantai, Borobudur and Arowi village. The method used is observation technique in the laboratory includes measurements of length and weight to find out the size distribution and growth pattern of captured Loligo sp. and surgery to determine the sex ratio. The male-female sex ratio of Loligo sp. was…
Population sex-ratio affecting behavior and physiology of overwintering bank voles (Myodes glareolus)
2016
Many boreal rodents are territorial during the breeding season but during winter become social and aggregate for more energy efficient thermoregulation. Communal winter nesting and social interactions are considered to play an important role for the winter survival of these species, yet the topic is relatively little explored. Females are suggested to be the initiators of winter aggregations and sometimes reported to survive better than males. This could be due to the higher social tolerance observed in overwintering females than males. Hormonal status could also affect winter behavior and survival. For instance, chronic stress can have a negative effect on survival, whereas high gonadal ho…
Coevolution of parental investment and sexually selected traits drives sex-role divergence
2016
Sex-role evolution theory attempts to explain the origin and direction of male–female differences. A fundamental question is why anisogamy, the difference in gamete size that defines the sexes, has repeatedly led to large differences in subsequent parental care. Here we construct models to confirm predictions that individuals benefit less from caring when they face stronger sexual selection and/or lower certainty of parentage. However, we overturn the widely cited claim that a negative feedback between the operational sex ratio and the opportunity cost of care selects for egalitarian sex roles. We further argue that our model does not predict any effect of the adult sex ratio (ASR) that is …
Sex roles and the evolution of parental care specialization
2019
Males and females are defined by the relative size of their gametes (anisogamy), but secondary sexual dimorphism in fertilization, parental investment and mating competition is widespread and often remarkably stable over evolutionary timescales. Recent theory has clarified the causal connections between anisogamy and the most prevalent differences between the sexes, but deviations from these patterns remain poorly understood. Here, we study how sex differences in parental investment and mating competition coevolve with parental care specialization. Parental investment often consists of two or more distinct activities (e.g. provisioning and defence) and parents may care more efficiently by s…
Daphnia females adjust sex allocation in response to current sex ratio and density
2018
Cyclical parthenogenesis presents an interesting challenge for the study of sex allocation, as individuals’ allocation decisions involve both the choice between sexual and asexual reproduction, and the choice between sons and daughters. Male production is therefore expected to depend on ecological and evolutionary drivers of overall investment in sex, and those influencing male reproductive value during sexual periods. We manipulated experimental populations, and made repeated observations of natural populations over their growing season, to disentangle effects of population density and the timing of sex from effects of adult sex ratio on sex allocation in cyclically parthenogenetic Daphnia…
Do bank voles (Myodes glareolus) trapped in live and lethal traps show differences in tick burden?
2020
In studies assessing tick abundance, the use of live traps to capture and euthanize rodent hosts is a commonly used method to determine their burden. However, captive animals can experience debilitating or fatal capture stress as a result prior to collection. An alternative method is the use of lethal traps, but this can potentially lead to tick drop-off between the time of capture and collection. In this study, in order to determine whether subjecting animals to capture stress is inevitable, we tested the difference in sheep tick (Ixodes ricinus) larval burdens between bank voles (Myodes glareolus) captured alive and euthanized, and lethally trapped bank voles. During 2017 and 2018, 1318 b…