Sex Ratio Distribution Research Articles

Litter sex ratios in the golden hamster vary with time of mating and litter size and are not binomially distributed

Pregnancy rates, litter sizes, and litter sex ratios vary strongly with the time in the estrous cycle at which female golden hamsters (Mesocricetus auratus) are mated. Early matings tend to produce relatively high pregnancy rates, large litters, and female-biased sex ratios, while late matings tend to produce low pregnancy rates, small litters, and male-biased sex ratios. Time of mating and litter size are therefore correlated, but each appears to have an independent effect on litter sex ratio: time of mating and sex ratio are positively correlated, holding litter size constant, while litter size and sex ratio are negatively correlated, holding time of mating constant. At each litter size greater than two, the variance of litter sex ratios is less than the binomial variance expected on the hypotheses of independent sampling with a constant probability of producing a male. The main features of the distribution of litter sex ratios can be generated from a causal model in which different probabilities of producing a male apply to “early” and “late” conceptions within each litter. The relationship between litter size and mean litter sex ratio is potentially consistent with several different models for the evolution of adaptive sex-ratio variation.

Histological types of thyroid cancer in hong kong chinese, 1986-1988

This study aims at comparing the histological, age and sex distribution of thyroid cancer in the Hong Kong Chinese with a similar study undertaken 13 years ago. Ninety consecutive cases from 1986 to 1988 were reviewed. Only cases diagnosed by biopsy or surgical excision were included. Autopsy cases and incidental occult papillary carcinoma were excluded. The revised WHO classification was used. 72.5% were papillary carcinoma, 23.1% follicular carcinoma, 1.1% undifferentiated carcinoma, 2.2% medullary carcinoma. The overall male:female (M:F) ratio was 1:3.5. Compared to the previous study, the proportion of papillary carcinoma was altered from 59.8% to 72.5%, that of follicular carcinoma from 21.3% to 23.1%, that of undifferentiated carcinoma from 16.4% to 1.1%. Although the overall M:F ratio was similar (1:3.1 versus 1:3.5), in papillary carcinoma, the M:F ratio was altered from 1:2.8 to 1:4.7; and in follicular carcinomas from 1:5.5 to 1:2.0. There was also a shift in age incidence of follicular carcinoma in males to the older age groups. While the changes in histological types might be due to changes in classification, the changes in sex ratio and age distribution were probably genuine. These changing patterns might help to determine the aetiology of thyroid cancer.

Requirement and supply of dental services in Victoria.

The appropriateness of dental manpower has become a great uncertainty in the changing practice of dentistry. This paper presents research on the requirement for and supply of dental services in Victoria between 1984 and 1996. The requirement for dental services was found to be increasing due to population growth and higher per capita demand due to decreased endentulism. The supply of dental services was found to be mildly decreasing due to balanced supplementation and attrition processes and subtle sex ratio and age distribution changes among dentists. The resulting market excess, even after consideration of idle capacity and transfer of services supplied to dental therapists, provides a marked contrast to many, but not all, developed countries. It also offers an opportunity to shape occupational and specialty distribution to the advantage of dental professions and the public.

Limb reduction defects in over one million consecutive livebirths.

Limb reduction defects occurring among 1,213,913 consecutive livebirths in British Columbia during the period 1952-1984 inclusive were reviewed. A total of 659 cases of limb reduction defects were identified, 393 of them involving the long bones and 190 of them more than one limb. The time period 1966-1984, during which ascertainment was consistent, was evaluated, and an incidence of 5.97 per 10,000 livebirths (1 in 1,692 live births) was found. The data were evaluated for trends over time, sex ratio, and regional and ethnic distribution. Associated anomalies of other organ systems in these cases were analyzed, and overall about one-half of the cases have additional defects. The majority of these additional defects affect the musculoskeletal system and include such entities as clubfoot, hip dislocation, and congenital contractures. Defects are also frequent in other organ systems, such as the cardiovascular, gastrointestinal, and genitourinary systems. By far the most common limb defects are terminal longitudinal defects then terminal transverse defects. Of all cases of limb defects, 75% are upper limb and 25% lower limb. We found no evidence that one side is affected more frequently. About 6.5% of cases had another family member registered with a skeletal defect; 12.9% of cases died within the first year of life, the majority (85%) of those dying having additional defects. Etiological considerations are discussed for some subgroups.(ABSTRACT TRUNCATED AT 250 WORDS)

The potential for sexual selection in males: Effect of sex ratio and spatiotemporal distribution of receptive females

An animal mating system characterized by male-male competition and active searching for sexually receptive females was modelled to study how varying sex ratio and spatiotemporal distribution of receptive females can affect the variance in male mating success (i. e. potential for sexual selection) in males. The temporal distribution of female receptivity periods appeared to be the variable that had the most pronounced effect on the potential for sexual selection in males. The potential for sexual selection increased monotonically as the degree of asynchrony of female reproduction increased. Female spatial distribution and sex ratio were important only when female reproduction was asynchronous. Then, the potential for sexual selection in males was at its peak when females were overdispersed in space and the sex ratio was female biased. Some of the results derived from the model analysis contrast with predictions from previous studies. The deviating results are most likely caused by different assumptions about modes of mate acquisition in males.

The Environmental and Genetic Components of Sex Ratio in Menidia menidia (Pisces: Atherinidae)

Comparison of sex ratios among families reared at different temperatures during larval development suggests that environmental sex determination is under the control of major sex determining genes in Menidia menidia. The response of family sex ratio to temperature within mothers was highly dependent on paternity. Moreover, the frequency distribution of family sex ratios within a temperature was multimodal: sex ratios at 15 C tended to be near 0, 0.5, or 1.0; while those at 21 C tended to be near 0, 0.25, or 0.5. The proportion of offspring that had gender determined by temperature within a family tended to be about 0, 0.25, or 0.5. Sex ratio had an inverse curvilinear relation to temperature, rather than the threshold response that has been identified in most of the other vertebrates with temperature-dependent sex determination. Sex ratio declined rapidly as temperature increased from 15-21 C, but less so at higher temperatures. The sex ratio among offspring batches from some isolated pairs of mated fish varied erratically, indicating an additional component of sex ratio variance attributable to non-genetic parental effects, or some form of environmental influence other than temperature. Photoperiod and salinity during development had no effect on sex ratio. Sex determination in M. menidia is apparently intermediate between that of the completely genetic or completely environmental forms of sex determination that have been identified in other lower vertebrates. In relation to the life history pattern of M. menidia, this observation is in accord with the predictions of sex ratio theory.

Effect of Density on Secondary Sex Characteristics and Sex Ratio in Silene alba (Caryophyllaceae)

A field survey of plant and flower sex ratio and secondary sex characteristics was made in Silene alba. Female-biased plant sex ratios were found, as seems typical for the species. Sex ratio distribution correlated with a gradient of soil moisture (with the more moist area having a more female-biased ratio) and with changes in the density of Silene (intermediate and higher density areas having greater female bias). The floral sex ratio was significantly female-biased only at the site that was most female-biased in terms of plant sex ratio. Otherwise the population of flowers was significantly male-biased. Male and female plants harvested from the field differed in secondary sexual characteristics. Males had more flowers and invested proportionately more biomass in leaf, but less in root, stem and reproductive tissue than did females. Although both males and females were larger in terms of total dry weight at the moist site, males produced more flowers at the driest (high density) site. Here the female bias in plant sex ratio was intermediate, but the floral sex ratio was significantly male-biased. A glasshouse experiment was performed in which plants were grown at four densities. Density significantly influenced plant survivorship and the probability of flowering, and increased female bias in the pots, but it did not affect patterns of biomass allocation in flowering plants. Patterns of male and female biomass allocation did not differ in the experiment, except in terms of reproductive allocation (greater in females) and allocation to leaf, greater in males, but only at the lowest density. This work urges caution in interpreting differences between males and females in the field as secondary sex characteristics, since we find such properties to be overlapping under experimental conditions. It supports the idea that males and females of a species may sustain different reproductive output under differing conditions.

EFFECT OF DENSITY ON SECONDARY SEX CHARACTERISTICS AND SEX RATIO IN SILENE ALBA (CARYOPHYLLACEAE)

A field survey of plant and flower sex ratio and secondary sex characteristics was made in Silene alba. Female‐biased plant sex ratios were found, as seems typical for the species. Sex ratio distribution correlated with a gradient of soil moisture (with the more moist area having a more female‐biased ratio) and with changes in the density of Silene (intermediate and higher density areas having greater female bias). The floral sex ratio was significantly female‐biased only at the site that was most female‐biased in terms of plant sex ratio. Otherwise the population of flowers was significantly male‐biased. Male and female plants harvested from the field differed in secondary sexual characteristics. Males had more flowers and invested proportionately more biomass in leaf, but less in root, stem and reproductive tissue than did females. Although both males and females were larger in terms of total dry weight at the moist site, males produced more flowers at the driest (high density) site. Here the female bias in plant sex ratio was intermediate, but the floral sex ratio was significantly male‐biased.A glasshouse experiment was performed in which plants were grown at four densities. Density significantly influenced plant survivorship and the probability of flowering, and increased female bias in the pots, but it did not affect patterns of biomass allocation in flowering plants. Patterns of male and female biomass allocation did not differ in the experiment, except in terms of reproductive allocation (greater in females) and allocation to leaf, greater in males, but only at the lowest density. This work urges caution in interpreting differences between males and females in the field as secondary sex characteristics, since we find such properties to be overlapping under experimental conditions. It supports the idea that males and females of a species may sustain different reproductive output under differing conditions.

Chillingham Cattle: Dominance and Affinities and Access to Supplementary Food

AbstractA herd of cattle of natural sex ratio and age distribution, inhabiting a 134‐ha park in northern England, was studied during supplementary feeding in 4 winters. Interactions could be summarised by conventional dominance hierarchies, more strictly linear and less stable among males than among females. Personal associations among individuals were not important, but affinities among social classes were, in determining the composition of feeding groups. Dominant males often fed in the same groups as dominant females. Dominant animals were less often seen to feed alone, implying that social dominance did not confer exclusive access to food. Cattle often fed in groups of two or three; certain combinations (notably those including two males, or one male and one female, or three calves) were stable, others unstable, notably combinations of females and calves, or of two or three females. This implies that females may defend resources more vigorously against other females than males do against other males.

Ecology of Hatchling Sex Ratio in Map Turtles

Incubation temperature is known to determine the sex of hatchlings in many species of turtles, including the map turtles. Graptemys ouachitensis, G. pseudogeographica, G. geographica, and painted turtle, Chrysemys picta. This paper presents a study of sex ratio and nest ecology in natural populations of these species in Wisconsin, but largely for G. ouachitensis and G. pseudogeographica. Nesting was monitored during June, and hatchlings were obtained from 236 nests during August and September 1980. The distribution of nest sex ratios samples of the two common species was bimodal, tending to be all—female or all—male within a nest, with an overall excess of females. Nests with males were located amid vegetation, with cool temperatures, and nests with females were located in open sand exposed to the sun, with high temperatures. The sex ratio differed significantly between nesting beaches, apparently because of differences in the availability of warm vs. cool nest sites. All—female nests hatched in less time than all—male nests, and the sex ratio of emerging hatchlings consequently changed from nearly all female early in August to all male in September. The data indicate major environmental influences on the hatchling sex ratio in map turtles.

Some reproductive parameters of stumptailed macaques (Macaca arctoides)

Reproductive records kept from 1969 to 1981 were used to study menstrual cycles, pregnancies and births of eight colony-housed stumptailed macaques. The findings for annual distribution of births, pregnancy duration and infant sex ratio were consistent with previous reports. The interbirth interval after infant loss was significantly shortened from the interbirth interval when infants were maintained with their mothers. Vaginal bleeding during early lactation indicates that stumptails are not necessarily characterized by a prolonged period of postpartum amenorrhea. Complete copulation was observed prior to six months postpartum, but interbirth intervals indicate that conception did not occur prior to that time. Interbirth intervals tended to be shorter for dominant than for subordinate females and to lengthen as a function of increasing age.

Binomial Sex-Ratio Distribution in the Lesser Snow Goose: A Theoretical Enigma

Several social and/or ecological conditions can be recognized that would make a strict adherence to an independent (random) sex-determination mechanism, if not maladaptive, certainly nonadaptive. Some conditions should lead to parental control over sex determination being adaptive; in others it can be reasonably argued that no one sex-determining mechanism should be favored. The population structure, methods of mate choice, and breeding biology of the lesser snow goose are such that theory would predict a virtual absence of selective pressure maintaining an independent sex-determination mechanism. Such a situation should lead to more variance in the distribution of intraclutch sex ratios than predicted by the binomial model of independent sex determination. A large sample of goslings does show a sex-ratio distribution which closely fits the binomial, thus refuting the theoretical argument. It can be speculated that pleiotropic effects of sex-skew mutations place a selective disadvantage on such mutations or that such mutations are, for one reason or another, impossible.

The Cultivation of Calanojdes Carinatus Krøyer (Copepoda: Calanoida) under Different Temperature and Food Conditions-with a Description of Eggs and Nauplii

According to its mouthparts Calanoides carinatus is a herbivorous filter-feeder (Mensah, 1974a; Schnack, 1978) that is often associated with phytoplankton blooms. The species has been reported from the three oceans and the Mediterranean (Vervoort, 1946). Interest in this copepod is increasing due to its apparent importance as a dominant link between phytoplankton and fish in upwelling areas. Its presence in surface waters is regarded as an indication for upwelled water (Bainbridge, 1972; Binet, 1973). Population dynamics and life-cycle have been studied best on the West African shelf (Mensah, 1974b; Binet & Suisse St Claire, 1975; Petit & Courties, 1976; Binet, 1977). Courties (1978) has recently given a comprehensive review of the literature on C. carinatus. In the above-mentioned studies, generation time usually is estimated by measuring successive peaks of larval stages and adults as well as using sex ratio and length distribution. In spite of its importance, C. carinatus has not yet been successfully reared in the labora-tory. Tomasini & Petit (1977) determined experimentally the developmental time of eggs and some copepodite stages, but could not obtain all stages. Schnack (1978) studied the feeding behaviour in feeding and assimilation experiments using various species of algae on board ship.

The changing distribution of sex ratios in the british urban system

The preponderance of females in society has steadily decreased since the last war. This paper uses Metropolitan Economic Labour Areas to examine the differential effect of these changes and suggests associations with retirement migration and increasing female economic activity rates.

Stress and the major psychiatric illnesses.

Sixty patients who had a major psychiatric breakdown following stress were studied. The mode of presentation of one group led to the suspicion of a reactive psychosis and comparison with the other group showed that in terms of the actual or threatened loss of an emotionally significant person, the temporal relationship between stress and illness and the distribution of vulnerable personalities, there was a significant difference between the groups. The sex ratio and frequency distribution for age were also suggestive. In view of the above and the known clinical course of the illness and comparison with the work of major workers in this field, it seems reasonable to believe that grounds exist for accepting the diagnosis of reactive psychoses in Sri Lanka.

Resistance to meiotic drive at the MD locus in an Indian wild population of Aedes aegypti.

SUMMARYFemales from an Indian wild population ofAedes aegyptiwere crossed to males carrying the sex ratio distorter factorMDwhich shows meiotic drive. Progenies from F1males were tested for sex ratio distortion, i.e. the chromosomes from the wild females were screened for their resistance to the action ofMD. The distribution of sex ratio in the progenies of different F1males indicated a polymorphism in the wild population for resistant and sensitive variants of theXchromosome. Seven discrete categories ofXappear to exist, associated with sex ratios ranging from 50% ♀ to less than 1·25% ♀. The overall level of resistance varied slightly but significantly in different parts of a town. The results are discussed in relation to the use of sex ratio distortion for genetic control of mosquitoes.

Spatial Pattern and Gamete Dispersal Distances in Atrichum angustatum, a Dioicous Moss

Spatial Pattern and Gamete Dispersal Distances in Atrichum angustatum, a Dioicous Moss

Geographic Distribution and Seasonal Variation of Sex Ratio at Birth in India

From the data of Indian Vital Statistics in 1962-1964, the geographic distribution of sex ratio at birth and seasonal variation of the ratio in different states of India are studied. In the yearly average of these three years, higher sex ratios at birth distribute in the northwestern inland states than in the southern and eastern coast states. In Rajasthan and Uttar Pradesh the sex ratio is over 120 males to 100 females, which is higher than the highest ever known in Korea. The seasonal variation of sex ratio at birth in the northwestern inland states is more distinct than that in the southern and eastern coast states, as well as the seasonal variation of birth ratio. Both curves of the seasonal variation of sex ratio and of birth ratio have some phase difference, and the sex ratio is rather low in the months of higher birth ratio, and vice versa. Although Indian vital statistics is not yet satisfactorily established, peculiar geographic distribution and seasonal variation of the sex ratio, which seem to be influenced by climate, are perceived. To interprete the phenomena some hypotheses are adapted and discussed.

The Influence of Sampling Methods on the Estimation of Population Structure in Painted Turtles

A natural population of painted turtles [Chrysemys picta (Schneider)] was studied in University Bay of Lake Mendota, Dane County, Wisconsin, from September 1960 to October 1962. Five methods were used to capture turtles for marking, measurement, and release. Each of the methods yielded a different size-class distribution and a sex ratio which, in four out of five cases, was significantly different from that of the total population estimate. Baited hoop nets yielded predominantly males and relatively few juveniles; basking traps tended to yield higher percentages of females than did nets, and large turtles were an important component of the sample. Hand capture resulted in a sample heavily weighted by juveniles and a 1: 1 sex ratio for adults. The influence of trapping method in the estimation of population structure in turtles must not be overlooked. This study indicates that even within a species, trapping method introduces considerable bias in the estimation of sex ratio and size-class distribution. INTRODUCTION The structure of turtle populations, as estiimated by different authors (Cagle, 1942, 1944, 1954; Pearse, 1923; Sexton, 1959), has varied considerably even within the same species. Although this variation may be due to inherent differences in the populations studied, or to various ecological factors affecting each population with different intensities, it is more probable that the disparity lies in the sampling method used by the investigators. Cagle and Chaney (1950) suggested that sampling methods are biased by the behavioral patterns of the size classes and sexes that make up the population, but we are unaware of any study that has compared the variation in estimation of population and its strutcture brought about by use of different sampling methods. A natural population of Chrysemys picta (Schneider) was studied in University Bay of Lake Mendota, Dane County, Wisconsin, from September 1960 to October 1962. The central painted turtle, Chrysemys picta marginata (Agassiz) and the western painted turtle, Chrysemys picta belli (Gray) intergrade in this region (Pope, 1949). Five methods were used to capture a maximum number of turtles for marking, measurement, and release. Variant results obtained from use of these methods were sufficiently striking to, warrant a comparison of the methods. Acknowledgments.-This study was done with the aid of two NSF Summer Fellowships for Teaching Assistants. Additional financial assistance for field equipment and limited field assistance was provided by a grant to Dr. W. G. Reeder from the Wisconsin Alumni Research Foundation through the University of Wisconsin Graduate School. Appreciation for encouragement and constructive criticism is given to Dr. W. G. Reeder, Dr. J. M. Legler, and Dr.

A Genetic Study of Ulcerative Colitis.

A group of 152 patients with a verified diagnosis of ulcerative colitis (including haemorrhagic proctitis) was compared with a control group with an identical sex ratio, age, and social class distribution. All patients attended an ulcerative colitis out-patient clinic, and had been examined and followed by the members of the team. By the use of questionnaires information was gathered concerning familial incidence of the following diseases: ulcerative colitis, regional ileitis, cancer of the colon and rectum, allergic diseases of the immediate type (bronchial asthma, urticaria, allergic rhinitis, and atopic dermatitis), diseases presumably caused by delayed hypersensitivity (erythema nodosum), or auto-allergy (rheumatoid arthritis and ankylosing spondylarthritis). Eight families with more than one case of ulcerative colitis were found in the patient group (5.3 per cent) compared to only one case in the control group (0.7 per cent). This difference is significant. No cases of regional ileitis were observed, either in the patient group or in the control group. Cancer of the colon and rectum did not occur significantly more often among the relatives of patients with ulcerative colitis. The preponderance of urticaria and allergic rhinitis in the ulcerative colitis families and the even distribution of rheumatoid arthritis, erythema nodosum, and ankylosing spondylarthritis in the two groups compared tends to support the hypothesis that an allergic pathogenesis of ulcerative colitis is of the immediate type.