Genetic and demographic structure of the yakut population: reproduction indices

Genetic and demographic information for the Yakut population living in the Republic of Sakha (Yakutia) is presented. The mean number of children per woman constituted 4.605. Crow's index and its components (Im and If) were 0.483, 0.104, and 0.343, respectively.     

Sexual reproduction and diversity: Connection between sexual selection and biological communities via population dynamics

Sexual reproduction is a mysterious phenomenon. Most animals and plants invest in sexual reproduction, even though it is more costly than asexual reproduction. Theoretical studies suggest that occasional or conditional use of sexual reproduction, involving facultative switching between sexual and asexual reproduction, is the optimal reproductive strategy. However, obligate sexual reproduction is common in nature. Recent studies suggest that the evolution of facultative sexual reproduction is prevented by males that coerce females into sexual fertilization; thus, sexual reproduction has the potential to enforce costs on a given species. Here, the effect of sex on biodiversity is explored by evaluating the reproductive costs arising from sex. Sex provides atypical selection pressure that favors traits that increase fertilization success, even at the expense of population growth rates, that is, sexual selection. The strength of sexual selection depends on the density of a given species. Sexual selection often causes strong negative effects on the population growth rates of species that occur at high density. Conversely, a species that reduces its density is released from this negative effect, and so increases its growth rate. Thus, this negative density-dependent effect on population growth that arises from sexual selection could be used to rescue endangered species from extinction, prevent the overgrowth of common species and promote the coexistence of competitive species. Recent publications on sexual reproduction provide several predictions related to the evolution of reproductive strategies, which is an important step toward integrating evolutionary dynamics, demographic dynamics and community dynamics.     

Sexual reproduction and sex determination in green algae

The sexual reproductive processes of some representative freshwater green algae are reviewed. Chlamydomonas reinhardtii is a unicellular volvocine alga having two mating types: mating type plus (mt⁺) and mating type minus (mt^?), which are controlled by a single, complex mating-type locus. Sexual adhesion between the gametes is mediated by sex-specific agglutinin molecules on their flagellar membranes. Cell fusion is initiated by an adhesive interaction between the mt⁺ and mt^? mating structures, followed by localized membrane fusion. The loci of sex-limited genes and the conformation of sex-determining regions have been rearranged during the evolution of volvocine algae; however, the essential function of the sex-determining genes of the isogamous unicellular Chlamydomonas reinhardtii is conserved in the multicellular oogamous Volvox carteri. The sexual reproduction of the unicellular charophycean alga, Closterium peracerosum-strigosum-littorale complex, is also focused on here. The sexual reproductive processes of heterothallic strains are controlled by two multifunctional sex pheromones, PR-IP and PR-IP Inducer, which independently promote multiple steps in conjugation at the appropriate times through different induction mechanisms. The molecules involved in sexual reproduction and sex determination have also been characterized.     

Iteroparous reproduction strategies and population dynamics

Asymptotic relationships between a class of continuous partial differential equation population models and a class of discrete matrix equations are derived for iteroparous populations. First, the governing equations are presented for the dynamics of an individual with juvenile and adult life stages. The organisms reproduce after maturation, as determined by the juvenile period, and at specific equidistant ages, which are determined by the iteroparous reproductive period. A discrete population matrix model is constructed that utilizes the reproductive information and a density-dependent mortality function. Mortality in the period between two reproductive events is assumed to be a continuous process where the death rate for the adults is a function of the number of adults and environmental conditions. The asymptotic dynamic behaviour of the discrete population model is related to the steady-state solution of the continuous-time formulation. Conclusions include that there can be a lack of convergence to the steady-state age distribution in discrete event reproduction models. The iteroparous vital ratio (the ratio between the maximal age and the reproductive period) is fundamental to determining this convergence. When the vital ratio is rational, an equivalent discrete-time model for the population can be derived whose asymptotic dynamics are periodic and when there are a finite number of founder cohorts, the number of cohorts remains finite. When the ratio is an irrational number, effectively there is convergence to the steady-state age distribution. With a finite number of founder cohorts, the number of cohorts becomes countably infinite. The matrix model is useful to clarify numerical results for population models with continuous densities as well as delta measure age distribution. The applicability in ecotoxicology of the population matrix model formulation for iteroparous populations is discussed.     

Sexual reproduction in Daphnia: interspecific differences in a hybrid species complex

To investigate whether reproductive variation in the Daphnia galeata-cucullata-hyalina hybrid species complex can explain the occurrence of hybrids and backcrosses, a total of 43 clones from three north German lakes were tested for allocation to sexual reproduction under equal stress conditions. Six replicates per clone were followed until the seventh adult instar. I used the following cues to promote sexual reproduction: short photoperiod, water from a crowded Daphnia culture, fish-conditioned water and low food concentration. For each animal, clutch size and clutch sex were recorded. Ephippia, which were empty since the animals were cultured individually, were only produced by D. cucullata and D. cucullata x hyalina (26% and 6% of the broods, respectively), whereas almost all taxa produced males (the range was 2–15%). Intraspecific variation for male and ephippial production was also found. The fact that the taxa tested show different responses to the stimuli of-fered may indicate that there is reproductive isolation between them. This is supported by field data from the Tjeukemeer (The Netherlands) which shows that D. galeata mostly produces ephippia in spring and D. cucullata in autumn. The presence of hybrids with ephippia in both seasons, however, shows that backcrossing is also possible.     

Metapopulation dynamics of the bog fritillary butterfly: demographic processes in a patchy population

Metapopulation models predicting the persistence of species on the verge of extinction in fragmented landscapes have to include local population dynamics. In this paper, we report on a 9-yr study in which a patchy population of the bog fritillary was monitored each year, with special focus on quantifying demographic parameters. We parameterised various constrained linear models (CLM) with capture-mark-recapture (CMR) data collected in the field each year and we tested the effects of several variables on demographic parameters. Selecting the best CLM, we estimated the mean and the variance of (1) individual parameters (survival and catchability) and (2) population features (population size, sex-ratio and recruitment). Survival was not related to the age of the individual but decreased continuously during the flight period, which means that lifetime expectancy is conversely related to the delay between the moment of the emergence of a given individual as compared to the emergence of the first adult in the population. Survival was lower in males than in females, as a consequence of male mate-locating behaviour. Daily population size fits a parabolic distribution in both sexes, males appearing, reaching their abundance peak and dying before females. Yearly variation in the sex-ratio is the consequence of the between-sex difference in the recruitment curve. Total adult population size shows large variations between years. Analysis of the relation between growth rate and abundance indicates density dependence, probably related to parasitism of the larval stages. Density at the equilibrium is about 200 adults/ha.     

Sexual differences and sex ratios of dioecious plants under stressful environments

雌雄异株植物对环境胁迫响应的性别差异与性别比例 雌雄异株植物在性特征(繁殖器官)和次级性特征(植物的特征)均表现出性二态。形态、生理与生态特征等次级性特征的性别差异,通常在繁殖成本和其他功能性状之间存在着权衡。尽管有证据表明性二态对环境胁迫的响应不一定存在于所有植物中,但次级性特征的权衡可能受到环境胁迫的影响。当植物表现出性二态时,不同的物种与胁迫因子可以导致性别特异性的响应。因此,胁迫作用对雌雄异株植物影响的概括性研究是必须的。另外,性二态可能会影响雌雄异株植物沿着环境梯度的频率和分布,引起生态位分化与性别空间分异。目前,控制性别比例偏差的原因和机制还知之甚少。本综述旨在讨论不利环境下的性别特异性响应与性别比例偏差,有利于深入的理解性二态对环境胁迫的响应。     

Phenotypic variation,sexual reproduction and evolutionary population dynamics

I studied the effects of introducing phenotypic variation into a well-known single species model for a population with discrete, non-overlapping generations. The phenotypes differed in their dynamic behaviour. The analysis was made under the assumption that the population was in an evolutionary stable state. Differences in the timing of the competitive impacts of the phenotypes on each other had a strong simplifying effect on the dynamics. This result could also be applied to competition between species. The effect of sexual reproduction on the dynamics of the population was analysed by assuming the simplest genetic model of one locus with two alleles. Sexual reproduction made the system much more stable in the (mathematical) sense that the number of attractors was reduced and their basins of attraction enlarged. In a dominant system sex tended to increase the frequency of the recessive allele, and in an overdominant system it induced gene frequencies of 1/2. Whether the attractors in the dominant system tended to be simpler or more complex than the attractors in the asexual system depended on the phenotype of the recessive homozygote. The overdominant sexual system tended to have simpler dynamics than the corresponding asexual population. A 2-locus model was used to study whether sexuals can invade an asexual population and vice versa. One locus coded for sexual and asexual reproduction, while the other coded for the dynamics. Enhanced stability through sexual reproduction seemed to be the reason why there was a clear asymmetry favouring sex in this evolutionary context.     

Disentangling demographic effects of red deer on chamois population dynamics

Investigating the impact of ecological factors on sex‐ and age‐specific vital rates is essential to understand animal population dynamics and detect the potential for interactions between sympatric species. We used block count data and autoregressive linear models to investigate variation in birth rate, kid survival, female survival, and male survival in a population of Alpine chamois Rupicapra rupicapra rupicapra monitored over 27 years within the Stelvio National Park, Central Italian Alps, as function of climatic variables, density dependence, and interspecific competition with red deer Cervus elaphus. We also used path analysis to assess the indirect effect of deer abundance on chamois growth rate mediated by each demographic parameter. Based on previous findings, we predicted that birth rate at [t] would negatively relate to red deer abundance at year [t − 1]; survival rates between [t] and [t + 1] would negatively relate to red deer abundance at year [t − 1] and to the interactive effect of winter precipitation at [t + 1] and chamois density at [t]. Our results showed that birth rate was positively related to spring–summer precipitation in the previous year, but this effect was hampered by increasing red deer abundance. Kid and female survival rates were negatively related to the combined effect of chamois abundance and winter precipitation. Male and female survival rates were negatively related to lagged red deer abundance. The path analysis supported a negative indirect effect of red deer abundance on chamois growth rate mediated by birth rate and female survival. Our results suggest that chamois population dynamics was largely explained by the synergistic effect of density dependence and winter harshness, as well as by interspecific competition with red deer, whose effects were seemingly stronger on the kid–female segment of the population.     

The potential role of chromosome telomere resetting consequent upon sex in the population dynamics of aphids: an hypothesis

Models of population structure have emphasized the importance of sex in maintaining lineages. This is because, despite the well known ‘two‐fold cost of sex’ compared with asex, it is considered that recombination rids the genome of accumulated mutations and increases its potential for adaptive variation. However, asexual lineages of eukaryotic organisms can also rapidly gain genetic variance directly by various mutational processes, thereby proving that so‐called ‘clones’ do not have strict genetic fidelity ( Lushai & Loxdale, 2002 ; Loxdale & Lushai, 2003a ), whereas the variation so produced may well have adaptive advantage during the evolutionary process. This being so, obligated asexuals or cyclical parthenogens that occasionally indulge in sexual recombination (‘rare sex’) cannot be deemed as ‘evolutionary dead‐ends’( Lushai, Loxdale & Allen, 2003a ). In addition, the persistence of asexual lineages (i.e. lineage longevity) may also involve the integrity of the telomere region, the physical end of the chromosomes ( Loxdale & Lushai, 2003b ). In this earlier study on this topic, we argued that the persistence and ultimate senescence of eukaryotic cell lineages (based upon the frequency of ‘capped’ and ‘uncapped’ chromosomes related to telomere functionality; Blackburn, 2000 ) may directly relate to the survival and persistence of lineages of whole asexual organisms. Aphids are a good model system to test this hypothesis because they show a variety of sexual/asexual reproductive strategies, whereas their mode of asexual reproduction is of the mitotic (= apomictic) type. We also suggested that many aphid lineages require occasional or even rare sexual recombination to re‐set telomere length to allow lineages to persist. Ample empirical evidence from diverse taxa, lineages, and different developmental stages now reveals that the telomere states are indeed re‐set by recombination (homologous or meiotic), thereby rejuvenating the lineage in question. The generational clock element of telomeric functionality has also been successfully described in artificially‐induced mammalian clonal systems. It thus appears that telomere function is a central molecular mechanism instigating and promoting lineage continuity per se. By contrast, we hypothesized that other long‐lived asexuals, or the rare category of ancient asexuals such as bdelloid rotifers, have compensatory mechanisms for maintaining chromosome functional integrity, which are somewhat different from conventional telomeric repeats. In the present study, we carry the analogy between eukaryotic cell functionality and aphid lineages a stage further. Here, we hypothesize that the changing frequency of capped and uncapped telomeres, progressing to senescence in a stochastic manner, may be an underlying factor that significantly contributes to population dynamics in asexual lineage evolution. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 90 , 719–728.     

Labour migration,sex, and polygyny: negotiating patriarchy in Tajikistan

This paper explores ways in which matrimonial arrangements are being transformed in Tajikistan by assessing the impact of labour migration in the increase of divorces as well as polygynous unions. I argue that instead of considering polygyny simply as a reification of patriarchy, we should view it as a way for both men and women to negotiate – and sometimes even subvert – the traditional patriarchal rules that dictate the institution of marriage in Tajikistan. The study is based primarily on fieldwork conducted in northern Tajikistan in 2010 and 2011.     

A population based twin study of sex differences in depressive symptoms.

Depressive symptoms reflect depressed mood over a relatively short period of time and are measured using symptom checklists such as the SCL-90. There is some evidence that depressive symptoms are associated with major depression (MD), which is a clinically diagnosed psychiatric illness. Genetic studies of depressive symptomatology suggest a role for genetic factors as well as unique environmental influences. While epidemiological research suggests that depressive symptoms may be influenced by sex-specific factors, few genetically informative findings support this result entirely. We used data from male and female same sex and opposite-sex twin pairs to assess the extent to which genetic, shared and unique environmental factors influence depressive symptoms. Furthermore, we tested for the presence of qualitative and quantitative sex differences in depressive symptoms. Our results suggest that similar to other studies, depressive symptomatology is moderately heritable (31%) with no evidence for shared environmental factors. Our best fitting model suggests that there are no qualitative or quantitative sex differences in depressive symptoms. Our analyses suggest that while there may be mean differences in the levels of depressive symptoms across sexes, the genetic and environmental factors that predispose males and females to depressive symptoms are not different.     

Greater sciatic notch morphology: sex, age, and population differences

The accuracy of a method for visually scoring sex differences in the greater sciatic notch was tested on 296 skeletons of known age and sex. The proportion of correct sex assignments is 80% when all specimens are classified, and 89% when os coxae assigned the score in which the sexes show the greatest overlap are excluded. Although many os coxae (35%) have this sexually intermediate morphology, excluding them has the advantage of substantially reducing sex biases in sexing errors. For both sexes, there is a strong relationship between age at death and sciatic notch score. People who die at a younger age tend to have wider, more feminine-appearing sciatic notches than people of greater longevity. There are also significant population differences. The 18th-19th century English sample from St. Bride's Church has a more feminine morphology than Americans of European or African ancestry. Environmental influences on skeletal development (vitamin D deficiency) appear to provide the most likely explanation for these population differences.     

The population dynamics of the mangrove Avicennia marina; demographic synthesis and predictive modelling

Population dynamics of the widespread mangrove Avicennia marina was studied over the complete life-history from zygotes through to adults in southeastern Australia. Zygote survival, propagule dispersal, seedling establishment, seedling recruitment and sapling recruitment were examined by demographic censuses over a range of spatial and temporal scales. Hypotheses about factors regulating survival were tested by manipulative field experiments. Life table statistics for survival and fecundity were used to calculate transition probabilities and their variance for seven stages of life history. These parameters were used as the basis of a stochastic model that predicts population structure after small and large scale perturbations.     

A population biological approach to the collective dynamics of countries undergoing demographic transition

Birth rates have been declining in higher-income countries since the middle of the 19th century. A growing number of other countries have entered this demographic transition to lower fertility, as socioeconomic development continues. Analyses of this demographic transition vary widely, but most analyze individual populations in isolation from others, and most come from fields outside the biological sciences. Here, we develop a population biological model of population dynamics in higher-income countries. Individual countries evolve through density-regulated growth, where gradual evolution toward higher population densities boosts productivity (and hence socioeconomic growth) through economics of agglomeration and scale, in turn reducing birth rates. The exchange of technology and capital between countries can further boost productivity gains in any given country, thus contributing to its demographic transition. As a result, countries can down-regulate one another's population growth through mutual improvements in productivity. The model is fitted to time series data on population size, GDP per capita, and birth rates for the United States, the United Kingdom, and France. The metapopulation dynamics are also characterized across a range of parameter values close to the fitted values. This work may help advance population biological approaches to understanding the implications of the fertility demographic transition for modern human populations. This is relevant to developing long-term predictions of the earth's total population size, which must be based upon a model that incorporates underlying mechanisms.     

Disentangling demographic co‐effects of predation and pollution on population dynamics

In nature species react to a variety of endogenous and exogenous ecological factors. Understanding the mechanisms by which these factors interact and drive population dynamics is a need for understanding and managing ecosystems. In this study we assess, using laboratory experiments, the effects that the combinations of two exogenous factors exert on the endogenous structure of the population dynamics of a size‐structured population of Daphnia. One exogenous factor was size‐selective predation, which was applied on experimental populations through simulating: 1) selective predation on small prey, 2) selective predation on large prey and 3) non‐selective predation. The second exogenous factor was pesticide exposure, applied experimentally in a quasi‐continuous regime. Our analysis combined theoretical models and statistical testing of experimental data for analyzing how the density dependence structure of the population dynamics was shifted by the different exogenous factors. Our results showed that pesticide exposure interacted with the mode of predation in determining the endogenous dynamics. Populations exposed to the pesticide and to either selective predation on newborns or selective predation on adults exhibited marked nonlinear effects of pesticide exposure. However, the specific mechanisms behind such nonlinear effects were dependent on the mode of size‐selectivity. In populations under non‐selective predation the pesticide exposure exerted a weak lateral effect. The ways in which endogenous process and exogenous factors may interact determine population dynamics. Increases in equilibrium density results in higher variance of population fluctuations but do not modify the stability properties of the system, while changes in the maximum growth rate induce changes in the dynamic regimes and stability properties of the population. Future consideration for research includes the consequences of the seasonal variation in the composition and activity of the predator assembly in interaction with the seasonal variation in exposure to agrochemicals on freshwater population dynamics.     

Effect of host sex and litter on the population dynamics of Echinococcus granulosus in dogs.

Twenty-one Beagle dogs consisting of 10 males and 11 females and belonging to 3 litters were infected with 60,000 E. granulosus protoscolices each. They were killed on day 40, the parasites from their intestines recovered, and the number of worms, average number of proglottides per worm, average length per worm, percentage of worms with a uterine cavity, and percentage of egg-bearing worms were determined for each dog and analyzed per sex and litter. On average, the dogs had 1,253 +/- 339 worms (means +/- standard error) with 2.42 +/- 0.1 proglottides, were 1.59 +/- 0.07 mm long, and 25.6 +/- 4.8% of the worms presented a uterine cavity and 1.2 +/- 0.6% bore eggs. The number of worms exhibited a bimodal distribution with 19 dogs having less than or equal to 2,565 worms and 2 greater than or equal to 5,520 worms. Average number of proglottides also showed a bimodal distribution with 7 dogs having less than or equal to 2.1 proglottides per worm and 14 dogs having greater than or equal to 2.4 proglottides per worm. The parasites were significantly more numerous in females than in the males (1,964 +/- 573 vs. 681 +/- 202), had more proglottides (2.67 +/- 0.08 vs. 2.15 +/- 0.16), and were longer (1.72 +/- 0.07 vs. 1.44 +/- 0.11 mm). The percentages of parasites with a uterine cavity (27.8 +/- 5.9 vs. 23.2 +/- 8.1) or bearing eggs (1.0 +/- 0.5 vs. 1.5 +/- 1.8) were comparable in females and males.(ABSTRACT TRUNCATED AT 250 WORDS)     

Otitis media: genetic factors and sex differences.

Although genetic factors are recognised as major contributors to otitis media, the presence of sex differences in heritability needs clarification. The aim of this study was to estimate the relative contribution of genetic and environmental effects in otitis media liability with particular focus on sex differences. Data from a cohort of Norwegian twins born between 1967 and 1979 with repeated measures on recurrent childhood otitis media were analysed. Altogether the sample included 4247 twin pairs. The tetrachoric correlations for monozygotic twins were .71 and .65 for males and females respectively. In dizygotic twins the correlations were .35 and .25 for males and females, respectively, and was.34 in opposite sexed pairs. The contribution of genetic and environmental effects was analyzed using structural equation modeling. The best fitting model showed that additive genetic effects explained 72% and 61% of the variance in males and females, respectively. The remaining variance was attributed to individual environmental effects. A model specifying equal heritability estimates for males and females yielded an almost equivalent fit. We found substantial genetic effects for liability to otitis media. There is no evidence that different sets of genes influence liability in males and females, but there may be sex differences in the relative importance of genetic effects.