Inferring transient dynamics of human populations from matrix non-normality

This is the final version of the article. Available from Springer Verlag via the DOI in this record.In our increasingly unstable and unpredictable world, population dynamics rarely settle uniformly to long-term behaviour. However, projecting period-by-period through the preceding fluctuations is more data-intensive and analytically involved than evaluating at equilibrium. To efficiently model populations and best inform policy, we require pragmatic suggestions as to when it is necessary to incorporate short-term transient dynamics and their effect on eventual projected population size. To estimate this need for matrix population modelling, we adopt a linear algebraic quantity known as non-normality. Matrix non-normality is distinct from normality in the Gaussian sense, and indicates the amplificatory potential of the population projection matrix given a particular population vector. In this paper, we compare and contrast three well-regarded metrics of non-normality, which were calculated for over 1000 age-structured human population projection matrices from 42 European countries in the period 1960 to 2014. Non-normality increased over time, mirroring the indices of transient dynamics that peaked around the millennium. By standardising the matrices to focus on transient dynamics and not changes in the asymptotic growth rate, we show that the damping ratio is an uninformative predictor of whether a population is prone to transient booms or busts in its size. These analyses suggest that population ecology approaches to inferring transient dynamics have too often relied on suboptimal analytical tools focussed on an initial population vector rather than the capacity of the life cycle to amplify or dampen transient fluctuations. Finally, we introduce the engineering technique of pseudospectra analysis to population ecology, which, like matrix non-normality, provides a more complete description of the transient fluctuations than the damping ratio. Pseudospectra analysis could further support non-normality assessment to enable a greater understanding of when we might expect transient phases to impact eventual population dynamics.This work was funded by Wellcome Trust New Investigator 103780 to TE, who is also funded by NERC Fellowship NE/J018163/1. JB gratefully acknowledges the ESRC Centre for Population Change ES/K007394/1

Reproductive hormones in infertility and infection in sub-saharan African males

The male factor is now recognised as a major contributor to a couples’ infertility. The role of reproductive hormones in male infertility is however controversial. This study therefore, was designed to investigate the role of reproductive hormones in male infertility in sub-Saharan Africa. 3 groups of subjects between 18-56 years were investigated. 25, 42 and 45 were recruited in fertile, infertile and sexually transmitted diseases (STDS). Follicle stimulating hormone (FSH), luteinising hormone(LH) and prolactin were estimated using the immunoradiometric assay technique while testosterone was estimated using radioimmunoassay technique utilizing commercially available kits (ICN Biomedical Inc.).Statistical analysis was done using students t-test and anova (one way) for comparison of means. FSH, LH, prolactin and testosterone were similar between fertile and infertile groups and between normospermic and dyspennic infertile groups. However, all except, prolactin were similar in STDs and fertile groups. Hormonal abnormalities may not be a major contributor to male infertility. However, role of prolactin in infertility and infection requires further studies

Spermatozoal, seminal plasma and blood sperm antibodies in Nigerian males

Infertility is common in Nigeria and the male role is now well recognized. Sperm antibodies (SA) have been observed as a cause of infertility and their production have in some circumstances been attributed to chronic infection of the genital tract. Sexually transmitted diseases (STDs) and infection-related infertility are reportedly highly prevalent in Nigeria. This study was therefore designed to evaluate the role of sperm antibodies and determine the involvement of STDs in the production of such SA among Nigerians. 122 adult males aged 18-56 years were investigated. 25 were normospermic, fertile males with no evidence of STDs and served as controls. 50 were infertile without STDs while 47 had proven STDs Immunobead binding technique was used for the detection of SA directly on the sperm cell, in seminal and blood plasma. Student’s t-test and anova (one-way) were used for statistical analysis of data obtained. Results showed that SA- IgG, IgA and IgM were present in blood and semen. However, mean percentage binding of these SA on motile sperm was low (0.05) The findings suggest that sperm antibodies are present but may not be associated with STDs or infertility in Nigeria males

Sexually transmitted diseases and male infertility in the Nigerian

Infection related infertility is common in Nigeria. The study was designed to evaluate the involvement of sexually transmitted diseases (STDs) in the pathogenesis of male infertility. One hundred and eighty-two male subjects aged 18-56 years were investigated-fertile (85), infertile (50), men with STDs (47). Semen was analysed according to WHO guidelines and appropriate statistical tests performed. Over 65% of subjects with STDs had gonorrhea and non-specific urethritis(NSU). More than two-thirds of STDs subjects (76.4%) were dyspermic and oligospermia was most frequently observed in infertile subjects (30%). Sperm count, percentage motility and morphology were significantly lower in infertile than fertile controls (P<0.001) while percentage motility was significantly lower in men with STDs than fertile controls (P = 0.005). Gonorrhea and NSU are still prevalent in the Nigerian society. STDs may cause infertility in the African male by reducing sperm motility and semen volume

Spermatozoal, seminal plasma and blood sperm antibodies in Nigerian males

Infertility is common in Nigeria and the male role is now well recognized. Sperm antibodies (SA) have been observed as a cause of infertility and their production have in some circumstances been attributed to chronic infection of the genital tract. Sexually transmitted diseases (STDs) and infection-related infertility are reportedly highly prevalent in Nigeria. This study was therefore designed to evaluate the role of sperm antibodies and determine the involvement of STDs in the production of such SA among Nigerians. 122 adult males aged 18-56 years were investigated. 25 were normospermic, fertile males with no evidence of STDs and served as controls. 50 were infertile without STDs while 47 had proven STDs Immunobead binding technique was used for the detection of SA directly on the sperm cell, in seminal and blood plasma. Student’s t-test and anova (one-way) were used for statistical analysis of data obtained. Results showed that SA- IgG, IgA and IgM were present in blood and semen. However, mean percentage binding of these SA on motile sperm was low (0.05) The findings suggest that sperm antibodies are present but may not be associated with STDs or infertility in Nigeria males

Immunologlubulin classes and nutritional factors in plasma and breast milk of lactating Mothers in Nigeria

Background: Breast milk is important for the overall well-being of infants. Although lactation is relatively robust in the face of poor nutrition, the implication of poor nutrition on non-nutritive factors in breast milk is inconclusive. Objective: This study was designed to find associations between nutritional and immune factors in maternal blood and breast milk with the aim to improve the needed public and individual strategies for a healthy infant. Method: A cross sectional study was conducted on 61 lactating Nigerian women aged 23-40years within the first 3 months postpartum. Anthropometric measurements were obtained while nutritional factors (total protein, albumin) and immunoglobulin classes (IgG, A and M) were estimated by Biuret, Bromocresol green and single radial immunodiffusion methods respectively in maternal plasma and breast milk. Results: Most (73.5%) of the lactating mothers had normal mean body mass index (i.e. not under weight nor obese) and the mean levels of plasma total protein, albumin, IgG, IgA and IgM were within normal reference ranges in these mothers. Nutritional and immunological indices increase in the plasma with length of lactation but decrease in breast milk with lactation. There were no correlation between BMI, plasma indices and milk indices in these lactating mothers. Conclusion: This study supports the superiority of colostrum over transitional or matured milk for the protection and nourishment of infants