Evolutionary theory is firmly grounded on the existence of trade-offs between life-history traits, and recent interest has centred on the physiological mechanisms underlying such trade-offs. Several branches of evolutionary biology, particularly those focusing on ageing, immunological and sexual selection theory, have implicated reactive oxygen species (ROS) as profound evolutionary players. ROS are a highly reactive group of oxygen-containing molecules, generated as common by-products of vital oxidative enzyme complexes. Both animals and plants appear to intentionally harness ROS for use as molecular messengers to fulfil a wide range of essential biological processes. However, at high levels, ROS are known to exert very damaging effects through oxidative stress. For these reasons, ROS have been suggested to be important mediators of the cost of reproduction, and of trade-offs between metabolic rate and lifespan, and between immunity, sexual ornamentation and sperm quality. In this review, we integrate the above suggestions into one life-history framework, and review the evidence in support of the contention that ROS production will constitute a primary and universal constraint in life-history evolution.

https://royalsocietypublishing.org/doi/pdf/10.1098/rspb.2008.1791

Reactive oxygen species as universal constraints in life-history evolution

Rheotaxis Guides Mammalian Sperm

Hydrodynamics of Sperm Cells near Surfaces

A hybrid boundary integral/slender body algorithm for modelling flagellar cell motility is presented. The algorithm uses the boundary element method to represent the ‘wedge-shaped’ head of the human sperm cell and a slender body theory representation of the flagellum. The head morphology is specified carefully due to its significant effect on the force and torque balance and hence movement of the free-swimming cell. The technique is used to investigate the mechanisms for the accumulation of human spermatozoa near surfaces. Sperm swimming in an infinite fluid, and near a plane boundary, with prescribed planar and three-dimensional flagellar waveforms are simulated. Both planar and ‘elliptical helicoid’ beating cells are predicted to accumulate at distances of approximately 8.5–22 μm from surfaces, for flagellar beating with angular wavenumber of 3π to 4π. Planar beating cells with wavenumber of approximately 2.4π or greater are predicted to accumulate at a finite distance, while cells with wavenumber of approximately 2π or less are predicted to escape from the surface, likely due to the breakdown of the stable swimming configuration. In the stable swimming trajectory the cell has a small angle of inclination away from the surface, no greater than approximately 0.5°. The trapping effect need not depend on specialized non-planar components of the flagellar beat but rather is a consequence of force and torque balance and the physical effect of the image systems in a no-slip plane boundary. The effect is relatively weak, so that a cell initially one body length from the surface and inclined at an angle of 4°–6° towards the surface will not be trapped but will rather be deflected from the surface. Cells performing rolling motility, where the flagellum sweeps out a ‘conical envelope’, are predicted to align with the surface provided that they approach with sufficiently steep angle. However simulation of cells swimming against a surface in such a configuration is not possible in the present framework. Simulated human sperm cells performing a planar beat with inclination between the beat plane and the plane-of-flattening of the head were not predicted to glide along surfaces, as has been observed in mouse sperm. Instead, cells initially with the head approximately 1.5–3 μm from the surface were predicted to turn away and escape. The simulation model was also used to examine rolling motility due to elliptical helicoid flagellar beating. The head was found to rotate by approximately 240° over one beat cycle and due to the time-varying torques associated with the flagellar beat was found to exhibit ‘looping’ as has been observed in cells swimming against coverslips.

/pdf/human-sperm-accumulation-near-surfaces-a-simulation-study-2ie0ofqg5m.pdf

Human sperm accumulation near surfaces: a simulation study

Nitric oxide inhibition of human sperm motility

Factors affecting spermatozoa motility are reviewed beginning with development of motility in the seminiferous tubules (at which time the spermatozoon is incapable of self-propulsion) progressing through the chemical and clinical aspects of motility in the seminal plasma and concluding with a description of the interaction with cervical mucus. The threatening environment of the vagina leaves a high percentage of spermatozoa tailless prohibiting entry into the uterine cervix. Tables give: methods used to study motility patterns found in both fertile and infertile men and the velocity of human spermatozoa under varying conditions. ATP is the main energy source of this propulsion; the contractile proteins flactin and spermosin may interact with the associated ATPase to generate the contraction and relaxation needed to propel the sperm. Factors affecting motility are discussed including: semen quality time after ejaculation time between ejaculations temperature ionic composition of the various fluids encountered electromagnetic radiation sperm cell orientation viscosity of fluids encountered pH of the vaginal and uterine fluids osmotic pressure and the presence of spermagglutinins. Motility is a good measure of semen "quality" since there is little likelihood that feeble sperm cells can ascent into the cervical canal. However motility is no guarantee of fertility. Environmental pollutants especially copper zinc mercury and lead salts inhibit human sperm motility by their sulfhydryl blocking action. The situation may become most hazardous for workers in metallurgical industries manufacturers of batteries or large users of pesticides and herbicides. The effects of cyclic nucleotides and neurotropic agents are surveyed. Areas needing further investigation are listed.

Mitchell Ja

Papers

Motility of spermatozoa.