Organisms must adapt to the temporal characteristics of their surroundings to successfully survive and reproduce. Variation in the daily light cycle, for example, acts through endocrine and neurobiological mechanisms to control several downstream physiological and behavioral processes. Interruptions in normal circadian light cycles and the resulting disruption of normal melatonin rhythms cause widespread disruptive effects involving multiple body systems, the results of which can have serious medical consequences for individuals, as well as large-scale ecological implications for populations. With the invention of electrical lights about a century ago, the temporal organization of the environment has been drastically altered for many species, including humans. In addition to the incidental exposure to light at night through light pollution, humans also engage in increasing amounts of shift-work, resulting in repeated and often long-term circadian disruption. The increasing prevalence of exposure to light at night has significant social, ecological, behavioral, and health consequences that are only now becoming apparent. This review addresses the complicated web of potential behavioral and physiological consequences resulting from exposure to light at night, as well as the large-scale medical and ecological implications that may result.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1600-079X.2007.00473.x

The dark side of light at night: physiological, epidemiological, and ecological consequences

Spermatogenesis is a complex biological process of cellular transformation that produces male haploid germ cells from diploid spermatogonial stem cells. This process has been simplified morphologically by recognizing cellular associations or ‘stages’ and ‘phases’ of spermatogenesis, which progress through precisely timed and highly organized cycles. These cycles of spermatogenesis are essential for continuous sperm production, which is dependent upon numerous factors, both intrinsic (Sertoli and germ cells) and extrinsic (androgens, retinoic acids), as well as being species-specific.

Spermatogenesis and cycle of the seminiferous epithelium.

Why Do Females Mate with Multiple Males? The Sexually Selected Sperm Hypothesis

The aim of this study was to establish whether the mobility of sperm of the domestic fowl, as measured by an in vitro assay, predicted the outcome of sperm competition. Thirteen pairs of New Hampshire roosters, comprising one male categorized as having high-mobility sperm and the other as having average-mobility sperm, were used. Each male provided 25 x 10(6) sperm, which were mixed and artificially inseminated into between four and seven New Hampshire hens, each of which produced 2-11 offspring. The experiment was conducted twice, such that the same pair of males inseminated the same females. Paternity was assigned by using microsatellite markers. There was a clear effect of sperm-mobility phenotype on the outcome of sperm competition: in all 13 pairs the high-mobility male fathered the majority of offspring (75.3% overall; p < 0.0001). The proportion of offspring fathered by the high-mobility male within pairs varied significantly between male pairs (p < 0.0005). This effect was associated with the difference in sperm-mobility scores between males within pairs; there was a significant positive relationship between the proportion of offspring fathered by the high-mobility male and the ratio of mobility scores between males (p < 0.05). In addition, compared with their success predicted from the non-competitive situation, in the competitive situation high-mobility males were disproportionately successful in fertilizing eggs compared with average-mobility males. This may occur because female sperm storage is limited in some way and a greater proportion of high-mobility sperm gain access to the female's sperm storage tubules. There was no evidence that female effects accounted for any of the variation in paternity.

/pdf/sperm-mobility-determines-the-outcome-of-sperm-competition-4slkscxhev.pdf

Sperm mobility determines the outcome of sperm competition in the domestic fowl.

Sequence variation in mitochondrial DNA (mtDNA) was traditionally considered to be selectively neutral. However, an accumulating body of evidence indicates that this assumption is invalid. Furthermore, recent advances indicate that mtDNA polymorphism can be maintained within populations via selection on the joint mitochondrial-nuclear genotype. Here, we review the latest findings that show mitochondrial and cytoplasmic genetic variation for life-history traits and fitness. We highlight the key importance of the mitochondrial-nuclear interaction as a unit of selection and discuss the consequences of mitochondrially encoded fitness effects on several key evolutionary processes. Our goal is to draw attention to the profound, yet neglected, influence of the mitochondrial genome on the fields of ecology and evolution.

https://www.cell.com/trends/ecology-evolution/pdf/S0169-5347(08)00251-6.pdf

Evolutionary implications of non-neutral mitochondrial genetic variation

Previous research demonstrated that sperm mobility is a quantitative trait of the domestic fowl. The trait is quantified by measuring the absorbance of an Accudenz solution after overlay with a sperm suspension and brief incubation at body temperature. In the present work, average and high sperm mobility phenotypes (n = 30 males per phenotype) were selected from a base population. Differences were found between sperm oxygen consumption (p < 0.0001), acylcarnitine content (p < 0.05), linear velocity (p < 0.001), and straightness (p < 0.001), a trajectory variable measured with the Hobson SpermTracker. Oxygen consumption and stearoylcarnitine content of sperm from the high-mobility phenotype were twice those observed with sperm from average males, implying a pivotal role for mitochondria. On the basis of these results, a graded relationship was predicted between fertility and sperm mobility. Males (n = 48) were chosen at random from another base population, sperm mobility was measured per male, and each ejaculate was used to inseminate 8-12 hens (8 x 10(7) viable sperm per hen). When fertility was plotted as a function of sperm mobility, data points approximated a skewed logistic function. The hypothesis that vaginal immunoglobulins constitute an immunological barrier to sperm transport was tested and rejected. Therefore, we concluded that sperm mobility is a primary determinant of fertility in the fowl.

/pdf/sperm-mobility-a-primary-determinant-of-fertility-in-the-1kk8zqgg1b.pdf

Sperm Mobility: A Primary Determinant of Fertility in the Domestic Fowl (Gallus domesticus)

Previously, inheritance of sperm mobility entailed a maternal additive genetic effect, and sperm ATP content was correlated (r = 0.80) with phenotype. The present study was conducted to determine if mitochondrial function was critical to phenotypic expression. Whereas phenotype was independent of mitochondrial helix length, phenotype was correlated with sperm oxygen consumption (r = 0.83) using random-bred roosters. Aberrant mitochondria characterized immobile sperm, as evidenced by transmission-electron microscopy. Such mitochondria were swollen and contained disorganized cristae. Additional experiments were performed with roosters from lines selected for low or high sperm mobility. A threefold difference in sperm oxygen consumption was observed between lines. Single nucleotide polymorphisms were observed in mitochondrial DNA by sequencing replicate mitochondrial genomes from each line. An A-to-G substitution in the gene encoding tRNA(Arg) was inherited consistently, as evidenced by restriction fragment length polymorphism analysis using two male and two female progeny per family group and 14 family groups per line. Motile concentration in semen from low-line males was half that observed in semen from high-line males, as evidenced by computer-assisted sperm motion analysis. Likewise, 47% of sperm from low-line males contained aberrant mitochondria, compared to 4% for high-line males. In summary, sperm mobility phenotype was dependent on mitochondrial function, which in turn was altered by genetic selection. Fowl deferent duct fluid contains a high concentration of glutamate. We propose that variation in sperm mobility phenotype stems from the extent to which glutamate induces excessive mitochondrial Ca2+ uptake before ejaculation.

/pdf/sperm-mobility-phenotype-in-roosters-gallus-domesticus-2d4ulbf7g2.pdf

Sperm Mobility: Phenotype in Roosters (Gallus domesticus) Determined by Mitochondrial Function

Reproduction is a process that can be organized into distinct developmental and functional phases. In the case of the male, these include fertilization, formation of a patent reproductive tract, production of sperm, manifestation of male-specific behavioral patterns, and expulsion of sperm from the body. This perspective can provide insight that may be missed if reproduction is viewed primarily as an isolated act. For example, although the reproductive tract is fully functional only in the adult, it is formed, for the most part, prior to hatching. Furthermore, although spermatogenesis is associated with puberty, spermatogenesis is not constrained by chronological age but rather by the extent to which testicular cells proliferate and differentiate, which in turn is coupled to the developmental limitations of gonadotropin secretion. Finally, androgens essential to the function of the reproductive tract, the appearance of secondary sexual attributes, and male behavior may have detrimental effects upon the development of immune and connective tissue if the hormonal signal appears during the period of rapid prepubertal growth and differentiation. Thus, this chapter will discuss the process of reproductive system development and function in the male bird.

Reproduction in Male Birds

Treatment of male rat pups with the reversible goitrogen 6-propyl-2-thiouracil (PTU), administered by adding 0.1% PTU to the mother's drinking water from birth to day 25, increases their testis size and daily sperm production (DSP) at 160 days of age by up to 80% and 140%, respectively. The purpose of this study was to examine the effectiveness of various concentrations of PTU and determine the PTU dose that would maximize testis growth while minimizing side effects such as decreased maternal water consumption and decreased pup growth. Whether this effect was specific to PTU was determined by evaluating the effects of another commonly used goitrogen, methimazole (MMI), in increasing adult testis size and sperm production. Dams were given PTU (0.1-0.0004% w/v) or 0.025% MMI (w/v) in their water from birth to day 25 post partum, then given no further treatment. Thyroxine concentrations were measured in all groups of pups at 25, 35 and 45 days, and testis weight and DSP were determined at 90 days of age. At 25 days of age, thyroxine concentrations were maximally decreased by PTU treatments of 0.0015% or greater; less severe decreases were produced by 0.0004% PTU or 0.025% MMI. Thyroxine concentrations increased in all treated groups at day 35 compared with day 25, and returned to normal by day 45. At 90 days of age, testis weight was increased by about 40% in rats whose mothers had been treated with doses of 0.006% PTU or greater, whereas testis weights in groups given 0.0015 and 0.0004% PTU or 0.025% MMI were increased 31, 15 and 18%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

/pdf/increased-testis-growth-and-sperm-production-in-adult-rats-44rvi8cq18.pdf

Increased testis growth and sperm production in adult rats following transient neonatal goitrogen treatment: optimization of the propylthiouracil dose and effects of methimazole.

J. D. Kirby

Papers

Sperm Mobility: A Primary Determinant of Fertility in the Domestic Fowl (Gallus domesticus)

Sperm Mobility: Phenotype in Roosters (Gallus domesticus) Determined by Mitochondrial Function

Reproduction in Male Birds

Increased testis growth and sperm production in adult rats following transient neonatal goitrogen treatment: optimization of the propylthiouracil dose and effects of methimazole.

Active immunization against ghrelin decreases weight gain and alters plasma concentrations of growth hormone in growing pigs