Old Sperm

Old Sperm

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Illustration of ancient ostracod sex.
He Wang et al.

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biology

marine life

myanmar

reproduction

sex

9/17/20

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Scientists have unearthed the largest and oldest sperm ever recorded — dating back nearly 100 million years — from an ancient crustacean encased in amber.
The Cretaceous period sex cells are not only many times larger than human sperm, but come from a tiny bivalve — or mollusk — about the size of a poppy seed, about 0.6 millimeters, according to a study published Wednesday in Proceedings of the Royal Society B .
They belong in a category of “giant sperm” common among some “micro-crustaceans” known as ostracods, which today includes the minuscule seed shrimp. Sperm from an ostracod is known for being up to 10 times larger than the animal’s own body. As another example, the modern fruit fly also boasts an outsize sperm measuring 2.2 inches, which is about 20 times the bug’s body size.
Compared to their marine findings, an equivalent ratio for humans would be a 24-foot-long sperm, according to study co-author Renate Matzke-Karasz, a geobiologist at Ludwig-Maximilians-Universität (LMU) in Munich.
“Previously, we were not sure if animals that ‘switched’ to using these giant sperm at a certain point in their history are doomed to become extinct very quickly. But in ostracods, it seemed to work for more than 100 million years,” she t old Vice .
Researchers called the results “a paramount example of evolutionary stasis” in their report.
It’s the swimmers’ lengthy tail that makes this possible, wrapping around themselves to form a sort of reproductive tumbleweed that can swiftly barrel through the female reproductive canal.
The researchers examined the specimen, which was found in Myanmar, using a microscopic computerized tomography (CT) scanner to analyze the amber — which, as it turns out, was packed with 39 different species of the minute shellfish. Their study sheds light on the characteristics of ancient ostracods still present today, including giant sperm and “clasper” appendages. They were also able to observe the ovum as well as ejaculate-filled “receptacles” among the females.
Biologists confess they aren’t able to precisely measure the male cells but estimate they are at least 0.2 millimeters long — about the width of two strands of hair — and about a third of the size of the primordial plankton.
The fact that ostracod sperm are comparatively large comes at an evolutionary cost. In some modern species, their reproductive system can take up a third of their entire body.
“This is a lot of biological energy that must be allocated to reproduction,” said Matzke-Karasz, “so you might think that this doesn’t make sense from an evolutionary standpoint.”
But for these sex machines, she said, “There must be an advantage. Otherwise, it wouldn’t exist anymore.”

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6 To whom correspondence should be addressed at: ANZAC Research Institute, Sydney, NSW 2139, Australia. Email: djh@anzac.edu.au

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Human Reproduction , Volume 19, Issue 8, 1 August 2004, Pages 1811–1815, https://doi.org/10.1093/humrep/deh315

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Human Reproduction vol. 19 no. 8 © European Society of Human Reproduction and Embryology 2004; all rights reserved
Human Reproduction vol. 19 no. 8 © European Society of Human Reproduction and Embryology 2004; all rights reserved

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K.K. Ng, R. Donat, L. Chan, A. Lalak, I. Di Pierro, D.J. Handelsman, Sperm output of older men, Human Reproduction , Volume 19, Issue 8, 1 August 2004, Pages 1811–1815, https://doi.org/10.1093/humrep/deh315
BACKGROUND: Declining fertility of couples from the fourth decade of life is largely attributable to the drop in female fertility. However, increasing numbers of men, whose fertility theoretically lasts until death, are seeking fertility treatment at older ages, yet there is little information on sperm production and function past the age of 50 years. The few studies of such older men have examined men attending fertility clinics, and therefore willing to provide semen samples, but the participation bias of such recruitment hinders extrapolation to the unselected general male population. METHODS: We have taken the opportunity to study a convenience sample of 55 healthy, non-infertile men ranging in age from 52 to 79 years old who provided semen samples as part of a prostate cancer screening project. They were compared with a control group ( n =409) of younger (<52 years) men from among 567 volunteers screened as potential sperm donors for an artificial insemination program. RESULTS: Older men had lower semen volume (mean semen volume 1.8 versus 3.2 ml; P <0.0001) and total sperm output (median 74 versus 206 million sperm per ejaculate; P <0.0001), whereas sperm density (median 64 versus 73 million sperm/ml; P =0.12) was non-significantly decreased. Older men had more abnormal sperm morphology with decreasing numbers of normal forms (mean 14% versus 25%; P <0.0001) and reduced vitality (mean 51% versus 80%; P <0.0001), as well as increased numbers of cytoplasmic droplets (median 1 versus 0; P <0.0001) and sperm tail abnormalities (30% versus 17%; P <0.0001). Sperm head or neck abnormalities were no different between the groups. CONCLUSIONS: While neither study group may be representative of the general male population, these findings suggest that sperm production, reflected in sperm output but not sperm density, as well as sperm morphology and viability are diminished in this population of healthy, non-infertile older men.
It is well known that the fertility of couples declines with age ( Leridon, 1977 ; Schwartz and Mayaux, 1982 ; Menken et al. , 1986 ). This is mostly attributable to declining female fertility evident from the age of 30 years ( Schwartz and Mayaux, 1982 ) and ceasing altogether by menopause. This precipitate decline in female fertility, together with couples usually being very closely matched in age, overshadows and complicates efforts to determine whether there are also significant declines in male fertility with age ( Kidd et al. , 2001 ). Very few studies have addressed actual fertility of older men controlling for declining female fertility ( Anderson, 1975 ), although the time to pregnancy questionnaire ( Joffe, 2003 ) is promising ( Hassan and Killick, 2003 ), but has yet to be applied to older men.
Although testicular function does not exhibit a precipitous age-related decline like the ovary at menopause, there is a gradual and variable decline of modest proportion in testosterone production in older men ( Gray et al. , 1991b ; Harman et al. , 2001 ). Whether there is any real decline in spermatogenesis and/or male fertility in the general male population is much less clear. As direct sampling of the human testis is not feasible for population studies, sperm output is widely used as the surrogate measure of human male fertility. However, men are reluctant to provide semen samples unless actively concerned about their fertility. For example, population-based studies typically recruit <20% of young men willing to provide semen samples ( Jensen et al. , 2004 ) constituting an inevitable participation bias in such studies ( Handelsman, 1997 ; Cohn et al. , 2002 ). The limited number of published studies of sperm output in older men are largely restricted to men attending infertility clinics, where few are older than 50 years ( Kidd et al. , 2001 ). An uncertain, but probably high, proportion of such men have unrecognized defects in sperm production and/or function. Furthermore, access to such specialized medical services may be strongly influenced by non-biological factors, and findings from infertility clinics may not be reliably extrapolated to the general male population. Hence, few studies of older men have managed to avoid severe participation and selection biases.
Therefore, in order to provide novel insight into sperm output among healthy, non-infertile older men, we took the opportunity to study a convenience sample of healthy older men without known reproductive disorders or prostate disease who provided semen samples for prostate cytology as part of medical screening for undiagnosed prostate disease ( Gardiner et al. , 2003 ).
The sample of older men comprised 55 consecutive men who were referred by urologists from private office practices for a prostate cancer detection program based on seminal cytology ( Gardiner et al. , 1996 ; Clements et al. , 1999 ). All these men were asymptomatic and had been identified by elevated blood prostate-specific antigen (PSA) concentrations that required prostate biopsy. The men provided a single semen sample to the Clinical Andrology laboratory on the same day immediately prior to their transrectal ultrasound and prostate biopsy for possible in situ prostate cancer. The diagnostic outcomes of the prostate cytology will be reported separately.
The control group comprised 409 men under the age of 52 years (lowest age of the older men) from the 567 younger men who volunteered between 1980 and 2000 for screening as potential sperm donors for an donor insemination program, as described previously ( Handelsman et al. , 1984 ; Handelsman, 1997 ). Both groups were studied by the same clinic and laboratory. Owing to changes in sperm morphology recommendations in the WHO Manual, the controls for sperm morphology were the most recent 84 younger men in whom sperm morphology assessment was performed according to the most recent WHO methodology.
The standard collection procedures for semen samples as defined by the WHO manual ( World Health Organization, 1999 ) were modified for these older men who were not concerned about their fertility. No period of sexual abstinence was specified. As an alternative to collection at the laboratory, men were offered the choice to collect specimens at home. In the latter case, sample handling was unsuitable for valid motility assessment so only sperm concentration and morphology were evaluated, a practical compromise recommended for studies of semen analysis among non-infertile men ( Cohn et al. , 2002 ).
Sperm concentration and morphology evaluation were performed according to WHO guidelines ( World Health Organization, 1999 ) using phase-contrast microscopy on unstained specimen, a modified Neubauer-type chamber and a Papanicolaou stain for morphology assessment performed according to ‘strict’ criteria. Defects were divided into head defects (large, small, tapered, pyriform, round and amorphous heads, vacuolated heads, heads with small acrosomal area and double heads), neck and midpiece defects, and tail defects (short, multiple, hairpin, broken tails, bent tails, tails of irregular width, coiled tails). Cytoplasmic droplets greater than one-third of the area of a normal sperm head were also recorded.
Data were analysed by NCSS software and are expressed as mean, SD, quartiles and extremes of the data distribution. Groups were compared by t -test for continuous Gaussian variables and by the non-parametric equivalent for non-Gaussian data. Categorical data were analysed by Fisher's exact test using StatXact software.
The age and semen analysis findings from 55 older and 567 younger men are summarized in Tables I and II . Among the older men, three were vasectomized, one provided a urine specimen and
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