Recent advances in bird sperm morphometric analysis and its role in male gamete characterization and reproduction technologies

Abstract

Postcopulatory sexual selection through sperm competition may be an important evolutionary force affecting many reproductive traits, including sperm morphometrics. Environmental factors such as pollutants, pesticides, and climate change may affect different sperm traits, and thus reproduction, in sensitive bird species. Many sperm-handling processes used in assisted reproductive techniques may also affect the size of sperm cells. The accurately measured dimensions of sperm cell structures (especially the head) can thus be used as indicators of environmental influences, in improving our understanding of reproductive and evolutionary strategies, and for optimizing assisted reproductive techniques (e.g., sperm cryopreservation) for use with birds. Computer-assisted sperm morphometry analysis (CASA-Morph) provides an accurate and reliable method for assessing sperm morphometry, reducing the problem of subjectivity associated with human visual assessment. Computerized systems have been standardized for use with semen from different mammalian species. Avian spermatozoa, however, are filiform, limiting their analysis with such systems, which were developed to examine the approximately spherical heads of mammalian sperm cells. To help overcome this, the standardization of staining techniques to be used in computer-assessed light microscopical methods is a priority. The present review discusses these points and describes the sperm morphometric characteristics of several wild and domestic bird species.

Method matters: Experimental evidence for shorter avian sperm in faecal compared to abdominal massage samples

“…Specifically, our additional analysis of using a paired t -test confirmed our results from linear mixed models and was restricted to males for which we collected faecal and massage samples during both events, so here males served as their own control. Therefore, the observed sperm size differences in heads and midpieces between methods might be explained by sperm in faeces resembling a different subpopulation of sperm within males and could be indicative of differences in the degree of post-meiotic sperm maturation [ 62 , 63 ].…”

Genetic manipulation of sex ratio in mammals: the Reaper comes for Mickey

“…Currently, the main alternative to culling individuals of the “wrong” sex after birth is to employ artificial insemination using sex‐sorted semen prepared by flow cytometry . This process is effective in some mammalian species but is expensive and technically complex and is not yet practical in birds due to their filiform sperm morphology . Similarly, technologies are available to determine the sex of unhatched chicks in eggs , but these methods are not currently economical at the scale needed for widespread adoption in commercial breeding programs.…”

Afterword to Sperm morphometrics today and tomorrow special issue in Asian Journal of Andrology

“…With these terms, neither the nature of the automation (with ASMA) nor the morphology examined (with CASMA-F) is clear from the abbreviation. In this Special Issue, for example, for spatulate spermatozoa, the sperm head itself, its acrosome, or its nucleus can each be analyzed by the system,13 and filiform spermatozoa permit additional values on the length of the head and tail 5. Thus, a change in terminology to one that indicates which sperm feature the system is measuring is needed.…”

“…This Special Issue on computer-aided sperm morphology assessment comprises four reviews (on sperm transport in mammals,3 the current status of sperm morphometry in mammals4 and birds,5 and the relevant statistical methods to assess the morphometric results6); three clinical research papers (on sperm subpopulations in split ejaculates from adult men with normozoospermia7 and in ejaculates from adolescents with or without varicocoele,8 including the use of computer-assisted sperm analysis in assessing sperm nuclear DNA fragmentation9); and six veterinary research papers on sperm populations in the epididymis (in normozoospermic and teratozoospermic domestic cats10) and in ejaculated spermatozoa (from an endangered puma species,11 roosters and guinea fowls,12 rams, bulls and boars,13 and on cryopreserved bovine semen14). …”