Morphometrically-distinct sperm subpopulations defined by a multistep statistical procedure in Ram ejaculates: intra- and interindividual variation

Abstract

The existence of sperm subpopulations within the mammalian ejaculate has now been widely recognized. However, to the best of our knowledge, no data exist regarding the existence of sperm morphometric subpopulations within the ovine ejaculate. Computer assisted sperm morphometry analysis (ASMA) data and clustering methods were used in this study to identify sperm-head subpopulations in ram semen. Two experiments were carried out. In Experiment 1, ejaculates from 226 mature rams of the Manchega breed belonging to 36 different herds were used. A minimum of 100 sperm heads were analyzed from each male and eight morphometric characteristics for each individual sperm were recorded. Subpopulation analysis was performed in sequential steps: variable group analysis and correlation analysis to select which morphometric characteristics to use in cluster analyses; nonhierarchical clustering analysis using sperm head length and p2a (also known as roundness) shape factor as initial classificatory variables; and hierarchical clustering analysis to obtain the final number of clusters. The clustering analyses, based on 26,306 individual cells, revealed the existence of four sperm subpopulations (SP1, SP2, SP3 and SP4) with different morphometric characteristics. Significant differences in the proportion of spermatozoa in the SP1 and SP3 were found between rams belonging to different herds. In Experiment 2, the intra- and intermale variability on the distribution of sperm subpopulations was assessed. Three ejaculates from each of 21 rams were collected and the same multistep clustering analysis was performed. For all subpopulations defined, the intermale variability resulted in high values, being the intramale variability much lower. This fact would allow the use of sperm head morphometry to characterize a male and might provide valuable information to asses its fertility. In conclusion, our results show that using computer assisted sperm morphometry analysis and multivariate cluster analyses, four sperm subpopulations with different head phenotype were identified in ram ejaculates.

Sperm variation within a single ejaculate affects offspring development in Atlantic salmon

“…Marked phenotypic variation across sperm cells within a single ejaculate is ubiquitous, both in terms of sperm morphology [6][7][8] and performance [9]. However, sperm are generally considered products of the diploid paternal genome with no endogenous haploid gene expression, and sperm phenotype is thus thought not to reflect the haploid genome they carry [10].…”

Computer assisted sperm morphometry in mammals: A review

“…Using these methods, the existence of sperm-head morphometric subpopulations has been identified in different mammalian species (Gravance et al, 1996;Thurston et al, 1999;Rubio-Guillen et al, 2007;Alvarez et al, 2008;Esteso et al, 2009;de Paz et al, 2011;Marti et al, 2011b;Maroto-Morales et al, 2012). In a recent study (Vicente-Fiel et al, 2013b), the combination of CASMA-F technology with multivariate cluster analyses allowed the study of morphometric sperm subpopulations in four species of domestic artiodactyls (cattle, goat, sheep and pigs).…”

“…Between these extremes, species such as bovine and porcine show an intermediate shape variability (Vicente-Fiel et al, 2013a,b). Size and shape sperm heterogeneity may be studied simultaneously using multivariate cluster Rubio-Guillen et al, 2007;Maroto-Morales et al, 2012;Vicente-Fiel et al, 2013b) and discriminant (Buendia et al, 2002;Hidalgo et al, 2008;Soler et al, 2014c) analysis.…”

“…Although the origin and function of the sperm subpopulations are not yet clear, the ability to undergo capacitation and fertility may vary depending on the subpopulation under consideration (Maroto-Morales et al, 2012). Consequently, heterogeneity of spermatozoa (number of sperm subpopulations) would ensure greater potential to fertilize an oocyte at some unpredictable interval after sperm deposition in the female genital tract (Curry, 2000), although further studies are necessary to confirm this hypothesis.…”

Genetics of fresh and frozen-thawed semen traits and their relationship with growth rate in rabbits

“…Most of the literature on sperm head morphometry among different species is focused on semen processing effects, including the effects of cryopreservation and smear preparation techniques previous to morphometric analyses ; Esteso et al, 2003;Gravance et al, 2008). Only a few studies conducted in rams, however, have examined the effects of other environmental influences as the season effect, associated with photoperiod (Martí et al, 2012), the herd of origin (Maroto- Morales et al, 2012), or the age of the male, related with the sexual maturity (Martí et al, 2011), suggesting that these effects could explain an important part of the observed variation in sperm head morphometry, both in fresh (Maroto-Morales et al, 2012) and after cryopreservation process (Martí et al, 2011 and2012). Regarding to the age of the male, Martí et al (2011) showed that except for L all morphometric dimensions (A, P, W) values decreased with the increase of male age.…”