Sperm subpopulations in avian species: a comparative study between the rooster (Gallus domesticus) and Guinea fowl (Numida meleagris)

Abstract

The main aims of this research were to study possible differences in objective morphometric sperm characteristics, establish normative sperm morphometry standards, and evaluate the presumed different subpopulation distribution of avian spermatozoa from the rooster (Gallus domesticus) and Guinea fowl (Numida meleagris) as model avian species. Seventy-two ejaculates (36 per species studied) were obtained manually, following a training period involving gently combined dorso-abdominal and lumbo-sacral massage of the birds. Ejaculates were processed for volume, sperm concentration, viability, motility, and morphology. Moreover, samples were submitted for sperm morphometric assessment using objective Computer-Assisted Semen Analysis for Morphometry (CASA-Morph) methods, with sperm morphometric descriptors evaluated by Principal Component Analysis (PCA) and multivariate clustering analyses. There were several differences observed between the avian species in values obtained for ejaculate volume and sperm concentration (P < 0.001). Irrespective of species, PCA revealed two Principal Components (PCs) explaining more than 80% of the variance. In addition, the number of subpopulations differed with species (three and five subpopulations for rooster and Guinea fowl, respectively). Moreover, the distribution of the sperm subpopulations was found to be structurally different between species. In conclusion, our findings from using CASA-Morph methods indicate pronounced sperm morphometric variation between these two avian species. Because of the strong differences observed in morphometric parameter values and their subpopulation distribution, these results suggest that application of objective analytical methods such as CASA-Morph could substantially improve the reliability of comparative studies and help establish valid normative sperm morphological values for avian species.

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

“…By integrating the original variables according to their coherence in a database into a new complex mathematical variable, clearly defined homogeneous subpopulations of spermatozoa can be defined. In support of the theory above, the papers presented here showed that most of the variance from up to 13 morphometric variables could be explained by only two or three PCs: two in bulls,16 adolescent humans,8 adult human sperm head DNA,9 domestic cats,10 puma,11 roosters, and guinea fowls12 and three PCs in adult human split ejaculate samples 7…”

“…Here, the number of subpopulations ranged from two to five: two (for the X-/Y-bearing bovine sperm heads,15 for large+elongated/small+elongated sperm heads in human adolescents8), three (for large+round/elongated/small spermatozoa in human sperm heads in split ejaculate fractions,7 for elongated+intermediate/large+high acrosome/short+small sperm heads in the puma,11 for small, wide and slightly elliptical/average size, long, narrow and very elliptical/very large, wide and elliptical sperm heads in the rooster12), four (for large/high medium/low medium/small in human sperm head DNA,9 for small/short/large/narrow sperm heads in the bull,14 for shape-related sperm heads in both normo- and terato-zoospermic cats10) to five (for very small, wide, very short and slightly elliptical/small, very short, very wide and slightly elliptical/very large, very wide, short and slightly elliptical/average size, very long, very narrow and very elliptical/average size, long, narrow and elliptical sperm heads in the guinea fowl12). …”

“…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). …”

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 ].…”

Sperm kinematics and morphometric subpopulations analysis with CASA systems: a review

“…In human's sperm, two (Vásquez et al, 2016) or three Yániz et al, 2016) morphometric subpopulations were observed. In other species, a different number of subpopulations were identified; for example, three for pumas (Cucho et al, 2016) and roosters (García-Herreros, 2016), four for cats (Gutiérrez-Reinoso & García-Herreros, 2016), and five for guinea fowls (García-Herreros, 2016). Following the observed motility, each animal inside the same species showed a different subpopulation frequency, probably a consequence of its particular genetic and physiological build.…”