Estimate of epididymal transit time in the chimpanzee

Functional evidence for differences in sperm competition in humans and chimpanzees

Sperm competition occurs when the gametes of or more males compete for opportunities to fertilize a given set of ova. Previous studies have demonstrated that certain morphological characteristics are affected by sperm competition intensity (e.g. relative testes size and sperm midpiece volume). This study examined whether aspects of sperm energetics may also be affected by sexual selection. We compared the membrane potential of mitochondria in live sperm between H. sapiens (single partner mating system) and P. troglodytes (multiple partner mating system). Flow cytometry of sperm stained with the carbocyanine fluorescent dye JC-1 (an assay for mitochondrial membrane potential) revealed marked differences in red fluorescence intensity. P. troglodytes sperm showed significantly higher mitochondrial membrane potential. Mitochondria provide a substantial part of the energy required for sperm motility. A higher mitochondrial loading may therefore be associated with enhanced sperm motility and/or longevity. Additionally, examination of JC-1 red fluorescence levels before and after in vitro capacitation revealed further differences. Whereas chimpanzee sperm showed maintenance of membrane potential after capacitation (in some cases even an increase), sperm from humans consistently showed reduction in membrane potential. These results indicate that the sperm of human beings and chimpanzees exhibit marked differences in mitochondrial function, which are affected by selection pressures relating to sperm competition and that these pressures differ significantly between humans and chimpanzees.

Spermatogenic cycle length and spermatogenic efficiency in the gerbil (Meriones unguiculatus)

The gerbil (Meriones unguiculatus) is a rodent native of the arid regions of Mongolia and China. Because the gerbil can be easily bred in laboratory conditions, this species has been largely used as an experimental model in biomedical research. However, there is still little information concerning the testis structure and function in the gerbil. In this regard, we performed a detailed morpho-functional analysis of the gerbil testis and estimated the spermatogenic cycle length utilizing 3H-thymidine as a marker for germ cell progression during their evolution through the spermatogenic process. The stage frequencies of the XII stages characterized according to the acrosome formation and development were (I-XII) 13.8, 10.1, 8.1, 7.8, 4.0, 11.2, 7.5, 7.1, 5.9, 7.6, 8.1, and 8.9. The mean duration of each seminiferous epithelium cycle was determined to be 10.6 +/- 1.0 days and the total duration of spermatogenesis, based on 4.5 cycles, was approximately 47.5 days. The volume density of tubular and interstitial compartments was approximately 92% and 8%, respectively. Based on the volume occupied by seminiferous tubules in the testis and the tubular diameter, about 9 and 18 m of seminiferous tubules were found per testis and per gram of testis, respectively. Twelve primary spermatocytes were formed from each type A1 spermatogonia. The meiotic index was 2.8, indicating that 30% of cell loss occurs during meiosis. The number of Leydig and Sertoli cells per gram of the testis was 28 million and each Sertoli cell was able to support approximately 13 spermatids. The daily sperm production per gram of testis (spermatogenic efficiency) was 33 million. Taken together, these data indicate that, mainly due to the high seminiferous tubule volume density and Sertoli cell support capacity for germ cells, the gerbil presents high spermatogenic efficiency compared with other mammalian species already investigated. The data obtained in the present study might provide the basis for future research involving the reproductive biology in this species.

Duration of spermatogenesis and sperm transit time through the epididymis in the Piau boar

The Piau boar is a rustic breed of economical importance in Brazil. The duration of spermatogenesis and sperm transit through the epididymis in Piau boars was estimated using intratesticular injections of tritiated thymidine. Animals were sacrificed 1 h, 7 days, 14 days, 21 days, 34 days, and 36 days after injections. Each cycle of spermatogenesis in Piau boars lasts 9 +/- 0.2 days. At least 9 days are necessary for spermatozoa to traverse the entire epididymis. Considering that the total duration of spermatogenesis takes about 4.5 seminiferous epithelium cycles, spermatogenesis was estimated to take 40.6 days. The primary spermatocytes life span is 13.5 days, while spermiogenesis in Piau boars lasts 14.5 days. Staging in Piau boars was based on tubular morphology system. The relative stage frequencies in these boars, based on approximately 1200 seminiferous tubule cross-sections for each animal, were as follows: stage 1, 11.7 +/- 0.7%; stage 2, 14.3 +/- 0.3%; stage 3, 5.4 +/- 0.1%; stage 4, 12.1 +/- 0.6%; stage 5, 9.6 +/- 0.4%; stage 6, 17.2 +/- 0.4%; stage 7, 15.4 +/- 0.8%; and stage 8, 14.3 +/- 0.9%. The duration of spermatogenic events and the relative stage frequencies in Piau boars differ slightly from those observed in improved swine breeds.

Sequential histology of the adult chimpanzee epididymis

The chimpanzee epididymis consists of three gross anatomical regions: caput (Cp), corpus (Cr), and cauda (Cd). During epididymal transit, chimpanzee sperm undergo maturational changes (affecting motility, capacitation, and the acrosome reaction), which enable fertilization. Elucidation of the sequential histology of the chimpanzee epididymis is preliminary to determining the role of each region of epididymal duct in the process of sperm maturation. We report the histology, in the adult male chimpanzee, of sequential segments of epididymis from the proximal efferent ductules through the Cp, Cr, and Cd regions of the epididymis proper to the proximal ductus deferens. These data illustrate the gross architecture of the tissue and reveal the histology characteristic of the diverse epithelia composing the epididymal ducts at each level. The tubules composing the epididymis of the adult male chimpanzee present at least 16 histologically-distinct epithelia and their transitional forms. Such diversity of epithelia suggests a corresponding diversity of function. Although there are some clear differences, the histological appearance of the ducts, and of the component epithelia of the chimpanzee epididymis, is remarkably similar to that reported for the human.