Structural variations of subterminal satellite blocks and their source mechanisms as inferred from the meiotic configurations of chimpanzee chromosome termini.

African great apes have large constitutive heterochromatin (C-band) blocks in subtelomeric regions of the majority of their chromosomes, but humans lack these. Additionally, the chimpanzee meiotic cell division process demonstrates unique partial terminal associations in the first meiotic prophase (pachytene). These are likely formed as a result of interaction among subtelomeric C-band blocks. We thus conducted an extensive study to define the features in the subtelomeric heterochromatic regions of chimpanzee chromosomes undergoing mitotic metaphase and meiotic cell division. Molecular cytogenetic analyses with probes of both subterminal satellite DNA (a main component of C-band) and rDNA demonstrated principles of interaction among DNA arrays. The results suggest that homologous and ectopic recombination through persistent subtelomeric associations (post-bouquet association observed in 32% of spermatocytes in the pachytene stage) appears to create variability in heterochromatin patterns and simultaneously restrain subtelomeric genome polymorphisms. That is, the meeting of non-homologous chromosome termini sets the stage for ectopic pairing which, in turn, is the mechanism for generating variability and genomic dispersion of subtelomeric C-band blocks through a system of concerted evolution. Comparison between the present study and previous reports indicated that the chromosomal distribution rate of sutelomeric regions seems to have antagonistic correlation with arm numbers holding subterminal satellite blocks in humans, chimpanzees, and gorillas. That is, the increase of subterminal satellite blocks probably reduces genomic diversity in the subtelomeric regions. The acquisition vs. loss of the subtelomeric C-band blocks is postulated as the underlying engine of this chromosomal differentiation yielded by meiotic chromosomal interaction.

A comparative study on testicular microstructure and relative sperm production in gorillas, chimpanzees, and orangutans.

We performed histological analyses for comparing testicular microstructure between the gorilla, chimpanzee, and orangutan. Testicular samples were obtained by autopsy or biopsy from 10 gorillas, 11 chimpanzees, and 7 orangutans from several zoos and institutes. The seminiferous epithelia were thick in the chimpanzee and orangutan but thin in the gorilla. Leydig cells in the interstitial tissue were abundant in the gorilla. The acrosomic system was extremely well developed in the orangutans. Our study reveals that the cycle of seminiferous epithelium in orangutan testis can be divided into ten stages, whereas that in human, chimpanzee, and gorilla testes can be divided into only six stages. Phylogenetic analyses of the number of divisions may indicate that the seminiferous epithelium of our common ancestor has changed since the orangutan diverged from it. Furthermore, we performed comparative analyses of testicular microstructure to estimate relative sperm production among these three animals, and proposed a new indicator (namely the spermatogenic index, SI) closely related to sperm production. The SI indicated that a chimpanzee usually produces about 223 times more sperm than a gorilla and about 14 times more than an orangutan. Our data demonstrate the significance of the SI for estimating sperm production, thus aiding our understanding of the reproductive strategy as well as testis weight and relative testis size in investigated primates.

How costly are ejaculates for Japanese macaques?

Much sexual selection theory is based on the idea that ejaculate is cheap. Since further details are unknown our aim was to determine the energy that primate males require for ejaculate production. We addressed this problem by measuring the energy content (in kJ) of ejaculates from Japanese macaques (Macaca fuscata) using standard bomb calorimetry. Then, we estimated the relative amount of energy that individuals require for ejaculate production by relating the net energy content of ejaculates to males' daily basal metabolic rate (BMR). Fresh macaque ejaculate contains 3.0 kJ ml(-1). Assuming a mean volume of 2.7 ml an average macaque ejaculate contains 8.1 kJ. Depending on the individuals' body mass (6-13 kg) and the number and volume of the ejaculates, macaque males are assumed to use between at least 0.8% and at most 6.0% of their BMR for ejaculate production per day during the breeding season. Even when regarding only the minimal energy investment of 0.8% of daily BMR for ejaculate production, clearly ejaculates come with some cost for primate males.

Testicular histological examination of spermatogenetic activity in captive gorillas (Gorilla gorilla).

To clarify the reproductive state of male gorillas, we performed histological examinations on the testicles of 10 male gorillas (Gorilla gorilla). The testicular samples were obtained by autopsy, and ordinal histological preparations were made for light microscopy. The poor spermatogenesis of this species was characterized by the following findings: First, spermatogenesis was evident in only four samples. Meiosis progressed in two samples, but they lacked spermatogenesis. In the remaining four specimens, seminiferous tubules hyalinized without any sign of spermatogenesis. Second, seminiferous epithelia were thin even in the males in which spermatogenesis was observed. Third, degenerated seminiferous tubules were found in all specimens. Fourth, abnormally large syncytial cells were found in the tubules. Six stages in the epithelial cycle of the seminiferous tubules were identified. Testosterone staining made it clear that there were many Leydig cells with spherical or fusiform nuclei in an abundance of interstitial tissue. The relevance of the testicular architecture of gorillas to the mating system is discussed.

Urinary steroids, FSH and CG measurements for monitoring the ovarian cycle and pregnancy in the chimpanzee.

Non-invasive methods for monitoring reproductive status of chimpanzee based on the measurement of urinary steroids and gonadotropins were examined. A typical pre-ovulatory urinary estrone conjugate (E1C) surge and post-ovulatory increase in pregnandiol glucuronide (PdG) were seen during the menstrual cycle. Urinary follicle stimulating hormone (FSH) showed two peaks over the infertile menstrual cycle. The earliest changes indicating pregnancy were a coincident rise in E1C and chorionic gonadotropin (CG) levels and a concomitant fall in FSH levels. Urinary PdG levels showed a prolonged rise. Urinary E1C in the pregnant chimpanzee was higher than during the menstrual cycle and increased with advancing gestation, with maximum levels occurring near term. In the case of stillbirth, E1C and CG levels from mid- through late-pregnancy were low and the prepartum progressive increase in E1C was not shown. The data presented here are of great practical value in captive breeding management of chimpanzees.

Population genetics of crab-eating macaques (Macaca fascicularis) on the island of mauritius.

Protein polymorphisms of the crab-eating macaque (Macaca fascicularis) on the island of Mauritius in the southwest Indian Ocean were examined electrophoretically for 201 blood samples. All of the variant types detected were those found previously in the Asian populations. Genetic variability of the island population was estimated to be Ppoly = 16% and H = 6.5%, which was lower than that of the Asian populations. A tendency that a small number of loci were highly polymorphic was observed. These results may reflect the establishment of the island population from a small number of introduced ancestors, or the existence of the bottleneck effect. For the origin of the Mauritian monkeys, comparison of electrophoretic variants suggested that they originated from the Malay Peninsula or the Greater Sunda Islands, especially from Java. Though the homozygous individuals exceeded in number as a whole, a significant subdivision was not detected in the population. © 1993 Wiley-Liss, Inc.