Collection and evaluation of semen from captive howler monkeys (Alouatta caraya)

Cryopreservation of spermatozoa from black-and-gold howler monkeys (Alouatta caraya) using egg yolk-based or soy lecithin-based extenders

There are more than 200 species and subspecies of Neotropical Primates of which more than 40% are listed as threatened by the IUCN Red List of Threatened Species. Both in situ and ex situ conservation programs can benefit from the use of assisted reproductive technologies. The objective of this study was to evaluate, for the first time, cryopreservation techniques for Alouatta caraya semen. Semen samples were collected from five adult males, analyzed, and frozen in either Test-egg yolk or Test-soy lecithin-based extenders containing either 3 or 4% glycerol. Frozen-thawed samples were analyzed at 10, 40, and 80 min post-thaw. Egg yolk-based extenders were overall better than soy lecithin-based extenders. There was no significant difference between 3 and 4% glycerol in any of the parameters analyzed, however, 4% glycerol in egg yolk-based extender produced more favorable results for total motility, intact plasma membrane, lipid peroxidation, and DNA fragmentation index. This study brought novel information on semen characteristics and cryopreservation aspects for A. caraya, which can help shape future experiments to improve the outcome of frozen-thawed sperm for this and other species of Neotropical primates.

Differences in sperm morphology between Alouatta palliata and Alouatta pigra are consistent with the intensity of sperm competition in each species

The intensity of sperm competition, in which sperm compete within the female reproductive tract to reach and fertilize her eggs, varies in species with different mating systems. Sperm competition is more intense in species where males cannot monopolize access to reproductive females and females mate with multiple males. In this scenario, a morphological change that increases the ability of sperm to reach and fertilize eggs should rapidly spread in the population, leading to sperm morphological differences between closely related species. Differences in sperm morphology have been reported among primate species with different mating systems. However, due to the inherent logistical and ethical difficulties to sample sperm from wild primates, the extent of variation in sperm morphology within species and among closely related species remains understudied. Here, we compared sperm morphological traits from two sister howler monkey species (Alouatta palliata and Alouatta pigra) that have different mating systems to investigate the effect of sperm competition on sperm morphological traits. We predicted that sperm from A. palliata, where females have more opportunities to mate with multiple males, would show differences in traits associated with increase sperm competitiveness compared to A. pigra where females mostly mate with the central male. We used linear mixed models to determine species differences in sperm morphology, controlling for individual variation. We found that midpieces and heads in A. palliata sperm were on average 26.2% and 11.0% longer, respectively, than those of A. pigra. Differences in these traits are important for sperm speed and hydrodynamic movement in other species and can affect fertilization success. This study provides empirical evidence of sperm morphological traits that evolved through sexual selection in sister primate species with different mating systems.

Semen collection by urethral catheterization and electro-ejaculation with different voltages, and the effect of holding temperature and cooling rate before cryopreservation on semen quality in the Japanese macaque (Macaca fuscata)

In the Japanese macaque, semen has been collected by electro-ejaculation (EE), using the higher voltage stimuli compared to other species including genus Macaca. Semen coagulate immediately after ejaculation, which makes difficult to produce high-quality semen for artificial insemination. Recently, semen collection using urethral catheterization (UC) has been reported in carnivore and this technique may allow semen collection without coagulation in a less invasive manner. Further, the temporal preservation temperature and cooling rate of semen during cryopreservation affect post thawing sperm quality. In this study, to improve semen quality and quantity, as well as the animal welfare, semen collection was performed by EE with high (5-15 V) or low (3-6 V) voltage, UC and a combination of the two (EE-UC). It has been suggested that a high voltage is necessary for semen collection, but 10 V stimulation was effective enough and 15 V is for additional sperm collection. Also, liquid semen was collected by EE-UC and this could increase the total number of sperm. Further, to improve the post thawing sperm motility, semen was kept at four temperatures (4, 15, 25 and 37˚C) for 60 min, and processed with two cooling procedures (slow cooling before second dilution and fast cooling after second dilution). Holding semen at 25˚C and fast cooling after the second dilution maintained progressive motile sperm rate. The present results will contribute to the improvement of semen collection and animal welfare of Japanese macaques.

Sexual selection and sperm diversity in primates

Many aspects of primate sperm physiology and reproductive behavior have been influenced by sexual selection, especially in taxa exposed to sperm competition where females mate with multiple partners. Primate sperm diversity reflects therefore the evolutionary divergences of the different primate species and the impact of a combination of variables exerting selection pressures on sperm form, function, and competition. Thereby, mating systems, life cycle or ecological variables are some of the important factors driving sperm diversity and explaining variation in terms of sperm morphology, parameters or male sexual characters. Here, we address primate sperm diversity through a compilation of all data available in the literature concerning primate sperm parameters and relationships between them. We also review the factors that can influence primate sperm diversity (e.g. mating systems, trade-off between investments in precopulatory and postcopulatory sexual traits, male and female sexual behaviors, seasonality, social constraints, testosterone levels), and discuss also their relevance to our understanding of human reproduction.

Testicular volume and semen characteristics in the endangered southern muriqui (Brachyteles arachnoides)

BACKGROUND

The southern muriqui (Brachyteles arachnoides) is an endangered Neotropical primate. Semen collection and description of its traits, as well as testicular morphometry, have never been reported for this species.

METHODS

Testicles from five healthy adult captive southern muriqui were measured, and semen was collected by rectal probe electrostimulation (RPE).

RESULTS AND CONCLUSIONS

A solid coagulum was identified in all ejaculates, and none of them liquefied, spontaneously or non-spontaneously. It was possible to collect semen using RPE, and although solids coagula did not liquefy, we managed to describe ejaculates characteristics and also confirmed that southern muriqui have relatively large testes size. Further investigations are needed to improve coagulum handling, to achieve a better spermatozoa recovery aiming its application in assisted reproductive technologies.

High efficient and non-invasive collection of ejaculates from rats using penile vibratory stimulation

BACKGROUND

The rat is one of the most important experimental animals, which plays an indispensable role in biomedical research, particularly in reproduction. However, according to our best knowledge, there is no easy and efficient method available for semen collection from rats.

RESULTS

In this study, we successfully collected semen through penile vibratory stimulation ejaculation (PVSE) from laboratory rats. This is an easier and more efficient method compared with rectal probe electro-ejaculation (RPE). We found that the ejaculation rate, volume, concentration and motility of semen collected with PVSE were substantially better than those of RPE. Although PVSE was time-consuming compared to RPE, the quality of semen was better; additionally, sperm concentration and motility of semen were significantly higher with a two-day interval between collections compared to a five-day interval. Moreover, we found that electrical stimulation, use of anesthesia and increased age of rats have a negative effect on sperm quality. In the last experiment, four fertile female rats were artificially inseminated with PVSE-collected semen, and healthy offspring were born.

CONCLUSION

Here, for the first time, we established the repeated collection of semen using the PVSE method in rats.

Semen collection, ejaculate characteristics and in vitro manipulation of spermatozoa from six species of captive flying-fox (Pteropus spp.)

Seminal characteristics are described in six Pteropus species including the critically endangered P. rodricensis. Spermic ejaculates (~40 μL) were collected using electro-ejaculation on 406 of 413 attempts. All flying-fox species had mean percentages of acrosome- and plasma-membrane (PM)-intact spermatozoa of >66% and >73%, respectively; the predominant sperm abnormalities found across all species were damaged, folded or missing acrosomes, bent midpieces and coiled tails. Seminal pH ranged from a low of 7.5 in P. giganteus to a high of 8.2 in P. alecto with the other species in between. Electro-ejaculates recovered in short succession from P. alecto revealed no differences in sperm quality, allowing spermatozoa to be utilised for multi-treatment experiments that evaluated the effects of transportation, incubation temperature and in vitro physico-chemical environments on acrosome and PM integrity. Pteropus alecto spermatozoa were successfully held at ~27°C and 37°C for up to 6 h before a reduction in PM integrity (P = 0.003) was observed. Acrosome and PM integrity decreased (P < 0.000) when P. alecto spermatozoa were incubated at 37°C for 30 min in a Tris–citrate buffer of pH 9.0 but remained stable at pH 5.0 to 8.0. Pteropus alecto mean (± s.e.m.) seminal osmolality was 307.0 ± 2.5 mOsm kg–1; nevertheless, spermatozoa were tolerant of media ranging from 160 to 1190 mOsm kg–1 but exposure to media of ≤160 mOsm kg–1 resulted in increased acrosome damage (P < 0.000).