Seasonal emission of seminal coagulum and in vivo sperm dynamics in the black-handed spider monkey (Ateles geoffroyi)

The ejaculate of diverse primate species consists of two portions, liquid and solid; the latter, known as the seminal coagulum, is thought to sequester large numbers of sperm. In the black-handed spider monkey (Ateles geoffroyi), ejaculates collected by electroejaculation did not always contain seminal coagulum. The objective of the present study was to determine seasonal emission of seminal coagulum and in vivo sperm dynamics in the black-handed spider monkey. Seminal coagulum emission was related to season; it was more frequent in the dry season, coincident with maximal female fertility. Sperm concentration was higher (P = 0.02) in the dry season (dry vs. rainy season: 137.9 ± 15.7 sperm/mL vs. 82.56 ± 14.7 × 106 sperm/mL; mean ± S.E.M.) but also in ejaculates (collected during the rainy season) that had seminal coagulum (coagulum vs. no coagulum: 140.0 ± 29.3 sperm/mL vs. 31.2 ± 0.1 × 106 sperm/mL, P < 0.001). In semen samples collected from the uterus after AI, the percentage of linearly motile sperm was higher during the dry season (dry vs. rainy: 9.1 ± 2.1% vs. 5.9 ± 2.5%), as well as whenever coagulum was present (coagulum vs. no coagulum: 13.0 ± 3.2% vs. 2.0 ± 0.9%, P < 0.001).