ORIGINAL ARTICLE Effect of photoperiod on characteristics of semen obtained by electroejaculation in stump-tailed macaques (Macaca arctoides) Mo ´nica Dafne Garcı ´a Granados • Leonor Estela Herna ´ndez Lo ´pez • Alejandro Co ´rdoba Aguilar • Ana Lilia Cerda Molina • Olivia Pe ´rez-Ramı ´rez • Ricardo Mondrago ´n-Ceballos Received: 3 October 2013 / Accepted: 8 February 2014 / Published online: 2 March 2014 Ó Japan Monkey Centre and Springer Japan 2014 Abstract Some environmental variables determining seasonal reproduction in mammals are temperature, humidity, food availability, and photoperiod. Among these, photoperiod is considered the main regulator of primates’ seasonal reproduction, thus the latitudinal distribution of primate populations is a key factor determining the appearance of seasonal reproduction. The present work presents supporting discrete seasonality in male stump- tailed macaques (Macaca arctoides). We investigated whether semen quality and testosterone covaried with Mexico City’s photoperiod and relative humidity by ana- lyzing variations in the portions that form the ejaculate: the seminal liquid, the seminal coagulum, and the copulatory plug. Five male adult stump-tailed macaques were elec- troejaculated once a month, obtaining three semen samples per male, from August 2011 to July 2012 (except for December 2011) (n = 165). Our results showed that stump-tailed macaque sperm counts were significantly different between the portions of the ejaculate. The seminal coagulum contained the significantly largest number of spermatozoids, followed by the copulatory plug and the seminal fluid. Photoperiod and relative humidity had major influence on the sperm count in the seminal coagulum and the testosterone concentrations. Testosterone reached its highest values around the time when days and nights lasted the same hours, decreasing when days either grew longer or became shorter. Concerning relative humidity, sperm counts in the seminal coagulum were highly variable on dry days, but decreased as the relative humidity increased. We conclude that stump-tailed macaques have a discrete seasonality, occurring in spring and fall when macaques’ reproductive condition and readiness for postcopulatory intrasexual competition increase. Keywords Macaca arctoides Á Photoperiod Á Relative humidity Á Seasonal reproduction Introduction Seasonal reproduction is the temporal distribution of copu- lations during one period of the year to be followed by births in another period. Three distinct forms of seasonal repro- duction are described in primates: (1) discrete seasonality, where births occur all year long but more frequently in some seasons or months, such as in Macaca fuscata; (2) strict seasonality, where copulations only occur in a certain period of the year (the mating season), so consequently births are clustered in a following period; (3) nonseasonality, where copulations and births occur throughout the entire year, as seen in lorises, mangabeys, and colobines (Lindburg 1987). Some environmental variables determining seasonal repro- duction in mammals are temperature and humidity (Bronson 1988), food availability (Koening et al. 1997), and photo- period (Hastings et al. 1985). Among these, photoperiod is considered the main regulator of primates’ seasonal repro- duction (Koening et al. 1997; Di Bitetti and Janson 2000; Anderson et al. 2006), thus the latitudinal distribution of M. D. Garcı ´a Granados Á L. E. Herna ´ndez Lo ´pez (&) Á A. L. Cerda Molina Á O. Pe ´rez-Ramı ´rez Á R. Mondrago ´n-Ceballos Departamento de Etologı ´a, Instituto Nacional de Psiquiatrı ´a, ‘‘Ramo ´ n de la Fuente Mun ˜iz’’, Calzada Me ´xico-Xochimilco 101, Col. San Lorenzo Huipulco, Tlalpan, 14370 Mexico, D.F., Mexico e-mail: lhl@imp.edu.mx A. Co ´rdoba Aguilar Departamento de Ecologı ´a Evolutiva, Instituto de Ecologı ´a, Universidad Nacional Auto ´noma de Me ´xico, Mexico, D.F., Mexico 123 Primates (2014) 55:393–401 DOI 10.1007/s10329-014-0414-6