Saimiri are neotropical primates with seasonal reproduction, males develop a seasonal fattening condition that has been suggested as a pre-copulatory sexual selection strategy. Furthermore, females mate with multiple males in the same season. This could also favor the evolution of a postcopulatory sexual strategy by sperm competition. In this study, we tested the hypothesis that there is a relationship between the fatted condition and advantageous seminal characteristics in Saimiri collinsi and evaluated its implications for sperm competition. Adult males (N = 10), aged 5-15 years, housed in mixed or only-male groups, were analyzed from June, 2015 to July, 2016. Measurements of weight, axilla, and arm skinfold, and testicular volume were taken monthly, and semen was collected by electroejaculation. A fattening index was developed to quantify and identify fatted males, biometrics, and seminal parameters were compared between the non-fatted and fatted conditions.The fatted males present a larger testicular volume. This is related to the increase in spermatogenic activity necessary to sustain a high ejaculation frequency during the mating season. An increase in seminal volume and in frequency of semen coagulation were detected in fatted males, advantages related to sperm protection in the female reproductive tract. Age and social context were not significant sources of variation for both morphological and seminal traits. A decrease in response from the fatted males in obtaining semen and an increase in the frequency of azoospermic ejaculates were observed. These unexpected results may be due to intense reproductive activities in a short period. The fattening phenomenon has many implications in the sexual selection of squirrel monkeys, and they are still not entirely unveiled. Our results corroborate the idea that, in S. collinsi, the fatted male condition is related to sexual selection, and we found evidence suggesting it may be also expressed by a post-copulatory component, sperm competition.

Viabilidade do sêmen de tatus-peba (Euphractus sexcinctus) centrifugado e diluído em Tris ou agua de coco em pó.Ciência Rural, v.44, n.9, set, 2014.

Background Anogenital distance is considered a non‐invasive measure to assess the development and functionality of sexual organs in different animal species. Hence, this measurement could potentially be used during the selection of non‐human primates for reproductive biotechnology programs. The aim of this study was to assess the correlation between anogenital distance and reproductive parameters in captive Saimiri collinsi. Methods Eight mature S. collinsi males were evaluated. Body weight, reproductive hormone levels, testicular volume, and seminal parameters were determined, and their relationship with anogenital distance measurements was assessed. Results Anogenital distance was correlated with seminal volume, sperm motility, vigor, and plasma membrane integrity, but not with body weight, reproductive hormones, and testicular volume. Conclusion The determination of anogenital distance is a non‐invasive method to predict seminal quality. This procedure has the advantage of providing andrologic information without a negative impact on animal welfare.

Background We hypothesized that seasonal variations in testicular biometry in Saimiri collinsi are influenced by body mass and that testicular enlargement is related to improved seminal quality. Therefore, the gonadosomatic index (GSI) can be a tool to determine reproductive seasons and the predictors of seminal quality. Methods Body mass, testicular biometry, and semen samples were obtained from eight adult males monthly and evaluated. Results In the non‐fattening/non‐reproductive season, the body mass and GSI decreased and increased, respectively, in the fattening. A positive correlation was only observed between the GSI and seminal volume. During fattening, high seminal volume and normal morphology were observed, but sperm concentrations were low. Conclusion The GSI cannot be used as a predictor of seminal quality, but selective pressure to improve seminal quality may increase the chances of fertilization at fattening. The GSI provides new information on seasonality and can be used to identify reproductive seasons in squirrel monkeys.