Vasconcelos Sampaio Wlaisa, Leite Leão Danuza, da Cunha Sousa Patrícia, Lima de Queiroz Helder, Farhayldes Souza Domingues Sheyla
Postgraduate Program in Animal Health and Production in the Amazon, Federal Rural University of the Amazon, Belém, Pará, Brazil.
Laboratory of Wild Animal Biotechnology and Medicine, Faculty of Veterinary Medicine, Federal University of Pará, Castanhal, Pará, Brazil.
Am J Primatol. 2022 Feb;84(2):e23353. doi: 10.1002/ajp.23353. Epub 2021 Dec 2.
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.
松鼠猴是新热带区的灵长类动物，具有季节性繁殖的特点，雄性会出现季节性育肥状况，这被认为是一种交配前的性选择策略。此外，雌性在同一季节会与多个雄性交配。这也可能通过精子竞争促进交配后性策略的进化。在本研究中，我们检验了以下假设：柯氏松鼠猴的育肥状况与有利的精液特征之间存在关联，并评估了其对精子竞争的影响。对2015年6月至2016年7月期间饲养在混合群体或全雄群体中的10只5至15岁成年雄性进行了分析。每月测量体重、腋窝和手臂皮肤褶厚度以及睾丸体积，并通过电刺激射精采集精液。制定了一个育肥指数来量化和识别育肥雄性，比较了非育肥和育肥状态下的生物特征和精液参数。育肥雄性的睾丸体积更大。这与在交配季节维持高射精频率所需的生精活动增加有关。在育肥雄性中检测到精液量增加和精液凝固频率增加，这些优势与精子在雌性生殖道中的保护有关。年龄和社会环境对于形态和精液特征而言并非显著的变异来源。观察到育肥雄性在获取精液时的反应下降以及无精子射精频率增加。这些意外结果可能是由于短期内强烈的繁殖活动所致。育肥现象在松鼠猴的性选择中具有许多影响，并且仍未完全揭示。我们的结果证实了在柯氏松鼠猴中，育肥雄性状况与性选择相关的观点，并且我们发现有证据表明它可能也通过交配后的成分，即精子竞争来体现。
