Reproductive strategies vary according to season length, individual reproductive traits, and factors associated with the social context such as density and sex ratio of the individuals. The social context predicts the intensity of sexual selection due to its effect on mate choice and intra-sexual competition. Moreover, it exacerbates the costs derived from sexual conflict and allows for the existence of alternative reproductive tactics to counteract such costs. However, these mechanisms are still underexplored in many animal taxa. Majoidea "spider crabs" show a diversity of life history, and behavioral and morphological adaptations for reproduction, which have evolved as an outcome of competition to maximize reproductive success. We aimed to analyze in this study, male reproductive strategies through mating behavior under different social contexts, density of individuals, and males size differences in two species of "spider crabs", Leurocyclus tuberculosus and Libinia spinosa. The experiments were as follows: one female and one male per aquarium (Experiment 1); a female and three males of similar sizes per aquarium (Experiment 2); and a female and three males of distinct sizes per aquarium (Experiment 3). The experiments showed that mating behavior and duration of mate guarding differ between species and among different social contexts. The presence of males with similar or different sizes showed a relevant different behavior, the female copulated with more than one male when males were similar in size (E2), and copulated only with the largest male when males were different in size (E3). In mate guarding, the shape and the use of the chelipeds had an important role: the male of Leurocyclus tuberculosus grasped the female with the chelipeds and did not fight with other males, but the male of Libinia spinosa surrounded the female with the chelipeds and fought with other males. The longest duration of mate guarding was during precopulatory guarding. Precopulatory guarding was present in all the experiments and its duration did not present significant differences among the experiments. However, in both species, the experiments differ in the duration of postcopulatory guarding until spawning. Gonopod morphology revealed important differences between species and are probably associated with sperm competition. The experiments under distinct social contexts linked to the use and shape of the chelipeds and the morphology of the gonopods, could allow to understand the functional significance of the different reproductive strategies.

中文翻译：

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两种蜘蛛蟹（Leurocyclus tuberculosus 和 Libinia spinosa）的雄性繁殖策略

生殖策略根据季节长度、个体生殖特征以及与社会环境相关的因素（例如个体的密度和性别比例）而有所不同。由于其对配偶选择和性内竞争的影响，社会背景预测了性选择的强度。此外，它加剧了性冲突产生的成本，并允许存在替代生殖策略来抵消这些成本。然而，这些机制在许多动物类群中仍未得到充分探索。Majoidea“蜘蛛蟹”表现出多样性的生活史，以及繁殖的行为和形态适应性，这些进化是为了最大限度地提高繁殖成功而进行的竞争的结果。我们的目的是在这项研究中分析，雄性繁殖策略通过不同社会背景下的交配行为、个体密度和两种“蜘蛛蟹”（Leurocyclus tuberculosus 和 Libinia spinosa）的雄性大小差异进行研究。实验如下：每个水族箱一雌一雄（实验1）；每个水族箱中一只雌性和三只体型相似的雄性（实验 2）；以及每个水族箱中大小不同的雌性和三只雄性（实验 3）。实验表明，交配行为和配偶守卫的持续时间在物种之间和不同的社会环境中是不同的。体型相似或不同的雄性的存在表现出相关的不同行为，当雄性体型相似时，雌性与不止一个雄性交配（E2），而当雄性体型不同时，雌性只与最大的雄性交配（E3）。在配偶守卫中，螯足的形状和使用有着重要的作用：Leurocyclus tuberculosus 雄性用螯足抓住雌性，不与其他雄性争斗，而利比尼亚刺足类的雄性用螯足包围雌性并与之战斗与其他男性。配偶守卫的最长持续时间是在交配前守卫期间。所有实验中都存在性前保护，其持续时间在实验之间没有显着差异。然而，在这两个物种中，实验在交配后保护直到产卵的持续时间上有所不同。生殖器形态揭示了物种之间的重要差异，可能与精子竞争有关。不同社会背景下的实验与螯足的使用和形状以及生殖器的形态有关，