Department of Chemical and Biological Sciences, Laboratory of Evolutionary Genetics, Japan Women's University, Bunkyo-ku, Tokyo, Japan.
PLoS One. 2021 Nov 15;16(11):e0259741. doi: 10.1371/journal.pone.0259741. eCollection 2021.
The three-chamber experiment, in which one test animal can choose between two animals placed in physically inaccessible compartments, is a widely adopted strategy for studying sexual preference in animals. Medaka, a small freshwater teleost, is an emerging model for dissecting the neurological/physiological mechanisms underlying mate choice for which intriguing findings have been accumulating. The three-chamber strategy has rarely been adopted in this species; therefore, here we investigated its validity using medaka colour variants that mate assortatively. First, a total of 551 movies, in which a test male and two choice females interacted for 30 min under a free-swimming condition, were manually analysed. The sexual preference of the males, calculated as a courtship ratio, was highly consistent between human observers (r > 0.96), supporting the objectivity of this manual-counting strategy. Second, we tested two types of three-chamber apparatuses, in which choice fish were presented in either a face-to-face or side-by-side location. Test fish (regardless of sex) spent most of the time associating with choice fish in the compartments. However, their sexual preference, calculated as an association ratio, was poorly reproduced when the locations of the choice fish were swapped. Third, the sexual preferences of males quantified using the manual-counting and either of the three-chamber strategies did not correlate (r = 0.147 or 0.297). Hence, we concluded that, even for individuals of a species like medaka, which spawn every day, sexual preference could not be reliably evaluated using the three-chamber strategy. Optimization of the protocol may solve this problem; however, the explanation for the observation that animals that are ready for spawning persist with never-accessible mating partners must be reconsidered.
三厢实验中，一只测试动物可以在两个被物理隔离的动物中进行选择，这是一种广泛采用的研究动物性偏好的策略。青鳉，一种小型淡水硬骨鱼，是一种新兴的模式生物，用于解析配偶选择的神经/生理机制，在这方面已经积累了有趣的发现。三厢策略在这个物种中很少被采用；因此，在这里我们使用青鳉的颜色变体来研究其有效性，这些变体可以进行交配。首先，总共分析了 551 部电影，在这些电影中，一只测试雄性和两只选择雌性在自由游动的条件下相互作用了 30 分钟。雄性的性偏好，计算为求偶比例，在人类观察者之间高度一致（r > 0.96），支持这种手动计数策略的客观性。其次，我们测试了两种类型的三厢设备，其中选择鱼类分别位于面对面或并排的位置。测试鱼类（无论性别）大部分时间都与隔间中的选择鱼类在一起。然而，当选择鱼类的位置交换时，它们的性偏好，计算为关联比例，就无法很好地再现。第三，使用手动计数和任何一种三厢策略量化的雄性的性偏好都没有相关性（r = 0.147 或 0.297）。因此，我们得出结论，即使对于像青鳉这样每天产卵的物种的个体，也不能使用三厢策略可靠地评估性偏好。优化方案可能会解决这个问题；然而，对于观察到的准备产卵的动物仍然与无法接触到的交配伙伴交配的解释，必须重新考虑。
