Department of Science Education, Cooperative Faculty of Education, Gunma University, Maebashi, Japan.
Department of Biology, Tokyo Gakugei University, Tokyo, Japan.
PLoS One. 2021 Dec 2;16(12):e0261004. doi: 10.1371/journal.pone.0261004. eCollection 2021.
The trade-up hypothesis is a female behavioral strategy related to mating with multiple males. In this hypothesis, females can produce high-quality offspring while avoiding the risk of losing reproductive opportunities by non-selective mating with males at first mating and then re-mating with more attractive males. As an internal mechanism to realize this behavioral strategy, we predicted that females would immediately fertilize their eggs when they mated with attractive males, whereas females would delay fertilization when they mated with unattractive males to trade-up sires of offspring. The guppy (Poecilia reticulata) is an ovoviviparous fish with internal fertilization, and females show a clear mate preference based on the area of orange coloration on the bodies of males. In addition, it is known that females show a re-mating strategy consistent with the trade-up hypothesis. We tested whether the attractiveness of mated males affected the gestation period and the timing of fertilization. Females were paired with either colorful males or drab males, and the gestation periods (the number of days from mating to parturition) were compared. In addition, we dissected the abdomens of the females at intervals of several days after mating and observed whether the eggs were fertilized. The gestation period in females that were paired with attractive colorful males was significantly shorter than that in females that were paired with drab males. We found that females that mated with colorful males also had their eggs fertilized earlier than those that mated with drab males. Our findings show that differences in the timing of fertilization according to attractiveness of the mate increase the opportunity for cryptic female choice and trading up.
性选择假说（trade-up hypothesis）是一种与与多个雄性交配有关的雌性行为策略。在这个假说中，雌性可以通过在初次交配时与非选择性的雄性交配，然后与更有吸引力的雄性重新交配，从而产生高质量的后代，同时避免失去繁殖机会的风险。作为实现这种行为策略的内在机制，我们预测雌性在与有吸引力的雄性交配时会立即使卵子受精，而在与无吸引力的雄性交配时会延迟受精，以换取后代的优质父本。孔雀鱼（Poecilia reticulata）是一种卵胎生鱼类，具有体内受精的特点，雌性根据雄性身体上橙色区域的大小表现出明显的配偶偏好。此外，已知雌性表现出与性选择假说一致的再交配策略。我们测试了交配雄性的吸引力是否会影响妊娠期和受精时间。雌性与色彩鲜艳的雄性或暗淡的雄性配对，并比较妊娠期（从交配到分娩的天数）。此外，我们每隔几天解剖交配后的雌性腹部，观察卵子是否受精。与色彩鲜艳的雄性配对的雌性的妊娠期明显短于与暗淡雄性配对的雌性。我们发现，与色彩鲜艳的雄性交配的雌性的卵子也比与暗淡雄性交配的雌性更早受精。我们的研究结果表明，根据配偶吸引力的不同，受精时间的差异增加了隐性雌性选择和性选择的机会。
