The effect of turbidity on female mate choice in the guppy

Animals often moderate behaviours based on environmental and social cues to enhance their chances of survival and reproductive success. This requires reliable cues that reflect changes in ambient conditions. Environmental pollutants can increase communication costs and distort the accuracy of received information, leading to negative effects on the outcome of behavioural adjustments. Consequently, selection may reduce behavioural plasticity to avoid errors or promote more prudent decision-making when certain cues become unreliable. In aquatic ecosystems, water turbidity shows high levels of natural variation, but human activities amplify its magnitude and extent by increasing algae and suspended solids in the water. Here, we investigated how elevated levels of water turbidity affected mating decisions made by female guppies (Poecilia reticulata) in a laboratory setting. Guppies are a widespread species with a broad tolerance of polluted environments, and females rely heavily on visual cues when making mate choice decisions. We manipulated turbidity by adding suspended solids to water and tested how this affected female preference for males with more orange coloration. We found that females spent more time near males with a greater area of orange colouration in low turbidity water, but that this preference disappeared in both the mid and high turbid water treatments. Moreover, female preferences were highly repeatable in low turbidity water and high turbidity water but not in mid turbidity water. Together, our results suggest that water turbidity impairs the ability of females to discern male colouration and affects the consistency of mate preferences. This could have consequences for the evolution of male colouration in turbid waters.动物通常会依据环境与社会线索（cue）调整自身行为，以提升生存与繁殖成功率。这依赖于能够反映环境条件变化的可靠线索。环境污染物会提升通讯成本，并扭曲接收信息的准确性，进而对行为调整的结果产生负面影响。因此，当某些线索变得不可靠时，自然选择可能会降低行为可塑性（behavioural plasticity）以规避错误，或是推动更审慎的决策过程。在水生生态系统中，水体浊度（water turbidity）本就存在较高的自然变异水平，但人类活动通过增加水体中的藻类与悬浮颗粒物，进一步放大了其变异程度与范围。本研究在实验室环境下，探究了升高的水体浊度对雌性孔雀鱼（Poecilia reticulata）择偶决策的影响。孔雀鱼是一类分布广泛且对污染环境耐受度较高的物种，雌性个体在做出择偶决策时高度依赖视觉线索。研究团队通过向水体添加悬浮颗粒物来操控浊度水平，以此检验浊度变化对雌性偏好橙色体色雄性这一行为的影响。实验结果显示，在低浊度水体中，雌性会在橙色体色面积更大的雄性身旁停留更久，但这一偏好会在中浊度与高浊度的实验组中消失。此外，雌性的择偶偏好在低浊度与高浊度水体中均具有较高的重复性，但在中浊度水体中则不具备重复性。综合来看，本研究结果表明，水体浊度会削弱雌性辨别雄性体色的能力，并影响其择偶偏好的一致性。这一效应可能会对高浊度水域中雄性体色的演化产生影响。