Sex differences in behavioural and anatomical estimates of visual acuity in the green swordtail Xiphophorus helleri

Among fishes in the family Poeciliidae, signals such as colour patterns, ornaments, and courtship displays play important roles in mate choice and male-male competition. Despite this, visual capabilities in Poeciliids are understudied, in particular visual acuity, the ability to resolve detail. We used three methods to quantify visual acuity in male and female green swordtails (Xiphophorus helleri), a species in which body size and the length of the male's extended caudal fin ('sword') serve as assessment signals during mate choice and agonistic encounters. Topographic distribution of retinal ganglion cells (RGC) was similar in all individuals and characterized by areas of high cell densities located centro-temporally and nasally, as well as a weak horizontal streak. Based on the peak density of RGC in the centro-temporal area, anatomical acuity was estimated to be approximately 3 cycles/degree (cpd) in both sexes. However, a behavioural optomotor assay found significantly lower mean ac...在花鳉科（Poeciliidae）鱼类中，体色图案、装饰结构以及求偶展示等信号在配偶选择和雄性间竞争中发挥着关键作用。尽管如此，学界对花鳉科鱼类的视觉功能，尤其是用于分辨细节的视敏度（visual acuity）的研究仍较为匮乏。我们采用三种方法对雌雄绿剑尾鱼（Xiphophorus helleri）的视敏度进行了量化分析；该物种的体型以及雄性延伸尾鳍（即‘剑尾’）的长度，是配偶选择与争斗互动过程中的评估信号。视网膜神经节细胞（retinal ganglion cells, RGC）的拓扑分布在所有个体中均无显著差异，其特征为在中心颞侧区与鼻侧区存在高细胞密度区域，同时存在一条较弱的水平条纹。基于中心颞侧区RGC的峰值密度，我们估算出雌雄个体的解剖学视敏度均约为3周/度（cycles/degree, cpd）。然而，一项行为学视动反应测定实验却得到了显著更低的平均视……