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

Citation

Caves, Eleanor M; De Busserolles, Fanny; Kelley, Laura A (2021), Sex differences in behavioural and anatomical estimates of visual acuity in the green swordtail Xiphophorus helleri, Dryad, Dataset, https://doi.org/10.5061/dryad.qjq2bvqhb

Abstract

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 acuity in males (0.8 cpd) than females (3.0 cpd), which was not explained by differences in eye size between males and females. An additional behavioural assay, in which we trained individuals to discriminate striped gratings from grey stimuli of the same mean luminance, also showed lower acuity in males (1-2 cpd) than females (2-3 cpd). Thus, although retinal anatomy predicts identical acuity in males and females, two behavioural assays found higher acuity in females than males, a sexual dimorphism which is rare outside of invertebrates. Overall, our results have implications for understanding how Poeciliids perceive visual signals during mate choice and agonistic encounters.

Methods

See manuscript for details. In brief, behavioral data were collected by EMC using either an innate optomotor assay or a conditioned choice assay. Retinal ganglion cell mapping data were collected by FdB using samples provided by EMC. For details of data processing, see the ReadMe file and associated R codes.

Usage Notes

See the ReadMe file for details about this dataset.

Funding

H2020 Marie Skłodowska-Curie Actions, Award: 793454

Australian Research Council, Award: DE180100949

Australian Research Council, Award: LE100100074

Royal Society, Award: DH160082