Population-level species’ cognitive traits have been well explored, as well as differences between species. However, the factors influencing variation in cognitive traits within species is less well known. I have used the swordtail fish species Xiphophorus multilineatus to explore factors potentially influencing variation in cognition, measured with two different classical conditioning tests. Males of this species have a polymorphism and exhibit two alternative reproductive tactics (ARTs) – sneaker and courter tactics. Overall, females prefer to mate with the courter tactic males. Males of the two ARTs differ morphologically and behaviorally. The courter males are larger and will only courtship display for females, while the smaller sneaker males exhibit behavioral plasticity in their mating tactic, and will use a “sneak-chase” tactic to attempt to coerce mating or will courtship display for females if no larger males are in the vicinity. In the first chapter, I compared learning both between males and females and between the two male ARTs. I detected both sexual and tactical dimorphism in performance in a classical conditioning task, as well as the potential for sexual conflict to influence the evolution of cognitive traits in this species. As predicted, the sneaker males that are plastic in their use of mating behaviors performed better in the learning task than the courter males. Additionally, sneaker males performed better than females with a sneaker sire, but not females with a courter sire, which may indicate maternal effects of resource allocation that thereby affects cognitive traits in their offspring. In the second chapter, I capitalized on a known female mate preference in X. multilineatus to explore the effect of cognitive trait variation on female mate preference. I used a shape discrimination task to measure variation in cognitive ability, and a standard dichotomous preference test to measure strength of preference for the larger courter males as compared to smaller sneaker males. Females were able to learn to discriminate between the two-dimensional stimuli shapes, which is the first documentation of shape discrimination in a species of swordtail fish. I also detected a learning bias for circular shapes over squares, potentially due to sensory bias entrenching circular shapes as a more salient cue. I did not detect an effect of cognitive performance on variation in female strength of preference for courter males over sneaker males for females as virgins, experienced, or in considering the change in preference from virgins to experienced females. I suggest that future studies consider using a more difficult learning test, which would increase the variation across females, in addition to increasing the sample size, as the lack of significance appeared to be due weak statistical power. Further study of the influence of sexual conflict on learning as well as how learning influences female mate preference in this species will provide valuable insights into the costs and benefits of learning and of mating with the alternative mating types of males.