Heritability of sexual traits in the common Japanese medaka (Oryzias latipes)

Abstract

Adaptation is a process that occurs through natural and sexual selection and can drive variation within species. By showing that certain sexual traits are inherited, I demonstrated that these traits can vary, at least in part, because of adaptation, rather than entirely because of plasticity across abiotic and social environments. Japanese medaka fish (Oryzias latipes) have observable and quantifiable morphological traits, making them a good model for monitoring the influence of operational sex ratio, OSR, the ratio of sexually available males to females, on population variability. The fish were isolated in mating pairs in standardized environmental conditions to determine whether variation in traits was because of the OSR or genetic factors. Anal fin area (mm²), standard body length (mm), and testis weight (mg) were measured for the parental fish and their offspring, which were collected as eggs and raised until sexual maturity. Linear regressions were used to indicate heritability between the parental and offspring traits. Average standard body length, male anal fin area, and testis weight had the highest narrow sense heritability factors (h²=0.5430, h²=0.3295, and h²=0.6286, respectively). The influence of OSR was determined for the parental traits using general linear models, as they had been bred in four independent OSRs (0.5, 1, 2, 5) for three generations previous to this experiment. All traits had a weak influence of OSR except for male and female anal fin area and testis weight, which was stronger only when body length was also factored in. By showing that these traits are inherited, I provide evidence that additive genetic variation is playing a role in the variation between and among populations of medaka.