The choice of a social context may depend on the relative quality of individuals, given by the phenotype of competitors or potential mates. Temporal variation in the presence of females and males might be associated with the variation in social context over the reproductive season. An organism’s phenotype is considered a causal link with its reproductive output and hence with its fit­ness. We evaluate the relationship between phenotypic variations of lizards with availability of mating partner thorough the reproductive period. As a model of study we focused on a big-sized lizard, Tupinambis merianae, which exhibits male-biased sexual dimorphism in jaw muscle as a secondary sexual character. We found that operative sexual ratio was biased to males, with this bias being more intense in the middle of the reproductive period. Tail length and tail and abdomen perimeter were the most important predictors of female reproductive output and varied during the reproductive period. Males exhibited investment alternatives in reproductive characters: testicular development, secondary sexual character development or both. We observed differences in the frequency of each investment thorough the reproductive period. Moreover, we found temporal variations in the relationship between secondary sexual character and sperm traits. Accordingly, we observed variations in female and male phenotypes during the reproductive period. The syntopic temporal variations could be expressing behavioral components in relation to sexual and social contexts of mate preference. These results suggest changes in the competitive scenarios.