INFLUENCE OF OPERATIONAL SEX RATIO, SIZE, AND BODY COLORATION OF MALES ON MATE SELECTION AND MALE-MALE COMPETITION IN Poecilia reticulata (GUPPIES)

Abstract

The operational sex ratio (OSR) in fishes fundamentally describes the intensity of sexual selection and potential reproductive success. It reflects the ratio of sexually active males to sexually receptive females, influencing the intensity of competition, including associate behaviours among males for mates. This research used wild guppies as the model organism to understand the influence of OSR in the behavioural display of both males and females, and to evaluate the relationship between male body colouration, body size of both sexes, and mating success. Methodology consisted of initial collection and acclimatisation of wild guppy populations from the canals around Colombo, like the Udahamulla Railway Station (6.8622720, 79.9086026), Pagiriwaththa Railway Station (6.8648125, 79.9024510), and Paramitha Dharmayathana Temple (6.8763484, 79.9083455), followed by subjecting them into three tests based on OSR, tail colouration of male guppies, and body size of both sexes. Different OSR levels were created, ranging from 1:5 (female-biased) to 5:1 (Male-biased). Under each level, mating tactics such as sigmoid displays (SG), sneak attempts (SA), mirror action (MA), and male-male interactions were recorded using videography tools. Measurement of tail colour and body size preference also consisted of the same behavioural recording protocol. Results indicated prominent SG display while male behaviour declined from 0.17 to 0.83 OSR treatments. The second test of tail colour preference indicated a higher preference for orange-tailed males by the females. In the last test of body size preference, both sexes preferred large-bodied counterparts with increased activity. Hence, the OSR influences the mate choice of both sexes and competition in the more biased sex, which ultimately affects the evolutionary trajectory of the species in the environment through secondary sexual traits.