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.
