The effects of novel mates and competitors on the courtship and aggression behaviour of Japanese Medaka (Oryzias latipes)

Abstract

Mating with novel individuals is a beneficial strategy to cope with environmental instability and increases the probability of offspring fitness. Additionally, for males to mate successfully, they must appropriately allocate their limited mating energy towards courtship (intersexual) and aggression (intrasexual) behaviour. In male Japanese medaka (<i>Oryzias latipes</i>), previous research has shown that sex ratio influences both male and female behaviour. However, there remains a research gap in investigating how the identity, or the novelty, of the surrounding individuals affects this balance. The goal of this study is to measure the effects of mate and competitor novelty on the ratio of inter- and intrasexual behaviour of male Japanese medaka, as well as the effects of mate novelty on female reproductive output. Male behaviour, both aggression (chasing and hitting) and courtship (following and circling), was quantified by observing each male on two different days for two minutes each and the frequency of inter- and intrasexual behaviour was recorded. For males, these observations were collected for all four sex ratios in three scenarios: familiar mates and familiar competitors, novel mates and familiar competitors, and novel mates and novel competitors. I found that in response to both novel mates, and novel mates and competitors, males prioritized intersexual interactions by increasing their allocation to courtship and following behaviour. I suggest that males use mate novelty as bet hedging strategy to increase offspring fitness in an unstable environment. In addition, female reproductive output, measured by the presence of eggs, was recorded daily in the first two scenarios (first with familiar and then with novel mates). I found that females decrease reproductive output in response to novel mates. I suggest that females are more receptive to familiar males because they take less risk relative to males with their limited gametes, and instead bet hedge with post-fertilization mechanisms.