Temporal dynamics of sexual selection in the red junglefowl (Gallus gallus)

Sexual selection has been evoked as a contributing cause of many morphological and behavioural adaptations aimed at increasing an individual’s reproductive success. Recent research has begun to unveil the roles of environmental variation, changes in the operational sex ratio, and behavioural plasticity as potential drivers of fluctuating selection in natural populations. Nevertheless, we have just started scratching the surface of the tempo of evolutionary change, and while the mechanisms underpinning different episodes of sexual selection have been increasingly elucidated in the past decades, very little remains known about how these mechanisms are modulated over time. The overarching goal of this thesis therefore, was to explore temporal dynamics in both pre- and post-copulatory episodes of sexual selection by analysing data of socio-sexual interactions and molecular parentage data across replicate flocks of red junglefowl (Gallus gallus), an established research model. Specifically, my thesis had four objectives: (i) characterise circadian patterns in mating and courtship behaviour, (ii) quantify phenotypic changes associated with mating and social status over the course of a mating trial, (iii) predict the probability of fertilization success across individual eggs laid over successive days, and (iv) quantify changes in the opportunity for selection over a mating trial. By addressing these objectives, I seek to demonstrate how temporally dependent expression of mating behaviour and post copulatory biases in fertilization can lead to changes in sexual selection over short-time scales.
The findings reported in my thesis demonstrate potential costs associated with precopulatory sexual selection. Males that mate more often and with more females, males that are chased more often by other males, and females that experience more coerced copulations, all tend to lose more body condition over a mating trial. I demonstrate female resistance to mating, and male courtship effort show clear circadian trends, differing between the morning and evening. I found evidence for temporal changes in post-copulatory sexual selection which are partially driven by variation in the relative importance of certain predictors of male fertilization success over successive days of a mating trial. Males that mate last and maintain consistent higher levels of remating with the same female than his competitors, increase the probability they will fertilize eggs laid by this female at the end of a laying sequence. Lastly, I observed sharp temporal changes in the opportunity for pre- and post-copulatory episodes of sexual selection over a mating trial, which demonstrates the importance of accounting for the cumulative sequence of copulations to properly estimate the strength of sexual selection. Moreover, I show that stochastic mechanisms also contribute to changes in variance in reproductive success over time, reinforcing the need for the incorporation of null models in sexual selection research.
In conclusion, this thesis contributes to refine our understanding of how different preand post-copulatory mechanisms may lead to temporal changes in sexual selection. Future work should attempt to increase the resolution of data collection by employing modern tracking technologies, and explore the generality of my results by comparisons with species with different mating systems.

Keywords: sperm competition
Temporal dynamics
Gallus gallus
Sexual selection
Advisor: Pizzari, T
McDonald, G