2024

Chartrain, Justine

The concept of mate choice involves complex behaviours and physiological adaptations that individuals use to select reproductive partners. In the past, research has mainly focused on mate choice in one sex, largely ignoring the involvement of the other. However, recent studies emphasize the importance of considering mate choice in both sexes to understand reproductive dynamics comprehensively. Environmental stressors play a crucial role in shaping mate choice strategies, influencing which traits are preferred by individuals and altering their reproductive behaviours. Understanding how ecological stress affects condition-dependent mate choice provides insights into the adaptive responses of organisms to changing ecological conditions. With their remarkable ability to withstand extreme environmental conditions, tardigrades offer a unique opportunity to investigate mate choice mechanisms under environmental stress. Despite their small size, tardigrades exhibit complex reproductive behaviours, including communication, courtship, and sperm storage. Moreover, due to the scarce knowledge of tardigrade behaviour and behavioural ecology, this study offers a chance to bridge crucial gaps in our understanding of these resilient organisms. My work aimed to investigate the process of mate selection throughout the reproductive process and in both sexes, providing a comprehensive understanding of the mechanisms involved in identifying and choosing a partner, engaging in sexual interactions, and investing in reproduction. Firstly, I showed that tardigrades can distinguish between sexes, determine their physiological state through chemical cues, and use those cues for mate choice. Then, I documented a consistent pattern of reproductive behaviour within a family and suggest that close-range contact pheromones could trigger courtship behaviour. Finally, I showed that although sperm storage organ presence in tardigrades does not result in greater female reproductive fitness, it is still beneficial. Overall, my thesis contributes to a better understanding of tardigrade evolutionary ecology, especially the fascinating world of mate choice and reproductive behaviour in these resilient organisms.