Understanding mechanisms underlying changes in parental care behaviour in response to perceived paternity in sunfish
Abstract
Parental care is essential for the survival of many young animals but presents significant costs to the caring parent. To mitigate these costs, parental care systems have evolved to optimize survival and fitness. According to parental investment theory, care allocation is influenced by the offspring’s value, which is often linked to their relatedness to the parent. In this thesis, I explore how hormones and gene expression influence parental care, focusing on bluegill sunfish (Lepomis macrochirus) and the hybrids they produce with pumpkinseed sunfish (Lepomis gibbosus). By manipulating direct and indirect paternity cues – swapping eggs between nests for the former and simulating cuckoldry for the latter – I investigated changes in parental investment via care behaviour. To do so, I examined variations in circulating endogenous 11-ketotestosterone, prolactin, and gene expression. I found that while 11KT levels in bluegill respond to paternity cues, they do not directly regulate parental care behaviour. Rather, these levels seem to indicate preparations for future reproductive events. In contrast, prolactin emerges as a critical hormone in fish parental care, with circulating levels correlating with nurturing behaviour and adjusting in response to perceived paternity. Additionally, I used whole-brain RNA sequencing to determine that gene expression associated with energy transport, immune response, and stress varies in response to paternity perception. Focusing on hybrids, known to provide care despite low genetic relatedness, I found they maintain distinct hormonal profiles and gene expression patterns. Specifically, they exhibit higher prolactin and lower 11-ketotestosterone levels compared to bluegills, pointing to a species-specific regulation of parental care, shaped by evolutionary and environmental factors. Overall, my thesis advances our understanding of parental care regulation in species with male-only care and complex reproductive systems. It underscores the significance of considering a range of endocrine, genomic, and environmental factors in understanding the evolution and maintenance of parental care, thereby enriching our knowledge within evolutionary biology and the neuroendocrine regulation of parental behaviour.