Neuropeptide diversity and evolutionary patterns in crustaceans: insights into adaptations, agonism, and functional importance in organs

<title>Abstract</title> Background Crustaceans exhibit great diversity in anatomical, physiological, and behavioral adaptations, all of which contribute to their evolutionary success, and neuropeptides are important regulators mediating these adaptations. While expansion of certain neuropeptide families in specific animal groups and organs typically reflects their adaptive roles, our understanding of their diversity and evolution in crustaceans has remained incomplete and underrepresented, partly because previous studies typically focused on a limited number of taxa and organs, with large-scale comparisons across multiple groups remaining scarce. Utilizing custom-made crustacean profile hidden Markov models constructed for 66 neuropeptide families, the present study examined their diversity and evolutionary patterns across four crustacean classes (Branchiopoda, Thecostraca, Hexanauplia, and Malacostraca), between non-agonistic and agonistic malacostracans, and among their three sensory and neuroendocrine organs through transcriptome mining. Results Our results revealed that the expansions of neuropeptide families in certain crustacean classes generally corresponded to their evolutionary adaptations. Specifically, those related to osmoregulation and detoxification were expanded in Thecostraca and Hexanauplia; those involved in the development of sessility were specifically expanded in Thecostraca; and those important for visual and nervous systems were expanded in Malacostraca. Furthermore, seven neuropeptide families, six of which play roles in sex-related functions, were potentially crucial in regulating agonism in malacostracans. Additionally, the significantly higher number of members in certain neuropeptide families within specific sensory and neuroendocrine organs likely reflected their greater functional importance to those organs in Malacostraca. Conclusions In conclusion, this study represents the first large-scale comparative analysis of the number of members in different neuropeptide families across multiple crustacean taxa and organs, providing a foundation for future research on neuropeptidergic regulation of physiologies and behaviors in crustaceans, with significant implications for their ecology and evolution.