Sexual reproductive cycle and gametogenesis in sea anemones (Cnidaria: Anthozoa): a scope review

ABSTRACT Sea anemones have a wide range of reproductive modes, which may contribute to their broad distribution. Understanding reproductive traits and patterns, such as seasonality, is important to elucidate the evolutionary processes that shaped the current distribution of this group. However, data on the reproductive cycles and gametogenesis of sea anemones remain fragmented. In this scope review, we compile existing knowledge, highlight topics requiring further investigation, identify patterns in the available data, and discuss potential methodological limitations in previous studies. We used the same search terms across three indexed scientific databases (Scopus, Web of Science, and ScienceDirect) and Google Scholar. The obtained articles were filtered for replicates and relevance to the topic (i.e., studies that included a description of the gametogenic process, with or without temporal sampling). To find articles not captured in the initial search, we conducted a forward and backward citation tracking. A total of 65 articles were included. According to our findings, research on gametogenesis and reproductive cycles of sea anemones began in 1964 and peaked in the late 1980s and early 1990s. Studies have investigated the reproductive cycles/gametogenesis of 43 sea anemone species across 14 families, with Actiniidae being the most studied. Most articles were conducted in temperate regions, analyzed oocytes and spermatic cysts together, employed microanatomical methods, did not use a classification system for spermatic cysts, and did not measure abiotic variables (e.g., salinity or temperature). The reproductive peak seems to be more closely associated with geographic location than with phylogenetic traits. Our findings provide an overview of the current state of research on sexual reproduction and gametogenesis studies in Actiniaria. We hope this review will serve as a guide for future studies to address gaps and improve existing methodological approaches in this field.